Sinus Endoscopic Surgery

Anatomy and Physiology

A thorough understanding of the nasal and paranasal anatomy is the key to safe endoscopic sinus surgery. There is a significant variance in the paranasal anatomy among individuals and sides. Therefore, studying computerized tomography and other radiologic studies before surgery is paramount. 

The external nose consists of nasal bones, upper later cartilages, and lower lateral cartilages. The internal part of the nose is divided into 2 nasal cavities by the septum. Each nasal cavity has a medial wall, a vertical septum, and a lateral wall. The crista galli, cribriform plates, and the sphenoid body form the roof of the nasal cavity. The floor consists of the maxilla's palatine process and the palatine bone's horizontal process.[4]

The septum is a rigid structure and consists of bony and cartilaginous parts. The septal cartilage forms the anterior part of the septum. The perpendicular plate of the ethmoid is found postero-superiorly, the vomer postero-inferiorly, and the crest of the maxillary and palatine bones form the base of the septum. The septum is covered by mucosa and has an extensive blood supply between the mucosa and the perichondrium. The arteries that supply the septum consist of the sphenopalatine artery, which is a branch of the maxillary artery; the anterior and posterior ethmoidal arteries originating from the ophthalmic artery; the septal branch of the superior labial artery deriving from the facial artery; and the septal branch of the ascending and more significant palatine arteries branching from the maxillary artery. Little's area is a vascular area where several arteries anastomose and form the Kiesselbach's plexus, a common area of anterior epistaxis.

The lateral nasal wall has bony outgrowths, which are the turbinates. There are 3 to 4 turbinates on each side. The superior, middle, and, if present, the supreme turbinate derive from the ethmoid bone and can contain conchas. As for the inferior turbinate, it derives from a separate bone. The turbinates are covered by mucosa and play a vital role in filtration, humidification, and regulation of inhaled airflow.

Inferior to every concha, there is a nasal passage called the meatus. The inferior meatus is where the nasolacrimal duct drains through the Hasner's valve. The middle meatus is the most complex and is the central passage through which most paranasal sinuses (frontal, maxillary, and anterior ethmoid sinuses) drain. Within the middle meatus, the first lamella that is identified is the uncinate process, which is a projection from the ethmoid and is attached to the lacrimal bone anteriorly, the inferior turbinate inferiorly, and has a 2-dimensional opening posteriorly, also identified as the hiatus semilunaris. The uncinate can have 3 attachments: the lamina papyracea, the middle turbinate, or the ethmoid sinus roof. The hiatus semilunaris is the crescent-shaped space between the ethmoid bulla superiorly and the uncinate inferiorly and is the area where the secretions drain from the sinuses into the nasal cavity; this structure expands antero-superiorly into the ethmoidal infundibulum.

The ethmoid sinuses are bordered by lamina papyracea laterally, fovea ethmoidalis superiorly, and by nasal cavity medially. A basal lamella divides The ethmoid sinuses into anterior and posterior cells. The anterior cells drain in the middle meatus, while the posterior cells drain in the sphenoethmoidal recess of the superior meatus. The most anterior cells, the agger nasi, are located at the superior middle turbinate attachment. The ethmoidal bulla is the largest ethmoidal cell and is always found posterior to the hiatus semilunaris. Posterior to the basal lamella, the posterior ethmoidal cells are found; these are larger in size and smaller in number compared to the anterior cells. The blood supply to the ethmoid sinuses derives from the anterior and posterior ethmoidal arteries, while the venous drainage is directed to the superior ophthalmic vein or pterygopalatine plexus.

The maxillary sinuses are located between the floor of the orbits superiorly, and the alveolar processes of the maxilla inferiorly. The maxillary sinus ostium is located in the medial wall of the sinus and most commonly opens into the posterior third of the ethmoid infundibulum. It is also usually located on the superior aspect of the medial wall; therefore, it is important not to penetrate the sinus superior to the ostium to avoid violation of the medial orbital wall.[5] In up to 43% of cases, accessory maxillary ostium can be seen and can be located in either the anterior nasal fontanelle or the posterior nasal fontanelle. It is crucial to differentiate the maxillary ostium from accessory ostia during FESS and to enlarge the true maxillary ostium. Occasionally, ethmoidal cells can enlarge and expand laterally into the maxillary sinus wall; these cells are also known as Haller cells. The blood supply of maxillary sinuses derives from branches of the maxillary and facial arteries. Venous return that drains into the facial vein or the pterygoid plexus.

The sphenoid sinuses are paired spaces located within the body of the sphenoid bone and separated by a septum. The sphenoid ostium is located in the anterior wall of the sinus and drains into the sphenoethmoidal recess within the superior meatus. The sphenoid sinus is surrounded by several structures, including the internal carotid arteries, the cavernous sinuses, and the optic, vidian, maxillary, oculomotor, trochlear, and abducent nerves. The sphenoid sinus provides a pathway to endoscopically access the skull base, pituitary, optic nerve, and many other structures.[6] Occasionally, sphenoethmoidal cells, also known as Onodi cells, can be found superolateral to the sphenoid and can be closely associated with the optic nerve. Identifying the presence of these sphenoethmoidal cells and their association with the optic nerves and optic nerve dehiscence and dehiscence of the carotid is extremely important to steer clear of catastrophic complications. Blood supply is derived from the sphenopalatine artery, and venous drainage is via the maxillary vein.

The frontal sinuses are the most superior sinuses and are situated between the inner and outer tables of the frontal bones. A septum separates both frontal sinuses. The frontal sinus ostium is located in the medial aspect of the floor of the sinus; it drains into a frontal recess. The drainage of the frontal recess can flow into the ethmoidal infundibulum or medial to it based on the superior attachment of the uncinate.

The recent classification of frontal sinus anatomy includes:

• Anterior cells: Agger nasi, supra agger cells (superior to agger nasi cells), supra agger frontal (extend into the frontal sinus)
• Posterior cells: Supra bulla (above bulla ethmoidalis), supra bulla frontal (above bulla ethmoidalis extending into frontal sinus), supraorbital ethmoid (above the roof of the orbit)
• Medial cells: Frontal septal ( attached or in the frontal septum) [7]

The blood supply derives from the supraorbital and supratrochlear arteries (branches of the ophthalmic artery); the venous drainage is via the superior ophthalmic vein.

Indications

Since functional endoscopic sinus surgery was introduced, the indications for performing this procedure have been expanding. The advances in the endoscopes, the camera, instrumentation, and navigation have laid the groundwork for an ever-expanding world of endoscopic surgery to access the skull base, optic nerve, cavernous sinus, pituitary, orbit, pterygopalatine fossa, and many other spaces and structures. 

The initial and most common indication for FESS is chronic rhinosinusitis. Rhinosinusitis is an inflammatory process of the paranasal sinuses; it is categorized into different groups based on the duration of the inflammatory process:

• Acute rhinosinusitis: Less than 4 weeks
• Subacute rhinosinusitis: between 4 to 12 weeks
• Chronic rhinosinusitis: longer than 12 weeks

These pathologies are some of the most commonly seen conditions by physicians. Sinus disease is also a significant financial burden on the health care system. For instance, there is, on average, a yearly expenditure of $8.3 billion for chronic rhinosinusitis in the United States.[8]

In addition to cost, CRS has a major negative implication on the quality of life of patients emotionally and physically.[9] Diagnosis of CRS should be based on symptoms and objective findings on physical examination using anterior rhinoscopy, nasal endoscopy, or computed tomography scans.[10] Based on the clinical practice guidelines, CRS is initially treated with saline irrigation and/or topical intranasal steroids.[10] When maximal medical therapy fails, the next step is endoscopic sinus surgery. There is still no universally accepted consensus on the criteria for what constitutes maximal medical therapy or on the timing of surgery.[11] The role of surgery in the treatment of CRS with or without polyposis has been studied for many years, and FESS has proven its role in significantly improving the quality of life of patients with CRS.[12]

In addition to CRS, FESS plays a role in the management of complicated acute rhinosinusitis (ARS). Extracranial and intracranial complications of ARS are often categorized according to Chandler's classification. They include, in order of increasing severity, pre-septal cellulitis, orbital cellulitis, subperiosteal abscess (SPA), orbital abscess (OA), and cavernous sinus thrombosis. In preseptal and orbital cellulitis cases, FESS is considered when there is visual impairment or increased intraocular pressure and in situations that do not improve with medical treatment. 

It also plays a fundamental role in managing SPA (especially those >1 cm) and OA. The abscess is drained, the sinuses are opened and drained to restore patency, and cultures are taken for targeted antibiotic therapy.[13] 

Given the intimate association between the ethmoid sinuses and the orbit, Endoscopic Sinus Surgery has also been used to access certain orbital pathologies trans-nasally while avoiding skin incisions. Some of the indications for an endonasal approach to the orbit include decompression of the orbit and optic canal in Graves disease or posttraumatic optic neuropathy, lesions of extraconal medial orbital apex or space, benign sinonasal tumors invading the orbit medially, and medial orbital wall fractures.[14]

ESS has also become the standard procedure for mucoceles, invasive and non-invasive fungal sinusitis, silent sinus syndrome, pituitary tumors, cerebrospinal fluid leaks, benign and malignant sinonasal tumors, and ventral skull base lesions, lesions of the petrous apex, or pterygomaxillary fossa. Expanded sinus surgery plays a role in cases of malignancies in the nasal and paranasal spaces, even for those that extend through the anterior skull base.[15]

Navigation-guided endoscopic sinus surgery has gained much recognition in the world of rhinology. It guides the surgeon intraoperatively based on imaging obtained before surgery. The tracking system in image-guided surgery helps achieve a more thorough and complete dissection of the sinuses, better visualization of tumor borders to get negative margins, and with a lower risk of complications. 

The indications for using the navigation system include:[16]

• Revision sinus surgery
• Distorted sinonasal anatomy
• Benign or malignant sinonasal tumors
• Repair of the cerebrospinal fluid leak; skull base defects or lesions
• Pathologies close to the optic nerve, orbit, carotid artery, or skull base
• Pathologies involving frontal, sphenoid, or ethmoid sinuses
• Extensive polyposis

Contraindications

Contraindications for FESS include patients who have general contraindications for general or local anesthesia.

Also, contraindications for purely endoscopic surgery include lesions/ pathologies extending into the palate, skin/soft tissues, laterally into or above the orbit, lateral recesses of the frontal sinus, or advanced intracranial involvement.[15] In cases with significant extensions, a combined endoscopic and open approach may be required instead.

Equipment

Equipment required in the OR includes a television monitor, navigation system (if being used), camera, sinus endoscopy tray including varied curettes, down-biters, backbiters, elevators, ball-tip probes, through-cut instruments, Kerrison rongeurs, giraffe instruments, sinus forceps with different angulations, punch instruments, endoscopes (0-, 30-, 45-, and 70-degree scopes and reverse scopes), and a powered debrider with straight and angled blades.

Personnel

For Functional Endoscopic Sinus Surgery, a surgeon, typically an otolaryngologist, scrub technician, nurse, and anesthesiologist are needed in the room. In cases of a transsphenoidal approach for pituitary tumors or removal of tumors with intracranial extension, a neurosurgeon is usually present in the room with the otolaryngologist.

Preparation

The patient is placed on the operating table with the table-oriented towards the television monitor. The head of the bed is elevated to have the patient placed in reverse Trendelenburg. The endotracheal tube is secured on the corner of the patient's mouth on the left side.

The patient's eyes are protected with a transparent covering or just partially covered while keeping the medial part accessible to the surgeon, who will be regularly checking for any swelling indicative of orbital hematoma.

Both nasal cavities are initially packed with oxymetazoline-soaked cotton for decongestion. The patient is then draped.

If navigation is being used, imaging obtained before surgery should be uploaded to the system, and registration of the tracking system should be performed and confirmed to be accurate.

Technique or Treatment

A thorough nasal endoscopy is performed using a 0- or 30-degree scope. Then, the lateral nasal wall near the uncinate and the axilla of the middle turbinate are infiltrated with 1% lidocaine with 1:100,000 epinephrine using a 3 ml syringe and 27 gauge needle. Following that, oxymetazoline-soaked cotton pledgetts are placed in the middle meatus (though some surgeons prefer a 4% cocaine solution).

The side to be operated on first is usually the side with more disease or the side that is more open in the case of septal deviation to one side.

Excision of Concha Bullosa

A concha bullosa within the middle turbinate can occasionally be present; excision of this cell is the first step to obtain better access to the lateral nasal wall. An incision in the anterior part of the middle turbinate is performed using a sharp sickle knife, and the lateral part of the turbinate is removed.

Uncinectomy

The middle turbinate is gently medialized using a Freer elevator to access the uncinate process. Uncinectomy can be performed retrograde where the uncinate is identified and medialized off the lamina payracea using a ball tip probe. A backbiter is used to cut the uncinate inferiorly to avoid injury to the medial orbital wall. Blakesley forceps are used to grab and remove the free edge of the uncinate. The remaining uncinate process is removed using biting instruments or the powered debrider until the maxillary ostium is visualized.

Another approach to uncinectomy would be to perform an incision in the uncinate process using a sickle knife or sharp edge of a Freer elevator.

Maxillary Antrostomy

The natural ostium of the maxillary sinus is visualized after removing the uncinate. It is elliptical and found in the lower part of the infundibulum. It is crucial to distinguish the natural ostium from the accessory ostium. The opening to the maxillary sinus is confirmed using a ball-tip probe and is best visualized with a 30- or 45-degree scope. Once confirmed, the natural ostium is enlarged using a through cutting instrument, punch forceps, and powered debrider. The ostium is enlarged posteriorly and inferiorly to avoid injury to the orbit superiorly and the nasolacrimal duct anteriorly.

Ethmoidectomy

Ethmoidectomy can be performed using a 0- or a 30-degree scope. The cell that is first encountered in the ethmoid sinus is the ethmoid bulla. This large cell is penetrated medially and inferiorly using the powered debrider, curette, or punch forceps, or it can be removed retrogradely from the retrobullar space. The lamina papyracea is identified and is recommended to preserve its mucosa. Dissection should be carried posteriorly until the basal lamella is encountered and penetrated. Posterior ethmoid cells encountered posterior to the basal lamella are dissected medially between the middle and superior turbinate and the lamina papyracea laterally. Once the skull base is identified posteriorly at the face of the sphenoid, the dissection of the ethmoid cells is continued superiorly from posterior to anterior, and septations are removed as the dissection moves forward. A 45-degree scope can be used while dissecting the superior cells. It is crucial to identify any dehiscence in the lamina payracea, to identify the ethmoid artery, and identify the skull base with direct vision (or with navigation, if being used) before dissecting superiorly; it is also important not to dissect medial to the superior attachment of the middle turbinate to avoid penetrating the fovea ethmoidalis.

Sphenoidotomy

The sphenoid ostium can be identified either transnasally medial to the middle turbinate or transethmoidally lateral to the middle turbinate. When identified transethmoidally, the sphenoid ostium is found in the inferno-medial part of the posterior ethmoid. The inferior part of the superior turbinate is sometimes removed better to visualize the spheno-ethmoidal recess and the sphenoid ostium. The ostium is identified by gently sliding a probe along the face of the sphenoid. The probe will slide into the ostium once it is reached. Once identified, the ostium is enlarged inferiorly using Kerrison instruments or curettes. The sphenoidotomy can then be widened with a powered debrider. If sphenoethmoidal cells are present, the navigation system should be used to identify these cells, their septations, the skull base, and other surrounding structures such as the optic nerve and carotid artery and identify any dehiscence of these structures.

Frontal Sinusotomy

The frontal sinus is the last to be addressed to prevent bleeding from the frontal recess area, obscuring visualization while working on more posterior and inferior cells. This sinus also has complex anatomy; therefore, navigation is beneficial when approaching the frontal recess. A 45 or 70-degree scope is used for better visualization while dissecting. The posterior wall of agger nasi cells obstructs the outflow of the frontal sinus. It is carefully examined to relieve the obstruction. As mentioned in the anatomy section, the uncinate can have different superior attachments. When the uncinate process attaches to the middle turbinate, the frontal sinus drains into the infundibulum; therefore, the superior part of the uncinate should be removed to gain access to the frontal recess. A registered frontal probe helps identify the frontal recess, and then curved curettes and frontal giraffe instruments are used to remove septations, dissect frontal cells, and widen the frontal recess.

During all steps, sparing the mucosa decreases the risk of scarring postoperatively and of osteogenesis. The middle turbinate's vertical and horizontal attachments should be preserved to avoid destabilization. In the case of destabilization, there is a high risk of lateralization of the turbinate, causing scarring and obstruction of sinus drainage. To avoid lateralization, the anterior part of the turbinate can be removed, suturing of the turbinates to the septum can be performed, or nasal packing can be placed in the middle meatus. These options will help keep the turbinate in a medial position.

At the end of the procedure, any bony septations left are removed, and hemostasis is obtained. A dissolvable nasal pack can be placed as a middle meatus spacer.

Complications

The proximity of the sinuses to critical structures is the main source of complications during ESS.

Orbital Injury

The maxillary sinus and ethmoid sinuses surround the orbit inferiorly and medially. While performing an uncinectomy, staying low and identifying and medializing the uncinate off the orbital wall is important. Also, during maxillary antrostomy, it is important to identify the ostium inferiorly and to find the inferior orbital wall as a landmark. When reviewing the CT scan, the lamina papyracea is studied carefully to identify any dehiscence that could lead to a breach of the orbital wall during an ethmoidectomy. Sphenoethmoidal cells should also be identified, and the optic nerve and carotid should be checked for any dehiscence. Suppose the lamina papyracea is violated, and bleeding occurs. In that case, the periorbita should be examined, and in case of breach and exposure of orbital fat, ophthalmology should be consulted intraoperatively to measure intraocular pressure. If that is elevated, massage of the eye should be performed along with administering mannitol and intravenous dexamethasone. More aggressive management with canthotomy/cantholysis is done if the intraocular pressure is greater than 40 mmHg in an anesthetized patient and if the patient is awake and has retro-orbital pain, cherry red macula, or Marcus-Gunn pupil.[17] Once the canthotomy is performed, the bleeding vessel should be identified, and hemostasis should be obtained. Addressing orbital hematomas should be fast to avoid compression and ischemia of the optic nerve.

Skull-Base Injury and Cerebrospinal Fluid Leaks

The preoperative CT scan is extremely useful to assess the slope of the skull base, the height of the sinuses, its thickness, and the presence of any dehiscence. The length of the lateral lamella varies among patients and sides; the Keros classification helps assess the length and risk of injury.

Keros Classification:

• Keros type I: 1 to 3 mm deep
• Keros type II: 4 to 7 mm deep
• Keros type III: 8 to 16 mm deep

The deeper the lamella is (higher Keros type), the higher the risk of injury to the skull base. The cribriform plate and lateral lamella are the most common sites of injury.

CSF leaks can be spotted intraoperatively or postoperatively.

If a CSF leak is noted intraoperatively, the site should be identified. This is a crucial step to be able to repair the leak and avoid delaying the repair. Delayed exploration leads to a higher risk of infection and longer hospital stays. Once the site of the leak is identified, the area is cleaned to get adequate access and good results. For small defects (<2 mm), overlay autogenous mucosal grafts are used for closure. If the defect is between 2mm and 6 mm, then the middle turbinate can be used as a composite graft (bone and mucosa); as for defects larger than 6 mm, a multilayered reconstruction is performed with cartilage or bone and fibrin glue can be applied.[18][19] Allogenic materials and vascularized flaps can also be used depending on the size and location of the defect.[20] At the end of the procedure, deep extubation helps minimize the Valsalva maneuver and increase intracranial pressure.

CT is obtained to rule out pneumocephalus and intracranial bleeding.

A patient presenting postoperatively with a CSF leak is diagnosed with Beta transferrin, intrathecal fluorescein, and imaging.

Epistaxis

Minimal bleeding for a few days postoperatively is normal, but in cases of profuse bleeding, intervention is needed. The patient should be stabilized, and in cases of severe bleeding, the airway should be protected initially. The nose is examined to identify the site of bleeding. Options for managing epistaxis include topical vasoconstrictors, resorbable or non-resorbable packing, and cautery ( silver nitrate or electrocautery). In severe cases with persistent and recurrent bleeding not controlled with the previously mentioned options, surgical arterial ligation or endovascular embolization is considered the next step.[21] The surgeon should have a thorough knowledge of the anatomy of the blood supply to the nasal cavity. The sphenopalatine artery enters the nasal cavity through the sphenopalatine foramen (SPF) located at the posterior end of the middle turbinate; this artery can be ligated in cases of severe posterior epistaxis.

Disease Recurrence Disease

When FESS is performed for CRS, there is always a risk of recurrence or persistence. Failure to perform a proper maxillary antrostomy and widen the natural ostium can lead to mucus recirculation through the accessory ostium.

Lateralization of the middle turbinates leads to obstruction of sinus drainage. Due to inadequate postoperative cleaning and management, Synechiae is another cause of nasal obstruction post-sinus surgery. Excessive mucosa removal, bone exposure, and failure to remove bony septations are all possible causes of the recurrence of rhinosinusitis.

Clinical Significance

Functional endoscopic sinus surgery is the most commonly performed procedure for CRS. With the availability of fine instruments and high-resolution imaging, rhinologists can now dissect and open sinuses more aggressively. However, rhinologists should not only rely on imaging studies, navigation, and instruments; they should understand the anatomy and be mindful of all the possible complications, the minor and the major. Safe operation requires following the steps of FESS and identifying the constant landmarks at every stage.

Enhancing Healthcare Team Outcomes

Functional endoscopic sinus surgery and technical advances in imaging, instrumentation, and navigation are in constant progress. With a better resolution and more detailed images, the application of FESS is spreading into the intracranial and oncological worlds. The group of multidisciplinary providers involved depends on the pathology and its extension. It can include rhinologists, neurosurgeons, oncologists, endocrinologists, pulmonologists, ophthalmologists, and allergy specialists.

A delicate stepwise technique following the anatomical landmarks guides the surgeon throughout the procedure and helps avoid possible complications. For patients with CRS, the 2 main intraoperative goals are to restore patency of the sinuses while preserving mucosa and to prevent injury to the surrounding structures.

Postoperative care is as essential as the applied technique to decrease the risk of recurrence of CRS. Medical therapy with nasal rinsing, topical or oral corticosteroids, and antibiotics are continued postoperatively to reduce the inflammation and the risk of recurrence. There is no clear consensus on the role of postoperative debridement in decreasing the risk of recurrence of disease and adhesions. It depends on the surgeon's preference, the inflammation level, and the surgery's extent.[22][23]