Info

Dorn Spinal Therapy

Spine Healing Therapy

Get Instant Access

Consistent and Reliable Anatomical Landmarks in Endoscopic Sinus Surgery: A Historical Perspective

Transnasal sinus surgery began in 1886, when Miculicz reported on the endonasal fenestration of the maxillary sinus (1). A transnasal approach to performing an ethmoidectomy was not described until 1915, when Halle reported his experience (2). Even then, it was immediately apparent that a transnasal ethmoidectomy posed significant inherent risks for the patient. Indeed, these risks were best paraphrased by Mosher, in 1929, when he described intranasal ethmoidectomy as being "one of the easiest operations with which to kill a patient" (3). In the three decades that followed Mosher's work, a number of significant anatomical studies helped further define the three-dimensional anatomy and variations of the ethmoid labyrinth, turbinates, and surrounding ostia and recesses that drain the dependent sinuses (maxillary, frontal, and sphenoid) (4-10). Initially designed to evaluate the feasibility of irrigating the antrum via direct transnasal cannulation of the natural ostium, these studies contributed significantly to our current understanding of paranasal sinus endoscopic anatomy. They describe the wide variability in distances and dimensions among virtually all the intranasal anatomical structures currently used as landmarks in endoscopic sinus surgery (ESS).

The first attempt at nasal and sinus endoscopy was made by Hirshman in 1901, using a modified cystoscope (11). In 1925, Maltz, a New York rhinologist, used the term sinoscopy and advocated the technique for diagnosis (12). However, ESS was not introduced in the European literature until 1967, by Messerklinger (13). Moreover, it did not gain wider acceptance in Europe until others continued development and clarification of the technique (14-21). In 1985, Kennedy introduced the technique of functional endoscopic sinus surgery (FESS) into the United States (22). Since then, there has been an ongoing effort to refine the ESS technique and identify consistent anatomical landmarks to facilitate safe entry into the maxillary or sphenoid sinus, or to navigate within the ethmoid sinus (23-32).

Most rhinologists agree that ESS should be a "disease-directed" and mucosal-sparing operation, recognizing the principle of the potential for re-establishing drainage and mucosal recovery of the dependent sinuses (13,14,16). Since first described in 1965 by Neuman, the concept of the osti-omeatal unit, or complex, continues to play a role in mucosal disease of the paranasal sinuses (15). The ostiomeatal complex theory states that most inflammatory conditions of the maxillary, ethmoid, and frontal sinuses arise from this common drainage pathway. Therefore, the surgical procedure can be limited to an absolute minimum. Even in cases with significant radiological involvement of the frontal or maxillary sinuses, correction of ethmoid disease usually results in re-establishment of drainage and mucosal recovery of the larger (dependent) sinuses.

Today, there are essentially two techniques available to endoscopically address the ethmoid, maxillary, and sphenoid sinuses: the anteroposterior (AP) approach and posteroanterior (PA) approach (14,17,18,20). Anteroposterior exenteration of the ethmoid sinuses is the technique most widely used in the United States (14,17). The surgeon proceeds as far posteriorly as needed to remove diseased ethmoid cells and polyps and establish drainage only to the dependent sinuses that are blocked. In contrast, the posteroanterior approach is based on retrograde exposure of the ethmoid cells, beginning at the posterior ethmoids and sphenoid sinus and working in a posteroan-terior direction along the skull base (18-20). The ethmoid cell septations are removed in a posteroanterior direction along the skull base and orbital wall using the roof and lateral wall of the sphenoid sinus as reference points for the superior and lateral limits of dissection, respectively.

In the AP approach, the surgeon begins with an anterior ethmoidectomy by removing the unc-inate process, bullar cells, and agger nasi cells, and occasionally entering the frontal recess. The surgeon proceeds as far posteriorly as needed to remove diseased ethmoid cells and polyps. A limited maxillary antrostomy is typically not performed until after the ethmoid cells have been addressed. Bone is removed circumferentially (anteriorly toward the lacrimal duct and posteriorly toward the posterior fontanelle) to enlarge the maxillary ostium as needed. If a sphenoidotomy is indicated, a transethmoidal operation through the common wall of the sphenoid and posterior ethmoid sinus is described.

Proponents of the AP approach argue that even though it enables the surgeon to proceed as far posteriorly (into the posterior ethmoids or sphenoid) as needed, extensive surgery is infrequently indicated (14,17,22). However, not all surgeons share this view, arguing that patients with advanced nasal polyposis frequently have pansinus disease affecting not only the anterior ethmoids and dependent sinuses (maxillary and frontal) but also the sphenoethmoidal recess and surrounding ostia draining the posterior ethmoids and sphenoid sinuses (33). Also, the AP approach assumes that the inexperienced surgeon will correctly identify critical anatomical structures such as the uncinate process, ostium of the maxillary sinus, middle and superior turbinate and surrounding recesses, the basal lamella of the middle and superior turbinates, the anterior ethmoid artery and anterior skull base, and the anterior and posterior ethmoid air cells. The surgeon is taught to identify these structures and to stay "inferomedially" as he or she progresses posteriorly to minimize the chances of inadvertently penetrating the orbital wall or skull base. The problem for the inexperienced surgeon is that often these structures are missing or distorted because of pathological conditions or prior surgery. In addition, during the course of the surgical procedure, the nasal telescope and/or camera may become rotated within the nose. The unsuspecting surgeon may think he or she is heading in an inferoposterior direction while in fact following a superior or lat eral trajectory toward the skull base or orbit. In the absence of other consistent anatomical landmarks as internal reference points, the surgeon may fail to see that he or she is improperly oriented and that the skull base descends posteroinferiorly (34). This may result in inadvertent penetration of the anterior skull base or orbit as the AP ethmoidectomy is performed.

To address the difficulties observed when performing a sphenoidotomy using the traditional AP approach, Parsons described his approach to the sphenoid sinus (29). An anterior and posterior ethmoidectomy is performed (as with the AP approach) and the superior turbinate is visualized. The natural ostium of the sphenoid sinus is visualized on the medial side of the superior turbinate. A measurement is obtained from the natural ostium of the sphenoid to the anterior nasal spine. The same measuring instrument is then placed through the operative field, lateral to the middle and superior turbinates, to the "suspected" posterior wall of the posterior ethmoid. The second measurement has to be equal to or greater than the first measurement (at the natural ostium) for the suspected wall to qualify as the real anterior wall of the sphenoid sinus and not a posterior wall or a suprasphenoidal (Onodi) cell. A rigid instrument, such as a straight suction tip, is placed in the inferomedial quadrant. The instrument is advanced as far posterior and inferomedially as the dissection will allow. The surgeon then sweeps the suction tip medially toward the septum. According to Parsons, the bony wall of the superior/supreme turbinate will fracture in a very "consistent fashion," exposing a near vertical fracture line, which he refers to as the "ridge." The surgeon continues to sweep the superior turbinate medially, exposing the lateral mucosa of the superior turbinate medial to the ridge, referred to as the "ethmoid fontanelle," thereby visualizing the natural ostium of the sphenoid sinus.

Like other modifications of the AP approach, Parsons' technique has significant flaws due to some erroneous assumptions. He assumes that most surgeons performing a total ethmoidectomy can correctly identify, in the presence of inflammatory conditions, the sphenoid natural ostium, the middle and superior turbinates, and the posterior wall of the posterior ethmoid. He further assumes that the surgeon will be able to safely perform an anterior and posterior ethmoidectomy, identify the "ridge" as described, and introduce the suction tip correctly "inferomedially" into the sphenoid sinus. Blindly "advancing" suction tips (or today, power instrumentation) into any cavity can yield disastrous consequences. The inexperienced surgeon may face orientation difficulties with respect to how far inferomedially he or she has to be.

In 1999, Bolger and colleagues also tried to address the difficulties in consistently and safely opening the sphenoid sinus using the AP approach (30). Like Parsons, Bolger noted that identification of the superior meatus and superior turbinates provides a reliable landmark within the dissection field that can facilitate the surgical identification of the sphenoid sinus. He advises resecting 2-3 mm of the inferior and medial aspect of the basal lamella of the middle turbinate, and notes that little has been written about an endoscopic approach to the sphenoid sinus that uses this "discrete, easily identifiable, and reliable anatomic landmark." Bolger describes a "parallelogram-shaped box": medially the lateral aspect of the superior turbinate and, when present, the supreme turbinate; laterally the lamina papyracea; superiorly the skull base; and inferiorly the horizontal portion of the superior turbinate as it courses to attach to the lateral nasal wall. The back of this box is the anterior wall of the sphenoid sinus. Bisecting the box with a line connecting the superomedial corner to the inferolateral corner forms two triangles. Dissection in the infero-medial triangular region will be safe, whereas dissection in the superolateral triangular region will be hazardous because of the proximity of the optic nerve and the carotid artery. Just as Parsons and his coworkers had, the authors of this study found the superior meatus and the inferior aspect of the superior turbinate (unlike the middle turbinate) to be a consistent and reliable anatomical landmark for the location of the sphenoid sinus that is rarely resected with prior surgery. How ever, like Parsons' technique, this approach relies on the surgeon's ability to perform a complete ethmoidectomy with correct identification of the lamina papyrecea and anterior skull base anterior to this point. In addition, most inexperienced surgeons often find that distortion due to scarring or inflammatory disease often makes it very difficult to reliably identify the remnant of the superior turbinate.

Despite Parsons' and Bolger's attempts to address the difficulties with safely and consistently identifying the sphenoid sinus through a transethmoidal (AP) approach, significant problems remain. First, a transethmoidal sphenoidotomy does not always afford optimal access: the bone of the anterior wall of the sphenoid is thicker than that paramedially adjacent to nasal septum in the area of the sphenoid natural ostium (31). Since this procedure is carried out relatively close to the optic nerve and the carotid artery, specific anatomical variations in these skull-base structures may preclude the use of these techniques because of the potential for significant complications. Second, anatomical characteristics, such as a deviated nasal septum, may force the surgeon to take a more lateral trajectory into the sphenoid sinus, which, without a consistent reference point for initial entry into the sphenoid, requires a great deal of experience. The unwary surgeon can easily misjudge the appropriate level of entry into the sphenoid or posterior ethmoid and inadvertently enter the skull base, carotid artery, or optic nerve. Lastly, if the osteomeatal complex theory also applies to the sphenoethmoidal recess and surrounding ostia to the posterior sinuses ("posterior osteomeatal complex" to the sphenoid and posterior ethmoids), then whichever endoscopic surgical technique is selected must also address the natural drainage areas of these sinuses. In other words, the natural ostium of the sphenoid needs to be enlarged rather than a new one created through the common wall of the sphenoid and posterior ethmoid sinus. The transethmoidal technique does little to ensure that the natural ostium is incorporated into the surgical sinusotomy (as is commonly done with the maxillary sinus ostium).

For these reasons, a sphenoidotomy adjacent to the nasal septum and medial to the superior turbinate has been proposed (26,31,32). Any bleeding during enlargement of the sphenoid ostium in-feriorly can be easily controlled with cautery. Hosemann et al. note that perforation of the anterior sphenoid wall 10-12 mm superior to the choanal arch in the area of the natural ostium, as described by Wigand, is the preferable strategy (31). This point corresponds to the middle third of the anterior sphenoid sinus wall in 88% of the cases and to the superior third in the remainder.

Recognizing the potential difficulties with the AP approach, especially with more extensive disease of the paranasal sinuses, Wigand described the PA approach (18-20). In this approach, the surgeon opens the sphenoid beginning with a posterior partial resection of the middle turbinate. The posterior ethmoid sinus is opened by limited removal of the posterior free body of the middle turbinate. The sphenoid is entered by using a suction tip with gentle pressure 1-2 cm above the upper edge of the posterior nasal choanal arch. Wigand notes that his technique poses little danger of perforating the skull base because the rigid plate of the sphenoid planum will be encountered if the surgeon goes too high. Nevertheless, he advises against exposing the posterior ethmoid cells as far as the ethmoid roof at this point. Rather, he advocates first exposing and removing the anterior wall of the sphenoid sinus to avoid dissection toward the skull base. Once the roof of the sphenoid and lateral wall are identified (as the superior and lateral limits of dissection, respectively), a retrograde dissection of the ethmoid cells is performed. Wigand describes performing an antrostomy last through the posterior fontanelle since this is a consistent reference point for safely entering the maxillary sinus.

According to Wigand, the PA approach gives a clear exposure of the surgical field, reducing the risk of serious complications and yielding reliable results without long-term crusting. This approach, however, is more extensive than the AP approach, irrespective of the extent of the disease.

It is usually combined with a septoplasty (to ensure medial entry into the sphenoid) and involves routine opening of the sphenoid, frontal, and maxillary sinuses (a pansinus operation). It also requires a certain degree of precision and experience in determining the exact location of the sphenoid sinus in the sphenoethmoidal recess. With advanced disease, the anatomy in this area may be significantly distorted. As with the AP approach, the superior or middle turbinate may be difficult to identify. There is also great variability when relying on internal measurements alone. The mean distance from the choanal arch to the sphenoid ostium is 8 mm (range 2-15 mm) (31). The mean distance from the sphenoid ostium to the skull base is also 8 mm (range 3-17). In addition, the sphenoid ostium can be even closer to the posterior cribriform plate than the skull base (approximately 3 mm) (6). As previously noted, anatomical characteristics such as a deviated nasal septum may force the surgeon to take a more lateral trajectory into the sphenoid sinus, which requires a great deal of experience. Moreover, in the event of inadvertent penetration, the use of suction tips (as advocated by Wigand) could further enhance the trauma by contusing brain parenchyma and other neural structures.

In 1994, May and colleagues introduced six friendly anatomical landmarks that are almost always present despite previous surgery: 1) the arch (or convexity) formed by the posterior edge of the lacrimal bone, 2) the anterior superior attachment of the middle turbinate, 3) the middle meatal antrostomy and the bony "ridge" along its superior border formed by the junction of the floor of the orbit with the lamina papyracea and posterior fontanelle, 4) the lamina papyracea, 5) the nasal septum, 6) and the arch of the posterior choana (27). Using these landmarks, revision ESS for recurrent or persistent disease in the maxillary, ethmoid, sphenoid, or frontal sinuses can be safely performed. May was one of the first to acknowledge that in advanced sinus disease anatomical landmarks such as the uncinate process, basal lamina, and superior or middle turbinate are not always readily identifiable. He was also one of the first to point out that the floor of the orbit, as seen through an antrostomy, serves as a consistent landmark from which other structures may be found. The bony "ridge" of the antrostomy represents the approximate level of the floor of the orbit as it inclines superiorly toward the orbital apex. This ridge is a useful landmark in identification of the lamina papyracea and in locating the posterior ethmoid and sphenoid sinuses. The posterior ethmoid sinus is located above this ridge and the sphenoid sinus lies below it. When a maxillary antrostomy is not performed, the natural ostium of the maxillary sinus can be alternatively used to help define the level of the orbit floor. The internal maxillary ostium is found at the junction of the medial maxillary wall and the floor of the orbit, halfway between the anterior and posterior maxillary walls and behind the convexity of the nasolacrimal duct.

Despite prior reports that showed great intersubject variability, May and Stankiewicz reintro-duced the possible clinical efficacy of using standard measurements from the columnella to orient the surgeon during ESS (28,32). They based this proposal on anecdotal experience and prior anatomical studies by others noting that the distance from the area of the anterior nasal spine to the sphenoid ostium is approximately 60 mm (range 47-70 mm) (6,35,36). Adding approximately one more centimeter for the length of the columnellar base would make the mean distance to the sphenoid ostium around 70 mm. For this reason, May advocates labeling instruments with colored tape to warn the surgeon when the anterior face of the sphenoid is reached (approximately 7 cm). However, there will likely be variability among surgeons' measurements of these distances. In isolation, these measurements have not been shown to be clinically reliable. Until recently there have been no studies looking at the columnellar to sphenoid (or posterior ethmoid) measurement as a reference point when used by itself or in combination with other, more consistent anatomical landmarks.

PM AS PS ON CA AA

Figure 1 Graph illustrating the minimum, maximum, and mean distances (in mm) and standard deviations (bars) from the columnellar base to the posterior wall of the maxillary sinus (PM) , anterior wall of the sphenoid sinus (AS), posterior wall of the sphenoid sinus (PS), distal canalicular portion of the optic nerve (ON), carotid artery (CA), and anterior ethmoid artery (AA). The dotted lines (50 and 90 mm) represent the zone of safety. The solid black line (70 mm) represents the critical measurement for accessing the sphenoid sinus.

PM AS PS ON CA AA

Figure 1 Graph illustrating the minimum, maximum, and mean distances (in mm) and standard deviations (bars) from the columnellar base to the posterior wall of the maxillary sinus (PM) , anterior wall of the sphenoid sinus (AS), posterior wall of the sphenoid sinus (PS), distal canalicular portion of the optic nerve (ON), carotid artery (CA), and anterior ethmoid artery (AA). The dotted lines (50 and 90 mm) represent the zone of safety. The solid black line (70 mm) represents the critical measurement for accessing the sphenoid sinus.

More recently, Schaefer was the first to described a "hybrid technique" that combines the conservation goals of the AP approach with the anatomical virtues of the PA approach (26). Surgery begins with identification and complete removal of the uncinate process. If further surgery of the ethmoid sinus is warranted, the maxillary natural ostium is enlarged posteriorly or inferiorly rather than anteriorly to avoid injury to the lacrimal canal. Schaefer notes that this immediately exposes the level of the orbital floor. Like May, Schaefer recognizes the importance of the medial orbital floor as a landmark to facilitate identification of the inferior lamina papyrecea prior to proceeding with an ethmoidectomy. Schaefer advocates removal of the inferior two-thirds of the ethmoid cells in an AP direction using a 0-degree telescope. Often this involves removal of most, if not all, of the basal lamella of the middle turbinate to address the drainage area of the posterior sinuses and to facilitate entry into the sphenoid sinus. If indicated, the sphenoid sinus is entered inferior to the superior turbinate, at a plane between the middle turbinate and nasal septum. If the ostium cannot be visualized or palpated, the sphenoid is entered in the inferomedial quadrant of the anterior wall of the sinus. This approach ensures that the surgeon will maintain a safe distance from the skull base. After the surgeon identifies the sphenoid sinus roof, the superior extent of dissection is determined and the ethmoidectomy is completed more superiorly using a 30-degree telescope.

Schaefer's approach, like May's, recognizes the importance of performing an antrostomy prior to an ethmoidectomy to identify the orbital floor and medial orbital wall. Schaefer was the first to note the importance of performing an inferior ethmoidectomy before proceeding posteriorly, recognizing that this directs the surgeon safely away from the skull base as the orbital wall is followed posteriorly. As the surgeon proceeds posteriorly, it is the orbital wall that dictates the trajectory and not some ill-defined and often distorted lamella or turbinate structure, as advocated

Was this article helpful?

0 0

Post a comment