Discussion
Diagnosis With Brief Discussion
- Diagnosis
- Thymoma, type AB (mixed)
- Radiologic Findings
- Chest PA and lateral views show sharply marginated large ovoid soft tissue mass in right cardiophrenic angle with obliteration of right cardiac border. Enhanced chest CT scans show heterogenous large ovoid solid masses with heterogenous enhancement and inner low density portion in right cardiophrenic angle.
- Brief Review
- Thymomas are benign or low-grade malignant tumors arising from the thymic epithelium. Thymomas represent 20% of all mediastinal neoplasms in adults; they are the most common anterior mediastinal primary neoplasm in adults. The peak prevalence of thymoma is during the fifth and sixth decades of life. Thymomas have no sex predilection. About one-half of thymomas are found in the upper and middle thirds of the mediastinum, and the remainder are found in the lower third. Patients with thymoma are frequently asymptomatic; however, 20%-30% of patients have pressure-induced symptoms such as cough, chest pain, dyspnea, dysphagia, hoarseness, or superior vena cava syndrome. One-third to one-half of thymoma patients develops myasthenia gravis. Patients with thymoma may also develop pure red blood cell aplasia, hypogammaglobulinemia, connective tissue disease, autoimmune disease, or inflammatory bowel disease.
At radiography, thymomas typically appear as sharply marginated retrosternal areas of increased opacity with smooth or lobulated borders. Thymomas may project to either side of the mediastinum and obscure the heart border.
On CT scans, thymomas usually appear as homogeneous solid masses with soft-tissue attenuation and well-demarcated borders. Thymomas may be oval, round, or lobulated and usually do not conform to the shape of the thymus. Large thymomas may show areas of cystic or necrotic degeneration. Calcification may be present in the capsule or throughout the mass. Well-defined fat planes between the thymoma and adjacent structures generally indicate absence of extensive local invasion. Certain findings, such as encasement of mediastinal structures, infiltration of fat planes, and an irregular interface between the mass and lung parenchyma, are highly suggestive of invasion. Pleural thickening, nodularity, or effusion generally indicates pleural invasion by the thymoma.
At MR imaging, thymomas commonly appear as homogeneous or heterogeneous masses with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. MR imaging can be used to help identify vascular invasion. Chemical shift MR imaging, which makes use of the difference in chemical shift ratio, can be valuable in differentiating thymic hyperplasia from thymomas and other thymic tumors.
- References
- 1. Clinical and Radiologic Review of the Normal and Abnormal Thymus: Pearls and Pitfalls. RadioGraphics 2010;30:413-428
2. Lesions of the Cardiophrenic Space: Findings at Cross-sectional Imaging. Pineda et al. RadioGraphics 2007; 27:19-32
3. A Diagnostic Approach to Mediastinal Abnormalities. Whitten et al. RadioGraphics 2007; 27:657-671
4. The Thymus: A Comprehensive Review. Nishino et al. RadioGraphics 2006; 26:335-348
- Keywords
- mediastinum, benign tumor,