Intracranial peripheral primitive neuroectodermal tumors of the cavernous sinus: a diagnostic peculiarity.

Peripheral primitive neuroectodermal tumors (pPNETs) are aggressive, poorly differentiated neoplasms that occur in children and young adults. These tumors are associated with a peak incidence in the second decade and a slight male preponderance. Recently, Ewing sarcoma and pPNET tumors have been proven to carry identical translocations, the most common being t(11;22)(q24;q12). Intracranial Ewing sarcoma/pPNETs have rarely been described in the literature. We studied a case of intracranial pPNET arising in the right cavernous sinus of a 46-year-old man. On imaging, the tumor had both sellar and suprasellar components and was centered within the right parasellar region. Histologically, the tumor was composed of intermediate to large cells with round to oval hyperchromatic nuclei with distinct nucleoli. The cells contained a moderate amount of slightly basophilic cytoplasm. The tumor was markedly fibrotic and had collagen bands surrounding both individual and groups of cells. A large immunohistochemical panel was positive only for CD99 and vimentin. Fluorescence in situ hybridization did not show translocations associated with Ewing sarcoma/pPNET. However, a small percentage of these tumors can be negative for this translocation. In these cases, histology and immunohistochemical techniques in the absence of an alternative diagnosis are the only tools available to establish the diagnosis.