Retroperitoneal Castleman's disease in a young Nepalese girl: A rare cause of childhood abdominal mass.

Introduction: Castleman's disease (CD), or benign angio-follicular lymph node hyperplasia, is an uncommon condition in childhood. When a child presents with a huge retroperitoneal mass and inconclusive findings on clinico-radiological evaluation or tissue sampling, management becomes exceedingly difficult. CD herein becomes an uncommon presentation of an uncommon diagnosis. Case presentation: A six-year-old girl with no past medical problems presented to the office with a slowly progressive, painless mass over the right lumbar region for a year. Abdominal ultrasound showed a well-defined oval mass in the right periumbilical region, further evaluation of which with a computed tomography scan suggested lymphoma. A preoperative core-cut biopsy could not confirm the findings and suggested a neoplastic lesion, probably an inflammatory myofibroblastic tumour or small round cell tumour. She underwent an exploratory laparotomy with in-toto excision of the mass. Intraoperatively, a solid retroperitoneal tumour measuring 8×8×6 cm was found. Histopathology and immunohistochemistry confirmed a unicentric CD of the hyaline-vascular type. At two years of follow-up, she remained asymptomatic and disease-free. Conclusion: While CD in children is rare, retroperitoneal localization of the same can further add to the diagnostic conundrum. However, if carefully considered, an en-bloc surgical resection offers complete treatment.