What is your diagnosis? Salivary gland mass in a dog

Abstract

A 6-year-old, female neutered, Shar Pei dog was presented at the University of Glasgow Small Animal Hospital for a routine recheck following a 6-month treatment with toceranib phosphate, a tyrosine kinase inhibitor. The dog had been treated for a previously diagnosed cutaneous, grade II mast cell tumor in the right axillary region that had been surgically removed. On clinical examination no tumor regrowth was noted, and hematologic and biochemical profiles, and urinalysis showed no significant abnormalities. However, during the physical examination, a firm mass was palpated in the region of the right submandibular lymph node. Fine-needle aspirates of the lesion were taken and smears were submitted for cytologic examination (Figure 1). A B Figure 1. Fine-needle aspirates of a mass in the right submandibular area in a dog. May-Grunwald Giemsa stain. (A) Bar = 100 lm, (B) Bar = 50 lm.Interpretation: Sialocele with osseous metaplasia and pyogranulomatous inflammationThe specimen was highly cellular and a moderate number of windrowing erythrocytes were noted in the background. Between lakes of basophilic mucus, there were large, foamy cells exfoliating individually or in clusters, and occasional biand tri-nucleated cells were noted. The majority of the foamy cells were interpreted as macrophages, and some of the most cohesive aggregates were interpreted as salivary glandular epithelial cells. Aggregates of spindle-shaped cells, tightly associated with extracellular, eosinophilic matrix material (osteoid or collagen) were also seen ( Figure 1A, 2C, and 2D). These cells were spindle to oval shaped, had a high nuclear to cytoplasmic ratio, deeply basophilic cytoplasm, and an oval nucleus with finely stippled chromatin. Anisokaryosis and anisocytosis were mild to moderate. Numerous neutrophils and low numbers of multinucleated osteoclasts were also noted ( Figure 1B). While the foamy macrophages and epithelial cells were indicative of sialocoele and sialadenitis, the presence of osteoclasts suggested the presence of osseous metaplasia (OM) or neoplasia. The salivary mass was surgically removed and processed for histopathology. On histologic examination, multiple lobules of serous and mucous salivary glandular tissue were observed, with a central large, markedly dilated duct that was inconsistently lined by a severely attenuated cuboidal epithelium (Figure 2A). Surrounding and radiating from the duct and surrounding multiple salivary gland lobules, there were large anastamosing bony trabeculae lined by mature osteoblasts and small numbers of osteoclasts, and numerous lacunae containing osteocytes (Figure 2A and B). Within the fibrovascular tissue surrounding the dilated duct and involving areas of adipose tissue and glandular tissue, there was multifocal necrosis. Scattered throughout the fibrovascular and glandular tissue, there were moderate numbers of lymphocytes and plasma cells forming follicle-like aggregates. The final diagnosis was sialocele with severe chronic, submandibular sialoadenitis, and OM.