Imaging in Skull base

The Skull Base

Rakesh C A

The NormalSkull Base

Normal skull base

• Concept of fossa does not work well for the skull base, because the bony anatomy spills over from one fossa to the next.

• Perspective of individual bones– Components– Apertures– Transmitted structures

Normal skull base

• Extend– root of nose anteriorly to the superior nuchal line

posteriorly

Normal skull base

• 5 bones:– Frontal– Ethmoid– Sphenoid– Temporal– Occipital

Ethmoid

Normal skull base

• Most important part: – Basisphenoid (anterior aspect of sella) – Basiocciput (posterior lip of the foramen magnum)

• The cranial nerves and cerebral vasculature traverse the skull base here.

Bones Of Skull Base

Occipital bone

• Floor of the posterior fossa

• 3 distinct areas:– Basiocciput (clivus and

jugulare tubercles)– Condylar (lateral)

portion– Squamous (posterior)

portion

Occipital bone

• Floor of the posterior fossa

• 3 distinct areas:– Basiocciput (clivus and

jugulare tubercles)– Condylar (lateral)

portion– Squamous (posterior)

portion

Occipital bone

• Apertures:– Foramen magnum– Posterior condylar canal– Hypoglossal canal

Temporal bone• Petrous pyramid and mastoid

process form most of the skull base between the posterior and middle skull base.

• Apex of the petrous pyramid joins the anterolateral margin of the clivus (i.e., basiocciput) and the posteromedial aspect of the greater wing of sphenoid along the basisphenoid synchondrosis.

• Apertures:– Jugular foramen– Internal auditory canal– Facial nerve canal– Petrous carotid canal– Eustachian tube

Sphenoid bone

• Mid section of the skull base• Anterior wall of middle cranial fossa

Sphenoid bone• 3 compartments:

– Basisphenoid:• Dorsum sella, posterior clinoids,

sella turcica, tuberculum sella, sphenoid sinus

• Fused to clivus in adult

– Greater wing of sphenoid• Medial two-thirds and anterior

wall of the middle cranial fossa floor

– Lesser wing of sphenoid• Medial and superior aspects of the

anterior wall of the middle cranial fossa and the anterior clinoids

• Superior and medial edges of the superior orbital fissure

Sphenoid bone• 3 compartments:

– Basisphenoid:• Dorsum sella, posterior clinoids,

sella turcica, tuberculum sella, sphenoid sinus

• Fused to clivus in adult

– Greater wing of sphenoid• Medial two-thirds and anterior

wall of the middle cranial fossa floor

– Lesser wing of sphenoid• Medial and superior aspects of the

anterior wall of the middle cranial fossa and the anterior clinoids

• Superior and medial edges of the superior orbital fissure

Sphenoid bone

• Apertures:– Foramen ovale– Foramen spinosum– Foramen rotundum– Optic canal– Superior orbital fissure– Precavernous carotid canal– Foramen lacerum

• Not a true foramen• Thinning of skull base, filled with fibrocartilage in life

Frontal bone

• Anterior cranial fossa is anteriorly and laterally bound by frontal bone; majority by orbital plate of frontal bone

• Foramen caecum– Indentation in the medial

anterior frontal bone– Normal (should not be

confused with cephalocoele)

– Complete bony floor (protrude through a gap in the frontal bone)

– Prominent at birth and gradually shrinks over first 10 years of life

Frontal bone

Ethmoid bone

• 2 distinct pieces:– Cribriform plate – Crista galli

Ethmoid bone

• Cribriform plate is perforated by approx 20 holes on each side of the crista galli

• Nerve fibres of olfactory nerve (CN I) pass from nasal mucosa to olfactory bulb

• Crista galli serves as the anchor for anterior margin of the falx cerebri

Ethmoid bone

• Cribriform plate is perforated by approx 20 holes on each side of the crista galli

• Nerve fibres of olfactory nerve (CN I) pass from nasal mucosa to olfactory bulb

• Crista galli serves as the anchor for anterior margin of the falx cerebri

BONES OF BASE OF SKULL IN CT

EMBRYOLOGY

Development of the skull base

• Development of the skull base begins only after the spinal cord, cranial nerves, and blood vessels have formed.

• The cranial base is relatively stable during development as compared with the rapid growth and expansion of the calvaria.

• Study of fetal developmental anatomy may lead to a better understanding of congenital skull base disorders.

The skull base originates predominately from cartilaginous precursors with a small contribution from membranous bone.

The components of the skull base are derived from neural crest cells and mesoderm during the fourth week of fetal life to form the cartilaginous and bony components of the cranial base.

Ossification of the skull base progresses in anorderly pattern from posterior to anterior.

RADIOGRAPHY OF SKULL BASE

Submento-vertical• Position of patient and cassette

– The patient may be imaged erect or supine. If the patient is unsteady, then a supine technique is advisable.

• Supine– The patient’s shoulders are raised and the

neck is hyperextended to bring the vertex of the skull in contact with the grid cassette or table.

– The head is adjusted to bring the external auditory meatuses equidistant from the cassette.

– The median sagittal plane should be at right-angles to the cassette along its midline.

– The orbito-meatal plane should be as near as possible parallel to the cassette.

• Erect– The patient sits a short distance away from a vertical Bucky.– The neck is hyperextended to allow the head to fall back

until the vertex of the skull makes contact with the centre of the vertical Bucky.

Submento-vertical• Position of patient and cassette

– The patient may be imaged erect or supine. If the patient is unsteady, then a supine technique is advisable.

• Supine– The patient’s shoulders are raised and the

neck is hyperextended to bring the vertex of the skull in contact with the grid cassette or table.

– The head is adjusted to bring the external auditory meatuses equidistant from the cassette.

– The median sagittal plane should be at right-angles to the cassette along its midline.

– The orbito-meatal plane should be as near as possible parallel to the cassette.

• Erect– The patient sits a short distance away from a vertical Bucky.– The neck is hyperextended to allow the head to fall back

until the vertex of the skull makes contact with the centre of the vertical Bucky.

Submento-vertical• Direction and centring of the

X-ray beam– The central ray is directed at

right-angles to the orbito-meatal plane and centred midway between the external auditory meatuses.

Submento-vertical

Essential image characteristics

• A correct projection will show the angles of the mandible clear of the petrous portions of the temporal bone.

• The foramina of the middle cranial fossa should be seen symmetrically either side of the midline.

Essential image characteristics

POSITIONING

• No rotation is evidenced by The lateral borders of the

foramen magnum are equidistant from the lateral borders of the skull.

• No tilt is evidenced by • The vomer and the bony nasal

septum are aligned with the long axis of the film.

Jugular foramina: Submento-vertical 20 degrees caudad

• The jugular foramina lie in the posterior cranial fossa between the petrous temporal and occipital bones on each side of the foramen magnum.

• Both sides are imaged simultaneously on a -single image by undertaking a submento-vertical (SMV) 20 degrees caudad projection.


• Position of patient and cassette– As per the SMV

projection described previously.


• Direction and centring of the X-ray beam– Using a well-collimated

beam, the central ray is angled caudally so that it makes an angle of 70 degrees to the orbitomeatal plane and centred in the midline to pass midway between the external auditory meatuses.

Notes: Alternative Technique

• With the patient’s neck less extended, the head can be positioned with the orbito-meatal plane at an angle of 20 degrees to the Bucky, in which case a horizontal central ray will make the required angle of 70 degrees to the base plane (see photograph).


The Pathological

Skull Base

Role of imaging

• Diagnosis• Extend of disease – criteria of surgical

resectability• Treatment planning – surgical approach• Follow up – recurrence vs post ttreatment

changes

Anterior skull base lesions

• Bones:– Orbital plates of frontal

bones– Cribriform plate of

ethmoid bone– Planum sphenoidale

Anterior Skull Base Lesions

Common:

Malignant sinonasal tumor (eg., SCC, RMS)

Meningioma

Metastases

Uncommon

Mucocoele

Osteoma

Polyposis

Inverted papilloma

Esthesioneuroblastoma

Lymphoma

Complicated sinusitis (bacterial, fungal, granulomatous)

Rare

Cephalocoele

Dermoid cyst

• Lesions arise:– Extracranially

• From the nasal vault, frontal and ethmoid sinuses

– Intrinsically• From the skull base itself

– Intracranially• From the brain, meninges and CSF spaces





Extra cranial lesions

• Most arise from the nose and paranasal sinuses

Common Benign Lesions

Mucocoele

Polyposis

Inverted papilloma

Osteoma

Common Malignant Lesions

Squamous cell carcinoma

Rhabdomyosarcoma

Adenoid cystic carcinoma


Mucocoele

• Accumulation of impacted mucus behind an occluded draining sinus ostium.

• Obstruction - Inflammatory > post traumatic, neoplastic

• Frontal > Ethmoid > Maxillary > Sphenoid

Mucocoele - Imaging

• Well delineated soft tissue mass with bony expansion and remodelling.

• Low density on NECT; inspissated secretions may appear hyperdense.

• MR signal is variable.• Aggressive bone erosion seen in 10 – 12% of

cases.

MucoceleA: Coronal T1 magnetic resonance image. The sphenoid sinus is enlarged and its contents are of high signal. Mucocele also involves the left anterior clinoid (arrow), which is markedly expanded and filled with the same high-signal contents as the rest of the sinus. B: Sagittal T1 magnetic resonance image again shows marked enlargement of the left anterior clinoid (large arrow).

Mucopyocoele

• Mucocoeles when infected

Axial T1 C+ MR shows left frontal mucopyocoele with thick, peripheral enhancement.Note linear enhancement of the anterior fossa dura (arrows) consistent with meningitis.

Inverted Papilloma

• Benign slow growing epithelial neoplasm.

• 1 to 4% of sinonasal neoplasms

• Arise near the nasal vault near the junction of ethmoid and maxillary sinuses.

• The surface epithelium proliferates by inverting into underlying stroma rather than growing outward.

Inverted Papilloma

• Benign slow growing epithelial neoplasm.

• 1 to 4% of sinonasal neoplasms

• Arise near the nasal vault near the junction of ethmoid and maxillary sinuses.

• The surface epithelium proliferates by inverting into underlying stroma rather than growing outward.

Inverted sinonasal or Schneiderian papilloma shows endophytic or “inverted” growth pattern. These nests of squamous epithelial cells grow down into the myxomatous to fibrous stroma with chronic inflammatory cells and vascularity

Inverted Papilloma - Imaging• A unilateral, polypoid nasal

fossa soft tissue mass• widens the nasal vault• sometimes destroying bone and

extending into the adjacent ethmoid and maxillary sinuses

• Focal erosion of the cribriform plate with cephalad extension occassionally occurs. (DD: sinonasal malignancies)

• No definitive MR findings to differentiate from various malignant tumors.

Inverted Papilloma - Imaging• A unilateral, polypoid nasal

fossa soft tissue mass• widens the nasal vault• sometimes destroying bone and

extending into the adjacent ethmoid and maxillary sinuses

• Focal erosion of the cribriform plate with cephalad extension occassionally occurs. (DD: sinonasal malignancies)

• No definitive MR findings to differentiate from various malignant tumors.

Osteoma

• Benign bony tumor• Mature well delineated

cortical bone as their primary component.

• Most common site: frontal sinus

• Expands and erodes the posterior and superior frontal sinus walls

Malignant Sinonasal Tumors• Intracranial extension

occurs in upto one-third of cases• Squamous cell carcinoma• Esthesioneuroblastoma• Adenocarcinoma• Melanoma• Non-Hodgkin Lymphoma

Rhabdomyosarcoma

• In children the most common extracranial malignancy that affects the skull base is Rhabdomyosarcoma.

• It is the most common soft tissue sarcoma in children.

• Head and neck is the most common site.• Orbit & nasopharynx > PNS & middle ear

• Anterior skull base invasion or cavernous sinus invasion - approx. 35% of nasopharyngeal RMS.

• Bulky soft tissue mass with areas of bone destruction.

• Isointense to muscle on T1, hyperintense on T2; some contrast enhancement.

• Meningeal and perineural spread are common

Nasal cavity RMS with extension through sinonasal roof, along the anterior cranial fossa

Intracranial extension of masticator fossa RMS through foramen ovale

Other Malignancies

• 98% of nasopharyngeal tumors in adults are carcinomas.

• Squamous cell carcinoma accounts for 80% of these tumors, and adenocarcinoma (most commonly from minor salivary glands) represent 18%.

• Nasopharyngeal carcinomas spread directly into skull base as well as along muscles and their tendinous insertions.

• They extend intracranially along neural and vascular bundles via osseous foramina.

• A nasopharyngeal mass with obliterated soft tisssue planes and adjacent bone destruction are the typical imaging findings with direct tumor invasion.

• Serous otitis media can be seen because the eustachian tube is frequently obstructed. T1C+ : NP Ca has destroyed large area of skull base

bone (arrows) surrounding the foramen ovale. Opposite foramen ovale has V3 traversing it (open arrow).

• Perineural tumor spread most commonly involves the second and third divisions of trigeminal nerve and facial nerve.

• Sometimes no dominant mass is present.• Enhancement of the affected nerve or

denervation atrophy of the muscles of mastication and face may be the only detectable abnormalities.


• Olfactory neuroblastoma

• Bipolar sensory receptor cells in the olfactory mucosa. (neural crest origin)

• Any age – bimodal peak (2nd and 4th/5th decade)

Esthesioneuroblastoma - imaging• Often confined to nasal

cavity; may extend to PNS or anterior cranial fossa (through cribriform plate)

• High nasal vault with focal bone destruction

• Variable signal intensity on MR

• Moderate but inhomogenous enhancement

• CNS dissemination as a late manifestation CECT - right nasal cavity ENB with destruction

of the cribriform plate (arrow) and lamina papyracea (open arrow).

Esthesioneuroblastoma - imaging• Often confined to nasal

cavity; may extend to PNS or anterior cranial fossa (through cribriform plate)

• High nasal vault with focal bone destruction

• Variable signal intensity on MR

• Moderate but inhomogenous enhancement

• CNS dissemination as a late manifestation

Miscellaneous

• Bacterial or fungal sinusitis

Misc

• Sarcoidosis

Misc

• Sinonasal lymphoma

Misc

• Cocaine granulomatosis– History of coccaine

abuse– Septal perforation with

nasal inflammatory changes

Misc

• Wegner granulomatosis– Soft tissue mass in nose

with septal and non-septal bone destruction

Enhancing soft tissue in maxillary sinuses extending into nasopharynx (arrows) with large septal perforation.





Intrinsic anterior skull base lesions

Intrinsic anterior skull base lesions

Fibrous dysplasia

Paget disease

Osteopetrosis





Intracranial lesions

• Arise from:– Meninges– CSF spaces– Brain

Meningioma

• Most common meningeal lesion to involve anterior skull base• Planum sphenoidale and olfactory groove – 10-15% of all

meningiomas• Broad based, anterior basal subfrontal mass that enhances

strongly and relatively uniformly after contrast administration is typical.

• Presence of tumor-brain interface or cleft with compressed cortex and white matter buckling indicate extraaxial location.

• Blistering and hyperostosis of the adjacent bone.• Enlargement of the air-containing ethmoid sinus

(pneumosinus dilatans) or even frank bone destruction is sometimes observed.

Figure. (A) Enlarged, air-filled ethmoid sinus extending into an isointense intracranial mass on T1-weighted MRI, which enhances uniformly on contrast agent administration (B). (C) Axial CT shows expansion of sinus beyond its normal boundaries into the meningioma, where the plate of bone lining the pneumosinus dilatans is preserved

Mai A et al. Neurology 2003;60:1861-1861

©2003 by Lippincott Williams & Wilkins

Cephalocoele

• The most common anterior skull base lesion that arises from the brain is nasoethmoidal cephalocoele.

• 15% of basal cephalocoeles occur in the frontonasal area.

Cephalocoele

• The most common anterior skull base lesion that arises from the brain is nasoethmoidal cephalocoele.

• 15% of basal cephalocoeles occur in the frontonasal area.

Misc

• Nasal dermoid sinuses and nasal cerebral heterotopias (nasal gliomas) are less common congenital lesions that occur in this location.

• Occasionally, a slow growing peripherally located primary brain neoplasms such as ganglioneuroma cause pressure erosion of the adjacent skull.

• Frank dural invasion or calvarial destruction can occur with anaplastic astrocytoma and glioblastoma multiforme, but uncommon.

Destructive Central Skull Base Lesions

Common

Metastases

Nasopharyngeal malignancy

Haematogenous

Uncommon

Osteomyelitis

Fungal sinusitis

Non fungal granulomas

Wegner granulomatosis

Cocaine abuse

Midline granuloma (probably a lymphoma variant)

Aggressive pituitary adenoma

Lymphoma

Myeloma

Meningioma

Juvenile nasopharyngeal angiofibroma

Chordoma

Rare

Leprosy

Rhinoscleroma

Syphilis

Sarcoidosis

Middle skull base

Central skull base

• It includes:– Upper clivus– Sella turcica– Cavernous sinuses– Sphenoid alae

Central Skull Base Lesions

• Lesions affecting the central skull base originate from:– Cavernous sinus– Pituitary gland– Basisphenoid bone– Nasopharynx

Cavernous sinus

• Multiseptated, extradural venous spaces that lie on both sides of the sella turcica.

• They communicate extensively with each other, the intracranial dural sinuses, and deep facial venous plexuses.

• Lateral wall is composed of 2 layers:– Thick outer dural layer– Thin inner membranous layer

• The inner layer is formed by the perineurium of CNs III, IV, V1 and sometimes V2. These nerves lie within the lateral wall, whereas the internal carotid artery and CN VI are inside the cavernous sinus proper.

• Medially, a thin poorly delineated medial dural wall separates the cavernous sinus from sella turcica.

• Meckel’s cave and its contents, the trigeminal ganglion, CSF, and investing arachnoid, invaginate into the cavernous sinus posteriorly.

Cavernous Sinus Masses

Unilateral Bilateral

Common Common

Schwannoma Invasive pituitary adenoma

Meningioma Meningioma

Metastasis Metastases

Aneurysm (Cavernous ICA)

Carotid-cavernous fistula

Uncommon Uncommon

Chordoma Lymphoma

Lymphoma Cavernous sinus thrombosis

Rare

Lipoma

Epidermoid

Cavernous haemangioma

Osteocartilagiomnous tumors

Plexiform neurofibroma (NF 1)

CENTRAL SKULL BASE LESIONS

Congenital/Developmental lesions Neoplasms

Cephalocoele Benign

Encephalocoele Pituitary adenoma

Meningocoele Meningioma

Trauma Nerve sheath tumors

Fractures Juvenile nasopharyngeal angiofibroma

CSF fistula Chordoma

Infection and Inflammatory disease Osteocartilaginous tumors

Osteomyelitis Tumor like lesions

Bacteral sinusitis Epidermoid tumor

Fungal sinusitis Lipoma

Wegner granulomatosis Malignant tumors

Leishmaniasis Nasopharyngeal carcinoma

Sarcoidosis Rhabdomyosarcoma

Leprosy, Treponemes, Mycobacteria, Rhinoscleroma

Multiple myeloma or Solitary plasmocytoma

Cocaine abuse Osteosarcoma

Midline lethal granuloma (T-cell lymphoma)

Chondrosarcoma

Miscellaneous Metastatic disease

Paget disease, Fibrous dyspasia Prostate, lung and breast carcinomas

Radiation necrosis Lymphoma – primary / secondary


Cephalocoele Benign

















Chondrosarcoma




Cephalocoele• Axial CT scan (b) photographed

with bone window and coronal CT scan (c) photographed with soft-tissue window reveal the presence of a persistent craniopharyngeal canal (arrow) in the sphenoid bone.

• Coronal (d) and midsagittal (e) Ti -weighted MR images through the central skull base demonstrate herniation of the pituitary gland into the craniopharyngeal canal through the sphenoidal defect (arrow) . Note the proximity of the pituitary gland to the roof of the nasopharynx.


Cephalocoele Benign

















Chondrosarcoma




Fractures

• Most commonly occur as extensions of cranial-vault fractures.

• Petrous temporal bone > orbital surface of the frontal bone > basiocciput.

Multiple skull-base fractures in a 23-year-old man after an automobile accident.

CSF fistula

• The most common cause of CSF fistula is skull-base trauma– Fractures through the frontoethmoidal complex and middle cranial

fossa.

• Nontraumatic cause of leakage:– Tumors, especially those arising from the pituitary gland – congenital anomalies, such as encephaloceles

Coronal CT scans through the sphenoid sinus were obtained before (a) and after (b) the intrathecal instillation of water-soluble contrast material. A mass with attenuation values of soft tissue (arrow in a) is seen involving the right lateral floor of the sphenoid sinus. After contrast enhancement increased attenuation is seen in this region, consistent with the accumulation of contrast material (curved arrow in b) . This finding confirms the presence of a CSF fistula.


Cephalocoele Benign

















Chondrosarcoma




Osteomyelitis

• Potentially lethal complication of:– Immunocompromised states– Diabetes– Chronic mastoiditis– Paranasal sinus inection– Trauma– Necrotising otitis externa

• Occasionally in the absence of predisposing factors

Bacterial sinusitis complicating Osteomyelitis

• Infection can extend :– Directly from frontal, ethmoid or sphenoid sinuses– Intracranially via emissary veins and the cavernous

sinus.• May result in:

– Cerebral infarct– Meningitis– Subdural empyema– Brain abscess

Left frontal SDE with leptomeningeal enhancement in a patient with left pansinusitis

Paranasal sinus fungal infections

• 4 different patterns:– Extramucosal disease with cavitating mycetoma

(fungus ball)– Allergic fungal sinusitis– Mucosal thickening from indolent, penetrating

fungal sinusitis– Fulminant invasive mycosis

• Manifestations include:– Multiple cranial nerve palsies– Septic cavernous sinus thrombosis– Internal carotid occlusion– Brain infarction– Brain abscess

Fungal sinusitis - Imaging

• Multisinus nodular mucoperiosteal thickening• High attenuation foci in soft tissue masses on

CT

17-year-old boy with allergic fungal sinusitis complicated by compression of right optic nerve. Painless decreased vision had been present in the right eye for 2 months. Coronal (A–C) and axial (D) CT images show high-attenuation opacification of left maxillary, left ethmoidal, and bilateral sphenoidal sinuses with bone expansion and thinning. Compression of right optic nerve (straight arrow, B and D) is caused by expanded right anterior clinoid process (asterisk, B and D). Bone dehiscence is present at left lamina papyracea (curved arrow, A and D) and around left optic nerve (arrowhead, B and D), and internal carotid arteries (arrows, C). These structures are at risk of injury during functional endoscopic sinus surgery.

Mycetomas• Best diagnostic clue: single PNS contains high density mass

with fine round to linear matrix calcifications• Very hypointense on MR with a high signal rim surrounding

the fungal ball.

Aggressive mycosis

• Extensive skull base destruction• Cavernous sinus thrombosis, blood vessel

invasion and rapid intracranial dissemination can occur

• CEMR / CECT – multiple filling defects within the cavernous sinus.

• Extensive skull base erosion is indistinguishable from nasopharyngeal malignancy

• Biopsy-proved aspergillosis in a 23- year oId black woman with right-sided facial pain.

• Axial (a) and coronal (b, c) non-contrast-enhanced CT scans show a large soft-tissue mass (*) with extensive bone destruction of the right maxillary sinus (m), nasopharynx (n), pterygoid plate (p), and sphenoid sinus (s) . The central high attenatuation may represent calcium deposits in mycetoma.

• T1-weighted MR images obtained before (d) and after (e) administration of gadopentetate dimeglumine show the extent of skull base and sinus ivolvement.

• The central low-signal-intensity areas within the sinus may represent inspissated secretions or fungal mycetoma containing metals.

Sarcoidosis

• Due to its propensity for leptomeningeal invasion, sinus and nasopharyngeal sarcoidosis is recognized as a more common cause of cranial nerve neuropathy.

• Central nervous system involvement occurs in 3%-8% of patients with sarcoidosis.

• The most frequent problem is cranial neuropathy secondary to facial, acoustic, optic, or trigeminal nerve involvement.

• Sarcoidosis should be considered when both the meninges and the cranial nerves are involved in a pathologic process.

Other granulomatous diseases

• Wegner granulomatosis• Leishmaniasis• Leprosy• Rhinoscleroma• Mycobacteria• Treponemes• Cocaine abuse• Midline lethal granuloma (T-cell lymphoma)


Cephalocoele Benign

















Chondrosarcoma




Pituitary Adenoma

• Usually indolent, non agresssive tumors that expand and slowly erode the bony sella turcica.

• Typically extend superorly through the diaphragma sellae and laterlally into the cavernous sinus.

• Occasionally, some variants behave more aggressively and may cause extensive destruction of the central skull base.

Meningioma

• Meningiomas of the central skull base are located along – the sphenoid wing, – diaphragma sellae, – clivus and – cavernous sinus

• Focal, globose or flat, en-plaque lesions• Occasionally, bony destruction or hyperostosis.• Cavernous sinus meningiomas cause multiple cranial

nerve palsies.

Medial sphenoid wing meningioma

Clival meningioma

Nerve Sheath Tumors

• Those involving the central skull base often affects the cavernous sinus and Meckel’s cave.

– Plexiform neurofibromas – Schwanommas

Plexiform neurofibromas

• Unencapsulated diffusely infiltrating masses that originate along peripheral nerve, usually ophthalmic division of trigeminal nerve, and involve BOS by central extension.

• Extension along mandibular and maxillary divisions of trigeminal nerve is also common.

Schwannoma

• Encapsulated, well delineated tumors.• Most are quite vascular• Haemorrhage or necrosis may occur

Trigeminal Schwannoma

• Most common schwannoma to involve the central BOS and cavernous sinus is a trigeminal schwannoma.

• Its symptoms, signs, and imaging appearance varies with the part of the nerve involved, direction and extent of tumor growth.– Meckel’s cave – extend into skull base– Cisternal – CP angle mass

• Cisternal and ganglion – “dumbbell” configuration• Circumscribed, rounded or lobulated soft tissue masses that

enhance strongly but heterogenously.• Most are isodense with brain on CT• Isointense on T1WI, hyperintense on T2WI

On an axial T1-weighted image, a normal nonenhancing Meckel’s cave is seen on the right side (arrow). In the left Meckel’s cave, a heterogeneous enhancing mass arrowheads) is depicted, extending in the cavernous sinus: trigeminal schwannoma.

Juvenile Angiofibroma• Highly vascular, locally

invasive lesion• Originates near

sphenopalatine foramen• Adolescent males• Most common benign

nasopharyngeal tumor• Typically spread along natural

foramina and fissures into pterygopalatine fossa, orbit, middle cranial fossa, sphenoid sinus, and cavernous sinus.

• Imaging – strongly enhancing, highly vascular nasopharyngeal soft tissue mass.

Chordoma

• Slowly growing destructive tumor

• Histologically benign, but locally invasive

• One-third in sphenooccipital region– Most in midline;

primarily involve clivus– Other – petrous apex

and Meckel’s cave

Destructive lesion in the central skull base – T1 hypontense and T2 hyperintense

Osteocartilaginous neoplasms

• Clivus and skull base – cartilaginous neurocranium by endochondral ossification

vs• Calvarium – mesenchymal membranous

neurocranium by intramembranous ossification

• Therefore, a spectrum of benign and malignant osteocartilaginous neoplasms can arise in the central skull base.

Enchondroma

• The most common benign osteocartilaginous tumor in this location.

• CT – Expansile lobulated soft tissue mass with scalloped

endosteal bone resorption and curvilinear matrix mineralisation

• MRI – isointense on T1; hyperintense on T2– Post contrast – enhancement of scalloped margins and

curvilinear septae (ring-and-arc pattern)

Multiple myeloma

• Diffuse skull vault and calvarial vault destruction.

• Solitary plasmacytoma– Focal destructive sphenoid sinus or calvarial vault

mass is typical, though nonspecific– Best diagnostic clue:

• CT shows solitary intraosseous osteolytic soft tissue mass with nonsclerotic margins

Osteosarcoma

• Craniofacial osteosarcomas are uncommon - when present, present in older patients, and commonly affect the maxilla or mandible.

• Skull base osteosarcomas are rare.– May occur spontaneously or – In association with Paget disease or previous radiation

therapy.• A soft tissue mass with tumor matrix mineralisation and

aggressive bone destruction is characteristic.• DD:

– Radiation osteitis, metastatic carcinoma, myeloma

MRIs of a radiation–induced osteosarcoma in a patient with severe fibrous dysplasia of the skull and skull base. (A) Gadolinium–enhanced, T1–weighted axial image with fat suppression shows a large tumor in the region of the sphenoid and sella. (B) T2–weighted fast spin–echo, axial and (C) gadolinium–enhanced, T1–weighted coronal image with fat suppression of the same lesion.

Chondrosarcoma

• Rare in skull base• Slow growing, locally invasive tumors• Soft tissue mass with focal bone destruction is

typical.• Matrix mineralisation in half of cases.• MR:

– low to intermediate signal on T1– Hyperintense on T2– Strong but heterogeneous enhancement

• Chondrosarcoma in a 65-year-old man with epistaxis and facial pain.

• (a) Axial CT scan with bone windows reveals the presence of a midline destructive lesion involving the sphenoid body and extending anteriorly to the ethmoid bones and nasal fossa with tumor calcification (arrow), within the mass.

• (b) Axial T1 -weighted MR image a relatively homogeneous midline mass (*) that is slightly less intense than brain and associated destruction of the clivus (arrows) .

• (c) Midsagittal T1-weighted MR image shows a destructive mass in the midline of the ethmoid bones and nasal fossa extending posteriorly and causing destruction of the sphenoid body and clivus(*).

Metastatic disease

• Central skull base metastases are more common than primary bone neoplasms.

• Arise via – regional extension of head and neck malignancies

or– perineural spread from regional or remote

malignancies or – haematogenous spread from extracranial sites

• Prostate, lung and breast carcinomas are the most common.

• Lung and breast – focal or diffuse lytic destructive lesions

• Prostate – mixed hyperostoses and bone destruction with an associated soft tissue mass (resembles meningioma). – Lateral orbital wall – favourite

site

Lymphoma

• CNS involvement – primary or secondary• Leptomeningeal involvement (most common type)• Cranial nerve palsies (most common presenting

signs)• Focal masses or perineural tumor can occur• MR:

– Replacement of normal high signal marrow with infiltrating soft tissue that has decreased signal intensity

• Cavernous sinus lymphoma can be unilateral or bilateral.

Unenhanced (A) and contrast-enhanced (B) axial T1-weighted images reveal homogeneous infiltrating lesions (arrow) in cavernous sinus, which exhibits homogeneous, intense enhancement.

Posterior Cranial Fossa

• Largest and the deepest of the 3 cranial fossae.

• Roughly two-fifths of the base of skull.

• Surrounds the foramen magnum

• Includes: – clivus below the

sphenooccipital synchondrosis

– petrous temporal bone– pars lateralis and– squamae of occipital

bone

NOTE!!!

• MR signal of normal clivus and posterior skull base depends on the amount and nature of the marrow elements the comprise the cancellous bone.

• Red marrow (haematopoetic tissue) predominates upto approximately 3 years of age and results in low and high intensity portions mixed in various proportions on T1WI.

• Enhancement of normal clivus marrow sometimes follows contrast administration.

• This is mild and infrequent in adults, but is common and may even be quite striking in young children.

• The skull base in children normally has signal irregularity and patchy enhancement.

Posterior Skull Base Lesions

Posterior Skull Base Lesions - location

• CP Angle – IAC cistern• Temporal bone• Clival and paraclival• Jugular foramen• Foramen magnum



CEREBELLO PONTINE ANGLE – INTENAL AUDITORY CANAL CISTERN

Normal anatomy

• CPA cistern lies between the anterolateral surface of pons & cerebellum and the posterior surface of the petrous temporal bone.

• Important structures:– Nerves – CNs V, VII and VIII– Arteries – SCA, AICA– Tributaries of superior

petrosal veins– Others – Flocculus, choroid

plexus

CPA-IAC cistern lesions

Normal variants in CPA-lAC• Normal structures, when unusually prominent, trouble radiologist evaluating

CPA – lAC.• AICA loop flow void on high-resolution T2 MR

– Will not prominently enhance on Tl1C+ MR– Subtle enhancement in lAC on TI C+ MR may be mistaken for small acoustic

schwannoma• Choroid plexus protruding through lateral recess of 4th ventricle

– T1 C+ MR shows enhancing bilateral tear-shaped masses of CPA cistern– Symmetry &. characteristic appearance make diagnosis

• Cerebellar flocculus is a lobule of cerebellum projecting into posterolateral aspect of CPA cistern– Signal follows intensity of cerebellum on all MR sequences

• Marrow space foci in walls of lAC can mimic lAC tumor on Tl C+ MR images– Correlate location of foci with lAC cistern– Bone CT of T-bone may be necessary to identify this normal variant

• High jugular bulb• Prominent jugular tubercles

Normal variants in CPA-lAC• Normal structures, when unusually prominent, trouble radiologist evaluating

CPA – lAC.• AICA loop flow void on high-resolution T2 MR

– Will not prominently enhance on Tl1C+ MR– Subtle enhancement in lAC on TI C+ MR may be mistaken for small acoustic

schwannoma• Choroid plexus protruding through lateral recess of 4th ventricle

– T1 C+ MR shows enhancing bilateral tear-shaped masses of CPA cistern– Symmetry &. characteristic appearance make diagnosis

• Cerebellar flocculus is a lobule of cerebellum projecting into posterolateral aspect of CPA cistern– Signal follows intensity of cerebellum on all MR sequences

• Marrow space foci in walls of lAC can mimic lAC tumor on Tl C+ MR images– Correlate location of foci with lAC cistern– Bone CT of T-bone may be necessary to identify this normal variant

• High jugular bulb• Prominent jugular tubercles

Cerebellopontine angle cistern masses

• Uncommon in children; very common in adultsCerebellopontine angle cistern masses

Common Uncommon

Acoustic schwannoma (75%) Arachnoid cyst

Meningioma (8 to 10%) Lipoma

Epidermoid (5%) Demoid

Other schwannomas Exophytic cerebellar/brainstem astrostoma

Vascular (VB ectasia, aneurysm, VM) Chordoma

Metastases Osteocartilaginous tumors

Paraganglioma

Ependymoma

Choroid plexus papilloma

Internal Auditory Canal Masses

Internal Auditory Canal Masses

Common Uncommon

Intracanalicular acoustic schwannoma

Neuritis (eg., Bell’s palsy, Ramsay Hunt syndrome)

Post operative fibrosis Haemangioma

Lymphoma

Metastases

Sarcoidosis

Meningioma



TEMPORAL BONE LESIONS

• Primary temporal bone lesions:– Gradenigo’s syndrome– Malignant otitis externa– Cholesterol granulomas– Paraganglioma (glomus tympanicum)

Gradenigo’s Syndrome

• Osteomyelitis of petrous apex with sixth nerve palsy, otorrhea, and retroorbital pain.

• NECT:– Destructive lesion of the

petrous apex with fliud in the adjacent middle ear and mastoid.

Gradenigo’s Syndrome

• Osteomyelitis of petrous apex with sixth nerve palsy, otorrhea, and retroorbital pain.

• NECT:– Destructive lesion of the

petrous apex with fliud in the adjacent middle ear and mastoid.

Malignant otitis externa

• Uncommon but fulminant form of temporal bone osteomyelitis

• Typical in insulin-dependent diabetics and immunocompromised patients

• Extension into parotid and masticator spaces, skull base, and occassionally the CPA cistern may occur.

Malignant otitis externa

• Uncommon but fulminant form of temporal bone osteomyelitis

• Typical in insulin-dependent diabetics and immunocompromised patients

• Extension into parotid and masticator spaces, skull base, and occassionally the CPA cistern may occur.

Cholesterol granulomas

• Expansile cystic lesions of petrous apex that contain haemorrhage and cholesterol crystals.

• Hyperintense on T1 and T2

Paragangliomas

• Slow growing hypervascular tumors

• Arise from neural crest cells

• Locaised to cochlear promontory in the middle ear cavity – glomus tympanicum tumors

Paragangliomas

• Glomus jugulotympanicum tumors extend from the jugular foramen into middle ear cavity.

• Large masses also extend into CPA cistern.

The axial post-gadolinium T1-weighted image above shows an enhancing lesion involving almost the entire petrous temporal bone and extending through the external auditory canal to protrude from the external ear (green arrow). The tumour extended beyond the skull base into the carotid sheath, and bulged into the posterior fossa



Clival and Paraclival Lesions

• Chordoma and Metastasis are the most common causes of destructive clival masses.

• The same infectious and inflammatory processes and primary and metastatic tumors that affect the anterior and central skull base can also involve the clivus.

• Replacement of the normal marrow that forms the cancellous clival bone by soft tissue masses is easily identified on MR studies in these cases.

• Compared to brain, most abnormalities exhibit low signal on T1 and high signal on T2WI.

Axial computed tomography shows a large midline chordoma involving the petrous apex bilaterally.



Jugular foramen

• Jugular foramen:– Located in the floor of

the posterior fossa, between the petrous temporal bone anterolaterally and the occipital bone posteromedially.

– Anterior and inferior to it is the hypoglossal canal

• Hypoglossal nerve

Divided into:• Pars nervosa

• (smaller anteromedial compartment)

• CN IX • Pars vascularis

• (larger posterolateral compartment)

• CN X and XI• Jugular vein

Jugular Foramen Masses

Non Neoplastic Masses

Common

Large jugular bulb (normal variant)

Jugular vein thrombosis

Uncommon

Osteomyelitis

Malignant otitis external

Neoplasms

Common

Paraganglioma

Metastasis

Nasopharyngeal carcinoma

Haematogenous

Uncommon

Scwannoma

neurofibroma

Epidermoid tumor

Prominent jugular bulb

• Normal variant• Most common “pseudomass” in the jugular

foramen.

Glomus Jugulare

• The glomus jugulare is situated in the jugular bulb adventitia immediately below the middle ear.

• .

Glomus Jugulare

• Expand the jugular foramen, eroding the jugular spine and surrounding cortex.

Glomus Jugulare

• T1 : low signal• T2 : high signal• T1 C+ (Gd) : marked intense

enhancement• Salt and pepper appearance

is seen on both T1 and T2 weighted sequences; the salt representing blood products from haemorrhage or slow flow and the pepper representing flow voids due to high vascularity.

Glomus Jugulare

• T1 : low signal• T2 : high signal• T1 C+ (Gd) : marked intense

enhancement• Salt and pepper appearance

is seen on both T1 and T2 weighted sequences; the salt representing blood products from haemorrhage or slow flow and the pepper representing flow voids due to high vascularity.

Glomus Jugulare

• Carotid arteriography is necessary for preoperative evaluation and/or embolization

Nerve Sheath Tumors• Jugular foramen is uncommon

location for nerve sheath tumors.• Schwannomas of CNs IX to XI• smooth well delineated rounded

or lobulated soft tissue masses that expand the jugular foramen.

• Pressure erosion is common (frank invasion is rare; c.f. paragangliomas)

• Isointense to brain on T1; hyperintense on T2

• Strong homogenous contrast enhancement















FORAMEN MAGNUM MASSES

Normal Aantomy• Large aperture in the occipital

bone though which posterior fossa communicates with the cervical spinal canal.

• It transmits:– Medulla and its meninges– Spinal segment of CN XI– 2 vertebral arteries– Anterior and posterior spinal

arteries– Vertebral veins

• Bony elements that contain these structures are collectively termed the craniovertebral junction (CVJ).

CVJ

• Formed by the occiput and the C1 and C2 vertebrae.

• 4 joints are present here:– Atlanto occipital– Anterior median atlanto

axial– Posterior median atlanto

axial– Lateral atlanto axial joints

Pathology

• Intraaxial (cervicomedullary) masses

• Extramedullary intradural masses– Anterior– Posterior

• Extradural masses– CVJ– Clivus & Skull base

Cervicomedullary masses Extradural masses

Common Craniovertbral junction

Syringohydromyelia Trauma

Demyelinating disease Arthropathies

Glioma Congenital anomalies

Fourth ventricle tumor Clivus and skull base

Uncommon Metastases

Haemangioblastoma Chordoma


Anterior extramedullary intradural masses Posterior extramedullary intradural masses

Common Common

Vertebrobasilar dolichoectasia Tonsillar herniation

Meningioma Ependymoma/subependymoma

Aneurysm (VA, PICA) Medulloblastoma

Uncommon

Schwannoma

Epidermoid tumor

Paraganglioma

Metastases

Arachnoid cyst







Uncommon Metastases




Common Common




Uncommon

Schwannoma

Epidermoid tumor

Paraganglioma

Metastases

Arachnoid cyst

Intraaxial (cervicomedullary) masses

• Non neoplastic intraaxial lesions– Syringohydromyelia

• 25% of patients with Chiari I malformation

• Acquired syrinxes – trauma, cystic neoplasms

– Demyelinating diseases• Including multiple

sclerosis• In medulla and upper

cervical spinal cord

Cervicothoracic ganglioneuroblastoma


• Non neoplastic intraaxial lesions– Syringohydromyelia

• 25% of patients with Chiari I malformation

• Acquired syrinxes – trauma, cystic neoplasms

– Demyelinating diseases• Including multiple

sclerosis• In medulla and upper

cervical spinal cordDemyelination extends from the cervicomedullary junction to the T2 vertebral level. ADEM post liver transplantation


• Neoplasms– Half of brain stem gliomas occur

here– Cephalad extension of cervical

spinal cord tumors into distal medulla is also common

– Most are low grade astrocytomas– Inferior extension of

medulloblastoma in children and haemangioblastoma in adults are common are the common nonglial neoplasms of the cervicomedullary junction.

– Intraaxial metastases are rare in this location.







Uncommon Metastases




Common Common




Uncommon

Schwannoma

Epidermoid tumor

Paraganglioma

Metastases

Arachnoid cyst

Extramedullary Intradural Masses

• Anterior foramen magnum masses– Most arise anterior to

cervicomedullary junction.

• Posterior foramen magnum masses







Uncommon Metastases




Common Common




Uncommon

Schwannoma

Epidermoid tumor

Paraganglioma

Metastases

Arachnoid cyst

Anterior foramen magnum masses• Vascular lesions

– Ectatic Vertebral Artery– Aneurysms

• Neoplasms– Meningioma– Schwannoma– Epidermoid tumors– Paragangliomas– Metastases

• Non-vascular Non-neoplastic lesions– Arachnoid, inflammatory and neurenteric cysts– Extraosseous intradural chordomas– Intradural rheumatiod nodules

Anterior foramen magnum masses – vascular lesions

• Ectatic vertebral artery– Most common intradural

mass anterior to the medulla– There is no correlation

between neurologic deficit and the presence of vascular grooves along the brainstem, regardless of their size.

• Aneurysms– Vertebral artery– Posterior inferior cerebellar

arteryPICA aneurysm

Anterior foramen magnum masses - neoplasms

• Meningioma:– The most common primary intradural extramedullary

neoplasm in this location.• Nerve sheath tumors

– Second most frequently encountered neoplasms– Schwannomas of CNs IX to XI– Neurofibromas from exiting spinal nerve segments

• Misc:– Epidermoid tumors– Paragangliomas– Metastases – cistenal, perineural and skull base

Left: Sagittal T2-weighted MR image obtained in a 48-year-old man, demonstrating an anteriorly situated foramen magnum meningioma (long arrow) causing compression and displacement of the rostral spinal cord (short arrow). Right: Axial T1-weighted Gd-enhanced MR image obtained at the level of the foramen magnum. The homogeneously enhancing tumor arises predominantly in an anterior location with some left lateral contribution. The large tumor occupies slightly more than half of the transverse diameter of the foramen magnum and affords an adequate surgical corridor of approximately 1 cm. The rostral spinal cord (arrow) is compressed and displaced posteriorly.

Anterior foramen magnum masses - Non-vascular Non-neoplastic lesions

• They are uncommon.– Arachnoid, inflammatory and neurenteric cysts– Extraosseous intradural chordomas or notochordal

remnants– Intradural rheumatoid nodules







Uncommon Metastases




Common Common




Uncommon

Schwannoma

Epidermoid tumor

Paraganglioma

Metastases

Arachnoid cyst

Posterior Foramen Magnum Masses

• Herniated tonsils– 5 to 10% of all foramen

magnum masses– Most frequent

extramedullary intradural mass posterior to the cervicomedullary junction.


• Herniated tonsils– Congenital

• Occur with Chiari I malformations

– Acquired• Causd by increased

intracranial pressure or posterior fossa masses.

• After lumboperitoneal shunting of subarachnoid spinal space.

• Reported with multiple traumatic lumbar punctures


• Ependymoma• Subependymoma• Medulloblastoma

– Are intraaxial neoplastic masses that sometimes extend posteroinferiorly behind the medulla


• Ependymoma• Subependymoma• Medulloblastoma

– Are intraaxial neoplastic masses that sometimes extend posteroinferiorly behind the medulla


Common Craniovertebral junction





Uncommon Metastases




Common Common




Uncommon

Schwannoma

Epidermoid tumor

Paraganglioma

Metastases

Arachnoid cyst

Extradural Masses• Most extradural masses at the

foramen magnum are osseous lesions.– Trauma– Arthropathies– Congenital malformations– Tumors

• High resolution MR delineates relationship between the osseous abnormalities, neural canal, and spinal cord in CVJ malformations.

• Plain film tomography and CT with multiplanar 3D reconstruction are helpful for detailing the complicated osseous abnormalities seen in these disorders.

Trauma • Odontoid fractures

– Relatively common– 20% of all cervical fractures– 25 to 40% cause death at the

site of accident.– Survivors do not experience

immediate neurologic impairment.

– Late-onset myelopathy secondary to non united dens fracture may occur.

– Chronic instability can lead to spinal stenosis and irreversible cord damage.The Anderson and D’Alonzo classification of odontoid fracture. Type I fractures involve

avulsion near the tip of the dens. Type II fractures occur at the base of the odontoid process. Type III fracture lines extend into the body of the axis.

Trauma

• Odontoid fractures– CT – delineates the

osseous abnormalities.– MR – best delineates the

relation to the spinal subarachnoid space and cord itself.

Trauma

• Odontoid fractures– CT – delineates the

osseous abnormalities.– MR – best delineates the

relation to the spinal subarachnoid space and cord itself.

Arthropathies

• True synovial joints– Full spectrum of degenerative and inflammatory arthropathies occur.

• Rheumatoid arthritis of spine is second in incidence only to that of hands and feet.

• Cervical spine is affected in 80% of patients.• Prominent pannus and atlantoaxial subluxation may cause

severe CVJ narrowing with spinal cord compression.• Occasionally, rheumatoid nodules may be present within the

dura and perineurium.• Less common CVJ lesions include:

– Osteoarthritis, Paget disease, CPPD disorders, osteomyelitis with or without epidural abscess.

MRI of rheumatoid arthritis of the cervical spine. A sagittal spin-echo T1-weighted MR image shows inflammatory pannus eroding odontoid (arrow), and cranial settling with cephalad migration of C-2 impinging on the medulla oblongata (open arrow).

Congenital anomalies

• Congenital CVJ anomalies are relatively uncommon, and include:– Vertrabralisation of occipital condyles– Arch hypoplasias and aplasias– Os odontoideum– Odontoid hypoplasia– Assimilations and – Ligament laxity

• Occur in isolation or with basilar invagination.• May be associated with other congenital abnormalities like

Down syndrome, Chiari I malformations, or syringohydromyelia.

Neoplasms • Primary and metastatic tumors• Most extradural tumors affect clivus and are therfore anterior to

medulla.• Primary neoplasms include:

– Chordoma– Osteocartilaginous tumors (chondroma, chondrosarcoma)

• Metastases– Haematogenous– Local extensions (nasopharyngeal or skull base tumors)

• All lesions replace normal fatty marrow– Hypointense on T1; hyperintense on T2 (regardless of etiology)

• Exception is Chordoma:– Very high, but heterogenous signal intensity on T2

Metastasis from a renal cell carcinoma at the jugular foramen and FM region

Contrast-enhanced computed tomography shows an enhancing mass at the base of the left posterior fossa destroying the lower clivus, occipital squama, and lateral mass of C1.

MRI shows large enhancing soft tissue mass in the region of the left jugular foramen and lateral to the foramen magnum.

DIFFUSE SKULL BASE MASSES

• Lesions that can occur in any or all BOS locations

Diffuse Skull Base Lesions

Non Neoplastic Masses

Uncommon

Fibrous dysplasia

Paget’s disease

Langerhans’ cell histiocytosis

Neoplastic Masses

Common

Metastasis

Uncommon

Myeloma

AnaemiasMeningioma

Meningioma

Lymphoma

Rhabdomyosarcoma

Fibrous dysplasia

• Among the most common skeletal disorders.

• Adolescents and young adults

• Monoostotic (70%) or polyostotic

• Skull and facial bone involvement:– 25% of patients with

monoostotic FD– 40 to 60% of patients with

polyostotic FD

• Expands and replaces the normal bone medullary spaces with vascular fibrocellular tissue.

• Varying degrees of ossification may be seen.

• CT:– Thickened sclerotic bone with a

“ground-glass” appearance.

• Cystic components may be present in the early active stage.

• MR:– Low to intermediate signal on T1 and

T2; scattered hyperintense regions may be present.

• Variable contrast enhancement.

• Expands and replaces the normal bone medullary spaces with vascular fibrocellular tissue.

• Varying degrees of ossification may be sen.

• CT:– Thickened sclerotic bone with a

“ground-glass” appearance.

• Cystic components may be present in the early active stage.

• MR:– Low to intermediate signal on T1 and

T2; scattered hyperintense regions may be present.

• Variable contrast enhancement.

Paget disease

• Osseous lesion of unknown etiology

• Monoostotic or polyostotic

• Focal or diffuse• 3 phases are identified:

– Early destructive phase– Intermediate phase with

combined destruction and healing

– Late sclerotic phase.

• Imaging findings vary with stage.

• Both CT and MRI scans show expanded bone of the skull base associated with calvarial involvement.

• MRI better demonstrates the basilar invagination often seen because of bone softening.

CT scan of the skull included an axial view at midcranial level (bone window), which confirmed the asymmetric broadening of the skull, increased density of the calvarium, and disturbance of the trabecular architecture due to diffuse mineralisation of the diploe with corticomedullary dedifferentiation.

• Imaging findings vary with stage.

• Both CT and MRI scans show expanded bone of the skull base associated with calvarial involvement.

• MRI better demonstrates the basilar invagination often seen because of bone softening.

MRI of the skullshows on the axial T2- weighted MR-image of the posterior fossa showing thickening of the skull with corticomedullary dedifferentiation and non-homogeneous, low to intermediate signal intensity of the diploe.

Langerhan Cell Histiocytosis• Solitary or monoostotic Eosinophilic

Granuloma is the most common presentation.

• Children between 5 and 15 years; occassionally in young to middle-aged adults.

• Typically affects skull vault• However, striking diffuse osteolytic skull

base and calvarial lesions can occur.• Single or multiple areas of pure

osteolysis are seen in the skull base and calvarium of children (i.e., eosinophilic granuloma).

• A soft tissue mass may be associated (i.e., Hand-Schuller-Christian or Letterer-Siwe disease)

Langerhan Cell Histiocytosis• Solitary or monoostotic Eosinophilic

Granuloma is the most common presentation.

• Children between 5 and 15 years; occassionally in young to middle-aged adults.

• Typically affects skull vault• However, striking diffuse osteolytic skull

base and calvarial lesions can occur.• Single or multiple areas of pure

osteolysis are seen in the skull base and calvarium of children (i.e., eosinophilic granuloma).

• A soft tissue mass may be associated (i.e., Hand-Schuller-Christian or Letterer-Siwe disease)

Metastases • Most common malignancy of

skull base• Direct or haematogenous

spread• MC primary – lung, breast

and prostate• CT – destructive mass

infiltrating the skull base• MRI – T1WI show a “muscle”

intensity mass within the skull base with loss of normal, low intensity cortical bone signal

Metastasis to the sphenoid triangle (greater wing of sphenoid). The tumor (T) expands in all directions, pushing the temporalis muscle laterally, extending into the middle cranial fossa, and impinging on the orbit causing proptosis.

Myeloma

• Multiple myeloma or solitary plasmacytoma is possible

• Indistinguishable from osteolytic metastases on CT or MRI

• In the diffuse form, all bones of the skull base are involved, with permeative changes. Bone window images demonstrates

destruction of clivus, petrous apex, sphenoid bone, lateral mass of C1, and the pedicle of C2 on left side

Anemias

CT of the 6 years old with thalassemia showing extensive hypertrophy of the diploic spaces mostly in the maxillary walls, skull base and frontal bones. Note obliteration of the maxillary, sphenoid and frontal sinuses. Also note increased trabeculation in the diploë. This results from bone marrow hypertrophy due to ineffective erythropoiesis.

Interventional Neuroradiology in Skull Base

Interventional Neuroradiology in Skull Base

• Image guided biopsy• Radio-frequency Ablation and Cryoablation for Tumors• Percutaneous Sclerotherapy – venous malformations• Preoperative Tumor Embolization• Management of Bleeding from the Head and Neck

– Transarterial Embolization for Epistaxis– Bleeding from Carcinoma of the Head and Neck– Carotid Blowout Syndrome

• Other lesions of vascular etiology– AVF– Dural AVF – Transverse, Sigmoid– CCF– Aneurysms

• Intra-Arterial Chemotherapy for Head and Neck Carcinoma

Image-Guided Biopsies

• A, Paramaxillary approach to the left parapharyngeal space mass, proven to be an oncocytoma. Slight turning of the head to the opposite side simplifies the approach to this parapharyngeal space lesion.

• B, Subzygomatic approach to the masticator space mass via the intercondylar notch. The core specimens in this patient with previously treated squamous cell carcinoma revealed scar tissue with no evidence of malignant cells.

• C, CT image in a patient with a mass at the C2 level reveals a subtle left-sided epidural soft-tissue (arrow) and cortical irregularity of the vertebral body (arrowhead). This image was acquired with contrast to map the location of the adjacent vertebral A.

• D, A posterolateral approach to the epidural mass was planned. A 22-gauge Franseen needle is advanced through a guiding needle, and aspiration biopsy is performed. Aspiration biopsy was consistent with a diagnosis of chordoma

Radio-frequency Ablation and Cryoablation for Tumors

• A 59-year-old man with severe dyspnea and dysphagia secondary to a large squamous cell carcinoma treated with radio-frequency ablation.

• A, Axial contrast-enhanced CT scan demonstrates a large necrotic tumor (arrows) in the floor of the mouth and hypopharynx.

• B, 3D volume-rendered reconstruction demonstrates the radio-frequency probe and electrode deployment within the tumor by means of a submental approach.

• Note that the tumor anterior and posterior to the hyoid bone could be ablated simultaneously.

Left cheek venous vascular malformation(A) Clinical picture before treatment showing left cheek mass. (B) T2-weighted, fat-saturated axial MR image showing a mass with heterogeneous signal intensity in the left masseter muscle extending to the masticator space. (C) Injection of 75% ethanol mixed with Ethiodol under live subtraction mode showing accumulation of the sclerosing agent in the lesion. (D) Further injection of the sclerosing agent with compression of the venous outflow of the lesion. (E) Non-subtracted image of the head after sclerotherapy showing stasis of the sclerosing agent within the lesion. (F) Clinical picture 5 months after treatment showing decreased size of the left cheek mass.

Preoperative Tumor Embolization• The tumors that require embolization in the head and neck most

commonly include – glomus tumors, – angiofibromas, and – meningiomas.

• Many other types of tumors that may also require preoperative embolization include the following: – hypervascular metastases, – esthesioneuroblastomas, – schwannomas, – rhabdomyosarcomas, – plasmacytomas, – chordomas, and – hemangiopericytomas.

Preoperative Tumor Embolization

• The embolic agents in common use are:– polyvinyl alcohol (PVA), – Embospheres (Bio- Sphere Medical, Rockland, Mass), – liquid embolic agents (glue, ethylvinyl alcohol copolymer, or Onyx), – gelatin sponge (Gelfoam), and – coils.

Glomus jugulare tumor. • (A) Contrast-enhanced head CT shows an enhancing

mass extending into right temporal bone at cerebellar pontine angle level (arrow).

• (B) Bony expansion and destruction at jugular fossa level (arrow) is seen on thin section temporal bone CT.

• (C) Axial and (D) coronal contrast-enhanced MRI shows a corresponding intensely enhancing mass (arrows), consistent with glomus jugulare paraganglioma tumor.

• Diagnostic angiography confirms dense tumor blush, consistent with glomus tumor.

• Multiple feeding arteries were found, indicating a multicompartmental tumor, and these feeding pedicles were embolized to stasis with polyvinyl alcohol particles.

• (E) Lateral view during injection of a common trunk of the right occipital artery and ascending pharyngeal shows dense stain from ascending pharyngeal artery. AP, ascending pharyngeal artery; Occ, occipital artery.

• (F) Tumor blush seen on selective catheterization of a feeding pedicle from posterior division of the right ascending pharyngeal artery.

Juvenile nasal angiofibroma• (A) Axial and (B) coronal T1-weighted

MRI with contrast confirms the intensely enhancing mucosal mass in left nasal cavity, with rightward displacement of the nasal septum (arrows).

• (C) Unsubtracted and (D) subtracted cerebral angiogram demonstrates intense tumor blush in nasal cavity during internal maxillary artery.

• (E) Postembolization angiogram of the sphenopalatine artery shows no residual tumor blush.

• The tumor subsequently was resected endoscopically, with an estimated total blood loss of 75 cm3.

Bleeding from Carcinoma of the Head and Neck

• An elderly man with a recurrent head and neck cancer presenting with pulsatile bleeding through the oral cavity.

• A, CT angiogram of the neck shows an ulcerated left oropharyngeal mass (arrowheads) that encases the left ECA (arrow).

• B, Common carotid angiogram reveals a long-segment tumor encasement of the left ECA. C, The ECA is embolized with fibered and detachable platinum coils. The patient did not have additional episodes of bleeding after the embolization.

Maxillary arteriovenous malformation

• (A) Clinical picture before treatment showing a soft tissue pulsatile mass in the left gingiva and palate.

• (B, C) Early (B) and late (C) phases of the left external carotid artery angiogram in the lateral projection showing a left maxillary arteriovenous malformation with large draining venous channel inside the maxilla.

• (D) Lateral view of the superselective angiogram of the left descending palatine artery showing arteriovenous shunts to the intraosseous vein.

• (E) N-butyl cyanoacrylate (NBCA) cast injected from the same microcatheter position as in (D), showing penetration of NBCA into the vein.

• (F) Lateral view of the external carotid artery angiogram after multiple embolization showing disappearance of the arteriovenous malformation.

• (G) Clinical picture after embolization showing ulceration of the left palate. No further hemorrhagic episodes were experienced.

Lower-grade dural arteriovenous fistula of the left sigmoid sinus

• Study confirms low-grade dural arteriovenous fistula of the left sigmoid sinus, with multiple feeding arteries, including (A) occipital artery, (B) ascending pharyngeal artery, (C) middle meningeal artery, and (D), and left vertebral artery.

• Each of these feeding arteries was embolized to stasis using polyvinyl alcohol particles. Coils were placed in the distal occipital artery to protect the cutaneous branches from the effects of the proximal embolization (∗, seen in B).

• Following transarterial embolization of the feeding arteries, transvenous embolization was performed for a combined transarterial-transvenous approach, resulting in complete obliteration of the fistula.

• This combined transarterial and transvenous treatment results in durable cure of this fistula without open surgery.

Higher-grade dural arteriovenous fistula of the torcular region

• Diagnostic angiogram confirms DAVF of the torcular region, with supply from multiple arteries including the middle meningeal artery and opacification of multiple cerebellar veins.

• Transvenous embolization of this fistula is not practical.

• After transarterial embolization with NBCA tissue adhesive, resulting in a glue cast of the distal feeding arteries and proximal recipient veins, the fistula is obliterated.

• CV, cerebellar veins; MC, microcatheter in middle meningeal artery; MMA, middle meningeal artery.

Direct (high-flow) carotid cavernous fistula – post traumatic

• (A) Coronal T1-weighted MRI shows dilated superior ophthalmic vein (SOV).

• (B) Axial image from MR angiogram also shows a dilated superior ophthalmic vein (SOV).

• (C) Angiogram of left internal carotid artery (IAC) (lateral projection) confirms a fistula (CCF) with opacification of cavernous sinus and retrograde flow in superior ophthalmic vein (SOV), draining to facial veins (FV).

• (D) After embolization with detachable balloons, the fistula is closed.

Symptomatic mid-basilar aneurysm• (A) 3-D reconstructions from

magnetic resonance angiography. • (B) Diagnostic cerebral angiogram,

anteroposterior projection from • (C) 3-D rotational angiography. (D)

Lateral projection from cerebral angiogram obtained after endovascular treatment with a combination of endovascular stents for reconstruction of the arterial lumen, followed by coiling.

• Patient's symptoms resolved following this treatment.

Intra-Arterial Chemotherapy for Head and Neck Carcinoma

ADVANCES

Advances in Skull Base Imaging

• Advances in the areas of diagnostic imaging, interventional radiology, surgical approaches and techniques, as well as electrophysiological monitoring, have all advanced the treatment of skull base tumors and disorders.

Advances in CT & MR technologies

• Better and precise diagnosis• Facilitated aggressive skull base surgery by

allowing precise preoperative delineation of the extent of lesions

• Post operative follow-up

Advanced image-guided skull base surgery.

Advanced image-guided skull base surgery.

The early localization of the major vessels or neural structures during transtumoral decompression is beneficial. A: Instrument points to the petrous portion of the internal carotid artery (ICA) during decompression of a cavernous sinus meningioma. B: Instrument points to the basilar artery (BA) during removal of a craniopharyngioma

CT/MR Fusion For Skull Base Imaging


• A: Axial CT visualized at bone window settings demonstrates lytic lesion with well-defined margins in left petrous apex (M). Note extent of bone erosion involving cortex of the posterior petrous portion of the temporal bone (curved arrow) and bony covering (straight arrows) of the petrous segment of the internal carotid artery (C).

• B: Axial T1-weighted noncontrast- enhanced MR imaging performed in same patient shows a high signal intensity mass located within the left petrous apex (curved arrow) which is characteristic of a cholesterol granuloma. Note relationship of the mass to the basilar artery (straight arrow).

• There is excellent visualization of the soft tissues of the brain and masticator spaces (M); however, the relationship of the mass to the carotid artery (c) and the extent of bone erosion is better seen on CT than on MR imaging.


Conclusion

• The central skull base is a highly complex region.

• Knowledge of the normal development and anatomic relationships will lead to more accurate diagnoses.

• This in turn helps in decision making, especially regarding challenging surgical procedures.

Health & Medicine

Imaging in Skull base