Answer: Mesonephric remnants

Histology: Multiple sections of cervix show small tubules arranged in both lobular and diffuse fashion, extending deep into the cervical wall. The tubules are small, often contain eosinophilic intraluminal material, and do not appear to incite a stromal response. The tubules are lined by a single layer of cuboidal cells containing uniform nuclei without nucleoli. No mitotic figures are identified.

Discussion: Mesonephric remnants (MR) occur deep in the wall of the cervix and are not uncommonly an incidental finding in hysterectomy and cold-knife conization specimens. Although rare mesonephric neoplasms have been associated with mesonephric hyperplasia, the usual clinical course is uneventful even in cases in which the mesonephric tubules are present at the margins of resection. The main differential diagnosis is with a well-differentiated (minimal deviation) adenocarcinoma (adenoma malignum), typical adenocarcinoma, and clear cell carcinoma. Typically, MR occur deep in the cervical wall, whereas adenoma malignum involves the mucosa and extends deeply through the cervical wall without a lobular pattern and often eliciting a stromal reaction. Adenoma malignum also demonstrates cytologic atypia, at least focally, with vesicular nuclei containing prominent red nucleoli. Features supporting the diagnosis of clear cell carcinoma include the presence of various growth patterns (tubulocystic, papillary, and solid types) within the tumor, clear cytoplasm, hobnail cells, and easily identifiable mitotic figures.