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Splenic Neoplasms and benign hyperplasia are a consideration once splenomegaly has been detected clinically by palpation or following radiography - some splenic neoplasms are surgically curable.
Hyperplastic Nodules or Benign Lymphoma
These are a very common incidental findings in older dogs that can occasionally be mistakenly for malignant masses. They consist of nodules of hyperplastic white and red pulp
- - usually 1-2 cms in size, but occasionally may be larger
- - spherical
- - protrude hemispherically from the surface as yellow and red mottled nodules
Rarely these nodules may rupture and give rise to haemorrhage.
Haemangiosarcomas are a highly malignant tumour of vascular endothelial origin (cf Haemangiomas which are more benign and generally affect other vascular tissue such as cutaneous vascular tissues). They commonly affect dogs and the most frequently affected areas are the spleen, pericardium, right atrium, liver and muscle. Cats are less frequently affected; the most common sites for feline haemangiosarcomas are the liver, spleen and mesentry. Metastasis occurs via the haematogenous route or via splenic capsule rupture and transabdominal spread. Metastatic sites include, lungs, liver, omentum and diaphragm. Surgery is the treatment of choice but even with this survival time remains very short.
Lymphosarcoma - (aka Lymphoma) is caused by malignant clonal expansion of lymphoid cells and most commonly arises from lymphoid tissues 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 cats following the introduction of widespread FeLV testing and vaccination the most common type of lymphoma affecting cats is alimentary when previously it had been the mediastinal and multicentric forms. Only 10% of lymphoma cases in cats are now associated with FeLV.
Myeloid (Granulocytic) Leukaemia
This is a rare condition in which myeloid cells proliferate in the bone marrow and increased numbers of granulocytes are found in the blood. It has been recorded in all species and in its extreme form the spleen approaches the same size as the liver.
Systemic mastocytosis (aka systemic mast cell disease) is a myeloproliferative neoplasm of mast cells and their precursors. Clinical symptoms are associated with the accumulation of mast cells in different tissues, including bone marrow, skin, the gastrointestinal (GI) tract, the liver and the spleen. It occurs very occasionally in the cat. The spleen can enlarge to liver size in extreme cases.
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