BACKGROUND: Extraskeletal osteosarcomas (ESOS) of the mediastinum are extremely rare and may present with concurrent nontuberculous mycobacteria infection.

CASE REPORT: We present the second documented case of high-grade anterior mediastinal extraskeletal osteosarcoma in a 59-year-old man with a history of treated, latent tuberculosis (TB). Sputum samples grew Mycoplasma avium complex and Mycobacterium fortuitum. Imaging showed a right-sided 7.6 cm mass with compression of the main bronchus. Subsequent biopsy with vimentin staining established the diagnosis of ESOS. Due to the patient’s rapidly declining performance status, he was not deemed a candidate for surgery or chemotherapy. He subsequently expired within one month of presentation.

CONCLUSIONS: We present a unique case of high-grade anterior mediastinum ESOS and a review of the literature regarding all documented cases of ESOS to date. We suggest there is a possible link between mediastinal masses and nontuberculous mycobacteria infection.

Keywords: Fatal Outcome, Mediastinal Neoplasms - diagnostic imaging, Mycobacterium Infections, Nontuberculous - diagnosis, Nontuberculous mycobacteria, Osteosarcoma - diagnostic imaging, Tomography, X-Ray Computed