Neoplasia, Nasal and Paranasal
Basic Information 
Definition
Tumors of the nasal passage and paranasal sinuses are uncommon and include a wide range of tumor types, reflecting the diverse tissues present in the head. Squamous cell carcinoma (SCC) is the most commonly diagnosed sinonasal tumor. Paranasal tumors are more common than nasal tumors. Most tumors are unilateral in occurrence.
Epidemiology
Species, Age, Sex
Surface and glandular epithelial tumors are more common in teenage and older horses. Young and immature horses are more likely to be diagnosed with fibro-osseous and bone tumors.
Associated Conditions and Disorders
• Secondary paranasal sinusitis is common with primary neoplasia of the sinuses because of disruption of normal sinus drainage mechanisms and the presence of necrotic tissue and secondary bacterial infection.
• Paranasal sinus cysts commonly present with similar clinical signs of nasal discharge and external facial swelling.
Clinical Presentation
Disease Forms/Subtypes
SCC, adenoma, adenocarcinoma, lymphoma, chondrosarcoma, fibroma, fibrosarcoma, osteoma (hamartoma), osteosarcoma, fibro-osseous tumors (fibrous dysplasia and ossifying fibroma), undifferentiated carcinomas and sarcomas, tumors of dental origin (eg, ameloblastoma), hemangioma, melanoma, mast cell tumor
History, Chief Complaint
• Most sinonasal tumors are slowly growing with an insidious onset of clinical signs. Horses typically have a history of developing nasal discharge (mucoid to purulent; maybe bloody) that persists and perhaps has a foul odor.
• The presence of an expanding external facial swelling is also a common presenting complaint.
• An increased respiratory noise and reduced nasal airflow may be reported.
• Some horses may be presented for head shaking.
• Clinical signs may advance over weeks to months before veterinary attention is sought.
Physical Exam Findings
Nasal discharge: Malodorous, mucoid to purulent, and often bloody; unilateral or bilateral; reduced nasal airflow; increased respiratory noise localized to the nasal passage; dyspnea; external facial swelling (frontal and maxillary regions) is common with advanced disease; enlarged submandibular lymph nodes; epiphora; exophthalmos; ocular discharge; neurologic deficits; halitosis; dysphagia; inappetence.
Etiology and Pathophysiology
• SCC and bone tumors are more common in the maxillary sinus. Glandular epithelial tumors (eg, adenocarcinoma) are more likely to arise from the frontal and ethmoidal sinuses.
• The frontal and ethmoidal sinuses have a greater density of mucosal glands, which may account for the increased incidence of glandular epithelial tumors in these locations compared with other sinus regions.
• Distant metastasis is rare; in addition to locally invasive and destructive growth, carcinomas frequently spread to other sites in the head (nasopharynx, oropharynx, periorbital, cranium, guttural pouch), resulting in diverse clinical signs.
• Osteomas are benign, generally well-circumscribed masses and are not infiltrative.
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