Neuro Smirn Posterior Fossa

Front 1

Internal auditory canal nerve arrangement

Back 1

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

Front 2

CP angle mass

Back 2

DDx is SAME


Schwannoma (8th, more commonly than 5th)


Aneurysm or Arachnoid cyst


Meningioma or mets


Epidermoid or ependymoma

and CPP

Front 3

Ependymoma and CPP

Back 3

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

Front 4

Vestibular schwannoma -- Where does it arise from usually?

Back 4

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

Front 5

Most common CP angle mass

Back 5

Vestibular schwannoma

Front 6

Second most common CP angle mass

Back 6

Trigeminal schwannoma

Front 7

Third most common CP angle mass

Back 7

Meningioma

Front 8

Fourth most common?

Back 8

Epidermoid inclusion cyst

Front 9

Appearance of vestibular schwannoma that you are not used to

Back 9

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

Front 10

CP angle mass, not coming from IAC

Back 10

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

Front 11

Hint that lesion is a meningioma

Back 11

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

Front 12

Meningioma mnemonic

Back 12

4 H's


HYPEROSTOSIS


Homogeneous enhancement


Hemispheric


?

Front 13

DDx for posterior fossa mass in child

Back 13

4 things:


Ependymoma -- 4th ventricle


Medulloblastoma -- starts in vermis, extends into 4th ventricle


Pilocytic astrocytoma -- cerebellar hemispheric mass with cystic component


Brainstem glioma

Front 14

Adult with posterior fossa mass (not in CP angle cistern)

Back 14

Infarct or Hemorrhage


Mets


Hemangioblastoma


Ependymoma


Astrocytoma -- brainstem or cerebellar

Front 15

Child with posterior fossa mass on CT

Back 15

LOOK AT THE DENSITY

Medullos are SMALL ROUND BLUE CELL TUMORS, thus high nuclear to cytoplasmic ratio, and thus high attenuation values.

Front 16

Location of 4th ventricle and vermis

Back 16

4th ventricle is located just ANTERIOR to the cerebellar vermis

Front 17

Mass in cerebellum in child with cystic and solid components

Back 17

PILOCYTIC


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

Front 18

Mass with cystic and solid components in 20 year old

Back 18

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.

Front 19

Hemangioblastoma

Back 19

MUST RULE OUT VHL


May be purely solid -- BRIGHT enhancement

Front 20

Multiple bright enhancing solid homogeneous posterior fossa masses

Back 20

Multiple hemangioblastomas of VHL

or

Mets

Front 21

Hemangioblastoma in VHL

Back 21

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.

Front 22

Mass conforming to 4th ventricle

Back 22

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.

Front 23

Hypodense cerebellar mass on CT

Back 23

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!!!!!

Front 24

Mass in petrous apex

Back 24

Cholesterol granuloma


Cholesteatoma


Glomus tumor


Endolymphatic sac tumor