Pediatric Extraaxial Posterior Fossa Tumors

Case A: An extraaxial lesion that is predominantly T2 hyperintense with central hypointensity is seen at the left CPA and skull base. The lesion contains posterior areas of T1 and T2 shortening consistent with hemorrhage or high protein content with heterogenous enhancement. On the coronal postgadolinium image, a large extracranial component is noted with abnormal enhancement within the occipital and petrous bones. A CT scan of the corresponding regions demonstrated mixed sclerotic and lytic appearance of the left petrous and occipital bones (not shown).

Case B: A large heterogeneous mass is seen centered within the left cerebellomedullary cistern and extends into the left pars nervosa. The extraaxial nature of this mass is best appreciated on the postcontrast image comfirmed with the cerebrospinal fluid left on the T2 sequence of the left posterior lateral margin of the lesion. The lesion also demonstrates peripheral and central enhancement with an intermediate zone of decreased enhancement.

Case C: A small, well-defined peripheral high signal extraaxial lesion is seen in the right CPA on T2 images. On the postcontrast T1 image, the lesion does not show any enhancement, whereas there is marked reduced diffusivity on DWI.

Case D: An axial T2 image demonstrates a well-defined lesion that shows T2 and T1 shortening of the cyst wall. Note the sinus tract communicating with the skin through the occipital bone ( arrow ). This lesion demonstrates rim enhancement and central low diffusivity representing a dermoid cyst. A second left lesion adjacent to this shows more avid rim enhancement associated with marked edema and mass effect with milder low apparent diffusion coefficient and fluid level, which was revealed to be an abscess.