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A 4-year-old Quarter Horse mare was presented to the Texas AM University Veterinary Medical Teaching Hospital for evaluation of a rectal tear. On initial evaluation, rectal palpation and colonoscopy revealed a grade IIIb rectal tear. Analysis of peritoneal fluid revealed a modified transudate. Preliminary supportive care included fluid therapy and mineral oil administration via nasogastric tube. Approximately 48 hours after presentation, a second abdominocentesis was performed, and cytologic examination of the fluid revealed a marked suppurative exudate. Round clear nonrefractile material observed within neutrophils and macrophages and in the background stained bright pink to red with Oil Red O, confirming the material as lipid, likely from leakage of mineral oil through the rectal tear. The condition of the mare deteriorated and euthanasia was elected due to the poor prognosis. At necropsy, gross and histologic findings included peritoneal effusion and a full-thickness rectal tear with transmural necrotizing pyogranulomatous colitis and fibrinous peritonitis. To the authors' knowledge, this is the first reported case of Oil Red O-positive lipid vacuoles in the peritoneal fluid of a horse from presumed leakage of mineral oil through a transmural rectal perforation. The frequency of this occurrence in horses is unknown, but it is important for cytopathologists to be familiar with the appearance and significance of lipid-type droplets in phagocytic cells in cytologic fluid analysis specimens.

Background — Morphology and cytochemistry are the foundation for classification of leukemias in dogs and cats. Advances in automated hematology instrumentation, immunophenotyping, cytogenetics, and molecular biology are significantly improving our ability to recognize and classify spontaneous myeloproliferative and lymphoproliferative disorders. Objective — The purpose of this study was to assess the utility of flow cytometry‐based light scatter patterns provided by the Cell-Dyn 3500 (CD3500) automated hematology analyzer to predict the lineage of leukemic cells in peripheral blood of dogs and cats. Methods — Leukemic cells from 15 dogs and 6 cats were provisionally classified using an algorithm based on the CD3500 CBC output data and were subsequently phenotyped by enzyme cytochemistry, immunocytochemistry, indirect flow cytometry, and analysis of antigen receptor gene rearrangement. Results — The algorithm led to correct predictions regarding the ontogeny of the leukemic cells (erythroid/megakaryocytic potential, myeloid leukemia, monocytic leukemia, chronic granulocytic leukemia, lymphoid leukemia) in 19/21 animals. Mismatches in the WBC impedance count and the WBC optical count in conjunction with microscopic assessment of blasts in the blood were useful for predicting myeloproliferative disorders with erythroid or megakaryocytic potential.The leukocyte light scatter patterns enabled distinction among myeloid leukemias (represented by acute myelomonocytic leukemia, acute monocytic leukemia, chronic granulocytic leukemia) and lymphocytic leukemias (including acute and chronic lymphocytic leukemias). One case of acute lymphocytic leukemia was misidentified as chronic lymphocytic leukemia. Conclusions — Algorithmic analyses can be applied to data generated by the CD3500 to predict the ontogeny of leukemic cells in the peripheral blood of dogs and cats. This rapid and quantitative technique may be used to improve diagnostic decisions, expand therapeutic choices, and increase prognostic accuracy. (Vet Clin Pathol. 2002;31:167-182)