Walthard Cell Nests on the Serosal Surface of the Small Intestine Mimicking Metastatic Carcinoma: A Report of a First Case.

Walthard cell nests (WCNs) are benign epithelial proliferations composed of urothelial-like transitional cells, most commonly encountered within the female reproductive tract and adjacent peritoneal surfaces. Although typically incidental findings, they may rarely occur in extragenital locations and can pose a diagnostic challenge due to their resemblance to metastatic tumors. To the best of our knowledge, following a review of the available literature, this is the first case of WCNs involving the serosal surface of the small intestine in a 58-year-old male patient with a history of urothelial carcinoma who presented with a strangulated umbilical hernia. Multiple small serosal nodules observed intraoperatively raised concern for metastatic disease. Histopathologic examination with immunohistochemistry confirmed the diagnosis of WCNs. This case expands the spectrum of reported anatomical locations of WCNs and highlights the importance of recognizing this benign entity to avoid misdiagnosis as metastatic disease.