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==Description==   

==Description==   

Lymphoma is caused by malignant clonal expansion of lymphoid cells and most commonly arises from lymphoid tisses including the bone marrow, thymus, lymph nodes and spleen. Lymphoma is documented to be the most common haematopoietic neoplasm in dogs. Certain varieties of lymphoma in cats is associated with FeLV and FIV.

Lymphoma is caused by malignant clonal expansion of lymphoid cells and most commonly arises from lymphoid tisses including the bone marrow, thymus, lymph nodes and spleen. Lymphoma is documented to be the most common haematopoietic neoplasm in dogs.  

 

In the dog, multicentric lymphoma is most common representing 80% of cases. Alimentary, cutaneous, mediastinal and extranodal sites are less common. Additionally the majority of lymphoma cases in dogs are of the B-cell immunophenotype.  

In the dog, multicentric lymphoma is most common representing 80% of cases. Alimentary, cutaneous, mediastinal and extranodal sites are less common. Additionally the majority of lymphoma cases in dogs are of the B-cell immunophenotype.  

In cats

In cats following the inroduction of widespread vaccination against FeLV testing and vaccination the most common type of lymphoma affecting cats is alimentary when previously it had been mediastinal and multicentric forms.

* Localised lymphoma: can be intramural or extend intraluminally. The lesion may be focal or multifocal. The tumour can be of a variety of shapes namely nodular, plaque-like or circumferential. Circumferential transmural or intramural tumours often bulge outward since the diseased muscle atrophies so that rows of lymphocytes remain supported by parallel bands of reticulum fibers only. The circumferential intramural form is the most frequently seen in the feline intestine.

Only 10% of lymphoma cases in cats is now associated with FeLV.

* Diffuse lymphoma: with these tumours there is a granular or cobblestone appearance to the mucosa. The mesenteric lymph nodes are often affected.

* In cats the most frequent sites are the jejunum, ileocaecocolic junction, duodenum, colon and stomach (in decreasing order of frequency).

* At the time of diagnosis in cats tumour nodules are often already apparent in the liver, kidney, spleen and abdominal and sternal lymph nodes. Differentiating AL and multicentric lymphoma may be difficult at this point.

* In most cats AL is not associated with FeLV and aetiololgy is idiopathic.

==Signalment==

==Signalment==