Glossary of Neuro Smirn Posterior fossa
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- Internal auditory canal nerve arrangement
- REMEMBER 7UP and Coke Down -- for the anterior aspect of the IAC.
Circle with 4 pie slices
Anterosuperior pie slice is 7
Anteroinferior pie slice is cochlear portion of 8
Posterosuperior slice is superior portion of vestibular nerve of 8
Posteroinferior is inferior portion of vestibular nerve of 8
- CP angle mass
- DDx is SAME
Schwannoma (8th, more commonly than 5th)
Aneurysm or Arachnoid cyst
Meningioma or mets
Epidermoid or ependymoma
- Ependymoma and CPP
- Yes, they ARE located in the 4th ventricle when in the posterior fossa, but they can squirt out through the exit foramina and grow out there in the CP angle cistern
- Vestibular schwannoma -- Where does it arise from usually?
- Superior portion of vestibular nerve.
THE IMPORTANCE OF THIS IS THAT YOU CAN HAVE NERVE SPARING SURGERY THAT DOES NOT INTERFERE WITH THE 7th or Cochlear nerves
BUT ALSO REMEMBER THE FOLLOWING: AS THE NERVE COMES OFF OF THE CP ANGLE, IT IS STILL COVERED BY OLIGODENDROCYTES, NOT YET SCHWANN CELLS. THE SCHWANN CELL COVERAGE DOES NOT BEGIN UNTIL THE NERVE IS ALREADY IN THE IAC. THUS ALL VESTIB SCHWANNOMAS BEGIN IN THE IAC, AND THEN GROW BACK INTO THE CP ANGLE JUST BECAUSE THEY ARE FOLLOWING THE PATH OF LEAST RESISTANCE.
THEY ALWAYS START AS AN INTRACANALICULAR MASS
- Most common CP angle mass
- Vestibular schwannoma
- Second most common CP angle mass
- Trigeminal schwannoma
- Third most common CP angle mass
- Fourth most common?
- Epidermoid inclusion cyst
- Appearance of vestibular schwannoma that you are not used to
- THEY CAN GET BIG
And when they do, they can dissect into the space between the pons and cerebellum and create a big mass there
ALSO, since they are just schwannomas, then like ALL schwannomas they have both Antoni A and B material, and so can have a very heterogeneous, even cystic apperarance. These cystic areas WILL NOT ENHANCE. Thus, while the solid portions will enhance very brightly, the liquid portions will NOT, so enhancement can be heterogeneous, and it is still a vestib schwannoma
- CP angle mass, not coming from IAC
- ASK FOR CT TO LOOK FOR HYPEROSTOSIS to rule in meningioma. Only lesion that will cause hyperostosis.
OR, look carefully on the MR at the medial margin of the petrous. It should be STRAIGHT. If it is heaped up at all, that is hyperostosis
- Hint that lesion is a meningioma
- HYPEROSTOSIS -- best sign
BROAD BASE of dural attachment. (IN CP ANGLE region this is along the medial surface of petrous bone)
Dural tail (non-specific)
Growing on both sides of falx, tentorium or into bone as well as brain
- Meningioma mnemonic
- 4 H's
- DDx for posterior fossa mass in child
- 4 things:
Ependymoma -- 4th ventricle
Medulloblastoma -- starts in vermis, extends into 4th ventricle
Pilocytic astrocytoma -- cerebellar hemispheric mass with cystic component
- Adult with posterior fossa mass (not in CP angle cistern)
- Infarct or Hemorrhage
Astrocytoma -- brainstem or cerebellar
- Child with posterior fossa mass on CT
- LOOK AT THE DENSITY
Medullos are SMALL ROUND BLUE CELL TUMORS, thus high nuclear to cytoplasmic ratio, and thus high attenuation values.
- Location of 4th ventricle and vermis
- 4th ventricle is located just ANTERIOR to the cerebellar vermis
- Mass in cerebellum in child with cystic and solid components
Unlike a hemangioma, there is not much variability between the size of the solid and the size of the cystic components. The solid component is usually quite significant. So dont expect a cyst and a tiny mural nodule. The reason the hemangioblastoma can have a tiny mural nodule and a huge cyst is that the mural nodule in hemangioblastoma is very hypervascular and secretes lots of fluid.
Cystic component is not surrounded by enhancing tumor on all sides, i.e. it is not encased by solid elements. If it were, you would think tumor necrosis
- Mass with cystic and solid components in 20 year old
- Dilemma age, because could be either pilocytic or hemangioblastoma
DIFFERENTIATE THEM NOT BY SIZE OF CYST VERSUS NODULE, BUT BY THE DEGREE OF VASCULARITY OF THE NODULE. A VERY BRIGHT ENHANCING NODULE WILL BE HEMANGIOBLASTOMA, NOT PILOCYTIC.
- MUST RULE OUT VHL
May be purely solid -- BRIGHT enhancement
- Multiple bright enhancing solid homogeneous posterior fossa masses
- Multiple hemangioblastomas of VHL
- Hemangioblastoma in VHL
- In a patient with VHL who has hx of RCCA, they are more likely to develop a PRIMARY HEMANGIOBLASTOMA than metastatic disease.
To tell the difference with more certainty? -- LOOK SUPRATENTORIALLY. If there is metastatic disease there, then its probably all mets. If not, then could likely be hemangioblastomas.
- Mass conforming to 4th ventricle
- Ependymoma. In the posterior fossa, ependymoma respects the boundaries of the 4th vent, but is still a bad tumor, because:
1) Early CSF dissemination -- these are the tumors that exude like toothpaste out of the outlet foramina
2) Start at floor of 4th ventricle, attached to brainstem.
- Hypodense cerebellar mass on CT
- Sure you can think of epidermoid, maybe even cystic portion of hemangioblastoma, but . . . DONT FORGET THE MOST COMMON THING LIKE YOU JUST DID . . . ITS INFARCT!!!!!!!!! INFARCT!!!!!
- Mass in petrous apex
- Cholesterol granuloma
Endolymphatic sac tumor
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