thymus pathology

thymus

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Normal

capsule
cortex
medulla
Hassall corpuscles

Non-neoplastic

cysts
- thymic cyst
- mesothelial cyst
- mediastinal cyst
  - bronchogenic cyst
  - esophageal cyst
  - duplication cyst
hyperplasia
hypoplasia
- DiGeorge syndrome
- stress involution
- SCID
- AIDS
- GVHD
other
- fibrosis
- mediastinitis

WHO neoplasms

thymoma
- Alphabet typing
  - A = spindle cell
  - AB = mixed (most common)
  - B1 = lymphocytic
  - B2 = polygonal cell
  - B3 = squamoid
- spindle cell thymoma
- mixed thymoma
- lymphocytic thymoma
- polygonal cell thymoma
- squamoid thymoma
- micronodular thymoma
- metaplastic thymoma
- microscopic thymoma
- sclerosing thymoma
- lipofibroadenoma
thymic carcinoma
- SCC
- basaloid carcinoma
- mucoepidermoid carcinoma
- lymphoepithelioma like carcinoma
- sarcomatoid carcinoma
- clear cell carcinoma
- adenocarcinoma
- papillary adenocarcinoma
- carcinoma with t(15;19) translocation
- undifferentiated carcinoma
- mixed
neuroendocrine
- carcinoid
- atypical carcinoid
- small cell carcinoma
- large cell neuroendocrine carcinoma
GCT
hematolymphoid
- lymphoma
  - Hodgkin lymphoma
  - B cell lymphoma
    - DLBCL
    - MALToma
  - T cell lymphoma
    - lymphoblastic lymphoma
    - anaplastic large cell lymphoma
  - histiocytic and dendritic
    - langerhans cell histiocytosis
    - langerhans cell sarcoma
    - histiocytic sarcoma
    - malignant histiocytosis
    - follicular dendritic cell tumor
    - follicular dendritic cell sarcoma
    - interdigitating dendritic cell tumor
    - interdigitating dendritic cell sarcoma
  - myeloid sarcoma
  - AML
mesenchymal
- thymolipoma
- lipoma
- liposarcoma
- solitary fibrous tumor
- synovial sarcoma
- vascular neoplasms
- rhabdomyosarcoma
- leiomyomatous tumors
- peripheral nerve tumors
rare mediastinal tumors
- ectopic thyroid tumor
- ectopic parathyroid tumor
metastasis

Type and grade

A: spindle cell thymoma
AB: mixed thymoma
B1: lymphocytic thymoma
B2: polygonal cell thymoma
B3: squamoid thymoma
C: thymic carcinoma
- low grade
  - basaloid carcinoma
  - mucoepidermoid carcinoma
  - well-differentiated SCC
- high grade
  - poorly differentiated
  - anaplastic/undifferentiated
  - clear cell carcinoma
  - sarcomatoid
  - neuroendocrine carcinoma

TNM (useful for grossing)

thymic epithelial tumors
- T1: encapsulated
- T2: pericapsular invasion
- T3: neighbor invasion
  - pericardium
  - mediastinal pleura
  - thoracic wall
  - great vessels
  - lung
- T4: pleura or pericardial dissemination
- N1: anterior mediastinal nodes
- N2: other intrathoracic nodes
- N3: scalene or supraclavicular nodes
thymic GCT
- T1: thymus confined
  - T1a: <= 5cm
  - T1b: > 5cm
- T2: infiltrates contiguous organs or malignant effusion
  - T2a: <= 5cm
  - T2b: > 5cm
- T3: neighbor invasion
  - pericardium
  - mediastinal pleura
  - thoracic wall
  - great vessels
  - lung
- T4: pleural or pericardial dissemination
- N1: regional node
- N2: other intrathoracic nodes excluding anterior mediastinal
- N3: scalene or supraclavicular

Staging

thymic epithelial tumors
- I: T1
- IIa: T2, microscopic
- IIb: T2, macroscopic
- III: T3
- IVa: T4
- IVb: N1, LVSI or M1
thymic GCT
- I: complete resection
- II: microscopic residual tumor
- III: gross residual tumor
- IV: metastasis