Presentation
10 days of dizziness and diplopia
Patient Data
CT demonstrates a mass arising from the clivus and protruding posteriorly and abutting and indenting the pons. No convincing enhancement. The clivus is superficially eroded.
Incidental note is made of a left middle cranial fossa arachnoid cyst.
A lobulated tumor measuring 2.8 x 1.6 x 2.7 cm centered at the prepontine cistern is brightly T2 hyperintense with internal small foci of T2 hypointensity, mild to moderately T2 FLAIR hyperintense and predominantly T1 hypointense. The bulk of the tumor moderately enhances. Several tiny foci of internal calcification are seen on CT, with erosion of the clivus, attenuation of part of the dorsum sellae, as well as breach of the medial posterior wall of the left carotid canal with small bony fragments.
The posterior aspect of the tumor abuts the basilar artery, but without evidence of significant compression, with preserved basilar flow void and enhancement. A tongue of tumor on the right protrudes to abut the right side of the basilar artery and mildly indents the right anterior pons with normal pontine signal preserved (thumb sign). Inferiorly, it drapes along the posterior surface of the clivus to 1 cm from the clival tip. Superiorly, it reaches at the level of the posterior clinoid process. Anteriorly, a component on the left extends medial to the medial wall of Meckel's cave, displacing it laterally, erode the posteromedial wall of the carotid canal, with tumor abutting the carotid artery from the medial left carotid canal and as it ascends in the posterior left cavernous sinus. The caliber of the left carotid artery at the medial most aspect of the left carotid canal appears narrowed.
Moderately large left temporal arachnoid cyst extends superiorly to splay the opercular left frontal and temporal lobes.
Paraffin sections show fragments of a densely hypercellular tumor. Tumor cells have small round hyperchromatic nuclei and a large amount of vacuolated cytoplasm imparting a physalliferous appearance. Tumor cells are arranged in solid aggregates and cords within a mucinous stroma. Tumor cells show strong immunostaining for cytokeratin CAM5.2 and weaker staining for S100 protein. The features are of chordoma.
FINAL DIAGNOSIS: Chordoma.
Case Discussion
This is a typical example of a chordoma, demonstrating the thumb sign and the characteristic signal intensity.
The main differential is that of a chondrosarcoma of the base of skull. The absence of chondroid calcifications, the shape of the tumor and midline location all weigh against this as a diagnosis.