Evaluation of Sinus DiseaseSymptoms referable to the nose and paranasal sinuses are very common, particularly in Hilo. Thirty million people are afflicted with sinusitis annually in the United States. 50% of these will seek the advice of a physician. 90% of these will be evaluated by primary care providers. Sinusitis is frequently overlooked. When it is recognized, it is often treated inappropriately, thus perpetuating a closed cavity infection. Rarely, sinusitis may progress to osteomyelitis and cerebral abscess. Up to 5% of cerebral abscesses have their origins from sinusitis. The clinical diagnosis of sinusitis is usually based upon symptoms referable to the maxillary and frontal sinuses. In actuality however, the ethmoid sinus is the most commonly affected sinus and is believed to be the precursor to disease in the frontal and maxillary sinuses. The signs and symptoms of sinusitis are vague, variable, and non-specific. Often one elicits a history of a "runny nose" or nasal stuffiness; symptoms often referred to as the common cold. The physical examination is frequently negative. When positive, one may find facial tenderness, nasal congestion, anosmia, a purulent nasal discharge, and halitosis. These limited findings may result in under-diagnosing and inadequate treatment. The basic principles of sinusitis therapy are to treat the infection, facilitate drainage, and to promote ongoing drainage to prevent relapse. The goals are to promote normal ciliary function and drainage and to provide normal ventilation through the sinus ostia.
Ciliated cuboidal epithelium lines the nasal cavity and nasal cavity. A thin layer of mucus normally coats the cilia. The cilia move the mucus towards the nasal cavity. In the maxillary sinus, the mucus is propelled from the dependent portion of the sinus towards the osteomeatal unit into the middle meatus. Mucus from the frontal sinus drains into the anterior ethmoid air cells and then drains into the middle meatus. The sphenoid sinus and posterior ethmoid air cells drain into the sphenoethmoid recess. All mucus is then propelled into the nasopharynx. Thus, there are two primary areas of mucus drainage, the middle meatus and the sphenoethmoid recess, which if obstructed, would result in mucociliary and ventilatory obstruction. If surgery is contemplated, then primary consideration is directed to the osteomeatal unit rather than to the maxillary sinus. Functional endoscopic surgery is directed to re-establishment of the ventilatory pathway of the sinuses. Limited resection of the anatomic and inflammatory defects that interfere with mucociliary drainage is performed. Since the technique involves limited surgical resection, an accurate diagnosis and detailed anatomical display is required prior to resection. Computed Tomography is the modality of choice for anatomical display and depiction of the extent of the disease. CT is the modality of choice for the patient suspected of having recurrent or chronic sinusitis. Standard X-rays are the most popular modality ordered to evaluate for sinusitis. The examination typically consists of an AP view to evaluate the frontal and ethmoid sinuses, a lateral view to evaluate the sphenoid sinus, and a Water's view to evaluate the maxillary and frontal sinuses. The AP view is the only view in which we can evaluate the ethmoid sinus, but even that view depicts the sinus poorly due to superimposition over other bony structures. Sometimes, we will receive an order for a Water's view only. In that scenario, we can only evaluate the maxillary and frontal sinuses. The ethmoid sinus is completely obscured by the overlying nasal cavity and the turbinates and cannot be seen at all.
These X-rays may demonstrate an air-fluid level, indicative of acute sinusitis. Other findings would include mucosal thickening or a soft tissue density mass consistent with either a retention cyst or polyp. CT is the modality of choice for the evaluation of the nasal cavity and paranasal sinuses. CT is performed in the coronal plane. It can optimally display the bony anatomy, soft tissue detail, and evaluate the osteomeatal complex for drainage abnormalities. CT will demonstrate the extent of the mucoperiosteal thickening and the regional morphology and anatomic variations that may explain why sinusitis recurs in some patients. Mucoperiosteal thickening can often be seen on a CT scan even in patients who have normal standard X-rays. This is particularly true in the ethmoid sinus, which is poorly seen on standard X-rays. However, considerable ethmoid sinus disease occurs that is subclinical in nature. Therefore, the CT findings should be interpreted in light of the clinical findings. In chronic sinusitis, one might see some thickening or sclerosis of the bone forming the wall of the sinus. Bony erosion is not usually seen, unless it is caused by a mucocele or neoplastic process. Although nasal anatomy varies considerably from one patient to another, there are certain anatomic variations that appear more frequently in patients who have chronic sinusitis. These variations are important as they may obstruct the osteomeatal complex and interfere with the normal mucociliary drainage of the paranasal sinuses. These are well depicted at CT. Concha bullosa and nasal septum deformity are the most common variants, seen in 36% and 21% of patients with chronic sinusitis. Concha bullosa is an aerated middle turbinate which may obstruct the middle meatus or even the infundibulum. This may be unilateral or bilateral. Deviation of the nasal septum may compress the middle turbinate laterally, narrowing the middle meatus and the nasal air passage. CT is the modality of choice for the evaluation of sinusitis, but it is considerably more expensive that a sinus X-ray series. However, there is a compromise solution. For patients who do not have recurrent sinusitis and who you do not consider a candidate for endoscopic surgery, but rather have symptoms suggestive of a solitary acute episode, yet have a negative sinus X-rays, we can perform a limited CT of the sinuses. In this scenario, we perform a few coronal images through the paranasal sinuses at a reduced cost. For that matter, we can perform this limited CT of the sinuses in lieu of standard X-rays. This results in greater diagnostic sensitivity. These limited slices demonstrate all mucoperiosteal disease, but the slices are not sufficiently thin to delineate the bony anatomical variants. MRI is unsurpassed in its ability to demonstrate soft tissue detail. It is extremely sensitive in the depiction of mucosal disease. However, the signal intensity generated by inflammatory disease and normal mucosa in the edematous phase of the nasal cycle is similar and therefore indistinguishable. Also bone and air have the same signal intensity at MRI, therefore bone detail cannot be demonstrated. As a result, the osteomeatal complex is virtually invisible at MRI. In-patients with known sinusitis however, MRI may sometimes be beneficial. It can determine the etiology of a few disease processes. Bacterial and viral inflammation presents with a bright signal on T2 weighted images. Neoplastic processes typically have an intermediate signal intensity on T2 weighted images. Fungal concretions may appear dark on T2 weighted images. In conclusion, sinusitis is a very common problem that is oftentimes difficult to diagnose. Contrary to popular belief, the ethmoid sinus is the most commonly infected sinus and is probably the precursor to frontal and maxillary sinusitis. CT is the modality of choice for the evaluation of sinusitis.
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The paranasal sinuses are named according to the bones in which they developed. These are the frontal, sphenoid, maxillary, and ethmoid sinuses. The ethmoid sinuses are two groups of cell residing on either side of the midline. They each consist of 3 to 18 cells. The sinuses are lined by mucoperiosteum.
The maxillary sinus ostium and infundibulum are the conduit between the maxillary sinus and the nasal cavity. The infundibulum is the superomedial portion of the ostium. The infundibulum drains into the middle meatus of the nasal cavity. These structures comprise the osteomeatal unit. Blockage of this area may lead to frontal and maxillary sinusitis.
