Abstract
Leiomyomas are a common type of benign soft tissue tumor arising from smooth muscle, most often occurring within females' genitourinary and gastrointestinal tract. However, primary leiomyomas of the chest wall residing in the extra-pleural space are an extremely rare subset of leiomyomatous lesion presentation. We present a case of a fifty-two-year-old male who initially presented complaining of dyspnea worsening with exertion. Computed tomography imaging was performed showing an extra-pleural mass residing under the left sixth rib. Subsequent core needle biopsy and immunohistochemical staining were performed, and the definitive diagnosis of primary leiomyoma of the posterior mediastinal chest wall. Although extremely rare, this neoplastic condition should be included in your differential diagnosis when diagnostic imaging reveals a benign mass residing in the extra-pleural space, and subsequent biopsy specimens consist of smooth muscle fibers.