Monophasic Synovial Sarcoma Presenting as Infantile Hemangioma: A Case Report

Abstract Objective: This report describes a case of a monophasic synovial sarcoma that was initially misdiagnosed as an infantile hemangioma in a 3-month-old female infant. We also discuss the basic elements of evaluating a soft-tissue mass and important radiological and clinical features that should raise the index of suspicion for a synovial sarcoma. Summary Background Data: Synovial sarcoma is a rare pathology that is often challenging to diagnose due to its similarities with more common vascular lesions that occur in infancy. Infantile hemangioma, in particular, is common, has distinctive clinical and radiological findings, and is frequently diagnosed without histological confirmation. This increases the risk of misdiagnosis of rare tumors in infancy. Case Report: A 3-month-old female infant presented with a soft-tissue mass on the left forearm. Physical examination showed a well-defined, subcutaneous mass on the left forearm, measuring approximately 3 cm × 5 cm, firm in consistency, with no cutaneous involvement and normal skin coverage. Imaging suggested an infantile hemangioma but, due to the atypical presentation, a trial of beta-blocker therapy was conducted to confirm the diagnosis. The patient showed no clinical response to beta-blocker therapy, and therefore an incisional biopsy was performed. Using histopathology, the tumor was diagnosed as a monophasic synovial sarcoma.Conclusions: We highlight a rare presentation of a synovial sarcoma in a neonate and caution against making a diagnosis without histopathologic analysis. Clinicians should include sarcoma in the differential diagnosis when assessing a mass in neonates, as early diagnosis and intervention can reduce morbidity and mortality.MINI ABSTRACT A 3-month-old infant presented with a left forearm soft-tissue mass, initially diagnosed as infantile hemangioma. Biopsy revealed a monophasic synovial sarcoma. We discuss the basic elements of evaluating a soft-tissue mass and important radiological and clinical features that should raise the index of suspicion for a synovial sarcoma.