Ultrastructural and Cytochemical Observations

Five canine cutaneous histiocytomas were studied by electron microscopy and esterase cytochemistry. The tumor cells contained irregular nuclei, characteristic lysosomal granules, and perinuclear microfilaments. The cells showed activity with anaphthyl acetate esterase stains. These characteristics are evidence that this tumor originates from the mononuclear phagocyte system. Canine cutaneous histiocytoma is considered to be a distinct morphologic entity, distinguishable from other neoplasms of the skin [lo, 113. The biologic and light-microscopic characteristics of this clinically benign tumor have been described [15]. Although it is considered to be of histiocytic origin, one ultrastructural study [5] found that the cells were compatible with histiocytes but did not definitely establish their origin from the mononuclear phagocyte system. Materials and Methods Cutaneous tumors from five dogs were surgically removed. Fresh tissue was used to make impression smears. Sections stained with hematoxylin and eosin (HE) were prepared in the routine manner. For electron microscopy, tissue fragments were fixed in 2% glutaraldehyde in Tyrode’s buffer at pH 7.3 [7, 141, then in Millonig’s phosphate buffered osmium tetroxide [6]. The tissues were stained en bloc with 0.5% uranyl acetate, dehydrated in a graded ethanol series and propylene oxide, and embedded in araldite. Ultra-thin sections were cut on an LKB ultratome, stained with uranyl acetate and lead citrate [13], and examined with a Philips EM 200 electron microscope. Impression smears were stained for esterase by the method described [18]. by guest on November 28, 2015 vet.sagepub.com Downloaded from GLICK/HOLSCHER/CAMIJBELL 375