Pelvic unicentric Castleman's disease mimicking accessory spleen: A rare presentation of Castleman's disease, a case report and literature report.

Castleman disease, a rare, mostly benign lymphoproliferative disorder, is classified as unicentric or multicentric Castleman disease, with HHV-8 association affecting the latter. Unicentric Castleman disease typically presents as a single enlarged lymph node, most often mediastinal, while multicenter Castleman disease involves multiple lymph nodes. Treatment depends on the type and severity, ranging from surgical resection for unicentric Castleman disease to chemotherapy for multicentric Castleman disease.

Methods: A 28-year-old Ethiopian man presented with three months of pelvic pain, altered bowel habits, and urinary frequency. The physical examination was unremarkable. Investigations revealed a retroperitoneal pelvic mass, initially suspected to be an accessory spleen. Surgery revealed a 10 × 8 × 4 cm mass. Histopathology showed features consistent with unicentric Castleman disease, confirmed by characteristic "onion skin" and "lollipop" appearances, CD20 positivity, and negative HHV-8 and Bcl-2. The patient recovered well after surgical resection. Methods: Pelvic unicentric Castleman disease is a rare presentation of this uncommon disorder, typically affecting the mediastinum. While its pathogenesis is unclear, it's not associated with HHV-8, IL-6 overproduction, or human immunodeficiency virus in all cases (as in this patient). Unicentric Castleman disease is characterized by localized symptoms or may be asymptomatic, unlike multicentric Castleman disease which presents with systemic manifestations. Imaging (ultrasound and CT in this case) guides diagnosis, with histopathology confirming the characteristic "onion skin" and "lollipop" appearances. Surgical excision is the treatment of choice for unicentric Castleman disease, offering excellent outcomes (as seen in the patient). Multicentric Castleman disease requires more extensive treatment, with a less favorable prognosis. Long-term follow-up is crucial due to the risk of malignant transformation.

Conclusions: Unicentric pelvic Castleman disease, a rare condition sometimes confused with accessory spleen, requires histopathological diagnosis. While often linked to HIV/AIDS or HHV-8, it can occur without risk factors and usually responds well to surgical excision.