In the Chest but not of the Chest

A 57-year-old man presented to our emergency department with acute onset substernal chest pain. The patient had not been seen by a physician for over 30 years and denied past medical or surgical history as well as any alcohol, tobacco, or illicit drug use. He was hemodynamically stable with normal oxygenation on room air. Physical exam demonstrated decreased breath sounds over the entire right lung field. Laboratory investigation, including cardiac biomarkers, was unremarkable. Chest X-ray revealed near complete opacification of the right lung. Computerized tomography with contrast revealed a large soft tissue mass in the right hemithorax with minimal enhancement and central hyperdensity suggestive of hemorrhage (See Image A). No pathologic lymph nodes were noted. The mass displaced cardiac structures without evidence of invasion. To better characterize the tumor, magnetic resonance imaging with contrast was performed, demonstrating a single, well-circumscribed soft tissue mass arising from the pleura (See Image B). The patient was admitted to the Internal Medicine service for further evaluation.

At the request of our thoracic surgeons, fine needle aspiration of the mass was performed which surprisingly demonstrated an immature T-Cell population with scattered epithelial cells consistent with a Type B1 (lymphocyte-rich) thymoma, not a solitary fibrous tumor despite characteristic radiographic appearance. The patient was subsequently taken to the operating room where a 17 x 15 x 9 cm encapsulated soft tissue mass was removed with pathology confirming a large thymoma with extensive central necrosis. The patient was presumed to have ectopic thymic tissue from which the tumor arose, leading to a non-mediastinal based thymoma. 

References:
1. Chick, J., Chauhan, N., Madan, R. Solitary Fibrous Tumors of the Thorax: Nomenclature, Epidemiology, Radiologic and Pathologic Findings, Differential Diagnoses, and Management. AJR Am J Roentgenol. 2013 March;200(3):W238-48. PMID: 23436868

2. Thway, K., Ng, W., Noujaim, J., Jones, R., and Fisher, C. The Current Status of Solitary Fibrous Tumor: Diagnostic Features, Variants, and Genetics. International Journal of Surgical Pathology. 2016: Jan 25th. Epub ahead of print. PMID: 26811389


About the authors:

Max Wattenberg, MD is a second year resident in Internal Medicine at UCSF in San Francisco, CA.

Mia Williams, MD is a first year resident in Internal Medicine at UCSF in San Francisco, CA.

Lawrence Haber, MD is an Assistant Clinical Professor of Medicine at UCSF in San Francisco, CA.