thymoma

Introduction

Most common tumor in the anterior mediastinum.

Also see thymic carcinoma.

Pathology

• ~30-40% are invasive.
• may be cystic.

Microscopic pathology

WHO classification

• type A (spindle cell; medullary)
• type AB (mixed)
• type B1 (lymphocyte rich; lymphocytic; predominantly cortical; organoid)
• type B2 (cortical)
• type B3 (epithelial; atypical; squamoid; well differentiated thymic carcinoma)
• micronodular thymoma
• metaplastic thymoma
• microscopic thymoma
• sclerosing thymoma
• lipofibroadenoma

microscopic subtyping does not correlate with clinical behavior:

• lymphocyte predominant
• mixed lymphoepithelial
• epithelial cell predominant
• spindle cell (variant of epithelial tumors)

correlates with degree of local invasion & appears to correlate with prognosis:

• cortical
• medullary (better prognosis)
• mixed

Clinical manifestations

(associations)

• myasthenia gravis (~30-40% incidence in thymoma)
• red cell aplasia
• hypogammaglobulinemia (IgA, IgG & IgM decreased)
• mucocutaneous candidiasis
• Cushing's syndrome (ACTH from thymic carcinoid)

Radiology

• computed tomography (CT) of thorax (mediastinum)

Staging

• Stage I. totally encapsulated
• Stage IIA. totally resected, microscopic invasion of capsule
• Stage IIB. transcapsular invasion of mediastinal soft tissue or pleura
• Stage III. invade pericardium, great vessels or lungs
• Stage IVA. seed pericardium or pleura
• Stage IVB. distant metastases

~30-40% of thymomas are invasive.

Complications

• bacterial infections
• viral infections
  • Herpes simplex
  • cytomegalovirus

Management

• surgery: thymectomy
• intravenous immunoglobulin for hypogammaglobulinemia
  • thymectomy does not improve hypogammaglobulinemia

More general terms

• thymic neoplasm
• embryonal neoplasm

Additional terms

• mediastinal neoplasm
• thymic carcinoma
• thymus

Patient information

thymoma patient information