Infratentorial Midline Cyst



Infratentorial Midline Cyst


Gregory L. Katzman, MD, MBA



DIFFERENTIAL DIAGNOSIS


Common



  • Mega Cisterna Magna


  • Arachnoid Cyst


Less Common



  • Neurocysticercosis


  • Dandy-Walker Continuum


  • Obstructive Hydrocephalus (“Trapped” or “Encysted” 4th Ventricle)


  • Pilocytic Astrocytoma


  • Hemangioblastoma


  • Epidermoid Cyst


  • Dermoid Cyst


  • Enlarged Perivascular Spaces


Rare but Important



  • Congenital Vermian Hypoplasia


  • Ganglioglioma


  • Pleomorphic Xanthoastrocytoma


  • Neurenteric Cyst


ESSENTIAL INFORMATION


Key Differential Diagnosis Issues



  • Is mass intra- or extra-axial?


  • If extra-axial, cistern or 4th ventricle?



    • CSF cistern (mega cisterna magna, Dandy-Walker continuum, arachnoid cyst, epidermoid cyst)


    • 4th ventricle (encysted ventricle, neurocysticercosis, dermoid or epidermoid cyst, cystic neoplasm)


  • If intra-axial, pons, vermis, or cerebellum?



    • Cerebellum (enlarged perivascular spaces, cystic neoplasm)


    • Vermis (cystic neoplasm, vermian hypoplasia)


    • Pons (cystic neoplasm > > enlarged perivascular spaces)


Helpful Clues for Common Diagnoses



  • Mega Cisterna Magna



    • Enlarged posterior fossa CSF space


    • Normal vermis completely covers 4th ventricle (rules out Dandy-Walker malformation/variant)


    • May show striking scalloping of skull (due to CSF pulsations)


  • Arachnoid Cyst



    • Sharply demarcated extra-axial cyst


    • Follows CSF attenuation/signal


    • Suppresses on FLAIR, no DWI restriction


    • Size varies from few millimeters to giant


    • Often asymptomatic, found incidentally


Helpful Clues for Less Common Diagnoses



  • Neurocysticercosis



    • Best clue: Cyst with “dot” inside



      • ± Discrete eccentric scolex


      • Cyst slightly hyperintense to CSF


    • Cisterns > 4th ventricle


  • Dandy-Walker Continuum



    • DWC: Broad spectrum of cystic posterior fossa malformations


    • DW malformation: Large posterior fossa + large CSF cyst, normal 4th ventricle absent, lambdoid-torcular inversion


    • DW variant: Failure of “closure” of 4th ventricle, vermian hypoplasia


    • Includes persistent Blake pouch cyst, mega cisterna magna


    • 2/3 have associated CNS &/or extracranial anomalies


  • Obstructive Hydrocephalus (“Trapped” or “Encysted” 4th Ventricle)



    • Due to obstructing lesions of 4th ventricle; all foramina must be involved (Magendie, Luschka, aqueduct)


    • May be from hemorrhage, infectious, inflammatory, or neoplastic causes


    • Ventricle enlarged but maintains basic shape


    • CSF intensity/attenuation


  • Pilocytic Astrocytoma



    • Cystic cerebellar mass with enhancing mural nodule


    • Cerebellum > vermis, 4th ventricle


    • Child > adult


  • Hemangioblastoma



    • Best diagnostic clue: Adult with intra-axial posterior fossa mass with cyst, enhancing mural nodule abutting pia


    • Size varies from tiny to several centimeters


    • 1-2% of primary intracranial tumors, 7-10% of posterior fossa tumors


    • May be associated with von Hippel-Lindau syndrome


  • Epidermoid Cyst



    • Congenital inclusion cyst


    • Lobulated, irregular, insinuating CSF-like mass with “fronds”


    • Cerebellopontine angle cistern > 4th ventricle



    • FLAIR usually doesn’t completely null; restricts on DWI


  • Dermoid Cyst



    • Congenital inclusion cyst


    • Looks like fat



      • Use fat-suppression sequence to confirm


      • ± Rupture (fat droplets in cisterns, sulci, ventricles)


      • May cause chemical meningitis, extensive enhancement


  • Enlarged Perivascular Spaces



    • Pial-lined interstitial fluid-filled structures that accompany penetrating arteries but do not communicate directly with subarachnoid space


    • Cluster of variably sized intra-axial cysts


    • Off-midline (dentate nuclei) > midline (vermis, pons)


    • Follow CSF



      • Suppress completely on FLAIR


      • No restriction on DWI


      • No enhancement


    • “Leave me alone” lesion that should not be mistaken for serious disease


Helpful Clues for Rare Diagnoses



  • Congenital Vermian Hypoplasia



    • Prototype = Joubert syndrome


    • Inherited hypoplasia or aplasia of vermis characterized by transient episodic hyperpnea, oculomotor abnormalities, ataxia, variable mental retardation


    • “Molar tooth” brainstem; “bat wing” or “umbrella” shaped 4th ventricle; vermian remnant variable size


    • Midline anomalies common (holoprosencephaly, frontonasal dysplasia, facial clefting)


  • Ganglioglioma



    • Best diagnostic clue: Partially cystic, enhancing, cortically based mass in child/young adult


    • Cortical dysplasia commonly associated


    • Excellent prognosis if surgical resection complete


    • Malignant degeneration rare, approximately 5-10% (glial component)


  • Pleomorphic Xanthoastrocytoma



    • Supratentorial cortical mass with adjacent enhancing dural tail


    • Cyst and enhancing mural nodule typical


    • 98% supratentorial, rarely found in cerebellum


    • Despite circumscribed appearance, tumor often infiltrates


  • Neurenteric Cyst



    • Benign malformative endodermal CNS cyst


    • Round/lobulated nonenhancing mass


    • Anterior to pontomedullary junction, slightly off-midline


    • Slightly/moderately hyperintense compared to CSF






Image Gallery









Sagittal T1WI MR in the midline shows a very large CSF-intensity space behind an intact vermis image. Note the thinned inner table of the occipital bone image.

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Aug 7, 2016 | Posted by in NEUROLOGY | Comments Off on Infratentorial Midline Cyst

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