Mast Cell Tumors, Canine - contd.
Microscopic study of aspirated or excised tissues provides important diagnostic information. A provisional diagnosis of mast cell tumor based on history, physical exam findings, and clinical signs is often confirmed with evaluation of tumor samples obtained by the fine-needle aspirate technique. Granulated mast cells are easily identified in fine-needle aspirates of mast cell tumors. Mast cells are round and typically contain large, purple cytoplasmic granules. However, undifferentiated tumor cells may not always be identified with this method.
Examination of excised MCT-tissues allows histologic grading and determination of the completeness of excision; it may be required for a definitive diagnosis in undifferentiated MCTs. Special staining techniques aid the pathologist in determining the diagnosis and extent of tissue invasion. Histologic classification of mast cell tumors typically follows the system based on the degree of differentiation and infiltration; it classifies MCTs as well differentiated, or grade I, moderately differentiated, or grade II, and poorly differentiated, or grade III. High-grade tumors have indistinct granules, with variable staining. The cells may be bizarrely shaped, rather than round, and are variably sized.
Additional diagnostic studies may be conducted to help identify the presence of metastatic, or spreading, disease. Diagnostic evaluation should include abdominal x-rays or ultrasonography to identify hepatomegaly, or liver enlargement, splenomegaly, or splenic enlargement, or lymph node involvement. Ultrasound may be more sensitive than abdominal x-rays in assessing the spread of mast cell tumors. Thoracic x-rays can detect lymph node disease in the chest.
A complete blood count, or CBC, can detect the presence of cytopenias, including low platelet count, low red blood cell count, and low white blood cell count. The CBC will also demonstrate mastocythemia, or elevated mast cell count, which suggests spread of the mast cell tumor into bone marrow. White blood cells may be elevated due to circulating inflammatory compounds or to the presence of gastrointestinal ulceration. The recognition of mast cells in circulation can be improved by concentrating the white blood cell fraction of blood in a buffy coat preparation.
