Functional Endoscopic Sinus Surgery: Anatomy, CT Screening, Indications, and Complications

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1 735 Review Functional Endoscopic Sinus Surgery: Anatomy, CT Screening, Indications, and Complications Mahmood F. Mafee,1 James M. Chow,2 and Robert Meyers3 The effectiveness of standard surgical techniques for inflammatory diseases of nasal and paranasal sinuses has been well established for more than a century. With the recent popularization of endoscopic sinus surgery, however, many of these techniques are now considered radical [1]. The classic transbuccal maxillorhinostomy, described first in by George CaIdwell [2] and then in 1897 by Henry Luc of Paris (Caldwell-Luc operation), was one of the most common techniques for the relief of maxillary sinusitis [1]. This operation is now rarely used for chronic hyperplastic rhinosinusitis. It is used mainly for the removal of tumors of the maxillary sinus and for patients in whom intranasal antrostomy or endoscopic decompression of the ostiomeatal complex is not effective [1]. Likewise, in many instances, for patients with chronic hyperplastic rhinosinusitis, procedures such as transantral ethmoidectomy, external ethmoidectomy, external frontoethmoidectomy, and standard intranasal sphenoethmoidectomy have been replaced by endoscopic sinus surgery. The proponents of endoscopic sinus surgery advocate conservative approaches for chronic hyperplastic nasal and paranasal diseases. They argue that limited procedures aimed at mechanical clearance of the ostiomeatal complex might be effective in controlling chronic sinonasal diseases [3]. The anterior ethmoidal air cells and the middle meatal area play important roles as sites of early involvement in most inflammatory sinus diseases, other than those infections arising from a dental origin [3]. Messerklinger [4-6] showed that in most cases, infection spreads from the anterior ethmoidal area and middle meatal region to secondarily affect the maxillary and frontal sinuses. It has been shown Article that severe mucosal disease in frontal and maxillary sinuses usually resolves when normal ventilation and mucociliary clearance of the middle meatus is restored and ethmoidal disease is eradicated [3]. According to Kennedy et al. [3], the term ostiomeatal unit was coined by H. Naumann, who used it to refer to the complex anatomic structures formed by the anterior ethmoidal area and the middle meatus. Some authors [3] refer to the ethmoidal infundibulum, frontal recess, anterior ethmoidal air cells and their ostia, and maxillary sinus ostium as the ostiomeatal complex. The concept of endoscopic sinus surgery [3] evolved from the work of Hilding [7, 8], Proctor [9, 10], and Messerklinger [4-6] on mucociliary clearance and air flow in the paranasal sinuses and on the importance of establishing drainage and preserving mucosae of the sinuses. Endoscopic sinus surgery is based on the hypothesis that the ostiomeatal complex is the key area in the pathogenesis of chronic sinus diseases [3-6, 11-17]. Minor pathologic changes in the nasal mucosa in the vicinity of the ostiomeatal complex may interfere with mucociliary clearance or with the ventilation of the maxillary, ethmoidal, and frontal sinuses. Because of the increased awareness of the role of these pathologic changes in the ostiomeatal complex and because of the knowledge that endoscopic surgical procedures could be used to correct the underlying problem in this region, with the resultant resolution of secondary mucosal diseases in the frontal, maxillary, and ethmoid sinuses, Kennedy et al. [3] termed this approach functional endoscopic sinus surgery. The underlying principle of functional endoscopic sinus surgery is that the sinus mucosa will return to normal if adequate drainage Received July 16, 1992; accepted after revision November 17, Presented at the annual meeting of the American Roentgen Ray Society, Orlando, FL, May Department of Radiology, University of Illinois at Chicago, P.O. Box 6998, M/C 711, Chicago, IL Address correspondence to M. F. Mafee. 2Department of Otolaryngology, Head and Neck Surgery, Loyola University School of Medicine, Maywood, IL Department of Otolaryngology, Head and Neck Surgery, University of Illinois at Chicago, Chicago, IL AJR 1993;160: X/93/ American Roentgen Ray Society

2 736 MAFEE ET AL. AJR:160, April 1993 can be established by removing the mucosal disease in the ostiomeatal region [3, 13]. No attempt is made to remove (by curettage) the sinus mucosa; rather, it is allowed to return to normal and to resume its normal function [3, 13]. The safe performance of functional endoscopic sinus surgery requires a clear understanding of the anatomic relationships of the paranasal sinuses to the surrounding structures. This review discusses the concepts of functional endoscopic sinus surgery, the anatomy of the ostiomeatal complex, CT scanning of the nasal cavity and paranasal sinuses before endoscopic sinus surgery, and the potential complications associated with this relatively new surgical technique. Mucociliary System and Physiologic Basis of Sinonasal Operations The paranasal sinuses, like other parts of the upper respiratory system, are lined with a pseudostratified, columnar, ciliated epithelium interspersed with goblet cells. Under the epithelium is a tunica propria containing mucous and serous glands that open onto the epithelial surface via branched ducts [13, 14, 18, 19]. The secretions of these glands form surface films of mucus and fluid (mucus blanket) that cover the epithelium. The abundant amount of mucus secreted by the glands and goblet cells makes the surface of the mucosa moist and sticky [18]. Dust in the inspired air is deposited on the surface of the mucosa, and the air is humidified. The contaminated film of mucus covering the epithelial membrane is moved by mucosal ciliary action toward the nasal cavity and then into the pharynx [3, 13, 14, 18, 19]. Cilia of the upper respiratory mucosa beat with a wavelike, synchronous rhythm that continuously propels the surface coat of mucus, containing entrapped particles, toward the pharynx [20]. In the paranasal sinuses and nasal cavity, the ciliated epithelium and the mucus blanket form the so-called mucociliary system, which protects the sinuses and nasal cavity [13, 16, 19]. It is important to realize that the mucus blanket is moved by the cilia toward the natural ostium of the individual sinus. This occurs regardless of any other openings that may or may not be present in the sinus [14]. In the maxillary sinus, mucociliary movement originates from the floor and radiates along the walls of the sinus to propel the mucus blanket toward the ostium [1 6], which is located in the posterosuperior part of the medial wall of the sinus. This mucociliary system captures 80% of inspired particles larger than 3-5 fim and 60% of those larger than 2 tm and exposes them to mast cells, polymorphonuclear leukocytes, eosinophils, lysozyme, immunoglobulin G, and interferon while sweeping them into the pharynx to be swallowed [1 3, 19]. latrogenic creation of an ostium in another location is not effective for sinus drainage, as the ciliacontinue to move the mucus blanket toward the natural ostium [14, 16]. Chronic or chronically recurrent sinusitis therefore implies a breakdown in the function of the mucociliary system [14, 16, 21]. Most frequently, this breakdown involves the anterior ethmoidal sinuses because they are ideally located for chronic obstruction. The majority of inspired particles are deposited on the anterior ends of the middle and inferior turbinates and in the anterior middle meatus, where their effect will be greatest on the drainage of the anterior ethmoidal cells. Three key elements are important to the normal physiologic function of the paranasal sinuses: the patency of the ostia, the function of the ciliary apparatus, and the quality of secretions [21 ]. Retention of secretions in the paranasal sinuses may be due to obstruction of the ostia, impairment of ciliary function, or overproduction or a change in the viscosity of secretions [21]. Knowledge of the pathophysiologic mechanisms that cause the chronic changes in the ostiomeatal region is still incomplete. Etiologic factors include a variety of exogenous factors such as aeroallergens, microorganisms (fungi, viruses, bacteria), and toxic inhalants and endogenous factors such as immunologic disorders [11]. Proctor [9], and later Messerklinger [6], introduced the principie that chronic or recurrent bacterial sinusitis is most commonly caused by unappreciated, untreated disease of the anterior ethmoidal sinus. Familiarity with the anatomy of the nasal cavity and paranasal sinuses, particularly the ethmoidal sinuses and the lateral nasal wall, is critical for successful functional endoscopic sinus surgery, as well as for appropriate interpretation of the imaging studies of the paranasal sinuses. In endoscopic sinus surgery, the most important landmarks are the agger nasi cells, frontal recess, middle turbinate, middle meatus, uncinate process of the ethmoid bone, ethmoidal infundibulum, semilunar hiatus, ethmoidal bulla, lateral sinus, natural ostium of the maxillary sinus, basal lamella, superior meatus, and sphenoethmoidal recess (Figs. 1-7). Anatomy Ethmoid Bone The ethmoid bone is a delicate and complex structure. It articulates with 13 other bones: the frontal, sphenoid, nasal, lacrimal, and palatine bones; the maxilla; the infenor nasal conchae; and the vomer [1 8, 22]. The ethmoid bone consists of four parts: a horizontal lamina, called the cribriform plate; a perpendicular plate; and two lateral masses, called the labyrinths. Each ethmoidal labyrinth consists of thin-walled, highly variable air cells, arranged in three groups: anterior, middle, and posterior clusters (Figs. 2 and 5-8). The anterior and middle groups are referred to by some anatomists and most otolaryngologists as anterior ethmoidal air cells [19]. These ethmoidal air cells are open only at their apertures or ostia of communication with the nasal cavity. (The ostia of these ethmoidal air cells cannot be definitively shown on CT images.) Some air cells are not entirely enclosed by the ethmoid bone (extramural cells); instead, the ethmoid bone may be perforated so that the mucosa of the air cell extends upward against the ethmoid notch of the frontal bone (Fig. SB), anteriorly against the lacrimal and maxillary (frontal process) bones (Figs. 2 and 6), and posteriorly against the sphenoid and palatine bones. The orbital plate of the ethmoid bone (lamina papyracea) covers the middle and postenor ethmoidal air cells (Figs. 7 and 8). The most anterior intramural ethmoidal air cells are the frontal recess cells, which extend toward the frontal bone anterosuperiorly (Figs. 3 and SB). The frontal sinus arises from these cells, as do the supraorbital frontoethmoidal air cells [13]. The

3 Fig. 1.-Anatomy of lateral nasal wall. A, Photograph shows dry skull with middle concha removed. Note anteroinferior (black arrows) and posterosuperior (white arrows) borders of uncinate process of ethmoid bone, and ethmoidal bulla (arrowheads). Passage (broken line) between posterosuperior border of uncinate process and anteroinferior border of ethmoidal bulla is semilunar hiatus, which courses around outer inferior anteroposterior border of bulla to reach middle meatus. Expected region of natural ostium of maxillary sinus is in midportion of maxillary hiatus (MH). Anterior and posterior to ostium are anterior and posterior fontanelles. B, Photograph shows cadaveric head with middle turbinate partially removed. Semilunar hiatus (white arrows) is a cleft bounded inferiorly by a sharp concave ridge produced by superior margin (black arrows) of uncinate process and inferior border (arrowheads) of ethmoidal bulla (BE). Semilunar hiatus is actually most medial portion of infundibulum, connecting infundibulum with middle meatus. Note accessory ostium (AO) of maxillary sinus. Natural ostium of maxillary sinus Is hidden by uncinate process. A = anterior. Fig. 2.-Ostiomeatal complex in cadaveric head. A, Midline sagittal CT scan of cadaveric head shows agger nasi cell (A), ethmoidal bulla (B), posterior ethmoidal cell (P), and sphenoidal sinus (5) with its ostium opening (short solid curved arrow) into sphenoethmoidal recess. Note middle turbinate (open, straight arrows), middle meatus (large solidcurvedarrow), and uncinate process (arrowhead) of ethmoid bone. Infundibulum (broken line) is a curved passage below bulla and above uncinate process. Note frontonasal duct or frontal recess (long straight arrow) opening into anterosuperior part of infundibulum. Cell anterior to bulla (open curved arrow) belongs to frontal recess air-cell group of anterior intramural ethmoidal air cells. As seen, these cells drain into ethmoidal infundibulum. Aggar nasi cells belong to infundibular air-cell group of anterior ethmoidal air cells. These cells also drain into Infundibulum. B, Sagittal CT scan through ostiomeatal complex shows agger nasi cell (A), ethmoidal bulla (B), posterior ethmoidal cell (P), lateral sinus (SL), and sphenoidal sinus (5). Basal lamella (arrowheads) is seen between ethmoidal bulla and lateral sinus and posterior ethmoidal air cells. Note frontal recess (long straight arrow), uncinate process (open curved arrow), middle turbinate (open arrow), and partially volumed inferior turbinate (short straight arrow). Note opening of agger nasi (short solid curved arrow) into ethmoidal infundibulum and close relationship of posterior ethmoidal air cell with optic canal (long solid curved arrow). Ant = anterior. (Reprinted with permission from Chow and Mafee [22a].) next most anterior group is the infundibular cells. From these arise the most anterior extramural cells, the agger nasi cells (Figs. 2 and 6), which pneumatize the lacrimal bone and frontal process of the maxilla [13, 23]. The posterior ethmoidal cells occupy the posterior ethmoid bone but also the posterior middle turbinate and may invade the sphenoid, palatine, and maxillary bones [13]. Pneumatization of the anterior middle turbinate results in concha bullosa [13] (Fig. 8). The optic nerve may be surrounded by posterior ethmoidal air cells (Fig. 2B). Lateral Nasal Wall The medial surface of the labyrinth forms a part of the lateral wall of the corresponding half of the nasal cavity (Figs. 1-3, SB, and SC). Within the nasal cavity, scrolls of bone on the lateral walls, the conchae, project medially to divide the passageway into meatus, or channels for air [18, 22] (Figs. SB and SC). The superior and middle conchae are parts of the ethmoid bone, but the inferior nasal conchae (a turbinate is a concha and its soft-tissue complex) are a separate pair of bones. The

4 738 MAFEE ET AL. AJR:160, April 1993 Fig. 3.-Ostiomeatal complex in cadaveric head. A, Sagittal CT scan shows most anterior intramural ethmoidal air cell (1), also called frontal recess air cell, which extends toward frontal bone anterosuperiorly. Frontal sinuses arise from these cells and drain via frontonasal duct (arrowhead). Note infundibular air cell (2). Bullar cell (B) is behind frontal recess air cell. Note well-developed uncinate process (long straight arrows) and ostium of sphenoidal sinus (curved arrow) opening into sphenoethmoidal recess (short straight arrow). B, Sagittal CT scan shows uncinate process (arrow), frontal recess air cell (1), infundibular air cell (2), and ethmoidai bulia (BE). Note infundibulum (broken line). Variation in ethmoidal air cells is the rule rather than the exception. Compare Figs. 2 and 3 for development of agger nasi cells, infundibular and frontal recess air cells, and size of uncinate process. A = anterior. Fig. 4.-Sagittal CT scan of cadaveric head after endoscopic surgery on anterior ethmoidal sinus. Compare this image with that of intact ostiomeatal complex and anterior ethmoidal sinus air cells in Figs. 2 and 3. Uncinate process, frontal recess air cell, infundibular air cell, ethmoidal bulla, and anterior portion of middle turbinate have been removed. Basal lamella (arrow) and posterior ethmoidai (P) and sphenoidal sinuses remain intact. A = anterior. Fig. 5.-A, Midsagittal CT scan shows levels of coronal sections, (lines A and B) seen in B and C, respectively. B, Photograph of coronal section through ostiomeatal complex of cadaveric head. Note inferior turbinate (IT), middle turbinate (Ml), infundibular cells (1), frontal recess air cells (2), and frontal recess (3). Frontal sinuses arise from frontal recess ethmoidal air cells and agger nasi cells arise from infundibular ethmoidal air cells. C, Note inferior turbinate (IT), middle turbinate (MD, uncinate process (U), and ethmoidal bulla (BE). Note attachment (arrowhead) of uncinate process to ethmoidal process of inferior concha. Infundibulum (short straight arrows) is passage area between uncinate process and inferior border of bulla. Curved arrow indicates communication of middle meatus (broken line) with infundibulum through semilunar hiatus. As seen, hiatus (curved arrow) is a passage between inferior aspect of bulla and superomedial aspect of uncinate process. Long straight arrows indicate ethmoidal fovea (roof of ethmoid bone). Note attachment of middle turbinate to junction of ethmoidal fovea and cribriform plate. superior, middle, and inferior meatus (air channels), which are respectively (Figs. 2A and 3A). The middle meatus connects formed under the respective conchae (Fig. SC), have via various ostia with the anterior and middle ethmoidal air increased contact with the nasal surfaces to permit more effective warming and moistening of inspired air [18, 19, 22]. cells and with the frontal and maxillary sinuses. The ostium of the sphenoidal sinus is located at the Frontal Recess anterosuperior portion of the sinus (Figs. 2A and 3A). The sphenoidal ostium and the posterior ethmoidal air cells drain into the sphenoethmoidal recess (cleft) and superior meatus, The frontal sinuses communicate with the middle meatus of the corresponding half of the nasal cavity by means of a

5 AJR:160, April 1993 FUNCTIONAL ENDOSCOPIC SINUS SURGERY 739 Fig. 6.-A, Coronal CT scan through anterior ethmoid bone of cadaveric head shows well-developed agger nasi cell (A). B, Coronal CT scan through nasolacrimal duct (curved arrow) shows agger nasi cell (A) and frontal sinuses (F). Nasolacrimal duct drains into inferior meatus (straight arrow). Fig. 7.-Coronal CT scan through ostiomeatal complex of cadaveric head shows uncinate process (arrowheads), ethmoidal bulla (BE), and suprabullar air cell. Infundibulum (broken line) is curved air space below bulla and above uncinate process. Area (opening) between superomedial border of uncinate process and bulla is semilunar hiatus (straight arrow), which connects infundibulum with middle meatus. Also note infraorbital ethmoidal air cell, so-called Hailer cell (H). Note uncinectomy, infundibulotomy, and anterior ethmoidectomy changes resulting from endoscopic surgery performed on opposite side of this cadaveric head. Lamina papyracea (long curved arrow) is intact. Fig. 8.-Coronal CT scan posterior to midportion of ethmoidal bulla (BE) shows uncinate process (u); bilateral conchae bullosae (C); and left infraorbital ethmoidal air cell, or HaIler cell (H). Lamina papyracea (open arrow) is lateral wall of ethmoidal bulla. Ethmoidal infundibulum is passage area (solid straight arrows) between uncinate process and bulla. Arrowhead indicates semilunar hiatus, which is communication passage between middle meatus (broken line) and infundibulum. Note that inferolateral portion of ethmoidal infundibulum is formed by Hailer cell on left side and by inferior portion of medial wall of orbit on right side. Expansion and inflammation of HaIler cells may result in narrowing of infundibulum. Ostia (o) of maxillary sinuses drain into posteroinferior part of respective infundibulum. On either side, a mucosal band (curved arrow) is seen in this region. It is not uncommon to see mucosal contact in posterior portion of ethmoidal infundibulum as ostium of maxillary sinus funnels into it. Persistence of this mucosal contact may result in ventilatory problem of maxillary sinus. Fig. 9.-Coronal CT scan of cadaveric head obtained after endoscopic surgery on anterior ethmoidal sinus on right side shows ethmoidal bulla (BE), lateral sinus (SL), and partially volumed anterior portion of basal lamella (arrowhead) on left side. passage called the frontonasal canal (Figs. 2, 3, and SB). This communication between frontal sinus and nasal cavity is not strictly a duct [16], but rather an internal somewhat curved channel positioned between the sinus and the anterior middle meatus. It is referred to as the frontal recess (Figs. 2, 3, and SB), or the frontal recess of the ethmoidal infundibulum [23], which is anatomically Close to the frontal sinus [23]. Agger Nasi Cells Just anterior to the anterosuperior attachment of the middle turbinate and anterior to the frontal recess is the agger (ridge) nasi [23] (Figs. 2 and 6A). When pneumatized, this prominence on the lateral nasal wall represents the most anterior of the anterior ethmoidal cells. These cells (agger nasi cells) can invade the lacrimal bone or the ascending process of the maxilla. The agger nasi cells are located on the lateral nasal wall immediately anterior to the anterior end of the middle turbinate (Fig. 2). These cells open into the ethmoidal infundibulum (Fig. 2B). Because of their closeness to the frontal recess, the agger nasi cells are excellent surgical landmarks. Opening these cells provides a good access to the nasofrontal duct [23]. The agger nasi cells are

6 the most common air cells that are not completely removed during functional endoscopic sinus surgery. The reason for this is their locations; 30#{176} or 70#{176} endoscopes are often required to visualize these cells, thus making removal difficult, potentially allowing persistent mucosal disease and recurrent Ostiomeatal symptoms. Complex The concept of obstruction of the ostiomeatal complex resulting in ethmoidal, frontal, and maxillary sinusitis is fundamental to functional endoscopic sinus surgery. Therefore, an understanding of endoscopic anatomy of the paranasal sinuses and ostiomeatal complex is important. The ostiomeatal complex or unit has been referred to by various authors as the middle meatus-anterior ethmoid complex; the area of ethmoidal infundibulum; frontal recess, anterior ethmoid, and maxillary sinus ostium [3]; the maxillary sinus ostium and ethmoidal infundibulum [16]; and the normal aerated channels providing air flow and mucociliary clearance for the maxillary, ethmoidal, frontal, and sphenoidal sinuses [24]. The area between the middle and inferior turbinates - that is, the confluence of the drainage of the frontal, ethmoidal, and maxillary sinuses-has also been called the ostiomeatal complex [21]. However, this term is often used to refer to the area encompassed by (1) the ostium of the maxillary sinus, the ostia of the anterior and middle ethmoidal air cells, the frontonasal duct (frontal recess), the ethmoidal infundibulum, and the middle meatus and (2) the sphenoethmoidal recess and superior meatus [1 9]. In several areas of the ostiomeatal unit, two mucosal layers contact each other, thus increasing the likelihood of local impairment of mucociliary clearance. Secretions may then be retained at the site, creating the potential for infection even without ostial closure [21]. Anatomically, the most likely areas of mucosal contact are in the narrow mucosa-lined channels of the middle meatus and the ethmoidal infundibulum [3]. Uncinate Process and Ethmoidal Infundibulum A clear understanding of the anatomy of the ethmoidal uncinate process and the ethmoidal infundibulum is of utmost importance for radiologists who are evaluating CT studies of the paranasal sinuses prior to endoscopic sinus surgery. Just posterior and inferior to the agger nasi cells lies the ethmoidal uncinate process (Figs. 1-3), the starting point in an anterior to posterior endoscopic sinus procedure [13]. The uncinate process is a thin, curved lamina of bone from the lateral side of the ethmoidal labyrinth that forms a portion of the lateral nasal wall (Figs. 1A, 2, 3, and SC). It projects downward and backward, and its size varies considerably from patient to patient (Figs. 2, 3, and SC). It is 1-4 mm tall and mm long [14]. Anteriorly, it articulates with the lacrimal bone, curves downward and backward across the maxillary hiatus (Fig. 1A), and articulates with the ethmoidal process of the inferior nasal concha (Figs. 1 and SC). In a disarticulated bone, the maxillary hiatus is a wide opening on the nasal surface of the maxilla; however, in life, its size is greatly reduced by the neighboring bones, which include the inferior concha and its maxillary process, the uncinate process of the ethmoid bone, and the anterior part of the perpendicular plate of the palatine bone. As a result, the maxillary hiatus is reduced sometimes to a single orifice, the natural maxillary ostium, in the floor of the posterior part of the semilunar hiatus [18] (Fig. 1). The ethmoidal infundibulum is a trough-shaped air space (deep curved passage) below the bulla and above and lateral to the uncinate process (Figs. 1-3, SC, 7, and 8). It receives drainage from the anterior and middle ethmoidal air cells and the frontal and maxillary sinuses. In more than 50% of crania, the infundibulum is continued superiorly as the frontonasal duct into the frontal sinus [18]. Kasper [25] found that in 62% of cases, the ethmoidal infundibulum and nasofrontal connections were discontinuous channels anatomically. The exact drainage system of the frontal sinus depends on its embryologic development. Drainage usually occurs by way of rudimentary ethmoidal cells into the frontal recess [25] (Figs. 2 and 3) or directly into the frontal recess [13]. Semilunar Hiatus The semilunar hiatus is a curvilinear opening of the lateral nasal wall that lies above the ethmoidal uncinate process and below the ethmoidal bulla (Figs. 1 and 2). This opening separates the uncinate process from the ethmoidal bulla and serves as a connection between the infundibulum and the middle meatus (Figs. SC, 7, and 8). The semilunar hiatus is, in fact, a curved furrow that continues from the infundibulum, superiorly in a posteroinferior direction, and past the natural ostium of the maxillary sinus (Fig. 1), to gradually fade away superior to the posteroinferior turbinate [1 3]. Thus, purulent secretions from the frontal and anterior ethmoidal air cells drain across the maxillary ostium [13]. The key locations of anterior ethmoidal cells and the frontal sinus drainage system as a cause of recurrent maxillary sinusitis have long been recognized. It was because of this anatomic relationship that Schaeffer [26] stated: The maxillary sinus is often a cesspool for infectious material from the sinus frontalis and certain of the anterior group of cellulae ethmoidalis. Ethmoidal Bulla, Lateral Sinus, and Grand (Basal) Lamella The middle ethmoidal air cells produce a round swelling, called the ethmoidal bulla, on the lateral wall of the middle meatus (Figs. 1-3, SC, 7, and 8), whose lateral border forms a portion of the medial orbital wall. These cells open into the ethmoidal infundibulum or onto the medial wall of the bulla into the middle meatus. Medial to the ethmoidal bulla and the uncinate process is the middle turbinate (Figs. SC, 7, and 8). Anteriorly, the middle turbinate attaches to the medial wall of the agger nasi and the superoanterior edge of the uncinate process [24]. Superiorly, it attaches to the cribriform plate at the junction between the fovea (roof) of the ethmoid bone and the cribriform plate. The attachment of the middle turbinate changes direction at its most posterior extent. Instead of running in an anteroposterior direction, it curves laterally, and the final lateral attachment of the middle turbinate is oriented in the frontal plane and is called the basal or ground (or grand) lamella [16, 23, 24] (Figs. 2B, 4, and 9). The posterior ethmoidal air cells are between the basal lamella and the sphenoidal sinus. The basal lamella is an anatomic landmark for separating the anterior and middle ethmoidal air cells from the posterior ethmoidal air cells (Figs. 2B and 4) [23]. The basal lamella slows the spread of infection posteriorly [13]. An air space is usually found between the basal lamella and the ethmoidal bulla, which

7 may extend superiorly to the bulla. This is called the lateral sinus (Figs. 2A, 2B, and 9). The lateral sinus is a cleft, not an air cell, and unlike the other anterior ethmoidal air cells that open into the middle meatus, it may communicate with the frontal recess [24] or may open directly and independently into the middle meatus. The lateral sinus may extend above the ethmoidal bulla (Fig. 9). The posterior ethmoidal cells occupy the posterior ethmoid bone but also the posterior middle turbinate and may invade the sphenoid, palatine, and maxillary bones [1 3]. Four primary lamellae must be crossed on the way to the sphenoidal sinus. They include the uncinate process of the ethmoid bone, the anterior wall of the ethmoidal bulla, the basal lamella, and the anterior wall of the sphenoidal sinus. The middle turbinate is a barrier to visualization of the posterior ethmoidal sinuses and the sphenoidal rostrum. Some authors [1] contend that this structure should be sacrificed for the sake of a complete intranasal sphenoethmoidectomy. The natural ostium of the maxillary sinus is extremely important in endoscopic sinus surgery. This ostium is located in the superior part of the medial wall of the sinus and drains into the posterior part of the ethmoidal infundibulum as the sinus funnels into it, usually posterior to the midpoint of the ethmoidal bulla [13] (Fig. 8). The posterior extent of the uncinate process points to the position of the maxillary ostium and is an excellent imaging and endoscopic landmark for its localization. Accessory ostia are present in % of patients, usually in the membranous medial sinus wall, the fontanelles. The fontanelles (anterior and posterior) are two areas along the medial aspect of the maxillary sinus where a double layer of mucosa with no intervening bone forms the nasoantral wall inferior to the uncinate process. The fontanelies lie anterior and posterior to the ethmoidal process of the inferior concha. Indications for Endoscopic Sinus Surgery Endoscopic sinus surgery has become increasingly popular since Messerklinger [27] and Wigand et al. [28] described the advantages of the intranasal endoscope and its surgical application. Endoscopes are available with 0#{176}, 30#{176}, 70#{176}, and 120#{176} angles of view and in 2.7- and 4.0-mm sizes, with the exception of the 120#{176} angle (4.0 mm only). In endoscopy, the 30#{176} and 70#{176} angles are the most useful. Endoscopic sinus surgery is reserved for patients in whom traditional noninvasive therapy is unsuccessful [13, 14]. The ideal patient is one who has repeated bouts of bacterial sinusitis that respond only briefly to antibiotics. Four other subgroups are important: (1) patients with severe bacterial sinusitis that does not respond to antibiotics and other usual measures; (2) patients with chronic hyperplastic rhinosinusitis and those with nasal polyps, with or without asthma (in this group, allergic diathesis willpersist,however, and allergy treatment is necessary); (3) patients with a mucocele (with the use of multiangled endoscopes, frontoethmoidal, sphenoidal, and maxillary mucoceles are easily treated [13, 14]); and (4) patients with periorbital cellulitis caused by ethmoiditis. This technique may not be indicated for asymptomatic, incidentally discovered mucous retention cysts [13, 14]. Chronic Hyperplastic Rhinosinusitis Chronic hyperplastic rhinosinusitis implies extensive disease throughout the paranasal sinuses [1]. The pathologic spectrum of this entity includes polypoid, fibrocystic, and papillary changes in the nasal and sinus mucosae [1]. Many factors are responsible for the development of chronic hyperplastic rhinosinusitis, including infection, allergy, and increased tissue response to inhalants and irritants. Mucosal abnormality and ciliary dysfunction begin with submucosal edema and infiltration, and eventually mucosal prolapse and development of polyps occur. This in turn causes obstruction and compromise of the sinus orifices and recurrent infections, with the production of mucous and accentuation of the already existing mucosal polyps. Eventually, demineralization or destruction of the underlying intraethmoidal bony framework takes place [1]. CT of the Sinuses Before Intranasal Endoscopic Surgery Recognition of the importance of the ostiomeatal complex has given the radiologist an important role in the examination of patients who are scheduled for functional endoscopic sinus surgery. Radiologists should be familiar with the principies of this operation and make a careful evaluation of the paranasal sinuses, in particular the ethmoid bone and the ostiomeatal region [29]. An optimal imaging protocol for operative CT of the sinuses, including preparation of the patient, CT technique, and data display (filming), has been reported [3, 16, 17, 19, 30]. Pretreatment of patients with appropriate medical therapy and adequate preparation of patients enable the best CT assessment of mucosal disease of the nasal and paranasal sinuses. Coronal CT scanning with the patient prone and the head hyperextended currently affords the best preoperative evaluation for endoscopic anterior ethmoidectomy (Figs. 10 and 11), frontal sinusotomy [14, 1 6, 17, 21], and posterior endoscopic total sphenoethmoidectomy [1 2]. The anterior and posterior walls of the frontal sinuses and the anatomic relationship between the posterior ethmoidal and sphenoidal sinuses are best evaluated in the axial plane. The combination of coronal and axial CT scans allows the surgeon to more easily assess the three-dimensional aspects of the ostiomeatal complex (Fig. 12) and the pathologic changes. Some authors [3, 16, 30] recommend an intermediate (2500 H/2S0 H) window width/ level technique. Others prefer CT scans obtained with an extended-window-width bone technique (4000 H/ H) and require that the technicians provide an additional set of images obtained with a soft-tissue technique [17, 19]. The soft-tissue technique allows better evaluation of inspissated mucosal debris, microcalcifications, and incidental findings in the orbit and eyeball, as well as evaluation of the part of the face and cranium included in the study. Coronal scanning extends from the frontal sinus anteriorly to the sphenoidal sinus posteriorly. For axial CT of the sinus, the scanning extends from the maxillary teeth inferiorly to the suprasellar region superiorly. Axial CT scans are included whenever coronal CT scans show a mass or mucosal disease with expansion of the sinuses. Erosion of the posterior table of the frontal sinus is best evaluated on axial CT scans. The sphenoethmoidal bony plate, pterygomaxillary fissure, and pterygopalatine fossa are also best evaluated on axial CT scans. Contrast-enhanced CT should not be part of preoperative CT of the paranasal sinuses. Contrast material is used only when the preliminary evaluation of coronal CT scans suggests a mass within the sinonasal cavities. In addition,

8 742 MAFEE ET AL. AJR:160, April 1993 Fig. 10.-Coronal CT scan shows left infundibular inflammatory mucosal disease (short arrow). Note cribriform plate (arrowhead) and ethmoidal fovea (long arrows). Fig. 12.-Axial CT scan shows uncinate processes (black arrows) of ethmoid bone. Infundibulum is air space just lateral to uncinate processes. Semilunar hiatus (white arrow) connects infundibulum to middle meatus, air space lateral to middle turbinate. I = nasolacrimal canal, 2= middle turbinate. Relationship between uncinate process and nasolacrimal canal would explain potential damage to nasolacrimal canal during anterior endoscopic surgery on ethmoidal sinus. Fig. 11.-A, Coronal CT scan shows marked left infundibular disease (polyps) (solid arrow), nasal polyp (p), and concha bullosa (C). Left infundibular disease encroaches on left nasolacrimal canal (open arrow). B, Coronal CT scan obtained after endoscopic sinus surgery shows that infundibular and nasal polyps have been removed and left middle turbinate partially resected. Note cribriform plate (arrowhead) and ethmoidal fovea (arrows). Fig. 13.-Chronic hyperplastic sinusitis with inspissated mucus. A, Unenhanced CT scan shows opacification of sphenoidal sinuses (5) and soft-tissue mass (M) within nasal choanae. Increased CT density is due to inspissated mucus. At surgery, hyperplastic polyps and dried gritty materials were removed. Histologic examination revealed inflammatory polyps and inspissated mucus. B, T2-weighted (2000/80) MR image, obtained at same level as A, shows sphenoidal sinuses(s) as uniformly hypointense, simulating air-containing normal sinuses. contrast material is given whenever intracranial complications of sinonasal infections (e.g., subperiosteal, intradural, and brain abscesses) or thrombosis of dural sinuses (such as of cavernous sinuses) is suspected. Complications of sinonasal infections also can be readily detected with MR imaging. MR imaging should not be used as a screening tool for evaluation of chronic inflammatory or allergic sinus diseases. Calcifications and inspissated mucous can be easily missed on MR images. At times, a sinus packed with inspissated mucus can appear as a perfectly aerated and normal sinus on MR (Fig. 13). Although the normal and altered mucosal linings of the paranasal sinuses (Fig. 14) and the ostiomeatal complex can be visualized on MR images, detailed bony structures such as the uncinate process, basal lamella, cribriform plate, ethmoidal fovea, and lamina papyracea make CT the most practical and the more cost-effective study for paranasal sinuses. Even for tumors of sinonasal cavities, we use MR imaging as a complementary study to better evaluate the extent of the disease and the presence of intracranial extension of the disease. One important contribution of MR imaging is the ability to differentiate neoplastic processes from associated underlying

9 AJR:160, April 1993 FUNCTIONAL ENDOSCOPIC SINUS SURGERY 743 Fig. 14.-MR image shows mucosal disease of left posterior ethmoidai sinus (arrow). Note proximity of posterior ethmoidal air cell (E) and sphenoidal sinuses (5) to optic canal and optic nerve (0). or obstructive mucosal disease. On T2-weighted MR images, the retained mucus or pus often appears hyperintense relative to brain, whereas tumors are isointense and even hypointense. Certainly, individual structural differences in ethmoidal and ostiomeatal complexes and other paranasal sinuses are to be expected, and illustrations in the literature will not be identical to scans of any individual patient. Certain anatomic variations are observed more commonly and should be included in the imaging report. These are as follows. (1) Concha bullosa, a pneumatized middle turbinate (Figs. 8 and ha). The otolaryngologist is interested to know whether the concha bullosa has compromised the middle meatus or even the ethmoidal infundibulum (Fig. 8). (2) Low position of the ethmoidal fovea (the roof of the ethmoidal labyrinth). A low position of the cribriform plate and ethmoidal fovea is a potentially dangerous anatomic variation, which can be penetrated easily unless the surgeon is aware of the finding. (3) Bulging of the optic canal into the posterior ethmoidal complex or sphenoidal sinuses (Figs. 14 and 15). In rare instances, the internal carotid artery may be exposed in the posterior ethmoidal sinus [31]. An important observation is extensive lateral pneumatization of the posterior ethmoidal air cells, which can increase the vulnerability of the optic nerve (Fig. 14). In addition, detection of an asymmetric intersphenoidal septum is important because the posterior extension of this partition usually marks the location of the internal carotid artery (Fig. 16). (4) Deviation of the uncinate process of the ethmoid bone. The superior edge of the uncinate process may deviate medially to obstruct the middle meatus or, more importantly, may deviate laterally to obstruct the infundibulum. Marked lateral deviation or even fusion of the uncinate process to the medial orbital wall may endanger the orbit and hence the optic nerve when uncinectomy is performed during anterior endoscopic sinus surgery. (5) HaIler cells. These are ethmoidal cells extending along the medial floor of the orbit (infraorbital air cells) (Figs. 7 and 8) that may cause narrowing of the infundibulum. Other anatomic Fig. 15.-Coronal CT scan shows dehiscent optic canals (arrows), bulging into sphenoidal sinuses. Note relationship of intersphenoidal septum with right optic canal. a = anterior clinoid process, fr = foremen rotundum, v = vidian canal entering into pterygopalatine fossa. Fig. 16.-Coronal MR image shows three intersphenoidal septa. Note extension of lateral septa (arrows) toward carotid sulcus of internal carotid arteries. variations include deviation of the nasal septum; paradoxical middle turbinate, bulla (pneumatization), and at times turbinate of the uncinate process; and posttraumatic or congenital deformity of the medial wall or floor of the orbit. Complications of Endoscopic Sinus Surgery Serious complications may be associated with this relatively new technique (Figs. 17 and 18). CT and endoscopy are complementary in the diagnosis and treatment of disorders of the nasal cavity and paranasal sinuses. Endoscopic nasal sinus surgery, like traditional sinus surgery, is associated with serious risks. Complications such as blindness, lacrimal dysfunction due to injury of the lacrimal drainage system, ocular motility dysfunction, orbital hematoma, leakage of CSF, damage to brain tissue or vessels in the anterior cranial fossa, brain abscess, pneumocephalus, carotid artery-cavernous sinus fistula, and death have been reported [32-36]. Buus et al. [35] reported bilateral blindness in a 39-year-old woman who had endoscopic ethmoidectomies. Pathologic specimens from both sides showed optic nerve tissues. In anterior endoscopic sinus surgery, the medial limit of the dissection and the medial limit of the middle and anterior ethmoidal complex are the upper attachment of the middle turbinate. There are several reasons to avoid this superior junction of the middle turbinate. The cribriform plate is thin and can be traumatized easily, particularly adjacent to the anterior ethmoidal artery (Fig. 1 8). The ethmoidal roof (ethmoidal fovea) is relatively thick, but at its most medial aspect it turns downward sharply in some patients to join the cribriform plate. The ethmoidal roof is quite thin in this most medial part. The close apposition of the optic nerve to the lateral aspect of the posterior ethmoidal cells makes it hazardous to use the lateral ethmoidal wall as a landmark for posterior ethmoidal surgery [23] (Fig. 14). As an entire generation of otolaryngologists learns these new techniques, other complications will emerge. Prevention begins with proper endoscopic and preoperative CT evaluation and surgical preparation [33, 37].

10 744 MAFEE ET AL. AJR:160, April 1993 ACKNOWLEDGMENTS We thank Kevin Ziffra for advice and assistance in the preparation of cadaveric heads and Dale Peal and Jennifer Martin for secretarial assistance. REFERENCES 1. Friedman WH, Katsantonis GP. The role of standard technique in modern sinus surgery. OtolaryngolClin NorthAm 1989;22: Caldwell G. Diseases ofthe nasal sinuses. N YMedl893; Kennedy DW, Zenrich J, Rosenbaum AE, Johns ME. Functional endoscopic sinus surgery: theory and diagnostic evaluation. Arch Otolaryngol Head Neck Surg 1985; 111: Messerklinger W. On the drainage of the normal frontal sinus of man. Acta Otolaryngol (Stockh) 1967;63: Messerklinger W. Uber die Drainage der Menschlichen Nasennebenhohlen unter normalen und pathologischen Bendingungen. II. Mitteilung: Die Stirnhohole und ihr Ausfuhrungssystem. Monatsschr Oxrenhellkd 1967;101 : Messerklinger W. Uber den recessus frontalis und Seine Klinik. Laryngorhinootologie 1982;61 : Hilding AC. The physiology of drainage of nasal mucus: I I. Drainage of the accessory sinuses in man. Otolaryngol Rhinol Laryngol 1944;53: Hilding AC. Physiologic basis of nasal operations. Calif Med 1950;72: Proctor DF. The nose, paranasal sinuses and pharynx. In: Walters W, ed. Lewis-Walters practice of surgery, vol. 4. Hagerstown, MD: Prior, 1966: Proctor DF. The mucociliary system. In: Proctor DF, Anderson IHP, eds. The nose: upper airway physiology and the atmospheric environment. New York: Elsevier, 1982: Winther B, Gross CW. Introduction and indications for functional endonasal (endoscopic) sinus surgery. Oper Techniq Otolaryngol Head Neck Surg 1990;2: Schaefer SD. Endoscopic sinus surgery: posterior approach. Oper Techniq Otolaryngol Head Neck Surg 1990;2: Rice DH. Basic surgical techniques and variations of endoscopic sinus surgery. Otolaryngol Clin North Am 1 989;22: Rice DH. Endoscopic sinus surgery: anterior approach. Oper Techniq Otolaryngol Head Neck Surg 1990; 1: Stammberger H. Endoscopic endonasal surgery: concepts in treatment of recurring rhinosinusitis. I. Anatomic and pathologic considerations. Otolaryngol Head Neck Surg 1 986;94: Fig. 17.-Patient with marked ocular motility disturbance after endoscopic surgery on ethmoidal sinus. Coronal Ti-weighted (800/20) MR image shows markedly hypertrophic right maxillary and ethmoidal mucosae. Note disruption of medial wail and floor of orbit (white arrows) and marked soft-tissue injury (hematoma and scar) in periorbital region (black arrows), resulting in deformity of medial rectus muscle and superior oblique muscle. Fig. 18.-Coronal CT scan of cadaveric head after endoscopic surgery on ethmoidal sinus shows cribriform plate (short arrow) has been removed. Ethmoidal foveae (long arrows) on both sides appear intact. 16. Zinreich SJ, Kennedy DW, Rosenbaum AE, Gayler BW, Kumar AJ, Stammberger H. Paranasal sinuses: CT imaging requirements for endoscopic surgery. Radiology 1987;163: Chow JM, Mafee MF. Radiologic assessment preoperative to endoscopic sinus surgery. Otolaryngol Clin NorthAm 1989;22: Warwick R, Williams PL, eds. Gray s anatomy. Philadelphia: Saunders, Mafee ME Endoscopic sinus surgery: role of radiologist. AJNR ;12: Wheater AR, Burkitt HG, Daniels VG. Functional histology. New York: Churchill Livingstone, 1979: Wald ER. Sinusitis in children. N EnglJ Med 1992;326: Zemlin WA, Stople SC. The structure of the human skull. Champaign, IL: Stipes, a.Chow J, Mafee ME Coronal section computed tomographic imaging of the paranasal sinuses for endoscopic sinus surgery. Oper Techniq Otolaryngol Head Neck Surg 1993;3: Becker SP. Anatomy for endoscopic sinus surgery. Otolaryngol Clin North Am 1989;22: Zinreich SJ, Abidin M, Kennedy DW. Cross-sectional imaging of the nasal cavity and paranasal sinuses. Oper Techniq Otolaryngol Head Neck Surg 1 990;2: Kasper KA. Nasofrontal connections: study based on one hundred consecutive dissections. Arch Otolaryngol Head Neck Surg 1936;23: Schaeffer JP. The genesis, development and adult anatomy of the nasofrontal region in man. Am JAnatl9l6;20: Messerklinger W. Endoscopy of the nose. Baltimore: Urban & Schwarzenberg, Wigand ME, Steiner W, Jaumann MP. Endonasal sinus surgery with endoscopical control: from radical operation to rehabilitation of the mucosa. Endoscopy 1978;10: Terrier F, Weber W, Ruefenacht D, Percellini B. Anatomy of the ethmoid: CT, endoscopic, and macroscopic. AJNR 1 985;6: Babbel A, Harnsberger HA, Nelson B, Sonkes J, Hunt S. Optimization of techniques in screening sinus CT. AJNR 1991;12: Kennedy DW, Zinreich SJ, Hassab MH. The internal carotid artery as it relates to endonasal sphenoethmoidectomy. Am J Rhinol 1990;4: Stankiewicz JA. Blindness and intranasal endoscopic ethmoidectomy. Laryngoscope 1987;97: Stankiewicz JA. Complications of endoscopic sinus surgery. Otolaryngol Clin NorthAm 1989;22: Maniglia AJ. Fatal and major complications secondary to nasal and sinus surgery. Laryngoscope 1989;99: Buus DR, Tse DT, Farnis BK. Ophthalmic complications of sinus surgery. Ophthalmology 1 990;97: Neuhaus RW. Orbital complications secondary to endoscopic sinus surgery. Ophthalmology 1990;97: Schaefer SD. Endoscopic frontal sinusotomy. Oper Techniq Otolaryngol Head Neck Surg 1990;1: