“Functional” endoscopic sinus surgery (FESS) is based on the logic that removing cause of obstruction to normal mucociliary clearance in the area of the Ostiomeatal Unit (OMU) will lead to subsequent clearance of secondary disease and restoration of normal mucociliary clearance. This is in contrast to more extensive interventions in which nearly all accessible mucosa is debrided. Although this is sometimes necessary, as in severe nasal polyposis, such extensive procedures usually are not required and add to the overall risk of complications. Endoscopic sinus surgery is most commonly performed for inflammatory and infectious sinus disease. Endoscopic surgery is planned preoperatively by nasal endoscopy and CT imaging, the gold standard of which is the high resolution CT in coronal plane which accurately images the OMU including its drainage pathways.
Preoperative imaging helps to identify unsuspected old fractures or congenital deformities that distort anatomy and predispose the orbit, optic nerves, and carotid arteries to injury during FESS and acts as a roadmap to the endoscopic surgeon. High-resolution CT scanning with thin coronal slices provides the most useful surgical information because the orientation of the anatomy is similar to the orientation of the anatomy encountered in FESS. Axial images do not show certain ostia as well as the coronal projection but can still provide additional information. Most protocols for CT scanning of the sinuses use a coronal position with slices 2-3 mm in thickness along with axial images. Some institutions use thin-section axial CT images that are reformatted in the coronal projection. Reformatted images in the coronal plane have less spatial resolution in the superior-inferior direction than direct coronal scans. However, these images may be digitized and downloaded to an intraoperative computer for virtual reality display, superimposing them over the direct endoscopic images seen by the surgeon. Dental metallic devices are one of the most significant causes of CT scan degradation. These devices cause considerable streak artifacts that obscure the nasal cavity and sinus anatomy. When streak artifacts degrade direct coronal scans, inversion of black and white may help. Bone is changed from its normal white to black, and air is changed from its normal black to white. Thus, white air channels and spaces are easier to visualize, and streak artifacts have been inverted to black, making them less obvious. Conversion of all sinus scanning to coronal imaging and CT scanning may prevent diagnosis of nasal cavity neoplasms. In the absence of bone destruction, a neoplasm may be mistaken for a nasal polyp, whereas on MRI, the nature of this tumor is quite apparent.
Beyond anatomic variants, anything suspicious should be imaged by means of MRI. Despite the advances of MR, insufficient tissue, plus the problems of susceptibility due to the air-containing passages, make MR a less effective study for nasal cavity sinusitis problems, unless of course the sinusitis turns out to be related to squamous cell carcinoma.
Indications : Endoscopic sinus surgery is most commonly performed for inflammatory and infectious sinus disease. The most common indications for endoscopic sinus surgery are as follows:
Ø Chronic sinusitis refractory to medical treatment
Ø Recurrent sinusitis
Ø Nasal polyposis
Ø Antrochoanal polyps
Ø Sinus mucoceles
Ø Excision of selected tumors
Ø Cerebrospinal fluid (CSF) leak closure
Ø Orbital decompression (eg, Graves ophthalmopathy)
Ø Optic nerve decompression
Ø Dacryocystorhinostomy (DCR)
Ø Choanal atresia repair
Ø Foreign body removal
Ø Epistaxis control
Contraindications of FESS: Certain conditions may require an external approach for complete treatment of disease; these include intraorbital complications of acute sinusitis, such as orbital abscess or frontal osteomyelitis with Potts puffy tumor. An open approach in these instances, with or without additional endoscopic assistance, may be preferable. A careful review of the preoperative CT scans films helps to guide the surgeon. Relevant Anatomy for the Radiologists: The floor of the nasal cavity is the hard palate. The lateral walls contain spiral-shaped mucosal folds overlying concha-shaped bone called turbinates and various sinus-drainage ostia. The roof is composed of the cribriform plate in the middle with the ethmoid air cells on either side. The nasal cavity is separated into halves by a midline, which is a partially bony and partially cartilaginous nasal septum that, unlike the lateral walls, is lined by squamous epithelium.
The Paranasal sinuses: Paired frontal, maxillary, ethmoid, and sphenoid sinuses surround the nasal cavity. Ethmoid sinuses form the roof, and maxillary sinuses form the walls. The major draining ostia are the anterior ostiomeatal complexes or unit (OMC or OMU) which drains the bilateral frontal and maxillary sinuses and the anterior and middle third of the ethmoid sinuses. The uncinate process (UP) and lateral wall of the nasal cavity form the ethmoid infundibulum (EI). The above sinuses drain into the EI via various ostia. The maxillary sinus ostia and the frontal sinus recess or duct drain into the anterior most portion of the OMC and are consistently identifiable on CT scan.
The most common cause for frontal and maxillary sinusitis is anterior ethmoid disease and a superimposed rhinitis, whether viral or bacterial. Clearing or treating anterior ethmoid disease clears frontal and maxillary sinusitis. The inferior turbinate extends along the inferior lateral nasal wall posteriorly toward the nasopharynx. The inferior meatus, where the naso lacrimal duct opens, is located approximately 1 cm beyond the most anterior edge of the inferior turbinate. As the endoscope is advanced into the nose, the most important structure encountered is the middle turbinate. The middle turbinate is a key landmark in endoscopic sinus surgery. It has both a vertical component (lying in the sagittal plane, running from posterior to anterior) and a horizontal component (lying in the coronal plane, running from medial to lateral). Superiorly, the middle turbinate attaches to the skull base at the cribriform plate. As such, care should always be taken when manipulating the middle turbinate. The horizontal component of the middle turbinate is referred to as the basal (or ground) lamella, and it represents the dividing point between anterior and posterior ethmoid air cells. Posteriorly and inferiorly, the middle turbinate attaches to the lateral nasal wall at the crista ethmoidalis, just anterior to the sphenopalatine foramen. The uncinate process (UP) is the next key structure to be identified in endoscopic sinus surgery. This L-shaped bone of the lateral nasal wall forms the anterior border of the hiatus semilunaris, or the infundibulum. The infundibulum is the location of the ostiomeatal complex, where the natural ostium of the maxillary sinus opens. Once the uncinate process is removed, the natural maxillary ostium can be seen, typically just posterior to the uncinate process. The natural maxillary ostium is the destination for the mucociliary flow within the maxillary sinus. Therefore, for optimal results, the surgically enlarged maxillary antrostomy must include the natural ostium. In fact, failure to include the maxillary ostium in endoscopic surgical antrostomy is one of the key patterns of failure in functional endoscopic sinus surgery. The maxillary sinus is bordered superiorly by the inferior orbital wall, medially by the lateral nasal wall, and inferiorly by the alveolar portion of the maxillary bone. The next structure to be encountered is the ethmoid bulla, which is one of the most constant anterior ethmoidal air cells. It is just beyond the natural ostium of the maxillary sinus and forms the posterior border of the hiatus semilunaris. The lateral extent of the bulla is the lamina papyracea. Superiorly, the ethmoid bulla may extend all the way to the ethmoid roof (the skull base). Sometimes, a suprabullar recess may exist above the roof of the bulla. A careful preoperative review of the patient’s CT scan clarifies this relationship. The ethmoid sinus consists of a variable number (typically 7-15) of air cells. The most lateral border of these air cells is the lamina papyracea, and the most superior border of these cells is the skull base. Supraorbital ethmoid cells may be present. Anterior ethmoid cells drain to the middle meatus, and the posterior cells drain into the superior meatus. The sphenoid sinus is the most posterior of the paranasal sinuses, just superior to the nasopharynx and anterior and inferior to the sella turcica. Several important structures are related to the sphenoid sinus. The internal carotid artery is typically the most posterior and medial impression seen within the sphenoid sinus. In approximately 7% of cases, the bone is dehiscent. The optic nerve and its bony encasement produce an anterosuperior indentation within the roof of the sphenoid sinus. In 4% of cases, the bone surrounding the optic nerve is dehiscent. Therefore, guarded opening of the sphenoid sinus, typically at its natural ostium, is critical for a safe outcome. The location of the natural ostium of the sphenoid sinus is variable; approximately 60% are located medial to the superior turbinate, and 40% are located lateral to the superior turbinate. The frontal recess, or the frontal outflow tract, is the tract that leads from the frontal sinus into the nasal cavity. Often, the ethmoid bulla is the posterior border of the frontal sinus outflow tract. Anteriorly, the frontal sinus outflow tract is bordered by the uncinate process or the agger nasi cells (frontal anterior ethmoid air cells). If any of these cells are enlarged or if scarring is present from a previous surgery, resultant outflow tract obstruction, leading to frontal sinusitis, may occur. Typically, the medial wall of the frontal recess is formed by the lamina papyracea. Intimate knowledge and understanding of the anatomy, in conjunction with a careful preoperative review of CT scans, are paramount in the safe and complete performance of endoscopic sinus surgery.
VARIATIONS OF NORMAL ANATOMY: The uncinate process (UP) anomalies are by far the most common anomalies encountered in the nasal cavity in individuals with chronic sinusitis. UP anomalies include elongated, lateral or medial deviation, and others.
– Elongation: The most common anomaly is elongation and apparent fusion of the UP tip to the floor of the ethmoid sinus However, although the semilunar hiatus appears to be absent, the maxillary sinus is fully developed. In FESS, the UP is not really fused and can still be surgically removed. This common distortion of the anatomy further restricts outflow of secretions by markedly narrowing the semilunar hiatus.
Lateral deviation :If the UP tip fuses to the inferomedial floor of the orbit, the maxillary sinus ostium is absent. In addition, the UP tip is deviated in a lateral direction. This fusion is real and congenital in nature. As a result, no semilunar hiatus exists; therefore, no communication occurs between the maxillary sinus and the middle meatus. The EI ends in a blind pocket (i.e., recessus terminalis). The sinus is usually hypoplastic and nonaerated and therefore has never developed. The usual surgical incision at the base of the UP in FESS would result in direct orbital injury. The UP tip can also fuse directly to the lateral wall or lamina papyracea of the orbit, producing the same findings. –
-Medial deviation :If the UP is deviated in a medial direction, it obstructs airflow into the middle meatus and may compress the mucosa of the nasal turbinate. The EI is patent and most likely communicates directly with the ethmoid ostia, thereby linking the maxillary sinus directly to the ethmoid sinuses.
– Pneumatization of the UP tip is another common anomaly. It expands the tip and may compromise the EI and semilunar hiatus. – Spurs: In rare cases, a spur may arise from the UP and compromise the EI or middle meatus, depending on which way the spur tilts.
–Absence of uncinate process: Rarely, the UP may be absent entirely. The endoscopist may mistakenly incise the lateral maxillary sinus wall or, more importantly, the medial and inferior walls of the orbit, resulting in injury to the orbital contents.
– Onodi Cell :is a posterior ethmoid cell that has encroached upon the area of the sphenoid sinus. It is of considerable significance because in a large majority of these, a frankly dehiscent optic nerve, carotid artery or both may be present in variable locations. Several other variants have been described. Among these are the uncinate bulla, which although relatively infrequent, may alter the anatomy at the OMC. Others include Bulla Gali (5.4%), pterygoid pneumatization (43.6%), and anterior clinoid pneumatization (13.3%). Preoperative recognition of these variations is useful as these at times may require special attention in order to prevent postoperative recurrent disease, and more importantly, complications by allowing the surgeon to better estimate the limits of resection.
CONCHA ANOMALIES : Concha anomalies are probably the most common anatomic variant of the nasal cavity, even more common than those of the UP. However, only a few concha anomalies lead to airway obstruction and chronic sinusitis with its attendant complications. – Pneumatization: The most common anomaly is pneumatization of the concha, which is called a concha bullosa. As the name implies, portions of the concha are aerated; this occurs either in the vertical portion that attaches to the cribriform plate or lateral nasal cavity walls or in the concha or curved (shell-like) portions of the concha. Most cases of concha bullosa involve the middle turbinate, but the superior turbinate can also be involved. To date, concha bullosa of the inferior or supreme turbinate has not been reported. Pneumatization of the vertical or conchal portion is usually of no clinical significance. However, if the conchal portion of the middle turbinate is expanded significantly, the concha may compress or deviate the UP against the lateral wall of the nasal cavity and narrow the EI. Likewise, overexpansion compresses the middle meatus into which the ethmoid infundibula drain. Therefore, concha bullosa can also be assified into the group of lesions that narrows the EI.
– Paradoxical turbinates : Another anomaly of the nasal cavity with the potential for airway compromise and chronic sinusitis is the paradoxical turbinate. As with the concha bullosa, the most significant paradoxical turbinates involve the middle turbinate. Normally, the curved portion of the turbinate concha is adjacent to the nasal septum or points toward the septum. If the curve is exaggerated enough, it compresses and deviates the UP toward the lateral nasal cavity wall, compromising the EI. Usually, the paradoxical turbinates occur where the mucosa is hyperplastic. The overgrowth causes the mucosa to buckle and fold inward, with the resultant curve pointing toward the septum. The curved portion of the more posterior portion of the turbinate is typically directed toward the nasal septum. Occasionally, the concha mucosal portion may be deformed where the mucosa starts to fold inward and resembles a boxing glove with the knuckle portion directed toward the floor of the nasal cavity.
– Accessory turbinates: The presence of accessory turbinates is another anomaly that most often occurs in the region of the middle turbinates. Like the main turbinates, the accessory turbinates have a curved surface and a thin, inner, shell-like, bony structure. The bony structure contained within allows this anomaly to be differentiated from polyps that lack the bony portion. The accessory middle turbinates are either attached to the lateral nasal cavity wall or to the floor of the ethmoid sinus. Usually, the accessory turbinates are too small to compromise the airway.
– Duplicate turbinates : Another rare anomaly is a duplicate turbinate, in which 2 of the same turbinate occupy the same region. The vertical and conchal portions are exact copies of the original turbinate. When this occurs in the region of the middle turbinate, the presence of the additional turbinate can narrow and compromise the EI.
– Turbinate-to-turbinate attachment : Attachment of the turbinate to another turbinate, and not the lateral wall of the nasal cavity, is another and even more rare anomaly. Spur can arise from the turbinate and may interfere with the airflow, depending on its location.
OTHER CAUSES OF ETHMOID INFUNDIBULAR NARROWING:
Haller air cell expansion :Haller air cells occur along the inferomedial orbital wall and, if expanded, can narrow the EI at the maxillary sinus ostia. Controversy exists over what constitutes a Haller air cell. Generally, the Haller air cell is related to the inferior medial wall/floor of the orbit. The Haller air cell has been suggested to simply be an over expanded ethmoid air cell. – Giant ethmoid bulla .: Overexpansion of the ethmoid sinuses or bulla (i.e., giant ethmoid bulla) is possible In this situation, downward bowing of the floor of the ethmoid sinus occurs, such that it encroaches on and narrows the semilunar hiatus. The downward bowing can also displace the UP in a lateral direction and narrow the EI. -Nasal polyps : Nasal polyps can also affect the EI. Most nasal polyps arise from the region of the anterior ethmoid air cells and in relation to the UP, middle turbinate, and EI. Nasal polyps also originate from the anterior aspect of the ethmoid floor. In this location, the mass effect from the polyp can compromise the semilunar hiatus, extend into the EI, or extend medially between the UP and middle turbinate, occluding the middle meatus. Polyps tend to arise from areas where opposing mucosal surfaces are in contact with each other. In this sense, the UP anomalies with the mucosal surface contact may be a causative agent for polyp development. The soft tissue mass of nasal polyps obliterates the airways and makes CT interpretation difficult, particularly if the entire nasal cavity is filled with soft tissue. If large enough to cause bony changes, the nasal cavity polyp displaces the medial wall of the maxillary sinus in a lateral direction.
–Choanal polyps : Choanal polyps are a special subclass of polyps, arising from the maxillary sinus posterior or lateral walls. The polyp can initially grow into the maxillary sinus ostia and then into the EI, causing obstruction. Because of their origin with the maxillary sinus, choanal polyps displace the medial wall in a medial direction into the nasal cavity.
OTHER ANATOMIC CONSIDERATIONS IN FUNCTIONAL ENDOSCOPIC SINUS SURGERY : Anatomic variations that do not lead to chronic sinusitis are also important for the endoscopists because they pose potential injury to the patient.
1.Fractures :Old fractures of the orbit or dehiscence of the lamina papyracea allow herniation of orbital contents into the ethmoid sinus, most notably orbital fat or middle rectus muscle. These structures and the arteries may be injured during FESS if the surgeon is unaware of these anatomic distortions. The herniated orbital contents are encountered after the UP is removed, the floor of the ethmoid sinus (bulla) is pierced, and the ethmoid sinus is entered.
2. UP anomalies: include fusion of the UP to the orbit wall or floor and absence of the UP. Fusion to the orbit may cause the endoscopist to inadvertently enter the orbit, injuring its contents during an attempt to resect the UP. Absence of the UP may cause the endoscopist to incorrectly identify the orbital wall or floor as the process, also leading to injury of the orbital contents. 3 Absence of basal or ground lamella
3.Absence of the basal or ground lamella is problematic only if FESS of the posterior OMC is being considered. Once the UP has been surgically removed, the endoscopist then punctures the floor of the ethmoid sinus. The basal or ground lamella separates the anterior two thirds of the ethmoid air cells from the posterior third. If the basal lamella is absent, the endoscopist may mistake the cribriform plate for the basal or ground lamella.
4.Bony septa: Other anomalies related to FESS of the posterior OMC include bony septa in the sphenoid sinus that attach directly to the bony carotid sulcus in the outer walls of the sphenoid sinus. Removing these septa may injure the carotid artery by fracturing the sulcus. Extensive skull base pneumatization may cause the Vidian nerve within the Vidian canal to appear as a bony elevated ridge that seems to float above the floor of the sphenoid sinus. What appears to be another bony septum contains the Vidian nerve. Injury to this nerve mainly affects tearing.
5. Accessory turbinates : Accessory turbinates may be mistaken for polyps or, if large enough, for 1 of the 3 major turbinates. Choosing the wrong turbinate causes the endoscopist to be in the wrong meatus. However, most of these accessory turbinates are small.
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