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An Urban Experience
histologically may resemble multicentric lymphoma has been reported to occur in young cats(J. Amer. Vet. Med. Assoc. 190 (2):897-899, 1987 and Vet. Pathol, 23:286- 392, 1986). In addition, Multicentric lymphoma, involving only the peripheral lymph nodes, is common in the dog, but rare in the cat. Therefore, a diagnosis of lymphoma cannot be made when evaluating aspirates taken from cats with only generalized peripheral lymphadenopathy.
Anatomic forms of feline lymphoma
Lymphoma involving the internal organs occurs with relative frequency in the cat. Various forms may include mediastinal, hepatic, alimentary, renal, ocular, and primary CNS lymphoma. There may be a relationship between alimentary and renal lymphoma and with
renal lymphoma and CNS metastasis. When aspirates from masses in any of organs yield a dense population
of lymphoid cells, lymphoma should be suspected. When the lymphocyte population consists of primarily lymphoblasts, as is seen in many cases, the cytologic diagnosis of lymphoma can reliably be made. However, many lymphomas of liver or intestinal origin are composed of small, well-differentiated, normal-looking, neoplastic lymphocytes (Figure to right; small-cell hepatic lymphoma). Many lymphomas in the cat are composed of T-cells transformed by the FeLV virus, but most arising from the gastrointestinal tract are FeLV-negative B-cell lymphomas.
An unusual form of alimentary lymphoma classified as large granular lymphoma (LGL) is also reported in the cat (Figure on right). It is characterized by a population of individually arranged round cells with fairly abundant cytoplasm. The cytoplasm contains a focal accumulation of azurophilic granules (resembling mast cell granules). These tumors usually involve the small intestine and
are believed to be of cytotoxic T-cell or natural killer
cell origin. The focal accumulation of the granules may help to distinguish this neoplasm from the intestinal
form of MCT also seen in the cat. LGLs generally have less cytoplasm, fewer, larger granules, and no or few eosinophils as compared to mast cell neoplasms. LGL stain positively for lymphoid tissue markers and with PTAH (phosphotungstic acid- hematoxylin), and negative with toluidine blue, mast cell tumors stain just the opposite.
Feline Hodgkin’s-like Lymphoma.
Feline-Hodgkin’s-like lymphoma resembles the condition in humans and has generally been recognized in older cats (> 6 yrs). Most affected animals presented with a mass in the ventral cervical region, submandibular and/ or prescapular node enlargement. As in humans, only a single node or group of nodes is generally involved with eventual contiguous nodal advancement. The cytologic diagnosis is very difficult since the neoplastic cells (Reed-Sternberg cells and their variants, BINUCLEATED
CELL ON BOTTOM RIGHT) only comprise 1% to 5%
of the cells in the affected lymph node, the rest of the cells are non-neoplastic lymphocytes, macrophages,
and granulocytes. The diagnosis needs to be confirmed histologically and various histological types of the disease exist (Vet. Pathol. 38:504-511, 2001).
Metastatic Disease.
Knowledge of the areas drained by specific lymph nodes is critical in determining the presence of metastatic disease. It is also important to remember that the absence of obvious metastatic disease in a cytology specimen does not rule out the possibility of early metastasis. Since many tumors will enter the nodes through afferent, subcapsular vessels (Figure on right), or begin as focal accumulations, early metastatic disease might be missed on cytologic preparations. Metastatic disease is characterized by the presence of a homogenous cell population not normally found in a lymph node. These cells usually appear anaplastic
and display obvious characteristics of malignancy. The remaining lymphoid population may appear reactive, however, the neoplasia may replace (efface) the lymph node parenchyma totally, making cytological identification of the swelling as a lymph node difficult. The absence
of lymphadenopathy does not rule out the presence
of metastatic disease. Mast cell tumors, amongst
other neoplastic processes, are renown to metastasize without creating lymphadenopathy. The presence of lymphadenopathy in a lymph node draining an area with a tumor does not automatically indicate metastasis has occurred. Lymph nodes draining an area where
a tumor is located often become reactive in response
to the regional inflammatory process induced by the neoplasm. In addition, many lymph nodes may be normal in size and have significant metastatic disease. This is particularly true of metastatic mast cell tumors.

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