Incidence and Types of Tumour
Nasal cavity tumours account for 1% of all neoplasms in dogs, the incidence is lower in cats. Approximately 75% of the tumours are malignant. Sinonasal tumours may be classified histopathologically as epithelial, non epithelial or miscellaneous neoplasms.
In dogs, neoplasms of epithelial origin are the most common type of tumour, with adenocarcinoma, squamous cell carcinoma and undifferentiated carcinoma being the most frequent tumours diagnosed. Dolichocephalic and mesaticephalic breeds are most frequently affected. Older dogs (9-11 yo) are the most represented. In a report of 285 dogs with sinonasal neoplasia, 5% were 1 to 4 years of age, while 63% were 9 to 16 years of age.
In a retrospective study, nearly 80% of adenocarcinoma affected dog were purebred dogs.
Non epithelial tumours include chondrosarcomas, osteosarcomas, fibrosarcomas, haemangiosarcomas and undifferentiated sarcomas. Other tumours have been described such as melanomas, mast cell tumours, neuroendocrine tumours, transmissible venereal tumours. Most of the tumours are malignant. They are characterized by progressive local invasion with destruction of bone early in the disease. Local invasion to the brain occurs in approximately 30% of dogs with epithelial tumours. At initial diagnosis the proportion of dogs with clinically detectable metastases is relatively low ranging from 0% to 12%. At the time of death, as many as 46% of dogs with nasal carcinomas have metastases to the lungs or regional lymph nodes. Nasal adenocarcinoma also metastasizes to the appendicular skeleton. Non epithelial tumours have a low rate of metastases.
In cats 92% of sino nasal tumours are malignant. Non-epithelial tumours account for 57% to 70% of them, lymphoma being predominant in most of the retrospective studies compared to adenocarcinomas.
In dogs most common clinical signs include epistaxis, mucopurulent nasal discharge, nasofrontal or palate deformity, sneezing, signs of upper airway obstruction with dyspnea, exophthalmus, ocular discharge. Neurological signs may occur when brain invasion is present. Epistaxis was retrospectively evaluated in 35 dogs. Twenty nine dogs had nasal disease. Among them 19 had nasal neoplasia. Clinical signs are often chronic signs affecting initially one side and sometimes becoming bilateral in the course of the disease. Facial and palate deformities are more frequent with non-epithelial tumours.
In cats, clinical signs are similar. Open-mouth breathing is often present related to nasal cavity obstruction. A retrospective study reported unilateral nasal discharge and evidence of haemorrhage, both being more than twice as common with neoplasia than with rhinitis. Upper respiratory noise was more common with neoplasia than foreign body or rhinitis.
Staging of the tumour includes thoracic X-rays, palpation and fine needle aspiration of regional lymph nodes in order to check for metastases. Complete blood count, serum biochemistry, coagulation profile, urinalysis should be performed prior to anaesthesia.
Radiographic examination of the nasal cavities includes open mouth dorso-ventral and frontal sinus views. Other views lead to superimposition of multiple bony and soft tissue structures and radiographic interpretation is often difficult. Canine primary neoplasia has been associated with a homogeneous increase in soft tissue opacity of the ipsilateral or bilateral frontal sinus and/or nasal cavity, generalized loss of turbinate detail, erosion of the vomer bone, palatine bone or maxilla, increased soft tissue density external to the nasal cavity. Positive predictive values (PPV) of radiologic signs in dogs with nasal neoplasia has been determined in a retrospective study. Invasion of surrounding bones had a PPV of 88%, lesions affecting the entire ipsilateral cavity 85%, soft tissue/fluid opacity in the ipsilateral frontal sinus 78%, generalized uni- or bilateral soft tissue opacity 78%, and general loss of turbinate detail 67%. When all signs occurred together in one dog the PPV was 94%.
It is however difficult to appreciate the extent of the tumour on radiographic views and wide differences can exist between observers.
Accurate evaluation of local invasiveness is an important feature to consider for treatment and prognosis of nasal tumours.
Further examination with CT or MRI is recommended.
CT and MRI
CT provides improved anatomic details and allows accurate determination of lateralization and extent of the tumour in peripheral tissues such as cribriform plate, brain, retro-orbital space, bones. CT has been shown to be more sensitive (88%) than radiography (72%) for determining locality and extent of lesions in dogs and cats.
MRI scan has been recommended, to evaluate soft tissue extension of nasal cavity tumours. It provides good resolution and excellent contrast of anatomical details. It allows distinction between fluid and soft tissue signals. In a study comparing radiography and MRI for evaluating the extent of nasal neoplasia, MRI often showed that the tumour was more extensive than appeared to be on radiography. On the other hand, radiography occasionally showed an over estimated size of the mass.
Definitive diagnosis is obtained through biopsy of the mass. A variety of techniques has been described including nasal flushing, blind biopsy, endoscopically guided biopsy. Care should be taken to avoid penetrating to the cribriform plate during the procedure especially when a rigid endoscope is used. Biopsy of abnormal tissue is performed through antegrade rhinoscopy or retrograde endoscopy of the choanae. Tumours are usually strongly suspected when white or yellowish tissue is obtained rather than turbinate or mucus only. Blind biopsy may result in non-diagnostic samples.
Treatment and Prognosis
Treatment of nasal tumours is directed primarily at controlling local invasion of the disease. Use of cytoreductive surgery via dorsal rostral or ventral rhinotomy has been described. Poor response to surgery alone has been reported and combination with adjuvant therapy, mainly radiotherapy, is recommended. The prognosis for dogs with nasal carcinomas that do not receive treatment other than palliative medications is poor. In a retrospective study on 139 cases, the median survival time was 3.1 months and the probability of surviving 1 and 2 years after diagnosis was only 12% and 2% respectively. Epistaxis as an initial clinical sign was associated with a short survival time. For 107 dogs with epistaxis, the median survival time was 3 months compared with 7.3 months for 32 dogs without epistaxis. Tumor stage was not prognostic for survival for untreated dog with nasal carcinomas.
Surgery alone is ineffective in the treatment of nasal cavity tumors resulting in survival times comparable to that observed in untreated dogs. The mean survival time for 41 dogs undergoing surgery alone was approximately 3 to 6 months. Surgery alone or in combination with radiation therapy is important in the management of squamous cell carcinoma of the rostral nasal cavity (nasal planum, nasal vestibule) in the dog, as radiation therapy alone to date has been shown to be ineffective.
Median survival times for dogs treated with high-energy megavoltage radiation therapy range from 7.4 to 47.7 months. The 1- and 2-year survival rates range from 43% to 60% (1 year) and 11% to 44% (2 years). Results of a study of 53 dogs with nasal adenocarcinomas that received radiotherapy indicate a median survival time of 14 months. This value was significantly longer than the median survival time (4.1 months) of 11 dogs that were not treated or treated with chemotherapy, surgical cytoreduction or both. Doses of 40 to 54 Gy usually are delivered in 10 to 18 treatments of 3 to 4.2 Gy fractions over 2 to 4 weeks to the entire nasal cavity and frontal sinuses. Pre treatment CT or MRI staging is helpful in mapping radiotherapy.
Radiation therapy has been shown to be efficacious in the treatment of transmissible venereal tumors. In one study 7 of 8 dogs obtained a cure with a single 10 Gy dose.
Radiotherapy induces adverse reaction in surrounding healthy tissues. Acute toxicities associated with irradiation include oral mucositis, rhinitis, desquamation, keratoconjunctivitis and blepharitis. Later effects can develop months to years after the initial treatment leading to irreversible lesions to the eye (cataracts, keratitis and keratoconjunctivitis, uveitis, retinal damage), to the central nervous system, to the bones, to the skin. New modalities for delivering radiation therapy, like intensity-modulated radiation therapy (IMRT) and IMRT combined with helical CT are under investigation in veterinary medicine in order to minimize adverse reactions and to optimize administration of radiation to the affected tissues.
Although radiotherapy is widely accepted as the treatment of choice for nasal cavity tumours, the risk of local recurrence is 60% and survival is generally associated with failure to control the tumour locally rather than metastatic disease.
Surgery alone in four cats with nasal adenocarcinoma or undifferentiated carcinoma resulted in a mean survival time of 2.5 weeks. In one report the interval between surgery and euthanasia ranged from 2-8 months.