A case of Castleman's disease that presented as a retroperitoneal mass

Background A 35-year -old man presented to a local emergency room with acute left-flank pain and a medical history of nephrolithiasis. There were no aggravating or relieving factors for the left-flank pain and no other presenting symptoms, and the physical examination was unremarkable.Investigations Complete blood count, urinalysis, serum tumor markers, scrotal ultrasonography, CT scan of the abdomen (with and without contrast), MRI of the abdomen.Diagnosis Unicentric Castleman's disease (hyaline-vascular type).Management Surgical exploration and excision. Pathologic and immunohistochemical work-up confirmed the diagnosis. CT scan after 7 months was normal with no evidence of recurrence.