Presentation
Followup of known skull base abnormality. Slowly growing.
Patient Data
A markedly T2 hyperintense lobulated mass arising from the right aspect of the clivus corresponding to a relatively homogeneous T1 iso/ hypointensity with heterogeneous enhancement post contrast is noted. No associated diffusion restriction.
The mass exerts mass effect on the right side of the pons, however the 4th ventricle and cerebral aqueduct remain capacious and there is no hydrocephalus. Adjacent flow void within the right petrous/cavernous ICA is preserved. No other intracranial or skull base lesion seen.
Conclusion:
Marked T2 hyperintensity can be seen with either chondroid lesions or chordoma. Less likely differentials include an ecchordosis physaliphora, cavernous sinus hemangioma and least likely (given morphology) a schwannoma.
Overall features favor a chondroid series tumor (including chondrosarcoma), although chordoma can occur off midline and evoke bony erosion/sequestration which can mimic a similar pattern of bony change.
Further assessment with CT to evaluate matrix calcification/ossification and bony margins is recommended.
A focal bony defect on the right side of the clivus, with small arcs of bone located within and over the dorsal surface of the lesion. Intact bone, albeit thinned, is seen separating the lesion from the sphenoid sinus. The posterior wall the pituitary fossa may however be deficient.
Conclusion: Off-center well circumscribed high T2 signal lesion seen on MRI, has calcification/ossification of the matrix in arcs and spicules. This suggests a low-grade chondroid lesion (low-grade chondrosarcoma) over the alternative diagnosis of an ecchordosis physaliphora or even less likely a chordoma (given only minor growth over the past 2 years).
The biopsies show a chondroid neoplasm. It is mildly hypercellular, containing lobules of cartilage. The chondrocytes have focal mild nuclear enlargement and hyperchromasia. Occasional binucleated forms are seen. There are no mitoses or necrosis. Some of the cartilage are surrounded by host bone. An invasive growth pattern is noted although no definite invasion through the bone is seen. The lesional cells are S-100 and M2A positive, confirming chondroid differentiation. They are CAM5.2 negative, excluding chordoma.
DIAGNOSIS: Grade 1 chondrosarcoma.
Case Discussion
The differential for a lesion of vividly high T2 signal in this location is relatively small including:
The presence of bony changes typical of chondrosarcoma, allows one to make the preoperative diagnosis with some confidence.
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