A Chest Wall Myofibroma in an Adult.

Introduction: Myofibroma is a rare benign tumor that often involves the skin, subcutaneous tissue, and/or bone in the head and neck, typically developing in children. Adult cases, particularly in the chest wall, are extremely rare.

Case presentation: A 22-year-old asymptomatic Chinese man presented with an abnormal chest X-ray showing a shadow in the left lung apex. Chest computed tomography (CT) revealed a 2.5 × 2.0 cm nodule infiltrating the second rib. Positron emission tomography showed an accumulation of ¹⁸F-fluorodexyglucose in the nodule. A CT-guided biopsy revealed spindle-shaped cells positive for alpha-smooth muscle actin (α-SMA), β-catenin, and p16 but was inconclusive for malignancy. Since a malignant tumor could not be ruled out, the decision was made to perform surgery. A 25 cm-high posterolateral incision was made, the latissimus dorsi muscle was preserved, and the trapezius and rhomboid muscles were split in the direction of their fibers to reach the bony thorax. The second rib and the chest wall tumor, including the first and second intercostal muscles, were resected with a 1.5 cm margin. The lesion involving the rib showed fibromyxoid/fibrosclerotic nodules with spindle cells in loose fascicles or whorls, hypercellular areas, and thin-walled hemangiopericytoma-like vessels. Immunohistochemistry was positive for α-SMA, NOTCH3, and PDGFR and negative for desmin and S100. Based on these findings, we diagnosed a myofibroma in the chest wall.

Conclusions: This case demonstrates that myofibroma can occur in the chest wall of an adult. The imaging findings of myofibromas are similar to those of malignant tumors, making them difficult to diagnose. Resection offers a good prognosis, and because these tumors occur in young patients, surgery should be performed with consideration for preserving function.