Odontogenic Diseases of the Maxillary Sinus

Embryology and Anatomy

The maxillary sinuses are air-containing spaces that occupy maxillary bone bilaterally. They are the first of the paranasal sinuses (e.g., maxillary, ethmoid, frontal, and sphenoid) to develop embryonically and begin in the third month of fetal development as mucosal invaginations or pouching of the ethmoid infundibula. The initial maxillary sinus development, also termed primary pneumatization , progresses as the invagination expands into the cartilaginous nasal capsule. Secondary pneumatization begins in the fifth month of fetal development as the initial invaginations expand into the developing maxillary bone.

After birth, the maxillary sinus expands by pneumatization into the developing alveolar process and extends anteriorly and inferiorly from the base of the skull, closely matching the growth rate of the maxilla and the development of the dentition. As the dentition develops, portions of the alveolar process of the maxilla, vacated by the eruption of teeth, become pneumatized. By the time a child reaches age 12 or 13 years, the sinus will have expanded to the point at which its floor will be on the same horizontal level as the floor of the nasal cavity. In adults, the apices of teeth may extend into the sinus cavity and can be identified in anatomic specimens or through computed tomography imaging. Expansion of the sinus normally ceases after the eruption of permanent teeth, but on occasion the sinus will pneumatize further, after the removal of one or more posterior maxillary teeth, to occupy the residual alveolar process. In many of the cases, the sinus often extends virtually to the crest of the edentulous ridge. The maxillary sinus is significantly larger in adult patients who are edentulous in the posterior maxilla compared with patients with complete posterior dentition.

The maxillary sinus is the largest of the paranasal sinuses. It is also known as the antrum or the antrum of Highmore. The term antrum is derived from the Greek word meaning “cave.” Nathaniel Highmore, an English physician in the 1600s, described a sinus infection associated with a maxillary tooth, and his name has long been associated with sinus nomenclature.

The maxillary sinus is described as a four-sided pyramid, with the base lying vertically on the medial surface and forming the lateral nasal wall. The apex extends laterally into the zygomatic process of the maxilla. The upper wall, or roof, of the sinus is also the floor of the orbit. The posterior wall extends the length of the maxilla and dips into the maxillary tuberosity. Anteriorly and laterally, the sinus extends to the region of the first bicuspid or cuspid teeth. The floor of the sinus forms the base of the alveolar process ( Figs. 20.1 and 20.2 ). The adult maxillary sinus averages 34 mm in the anteroposterior direction, 33 mm in height, and 23 mm in width. The volume of the sinus is approximately 15 to 20 mL.

The sinuses are primarily lined by respiratory epithelium, a mucus-secreting pseudostratified and ciliated columnar epithelium. The cilia and mucus are necessary for the drainage of the sinus because the sinus opening, or ostium, is not in a dependent (inferior) position but lies two-thirds the distance up the medial wall and drains into the nasal cavity (see Figs. 20.1 and 20.2 ). The maxillary sinus opens into the posterior or inferior end of the semilunar hiatus, which lies in the middle meatus of the nasal cavity between the inferior and middle nasal conchae. Beating of the cilia moves the mucus produced by the lining epithelium and any foreign material contained within the sinus toward the ostium, from which it drains into the nasal cavity. The cilia beat at a rate of up to 1000 strokes per minute and can move mucus a distance of 6 mm/min. The environment within the sinus is a constantly moving thin layer of mucus that is transported along the walls of the sinus through the ostium and into the nasopharynx.

Clinical Examination of the Maxillary Sinus

Clinical evaluation of a patient with suspected maxillary sinusitis should begin with a careful visual examination of the patient's face and intraoral vestibule for swelling or redness. Nasal discharge may be evident during the initial evaluation. Examination of the patient with suspected maxillary sinus disease should also include tapping of the lateral walls of the sinus externally over the prominence of the cheekbones and palpation intraorally on the lateral surface of the maxilla between the canine fossa and the zygomatic buttress. The affected sinus may be very tender to gentle tapping or palpation. In some cases, the lateral wall of the sinus (lateral maxillary wall) may be eroded and have a palpable defect. Patients with maxillary sinusitis frequently complain of dental pain, and pain to percussion of several maxillary posterior teeth is often indicative of an acute sinus infection.

Further examination may include transillumination of the maxillary sinuses. This is done by placing a bright fiberoptic light against the mucosa on the palatal or facial surfaces of the sinus and observing, in a darkened room, the transmission of light through the sinus ( Fig. 20.3 ). In unilateral disease, a sinus may be compared with the one on the opposite side. The involved sinus shows decreased transmission of light because of the accumulation of fluid, debris, or pus and the thickening of the sinus mucosa. These simple tests may help distinguish sinus disease, which may cause pain in the upper teeth from abscess or other pain of dental origin associated with molar and premolar teeth. Nasal and sinus endoscopy can be performed to obtain additional information regarding anatomic factors that may be contributing to sinus disease as well as the overall health of the mucosa.

Radiographic Examination of the Maxillary Sinus

Radiographic examination of the maxillary sinus may be accomplished with a wide variety of exposures readily available in the dental office or radiology clinic. Standard dental radiographs that may be useful in evaluating the maxillary sinus include periapical, occlusal, and panoramic views. A periapical radiograph is limited in that only a small portion of the inferior aspect of the sinus can be visualized. In some cases, the apices of the roots of posterior maxillary teeth may be seen to project into the sinus floor ( Fig. 20.4 ). Panoramic radiographs may provide a “screening” view of the maxillary sinuses ( Fig. 20.5 ). This projection is the best radiograph that can be obtained in most dental offices to provide a view of both maxillary sinuses for comparison. Because a panoramic radiograph provides a focused image within a limited focal trough, structures outside of this area may not be clearly delineated.

Periapical, occlusal, and occasionally panoramic radiographs are of value in locating and retrieving foreign bodies within the sinus—particularly teeth, root tips, or osseous fragments—that have been displaced by trauma or during tooth removal ( Fig. 20.6 ). These radiographs should also be used for the careful planning of surgical removal of teeth adjacent to the sinus.

If additional radiographic information is required, the Waters and lateral views, two plain film radiographs, are frequently useful. The Waters view is taken with the head tipped 37 degrees to the central beam ( Fig. 20.7 ). This projection places the maxillary sinus area above the petrous portion of temporal bones, allowing for a clearer view of the sinuses than a standard posteroanterior view of the skull. The lateral view can be obtained in a standard cephalometric machine with the patient's head tipped slightly toward the cassette ( Fig. 20.8 ). Tipping of the patient's head avoids superimposition of the walls of the sinus.

Computed tomography is a useful technique for imaging of the maxillary sinuses and other facial bony structures. Lower cost and better accessibility combined with clear, easily visualized images have made computed tomography scans increasingly popular for evaluating all types of pathologic conditions of facial bone, including abnormalities of the maxillary sinus ( Fig. 20.9 ).

Interpretation of the radiographs of the maxillary sinus is not difficult. The findings in the normal antrum are those to be expected of a rather large, air-filled cavity surrounded by bone and dental structures. The body of the sinus should appear radiolucent and be outlined in all peripheral areas by a well-demarcated layer of cortical bone. Comparison of one side with the other is helpful in examining radiographs. Thickened mucosa on the bony walls, air-fluid levels (caused by the accumulation of mucus, pus, or blood), or foreign bodies lying free should not be present. Partial or complete opacification of the maxillary sinus may be caused by the mucosal hypertrophy and fluid accumulation of sinusitis, by blood filling the sinus following trauma, or by neoplasia. Radiographic changes are to be expected with acute maxillary sinusitis. Mucosal thickening caused by infections may obstruct the ostium of the sinus and allow the accumulation of mucus, which will become infected and produce pus. The characteristic radiographic changes may include an air-fluid level in the sinus (see Fig. 20.7 ), thickened mucosa on any or all of the sinus walls ( Fig. 20.10 ), or complete opacification of the sinus cavity. Radiographic changes indicative of chronic maxillary sinusitis include mucosal thickening, sinus opacification, and nasal or antral polyps. Air-fluid levels in the sinuses are more characteristic of acute sinus disease but may be seen in chronic sinusitis during periods of acute exacerbation.

Disruption of the cortical outline may be a result of trauma, tumor formation, an infectious process with abscess and fistula formation ( Fig. 20.11 ), or a surgical procedure that violates the sinus walls. Expansion of the bony walls may also be apparent ( Fig. 20.12 ). Dental pathologic conditions such as cysts or granulomas may produce radiolucent lesions that extend into the sinus cavity. These conditions may be distinguished from normal sinus anatomy by their association with the tooth apex, the clinical correlation with the dental examination, and the presence of a cortical osseous margin on the radiograph, which generally separates the area in question from the sinus itself.