105 Acinar Melanosis of the Bartholin Gland: Findings from the Fourth Reported Case

Introduction/Objective Pigmented lesions of the vulva present a diagnostic challenge due to their broad differential diagnosis including benign and malignant melanocytic proliferations, as well as pigmented epithelial lesions. Recognizing rare, benign entities presenting as pigmented lesions could help prevent over diagnosis and over treatment. Acinar melanosis of the Bartholin gland (AMBG) is one such entity that has only been reported three times in the extant literature. Herein, we describe a case of AMBG, its presentation, histologic/ immunophenotypic characterization, and other rare lesions with a similar clinical/histologic appearance. Methods/Case Report A 22-year-old female patient presents with clitoral pain that had been reported for 5 months preceding presentation. On physical examination, a 3-4mm pigmented lesion was identified in the posterolateral aspect of the vestibule. The lesion was biopsied, and histologic examination showed benign squamous mucosa overlying clusters of cystically dilated acini. These acini were lined by low cuboidal to columnar epithelial cells with uniform, round nuclei. These cells did not exhibit mitotic activity, pleomorphism, or hyperchromasia. The acinar lumina contained eosinophilic and brown-pigmented debris. Interestingly, melanocytes were identified in association with the acili, confirmed by positive staining with SOX10 and Melan-A immunohistochemical stains, and melanin pigmentation was identified in the acinar epithelium, highlighted by positive Fontana Masson staining result. Since the biopsy, the patient has continued to experience clitoral pain of unknown etiology, but the lesion has not significantly progressed over the two years since biopsy. Results NA Conclusion AMBG is an exceedingly rare, benign lesion characterized by melanocytic cells within the acinar epithelium. It may clinically and histologically mimic other pigmented lesions of the vulva, including malignant melanoma. The differential diagnosis for pigmented cystic lesions of the lower female genital tract includes hemosiderin-containing lesions like endometriosis or hemangioma, melanocytic lesions like vulvar melanosis or melanocytic nevus, and pigmented squamous-lined Bartholin duct cysts. The pigmented Bartholin duct cyst is most similar in histologic appearance but would contain melanocytes within the squamous lining of the cystic duct. This is in contrast to AMBG, which is defined by the presence of melanocytes within the glandular acini. Recognition of this benign entity is critical to avoid overdiagnosis and unnecessary treatment.