76 A Rare Case of Primary Solitary Intrathyroidal Myofibroma in a Pediatric Patient

Introduction/Objective Myofibromas are benign pediatric soft tissue tumors commonly affecting the skin and subcutaneous tissue. In children, common thyroid lesions originate from follicular or C-cells. Thyroidal myofibroma is exceptionally rare, with fewer than a total of 10 cases reported in the medical literature. Methods/Case Report An enlarging right neck mass was noticed in a previously healthy 3 year-old male. An ultrasound detected a 1.5 cm right thyroid nodule. Fine needle aspiration showed spindle cells. Right thyroid lobectomy was performed, and a 1.5x1.5x1.2 cm solid nodule with a homogenous firm white cut surface on examination. The background thyroid tissue was normal. Histologically, the tumor was composed of spindle cells forming a fascicular pattern. The spindle cells were positive for SMA, and negative for SS18-SSX, CD34, beta catenin, cytokeratin, desmin, and myogenin. The diagnosis was intrathyroidal myofibroma. Surgical resection margins were free of tumor. Post surgically, imaging studies revealed no other lesions, and there has been no recurrence to date (2 years post surgery). Results NA Conclusion We present a rare case of a primary solitary intrathyroidal myofibroma in a pediatric patient. This case is important because it may help raise awareness in clinicians for myofibromas in the differential diagnosis of solitary thyroid nodules in pediatric patients.