= uncommon congenital malformation developing within subarachnoid space as a result of abnormal differentiation of the meninx primitiva (which differentiates into pia mater, arachnoid, inner meningeal layer of dura mater)
Incidence:<1% of brain tumors
Age: presentation in childhood / adulthood
Associated with congenital anomalies:
- in anterior location: various degrees of agenesis of corpus callosum (in 50–80%)
- in posterior location (in <33%)
- asymptomatic in 50%
Location: tendency to involve midline structures (usually in subarachnoid space): callosal cistern (25–50%), sylvian fissure, quadrigeminal cistern, chiasmatic cistern, interpeduncular cistern, CP angle cistern, cerebellomedullary cistern, tuber cinereum, choroid plexus of lateral ventricle
- NO enhancement
CT:
- well-circumscribed mass with CT density of –100 HU
- occasionally calcified rim (esp. in corpus callosum)
MR:
- hyperintense mass on T1WI + less hyperintense on T2WI (CHARACTERISTIC)
- saturation on fat-suppressed sequences
Rx: insinuating mass around vessels + nerves → difficult to resect
= congenital pericallosal tumor not actually involving corpus callosum ← faulty disjunction of neuroectoderm from cutaneous ectoderm during process of neurulation
Incidence: ~ 30% of intracranial lipomas
Associated with:
- anomalies of corpus callosum (30% with small posterior lipoma, 90% with large anterior lipoma)
- frontal bone defect (frequent) = encephalocele
- cutaneous frontal lipoma
- in 50% symptomatic:
- seizure disorder, mental retardation, dementia
- emotional lability, headaches, hemiplegia
Plain film:
- midline calcification with associated lucency of fat density
CT:
- area of marked hypodensity immediately superior to lateral ventricles with possible extension inferiorly between ventricles / anteriorly into interhemispheric fissure
- curvilinear peripheral / nodular central calcification within fibrous capsule (more common in anterior compared with posterior lipomas)
MR:
- hyperintense midline mass superior + posterior to corpus callosum on T1WI
- no callosal fibers dorsal to lipoma
- branches of pericallosal artery frequently course through lipoma
DDx: dermoid (denser, extraaxial), teratoma
Incidence: extremely rare (30 cases in literature)
Location: between mamillary bodies + infundibular stalk
- rarely symptomatic: variety of neurologic symptoms + endocrinologic disturbances
- one / more masses directly behind infundibular stalk
- central adipose (hyperintense on T1WI + T2WI with positive fat suppression) + peripheral osseous tissue (hypointense on T1WI + T2WI)
- consistent size