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Thymoma

Vivek David, MD
Robert D Pugatch, MD

Presentation

A 26-year-old woman with a history of myasthenia gravis presented for a routine chest radiograph. An abnormality was noted in the study.

Imaging Findings

Radiograph of the chest, anteroposterior view
Radiograph of the chest, lateral view
Close-ups of relevant area

Anteroposterior and lateral radiographs of the chest show a smooth, rounded anterior mediastinal mass (arrows) (close-up arrows).

Differential Diagnosis

The differential diagnosis of an anterior mediastinal mass includes a thymic mass (eg, thymoma, thymolipoma, thymic cyst, carcinoid), teratoma, a mass arising from the thyroid, lymphoma, and a vascular lesion. In this patient, a reasonable differential diagnosis would include these entities although a mass related to thyroid tissue would be unlikely given the lack of anatomic connection to the thyroid. The history of myasthenia gravis suggests the diagnosis of thymoma.

Diagnosis

Thymoma

Discussion

Thymomas are the most common primary thymic tumor. They are slow-growing lesions and usually behave in a benign fashion. A subgroup of these tumors have an aggressive nature and are called invasive thymomas. Invasive thymomas typically invade locally and spread along pleural and pericardial surfaces, but they can exhibit extrathoracic metastasis. A thymoma can appear at any age, but most patients are over the age of 40. Radiographically, thymomas are typically round or oval, well-marginated masses that may contain some peripheral calcification.

The association with myasthenia gravis: 50% of patients with thymoma have myasthenia gravis, and 15% of patients with myasthenia gravis have a thymoma. Among patients with myasthenia gravis and a thymoma, 25% show remission of their myasthenic symptoms after thymectomy.

References

1. Ellis K, Austi JHM, Ill AJ. Radiologic detection of thymoma in patients with myasthenia gravis. AJR 1988; 151: 873.

2. Fraser RG, Pare JAP, Pare PD, Fraser RS, Genereux GP. Diagnosis of diseases of the chest. 3rd ed. Philadelphia: WB Saunders, 1991: 2820-2831.

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