Surgically Resected Early Anal Gland Mucinous Adenocarcinoma Resemble a Benign Perianal Cyst: A Case Report

Adenocarcinoma of anal gland origin is a rare tumor that develops extramurally in the submucosal space and presents with nonspecific symptoms. Consequently, it is difficult to distinguish from benign conditions, such as anal cysts and abscesses, making early diagnosis challenging. Herein, we report a rare case of early-stage mucinous adenocarcinoma with a partially solid mass that appeared to have arisen from the anal glands and was initially diagnosed and treated as a perianal cyst.

A 68-year-old man presented to a local clinic with difficulty in defecation. A palpable mass, thought to be either a perianal cyst or abscess, was identified near the anus and was surgically resected. Histopathological examination revealed glandular tissue with mucinous components, but the lack of epithelial structures precluded a definitive diagnosis. Two years later, the patient developed a cystic lesion in the anus, which gradually enlarged, prompting referral to our department (Department of Surgery, Gastroenterological Center, Shunan Memorial Hospital). MRI suggested a cyst, but an attempt to aspirate the contents was unsuccessful. Local resection was performed because a mucinous cystic tumor was suspected. Pathological examination identified the lesion as a mucinous adenocarcinoma. Immunohistochemistry revealed strong positivity for cytokeratin 7, weak positivity for cytokeratin 20, and negativity for caudal-type homeobox 2, suggesting anal gland origin. The patient did not experience a recurrence during 13 months of follow-up.

This case highlights the difficulty in diagnosing mucinous adenocarcinoma of anal gland origin, which can resemble benign perianal cystic lesions, particularly in the early stage. Malignancy should be considered in recurrent or atypical extramucosal cystic lesions of the anal region, even when clinical and imaging evidence of malignancy is limited. Careful histopathological evaluation, together with clinical and imaging findings, is essential for accurate diagnosis and appropriate treatment selection.