Giant cystadenoma of the seminal vesicle mimicking a malignant pelvic tumor: a case report and literature review

Introduction and importance: Primary tumors of the seminal vesicles are extremely rare, and among these, cystadenomas are benign tumors that can grow to considerable size, mimicking malignant pelvic masses. The rarity and non-specific presentation of these tumors make preoperative diagnosis particularly challenging, often leading to delays and complex surgical scenarios. We present a case of a giant seminal vesicle cystadenoma to highlight its unusual presentation, diagnostic complexity, and management. Case presentation: An 80-year-old man, classified as ASA II (body mass index 20 kg/m 2 ), presented with a 3-month history of a large abdominopelvic mass associated with abdominal pain, urinary disturbances, and significant weight loss. Social and surgical histories were unremarkable. Physical examination and abdominopelvic CT scan revealed a massive multiloculated cystic mass measuring 297 × 180 mm in the retrovesical space, displacing adjacent organs. Despite an elevated prostate specific antigen (PSA) (90.36 ng/mL), malignancy was not confirmed, and prostate biopsies were performed and demonstrated benign prostatic hyperplasia without evidence of carcinoma. The patient underwent exploratory laparotomy (favored over minimally invasive surgery due to tumor size) and en bloc resection of the mass with the sigmoid colon and upper rectum due to dense adhesions. Histopathological examination confirmed a seminal vesicle cystadenoma with negative surgical margins (R0 resection), positive for estrogen and progesterone receptors. At 12-month follow-up, PSA had normalized, and the patient remained recurrence free. Clinical discussion: Seminal vesicle cystadenomas are rare, and their non-specific symptoms and presentation as a giant mass necessitate a high index of suspicion. Imaging, particularly pelvic magnetic resonance imaging, is crucial for characterization, but definitive diagnosis rests on histopathology. Complete surgical resection is the mainstay of treatment, often requiring a laparotomy for large, adherent tumors, as in our case. Despite the size and complex resection, the prognosis is favorable after complete excision, but regular follow-up is recommended. Conclusion: This case underscores the rarity and diagnostic difficulty associated with giant seminal vesicle cystadenomas, emphasizing the need to include them in the differential diagnosis of pelvic masses in men. A multidisciplinary approach and appropriate, complete surgical excision are critical for effective management and a good patient outcome.