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Thymoma is a primary epithelial tumor of the thymus gland, typically located in the anterior mediastinum. It is the most common primary anterior mediastinal neoplasm in adults and can be benign or malignant, with potential for local invasion or paraneoplastic syndromes—most notably myasthenia gravis.
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| Feature | Details |
|---|---|
| Incidence | Rare (1.5 per million/year) |
| Age group | Peak: 40–60 years |
| Sex | No significant predilection |
| Association | • 30-50% of thymoma patients have myasthenia gravis |
| • 10-15% of MG patients have thymoma |
WHO Histologic Classification of Thymoma (2021):
https://www.youtube.com/watch?v=wfyixp6JxQM
| Type | Histology | Behavior |
|---|---|---|
| Type A | Spindle/oval epithelial cells | Benign |
| Type AB | Type A + lymphocytes | Benign |
| Type B1 | Resembles normal thymic cortex | Indolent |
| Type B2 | Epithelial cells + many lymphocytes | Intermediate |
| Type B3 | Predominantly epithelial cells | More aggressive |
| ‣ | Cytologically malignant, overt carcinoma | High-grade malignant |
Paraneoplastic Syndromes:
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CT imaging goal: Assess capsule integrity, adjacent invasion, and pleural seeding.
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| Features | Details |
|---|---|
| Location | Well-defined mass in anterior mediastinum |
| Margins | Smooth or lobulated; irregular if invasive |
| Density | Soft-tissue attenuation |
| Enhancement | Moderate, homogeneous or heterogeneous enhancement |
| Calcifications | Present in ~20%; linear or punctate |
| Cystic/necrotic areas | More common in aggressive types or thymic carcinoma |
| Invasion | Look for pericardial, pleural, vascular invasion (especially SVC, aorta) |
| **Pleural nodules | |
| “drop metastases”** | Suggests stage IVa disease |
| Associated findings | Thymic hyperplasia (in MG), effusions in advanced cases |
Thymoma. (A) Chest radiograph shows a widened mediastinal border with lack of visualization of the anterior junction line (double-headed arrow). (B) Axial CT image shows a low-attenuation anterior mediastinal mass () with central calcifications. AO = aorta, S = spine. (C, D) Coronal (C) and axial (D) 3D cinematic renderings show draping of the pleura along the mediastinum without midline apposition (arrowheads in C; double-headed arrow in D) due to a prevascular mediastinal mass (). Biopsy confirmed that the prevascular mediastinal mass represents thymoma.
AO = aorta, PA = pulmonary artery, S = spine Jiao A, Bardia Nadim, Hammer MM, Khushboo Jhala. 3D Visual Guide to Lines and Stripes in Chest Radiography. Radiographics. 2023;43(9). doi:10.1148/rg.230017
(a, b) Thymoma. CXR (a) reveals an anterior mediastinal mass (arrow) obscuring the right heart border. CECT (b) shows the mass to be solid and heterogeneously enhancing
Jana, M., Bhalla, A.S. (2020). Radiology of Normal Thymus, Thymic Lesions, and Tumors. In: Jain, D., Bishop, J.A., Wick, M.R. (eds) Atlas of Thymic Pathology. Springer, Singapore. https://doi.org/10.1007/978-981-15-3164-4_3