Incidence/Epidemiology/Risk Factors: Cancers arising in the sinonasal cavity and the base of skull are extremely rare. It has been estimated that the incidence of sinonasal cancers is approximately 1/500,000 to 1/1,000,000 people. Unlike other cancers, in the head and neck there does not appear to be any predominant risk factor. Tobacco use, alcohol use, sun exposure, exposure to ionizing radiation, do not appear to be causative factors in sinonasal cancer. There are some rare industrial exposures which may account for the development of these cancers. One such exposure is for individuals working in the wood industry. There appears to be some association with exposure to both hard and soft wood dust. In addition, there have been reported clustering of these cancers in individuals who mine such minerals as cadmium, nickel, and other rare minerals. As a consequence of industrial exposure, these malignancies appear to occur more commonly in males than females. There does not appear to be any other racial, ethnic, or geographic propensity for these cancers to develop.
Anatomy/Pathology: The anatomy of the sinonasal tract in skull base is complex. The most common sites of origin for sinonasal/skull base tumors is the maxillary sinus, the nasal cavity, and the ethmoid sinus, in that order. Maxillary sinus is denoted in the illustration below. The maxillary sinus occupies the space between the eye and the upper jaw. One can think of the maxillary sinus as a room. The floor of the maxillary sinus is the hard palate, including the upper teeth. The ceiling of the maxillary sinus is the bone which supports the eye. The tumors that invade through the maxillary roof can invade the eye and ultimately have an impact upon its function. Maxillary sinus tumors that invade through the back wall gain access to the nerves a vessels at the base of skull and have the opportunity to invade directly into the brain. These lesions represent extremely advanced disease. Lesions arising in the ethmoid sinus and nasal cavity have similar anatomic considerations. This anatomic region is in close proximity to the eye, as noted in the diagram. These tumors can directly invade the eye or the optic nerve, the nerve that provides vision to the eye. In addition, these tumors can invade the thin bone at the base of skull and directly invade the brain. Tumors arising in other sinuses are extremely rare. Additional sites include the frontal sinus, the sphenoid sinus, primary orbital tumors, and the rare skin cancer which invades from the surface of the skin to involve the sinonasal tract base of skull. Many different types of cancer arise in the sinonasal cavity. The most common is squamous carcinoma of the maxillary sinus. In addition, salivary gland cancers occur in the sinonasal tract, including adenocarcinoma, mucoepidermoid carcinoma and adenoid cystic carcinoma. Another extremely common cancer occurring in the nasal cavity is ethesioneuroblastoma. This is a cancer that arises from the olfactory nerves in the roof of the ethnoid sinuses and has an extremely good prognosis. Sarcomas, tumors arising from soft tissue, cartilage, and bone, also occur in the nasal cavity and base of skull. Their prognosis varies considerably. Low grade tumors have an excellent prognosis while the outcome for high grade lesions is worse. Melanoma also arises in the nasal cavity mucosa, similar to the melanomas that occur on the skin. This is an aggressive tumor even in the face of treatment. Skin cancers, such as basal cell carcinoma, squamous carcinoma, and cutaneous melanoma, whether locally aggressive of multiply recurrent, can invade the base of skull. In rare occasions, lymphomas will arise in the sinonasal cavity. Lastly, a benign but locally aggressive tumor known as an inverted papilloma occurs on the lateral nasal wall.
Symptoms: Tumors arising in the sinonasal cavity/base of skull region often mimic signs and symptoms of sinusitis. Discharge, nasal obstruction, difficulty breathing through the nasal cavity, pressure sensation in the midface, and nosebleeds are symptoms of sinusitis and allergic rhinitis that affect up 20% of the adult population. Since these symptoms are often present in sinonasal cancer, these tumors can present as advanced stage lesions. Symptoms that are specific to sinonasal cancers included loosening and numbness of the upper teeth, eye bulging, double or blurred vision, tearing, and, for very advanced lesions, loss of vision. Tumors arising in the nasal cavity often present with bleeding, inability to breath through the nose, and loss of smell. Extremely advanced lesions will present with an inability to open the mouth, hearing loss, headaches, ear pain, and even mental status changes.
Diagnosis: Diagnosis begins with a thorough office examination. With the increased use of endoscopes, it is possible to examine the sinonasal tract and nasopharynx. Prior to biopsy, imaging is essential. Both CT and MRI are utilized to further characterize sinonasal tumors. Generally, the MRI is thought to be a little more accurate as it provides better definition of the tumor in relation to the surrounding structures. At minimum, a chest x-ray should be obtained to exclude metastatic disease to the lung. In some instances, CT scan of the chest and/or PET scan may be useful. Ultimately, biopsy is indicated for the purpose of determining tissue type. After numbing the area that will be biopsied, the surgeon will remove a small piece of tissue. The sample is sent to the pathologist and examined under a microscope and the tumor type can be identified. This information is essential to determine the optimal treatment.
Treatment options: There are a number of treatment options in the management of patients with sinonasal cancer. Currently, the majority of patients undergo surgery with postoperative radiation. Chemotherapy and radiation may also be an option. Treatment planning is done on a case-by-case basis and depends on the extent and location of the tumor. Often, these surgical procedures necessitate the involvement of neurosurgeons, plastic surgeons, and maxillofacial prosthodontic surgeons.
Follow up: After completion of treatment, patients are typically seen in follow up every 6 weeks to 3 months for the first 2-3 years. Then every 6 months for the next 3 years. Patients are then seen annually after 5 years of follow up. The surgeon performs an examination and may order CT, MRI and/or PET scans at frequent intervals. Patients should also have an annual chest x-ray to exclude the possibility of metastatic disease to the lungs. Analogous to many cancers, once 2 years have past since completion of all treatment, the likelihood of recurrence drops significantly.
Additional information: North American Skull Base Society at www.nasbs.org
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