Pediatric Focal Nodular Hyperplasia Mimicking Hepatic Metastasis from Wilms Tumor: A Case Report

Focal nodular hyperplasia (FNH) is a rare benign liver lesion in children, representing approximately 2% of pediatric liver tumors and occurring far less frequently than in adults. Preoperative diagnosis is often challenging because FNH can closely mimic malignant or metastatic liver tumors on imaging, particularly in patients with a history of malignancy. Indocyanine green (ICG) fluorescence imaging has emerged as a useful intraoperative navigation tool in pediatric liver surgery; however, its role in distinguishing FNH from metastatic lesions remains underexplored.

A 5-year-old girl with a history of stage IV Wilms tumor-treated with systemic chemotherapy and in complete remission since 3 years of age-underwent routine follow-up imaging. MRI identified a small hepatic lesion in segment 1 (S1) that gradually enlarged on serial examinations. Contrast-enhanced CT demonstrated a 10-mm nodule with arterial phase enhancement and gradual relative washout in the portal and venous phases, raising concern for hepatic metastasis. Given the oncologic history and indeterminate imaging findings, laparoscopic partial hepatectomy of S1 was performed for diagnostic confirmation and treatment. For intraoperative localization, ICG (0.5 mg/kg body weight) was administered intravenously 36 h preoperatively. The lesion was not detectable under conventional white-light laparoscopy; however, near-infrared fluorescence imaging revealed diffuse fluorescence corresponding to the tumor location, enabling precise resection with minimal loss of hepatic parenchyma. Histopathological examination confirmed FNH, characterized by hyperplastic hepatocytes with proliferating bile ductules and small vessels, and a central stellate scar. The postoperative course was uneventful, with no evidence of recurrence at 9-month follow-up.

Differentiating pediatric FNH from metastatic liver tumors remains challenging. Intraoperative ICG fluorescence imaging may assist not only with tumor localization but also by providing supplementary information about tumor characteristics, potentially facilitating safe and minimal hepatic resection. In this case, the fluorescence pattern was suggestive of FNH in retrospect. Further case accumulation is needed to clarify the utility of ICG fluorescence patterns for differential diagnosis and surgical planning in pediatric liver lesions.