Intralymphatic Histiocytosis of the Appendix and Fallopian Tube Associated With Primary Peritoneal High-Grade, Poorly Differentiated Adenocarcinoma of Müllerian Origin.

Intralymphatic histiocytosis (ILH) is a peculiar pathological process characterized by the collections of benign histiocytes in dilated lymph vessels. Although the majority of ILH patients present clinically with various forms of cutaneous manifestation, rare extracutaneous incidences have been reported in the literature. To date, ILH has not been described in an internal visceral organ. We report the case of a 68-year-old woman who underwent an appendectomy during a surgical procedure for a primary peritoneal high-grade, poorly differentiated adenocarcinoma of Müllerian origin. Although no malignancy was identified in the appendix, the appendiceal mucosa and submucosa were expanded by dilated vascular channels harboring aggregates of uniform epithelioid cells. Similar histological changes were also identified in the right fallopian tube. Immunohistochemical studies revealed the lymphatic nature of the vessels and the histiocytic origin of the intravascular cells. Of note was the presence of scattered multinucleated giant cells in the histiocytic population, a histological feature not described hitherto in ILH. To the best of the authors' knowledge, this is the first case of ILH harboring multinucleated giant cells, involving internal visceral organs, and associated with a malignant tumor of the gynecological system. As such, the current case report expands the clinical and histological spectrum of ILH.