Fibrous hamartoma of infancy: a case report.

Introduction: Fibrous hamartoma of infancy is a rare benign mesenchymal soft-tissue tumor characterized by a triphasic organoid architecture. Because its clinical and imaging features are variable, fibrous hamartoma of infancy may mimic inflammatory, vascular, benign fibro-fatty, intermediate, or malignant soft-tissue lesions. Case description: We report an approximately 6-month-old boy with a painless, progressively enlarging subcutaneous mass in the right axillary/medial upper-arm region. The lesion was initially interpreted as BCG-associated lymphadenitis; aspiration yielded no purulent material, and serial ultrasonography demonstrated progressive enlargement. Magnetic resonance imaging revealed a 67  ×  40 × 58 mm well-circumscribed subcutaneous mass with marked contrast enhancement and no definite diffusion restriction or muscle invasion; infantile myofibroma and an intermediate soft-tissue lesion were considered. Complete gross excision was achieved while preserving the visualized muscle and neurovascular structures. Histopathologic examination demonstrated the characteristic triphasic pattern of fibrous hamartoma of infancy, and the immunohistochemical findings supported the diagnosis. Discussion: This case illustrates how sequential clinical assessment, multimodal imaging, operative findings, and histopathologic correlation can resolve a broad differential diagnosis in an infant with a rapidly enlarging soft-tissue mass. Conclusion: Fibrous hamartoma of infancy should be considered in infants with a painless, enlarging axillary or upper-extremity mass, particularly when imaging findings are nonspecific. Histopathologic confirmation is essential to establish the diagnosis and avoid unnecessarily aggressive oncologic treatment.