Skull Base Tumors

            Primary, secondary, and metastatic tumors of the skull base can involve the parasellar region. The primary tumors include chordoma, chondroma, chondrosarcoma, and plasmacytoma. Secondary tumors are most often carcinomas from the nasopharynx and paranasal sinuses. The common metastases are from lung, breast, and prostatic carcinoma, but other tumors can also metastasize to the skull.

            Chordoma is a rare neoplasm, but it is the most common primary of the clivus. They arise from notochordal remnants in the clivus, meninges along the prepontine cistern, sphenoid or nasopharynx. The most common site is near the spheno-occipital synchondrosis. Chordomas are slow-growing and erode bone by direct extension. The soft tissue mass readily extends into the sella, perisellar, prepontine cistern, sphenoid sinus and middle fossa. Cartilaginous foci, bone fragments and calcifications are interspersed within the tumor matrix. Chondroma is a benign tumor that arises from cartilage cell rests at the skull base. Chondrosarcoma is the malignant counterpart that often originates from a preexisting benign lesion. Calcification is common in both tumors. Plasmacytoma is another rare tumor of the skull base that is derived from plasma cells. With time, many evolve to multiple myeloma.

            Chordomas and chondrosarcomas can be difficult to identify on T1-weighted axial images alone due to low contrast with the adjacent cortical bone and CSF, but alteration of the normal high signal clival fat is a sensitive indicator of disease. Plasmacytoma also has no distinctive MR features to allow for a definitive diagnosis. Enhancement with gadolinium is helpful to assess the intracranial components of these tumors. 

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