1. A Tour of the Thymus: A Review of Thymic Lesions With Radiologic and Pathologic Correlation 
Alan J. Goldstein, MD, Isabel Oliva, MD, Hedieh Honarpisheh, MD, Ami Rubinowitz, MD 
Canadian Association of Radiologists Journal 
Volume 66, Issue 1, Pages 5-15 (February 2015)
DOI: /j.carj
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2. Figure 1
Thymic tissue migrates caudally and medially from its origin in the neck (originating in the region of the angle of the mandible) along the thymopharyngeal duct to the anterior mediastinum, where the thymic primordia generally fuse in the midline. The duct passes deep to the sternocleidomastoid muscle, and ectopic thymic tissue or thymic lesions can arise anywhere along the path of this duct. This figure is available in colour online at
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3. Figure 2
Noncontrast computed tomographic image in a young patient, demonstrating the normal configuration of the thymus, in this case, arrowhead shaped.
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4. Figure 3
Photomicrograph of the normal thymus, demonstrating a thymic lobule (H&E, original magnification ×10). The cortex is mainly composed of immature lymphocytes, and the medulla is composed of thymic epithelial cells arranged in Hassall corpuscles (keratinized epithelial cell formations) and maturing lymphocytes. The thymic capsule with adjacent mediastinal fat is also visualized. (Inset) Lower magnification image, demonstrating multiple normal thymic lobules separated by invaginations of fat (H&E). This figure is available in colour online at
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5. Figure 4
Photomicrographs, demonstrating the 2 histologic subtypes of thymic hyperplasia. (A) Photomicrographs of true thymic hyperplasia, demonstrating increased numbers of thymic epithelial cells (black arrows) and lymphoid germinal centers (yellow arrows) throughout the gland, which is increased in size but otherwise normal in configuration with interspersed fat (H&E, original magnification ×10). (B) Photomicrographs of lymphoid follicular hyperplasia, when enlarged germinal centers are present throughout the gland (yellow arrows), which accounts for the increased thymic mass (H&E, original magnification ×20). This figure is available in colour online at
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6. Figure 5
Examples of rebound thymic hyperplasia in 2 young patients. (A) Contrast-enhanced computed tomography (CT) in a 26-year-old woman with Crohn disease on steroid treatment, demonstrating thymic tissue with fatty and soft-tissue components (arrow). (B) Several months after cessation of steroid therapy, the thymus has enlarged, with decreased macroscopic fat noted (arrow). (C) Noncontrast CT in a 21-year-old woman with T-cell lymphoma, revealing a relatively small thymus during the initial staging study (arrow). (D) After treatment, including bone marrow transplantation, there is increased soft tissue within the thymus compatible with rebound hyperplasia (arrow).
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7. Figure 6
A 55-year-old woman who presented with anxiety, tremors, and palpitations. Clinical workup revealed hyperthyroidism secondary to Graves disease. (A) Noncontrast computed tomography, demonstrating soft-tissue prominence of the thymus (arrow), which retains its normal arrowhead shape but is unusual for a middle-aged patient. (B) After treatment for Graves disease, the thymus has involuted and become mostly fatty replaced (arrow).
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8. Figure 7
(A) Contrast-enhanced computed tomography (CT), demonstrating a somewhat lobulated anterior mediastinal mass (arrow) in a 37-year-old woman with shortness of breath. The mass was thought to represent thymic hyperplasia vs thymoma. (B) Subsequent magnetic resonance imaging, revealing an anterior mediastinal mass that is isointense to muscle on in-phase images (arrow), and (C) demonstrating a decrease in signal intensity on opposed-phase images indicative of microscopic fat (arrow). These findings are compatible with thymic hyperplasia, which remained stable on a subsequent study performed for other reasons (not shown).
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9. Figure 8
Examples of thymic cysts (arrow in each image). (A) Contrast-enhanced computed tomography (CT), demonstrating a fluid-attenuation mass without apparent enhancement. (B) Another thymic cyst, demonstrating an imperceptible wall on noncontrast CT. (C) A different patient with a thymic cyst on noncontrast CT; note that the fat plane with the aorta is preserved, suggestive of benignity.
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10. Figure 9
A 5-year-old girl with cough and fever. (A) Frontal radiograph of the chest, revealing an abnormal mediastinal contour (arrow), which was further evaluated with magnetic resonance imaging. (B) Coronal T2-weight fat-suppressed image, demonstrating a well-circumscribed, hyperintense, anterior mediastinal mass (arrow). (C) Axial T1-weight contrast-enhanced image, demonstrating no contrast enhancement (arrow), which is consistent with a benign cyst, likely thymic in origin given its location; the main differential diagnosis would include a bronchogenic cyst.
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11. Figure 10
Photomicrograph, showing the wall of a typical thymic cyst, which can be composed of squamous, columnar, or glandular epithelium (dashed arrow) with thymic tissue focally present within the wall of the cyst (solid arrow) (H&E, original magnification ×10). This figure is available in colour online at
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12. Figure 11
Examples of thymolipoma. (A) Contrast-enhanced computed tomography (CT), demonstrating a large anterior mediastinal mass (arrow) in a 22-year-old man with an abnormal mediastinal contour on a prior chest radiograph. The mass is mixed soft tissue and fat attenuation, and appears well encapsulated. (B) Noncontrast CT, demonstrating a similar mass (arrow) in another patient, with a more prominent fatty component.
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13. Figure 12
Photomicrograph, demonstrating the histologic appearance of a thymolipoma; the mass is predominantly composed of mature adipose tissue with interspersed non-neoplastic thymic epithelial cells and fibrous septae (H&E, original magnification ×10). This figure is available in colour online at
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14. Figure 13
A 50-year-old man with worsening muscle weakness and diplopia. (A) Frontal radiograph, demonstrating a right-sided mediastinal mass (arrow) with the hilar vessels visible through the mass and demonstrating a “hilum overlay” sign, which indicates that the mass is located either anterior or posterior to the right hilum. (B) Contrast-enhanced computed tomography, revealing a lobulated, homogeneous, right anterior mediastinal mass (arrow), which was surgically removed and diagnosed as type A thymoma, Masaoka-Koga stage I.
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15. Figure 14
Examples of thymoma (arrow in each image). Contrast-enhanced computed tomographic images in 3 separate patients, demonstrating some of the findings seen with thymoma. (A) Image, showing a lobulated, soft-tissue attenuation anterior mediastinal mass. (B) Image, demonstrating central low attenuation in an anterior mediastinal mass due to necrosis. (C) Image, revealing a focal soft-tissue anterior mediastinal mass within an otherwise fatty-replaced gland.
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16. Figure 15
Photomicrographs that demonstrate the histologic appearance of thymoma (H&E, original magnification ×10). (A) Masaoka-Koga stage I thymoma appears as densely packed neoplastic thymic cells that do not demonstrate spread beyond the capsule (arrows). (B) Masaoka-Koga stage IIa thymoma in a 40-year-old woman who presented with palpations, subsequently found to have a lobulated anterior mediastinal mass; the tumour appears as densely packed thymic epithelial cells that lack normal thymic corticomedullary differentiation; the neoplastic cells extend beyond the thymic capsule (arrows) and into the mediastinal fat. This figure is available in colour online at
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17. Figure 16
A 50-year-old woman with worsening shortness of breath. (A) Contrast-enhanced computed tomographic images, demonstrating a lobulated right anterior mediastinal mass abutting and resulting in mass effect upon the right atrium (arrow). (B) Soft-tissue masses are seen more inferiorly within the pleural space compatible with “drop metastases” (arrows); this denotes Masaoka-Koga stage IVa disease.
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18. Figure 17
A 36-year old woman with chest tightness and facial swelling. (A, B) Frontal and lateral radiographs, revealing a lobulated anterior mediastinal mass (arrow in each image). (C, D) Axial and coronal contrast-enhanced computed tomographic images, demonstrating an anterior mediastinal mass encasing the ascending aorta, great vessels, and superior vena cava (arrow in each image); numerous collateral vessels were noted (not shown), and the superior vena cava was completely obstructed, compatible with superior vena cava syndrome; pathologic sampling proved to be a thymic carcinoma.
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19. Figure 18
Photomicrographs, demonstrating the histologic appearance of locally advanced thymoma and thymic carcinoma (H&E, original magnification ×10). (A) A pleural “drop” metastasis from locally advanced thymoma abuts the pleural surface; (inset) a photomicrograph of the pleura at a different location, demonstrating malignant thymic cells within. (B) A pleural metastasis from thymic carcinoma, also with frank pleural invasion; this proved to be a squamous-cell type thymic carcinoma with neuroendocrine differentiation. This figure is available in colour online at
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20. Figure 19
A 27-year-old man with chest discomfort. (A) A frontal chest radiograph, revealing a mediastinal mass (arrows). (B, C) Axial and coronal contrast-enhanced computed tomographic images, demonstrating a large, homogeneous, soft-tissue attenuation mass in the anterior mediastinum (straight arrow); the superior vena cava is patent (curved arrow); a pathology specimen demonstrated Reed-Sternberg cells, compatible with Hodgkin lymphoma.
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21. Figure 20
A 24-year-old man with fatigue, weakness, and cough. A contrast-enhanced computed tomographic (CT) image, revealing a mass centered within the thymus, with a punctate hyperattenuating focus (yellow arrow) that represented calcification on a prior noncontrast CT (not shown); surgical pathology revealed a thymic carcinoid tumour. This figure is available in colour online at
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22. Figure 21
A 50-year-old woman with chest discomfort. Contrast-enhanced computed tomography, demonstrating a relatively well-defined, soft-tissue attenuation, anterior mediastinal mass (arrow), with a low-density central region, which was initially thought to represent a type A thymoma, but subsequent interinstitutional consultation and immunohistochemical staining revealed follicular dendritic cell sarcoma, an extremely rare tumour.
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