Prenatal Ultrasound and MRI Findings in Two Fetuses With Perineal Lipoma

Abstract

Congenital perineal lipoma is a rare benign adipose lesion that may present prenatally as a fetal perineal mass. These lesions are frequently associated with ambiguous genitalia, anorectal malformations, and other urogenital anomalies, whereas isolated cases are uncommon. Recognition of isolated lesions is clinically important because of their favorable prognosis and their implications for prenatal counseling and perinatal management. We report the prenatal imaging findings of two fetuses with isolated congenital perineal lipoma. Prenatal ultrasonography demonstrated well-defined echogenic perineal masses with minimal or absent vascularity and interval growth during gestation. No associated anorectal, spinal, or genitourinary abnormalities were identified. In one case, fetal magnetic resonance imaging (MRI) demonstrated a pedunculated fatty perineal mass with a small internal cystic component, further supporting a lipomatous lesion. Both pregnancies were managed expectantly, and postnatal surgical excision was performed. Histopathologic examination confirmed congenital perineal lipoma in both neonates. These cases highlight the importance of careful prenatal evaluation of fetal perineal masses to exclude associated anomalies and refine the differential diagnosis. Fetal MRI may provide additional characterization in selected cases and assist prenatal counseling and postnatal management.