Thymoma, Type B1

Marc J Lee, MD - Case Coordinator
Salvatore G Viscomi, MD - Radiology Discussion
Jason H Smouse, MD - Pathology Discussion
Paul Whiston Spirn, MD - Attending Radiologist
Philip Costello, MD, MPH - Attending Radiologist
Pablo R Ros, MD, MPH - Attending Radiologist
Koenraad Mortele, MD - Attending Radiologist

March 10, 2003

Presentation

Imaging Findings

The lateral radiograph does not show any expansile lesion in the sternum. The frontal view demonstrates a convex bulge in the left cardiac border in the region of the atrial appendage. This suggests the possibility of left atrial enlargement, although the lateral view does not show any protrusion to the posterior aspect of the left cardiac border. A superimposed mediastinal lesion is another possibility.

Computed tomography images with IV contrast (soft tissue algorithm) begin in the superior aspect and move down through the aortic arch and the pulmonary outflow tract. The image on the right shows a mediastinal mass with attenuation similar to skeletal muscle. The mass juts into the left aspect of the mediastinum adjacent to the pulmonary outflow tract; it is approximately 2 cm and roughly oval. The serial axial images demonstrate the lesion with high attenuation material--perhaps calcification--centrally.

Differential Diagnosis

Diagnosis

Discussion

The mass was resected and a 7-cm, lobulated, fleshy well-encapsulated mass with focal hemorrhage and focal calcification. Low-power microscopy demonstrates densely cellular lobules separated by a fibrous septum in a "jigsaw" pattern. There are focal areas of minimal capsular invasion. High-power microscopy demonstrates that the cells are predominantly lymphoid cells that stained with CD-3, indicating that these are T-cells. There are also some larger, epithelioid cells that stained with cytokeratin; these are thymic epithelial cells.

Radiology Discussion

Thymoma is the most common tumor of thymus and the most common neoplasm of the anterior/superior mediastinum. Seventy percent of cases occur in 5th & 6th decades; thymoma is rare in children and young adults. Presenting symptoms are typically related to compression of adjacent mediastinal structures, such as the trachea, recurrent laryngeal nerve, esophagus, and right atrium (this can, rarely, cause sudden death).

Thymoma is associated with a number of autoimmune and paraneoplastic phenomena. Fifty percent of patients with pure red aplasia also have thymoma, representing 5% of all thymomas. Five percent of hypogammaglobulinemia are associated with thymoma, representing 10% of all cases, and 10-15% of patients with myasthenia gravis also have thymoma, representing 33% of all cases.

Radiographically, thymoma appears as a prevascular mediastinal soft tissue mass adjacent to the great vessels and pericardium (or, less commonly, at the cardiophrenic angle). Small calcifications are common. The mass typically displays uniform enhancement, but may have varying amounts of cystic and hemorrhagic components. Smooth borders suugest encapsulation, whereas irregular borders with adjacent lung or mediastinal structures suggest invasion, but the definitive assessment must be made surgically. Thymoma needs to be differentiated from other thymic lesions. Thymic hyperplasia usually enlarges the gland but maintains its normal pyramidal configuration of the thymic gland. Thymolipoma is generally recognized as a fat containing lesion. Thymoma most often metastasizes locally to the pleura; exceedingly rare extrathoracic metastases have been reported in kidney, bone, and liver.

References

Vail CM, Ravin CE: Mediastinal masses. In Freundlich IM, Bragg DG, editors: Radiologic Approach to Diseases of the Chest. Baltimore: William and Wilkins, 1992:360-373.

McCloud TC. Thoracic Radiology: The Requisites. St. Louis: Mosby, 1988.

• Return to the Teaching Case Database search page
• Return to Professional Education
  
• About BrighamRAD

Dear Visitors: Nothing on this World Wide Web site should be considered medical advice. Only your own doctor can help you make decisions about your medical care. It is not the policy of the Brigham and Women's Hospital Department of Radiology to provide consultation on the World Wide Web or via e-mail. If you have a specific medical question or are seeking medical care, please call the Brigham and Women's Hospital toll-free physician referral line at 1-800-294-9999.

Is this a mirrored page?
The official homepage of the BrighamRAD Teaching Case Database is http://brighamrad.harvard.edu/education/online/tcd/tcd.html