Felis ISSN 2398-2950


Contributor(s): Philip K Nicholls, Marion O'Leary


  • Thymoma is an uncommon (17/3284 feline neoplasms in one study) cranial mediastinal tumor.
  • Disease due to space occupying effects (lung compression) and paraneoplastic syndromes including myasthenia gravis, polymyositis, myocarditis, dermatitis and megaesophagus.
  • Diagnosis: thoracic imaging (radiography, ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI), direct sampling (cytology, histopathology), and testing for related effect, eg serum levels of anti-acetylcholine-receptor antibody.
  • Treatment: surgery, may be combined with radiotherapy.
  • Prognosis: fair to guarded.



  • Neoplastic transformation of thymic epithelium.
  • No clear risk factors or etiological agents.
  • Distinct from thymic lymphosarcoma, which is more common, and is associated with FeLV infection, and more common in younger cats.


  • Neoplastic transformation causes uncontrolled cellular proliferation and a mass lesion.
  • Direct effects of space-occupying lesion include compression of lungs, caudal displacement of heart, and compression / displacement of trachea, leading to clinical signs such as dyspnea and coughing.
  • Thoracic effusion may compound dyspnea.
  • Immune disorders sometimes associated with thymoma, with anti acetylcholine receptor antibodies causing neuromuscular junction blockade and flaccid paresis (myasthenia gravis Myasthenia gravis - regurgitation, head & neck ventroflexion).
  • Malassezia dermatitis Malassezia dermatitis is associated with internal neoplasia including thymoma in cats.


  • Signs reported for 2 wk - 3y prior to presentation.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Patnaik A K, Lieberman P H, Erlandson R A et al (2003) Feline cystic thymoma: a clinicopathologic, immunohistologic, and electron microscopic study of 14 cases. J Feline Med Surg (1), 27-35 PubMed.
  • Mauldin E A, Morris D O & Goldschmidt M H (2002) Retrospective study: the presence of Malassezia in feline skin biopsies. A clinicopathological study. Vet Dermatol 13 (1), 7-13 PubMed.
  • Kaser-Hotz B, Rohrer C R, Fidel J L et al (2001) Radiotherapy in three suspect cases of feline thymoma. J Am Anim Hosp Assoc 37 (5), 483-488 PubMed.
  • Smith A N, Wright J C, Brawner W R Jr. et al (2001) Radiation therapy in the treatment of canine and feline thymomas: a retrospective study (1985-1999). J Am Anim Hosp Assoc 37 (5), 489-496 PubMed.
  • Day M J (1997) Review of thymic pathology in 30 cats and 36 dogsJSAP 38 (9), 393-403 PubMed.
  • Forster-Van Hijfte M A, Curtis C F & White R N (1997) Resolution of exfoliative dermatitis and Malassezia pachydermatis overgrowth in a cat after surgical thymoma resection. J Sm Anim Pract 38 (10), 451-454 PubMed.
  • Galloway P E, Barr F J, Holt P E et al (1997) Cystic thymoma in a cat with cholesterol-rich fluid and an unusual ultrasonographic appearance. J Small Anim Pract 38 (5), 220-224 PubMed.
  • Malik R, Gabor L, Hunt G B et al (1997) Benign cranial mediastinal lesions in three cats. Aust Vet J 75 (3), 183-187 PubMed.
  • Gores B R, Berg J, Carpenter J L et al (1994) Surgical treatment of thymoma in cats: 12 cases (1987-1992). J Am Vet Med Assoc 204 (11), 1782-1785 PubMed.
  • Carpenter J L & Valentine B A (1992) Squamous cell carcinoma arising in two feline thymomasVet Pathol 29 (6), 541-543 PubMed.

Other sources of information

  • Withrow S J & MacEwen E G (1996) Thymoma. In: Small animal clinical oncology2nd Ed Saunders W B, Philadelphia pp 530-533.
  • Carpenter J L, Andrews K L and Holzworth  J (1987) Chapter 11. Tumors and tumor-like lesions. In: Holzworth J (Ed) Diseases of the cat  - Medicine and surgery. pp 439-441. WB Saunders.