Signet ring epithelioid stromal tumor of the small intestine

Cells having a signet ring appearance can occur in mesenchymal, lymphoid, a nd other nonepithelial neoplasms. We report the case of an intestinal strom al tumor with smooth muscle differentiation and a prominent signet ring cel l component. The presence of signet ring forms of smooth muscle cells in se ctions of paraffin-embedded tissue often contrasts with a lack of cytoplasm ic spaces by electron microscopy, and the ultrastructural finding of signet ring-like areas in the present case can be attributed to the fact that the tissue for electron microscopy was retrieved from paraffin blocks where th is peculiar artifact already existed. Ultrastructural examination of the si gnet ring-like areas suggests that they originated as retraction spaces whi ch may have resulted from variations in intracellular tension forces relate d to the distribution of actin filaments.