Chondroblastoma - occipital condyle

Case contributed by Frank Gaillard
Diagnosis certain

The right occipital condyle is destroyed by a hyperdense/enhancing mass. The bony margins are sharply demarcated.  

An enhancing, relatively high T2 signal, mass replaces the right occipital condyle. 

Case Discussion

The patient went on to have a biopsy.


Microscopic description:

Sections show the specimen to consist of needle core biopsies that include portions of lamellar bone, and soft tissue containing portions of tumor. The tumor cells are arranged in lobules and sheets. There is a distinct margin between tumor and adjacent soft tissue. The individual tumor cells are characterized by relatively large cells with frequently eccentrically located nuclei, large nuclei with occasionally prominent nucleoli. Some nuclei display linear grooves. Perinuclear cytoplasm is relatively abundant, and a delicate basophilic hue is noted in the peripheral margins of the cellular cytoplasm.

Some multinucleated tumor cells are seen. In areas, there is a nidus of fibrillar calcification that is turn surrounded by tumor cells. Some delicate strands of fibrillar calcification are noted, some of these appear to be tumor cells.

A well-defined chondroid mesenchymal component is not seen in the material examined. The adjacent soft tissues display a relatively prominent reactive inflammatory infiltrates that consists of reactive lymphocytes and plasma cells.

The tumor cells are immunopositive for vimentin, and, for the most part, are immunonegative for S100, although some scattered cells may display some modest immunoreactivity for S100. There are variable and relatively weak patterns of immunoreactivity within cellular cytoplasm for keratin, CK20, and the significance of this is unclear. Of particular note, the negative control also displays areas of relatively weak immunoreactivity. Very occasional mitotic figures are identified.

Final Diagnosis: chondroblastoma.

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