Purpose or Case Report: Infantile myofibromatosis is a rare condition consisting of benign fibrous tumors typically deposited in the skin, soft tissues, muscles, bones, and visceral organs. The entity can be solitary or multicentric. Although controversial, outcomes are generally worse in cases with visceral organ involvement. The prognosis is generally favorable in cases that lack visceral organ involvement, with a majority of cases showing spontaneous regression.

The imaging findings of infantile myofibromatosis will be illustrated using both prenatal and postnatal imaging including ultrasound, MRI, radiography, CT, and bone scintigraphy. We also present gross specimen and pathology images.

Our case involves a 33 week 4 day gestational age male fetus that initially revealed dilated loops of bowel on ultrasound. Fetal MRI was performed at 34 weeks and 4 days, which demonstrated the dilated loop was colon in the region of the hepatic flexure. Additionally, multiple solid-appearing lung masses were noted, which had not been visualized on ultrasound. Because of concern for a possible metastatic process, the entire fetus was thoroughly imaged, but no primary source was found. The differential diagnosis that was given on the fetal MRI included metastatic disease from the mother or fetus, infantile myofibromatosis, or infectious etiology.

The mother underwent induction of labor at 35 weeks 4 days, and the baby was born via uncomplicated vaginal delivery. To exclude transplacental metastases, the mother underwent dermatologic skin check, mammography, colonoscopy, and head CT, all of which were negative.

Postnatal radiographs of the baby revealed a focally dilated loop of bowel, and the patient underwent exploratory laparotomy. In the OR, nodules were noted on the small bowel serosa resulting in a bowel obstruction. Chest radiograph and CT also confirmed the presence of multiple solid lung masses. Bone scintigraphy was negative. Pathology from one of the bowel nodules revealed infantile myofibroma. Our patient has not undergone any therapeutic treatment, and follow up imaging has demonstrated continued spontaneous regression of the lung masses.

Although infantile myofibromatosis is a rare entity, it is important to include in the differential diagnosis in a fetus with multiple solid-appearing lung masses. Throughout the clinical course of these patients, imaging plays an imperative role in the assessment of these lesions.

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