Imaging description

A 32-year-old patient at 22 weeks of gestation was referred carrying a female fetus that had previously been diagnosed with a left thigh mass on ultrasound (US). Repeat US demonstrated a hypoechoic cystic soft tissue mass of the left thigh, most consistent with a lymphatic malformation (Fig. 75.1a). The mass was well circumscribed in the subcutaneous soft tissues and anterior muscle, but follow-up US demonstrated extension of the mass into the retroperitoneum. Displacement of the fetal bladder to the right and mild hydronephrosis in the left kidney was noted. Follow-up US studies were performed on a weekly basis to follow the size of the mass and check for development of hydrops fetalis. These showed progression of the lymphatic malformation with further extension into the retroperitoneum. A fetal MRI at 32 weeks showed a high T2-and low T1-signal cystic mass of the left thigh with an extensive retroperitoneal component (Fig. 75.1b, c), infiltrating the pelvic structures. Postnatally, the mass appeared as a multiseptated hypoechoic mass infiltrating most of the soft tissues of the left thigh, labia, and perineum, and extending into the retroperitoneum, surrounding the ureters (Fig. 75.1d). Slow Doppler flow was detected in the septations; the diagnosis of lymphatic malformation was confirmed, and sclerotherapy was begun.