Micronodular Thymoma with Lymphoid Stroma
Definition
- Thymoma composed of multiple epithelial nodules surrounded by prominent lymphoid stroma
Alternate / Historical Names
-
Micronodular thymoma with lymphoid B cell hyperplasia
Diagnostic Criteria
- Multiple small epithelial nodules resembling Type A thymoma
- Bland oval nuclei
- Nucleoli inconspicuous or absent
- Few lymphocytes within epithelial nodules
- May form micro and macroscopic cysts
- Mitotic figures very rare
- No Hassall corpuscles or perivascular spaces
- Frequently merges with Type A pattern
- Bland oval nuclei
- Abundant surrounding lymphocytic stroma
- Mostly B cells
- Frequent prominent germinal centers
- Immature T cells may be rare to numerous in and between the nodules
- No epithelial cells within lymphoid areas
- Mostly B cells
- Frquently lacks dense fibrous septa and thick capsule
- Monoclonal B cell populations have been reported in 33% of cases in one series
- Extranodal marginal zone B cell lymphoma reported in half of monoclonal cases
- None of the patients developed systemic lymphoma
- Follicular lymphoma in one case
- Extranodal marginal zone B cell lymphoma reported in half of monoclonal cases
Supplemental Studies
- Epithelial cells
- Keratin positive
- No epithelial cells in lymphoid areas
- CD20 negative
- Keratin positive
- Lymphocytes
- Lymphoid stroma
- Predominantly B cells
- Scattered mature T cells
- Frequently has scattered germinal centers
- Immature T cells variable
- May be scattered to numerous in and surrounding the nodules
- Absent in some cases
- Lymphoid stroma
Clinical
- Infrequently associated with myasthenia gravis or other autoimmune disorders
- No reported deaths
Differential Diagnosis
| Type AB Thymoma | Micronodular Thymoma with Lymphoid Stroma |
|---|---|
| Lymphocyte rich areas contain scattered epithelial cells | Lymphocyte rich areas lack epithelial cells |
| Lymphocyte rich areas composed predominantly of T cells | Lymphocyte rich areas contain many B cells, frequently with germinal centers |
| Micronodular Thymoma with Lymphoid Stroma | Metastatic Carcinoma in a Lymph Node |
|---|---|
| Epithelial nodules usually scattered throughout | Carcinoma usually subcapsular, sinusoidal or focal |
| Cytologically very bland | Usually cytologically atypical |
| Mitotic figures very rare | Mitotic figures may be numerous |
| Lacks a subcapsular sinus | Subcapsular sinus present |
| Presence of adjacent nonneoplastic thymus supports a thymic neoplasm | Typically no adjacent thymus |
| Immature T cells may be present | Immature T cells absent |
| Micronodular Thymoma with Lymphoid Stroma | Thymic Lymphoid (Germinal Center) Hyperplasia |
|---|---|
| Small almost purely epithelial nodules with appearance of Type A thymoma alternating with B cell rich areas that frequently contain germinal centers | Residual normal thymus or ribbons and nests of dendritic epithelial cells containing Hassall corpuscles |
Bibliography
- Shimosato Y, Mukai K, Matsuno Y. Tumors of the Mediastinum, Atlas of Tumor Pathology, AFIP Fourth Series, Fascicle 11, 2010
- Travis WD, Brambilla E, Burke AP, Marx A, Nicholson AG eds. World Health Organization Classification of Tumors. Pathology and genetics of tumors of the lung, pleura, thymus and heart. IARC Press: Lyon 2015
- Ströbel P, Marino M, Feuchtenberger M, Rouzière AS, Tony HP, Wulbrand U, Förster R, Zettl A, Lee Harris N, Kreipe H, Laeng RH, Müller-Hermelink HK, Marx A. Micronodular thymoma: an epithelial tumour with abnormal chemokine expression setting the stage for lymphoma development. J Pathol. 2005 Sep;207(1):72-82.
- Tateyama H, Saito Y, Fujii Y, Okumura M, Nakamura K, Tada H, Yasumitsu T, Eimoto T. The spectrum of micronodular thymic epithelial tumours with lymphoid B-cell hyperplasia. Histopathology. 2001 Jun;38(6):519-27.
- Suster S, Moran CA. Micronodular thymoma with lymphoid B-cell hyperplasia: clinicopathologic and immunohistochemical study of eighteen cases of a distinctive morphologic variant of thymic epithelial neoplasm. Am J Surg Pathol. 1999 Aug;23(8):955-62.
- Thomas De Montpréville V, Zemoura L, Dulmet E. [Thymoma with epithelial micronodules and lymphoid hyperplasia: six cases of a rare and equivocal subtype] Ann Pathol. 2002 Jun;22(3):177-82.
- Weissferdt A, Moran CA. Micronodular thymic carcinoma with lymphoid hyperplasia: a clinicopathological and immunohistochemical study of five cases. Mod Pathol. 2012 Jul;25(7):993-9.
