History
An 8-year-old 10.1-kg neutered male mixed-breed dog was euthanized after a 1-month history of chronic coughing, upper airway stridor, and fainting episodes 2 or 3 times a day.
Clinical and Gross Findings
Prior to euthanasia, physical examination revealed mucous nasal discharge and a mass that expanded the soft palate and protruded into the right aspect of the nasopharynx. The mass completely blocked the left nasal airway and partially blocked the right nasal airway. The dog was euthanized with an IV overdose of pentobarbital because of its poor prognosis and submitted for necropsy. Gross anatomic changes were restricted to the caudal nasal cavity and pharynx. A longitudinal section of the head revealed a well-demarcated, 2.8-cm-diameter, soft white mass that expanded the soft palate and extended dorsally into the nasopharynx (Figure 1). No other gross changes were observed.
Photograph of the sagittal section of the head of an 8-year-old neutered male mixed-breed dog that was euthanized because of chronic coughing, upper airway stridor, and fainting episodes of 1 month’s duration. The soft palate is expanded with a well-demarcated white mass that dorsally occludes the nasopharynx (arrow).
Citation: Journal of the American Veterinary Medical Association 259, S2; 10.2460/javma.19.06.0308
Photograph of the sagittal section of the head of an 8-year-old neutered male mixed-breed dog that was euthanized because of chronic coughing, upper airway stridor, and fainting episodes of 1 month’s duration. The soft palate is expanded with a well-demarcated white mass that dorsally occludes the nasopharynx (arrow).
Citation: Journal of the American Veterinary Medical Association 259, S2; 10.2460/javma.19.06.0308
Photograph of the sagittal section of the head of an 8-year-old neutered male mixed-breed dog that was euthanized because of chronic coughing, upper airway stridor, and fainting episodes of 1 month’s duration. The soft palate is expanded with a well-demarcated white mass that dorsally occludes the nasopharynx (arrow).
Citation: Journal of the American Veterinary Medical Association 259, S2; 10.2460/javma.19.06.0308
Formulate differential diagnoses, then continue reading.
Histopathologic findings
Samples of the mass and multiple organs were collected, placed in neutral-buffered 10% formalin, and routinely processed for histologic examination; sections were stained with H&E stain. The nasopharyngeal mass consisted of closely apposed sheets and cords of neoplastic mast cells supported by a scant fibrovascular stroma and preexisting submucosal collagen bundles (Figure 2). Neoplastic cells infiltrated the deep submucosa and dissected adjacent palatine salivary glands. Neoplastic mast cells were round and had faintly eosinophilic cytoplasm that contained numerous basophilic, Giemsa– and toluidine blue–positive granules (Figure 3). Nuclei were round or oval and had finely stippled chromatin with 1 or 2 nucleoli. Mild to moderate anisocytosis and anisokaryosis were present, and the mitotic count was 20 mitotic figures/2.37 mm2. Scattered throughout the mass were moderate numbers of eosinophils and small necrotic foci containing cell debris and neutrophils. The cortex and medullary sinuses of the retropharyngeal and submandibular lymph nodes were partially obliterated by neoplastic mast cells that were morphologically similar to those within the main mass. No pathological changes were observed in the other examined organs.
Photomicrograph of a section of the nasopharyngeal mass. The palatine submucosa is expanded and partially effaced by neoplastic mast cells arranged in sheets and cords supported by preexisting stroma. H&E stain; bar = 500 µm.
Citation: Journal of the American Veterinary Medical Association 259, S2; 10.2460/javma.19.06.0308
Photomicrograph of a section of the nasopharyngeal mass. The palatine submucosa is expanded and partially effaced by neoplastic mast cells arranged in sheets and cords supported by preexisting stroma. H&E stain; bar = 500 µm.
Citation: Journal of the American Veterinary Medical Association 259, S2; 10.2460/javma.19.06.0308
Photomicrograph of a section of the nasopharyngeal mass. The palatine submucosa is expanded and partially effaced by neoplastic mast cells arranged in sheets and cords supported by preexisting stroma. H&E stain; bar = 500 µm.
Citation: Journal of the American Veterinary Medical Association 259, S2; 10.2460/javma.19.06.0308
Photomicrographs of sections of the nasopharyngeal mass. The neoplastic mast cells have cytoplasmic granules. H&E stain; inset bar applies. Inset—The cytoplasmic granules are Giemsa stain positive. Giemsa stain; bar = 100 µm.
Citation: Journal of the American Veterinary Medical Association 259, S2; 10.2460/javma.19.06.0308
Photomicrographs of sections of the nasopharyngeal mass. The neoplastic mast cells have cytoplasmic granules. H&E stain; inset bar applies. Inset—The cytoplasmic granules are Giemsa stain positive. Giemsa stain; bar = 100 µm.
Citation: Journal of the American Veterinary Medical Association 259, S2; 10.2460/javma.19.06.0308
Photomicrographs of sections of the nasopharyngeal mass. The neoplastic mast cells have cytoplasmic granules. H&E stain; inset bar applies. Inset—The cytoplasmic granules are Giemsa stain positive. Giemsa stain; bar = 100 µm.
Citation: Journal of the American Veterinary Medical Association 259, S2; 10.2460/javma.19.06.0308
Morphologic Diagnosis and Case Summary
Morphologic diagnosis: nasopharyngeal mast cell tumor (MCT) with metastasis to the retropharyngeal and submandibular lymph nodes.
Case summary: nasopharyngeal MCT in a dog.
Comments
The diagnosis of nasopharyngeal MCT with metastasis to the retropharyngeal and submandibular lymph nodes in the case described in the present report was made based on the characteristic round cell morphology of neoplastic cells and Giemsa– and toluidine blue–positive cytoplasmic granules.1 The chronic cough and upper airway stridor were likely associated with the presence of the mass. No changes were observed in the brain and heart, and the reported fainting episodes were likely associated with dyspnea and hypoxia resulting from physical obstruction of the upper respiratory tract by the MCT. Mast cell tumors are malignant round cell neoplasms that develop mainly in the dermis and subcutaneous tissues of dogs.2 In dogs, extracutaneous MCTs are uncommon to rare and have been reported particularly in the mucocutaneous junctions, oral cavity, nasal cavity, tonsil, gastrointestinal tract, liver, and spleen.3–10,11,12 The clinical behavior of extracutaneous MCTs differs from that of cutaneous MCTs.8–10,13 Oral MCTs account for < 5% of all oral neoplasms of dogs and develop predominantly on the lips and gingiva and rarely on the tongue, palate, pharynx, and larynx.4,7,8 No age, sex, or breed predisposition has been reported for extracutaneous MCTs in dogs to date.8 The MCTs affecting the perioral skin, oral mucocutaneous junction, and oral mucosa tend to be highly biologically aggressive4,11 with regional metastatic rates varying from 55% to 72%. Dogs with oral MCTs have a median survival time of 9 to 14 months after the diagnosis,4,8 which is reportedly shorter than that of dogs with no regional lymph node metastasis (median survival time, 52 months).4 Nasal and nasopharyngeal MCTs are exceedingly rare and also have an aggressive biological behavior with high rates of metastases to regional lymph nodes, as observed in the case described in the present report.6,11,12 Similarly, visceral MCTs are biologically aggressive and have a high prevalence of regional and distant metastasis at the time of diagnosis, which may often lead to systemic disease and death.4,9,10,13 A less aggressive tonsillar MCT has been reported, suggesting that there may be variations in the clinical behavior of extracutaneous MCTs.5 Extracutaneous MCTs also tend to have different drug susceptibilities, compared to those of cutaneous MCTs, which may contribute to the overall poor prognosis for affected dogs as a result of ineffective treatment protocols.9
The classic 3– and 2–tier grading schemes for cutaneous MCTs14,15 have not been standardized for extracutaneous MCTs. However, for dogs with mucosal MCTs, a mitotic count > 5 mitotic figures/2.37 mm2 (equivalent to 10 FN22/40X fields), as observed in the dog of this report, has been associated with a poor prognosis.8
The main clinical and gross differential diagnosis for the soft pharyngeal mass in the dog of the present report was lymphoma followed by pharyngeal carcinoma or pharyngeal sarcoma,16 and diagnostic confirmation of nasopharyngeal MCT was easily achieved after histologic examination of the mass.1
Acknowledgments
Dr. Oliveira was a visiting student at the Department of Pathology, College of Veterinary Medicine, University of Georgia.
References
- 1.↑
Pedraza F, Grandi F, Rocha NS. The need for cytologic/histologic correlation studies to establish a cytologic grading system for canine mast cell tumors in veterinary medicine. Vet Clin Pathol. 2011;40:280–281.
- 2.↑
Villamil JA, Henry CJ, Bryan JN, et al. Identification of the most common cutaneous neoplasms in dogs and evaluation of breed and age distributions for selected neoplasms. J Am Vet Med Assoc. 2011;239:960–965.
- 3.↑
Thamm DH, Vail DM. Mast cell tumors. In: Withrow SJ, Vail DM, eds. Withrow and MacEwen’s Small Animal Clinical Oncology. 4th ed. Saunders Elsevier; 2007:402–424.
- 4.↑
Hillman LA, Garrett LD, de Lorimier LP, et al. Biological behavior of oral and perioral mast cell tumors in dogs: 44 cases (1996–2006). J Am Vet Med Assoc. 2010;237:936–942.
- 5.↑
Shekell CC, Thomson MJ, Miller RI, et al. Primary tonsillar mast cell tumour in a dog. Aust Vet J. 2018;96:184–187.
- 6.↑
Fortin JS, Shomper J, Williams F, et al. What is your diagnosis? Nasopharyngeal mass in a mixed breed dog. Vet Clin Pathol. 2018;47:320–321.
- 7.↑
Patnaik AK, MacEwen EG, Black AP, et al. Extracutaneous mast-cell tumor in the dog. Vet Pathol. 1982;19:608–615.
- 8.↑
Elliott JW, Cripps P, Blackwood L, et al. Canine oral mucosal mast cell tumours. Vet Comp Oncol. 2016;14:101–111.
- 9.↑
Takahashi T, Kadosawa T, Nagase M, et al. Visceral mast cell tumors in dogs: 10 cases (1982–1997). J Am Vet Med Assoc. 2000;216:222–226.
- 10.↑
Ozaki K, Yamagami T, Nomura K, et al. Mast cell tumors of the gastrointestinal tract in 39 dogs. Vet Pathol. 2002;39:557–564.
- 11.↑
Gieger TL, Theon AP, Werner JA, et al. Biologic behavior and prognostic factors for mast cell tumors of the canine muzzle: 24 cases (1990–2001). J Vet Intern Med. 2003;17:687–692.
- 12.↑
Khoo A, Lane A, Wyatt K. Intranasal mast cell tumor in the dog: A case series. Can Vet J. 2017;58:851–854.
- 13.↑
Kaufman KL, Mann FA. Short- and long-term outcomes after digit amputation in dogs: 33 cases (1999–2011). J Am Vet Med Assoc. 2013;242:1249–1254.
- 14.↑
Patnaik AK, Ehler WJ, MacEwen EG. Canine cutaneous mast cell tumor: morphologic grading and survival time in 83 dogs. Vet Pathol. 1984;21:469–474.
- 15.↑
Kiupel M, Webster JD, Bailey KL, et al. Proposal of a two-tier histologic grading system for canine cutaneous mast cell tumors to more accurately predict biologic behavior. Vet Pathol. 2011;48:147–155.
- 16.↑
Billen F, Day MF, Clercx C. Diagnosis of pharyngeal disorders in dogs: a retrospective study of 67 cases. J Small Anim Pract. 2006;47:122–129.
