Vermis Mass
Gregory L. Katzman, MD, MBA
DIFFERENTIAL DIAGNOSIS
Common
Medulloblastoma (PNET-MB)
Pilocytic Astrocytoma
Less Common
Metastasis
Hemangioblastoma
Rare but Important
Dural A-V Fistula
Arteriovenous Malformation
Cavernous Malformation
Cerebellitis
Atypical Teratoid-Rhabdoid Tumor
Dermoid Cyst
Glioblastoma Multiforme
Ganglioglioma
Dysplastic Cerebellar Gangliocytoma
Rhombencephalosynapsis (Mimic)
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
Patient age
Child: PNET-MB, pilocytic astrocytoma (PA), ATRT most common
Adult: Metastasis, hemangioblastoma most common
Does mass originate in vermis or 4th ventricle (V)?
Vermis: PA, metastasis, hemangioblastoma, cerebellitis, ATRT
4th ventricle: PNET-MB (from superior medullary velum), ATRT
Helpful Clues for Common Diagnoses
Medulloblastoma (PNET-MB)
30-40% of childhood infratentorial tumors
Round, hyperdense 4th ventricle mass
Arises from 4th ventricle roof
Posteroinferior spread into cisterna magna
Distinguishes PNET-MB from ependymoma (arises from floor, extrudes laterally)
Look for early subarachnoid spread
Lateral cerebellar hemisphere location
Desmoplastic variant
More common in older children, adults
Pilocytic Astrocytoma
Cystic mass with enhancing mural nodule
Hemispheres > vermis
Ca++ 20%, hemorrhage rare
Helpful Clues for Less Common Diagnoses
Metastasis
ALWAYS include metastasis in differential diagnosis of posterior fossa parenchymal mass in adult!
Seen in 25% of cancer patients at autopsy
Location approximately 80% hemispheres, 15% vermis, 5% pons/midbrain
Metastases have rounded configuration
Usually displace rather than infiltrate tissue
Virtually 100% enhance
Variable edema
Can be hematogenous or originate from leptomeningeal carcinomatosis
Hemangioblastoma
Adult with intra-axial posterior fossa mass = metastasis vs. hemangioblastoma
Classic imaging of hemangioblastoma = cyst + enhancing mural nodule abutting pia
Solid mass ± hemorrhage less common
Size varies (tiny to several centimeters)
Only 1-2% of 1° intracranial tumors but 7-10% of posterior fossa tumors
80% cerebellar hemispheres
15% vermis, 5% other (medulla, 4th V)
± von Hippel-Lindau syndrome
Hemangioblastomas in VHL typically don’t develop until young adulthood, middle age
Rare in children
Helpful Clues for Rare Diagnoses
Dural A-V Fistula
10-15% of all cerebrovascular malformations
Dural AVF involving foramen magnum, tentorium, torcula Herophili, or posterior fossa veins (e.g., inferior vermian vein) may affect vermis
May be occult, cause tinnitus
Can present with hemorrhage
Rare: Dementia
Arteriovenous Malformation
“Bag of black worms” on MR with minimal/no mass effect unless hemorrhage
Posterior fossa < hemispheres
Headache, hemorrhage in 50%
Cavernous Malformation
Benign vascular hamartoma with masses of immature blood vessels (“caverns”), intralesional hemorrhages, no neural tissue
Seizure 50%, neurologic deficit 25%, asymptomatic 20%
NECT: 40-60% Ca++
MR
Most common pattern = “popcorn ball” with hypointense rim
May present initially with large hematoma
Can be familial, multiple (multiple cavernous malformation syndrome)
Do T2* scan (GRE or SWI) in all cases of spontaneous, “unexplained” intracranial hemorrhage!
Cerebellitis
Rare inflammatory syndrome
Can be primary infectious, post-infectious, post-vaccination, or idiopathic
Imaging often nonspecific
MR > > CT
Bilateral hemispheric involvement (75%)
T2 hyperintensity
Variable enhancement (none to intense)
Atypical Teratoid-Rhabdoid Tumor
Infant/young child
50% infratentorial
Off-midline > vermis
Mass often large, heterogeneous
Can mimic PNET-MB
Dermoid Cyst
Rare: < 0.5% of 1° intracranial tumors
Fat appearance: Use fat-suppressed sequence to confirm
With rupture find fat droplets in cisterns, sulci, ventricles w/extensive enhancement possible from chemical meningitis
Glioblastoma Multiforme
Rapidly enlarging tumor with necrosis, neovascularity
Peak 45-70 years but may occur at any age
Cerebellum uncommon primary site
95% have thick, irregular enhancing rind of neoplastic tissue surrounding necrotic core
Ganglioglioma
Well-differentiated, slowly growing neuroepithelial tumor composed of neoplastic ganglion cells & glial cells
Partially cystic, enhancing, cortically based mass in child or young adult
Hemispheres > > cerebellum
Ca++ common (35-50%)
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