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Case 2: A dog with nasal bleeding

In december we received nasal mucosa biopsies from an elderly mixed-breed dog, which was presented to the vet due to non-stoppable nasal bleeding for 2 days. The weeks before the owner noticed few blood droplets at the right nostril every now and then. Endoscopical examination of the nasal cavity revealed a polypoid mass of about 5 mm diameter in the right medial nasal meatus. This mass was biopsied and submitted for histopathological examination.

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Image 1: Photomicrograph of the nasal mucosa biopsies from December '21, HE stain, 10x magnification. The samples are composed of normally organized nasal mucose with intact respiratory epithelium. (1). Nasal glands (2) appear increased in number. Vessels (3) show a hypertrophic endothelium, but no sign of damage, which could explain the nasal bleeding. As the clinical lesion was described as polypoid, the tentative diagnosis of a nasal polyp was made. Nasal polyps are composed of hyperplastic nasal mucosa.

The dog showed persistent nasal bleeding, and the vet suspected a nasal tumor, thus it was referred to a CT imaging.

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Image 2: CT findings of the nasal cavity. The right ventral nasal meatus is filled with a well demarcated mass of several centimeter in diameter, which infiltrates the nasal conchae and the nasal septum. Radiological suspicion of a malignant neoplasm; DD: granulomatous inflammation unlikely.

Because the dog was in a good general condition despite its age, but showed persistent nasal bleeding, the surgical removement of the mass was decided. The removement of the mass was performed in pieces through a transpalatal surgery (image 3). 


Pieces of the removed mass were submitted for histopathological examination to Vetscope Pathologie in March.

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Image 4. Photomicrograph of the nasal mucosa mass removed in March '22, HE stain, 100x. The lamina propria comprises a dense, poorly demarcated neoplastic infiltrate (4). Respiratory epithelium (1), nasal glands (2) and bony tissue (3) are preserved in this detail view, but were distroyed in other areas.

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Image 5. Photomicrograph of the nasal mucosa mass removed in March '22, HE stain, 200x. The neoplastic infiltrate consists of densly packed sheets of round cells, which are more individualized at the border of the samples (left parts of the image).The cells are medium to large size, have moderate to abundant pale amphophilic cytoplasm and a big ovoid nucleus with clear, finely stippled chromatin and one prominent nucleolus. Anisiocytosis and anisocaryosis are marked, mitotic figures are frequent (above M). Between the neoplastic cells, numerous eosinophils (E) are present.

Considering the cellular morphology at the sample borders and the presence of interspersed eosinophils, a tentative diagnosis of a nasal mast cell tumor was made. To confirm this suspicion, an immunohistochemical stain was performed.

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Image 6. Photomicrograph of the immunohistochemistry specimen, CD117/KIT, 200x. The neoplastic cells show a membrane-bound signal. In some cells, an additional perinuclear granular cytoplasmic signal is visible (*). Mitotic figures are also evident (above M).

Diagnosis: Nasal mast cell tumor, poorly differentiated (high grade)

Comment: Nasal tumors are generally rare in dogs (1-2% of all canine neoplasms) and are commonly malignant. Roughly 2/3 of the canine nasal tumors are carcinomas, followed by chondrosarcoma, osteosarcoma and fibrosarcoma. Mast cell tumors are very rare in the nasal cavity, in contrast to their frequent occurrence in the haired skin, where benign and malignant forms exist. This patient had no previous history neither of a cutanous mast cell tumor nor of an internal disease, thus a primary nasal mast cell tumor can be supposed. The prognosis is guarded, as most mast cell tumors of mucous membranes behave in a malignant fashion. The only publication describing a case series of 4 dogs with nasal mast cell reports a survival of 27 to 134 days. Those dogs were treated with chemotherapy but not surgery, because the masses were not removable. That study describes vomitus, stridor/stertor, sneezing and exclusive mouth-breathing as clinical signs before diagnosis.

In the herein presented case, the first biopsies only revealed hyperplastic nasal mucosa, which was interpreted as a nasal polyp considering the endoscopy findings. A recently published study showed that 16% of dogs with nasal tumors also have concurrent polyps. And in 1/3 of the cases with a histological diagnosis of a nasal polyp, a second biopsy revealed an additional nasal neoplasm.

Important to know: Because of the small sample size of nasal mucosa biopsies they may not be representative for the primary pathological process. There may be the co-occurrence of neoplasms and reactive-hyperplastic lesions such as polyps. This case shows that by histopathology one can only examine parts of a lesion, and the consideration of all clinical findings including imaging are required to find the final diagnosis of a case.


- Meuten DJ (ed.). Tumors in Domestic Animals, 5th ed, 2017.

- Khoo A. et al. Intranasal mast cell tumor in the dog: A case series. Can Vet J 2017;58:851–854.
- Tarrant J. et al. Co-occurrence of Nasal Polyps and
Neoplasms of the Canine Nasal Cavity. Vet Pathol 2019;56(6):885-888.


CT image and image of the intraoperative situs by courtesy of the referring vet, who wants to remain anonymous.

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