Skull Base Imaging

24-5-20169.21 pm

Great teachers – All this is their work . I am just the reader of their

books .Prof. Paolo castelnuovo

Prof. Aldo Stamm Prof. Mario Sanna

Prof. Magnan

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Dr.Prahlad sir https://www.facebook.com/prahlada?fref=tsskull base imaging lecture

Click link for skull base imaging video = https://www.youtube.com/watch?v=HYYB-8pv7k4&feature=youtu.be

Popular videos of skull base imaging in youtube

https://www.youtube.com/playlist?list=PLxfT3LHUjLuJD3JsWQU4vL

h4X5f_5OD0g

• In book of Mario sanna – “Microsurgery of paragangliomas” given – “ Radiological Anatomy ” in 3rd chapter – click https://books.google.co.in/books?id=7k_jwKyT6d0C&lpg=PP1&dq=mario%20sanna%20paraganglioma&pg=PP101#v=snippet&q=Radiological%20Anatomy&f=false

Content

• Normal skull base anatomy

• Pathology intrinsic to skull base – some case examples

• Pathology affecting skull base from below – some case examples

• A few hints and tips!

Anatomy

Five Bones:

• Ethmoid - CP• Sphenoid-

GW+LW• Occipital• Temporal- paired• Frontal-paired

Cranial Fossae

• Anterior

• Middle

• Posterior

Anterior Cranial Fossa• Anterior

• Frontal bone: frontal sinus,supra-orbital foramen

• Posterior• Post. edge of lesser

wing sphenoid and its ant. Clinoid processes

– Intracranial landmarks: foramen ceacum, crista galli, cribiform plate, planum sphenoidal

– Extracranial landmarks: nasal cavity, ethmoid and sphenoid sinuses, orbits

Middle Cranial Fossa

• Anterior• Posterior edge of lesser

wing of sphenoid

• Posterior• Post-sup edge of

petrous temporal bone

Posterior Cranial Fossa• Anteriorly

– Post-sup edge of petrous temporal bone

• Posteriorly– it is enclosed by the

occipital bone.• Laterally

– portions of the squamous temporal and mastoid part of the temporal bone form its walls.

• It contains the brainstem and cerebellum.

Skull Base Anatomy

Temporal Bone

Temporal bone- petrous portion

Sphenoid Bone

Occipital Bone

Key Fissures

• Petro-sphenoidal fissure

• Petro-occipital fissure

Key Sutures

• Sphenosquamous Suture

• Occipitomastoid Suture

Skull base foramina

FORAMEN OVALE

FORAMEN SPINOSUM

CAROTID CANAL

JUGULAR FORAMEN

IACINTERNAL AUDITORY CANAL

CAROTID CANAL

OSSICLES

MALLEUS

INCUS

Skull Base Anatomy

Skull Base Anatomy

Foramen spinosum

Sphenoid spine- lower level

Foramen rotundum- higher level

Pterygopalatine fossa

Foramen ovale

Petro-occipital fissure

Pterygoid canal

f. lacerum

Skull Base AnatomyForamen Spinosum• Middle meningeal artery/vein

• CV V3, recurrent branch

• Lesser superficial petrosal nerve

Foramen Ovale• CN V3

• Lesser petrosal nerve

• Accessory meningeal artery

• Emissary veins

Skull Base Anatomy

Foramen Lacerum• Ascending pharyngeal artery- meningeal branch

• Nerve of pterygoid canal

Vidian Canal • aka pterygoid canal

• Pterygopalatine fossa - foramen lacerum

• Vidian nerve

• Vidian artery

Skull Base Anatomy

Foramen rotundum• CN V2

• Artery of foramen rotundum

• Emissary veins

*

Skull Base Anatomy

Foramen magnum• Medulla oblongata

• Vertebral arteries

• Anterior/Posterior spinal arteries

Hypoglossal canal• CN XII

• Hypoglossal artery*

Skull Base Anatomy

Jugular Foramen• Pars nervosa: CN IX, inferior petrosal sinus

• Pars vascularis: CN X, XI, jugular bulb

*

* Carotid canal

Skull Base Anatomy

Pterygopalatine Fossa• Pterygopalatine ganglia V2

• Pterygopalatine plexus

• Communicates with:Inferior orbital fissure

Orbital apex

Sphenopalatine foramen

Pterygomaxilary fissure

Foramen rotundum

Vidian canal

Greater/lesser palatine canals and foramina

Receives: Superior opthalmic vein Inferior opthalmic vein Sphenoparietal sinus

Drains via: Petrosal sinuses Basilar plexus

Pterygoid plexus

Connection: Circular sinus

Contains: CN III, IV, V1, V2, VI

Skull Base Anatomy

Cavernous Sinus

Meckel’s Cave• Posterior aspect of cavernous sinus

• Gasserian ganglion (sensory root ganglion of CN V)

Skull Base AnatomySuperior Orbital Fissure• CN III, IV, V1, VI

• Middle meningeal artery- orbital branch

• Recurrent meningeal artery

• Superior opthalmic vein

Inferior Orbital Fissure• Infraorbital artery, vein, and nerve (V2 branch)

Optic Canal• Optic nerve

• Opthalmic artery

Orbital landmarks• Superior orbital fissure

• Optic canal

• Inferior orbital fissure – other end of foramen rotundum

• Ant. And Post. Ethmoidal foramina

• Anterior & Posterior ethmoidal arteries

• Foramina = constant guide to level of ethmoid roof as position of fronto-ethmoid suture.

Skull base Pathology

• Intra-axial – brain lesions/tumours

• Extra-axial – lesions from adjacent structures, usually from below skull base

• Metastatic eg breast, lung, prostate ca

Extra- axial pathology of anterior and middle cranial fossae

• Paranasal sinus Lesions

• Malignant: SCC, adenocarcinoma, sarcoma, melanoma, olfactory neuroblastoma, adenoid cystic, distant mets.

• Benign: mengioma juvenille nasopharyngeal angiofibroma, fibrous dysplasia, Inverting papilloma, fibro osseous disease

Paranasal sinus malignancy• Maxillary sinus carcinoma

• SCC commonest

• T4b- involvement of dura, brain, clivus, nasopharynx (inoperable)

• Multiplanar CT with contrast and MRI to fully assess – unilateral sinus mass with bony wall destruction (sinus wall is rarely expanded).

• MRI good for perineural, dural and intra cranial spread

Extra-axial pathology of posterior cranial fossa

• CPA lesions• Acoustic neuromas, meningioma’s, other

neuromas (rare eg VII nerve neuroma), epidermoids, glomus tumours, arachnoid cysts, haemangiomas

• Rare – mets, chordomas, chondrosarcoma, lipoma, dermoids, teratomas

• Petrous apex lesions• Cholesterol granuloma, cholesteatoma,

meningioma, asymmetric petrous( extra bone marrow – can be mistaken for neoplasm!), mucocele, petrous ICA aneurysm, giant cell tumour.

Intra-axial Pathology of skull base

• Brainstem – gliomas (commonest CPA tumour in children)

• Cerebellum/ brain – medulloblastomas, astrocytomas, haemangioblastomas

• Fourth ventricle – choroid plexus papillomas, ependymomas

Brainstem Glioma

Case 1

Chondrosarcoma

CT Findings:• Irregular, destructive mass

• Centered off midline

• Petro-occipital fissure

• Calcifications, 70%; “rings/arcs”

MRI Findings:• Low T1 signal, high T2 signal

• Enhance with contrast

• Scalloped, well circumscribed margins

ChondrosarcomaOrigin:• Preexisting cartilaginous lesion, synchondroses, cartilage endplates

Location:• Paranasal sinuses, skull base, parasellar region

• Long bones, pelvis, sternum, ribs

Clinical:• 45 yo, median age

• Classic, mesenchymal, or undifferentiated

Case 2

CT/MRI Findings:• Expansile lytic lesion, midline

• Well delineated mass arising from bone

• Large soft tissue component

• Variable calcification

• Anteroposterior extension

• Heterogeneous enhancement on T1, T2

• Dark on T1, bright on T2

Chordoma

Diff. Dx:• Chondroma

• Chondrosarcoma

• Clivus meningioma

ChordomaOrigin• Notochord remnants

Location• Clivus 35%

• Sacrum 50%, Vertebral bodies 15%

Clinical• age 30-70

• Slow growing, locally aggressive

• CN VI- CN deficits

• Mets late

• Tx: surgery, radiation

Case 3

Glomus Tumor

Glomus jugulare CT/MRI Findings:• Center: jugular foramen

• Limit: hyoid bone

• Enhance w/ contrast

• Salt and pepper appearance on MRI

• Bone erosion

Glomus Tumor

Origin:• Chemoreceptor cells

Location:• 10% multiple

• glomus jugulare: jugular bulb

• glomus tympanicum: cochlear promontory;

Clinical:• Pulsatile tinnitus

• Hearing loss

• arrythmia, BP fluctuation

Hints and tips!• MRI-Talk about signal intensity (low vs high)

• Marrow=hyper intense• Bone=hypointense• High flow blood vessels – black on MR

• MRI T1weighted• water=black• Fat=white• Look for CSF around spinal cord to see

• MRI T2 weighted• Water=white• Fat=black• Nodes show up brighter on T2 as cystic necrosis

Hints and tips - MRI• Lipomas signal suppresion on STIR

• Adenoid cystics – peri neural spread seen only after gadolinium contrast on T1 – makes them shine!

• Parapharyngeal space –Schwannomas and paragangliomas are behind carotid so push carotid antero-medially and up to skull base. Best seen on T1 after gadolinium

• Paragangliomas – look shaggy, light up quickly with contrast then wash out

• Schwannomas – look smooth and have delayed enhancement after contrast

Paraganglioma on T2

Lipoma at petrous apex

Hints and tips - MRI• Glomus Jugulare – slow

growing, shows irregular bone destruction

• Fibrous dysplasia – inhomogenous enhancement

• Meningioma – bright on T1 and light up with gadolinium, broad based and dural tail

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