CHAPTER 52 Concepts of Endoscopic Sinus Surgery

Causes of Failure

• The concept of functional endoscopic sinus surgery is to surgically remove inflamed tissue and involved bone from critical points in the mucociliary clearance pathways.

• Chronic rhinosinusitis is a disease of inflammation, and therefore the successful approaches to treatment, including surgery, are directed at that inflammation.

• In the overall spectrum of radical to minimal surgery of the sinuses, the successful practitioner of functional endoscopic sinus surgery is somewhat radical in the involved regions of the ethmoid cavity, removing all partitions while carefully leaving a mucosa-lined cavity on the skull base and medial orbital wall.

• In appropriately selected patients, the long-term success rate of functional endoscopic sinus surgery, combined with appropriate medical therapy, is 80% to 90%.

• Absolute indications for surgery in sinus disease include the development of complications of rhinosinusitis, expansile mucoceles, allergic or invasive fungal rhinosinusitis, and suspected neoplasia.

• Relative indications for surgery in inflammatory rhinosinusitis include the presence of symptomatic nasal polyps that are unresponsive to medical therapy and symptomatic chronic or recurrent acute rhinosinusitis that persists despite appropriate medical therapy.

• Anatomic variations are no longer considered important in the pathogenesis of chronic rhinosinusitis, as was previously believed.

• Poor indicators of successful functional endoscopic sinus surgery include persistent environmental exposures after surgery, uncontrolled allergies, continued chemical exposures, and smoking.

• Prior to surgery, the computed tomography scan must be reviewed and the relevant anatomy conceptualized by the surgeon so as to decrease complications and minimize surgical trauma.

• Postoperative medical care augmented by endoscopic examination and débridement as necessary is required for success.

The hallmark of chronic rhinosinusitis (CRS) is inflammation, which may be incited by many different mechanisms. Therefore, therapies used for treatment of CRS are aimed at the inflammation and the inciting factors causing that inflammation rather than specifically at disease identified on imaging. In many cases microbial contamination is a significant factor in this inflammatory process. Chronic or recurrent bacterial infection with or without fungal presence is associated with a change in the inflammatory profile and an inability of the body’s own mucociliary clearance mechanisms to function normally, giving rise to the symptoms of CRS. Unfortunately, medical therapy alone directed at this inflammation may be unable to clear the disease, and surgical treatment of what is ultimately an inflammatory disease is considered after failure of medical treatment. Small areas of persistent inflammation that are poised at critical areas can block mucociliary clearance and allow further inflammation to appear at those distal areas. Removing the inflamed mucosa and bone of the obstructed area allows appropriate drainage of the distal sinuses. Therefore the concept of functional endoscopic sinus surgery (FESS) is to surgically remove inflamed tissue from critical points in the mucociliary clearance pathways.

The extent of surgery is somewhat flexible in the overall concept of FESS—that is, the extent of surgery performed, the number of sinuses opened, and the inflamed diseased mucosa and bony partitions removed depend on the amount of disease identified on preoperative evaluation. It is therefore not a “one size fits all” operation but, rather, a procedure that is tailored to each patient’s set of findings from history, endoscopy, and radiologic evaluation. Optimally, surgery removes diseased bone and mucosa in the critical areas, with the recognition that the more distal linings of the maxillary, ethmoid, sphenoid, and frontal sinuses do not contain “condemned” mucosa, as was once taught. In the overall spectrum of radical to minimal surgery, the successful practitioner of FESS is probably somewhat radical in removing all bony partitions in areas of the ethmoid cavity involved in the disease process but is also able to preserve a mucosa-lined cavity on the skull base, medial orbital wall, and middle turbinate (Fig. 52-1).

Figure 52-1. Computed tomography scans of a patient with an ethmoid mucocele. A, A middle meatal antrostomy has not been performed on the patient’s right side. B, Scan taken 1 year after surgical drainage of the mucocele and middle meatal antrostomy demonstrates clearance of the ostiomeatal complex.

It should be noted that the importance of the ostiomeatal unit was highlighted in the early years of FESS as a critical final common pathway in the disease process.¹^–³ Appropriate surgery in this critical area was found to have exceptionally good results in reversing patient symptoms, with positive outcomes in 80% to 90% of patients.^4,⁵ However, over subsequent years, anatomic abnormalities in the ostiomeatal complex (OMC) came to be seen by some as the underlying cause of sinusitis, and not merely as a critical point in disease pathogenesis—that is, as a “bottleneck” for the sinonasal drainage pathways. The overemphasis of the importance of the role of the OMC in CRS led to an inappropriate overemphasis on surgically correcting abnormalities in the OMC. Anatomic variations should be regarded only as potential predisposing or potentiating factors in CRS, and not the underlying etiology of the disease; therefore appropriate surgery is only an adjunct treatment for chronic and recurrent rhinosinusitis, not primary therapy.

As discussed, surgery plays an adjunctive and important role in the treatment of rhinosinusitis, but medical therapy is the cornerstone of management of inflammatory disease.⁶ CRS is a multifactorial disease. The underlying pathogenesis can be broken into categories of causes that are environmental, generalized host factors, or local host factors. Environmental issues include smoking, allergy, mold/fungus exposure, and, possibly, emotional stress. General host factors include reactive airways disease, Samter’s triad, and genetic influences such as immunodeficiency. Local host factors include iatrogenic disease, nasal polyps, and diseases of poor mucus transport. Except in the cases of potential complications such as an expansile mucocele, the adjunctive procedure of surgical intervention (FESS) should be instituted when appropriate environmental control and medical therapy have failed. Continued medical therapy is usually required after surgery to avoid disease recurrence, and failure of the original surgery is often associated with abandonment of the basic concepts of FESS.

Extent of Surgery

Debate about the appropriate extent of surgery for CRS will most likely continue until the pathogenesis is better understood. However, the concept of “irreversibly diseased” or “condemned” mucosa that requires surgical removal is incorrect. In fact, Moriyama and colleagues ⁷ have shown that denuding of bone results in extremely delayed healing. The bone may remain exposed for 6 months or more, and ciliary density may never return to normal at these sites. The underlying bone of an area of stripped mucosa is also prone to long-term inflammation and is a cause of failure, especially when associated with narrow areas such as the frontal recess. Therefore great emphasis should be placed on mucosal preservation in all sinuses during surgery, especially within the ethmoid sinus, owing to its central position in the paranasal sinuses.

The initial understanding of FESS has been modified, on the basis of continued improvement of the understanding of the disease process. Simply draining involved cells or sinuses may be insufficient in chronic disease. The surgery should be extended one stage beyond the diseased mucosa, which is identified either by computed tomography (CT) or at the time of surgery. Close endoscopic observation of postsurgical healing cavities led us to suspect that the underlying bone may play a significant part in the overall chronic disease process. The inflammatory aspects of the disease usually persist in localized areas, and the disease tends to recur at that same site.⁸^–¹⁰ The inflammation of the mucosa typically resolves after the underlying bone is resected, but it will not improve if only the inflamed mucosa is removed. In experimental animals there is evidence of early bone involvement in sinusitis; chronic osteomyelitis and inflammation spread within the haversian canals of bone despite an inability to demonstrate the organisms within the bone. These clinical and experimental findings lead us to believe that resection of inflamed bone is important to the success of FESS. We hold that reduced viability and inflammation of the underlying bone may be a significant factor in the disease process, at least in more severe cases of CRS.

Because of the inflammation in the bone, the underlying osteitic bony partitions should be removed as completely as possible from the sites of mucosal disease involvement during surgery. In addition to the fact that these partitions may potentiate persistence of the disease, they tend to thicken up in the presence of persistent and ongoing inflammation, making them less easy to remove. Removal of these osteitic partitions is especially important in the uncinate process and partitions of the ethmoid sinuses. Advocates of transition space or minimally invasive surgical therapy (MIST) recommend removing only enough tissue to allow sinus ventilation and mucociliary clearance. There are good aspects to this concept, owing to its advocacy of meticulous atraumatic and mucosal preservation techniques. However, there is also significant concern that the MIST approach is suitable primarily in children and, in adults, for early and mild disease that might be better treated by aggressive medical therapy. The current recommended approach in adults tends toward more complete removal of the underlying bony partitions in the areas where the mucosa is involved with disease with preservation of both the normal mucosa and the mucoperiosteal layer over any remaining bone. The avoidance of leaving exposed bone is an important goal, especially in areas prone to scarring and stenosis.

Surgical Indications in Inflammatory Disease

Absolute indications for surgery in sinus disease include the development of complications of rhinosinusitis, expansile mucoceles, allergic or invasive fungal rhinosinusitis, and suspected neoplasia. Relative indications for surgery in inflammatory rhinosinusitis include the presence of symptomatic nasal polyps that are unresponsive to medical therapy and symptomatic chronic or recurrent acute rhinosinusitis that persists despite appropriate medical therapy.

As discussed, there are several absolute indications for surgical intervention in sinus disease, but there are essentially no absolute indications for an endoscopic approach rather than other endonasal or external operations. Several publications have demonstrated both better results and lower morbidity with FESS, and therefore it is normally the approach of first choice in CRS. Patients with recurrent acute rhinosinusitis benefit from endoscopic surgical intervention when low-grade mucosal disease persists between episodes. The relation between anatomic variations and recurrent disease is more controversial, but it is reasonable to consider surgery when such obstructing anatomic variations correspond to the area of recurrent symptomatology.

Chronic Rhinosinusitis

In evaluating patients with CRS, it is worthwhile to identify on evaluation some overall factors that are associated with good and poor outcomes. Good outcomes are associated with less severe total mucosal disease and associated obstructive abnormalities that can be corrected. A decision to intervene surgically is relatively easy in patients with persistent severe symptomatic sinus disease despite medical treatment or in patients with impending complications. Nasal obstruction and nasal congestion, the most common symptoms of uncomplicated ethmoid sinusitis, normally respond well to surgery. Additionally, a history of severe pain with pressure change during air travel is strongly suggestive of sinus obstruction that often has a good outcome from surgery.

Headache or facial pain alone requires careful evaluation. In the absence of symptoms of nasal congestion, obstruction, and postnasal drainage, a surgeon should be very cautious about ascribing a complaint of pain to sinus disease. Additionally, several publications have demonstrated a radiographic incidence of mucosal thickening of between 30% and 50% in patients undergoing CT for indications other than sinus complaint. However, it should be noted that the normal sinus mucosa appears to be more sensitive than chronically thickened mucosa to pain from ostial obstruction. Thus, localized, minor ostiomeatal disease may result in severe pain in a dependent sinus, whereas it is less common for a patient with massive polyposis to identify marked facial pain or headache as a major complaint.

Several identified factors are associated with poor outcomes from FESS for CRS. Poor indicators of successful FESS include persistent environmental exposures after surgery, uncontrolled allergies, continuing chemical exposures, and smoking. Allergic patients with middle meatal and OMC disease may be relatively protected from their environmental allergens by their disease; after surgery, however, virgin mucosa is widely exposed to nasal airflow. Cigarette smokers have such bad outcomes with FESS that smoking is a relative contraindication to elective ESS. In patients who continue to smoke, a significantly greater than usual amount of granulation tissue develops over any areas of exposed bone, and the incidence of frontal recess stenosis is higher. In a long-term follow-up study, smoking was the most significant factor in the need for revision surgery and a significantly greater factor than prior surgical procedures, allergies, and asthma in determining the need for revision surgery.¹¹^–¹³

Complicated Acute Rhinosinusitis

Endoscopic sinus surgery has been demonstrated to be effective in acute rhinosinusitis that is not resolving with appropriate medical therapy and in cases with threatened or established complications. However, certain cautions must be observed in performing surgery in acute disease. The acutely inflamed mucosa tends to be hyperemic and to bleed easily, with greater potential for the intraoperative bleeding to obscure surgical vision. This difficulty with surgical vision is also complicated by the fact that if a diseased cell is not opened, such an omission can be serious or even life-threatening. Thus, it is important that the surgeon be very skilled in endoscopic surgical techniques undertaking an endoscopic surgical procedure for orbital or intracranial complications of sinusitis. In some cases, a surgeon chooses to perform the operation in acute sinusitis through an open approach to ensure that all cells targeted are cleared of disease and to avoid potential complications such as entry into the orbit.

Mucoceles

In general, the functional endoscopic approach is of most benefit when extensive sinus disease results from a limited cause. Thus, frontal sinus obstruction resulting in an extensive frontal sinus mucocele with posterior table erosion is an ideal case for endoscopic intervention. Such an approach maintains the bony framework of the frontal recess and allows wide marsupialization with minimal morbidity. Indeed, in the presence of posterior table erosion, sinus obliteration is not a good alternative because of the difficulty of completely removing the lining mucosa from exposed dura (Fig. 52-2).

Figure 52-2. A, Preoperative computed tomography scans of a patient who presented with frontal lobe compression symptoms. The massive, long-standing frontal sinus mucocele had eroded bone. B, The mucocele was treated by endoscopic drainage, as can be seen in these scans, which demonstrate an open draining cavity at 6 months after surgery.

Preoperative evaluation of the patient with frontal sinus mucocele should include careful evaluation of the lesion relative to the skull base. At surgery, the skull base is identified within the posterior ethmoid and then followed anteriorly until the bone of the lesion is identified and the inferior portion removed. It is important that all the osteitic bone be removed from the region of the obstruction. If the bony margins are not made flush with the surrounding wall, narrowing of the opening due to scarring and even closure of the opening may occur. Occasionally upon surgical entry into the lesion, clear fluid drainage may be identified, raising suspicion of a cerebrospinal fluid leak. It appears that this fluid, assuming an intact skull base, represents marked hypersecretion from the mucosa of the lesion.

In the postoperative period, the mucosa lining the mucocele cavity may undergo significant hypertrophy, and secretions may reaccumulate, necessitating suctioning from time to time. However, mucociliary clearance becomes re-established, typically in a few weeks, and the mucosal hypertrophy resolves over time.

Fungal Rhinosinusitis

Fungal rhinosinusitis is classifiied as invasive or noninvasive. Fungal balls and allergic fungal rhinosinusitis are categorized as noninvasive fungal rhinosinusitis. Invasive fungal rhinosinusitis includes both chronic invasive fungal rhinosinusitis and the more common fulminant invasive disease that occurs in the immunosuppressed patient.

Complete removal of a fungal ball results in resolution of the disease, although associated bacterial sinusitis is often also present and frequently requires antibiotic treatment. Fungal balls can usually be removed from the maxillary sinus with a curved suction through a very wide middle meatal antrostomy. If the mass cannot be satisfactorily removed in this fashion, a canine fossa trocar can be introduced and used as a spoon to scoop the mass toward the antrostomy. Angled telescopes (45- and 90-degree) are required for looking into the sinus transnasally to ensure that the mass has been adequately removed.

Allergic fungal rhinosinusitis may be associated with marked bone remodeling that may distort anatomic relations dramatically. In addition to dural exposure, erosion of bone and displacement of the optic nerve and carotid artery may occur when the disease involves the sphenoid or posterior ethmoid sinuses (Fig. 52-3). The aim of surgery in allergic fungal rhinosinusitis is complete removal of all of the inspissated material and polypoid mucosa. It is important to achieve complete removal of the intersinus partitions throughout the ethmoid and sphenoid cavities as well as a very wide middle meatal antrostomy and wide frontal sinusotomies. However, as in all surgery for inflammatory disease, care should be taken to maintain mucoperiosteal coverage of the bone within the cavity. Intensive medical therapy, both preoperative and postoperative, is important for success.¹⁴