Case-of-the-Month - February 1997

Submited by:
Cyril Fisher, Department of Histopathology, Royal Marsden Hospital, London, England

Clinical history

A 13 year old boy had a painless mass in the lower part of his abdomen for one year. Examination showed a well circumscribed lesion 4.5 x 4 x 3 cm within the abdominal wall muscles, medial and unrelated to the inguinal canal. Following needle biopsy diagnosis, the mass was excised with a cuff of normal tissue.

Pathology

Light microscopy

The needle core biopsy (Fig. 1) showed small polygonal tumor cells in branching and anastomosing cords in a fibrous and myxoid stroma, without mitoses or necrosis. Immunohistochemistry was positive for S100 protein and vimentin and a provisional diagnosis of extraskeletal myxoid chondrosarcoma was made. The excised mass had similar appearances, but was enclosed within a distinct fibrous capsule (Fig. 2) from which extensions divided the tumor into lobules. The tumor cell nuclei were rounded and bland without mitoses (Fig. 3), and some cells had cytoplasmic processes. Further immunohistochemistry revealed, in addition to S100 protein (Fig. 4), widespread positivity for glial fibrillary acidic protein and for desmin and smooth muscle actin in a few single cells, whereas cytokeratin, epithelial membrane antigen and CD34 were negative.

Figure 1. Needle core biopsy shows cords of darkly staining small polygonal cells in a fibrous and myxoid stroma, resembling myxoid chondrosarcoma.	Figure 2. The lesion is homogeneous and enclosed within a thick fibrous capsule.
Figure 3. Tumor cells have rounded, only mildly pleomorphic nuclei. Some of the cells have long thin processes.	Figure 4. There is strong nuclear immunoreactivity for S100 protein in most cells.

Electron Microscopy - Page 2

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