DOI: 10.1148/rg.262045213
The Thymus: A Comprehensive Review1
Mizuki Nishino, MD,
Simon K. Ashiku, MD,
Olivier N. Kocher, MD,
Robert L. Thurer, MD,
Phillip M. Boiselle, MD and
Hiroto Hatabu, MD, PhD
1 From the Departments of Radiology (M.N., P.M.B., H.H.), Thoracic Surgery (S.K.A., R.L.T.), and Pathology (O.N.K.), Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215. Presented as an education exhibit at the 2004 RSNA Annual Meeting. Received December 22, 2004; revision requested May 9, 2005, and received June 8; accepted September 22. All authors have no financial relationships to disclose.
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Figure 1a. (a) Photomicrograph (original magnification, x10; hematoxylineosin [H-E] stain) of the thymus shows the cortex, mainly composed of lymphocytes (thymocytes), and the medulla, mainly composed of epithelial cells. (b) Photomicrograph (original magnification, x40; H-E stain) of the medulla shows Hassall corpuscles (arrows) as round, keratinized formations with mature epithelial cells.
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Figure 1b. (a) Photomicrograph (original magnification, x10; hematoxylineosin [H-E] stain) of the thymus shows the cortex, mainly composed of lymphocytes (thymocytes), and the medulla, mainly composed of epithelial cells. (b) Photomicrograph (original magnification, x40; H-E stain) of the medulla shows Hassall corpuscles (arrows) as round, keratinized formations with mature epithelial cells.
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Figure 2. Contrast material–enhanced chest CT scan shows a normal thymus (arrow) as a triangular structure in the mediastinum anterior to the ascending aorta and the main pulmonary arterial trunk.
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Figure 3. Thymoma in a 40-year-old woman with myasthenia gravis. Contrast-enhanced CT scan shows a partially lobulated, homogeneously enhancing anterior mediastinal mass. The mass was surgically removed, and pathologic analysis demonstrated an invasive type B2 thymoma.
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Figure 4. Thymic hyperplasia in a 25-year-old woman with Graves disease. Contrast-enhanced CT scan demonstrates a bilobed, homogeneous soft-tissue lesion (arrows) in the anterior mediastinum.
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Figure 5a. WHO type B1 thymoma (lymphocyte rich, predominantly cortical) in a 57-year-old woman. (a) Unen-hanced CT scan shows a well-circumscribed, flattened soft-tissue lesion in the anterior mediastinum, with a maintained fat plane surrounding the lesion. (b) Photomicrograph (original magnification, x40; H-E stain) shows cellular lobules consisting predominantly of lymphocytes, along with scattered small foci of medullary differentiation.
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Figure 5b. WHO type B1 thymoma (lymphocyte rich, predominantly cortical) in a 57-year-old woman. (a) Unen-hanced CT scan shows a well-circumscribed, flattened soft-tissue lesion in the anterior mediastinum, with a maintained fat plane surrounding the lesion. (b) Photomicrograph (original magnification, x40; H-E stain) shows cellular lobules consisting predominantly of lymphocytes, along with scattered small foci of medullary differentiation.
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Figure 6a. WHO type B3 thymoma (epithelial, well-differentiated thymic carcinoma) in an 83-year-old woman. (a) Contrast-enhanced CT scan shows a lobulated anterior mediastinal mass with calcification, a finding that is commonly seen in type B tumors. Note the lobulated contour of the mass and the loss of the fat plane between the mass and the pleura-pericardium. (b) Photomicrograph (original magnification, x40; H-E stain) shows a predominance of polygonal epithelial cells with nuclear atypia.
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Figure 6b. WHO type B3 thymoma (epithelial, well-differentiated thymic carcinoma) in an 83-year-old woman. (a) Contrast-enhanced CT scan shows a lobulated anterior mediastinal mass with calcification, a finding that is commonly seen in type B tumors. Note the lobulated contour of the mass and the loss of the fat plane between the mass and the pleura-pericardium. (b) Photomicrograph (original magnification, x40; H-E stain) shows a predominance of polygonal epithelial cells with nuclear atypia.
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Figure 7a. Incidentally noted thymic carcinoma in a 79-year-old man who presented with bronchiectasis and cough. (a) Unenhanced chest CT scan shows an anterior mediastinal mass with a somewhat lobulated contour. (b) On a sagittal reformatted image, the mass is closely attached to the pericardium with loss of the fat plane (arrow) between the two entities, findings that suggest pericardial involvement. Pericardial effusion is also noted. At surgery, pericardial invasion was noted, and pathologic analysis showed squamous cell thymic carcinoma.
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Figure 7b. Incidentally noted thymic carcinoma in a 79-year-old man who presented with bronchiectasis and cough. (a) Unenhanced chest CT scan shows an anterior mediastinal mass with a somewhat lobulated contour. (b) On a sagittal reformatted image, the mass is closely attached to the pericardium with loss of the fat plane (arrow) between the two entities, findings that suggest pericardial involvement. Pericardial effusion is also noted. At surgery, pericardial invasion was noted, and pathologic analysis showed squamous cell thymic carcinoma.
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Figure 8a. Pleural seeding from a WHO type B2 (cortical) thymoma in a 40-year-old woman who presented with myasthenia gravis. (a) Contrast-enhanced CT scan shows a lobulated anterior mediastinal mass. (b) Contrast-enhanced CT scan obtained at the level of the upper abdomen shows an enhancing pleura-based nodule (arrow), a finding that represents pleural seeding. Pathologic analysis showed a predominance of lymphoid cells (type B2 tumor).
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Figure 8b. Pleural seeding from a WHO type B2 (cortical) thymoma in a 40-year-old woman who presented with myasthenia gravis. (a) Contrast-enhanced CT scan shows a lobulated anterior mediastinal mass. (b) Contrast-enhanced CT scan obtained at the level of the upper abdomen shows an enhancing pleura-based nodule (arrow), a finding that represents pleural seeding. Pathologic analysis showed a predominance of lymphoid cells (type B2 tumor).
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Figure 9a. WHO type AB thymoma in a 68-year-old woman. (a) Axial half-Fourier acquisition single-shot turbo spin-echo MR image shows an anterior mediastinal mass that is slightly hyperintense relative to skeletal muscle. Although the fat plane between the mass and mediastinal structures appears to be maintained, the possibility of minimal chest wall invasion cannot be excluded with certainty. At surgery, the mass appeared well circumscribed and was excised entirely. No extracapsular invasion was noted. (b) Photomicrograph (original magnification, x40; H-E stain) demonstrates mixed histologic features, with foci of medullary and spindle cells admixed with lymphocytes.
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Figure 9b. WHO type AB thymoma in a 68-year-old woman. (a) Axial half-Fourier acquisition single-shot turbo spin-echo MR image shows an anterior mediastinal mass that is slightly hyperintense relative to skeletal muscle. Although the fat plane between the mass and mediastinal structures appears to be maintained, the possibility of minimal chest wall invasion cannot be excluded with certainty. At surgery, the mass appeared well circumscribed and was excised entirely. No extracapsular invasion was noted. (b) Photomicrograph (original magnification, x40; H-E stain) demonstrates mixed histologic features, with foci of medullary and spindle cells admixed with lymphocytes.
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Figure 10a. Thymic cyst in a 66-year-old woman. (a) Contrast-enhanced CT scan shows an incidentally noted anterior mediastinal lesion (arrow) with well-circumscribed borders and soft-tissue attenuation. The lesion is indistinguishable from a solid mass. (b) On a T2-weighted MR image, the lesion (arrow) is hyperintense and contains a fluid level, findings that indicate a hemorrhagic or mucin-containing cystic lesion. The lesion was surgically removed, and pathologic analysis demonstrated a thymic cyst.
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Figure 10b. Thymic cyst in a 66-year-old woman. (a) Contrast-enhanced CT scan shows an incidentally noted anterior mediastinal lesion (arrow) with well-circumscribed borders and soft-tissue attenuation. The lesion is indistinguishable from a solid mass. (b) On a T2-weighted MR image, the lesion (arrow) is hyperintense and contains a fluid level, findings that indicate a hemorrhagic or mucin-containing cystic lesion. The lesion was surgically removed, and pathologic analysis demonstrated a thymic cyst.
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Figure 11. Cystic thymoma in a 48-year-old woman. Axial short inversion time inversion-recovery MR image shows hyperintense cystic lesions in the mediastinum abutting the pericardium. Note the hypointense nodular lesion (arrow), a finding that suggests the presence of a solid component. The nodule demonstrated enhancement after contrast material administration. Surgery was performed, and pathologic analysis helped confirm a cystic type AB thymoma.
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Figure 12a. Thymic carcinoid in a 74-year-old man. (a) Contrast-enhanced CT scan demonstrates a lobulated, heterogeneously enhancing mass in the anterior mediastinum. Note the loss of the fat plane between the mass and the pericardium, a finding that suggests invasiveness. (b) Photomicrograph (original magnification, x40; H-E stain) shows tumor cells in a trabecular growth pattern with oncocytic cytoplasm and oval to irregular nuclear contours.
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Figure 12b. Thymic carcinoid in a 74-year-old man. (a) Contrast-enhanced CT scan demonstrates a lobulated, heterogeneously enhancing mass in the anterior mediastinum. Note the loss of the fat plane between the mass and the pericardium, a finding that suggests invasiveness. (b) Photomicrograph (original magnification, x40; H-E stain) shows tumor cells in a trabecular growth pattern with oncocytic cytoplasm and oval to irregular nuclear contours.
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Copyright © 2006 by the Radiological Society of North America.
