Antenatal diagnosis of acardiac, acephalic twin.

A case of acardiac, acephalic twin diagnosed by antenatal ultrasound is reported. The obstetrical significance of this condition is discussed.

Clefts in intradermal nevi: an ultrastructural study.

Six intradermal melanocytic nevi, two with and four without intercellular slitlike spaces, were examined by light microscopy and electron microscopy of deparaffinized tissue. The spaces were partially lined by elongated nevus cells and contained a few collagen fibrils. Other features in both groups included an abundance of (1) immature elastic tissue comprised of aggregates of microfibrils lacking an amorphous component and (2) collagen fibrils that were finer than in normal dermis and did not form compact bundles. We propose that these elastic tissue and collagen fiber changes diminish the resistance of the dermis to the mechanical stress of the biopsy procedure and histologic processing, resulting in the formation of artifactual clefts.

Adenomatoid tumor of the epididymis: ultrastructural evidence of its biphasic nature.

Two adenomatoid tumors of the epididymis were examined by light and electron microscopy. Epithelial elements were characterized by the presence of a basal lamina investment, gland formation, luminal microvilli, apical junctional complexes, and cytoplasmic tonofibrils. The stomal cells lacked these features and demonstrated marked cytoplasmic elongation, complex cell processes, a more prominent granular endoplasmic reticulum, evidence of phagocytic activity, and an intimate association with the surrounding collagen and elastic fibers. A continuity of cell-to-cell contact between the epithelial and stromal cells was demonstrated along with the presence of cells displaying both epithelial and mesenchymal differentiation. This evidence of the biphasic nature of the neoplasm is consistent with its presumed mesothelial derivation.