A 52-year-old woman presents with progressive dyspnea and proximal muscle weakness. Chest radiograph shows a widened anterior mediastinum on PA view (marked **A**). CT chest confirms a large anterior mediastinal mass with well-defined borders and areas of calcification. Serum tumor markers (β-hCG, AFP) are negative. Which of the following is the most likely diagnosis?

Question

Accepted Answer

C. Thymoma with associated myasthenia gravis. ## Why Thymoma with associated myasthenia gravis is right

The widened anterior mediastinum on PA view (marked **A**) indicates an anterior mediastinal mass. The clinical presentation of a 52-year-old woman with dyspnea and proximal muscle weakness (myasthenic symptoms) combined with a well-defined anterior mediastinal mass with calcification is classic for thymoma. Thymoma typically affects adults aged 40–60 years and is strongly associated with myasthenia gravis in 30–40% of cases. The negative tumor markers exclude germ-cell tumors. According to Sutton's Textbook of Radiology and Bailey & Love, thymoma is the most common anterior mediastinal mass in this age group and is the leading cause of anterior mediastinal masses overall.

## Why each distractor is wrong

- **Non-seminomatous germ-cell tumor**: While germ-cell tumors are part of the '4 Ts' differential for anterior mediastinal masses, they typically occur in young males (adolescents to young adults) and present with elevated β-hCG and/or AFP. This patient's negative tumor markers and age (52 years) make this diagnosis unlikely.
- **Retrosternal goiter**: Although retrosternal thyroid extension can present as an anterior mediastinal mass, it would demonstrate high attenuation on non-contrast CT due to iodine content and continuity with the cervical thyroid. The clinical presentation of myasthenic symptoms and the calcification pattern are more consistent with thymoma.
- **Hodgkin lymphoma, nodular sclerosing subtype**: While Hodgkin lymphoma is a '4 Ts' differential diagnosis and commonly presents in young women, it typically occurs in younger patients (adolescents to young adults) and would not typically present with myasthenic symptoms. The well-defined borders and calcification are more suggestive of thymoma.

**High-Yield:** Thymoma is the most common anterior mediastinal mass in adults aged 40–60 years; always screen for myasthenia gravis (30–40% association) and other paraneoplastic syndromes.

[cite: Sutton's Textbook of Radiology, 8th ed; Bailey & Love, 28th ed]

Answer

A. Hodgkin lymphoma, nodular sclerosing subtype

Answer

B. Retrosternal goiter

Answer

D. Non-seminomatous germ-cell tumor

Explanation

Why Thymoma with associated myasthenia gravis is right

Why each distractor is wrong

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