CPA angle lesions

Question 1

Cerebellar Pontine Angle DDx (3)

Answer 1

Vestibular Schwannoma.
Meningioma.
Epidermoid

Question 2

Vestibular Schwannoma (5)

Answer 2

75% of CPA masses.
Bilateral suggests NF2.
Enhances strongly, but more heterogenously than meningiomas.
May widen porus acousticus, resulting in a “trumpet shaped” IAC.

Question 3

Meningioma (6)

Answer 3

Second commonest CPA mass.
More common in women.
Can calcify, and can have dural tail (almost pathognomonic).
Extradural, so they enhance strongly.
Radiation of the head is known to cause these.
Most common location of a meningioma is over cerebral convexity.
They take up octreotide and Tc-MDP on nuclear medicine.

Question 4

Epidermoid (5)

Answer 4

Can be congenital or acquired (after trauma, classically after LP and in the spine).
Unlike dermoids, they’re usually off the midline.
Follows CSF density and intensity on CT and MRI.
Unlike arachnoid cyst, they are bright on FLAIR (sometimes warm) and will restrict diffusion.

Question 5

Dermoid cyst (6)

Answer 5

Less common than epidermoid (4x less).
More common in kids/young adults.
Usually midline, usually found in 3rd decade.
Contain lipoid material and are usually hypodense on CT and very bright on T1.
Associated with NF2.
Usually midline.
Most common location is suprasellar cistern (posterior fossa is #2).
Epidermoid behaves like CSF, dermoid behaves like fat.

Question 6

IAC Lipoma (3)

Answer 6

It can occur, and is why we look at T1 sequences when working up CPA masses.
Will fat sat out, because it’s a lipoma.
Associated with sensorineural hearing loss, as the vestibulocochlear nerve often courses through it.

Question 7

Arachnoid cyst (4)

Answer 7

Common benign lesion that is located within the subarachnoid space, contains CSF.
Increased in frequency in mucopolysaccharidoses (as are periventricular spaces).
Dark on FLAIR like CSF. Will NOT restrict with diffusion.