A 12-year-old male neutered Toy Poodle was presented to the University of Minnesota Veterinary Medical Center (UMN-VMC) for a swollen right upper eyelid. The swelling developed one year previously and had reportedly responded to therapy with amoxicillin trihydrate, clavulanate potassium, and dexamethasone, neomycin, polymyxin ophthalmic ointment. However, upon recurrence, the swelling was not responsive to these therapies or addition of cefpodoxime proxetil. Physical examination at the time of presentation revealed a fluctuant swelling on the right upper eyelid that was slightly firmer caudally and medially toward the medial canthus. Aside from incipient anterior cortical and equatorial cataracts in the right lens, the remainder of the ophthalmic examination was within normal limits. A CBC was unremarkable and a serum chemistry profile indicated a mildly elevated GGT activity (10 U/L, reference interval 0–6 U/L). Thoracic radiographs revealed mild right atrial enlargement. Magnetic resonance imaging revealed a noninvasive 2.7 × 2.0 × 1.0 cm mass originating from the dorsolateral right orbit that conformed to the shape of the globe and extended medially and caudoventrally into the retrobulbar space. No surrounding bone reaction was evident. A fine-needle aspirate was taken from 2 sites of the swelling and submitted for cytology (Figure 1A,B).
Diagnosis: Canine lobular orbital adenoma
Smears were moderately cellular with abundant RBCs, associated blood WBCs, and clusters of epithelial cells on a finely granular streaming eosinophilic background. RBCs exhibited “windrowing.” Epithelial cells had rounded to polygonal, relatively indistinct cell margins, and contained a moderate to large amount of foamy basophilic to amphophilic cytoplasm, and a round to oval central nucleus. There were minimal anisocytosis and anisokaryosis in the epithelial cell population. These findings were consistent with aspiration of cytologically well-differentiated lacrimal or salivary gland tissue. Given the clinical presentation, a well-differentiated tumor or hyperplasia of these tissues was suspected.
Following cytologic diagnosis, an incisional biopsy was taken. Histologically, there was a well-delineated, partially encapsulated multilobular mass that formed aggregates of neoplastic glandular cells separated by trabeculae of fibrous tissue of variable thickness (Figure 2). Neoplastic cells were polygonal with eosinophilic cytoplasm, and had a round nucleus with dense chromatin. Cells were arranged in tubules and acini, with empty spaces filled by eosinophilic material. Anisokaryosis and anisocytosis were mild and mitotic figures were scarce. Neoplastic cells extended to the margin of the tissue sampled. Based on histopathologic findings, the mass was diagnosed as a canine lobular orbital adenoma with incomplete margins.
To our knowledge, this is the first report of the cytologic appearance of a canine lobular orbital adenoma, a rare orbital epithelial tumor.[1-3] Findings on physical examination often include an eyelid mass or subconjunctival mass, swelling or hyperemia of the eyelids, third eyelid protrusion, and exophthalmos. Grossly, the tumors are friable and usually nodular, but occasionally solid. Histologically, they resemble well-differentiated lacrimal or salivary gland, but completely lack ductal differentiation. These features distinguish canine lobular orbital adenoma from other tumors, such as lacrimal and salivary adenomas, adenocarcinomas, and pleomorphic lacrimal adenomas.[1-3] Canine lobular orbital adenomas are composed of large epithelial cells with a granular, periodic acid Schiff (PAS)-positive staining cytoplasm, and uniform small nuclei. Although presumed to originate from the lacrimal gland, these tumors are dispersed throughout the connective tissue, unrelated to a particular anatomic structure.[1, 3] Due to the friable nature, the tumors are difficult to remove and recurrence is common unless removed by orbital exenteration.[1, 4] Therefore, recognition of canine lobular orbital adenomas is important for treatment planning and prognosis.
Surgical removal of the mass was elected for treatment and histologically it was similar to the initial incision biopsy. Clean margins were not attained, although the patient had no signs of recurrence as of the last report, 10 months following surgery.