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EXTRA-AXIAL SPACES
• Anatomically-based ExpDDxs:• Epidural mass• CPA mass• Prepontine cistern mass• Foramen magnum mass
• Generic imaging patterns• Sulcal-cisternal enhancement• Enhancing cranial nerves
• Modality-specific ExpDDxs:• FLAIR hyperintense CSF
EPIDURAL MASS
• Common• Epidural hematoma
• Meningioma
• Skull/dural mets
• Less common• Lymphoma/leukemia
• Neurosarcoid
• Epidural empyema
• Rare but important• Tuberculoma
• Plasmacytoma
• Meningioma, Atypical/Malignant
• Hemangiopericytoma
• Extramedullary hematopoiesis
• Gliosarcoma
• Histiocytoses
EPIDURAL HEMATOMA
• Fx in 85-95%
• “Swirl sign”• Unclotted blood
• Rapid accumulation
• Arterial EDH 90%• Most adjacent to fx,
laceration of MMA
• Venous 10%• Lacerated dural
venous sinus
• Slower, more insidious
“swirl sign” crosses dura
MENINGIOMA
• “Typical” meningioma• WHO I
• Clues to diagnosis:• Hyperdense +/- Ca++• Vascular “pedicle”• +/- hyperostosis• Isointense to GM• CSF-vascular “cleft”• Intense enhancement• Dural “tail”
• All have mimics• Metastases (esp. breast)
DURAL METASTASES
• Look for skull, scalp lesions
• Often multiple
• Use T1C+FS for subtle lesions
• Can mimic meningioma!
SKULL/DURAL METASTASES
• Bone + dural invasion often present
• Mode of tumor spread varies with histologic type• Most common = direct spread from calvarium
to dura• Adults = Lung, breast, prostate
• Children = neuroblastoma, Ewing, hemopoietic
• Less common = hematogenous spread to dura• Lymphangitic, intravascular pulmonary tumor
• Rare• Extension from dural metastasis to brain parenchyma
• Brain parenchyma spread into dura
SKULL/DURAL METASTASES:CT
• Lytic/destructive
• Use wide windows!
• Usually enhance
• Subgaleal, dural involvement common
SKULL/DURAL METASTASES:MR
• Marrow fat replaced
• +/- Cortical destruction
• +/- Adjacent dura often thickened, enhancing
• Can be solitary or multifocal
• Often extensive, diffuse, both sub- and epidural
LESS COMMON/RARE BUT IMPORTANT EPIDURAL MASSES
Lymphoma,
leukemia
Tuberculoma
Extramedullary
hematopoiesis
Plasmacytoma
CPA MASS, ADULT
• Common• Vestibular schwannoma
• Less common• Meningioma
• Epidermoid cyst
• Aneurysm
• Arachnoid cyst
• Metastasis
• Rare but important• NF2
• Sarcoidosis
• Rare (contd)• Choroid plexus papilloma
• Lipoma
• Ependymoma
• Pseudotumor
• Schwannoma, facial n.
• Schwannoma, JF
• Hemangioma
• Neurenteric cyst
CPA MASS, ADULT
• “Big kahuna” = vestibular schwannoma• 90% of all CPA-IAC masses
• Classic “ice cream on cone”
• “Small chiefs”• Meningioma, epidermoid, aneurysm, arachnoid cyst
• Together = approximately 8%
• Everything else• 10 rare dxs together = 2%
CPA MASS, ADULT:Imaging Protocols
• T1C+ FS MR = gold standard
• T2 FS thin-section/hi res CISS if VS suspected
• Helpful additions• FS for VS vs. lipoma
• FLAIR + DWI for epidermoid vs. arachnoid cyst
• GRE/SWI for aneurysm, blood, Ca++
ENHANCING CPA MASS:Helpful Clues in DDx
Meningioma
(mushroom
cap, dural tail)
Facial n. schwannoma
(geniculate ganglion)
Hemangioma
(speckled)
Metastasis
(flocculus, not
nerve)
CYSTIC CPA MASS
Arachnoid cyst
(smooth,
suppresses,
doesn’t restrict)
Epidermoid cyst
(cauliflower,
restricts, doesn’t
suppress)
Neurenteric cyst
(not like CSF)Cystic VS (extends
into IAC)
SULCAL-CISTERNAL ENHANCEMENT
• Common• Meningitis• Meningeal
carcinomatosis• Lymphoma
• Less common• Neurosarcoid• Sturge-Weber• Fungal disease• Subacute aSAH• Opportunistic
infections
• Rare but important• Leukemia• Neurocutaneous
melanosis
• Contrast
MENINGITIS (INFECTIOUS)
• Clinical-lab dx• Why image?
• Can be – when LP +• FLAIR may be + early• Look for complications• Agents (bacterial, TB, viral, etc)
look same
• Intense enhancement• Pia, subarachnoid space > > dura-
arachnoid pattern
• Caution: Infectious meningitis, carcinomatous may look identical!
ENHANCING CRANIAL NERVES
• Common• Metastases
• NF2
• NF1
• MS
• Less common• Neuritis (viral, post-
viral)
• Lyme disease
• Lymphoma
• Sarcoid
• Opportunistic infection (HIV/AIDS)
• Rare but important• Leukemia
• Ischemia (diabetes, ASVD)
• LCH
• CIDP
ENHANCING CRANIAL NERVE(S):Key Considerations
• Enhancement of cisternal, cavernous sinus CN segments always abnormal
• Solitary or multiple CNs involved?
• Which CN(s) affected?• Optic nerve: MS, NF1, viral/post-viral
• CN3, 6: Ischemia (diabetes, microvascular disease)
• CN7: Bell palsy, Herpes zoster (Ramsay Hunt), schwannoma
• CN8: Schwannoma (sporadic, NF2), metastasis
MULTIPLE ENHANCING CRANIAL NERVES
• Common• Metastases• NF2
• Less common• Viral, post-viral neuritis• Lyme disease• Lymphoma• NF1• Leukemia
• Rare but important• MS• CIDP
SOLITARY ENHANCING CRANIAL NERVE
• Common• Metastasis
• Schwannoma (VS)
• MS
• NF1 (plexiform nf, optic glioma)
• Less common• Viral, post-viral (Bell, Herpes, ADEM)
• Ischemia (diabetes, ASVD)
FLAIR HYPERINTENSE CSF
• Common• Subarachnoid hemorrhage
• Meningitis
• MR artifact
• Metastases (carcinomatous meningitis)
• Less common• Gadolinium in CSF
• BBB leakage
• Renal failure
• Acute cerebral infarct
• Rare but important• Dermoid cyst (ruptured)
• Moyamoya (“ivy sign”)
SUBARACHNOID HEMORRHAGE
• Trauma > aneurysm
• Other etiologies• Nonaneurysmal
perimesencephalic SAH
• Vein, dural sinus occlusion
• Vascular malformation
• CT > MR
• Hyperintense CSF in basal cisterns, sulci
MENINGITIS
• Sulcal exudate
• Basilar > convexity
• Can be so FLAIR hyperintense that mimics nl T2WI!
• Look for• Sulcal effacement on T1WI
• Ventriculitis
• Enhancement on T1C+
MR ARTIFACTS:Magnetic Susceptibility
• Metal (braces, root canal, aneurysm clips)
• Air interfaces
• Incomplete suppression
• Local magnetic field alterations →• Null point for fluid (T1)
altered
• Inappropriate high signal intensity
2 hr later
? abnormal
MR ARTIFACTS, MISCELLANEOUS
• Flow-related
• Patient-related• Motion
• Supplemental oxygen (4-5x signal ↑ with 100%)
• ? Propofol anesthetic
• Renal failure → Gd leaks into CSF
CRF 12h
after Gd
Sedation,
↑ O2
METASTASES (CARCINOMATOUS MENINGITIS)
• Causes of hyperintense CSF• ↑ cellularity
• ↑ protein
• Can be focal, regional or diffuse
• Pial enhancement in sulci
• Breast, lung most common
LESS COMMON/RARE CAUSES OF FLAIR HYPERINTENSE CSF
Cerebritis
post contrastCerebral ischemia
(slow flow)
Moya-moya (ivy
sign)
PRES