Large congenital mesoblastic nephroma resected in a newborn: A case report

Abstract

Congenital mesoblastic nephroma (CMN) is the most common renal tumor of infancy, typically diagnosed in the third trimester or early neonatal period. We present the case of a male infant born at 36 weeks and 3 days via emergency cesarean section after late prenatal ultrasound revealed a large abdominal mass. Postnatally, he developed respiratory distress, obstructive uropathy, acute kidney injury, and disseminated intravascular coagulation. Imaging revealed a large, heterogeneous left renal mass with features concerning for neuroblastoma. On day of life 4, the patient underwent radical nephrectomy with en bloc adrenalectomy. Gross pathology revealed a 9.0 × 7.0 × 6.5 cm cellular CMN weighing 263 g, with renal sinus extension and capsular disruption consistent with stage III disease. Surgical margins and lymph nodes were negative, and no metastatic disease was identified. Postoperatively, the patient experienced transient renal dysfunction but recovered baseline function with supportive care. Given tumor size, histology, and capsular involvement, adjuvant chemotherapy with vincristine and actinomycin D was initiated. This case highlights the diagnostic challenges of differentiating CMN from other neonatal renal and abdominal tumors, the complications associated with exceptionally large lesions, and the importance of prompt multidisciplinary intervention. Early diagnosis, coordinated perioperative management, and complete surgical excision remain critical for optimizing outcomes in neonates with CMN.