Mediastinum
Thymoma and related entities
Thymoma

Author: Hanni Gulwani, M.D. (see Authors page)

Revised: 19 June 2018, last major update December 2012

Copyright: (c) 2003-2018, PathologyOutlines.com, Inc.

PubMed Search: Thymoma mediastinum[TI]

Cite this page: Gulwani, H. Thymoma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/mediastinumthymoma.html. Accessed September 21st, 2018.
Definition / general
  • Most common primary anterior mediastinal neoplasm
Epidemiology
  • Commonly ages 49 - 62 years
  • Childhood thymomas are rare (usually are lymphoblastic lymphomas), usually near puberty, similar behavior and morphology as adult tumors but only occasionally associated with myasthenia gravis
Sites
  • Usually anterosuperior mediastinum
  • Rarely posterior mediastinum, lung hilum or parenchyma, neck, pleura, thyroid
Clinical features
  • Associated with myasthenia gravis (MG) (10% with MG have thymoma, 30 - 45% with thymoma develop MG, higher risk for MG if lymphoid follicles are present in thymoma or adjacent thymus)
  • Associated with other immune mediated disorders: acquired hypogammaglobulinemia (12%), aplastic anemia, pure anerythrogenesis, dermatomyositis, leukemia, lymphoma, lymphopenia, motor neuropathy, mucocutaneous candidiasis, myeloma, myocarditis, myositis, relapsing polychondritis, rheumatoid arthritis, scleroderma, Sjögren disease, syndrome of inappropriate antidiuretic hormone secretion, systemic lupus erythematosus
  • Patients with thymomas have increased risk of developing additional malignancies, especially thymomas with predominantly cortical component (Histopathology 2012;60:437)
  • All thymic tumors, regardless of histology, are associated with invasion and metastases (Mod Pathol 2012;25:370)
  • Although much emphasis in recent years has been placed on the histological classification of thymoma, the bulk of the evidence continues to point to clinical staging as the most important parameter for prognostication (J Clin Pathol 2006;59:1238)
Prognostic factors
Case reports
Treatment
  • Surgical excision
  • Possibly chemotherapy or radiation
Gross description
  • 80% encapsulated, 20% infiltrative into surrounding structures
  • Usually large unless incidental with coronary bypass surgery
  • Multinodular, yellow-gray
  • Sharp lobulations due to fibrous bands with some nodules having pointed ends
  • Cystic degeneration common
Gross images

Images hosted on other servers:

Pink-tan, solid and composed of lobules

Microscopic (histologic) description
  • Spindle cell histologic patterns have indolent behavior, may be associated with hematologic malignancies
  • Non spindle cell thymomas are also called cortical thymomas
  • Cytologically bland epithelial cells and nonneoplastic lymphocytes
  • Capsule may be thick and calcified
  • May have prominent vasculature, microcystic and pseudopapillary patterns, extensive sclerosis
  • Rarely has marked plasma cell infiltrate, amyloid, rosettes without central lumina
  • Usually no well formed Hassall corpuscles
  • Thymoma with pseudosarcomatous stroma: highly cellular spindle cell proliferation without nuclear atypia (Am J Surg Pathol 1997;21:1316)

Microthymoma:
  • Incidental small thymomas, not grossly evident, morphologically identical to conventional B1 / B2 thymoma (Am J Surg Pathol 2005;29:415)
  • May represent early phase of thymoma development
  • Ovoid epithelial cells with pale nuclei and distinct nucleoli, in background of small lymphocytes
  • Foci of medullary differentiation and perivascular spaces present
Microscopic (histologic) images

Images hosted on other servers:

Low power

Cyst formation

Perivascular space

Glandular structures

Various stains

Positive stains
Electron microscopy description
  • Branching tonofilaments, complex desmosomes, elongated cell processes, basal lamina
Molecular / cytogenetics description
Differential diagnosis