Posterior Fossa Neoplasm, Adult



Posterior Fossa Neoplasm, Adult


Anne G. Osborn, MD, FACR



DIFFERENTIAL DIAGNOSIS


Common



  • Vestibular Schwannoma


Less Common



  • Meningioma, CPA-IAC


  • Metastases, CPA-IAC


  • Metastasis, Parenchymal


  • Hemangioblastoma


  • Other Schwannomas



    • Schwannoma, Trigeminal, Intracranial


    • Schwannoma, Facial Nerve, CPA-IAC


    • Schwannoma, Jugular Foramen


    • Schwannoma, Hypoglossal Nerve


  • Subependymoma


  • Choroid Plexus Papilloma


Rare but Important



  • Astrocytomas



    • Glioblastoma Multiforme (GBM)


    • Anaplastic Astrocytoma


    • Diffuse Astrocytoma, Low Grade


    • Pilocytic Astrocytoma


  • Paraganglioma, Glomus Jugulare


  • Dysplastic Cerebellar Gangliocytoma (Lhermitte-Duclos)


  • Medulloblastoma (Desmoplastic Variant)


  • Hemangiopericytoma


  • Lymphoma


  • Ecchordosis Physaliphora


  • Rosette-Forming Glioneuronal Tumor of the Fourth Ventricle


  • Cerebellar Liponeurocytoma


ESSENTIAL INFORMATION


Key Differential Diagnosis Issues



  • With exception of vestibular schwannoma, posterior fossa (PF) neoplasms rare in adults


  • Most important question: Is lesion intra- or extra-axial?


  • Extra-axial



    • Most adult PF neoplasms are extra-axial


    • By far most common is vestibular schwannoma


    • Meningioma > metastasis > other schwannomas > glomus jugulare paraganglioma


  • Intra-axial: Parenchymal or intraventricular?



    • Adult parenchymal neoplasms all uncommon/rare



      • Overall most common by far is metastasis


      • Hemangioblastoma most common primary


      • Astrocytomas, most common supratentorial tumors, rare in PF


    • Fourth ventricle



      • Subependymoma > choroid plexus papilloma (CPP)


      • Subependymoma in inferior fourth ventricle (obex)


      • CPP in body/lateral recess, CPA


Helpful Clues for Common Diagnoses



  • Vestibular Schwannoma



    • By far most common adult posterior fossa neoplasm; all others less common or rare!


    • 90% of all CPA-IAC masses


    • Looks like “ice cream on cone” (CPA-IAC)


    • Enhances strongly


    • ± Intra- or extratumoral cysts


Helpful Clues for Less Common Diagnoses



  • Meningioma, CPA-IAC



    • “Mushroom-shaped” mass caps IAC


    • Flat base towards dural surface


    • ± Hyperostosis, dural tail sign


    • 25% show IAC involvement!


  • Metastases, CPA-IAC



    • CPA metastases can arise in 4 locations



      • Dura-arachnoid


      • Cranial nerves (7, 8 most common)


      • Flocculus


      • Choroid plexus (foramen of Luschka)


    • Irregular, invasive margins


  • Metastasis, Parenchymal



    • Second only to VS as adult PF neoplasm


    • Most common parenchymal PF tumor


    • Rarely may be only brain metastasis!


  • Hemangioblastoma



    • 95% posterior fossa (hemispheres > > vermis > brainstem, 4th ventricle)


    • < 50% of patients have VHL (look for multiple lesions, visceral cysts, etc.)


    • Imaging



      • 60% nonenhancing cyst + strongly enhancing mural nodule abutting pia


      • 40% solid, ± blood products


  • Other Schwannomas



    • Trigeminal (CN5) schwannoma



      • Upper CPA mass


      • Look for “dumbbell” shape (CPA + Meckel cave components)



    • Facial nerve (CN7) schwannoma



      • CPA-IAC mass with “labyrinthine tail”


      • Look for labyrinthine segment tumor (if absent, can’t distinguish from VS)


    • Jugular foramen (JF) schwannoma



      • Enhancing mass arising from JF


      • Smooth remodeling of bony margins


      • Projects cephalad into CPA cistern


    • Hypoglossal (CN12) schwannoma (rare)



      • Smooth remodeling of hypoglossal canal


      • Look for ipsilateral tongue atrophy


  • Subependymoma



    • Middle-aged/elderly adult


    • Most small, asymptomatic


    • T2 hyperintense lobulated mass in inferior 4th ventricle (obex)


    • May have cysts, Ca++; hemorrhage rare


  • Choroid Plexus Papilloma



    • 40% of CPPs occur in 4th V, CPA


    • Most common in adults


    • Cauliflower or frond-like excrescences


    • Intense, relatively uniform enhancement


Helpful Clues for Rare Diagnoses

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Aug 7, 2016 | Posted by in NEUROLOGY | Comments Off on Posterior Fossa Neoplasm, Adult

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