[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [White cells, lymph nodes, spleen and thymus](https://durgical.com/en/general-pathology/areas/hematolymphoid/) › Diseases of the thymus # Diseases of the thymus - Lesion The thymus can fail to form, grow lymphoid follicles in autoimmune disease, or give rise to thymoma, an epithelial tumour linked to myasthenia. Updated Nov 12, 2026 ## Key points - DiGeorge syndrome: absent thymus and parathyroids, cardiac outflow defects, T-cell deficiency. - Follicular hyperplasia of the thymus in about two-thirds of patients with myasthenia gravis. - Thymoma: anterosuperior mediastinal mass in adults over forty; about a third to a half have myasthenia gravis. - Other paraneoplastic associations: pure red cell aplasia, hypogammaglobulinaemia (Good syndrome) and other autoimmune disorders. - Thymic carcinoma is usually squamous and invasive, without the immature T-cell population. ## What it is Thymic disease is limited but important. Hypoplasia or aplasia occurs in DiGeorge (22q11.2 deletion) syndrome with loss of T cells. Cysts are usually incidental but can hide a tumour. Thymic follicular hyperplasia, with B-cell germinal centres in the medulla, is found in most patients with myasthenia gravis and in other autoimmune diseases. Thymoma, a tumour of thymic epithelial cells with admixed immature T cells, is the commonest thymic neoplasm; its behaviour depends mainly on invasion, and it is tied to paraneoplastic autoimmunity. Thymic carcinoma is cytologically malignant. ## Structure - Thymoma gross: lobulated, firm grey-white encapsulated mass; some invade the capsule and surrounding structures. - Medullary-type thymoma: spindle-shaped bland epithelial cells with few thymocytes, usually noninvasive. - Cortical-type thymoma: plump polygonal epithelial cells with many immature T cells; more often invasive. - Thymic carcinoma: overtly malignant squamous or other carcinoma cells. ## Step by step - Thymic epithelial cells normally teach developing T cells to tolerate self, partly through AIRE. - In thymoma, neoplastic epithelium supports T-cell development but selects them poorly. - Autoreactive T cells leave the tumour and help B cells make autoantibodies (for example against the acetylcholine receptor). - Myasthenia gravis, red cell aplasia or other autoimmunity follows. - Local growth compresses mediastinal structures; invasive thymomas spread to pleura and pericardium. ## Thymic lesions | Lesion | Main features | Association | | --- | --- | --- | | [Hypoplasia or aplasia](https://durgical.com/en/conditions/digeorge-syndrome/) | Absent or tiny thymus, T-cell deficiency | DiGeorge (22q11.2 deletion) syndrome | | Thymic cyst | Serous or mucinous cyst, often incidental | May coexist with lymphoma or thymoma | | [Thymic follicular hyperplasia](https://durgical.com/en/conditions/myasthenia-gravis/) | B-cell germinal centres in the medulla | Myasthenia gravis, Graves disease, lupus, rheumatoid arthritis | | [Thymoma](https://durgical.com/en/conditions/mediastinal-masses/) | Bland epithelial cells with thymocytes; invasive or not | Myasthenia gravis, pure red cell aplasia, hypogammaglobulinaemia | | Thymic carcinoma | Cytologically malignant, often squamous | Aggressive, poor prognosis | ## Clinical notes - Anterior mediastinal masses: thymoma, lymphoma (Hodgkin, T-lymphoblastic, primary mediastinal B), germ cell tumours and retrosternal thyroid. - Thymectomy helps many patients with myasthenia gravis, with or without thymoma. ## Memory aid The thymus teaches tolerance; a thymoma is a bad teacher whose pupils attack the muscle and the red cells. ## Test yourself Think of the answer, then tap the question to see it. ## Which autoimmune disease is most often associated with thymoma? Myasthenia gravis. ## What is the most important prognostic feature of a thymoma? Whether it has invaded through its capsule into surrounding structures (stage). ## Which thymic change is seen in most patients with myasthenia gravis without a tumour? Thymic follicular hyperplasia, with B-cell germinal centres in the medulla. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/diseases-of-the-thymus/) [More Pathology questions →](https://durgical.com/en/practice/?f=pathology) ## Elsewhere in DurgiPedia - [Thymus and tonsils under the microscope](https://durgical.com/en/histology/thymus-and-tonsils-under-the-microscope/) - [Thymus: where T cells learn](https://durgical.com/en/immunology/thymus-where-t-cells-learn/) - [Pharyngeal pouches: tonsil, thymus, parathyroids and C cells](https://durgical.com/en/embryology/pharyngeal-pouches-tonsil-thymus-parathyroids-and-c-cells/) - [T-cell and combined deficiencies: DiGeorge, SCID, Wiskott–Aldrich, ataxia-telangiectasia](https://durgical.com/en/immunology/t-cell-and-combined-deficiencies-digeorge-scid-wiskott-aldrich-ataxia-telangiect/) ## Connections ## Related 4 - [Paraneoplastic syndromes: the table to know](https://durgical.com/en/general-pathology/paraneoplastic-syndromes-the-table-to-know/) - [Acute lymphoblastic leukaemia/lymphoma](https://durgical.com/en/general-pathology/acute-lymphoblastic-leukaemia-lymphoma/) - [Hodgkin lymphoma](https://durgical.com/en/general-pathology/hodgkin-lymphoma/) - [Other marrow failure: PRCA and myelophthisis](https://durgical.com/en/general-pathology/other-marrow-failure-prca-and-myelophthisis/) ## Related conditions 5 - [Mediastinal masses (thymoma and anterior mediastinal mass)](https://durgical.com/en/conditions/mediastinal-masses/) - [Myasthenia gravis](https://durgical.com/en/conditions/myasthenia-gravis/) - [DiGeorge syndrome (22q11.2 deletion syndrome)](https://durgical.com/en/conditions/digeorge-syndrome/) - [Pure red cell aplasia (incl. Diamond–Blackfan anaemia)](https://durgical.com/en/conditions/pure-red-cell-aplasia/) - [Hodgkin lymphoma](https://durgical.com/en/conditions/hodgkin-lymphoma/) [← All of general pathology](https://durgical.com/en/general-pathology/) Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [Thymoma and Thymic Carcinoma](https://www.cancer.gov/types/thymoma/patient/thymoma-treatment-pdq) (National Cancer Institute (NCI), 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/general-pathology/diseases-of-the-thymus/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/diseases-of-the-thymus/