IS case 483: Thymoma
Imaging Sciences URMC 2010
Publication Date: 2010-08-30
PA and lateral chest radiographs were obtained prior to evaluation by the thoracic surgery service. A mass measuring at least 7 cm in diameter was seen projecting in the anterior right hemithorax. Due to its location, differential diagnoses must be considered arising from the right hilum, right medial lung, or anterior mediastinum.
Thymomas are thymic epithelial neoplasms that are the most common primary anterior mediastinal neoplasms in adults, usually presenting in late adulthood. There is no gender predilection. Although this example is large and solid in appearance, cystic degeneration and necrosis are common features, especially in larger tumors. Classically, thymomas are large at time of diagnosis (greater than 4 cm in diameter) and eccentric in appearance, with associated mass effect on local mediastinal structures.
Histologically, encapsulated and invasive thymomas are identical, requiring careful evaluation of the margins of the tumor both radiographically and at surgical excision. Invasive thymoma may be suggested radiographically by the presence of indistinct margins, pleural nodularity, pericardial thickening, or frank encapsulation of vascular structures and airways, although differentiation between encapsulated and invasive subtypes by imaging are unreliable. Calcifications are seen on CT in up to 1/3 of patients. In this patient, there was no evidence of invasion of surrounding tissues following excision. Patients may be asymptomatic, present with symptoms arising from mass effect, or with paraneoplastic syndromes (in up to 40%). Paraneoplastic syndromes may include secondary myasthenia gravis, hypogammaglobulinemia, or red cell aplasia.
Differential diagnoses of anterior mediastinal masses include thymic hyperplasia (especially in patients with myasthenia gravis), thymic carcinoma, germ cell tumors (especially in younger patients), thyroid hyperplasia/goiter, lymphoma (usually with associated regional lymphadenopathy), metastatic lymphadenopathy (especially adenocarcinoma arising from the lung, breast, head, or neck), and less often neuroendocrine neoplasms (including carcinoid) and thymolipoma (especially if high proportion of fat).
- Federle MP, Rosado-de-Christenson ML, Woodward PJ, et al. Diagnostic and Surgical Imaging Anatomy: Chest, Abdomen, Pelvis. Amirsys, 2006.
- Dahnert WF. Radiology Review Manual, 6th ed. Lippincott Williams & Wilkins, 2007.
- Jeong YJ, Lee KS, Kim J, et al. Does CT of thymic epithelial tumors enable us to differentiate histologic subtypes and predict prognosis? AJR Am J Roentgenol. 2004 Aug;183(2):283-9. PMID: 15269013