A rare case of infantile myofibromatosis and review of literature.

Infantile myofibromatosis is a rare benign tumor-disease (1/400,000). Four different types have been reported in literature. The most commonly affected body areas are the head, the neck, and the trunk. We would like to present a rare case of a multicentric type with singular visceral involvement and a literature review of all case series with more than five patients. A 9-month-old boy presented with a swelling on the medial side of his proximal left tibia. The lesion which was present since birth, was well palpable, indolent, hard, and mobile in relation to the surrounding tissue. Radiographic films and ultrasound examination presented a pretibial soft-tissue tumor mass with calcifications and two osteolytic lesions with a sclerotic rim. A skeletal survey showed more osteolytic lesions, but the magnetic resonance imaging showed no more soft-tissue lesions. The rapid frozen section biopsy hinted at the diagnosis of histiocytosis X. The definitive histological result 6 days later was infantile myofibromatosis. As therapy, we determined a wait-and-see policy with controls all 3 months. At 20 months follow-up, the boy showed beginning of regression of all lesions. Infantile myofibromatosis is a very rare benign tumor-disease. Radiologically often soft-tissue masses with calcifications and osteolytic lesions with sclerotic rims are described. These findings also can be interpreted as histiocytosis X, which is a potential differential diagnosis. Histopathologically, cells characteristically appear as spindle-shaped fibroblast cells with pale pink cytoplasm and elongated nuclei and the immunophenotype is defined with a positive reaction on smooth-muscle antigen vimentin and the muscle-specific antigen HHF-35. The data of the literature review underline that a wait-and-see-policy should be considered as the first treatment of choice as in most instances the bony lesions regress spontaneously. However, a thorough examination has to be carried out to exclude lesion in other organs like gastro-intestinal or cardio-pulmonary nodular tumor masses. In conclusion, the present case report and the literature review support the notion that infantile myofibromatosis should be considered as a possible differential diagnosis for soft tissue expansions and/or osteolytic lesions in a newborn.