Ectopic decidua of pelvic lymph nodes: a potential diagnostic pitfall.

Ectopic decidua is one of several benign lymph node inclusions that have been increasingly documented in the literature, most often in postmortem examinations of pregnant woman and recently in pregnant women with cervical squamous cell carcinoma. Although lacking clinical significance of its own, the major diagnostic implication would be misdiagnosis as metastatic carcinoma in the lymph node. Intraoperative frozen sections are often performed prior to radical hysterectomy, leading to a potential alteration of therapy if metastatic carcinoma is identified in the lymph nodes. We report such a case of a pregnant woman with cervical squamous cell carcinoma requiring lymphadenectomy and hysterectomy, in which the intraoperative frozen section of a pelvic lymph node with ectopic decidual change was mistakenly identified as metastatic carcinoma. Its histologic resemblance to carcinoma and location within subcapsular sinuses, compounded with the fact that ectopic lymph node decidua is not commonly seen in routine practice, can lead to this diagnostic pitfall. We review the literature regarding ectopic decidua, its presence in lymph nodes, and its pathogenesis, as well as review the literature on benign lymph node inclusions.