An Unusual Sinonasal Tumor

Electron microscopy:
Figure 4 shows that the cords of cells are separated by considerable amounts of glycosaminoglycans and, more importantly, there are many aggregates of excess basal lamina between the tumor cells often enclosed by cellular processes. Both the cellular processes, at times joined by small, but well-formed desmsomes, and basal lamina lining intercellular spaces are better detailed in Figure 5. No glandular lumens, microvilli or neuroendocrine secretory granules were found. With these findings, antibody to muscle-specific actin was ordered and was found to be focally positive (1 to 2+) (Fig. 6).

Figure 4: Irregularly shaped tumor cells with a number of cellular processes, some of which enclose excess basal lamina (arrows). Glycosaminoglycan material (G) separates tumor cells.	Figure 5: Desmosomes (arrows), associated with tonofilaments, join some cellular processes. Basal lamina (arrowhead) lines some cell surfaces.

Figure 6: Immunostained for muscle-specific actin, which is focally positive.