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Thymic epithelial tumors classified according to a newly established WHO scheme: CT and MR findings.

Han J, Lee KS, Yi CA, Kim TS, Shim YM, Kim J, Kim K, Kwon OJ - Korean J Radiol (2003 Jan-Mar)

Bottom Line: Thymic epithelial tumor is a distinctive pathologic entity exhibiting variable histologic features and heterogeneous oncologic behavior.Among the various classification systems, that of the World Health Organization has been adopted because of good correlation between histologic appearance and oncologic behavior.However, imaging findings among the various types overlap to some extent, and the ability of imaging studies to differentiate types AB, B1, B2, and B3 is limited.

View Article: PubMed Central - PubMed

Affiliation: Department of Diagnostic Pathology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.

ABSTRACT
Thymic epithelial tumor is a distinctive pathologic entity exhibiting variable histologic features and heterogeneous oncologic behavior. Among the various classification systems, that of the World Health Organization has been adopted because of good correlation between histologic appearance and oncologic behavior. Radiologically, a smooth contour and round shape are most suggestive of a type-A tumor, whereas an irregular contour most strongly suggests type C. Pleural seeding is rare in type-A and AB tumors; calcification is suggestive of type B. Type-C tumors are significantly larger and more commonly associated with lymphadenopathy than type B3. At T2-weighted MR imaging, lobular internal architecture is more prominent in types B1, B2, and B3 tumors than in others. However, imaging findings among the various types overlap to some extent, and the ability of imaging studies to differentiate types AB, B1, B2, and B3 is limited.

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Type-AB thymoma in a 46-year-old-man.A. Enhanced 7.0-mm-collimation CT scan obtained at the level of the azygos arch reveals the presence of a round mass in the right anterior mediastinum.B. T1-weighted (TR/TE, 723/9) MR image obtained at a similar level to A depicts an iso-intense mass.C. Gd-enhanced T1-weighted MR image demonstrates strong tumoral enhancement.D. T2-weighted (TR/TE, 5700/89) MR image shows a mass lesion with slightly higher signal intensity than muscle.
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Figure 3: Type-AB thymoma in a 46-year-old-man.A. Enhanced 7.0-mm-collimation CT scan obtained at the level of the azygos arch reveals the presence of a round mass in the right anterior mediastinum.B. T1-weighted (TR/TE, 723/9) MR image obtained at a similar level to A depicts an iso-intense mass.C. Gd-enhanced T1-weighted MR image demonstrates strong tumoral enhancement.D. T2-weighted (TR/TE, 5700/89) MR image shows a mass lesion with slightly higher signal intensity than muscle.

Mentions: The histologic features of thymic epithelial tumors vary, their neoplastic epithelial cells showing differing shapes and degrees of atypia. In addition, various degrees of non-neoplastic lymphoid cells coexist with neoplastic epithelial cells within the tumors (2,6). Numerous classification systems for thymic epithelial tumors have been proposed but have fallen out of favor because the suggested morphologic types lacked consistent prognostic significance. In the mid 1980s, Muller-Hermelink et al. (7) proposed a new functional classification of thymomas based on their histologic and immuno-phenotypic resemblance to cortical or medullary areas of the thymus. The recently published WHO classification of thymomas adopted the Muller-Hermelink classification, but used alpha-numeric terms (3). The new system is based on the morphology of epithelial cells as well as the lymphocyte-to-epithelial cell ratio (Fig. 1): in thymomas are divided into two groups (type A and B) depending on whether the neoplastic epithelial cells and their nuclei are spindle-or oval-shaped (type A), or have a dendritic or epithelioid appearance (type B) (Fig. 2); type AB tumors are those which combine these two morphologies (Fig. 3). Type B tumors are further divided into three subtypes according to the proportional increase in their epithelial component and the emergence of atypical neoplastic cells (Figs. 4-6). All types of thymic carcinomas are classified as type C (Figs. 7, 8). The relationship between the new WHO classification and previous histologic classification systems is summarized in Table 1. The WHO classification reflects the clinical features of these tumors and correlates with prognosis. According to Okumura et al. (8, 9), type-B2 and B3 tumors show aggressive behavior compared with types A, AB, and B1 in terms of invasiveness, postoperative survival, and tumor recurrence. For type-A, AB, or B1 thymomas, there is more likelihood of complete resection than for types B2 or B3.


Thymic epithelial tumors classified according to a newly established WHO scheme: CT and MR findings.

Han J, Lee KS, Yi CA, Kim TS, Shim YM, Kim J, Kim K, Kwon OJ - Korean J Radiol (2003 Jan-Mar)

Type-AB thymoma in a 46-year-old-man.A. Enhanced 7.0-mm-collimation CT scan obtained at the level of the azygos arch reveals the presence of a round mass in the right anterior mediastinum.B. T1-weighted (TR/TE, 723/9) MR image obtained at a similar level to A depicts an iso-intense mass.C. Gd-enhanced T1-weighted MR image demonstrates strong tumoral enhancement.D. T2-weighted (TR/TE, 5700/89) MR image shows a mass lesion with slightly higher signal intensity than muscle.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2698058&req=5

Figure 3: Type-AB thymoma in a 46-year-old-man.A. Enhanced 7.0-mm-collimation CT scan obtained at the level of the azygos arch reveals the presence of a round mass in the right anterior mediastinum.B. T1-weighted (TR/TE, 723/9) MR image obtained at a similar level to A depicts an iso-intense mass.C. Gd-enhanced T1-weighted MR image demonstrates strong tumoral enhancement.D. T2-weighted (TR/TE, 5700/89) MR image shows a mass lesion with slightly higher signal intensity than muscle.
Mentions: The histologic features of thymic epithelial tumors vary, their neoplastic epithelial cells showing differing shapes and degrees of atypia. In addition, various degrees of non-neoplastic lymphoid cells coexist with neoplastic epithelial cells within the tumors (2,6). Numerous classification systems for thymic epithelial tumors have been proposed but have fallen out of favor because the suggested morphologic types lacked consistent prognostic significance. In the mid 1980s, Muller-Hermelink et al. (7) proposed a new functional classification of thymomas based on their histologic and immuno-phenotypic resemblance to cortical or medullary areas of the thymus. The recently published WHO classification of thymomas adopted the Muller-Hermelink classification, but used alpha-numeric terms (3). The new system is based on the morphology of epithelial cells as well as the lymphocyte-to-epithelial cell ratio (Fig. 1): in thymomas are divided into two groups (type A and B) depending on whether the neoplastic epithelial cells and their nuclei are spindle-or oval-shaped (type A), or have a dendritic or epithelioid appearance (type B) (Fig. 2); type AB tumors are those which combine these two morphologies (Fig. 3). Type B tumors are further divided into three subtypes according to the proportional increase in their epithelial component and the emergence of atypical neoplastic cells (Figs. 4-6). All types of thymic carcinomas are classified as type C (Figs. 7, 8). The relationship between the new WHO classification and previous histologic classification systems is summarized in Table 1. The WHO classification reflects the clinical features of these tumors and correlates with prognosis. According to Okumura et al. (8, 9), type-B2 and B3 tumors show aggressive behavior compared with types A, AB, and B1 in terms of invasiveness, postoperative survival, and tumor recurrence. For type-A, AB, or B1 thymomas, there is more likelihood of complete resection than for types B2 or B3.

Bottom Line: Thymic epithelial tumor is a distinctive pathologic entity exhibiting variable histologic features and heterogeneous oncologic behavior.Among the various classification systems, that of the World Health Organization has been adopted because of good correlation between histologic appearance and oncologic behavior.However, imaging findings among the various types overlap to some extent, and the ability of imaging studies to differentiate types AB, B1, B2, and B3 is limited.

View Article: PubMed Central - PubMed

Affiliation: Department of Diagnostic Pathology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.

ABSTRACT
Thymic epithelial tumor is a distinctive pathologic entity exhibiting variable histologic features and heterogeneous oncologic behavior. Among the various classification systems, that of the World Health Organization has been adopted because of good correlation between histologic appearance and oncologic behavior. Radiologically, a smooth contour and round shape are most suggestive of a type-A tumor, whereas an irregular contour most strongly suggests type C. Pleural seeding is rare in type-A and AB tumors; calcification is suggestive of type B. Type-C tumors are significantly larger and more commonly associated with lymphadenopathy than type B3. At T2-weighted MR imaging, lobular internal architecture is more prominent in types B1, B2, and B3 tumors than in others. However, imaging findings among the various types overlap to some extent, and the ability of imaging studies to differentiate types AB, B1, B2, and B3 is limited.

Show MeSH
Related in: MedlinePlus