This article presents a case report of a 37-week gestational age (GA) female infant (CK) whose first ultrasound at 35 weeks' GA revealed polyhydramnios, fetal ascites, and a possible diaphragmatic hernia. At birth, CK had a grossly distended abdomen, prominent abdominal veins, hepatomegaly, bounding femoral pulses, and generalized edema. Initial imaging identified an absent ductus venosus, absent segment of the inferior vena cava (IVC), and prominent superior vena cava to the right atrium. A computed tomography (CT) scan showed a mass contiguous with the liver causing compression of the IVC. Biopsy confirmed infantile myofibromatosis (IM), an uncommon soft tissue neoplasm that may present at birth or in early infancy. Although rare, this neoplasm is the most common fibrous tumor of infancy. The case of CK was unusual because the solitary IM lesion was in an atypical location; a solitary lesion is not commonly found in the viscera, and solitary lesions are predominant in males. Although lesions are often benign, visceral involvement is associated with high mortality. The cause is unknown, although familial cases have been reported. This article describes the key features of IM, possible treatment options, nursing care, and prognosis for infants with the disease.