Surgical Anatomy of the Nasal Cavity and Paranasal Sinuses

S u r g i c a l An a t o m y o f the Nasal Cavity and Paranasal Sinuses Orrett E. Ogle, DDSa,*, Robert J. Weinstock, DDSb, Ezra Friedman, DDSc KEYWORDS  Paranasal sinuses  Nasal anatomy  Sinus anatomy  Maxillary sinus  Ethmoid sinus  Frontal sinus  Sphenoid sinus  Surgical anatomy THE NASAL CAVITY The nasal cavities are located in the middle of the face between the frontal sinus above, the oral cavity below, and the orbits and maxillary sinuses to the sides (Figs. 1 and 2). The nasal cavity is encased in a pyramidal-shaped osseo-cartilaginous framework and is divided into two compartments by the nasal septum. The osseous portion consists of two nasal bones that articulate with the nasal process of the frontal bone superiorly and fuses with the maxilla laterally. Their lower borders are beveled on their inner surfaces where they articulate with the upper lateral nasal cartilages. The upper lateral nasal cartilages project up below the nasal bones and are attached to them with dense connective tissue. The cartilaginous portion of the framework consists of two components: the upper lateral and lower lateral nasal cartilages. Upper Lateral Nasal Cartilages The upper lateral nasal cartilage is roughly triangular-shaped. Its superior edge is thin and articulates with the nasal bones via dense connective tissue and fuses to the maxilla. The inferior border is also thin and inserts below the border of the lower lateral cartilage (this is not always a consistent relationship, however).1 This inferior end is free and is the site of the intercartilaginous incision during rhinoplasty. The medial border is thick and continuous with the septal cartilage. The authors have nothing to disclose. a Oral and Maxillofacial Surgery, Department of Dentistry, Woodhull Medical and Mental Health Center, 760 Broadway, Brooklyn, NY 11206, USA b Oral and Maxillofacial Surgery, Woodhull Medical and Mental Health Center, 760 Broadway, Room 2C-320, Brooklyn, NY 11206, USA c General Practice, Woodhull Medical and Mental Health Center, 760 Broadway, Room 2C-320, Brooklyn, NY 11206, USA * Corresponding author. Oral and Maxillofacial Surgery, Woodhull Medical and Mental Health Center, 760 Broadway, Room 2C-320, Brooklyn, NY 11206. E-mail address: [email protected] Oral Maxillofacial Surg Clin N Am 24 (2012) 155–166 doi:10.1016/j.coms.2012.01.011 1042-3699/12/$ – see front matter Ó 2012 Elsevier Inc. All rights reserved. oralmaxsurgery.theclinics.com The oral cavity and its bony components (maxilla and mandible), along with the nose and its related sinuses, constitute most of the face. Because of their proximity, disease in one may affect the other, whereas trauma of the midface will involve bones common to the oral cavity, nose, and paranasal sinuses. The two serve important lifesupporting functions, being the portals for nutrition and respiration. The nasal cavity receives air and conditions the air that is passed on to the other areas of the respiratory tract. The paranasal sinuses are pneumatic cavities lined by mucous membrane and communicate directly with the nasal cavity. The paranasal sinuses are the frontal sinus, ethmoid cells, maxillary sinus, and sphenoid sinus. This article presents a brief but relevant view of the surgical anatomy of the nasal cavity and paranasal sinuses that will be germane to the topics discussed in other articles elsewhere in this issue. 156 Ogle et al Fig. 1. Sagittal view of the nasal cartilages. subcutaneous tissue, and the thickness of the overlying skin. The external valve is a variable area dependent on the size, shape, and strength of the lower lateral cartilages. The medial crus is the downward continuation of the lateral crus from the apex. It extends inferiorly to the region of the area of the anterior nasal spine of the maxilla, passing anterior to the free end of the nasal septum. It is more slender than the lateral crus, and these are loosely joined to each other and to the inferior border of the septal cartilage with connective tissue. The medial crus and lateral crus form the nostril, which is the opening into the nasal cavity itself. The Nasal Cavity The upper lateral cartilage is fused to the dorsal septum in the midline, where the angle formed between them is normally 10 to 15 . The angle formed by the septum and upper lateral cartilage constitutes the internal valve. This angle between the septum and upper lateral cartilage is important during respiration, and obstruction of the angle by scar tissue or trauma will produce symptoms of nasal obstruction. The total composition of the internal nasal valve encompasses the area bounded by the angle of the upper lateral cartilage and septum, the nasal floor, and the superior portion of the inferior turbinate. Lower Lateral Nasal Cartilages Two lower lateral nasal cartilages, each having medial and lateral crus, form the shape of the nasal tip and maintain the patency of the nostrils. The upper border of the lateral crus is in contact with the upper lateral cartilage. Laterally, the extension is variable, but it is always connected to the maxilla with a thick fibrous membrane, with several lesser alar cartilages embedded in it. The lower border is free but does not reach the clinical border of the nose, which is formed by a double layer of skin. In the midline they are loosely connected to each other by the interdomal ligament. In this area, the structure is supported only by the septal cartilage, Fig. 2. Frontal view of nasal cartilages. The nasal cavity is divided by a vertical septum into two similarly paired cavities. Each half has a medial wall (the nasal septum) and a lateral wall that contains ridges called conchae or turbinates that participate in the drainage and ventilation of the paranasal sinuses. The roof of the nasal cavity consists of the crista galli, the cribriform plate, and the body of the sphenoid containing the sphenoid sinus. The cribriform plates contain nerves associated with the sense of smell passing through tiny openings in them. The bony floor is made up anteriorly of the palatine process of the maxilla and posteriorly by the horizontal process of the palatine bone. Nasal septum The nasal septum is a midline bony and cartilaginous structure that is composed of five parts (Fig. 3):      Perpendicular plate of ethmoid bone Vomer bone Crest of the maxillary bone Crest of the palatine bone Cartilage of the septum. The vertical or perpendicular ethmoid plate forms the upper half of the bony nasal septum and is continuous superiorly with the cribriform Surgical Anatomy Fig. 3. Sagittal view of nasal septum. plate. It is generally deflected a little to one or the other side. It articulates with the frontal and nasal bones anterosuperiorly, the crest of the sphenoid bone posteriorly, the vomer posteroinferiorly, and with the septal cartilage anteroinferiorly. At its superior aspect, numerous grooves and canals lead from the medial foramina on the cribriform plate and carry filaments of the olfactory nerves. The vomer is the posteroinferior portion of the septum. It articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones. It also articulates anteriorly with the septal cartilage of the nose. Separation of the cartilage from the vomer can occur in traumatic injuries. The palatine process of maxillary and nasal crest of the palatine bone are midline bony projections that contribute small portions to the septum. Both the inferior borders of the vomer and the septal cartilage articulate with these structures. With nasal trauma, a common finding is dislocation of the septal cartilage off the maxillary crest. The cartilage of the septum is somewhat quadrilateral in shape and provides dorsal support and helps to maintain the position of the columella and nasal tip. It is thicker at its margins than at its center. Its superoanterior margin is the thickest and is connected with the nasal bones, and is continuous with the medial margins of the upper lateral cartilages. Below, it is connected to the medial crura by fibrous tissue. Its posterior margin is connected with the perpendicular plate of the ethmoid, its posteroinferior margin with the vomer, and its base is along the palatine processes of the maxilla. The articulation of the septal cartilage inferiorly with the vomer and the maxilla may form horizontal “premaxillary wings,” which make elevation of the mucoperichondrium difficult.2 (These are sharp angulations seen in the nasal septum occurring at the junction of the vomer below, with the septal cartilage and/or ethmoid bone above.) The cartilage of the septum is firm but bendable and is covered by mucosa that has a substantial supply of blood vessels. This blood supply derives contribution from the anterior and posterior ethmoidal arteries, the sphenopalatine artery, the septal branch of the superior labial artery, and the greater and ascending palatine arteries. The vasculature of the septum runs between the perichondrium and the mucosa. Thus the subperichondrial space is the recommended avascular dissection plane when raising the mucoperichondrial flap during the first step in septoplasty. The anterior part of the septum, known as Little’s area, is richly endowed with blood vessels and is the source of most nose bleeds. Little’s area is an area of confluence of the labial, sphenopalatine, and ethmoidal arteries known as Kiesselbach’s plexus. The membranous septum (septum mobile nasi) is the narrow portion at the lower end of the nasal septum, lying between the semirigid columella and the more-rigid septal cartilage. It is the most flexible part of the septum and is formed by a union of the septum mucous membranes that envelop the septal cartilage. This united membrane then blends with the skin of the columella. This mucocutaneous junction is often the site of incisions for septal surgery. Lateral wall On examination of the nasal cavity, only a small section of the anatomy of the lateral nasal wall will be visible (Fig. 4). Its most prominent features are the turbinates, which project from the lateral wall. They are usually three or sometimes four in number. The superior turbinate is situated on the 157 158 Ogle et al Fig. 4. Lateral wall of nasal cavity with nasal conchae intact. upper part of the outer wall in the posterior onethird of the cavity, with its anterior and highest portion opposite the medial canthal tendon. The middle turbinate extends along the posterior twothirds and the inferior turbinate bone extends along the entire length of the nasal floor (about 60 mm). The turbinates are vertical and slightly curved. The medial surface, which is directed toward the septum, is convex and the lateral surface is concave. The inferior turbinate is the largest and is an independent bone, whereas the middle and superior turbinates and a variable supreme turbinate are parts of the ethmoid bone. The middle and superior turbinates are incompletely separated from each other by fissures that start at the posterior border of the conchal plate of the ethmoid bone and extends anteriorly to end slightly behind the anterior end of these turbinates. At the superior attachment of the middle turbinate, a prominence known as the agger nasi air cells may be seen. These agger nasi cells are the most anterior ethmoidal air cells, and the mound is formed by mucous membrane that is covering the ethmoidal crest of the maxilla. They lay below the lacrimal sac from which they are separated by only a very thin layer of bone. The passage in the nasal cavity formed by the projection of the turbinates are referred to as a nasal meatus, of which there are three. The inferior meatus is between the inferior turbinate, the floor of the nose, and the lateral nasal wall. It opens chiefly downward and backward so that more exhaled than inhaled air passes through it.3 The nasal opening of the nasolacrimal duct opens in the anterior third of the inferior meatus. This opening is covered by a mucosal valve known as Hasner’s valve. The course of the nasolacrimal duct from the lacrimal sac lie under the agger nasi cells. The middle meatus lies between the inferior turbinate inferiorly, middle turbinate superiorly, and the lateral nasal wall. The middle meatus has a significant anatomic relationship with the paranasal sinuses and is the most complex of the meatuses. It is the major drainage area for the paranasal sinuses, which are divided into an anterior group and a posterior group. The anterior group of sinuses are frontal, maxillary, and anterior ethmoidal sinuses. These anterior sinuses drain into a curved fissure along the lateral wall of the middle meatus called the hiatus semilunaris, which acts as a pool for all the secretions from the anterior group of sinuses. The features of the lateral wall of the meatus cannot be satisfactorily studied, however, unless the turbinates are removed (Fig. 5). The hiatus semilunaris will be seen after removal of the middle and inferior turbinates. The hiatus semilunaris is bordered inferiorly by the thin sharp edge of the uncinate process of the ethmoid and superiorly by an elevation known as the bulla ethmoidalis. The ethmoid bulla is the largest and most constant air cell of the anterior ethmoid complex. The middle ethmoidal cells are contained within this bulla, and their opening is slightly superior and posterior to the bulla. Below the bulla ethmoidalis and hidden by the uncinate process of the ethmoid is the ostium for the maxillary sinus, which opens posteriorly and is the largest ostium within the semilunar hiatus. Following the curvature of the hiatus semilunaris anterosuperior leads to a communication with another curved passage called the infundibulum. The infundibulum then communicates in front with the anterior ethmoidal cells, and in approximately 77% of the population it is continued upward into the frontal sinus as the frontonasal duct. In 23% of individuals, the anterior end of the uncinate process fuses with the Surgical Anatomy Fig. 5. Lateral wall of nasal cavity with nasal conchae removed. front part of the bulla and the continuity is interrupted. In these people, the frontonasal duct drains directly into the anterior end of the meatus via a frontal sinus ostium.4 The uncinate process is a concaved wingshaped projection of the ethmoid and forms the first lamella of the middle meatus. It attaches anteriorly to the posterior edge of the lacrimal bone and inferiorly to the superior edge of the inferior turbinate. The superior attachment is highly variable, because it may be attached to the lamina papyracea, the roof of the ethmoidal sinus, or to the middle turbinate. The configuration of the infundibulum and its relationship to the frontal recess depends largely on the superior attachment of the uncinate process. The basal lamella of the middle turbinate separates the anterior and posterior ethmoid cells. The basal lamella as an important anatomic landmark to the posterior ethmoidal system, which has separate drainage systems from the anterior system. When disease is limited to the anterior compartment of the osteomeatal complex, the ethmoid cells can be opened and diseased tissue removed as far as the basal lamella. Leaving the basal lamella undisturbed will minimize the surgical risks. Blood supply to the lateral nasal wall is from the sphenopalatine artery. The sphenopalatine artery is a branch of the maxillary artery that passes into the nasal cavity through the sphenopalatine foramen at the back part of the superior meatus. Here it gives off its posterior lateral nasal branches. It ends on the nasal septum as the posterior septal branches. In 72% of people, the feeding vessel to the superior turbinate is from the septal artery. The feeding vessel to the middle turbinate is from the proximal portion of the posterior lateral nasal artery just after exiting the sphenopalatine foramen in 88% of people. In most people (98%), the inferior turbinate branch is the end artery of the posterior lateral nasal artery.5 The pattern of blood supply to the inferior turbinate is pretty consistent, with a single branch of the sphenopalatine artery entering its substance from above at the superior aspect of its lateral attachment at 1 to 1.5 cm from its posterior border. This large vessel crosses the middle meatus posteriorly and will be at risk of injury if surgery proceeds too far posteriorly. As the artery travels anteriorly within the turbinate, it remains close to the bone or travels most often within a bony canal. On its forward path it gives off several branches, forming an arterial arcade, which also remains close to or within the bone. Trimming of any part of the turbinate bone may be followed by brisk and prolonged bleeding. The artery travels mostly within a bony canal and will be splinted open by fibrous attachments to the bone, making it unable to contract. Because the artery at the posterior tip of the inferior turbinate is not in a bony canal, it provides a location to ligate the artery in the presence of persistent bleeding from the inferior turbinate. The diameter of the artery widens as it passes anteriorly, which may be from anastomosis with the facial artery via the pyriform aperture or with other intranasal vessels.6 ETHMOIDAL SINUS Ethmoid Air Cell Development The ethmoid sinus begins forming in the third to fourth month of fetal life as evaginations of the lateral nasal wall. At birth the anterior ethmoid cells are aerated, whereas the posterior ethmoid cells are fluid-filled. The posterior ethmoid air cells 159 160 Ogle et al pneumatize with advancing age, and air replaces the fluid in these cells. The last air cells to finish forming are the anterior-most agger nasi and bulla cells. When pneumatization is complete, the average size of the anterior ethmoid cells are 20 to 24 mm  20 to 24 mm  10 to 12 mm and the average size of the posterior ethmoid cells are 20 to 21 mm  20 to 22 mm  10 to 12 mm.7 Ethmoid Bone The ethmoid bone consists of five distinct components: cristae galli, cribriform plate, perpendicular plate, and paired ethmoidal labyrinths that contain the ethmoid air cells. The cristae galli marks the superior extent of the ethmoid bone as it rises into the anterior cranial fossa to provide attachment for the falx cerebri. The cristae galli ends inferiorly at the cribriform plate. The ethmoid bone continues inferior to the cribriform plate as the perpendicular plate of the ethmoid. The bilateral ethmoidal labyrinths come off the perpendicular plate at the level just inferior to the cribriform plate. The paired labyrinths continue inferiorly and terminate as the middle nasal concha. The perpendicular plate continues inferiorly, between the labyrinths, where it terminates at its articulations with the nasal septum anteriorly and the vomer posteriorly. The cristae galli is a vertically oriented, triangular-shaped, superior-most extension of the ethmoid bone. The cristae galli provides attachment for the falx cerebri, which is the dural partition of the cerebral hemispheres at the level of the longitudinal fissure of the brain. The cristae galli ends inferiorly at the cribriform plate. The cribriform plate is a thin horizontally oriented plate of bone that supports the olfactory bulb on its superior aspect. Vertical perforations throughout the cribriform plate allow for passage of olfactory Fig. 6. Frontal view of ethmoid bone. nerve terminals to reach the nose. The cribriform plate is 2 mm thick  20 mm long  5 mm wide.8 Facial trauma may fracture this thin cribriform plate, resulting in a cerebrospinal fluid rhinorrhea. Anosmia can also result from traumatic damage to olfactory nerve terminals. The optic nerve also may potentially be damaged with overzealous exenteration of the posterior ethmoidal air cells. The ethmoid continues inferior to the cribriform plate as the perpendicular plate. The perpendicular plate forms the superior portion of the nasal septum and gives off the ethmoid labyrinths bilaterally. The perpendicular plate articulates with the frontal bone anterosuperiorly, the nasal septal cartilage anteroinferiorly, and the vomer posteroinferiorly. The ethmoid labyrinths project from the perpendicular plate at a point just inferior to the cribriform plate. Following their horizontal projection from the perpendicular plate, the labyrinths rise superiorly to a point one-eighth of an inch superolaterally to the cribriform plate.9 The labyrinths are quadrangular-shaped structures situated between the orbit and olfactory portion of the nasal fossa. The labyrinths are formed by the laminae papyracea externally and the superior and middle turbinates internally; they are bordered anteriorly by the lacrimal and frontal bones and posteriorly by the body of the sphenoid.10 The lamina papyracea forms part of the medial wall of the orbit and lateral nasal wall (Fig. 6). Ethmoid Air Cells Within the labyrinth lie the ethmoid air cells, which are lined by pseudostratified ciliated columnar epithelium. The ethmoid air cells are bordered medially by the nasal cavity, laterally by the lamina papyracea, and superiorly by the fovea ethmoidalis. The basal lamina of the middle turbinate divides Surgical Anatomy the ethmoid cells into anterior and posterior divisions.11 The anterior cells empty into the middle meatus and the posterior cells drain into the superior meatus. Hajek12 presented a simplified scheme to describe the location of the ethmoid air cells. Hajek’s scheme depicted the air cells as existing in three sets of grooves, which form as valleys between four lamellar projections of bone. Anteriorly the unciform groove (hiatus semilunaris) is formed by the unciform process anteriorly and the ethmoid bulla posteriorly; the hiatus semilunaris is the site of orifices to the frontal sinus, maxillary sinus, and anterior ethmoidal cells. The second groove is the middle meatus, which lies between the ethmoid bulla anteriorly and the middle turbinate posteriorly; the ethmoid bulla located in this lamella is often involved in nasofrontal duct obstruction. The third groove is the superior meatus that is formed between the middle and superior turbinates (Fig. 7).13 The numbers of ethmoid cells vary by individual; however, seven smaller anterior cells and four larger posterior cells are typically present. The posterior air cells occasionally present as two very large air cells. The previous paragraph discussed the grooves in which the air cells are present. The uncinate groove is the most anterior and has three to four air cells at its superior border. At the middle meatus are one to two agger nasi cells, and posterior to the agger nasi is the ethmoid bulla that contains a superior and inferior cell.9 The posterior ethmoid air cells drain via the superior meatus. The anterior ethmoid air cells drain via the middle meatus. enters the anterior ethmoid foramen 24 mm posterior to the anterior lacrimal crest and supplies the anterior ethmoid air cells. The posterior ethmoidal artery enters the posterior ethmoid foramen 36 mm posterior to the anterior lacrimal crest14 and supplies the posterior ethmoidal air cells. Venous drainage is via the named veins accompanying the arteries to the superior ophthalmic vein or pterygopalatine plexus. Lymphatic drainage from the anterior ethmoid cells is via the submandibular nodes, and the posterior ethmoid cells drain via the retropharyngeal nodes. Innervation is via anterior and posterior ethmoid nerves of the ophthalmic nerve (V1) and the posterior nasal branch of the maxillary nerve (V2) (Fig. 8).7 Blood Supply and Innervation Size and Location Blood supply to the ethmoid air cells is via the ethmoidal arteries that are branches from the ophthalmic artery. The anterior ethmoidal artery The maxillary sinuses are paired paranasal sinuses that develop around the adult dentition to a volume of 15 mL, although the volume is smaller in MAXILLARY SINUS Development The maxillary sinus begins developing in the third week of gestation. In the twelfth week of gestation, the maxillary sinus forms as an ectodermal invagination from the middle meatal groove and grows internally to a size that at birth is approximately 7  4  4 mm and has a volume of 6 to 8 mL. In utero the maxillary sinus is fluid-filled; however, after birth the maxillary sinus pneumatizes in concordance with biphasic rapid growth: during the first 3 years of life and then again from ages 7 to 12 years. By 12 years of age, the sinus is level with the floor of the nasal cavity15; however, as further pneumatization occurs into adulthood, with the eruption of the adult molars, the floor of the sinus descends to approximately 1 cm below the floor of the nasal cavity.16 Fig. 7. Diagrammatic representation of ethmoid air cell anatomy. 161 162 Ogle et al Fig. 8. Sagittal view of ethmoid air cells. children and enlarges with sinus pneumatization that occurs with advancing age. The span of these sinuses is from the region of the third molar posteriorly to the premolar teeth anteriorly. The dimensions of the sinus vary and range from 25 to 35 mm mesiodistal width, 36 to 45 mm vertical height, and 38 to 45 mm deep anteroposteriorly.17 Mesiodistal width differences are usually attributed to growth toward the zygomatic arch posteriorly rather than toward the canine teeth anteriorly. The maxillary sinus is shaped like a quadrangular pyramid, with the base facing the lateral nasal wall and the apex oriented at the zygomatic arch. The roof of the sinus contributes to the floor of the orbit, the floor faces the alveolar process, and the sinus proceeds deep and adjacent to the palate. The Schneiderian membrane lines the maxillary sinus and is composed of pseudostratified ciliated columnar epithelium. The concentration of cilia increases with proximity to the sinus ostium. The thickness of this membrane is 0.8 mm. Compared with the nasal mucosa, the antral mucosa is thinner and less vascular.18 Pneumatization of the Sinus with Age At birth, the maxillary sinus begins medial to the orbit and its dimensions are largest anteroposteriorly. At 2 years of age, the sinus continues inferiorly below the medial orbit and continues to pneumatize laterally. By 4 years of age, the sinus reaches the infraorbital canal and continues laterally. By 9 years of age, inferior growth reaches the region of the hard palate. Pneumatization continues as the permanent teeth erupt.19 VITAL STRUCTURES The roof of the maxillary sinus contributes to the floor of the orbit. The roof contains the infraorbital neurovascular bundle. The infraorbital foramen opens approximately 1 cm below the infraorbital rim.20 The floor of the maxillary sinus abuts the alveolar process of the maxilla, frequently approximating the apices of the molar teeth, as is discussed in the next section. The inferior extent of the sinus floor is 1 cm inferior to the floor of the nasal cavity. The medial wall of the maxillary sinus houses the sinus ostium (os) at its superomedial aspect and the nasolacrimal duct, through which drainage of the lacrimal apparatus occurs. The maxillary os empties into the posterior aspect of the semilunar hiatus. The nasolacrimal duct runs 4 to 9 mm anterior to the os and empties at the anterior portion of the inferior meatus.17 Anatomic Relationship of Maxillary Sinus with Teeth Sinus development follows a three-compartment model described by Underwood21 in which these compartments, frequently separated by septae, are associated with three different dental milestones. The anterior compartment forms around the primary molars between 8 months and 2 years of age. The middle compartment forms around the adult first and second molars from 5 to 12 years of age. The posterior compartment forms around the third molars from 16 to 30 years of age.21,22 The most inferior portion of the maxillary sinus is in the region of the first molar.18 The distance from the sinus floor to the root tips of the teeth is longest for the first premolar and shortest for the second molar distobuccal root tip.23 The roots of the maxillary first and second molars communicate with the floor of the maxillary sinus with an incidence of 40%.24 The palatine roots of these teeth are 50% closer to the antral floor than to the palate, and in 20% of cases apical communication Surgical Anatomy is present between the palatal roots of the maxillary first and second molars with the maxillary sinus (Fig. 9, Table 1).25 Clinical Significance of Septa A septum is defined as a strut of bone that is at least 2.5 mm in height. Septae within the maxillary sinus are of two varieties. The first, discussed in the last section, are formed as part of the threecompartment model of sinus development and act as dividers of the anterior, middle, and posterior components. These septae are referred to as primary septae and are found between the roots of the second premolar and the first molar and the roots of the first and second molars, and distal to the roots of the third molar. Septae extrinsic to those of maxillary development are called secondary septae and occur as a result of pneumatization after dental extraction. The overall prevalence of septae present in any given maxillary sinus is 35%.21 Septae in edentulous regions tend to be larger than those in partially edentulous regions that are larger still than dentate regions of the alveolus. The presence of septae is pertinent for sinus lift procedures, because they complicate the process of luxating the boney window to expose the sinus and increase the likelihood of sinus membrane perforation. Ostium of Maxillary Sinus The size and numbers of maxillary sinus ostia are variable. Simon26 found that the sinus ostium existed as a canal greater than 3 mm in mesiodistal width from the infundibulum to the antral opening in 82.7% of individuals, in contrast to the 13.7% in whom the ostium existed as just an opening. The average length of the sinus ostium is 5.55 mm and is oriented inferolaterally from the infundibulum to the antrum to drain the maxillary sinus into the hiatus semilunaris. Approximately 16% of individuals have an accessory ostium (ie, an ostium Fig. 9. Sagittal view of maxillary sinus anatomy. opening outside the infundibulum and semilunar hiatus). The accessory ostium typically exists only as an opening and not a canal, with an average length of 1.5 mm. The clinical significance of the ostium existing as a canal is an appreciation for how readily a canal obstruction can occur (Fig. 10). The Superior Alveolar Nerves Harrison8 presented the anatomic location of the superior alveolar nerves described in this section. The superior alveolar nerves are in close apposition to the maxillary sinus and are therefore discussed. The anterior superior alveolar nerve (ASA) arises 15 mm behind the infraorbital foramen and runs inferiorly in the anterior wall of the maxilla. Occasionally the ASA forms an elevation at the anterior part of the sinus cavity approximately 6 mm inferior to the infraorbital foramen on its way to supply the lateral nasal wall and septum, and the anterior maxillary teeth. The middle superior alveolar nerve (MSA) often arises off the infraorbital nerve and courses along the posterolateral or anterior wall of the sinus to supply the premolar teeth. The posterior superior alveolar nerve (PSA) is a branch of the infraorbital nerve given off at the posterior end of the infraorbital canal. Two branches of this nerve are usually present: a smaller superior branch and the larger inferior branch. The superior branch of the PSA passes through the antrum and runs posteriorly along the maxillary tuberosity. The inferior branch supplies the molar teeth and joins the MSA and ASA to form the alveolar plexus. The significance of this presentation of the superior alveolar nerves is to present a safe area at the anterior region of the maxilla where bone can be safely removed (eg, Caldwell-Luc procedure), with minimal risk of damage to the superior alveolar nerves. Blood Supply and Innervation The maxillary sinus possesses rich anastomoses and receives its arterial supply from the infraorbital, 163 164 Ogle et al Table 1 Distance from the roots of maxillary teeth to maxillary sinus floor Root Distance (mm) SD Buccal first premolar Lingual first premolar Second premolar Mesiobuccal first molar Palatal first molar Distobuccal first molar Mesiobuccal second molar Palatal second molar Distobuccal second molar 6.18 7.05 2.86 2.82 1.56 2.79 0.83 2.04 1.97 1.60 1.92 0.60 0.59 0.77 1.13 0.49 1.19 1.21 Data from Eberhardt JA, Torabinejad M, Christiansen EL. A computed tomographic study of the distances between the maxillary sinus floor and the apices of the maxillary posterior teeth. Oral Surg Oral Med Oral Pathol 1992;73(3): 345–6. sphenopalatine, posterior lateral nasal, facial, pterygopalatine, greater palatine, and posterior superior alveolar arteries. Venous return from the maxillary sinus occurs anteriorly via the cavernous plexus that drains into the facial vein and posteriorly via the pterygoid plexus and to the internal jugular vein. Innervation of the maxillary sinus is via the anterior superior, middle superior, and posterior superior alveolar nerves. Lymphatic drainage occurs through the infraorbital foramen via the ostium to the submandibular lymphatic system.16 FRONTAL SINUS The frontal sinuses are the most superior of the anterior sinuses. They are situated in the frontal bone between inner and outer plates. The inner plate, or posterior wall (separates the frontal sinus Fig. 10. Coronal view of osteomeatal complex. from the anterior cranial fossa), is much thinner than the outer wall and may be penetrated accidentally during surgery.2 The septum between right and left is almost always asymmetrically placed and divides the frontal sinuses into two unequal sinuses. The larger sinus may pass across the midline and overlap the other. The sinuses often have incompletely separated recesses, which make the anatomy highly variable. Superficial surgical landmarks for the frontal sinus was described by Tubbs and colleagues27 from adult cadaveric frontal sinus dissections. In their study of 70 adult cadavers, these investigators reported that the lateral wall of the frontal sinus never extended more than 5 mm lateral to a midpupillary line. At this same line and at a plane drawn through the supraorbital ridges, the roof of the frontal sinus was never higher than 12 mm, and in the midline, the roof of the frontal sinus never reached more than 4 cm above the nasion. The frontal sinus is separated from the orbit by a thin triangular plate. Regarding the lateral extension of the frontal sinuses, the authors have observed several cases in which the lateral extension of the frontal sinuses extended more lateral than described by Tubbs and colleagues.27 Further, Maves28 states that the degree of pneumatization of the frontal sinuses varies and that it may extend laterally as far as the sphenoid wing. The ostium of the frontal sinus lies in the posteromedial aspect of the sinus floor. The frontonasal duct opens into the anterior part of the middle meatus and the frontal recess, or directly into the anterior end of the infundibulum (Fig. 11). This relationship to the infundibulum and middle meatus serves to protect the frontal sinus from the spread of disease in the osteomeatal complex. The agger nasi is intimately involved, in that the posterior wall of the agger nasi forms the anterior border of the frontal recess, which Surgical Anatomy Fig. 11. Frontonasal duct in situ (arrow). then passes posteromedially to the agger nasi and supraorbital cells. This recess is present in 77% of patients. In the other 23%, drainage occurs via a frontal sinus ostium.4 There are also two patterns to the frontal sinus outflow tract: those that drain medial to the uncinate process and those that drain lateral to the uncinate process. Those that drain medially are more common and are significantly related to the presence of frontal sinusitis. The borders of the frontonasal duct are the 1) anterior border, which is the superior portion of the uncinate process; 2) posterior border, which is the superior portion of the bulla ethmoidalis; 3) medial border, which is formed by the conchal plate; and 4) lateral border, which is the suprainfundibular plate.29 The nasofrontal duct can safely be widened through removing the upper portion of the ground lamella of the ethmoid bulla at the posterior boundary of the nasofrontal duct with cutting forceps.29 Blood Supply The supraorbital and supratrochlear arteries, which branch off the ophthalmic artery, form the arterial supply of the frontal sinus. The superior ophthalmic vein provides venous drainage. Actual venous drainage for the inner table, however, is through the dura mater and the cranial periosteum for the outer table. 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