History
An 8-year-old 4.8-kg (10.6-lb) neutered male domestic medium-haired orange tabby cat was evaluated because of a skin mass behind the right ear. The owner reported first noticing this mass 8 months prior. Initially, the cat was not clinically affected by the mass. However, the cat progressively developed an aversion to hard food, the signs of which included hissing at and spitting kibbles out of its mouth. Cytologic examination of a specimen of the skin mass, performed 5 months earlier at another veterinary hospital, revealed a hypocellular fluid consistent with a cystic lesion.
Clinical Findings
On examination, the cat had a focally extensive, 5.0 × 4.5 × 3.0-cm, firm, poorly circumscribed subcutaneous mass affecting the right lateral aspect of the face. The mass extended ventrally underneath the mandible and ventral to the base of the ear. Multiple fluid-filled cavities were detected on palpation. No intraoral mass lesions or deviation of soft tissues was evident. Signs of pain were not associated with opening of the mouth. A fine-needle aspirate specimen of the mass was obtained.
Cytologic Findings
The fine-needle aspirate specimen was moderately cellular with moderate numbers of nondegenerate neutrophils, macrophages, and lymphocytes admixed with rare clusters of epithelial cells against a background containing abundant erythrocytes and copious amounts of basophilic amorphous to granular material (Figure 1). Epithelial cells were present in small, thick, tightly cohesive clusters. The epithelial cells were oval to columnar and had scant to moderate amounts of basophilic cytoplasm, a large central to eccentric nucleus, a densely stippled chromatin pattern, and sometimes a prominent nucleolus. Anisocytosis and anisokaryosis were moderate. These cells rarely formed acinar-like structures, and the cytoplasm rarely contained vacuoles of variable size and blue granular material. The macrophages were often vacuolated and contained blue granular debris similar to that present in the background, and sometimes erythrophagia was evident. No infectious agent was visible.
Photomicrographs of a fine-needle aspirate specimen from a multiloculated skin mass affecting the right lateral aspect of the face (extending ventrally underneath the mandible and ventral to the base of the ear) of an 8-year-old cat. A—A large number of vacuolated macrophages is present amid copious amounts of basophilic, amorphous to coarsely granular material. Modified Wright stain; bar = 100 μm. B—Few clusters of pleomorphic epithelial cells are present. Modified Wright stain; bar = 50 μm. Inset—The epithelial cells rarely form acinar-like structures. Modified Wright stain; bar = 20 μm.
Citation: Journal of the American Veterinary Medical Association 254, 4; 10.2460/javma.254.4.475
Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page →
Additional Clinical Findings
Computed tomography of the skull revealed that the mass originated from the right parotid salivary gland and contained multiple interconnected liquid-filled pockets. The mass and local mandibular lymph node were removed surgically and submitted for histologic examination.
Histopathologic Findings
On histologic examination, the parotid gland had been replaced by a focally extensive, poorly circumscribed, unencapsulated solid-cystic mass comprised of a poorly differentiated epithelial cell population that primarily formed irregular acinar, tubular, and ductular structures; haphazard sheets, cords, packets, and papillary structures were also noted (Figure 2). These cells frequently surrounded large cystic spaces, which corresponded with the liquid-filled pockets detectable on palpation and in CT images. The epithelial cells were oval to columnar and had scant eosinophilic cytoplasm and oval hyperchromatic nuclei with finely stippled chromatin and occasional prominent nucleoli. The mitotic rate ranged from 0 to 2 mitotic figures/hpf (400X). There was abundant necrosis in the mass. Tumor cells were present at the surgical margins of the submitted tissue. The mandibular lymph node was also assessed microscopically and did not have evidence of nodal metastasis.
Photomicrograph of sections of the parotid salivary gland mass from the cat in Figure 1. The parotid salivary gland is completely replaced by a focally extensive, poorly circumscribed, unencapsulated solid-cystic neoplasm. Notice the multiple cystic pockets (asterisks). H&E stain; bar = 500 μm. Inset—The neoplasm is composed of poorly differentiated epithelial tumor cells that primarily form irregular acinar, tubular, and ductular structures. H&E stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 254, 4; 10.2460/javma.254.4.475
Cytologic Interpretation and Case Summary
Cytologic interpretation: salivary gland carcinoma and mixed inflammation.
Case summary: parotid salivary gland cystadenoadenocarcinoma in a cat.
Comments
Salivary gland tumors are exceedingly rare in dogs and cats, with an overall incidence of 0.17%.1 The etiopathogenesis of salivary gland tumors is unknown. It has been suggested that these tumors develop as a result of age-related acquired mutations of the epithelial cells in the salivary glands.2 Among cases of salivary gland carcinomas in humans, males are overrepresented3; in reported cases involving cats, Siamese are overrepresented.4 Most cats with salivary gland tumors are aged 10.9 years or older.5 In cats, mandibular salivary glands have been reported to be most commonly affected (18/30 [59%] cats), followed by parotid salivary glands (6/30 [19%] cats).4 The most commonly reported tumor types in the salivary glands of cats are adenocarcinomas, followed by squamous cell carcinomas, adenomas, and others. Among all types of salivary gland tumors in 30 cats, 39% were associated with nodal involvement at the time of diagnosis and 16% had distant metastases.4
Most cats with salivary gland tumors develop a firm, apparently painless, asymmetric swelling under the jaw. Frequently, the local mandibular lymph nodes are enlarged as well.1 In addition to localized swelling, affected cats are usually bright and alert6 but may have clinical signs of halitosis, dysphagia, or exophthalmos.4 Diagnosis may be made on the basis of results of cytologic examination of a fine-needle aspirate specimen from the affected salivary gland or by histologic examination of tissue samples obtained by excisional biopsy. In the case described in the present report, initial cytologic assessment revealed nonspecific inflammation but no tumor cells. This was likely related to the hypocellularity of the cystic content in the tumor. Examination of a second fine-needle aspirate specimen revealed copious blue amorphous material that resembled saliva and few atypical epithelial cells with vacuolated cytoplasm. Cytologic features of these cells were similar to those described for cells in cystic fluid samples collected from parotid gland cystadenocarcinomas in humans.5
In cases of salivary tumors in cats, surgical removal of well-encapsulated salivary tumors with no signs of metastasis was reported to be associated with a good prognosis.7 The mean survival time was 516 days in cats that had undergone tumor excision, and adjunct radiotherapy and chemotherapy did not result in prolonged survival.4 Regional lymph node involvement was common,4 and the sites for distant metastasis included bones, lungs, kidneys, heart, and brain.6 The cat of the present report was discharged from the hospital fitted with an esophageal feeding tube 1 day after surgery. The owner reported that the patient was “like a new cat” immediately following surgery but that its jaw would sometimes “lock up” during eating. During a hospital visit for suture removal at 2 weeks after surgery, the feeding tube was removed. Five days later, the cat stopped eating and it had to be force-fed by its owner. Four days later at a hospital visit, the cat was unable to open its jaws and appeared emaciated. The cat was subsequently euthanized because of deterioration of its condition and poor prognosis.
Parotid salivary gland cystadenocarcinoma is an uncommon condition that can be difficult to diagnose on the basis of clinical and cytologic findings, largely because the cystic content may contain mostly saliva or other debris with few neoplastic cells. Complete surgical excision is the treatment of choice. Prognosis for cats with parotid salivary gland cystadenocarcinoma is guarded, especially when metastasis has already occurred.
Acknowledgments
This work received no specific funding from any public, commercial, or not-for-profit funding agencies.
References
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