Solitary infantile myofibromatosis presenting as multiple subcutaneous lesions: a case report.

Background: Infantile myofibromatosis is a rare benign mesenchymal disorder characterized by the proliferation of myofibroblasts, representing the most common fibrous tumor of infancy and early childhood. Solitary infantile myofibromatosis is the most common variant, typically presenting as a firm, painless dermal or subcutaneous mass. This case is notable for the early prenatal detection of multiple subcutaneous lesions, initially presumed to be lymphangiomas, but later confirmed as infantile myofibromatosis postnatally. The diagnostic challenge highlights the importance of prenatal imaging and histopathological confirmation for accurate diagnosis and management.

Case Presentation: An Iranian male preterm neonate, born at 34 weeks of gestation, was admitted to the neonatal intensive care unit due to prematurity, respiratory distress syndrome, and multiple subcutaneous masses. Prenatal imaging at 34 weeks identified multiple cystic subcutaneous lesions, leading to a provisional diagnosis of lymphangiomas. Postnatal examination exhibited multiple firm, well-circumscribed subcutaneous nodules over the trunk, back, abdomen, periauricular region, and right thigh. Ultrasonography showed well-defined hypoechoic lesions with some demonstrating necrotic centers. Differential diagnoses included neonatal myofibromatosis, infantile rhabdomyosarcoma, and soft-tissue metastases. The neonate underwent surgical excision of a thoracic lesion, and histopathological examination with immunohistochemistry confirmed infantile myofibromatosis. The patient was discharged in stable condition, with parental counseling on prognosis and follow-up. At 1-year follow-up, no new lesions or morphological progression were noted, and some previously visualized lesions showed regression.

Conclusions: This case highlights the importance of prenatal imaging-particularly fetal magnetic resonance imaging-in the identification of soft-tissue lesions and guiding postnatal evaluation. It highlights the necessity of histopathological confirmation for distinguishing infantile myofibromatosis from other neonatal soft-tissue tumors. Given the potential for spontaneous regression, a conservative, individualized management approach is recommended, avoiding unnecessary interventions while ensuring appropriate follow-up.