A rapidly growing mesenchymal hamartoma in a neonate with known placental anomalies

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Hepatic mesenchymal hamartomas (HMH) are benign liver lesions that present as cystic, slow growing masses within the first few years of life. Few cases demonstrate placental abnormalities and abnormal levels of alpha-fetoprotein (AFP). We report an unusual case of a rapidly growing HMH with associated placental anomalies and elevated AFP. A 2-month-old female born prematurely due to concerning placental findings presented with a prenatally-identified liver mass. Magnetic resonance imaging (MRI) showed a marked increase in the size of the mass over a three-month period. Prior to surgery, the AFP was elevated and decreased after operative resection. Histopathology confirmed the diagnosis HMH. Rapid growth of HMH is not commonly reported and raises concerns for malignancy. Abnormal placental findings may lead to prematurity, which can affect surgical management. We identified 27 cases of prenatally diagnosed HMH since 1983. The mean gestational age for identification was 29 weeks, with the majority managed by delayed resection. The timing for surgical intervention lacks consensus, but malnutrition and perioperative complications should be considered. High AFP levels with an infantile hepatic mass may indicate a more malignant process but does not exclude HMH. • Consider hepatic mesenchymal hamartomas in a rapidly growing pediatric liver tumor. • Prenatally-identified cases of HMH may be associated with placental abnormalities. • Elevated alpha-fetoprotein levels should not preclude benign liver tumors like HMH.