Cytologic features of normal canine ovaries in different stages of estrus with histologic comparison

Abstract

Cytologic evaluation plays an important role in the diagnosis of ovarian neoplasia in dogs, but is supported by only scant information on cytologic features of canine ovaries. The aim of this study was to provide detailed cytologic descriptions of normal canine ovaries in different stages of estrus with comparison to histologic features. Client-owned dogs admitted for elective ovariohysterectomy were studied. For each dog, fine-needle aspirates of both ovaries were collected, stained, and examined and were compared with histologic sections of the same ovary. The stage of estrus was confirmed by examination of histologic sections and cytologic specimens of vaginal cells collected with swabs. Thirty-two ovaries from 16 dogs were examined. Luteal cells were observed in 82% of the dogs in diestrus. In early diestrus these cells were polygonal with amphophilic to deeply basophilic cytoplasm, and in late diestrus luteal cells had blebbed cell borders and clear cytoplasm with numerous small vacuoles. Perivascular arrangements and leuko-emperipolesis were noted in both phases of diestrus. Granulosa cells and spindle cells were found in cytologic specimens from most of the ovaries, and blue-gray extracellular material, sometimes associated with granulosa cells, was present. Medium-sized discrete round cells of undetermined origin were observed in some stages of estrus, and structures classified as corpora albicans were noted occasionally. Knowledge of specific cytologic features of normal canine ovaries is important for identification of pathologic processes in this organ. The novel findings of luteal cell emperipolesis, extracellular material associated with granulosa cells, and round cells of undetermined lineage warrant further study, which may provide new information on canine ovarian structure and function.