Castleman's Disease Presenting as an Unusual Pelvic Retroperitoneal Mass

Castleman's disease (CD) is characterised by benign lymphoepithelial proliferation and is a peculiar form of angiofollicular lymph node hyperplasia rather than a neoplasm or a hamartoma. CD is broadly classified as unicentric CD (UCD) and multicentric CD. In the unicentric variant, patients have localised disease affecting only a single lymph node or a group of adjacent nodes in a single region, which clinically presents as an enlarging mass without any other significant symptoms. The mediastinum and thoracic lymph nodes are commonly involved. However, it is uncommon for CD to occur in the pelvic presacral region of the retroperitoneum. A 31-year-old male presented with progressive, dull aching, intermittent lower abdomen pain for three months with no aggravating or relieving factors or any associated symptoms. He was haemodynamically stable, and his general physical examination was normal. An abdominal examination elicited mild tenderness in the left iliac region of the abdomen. Contrast-enhanced computed tomography of the abdomen and pelvis revealed an encapsulated nodal mass with intralesional calcification displacing the bladder to the right side, and fine needle aspiration cytology showed atypical cells. An exploratory laparotomy was performed with an in toto excision biopsy of the pelvic retroperitoneal mass, and it was diagnosed as a hyaline-vascular variant of UCD. Immunohistochemistry revealed angiofollicular hyperplasia and atretic germinal centres that are crossed by sclerotic vessels and hyalinisation, confirming the diagnosis. The patient is currently asymptomatic and is leading a routine life. The hyaline-vascular variant is the most common variant seen in UCD. Compared to the multicentric type, the unicentric type seldom exhibits systemic involvement. Surgical resection is typically curative. Although it is asymptomatic, it is essential to achieve complete surgical resection to prevent the neoplastic potentialities of CD. In the presence of an uncertain solitary solid pelvic retroperitoneal mass, the diagnosis of UCD should be considered, as surgical resection can achieve a favourable outcome.