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Over the past three decades there has been great evolution in nose and paranasal sinus surgery compared with classical approach techniques that have been used. Interest in nasal anatomy dates to practitioners in ancient Egyptian (c. 1500 B.C.) who used the nose as a route for removing the contents of the cranial vault as part of the mummification process to avoid any facial disfiguration.1 From those times until the last century, the progress of medical science, technological developments, and the contribution of excellent physicians throughout the years havemade the techniques performed today possible. By reviewing the medical literature related with the history of paranasal sinus, diagnosis, and treatment, it is possible to conclude that there are five important reasons for the present state of the field of nose and paranasal sinus surgery.

The first reason is the introduction of the binocular Zeiss operating microscope with coaxial illumination for endonasal surgery invented by Hans Heermann (1958).² At about the same time, Harold Hopkins (1956) applied a new concept of lens systems and proximal illumination to the rigid telescope and used glass fibers for transmission of cold light.³ Nowadays, endoscopes use a light source connected by fiberglass cable that is fitted with a halogen lamp and is available with assorted angles of vision. With its improved illumination and wider field of vision, this newly designed endoscope was immediately used for diagnostic endoscopy. However, the use of telescopes for intranasal surgical procedures is a more recent development because it was necessary to improve the endoscopes and manufacture finer microinstruments that would be suitable for endoscopic sinus surgery.

The second reason is the concept pioneered by Messerklinger (1972),⁴ who showed that most of the sinus pathology occurs in the anterior ethmoid sinus at the level of the ostiomeatal unit. He used endoscopy in fresh cadaver specimens to demonstrate a disruption of mucociliary clearance in areas obstructed by the contact of two mucosal-covered surfaces in the middle meatus. Stasis of secretions follows this obstruction, which, in turn, leads to infection. According to Messerklinger, such areas of obstruction are most likely to develop in the middle meatus and to involve the anterior and middle ethmoids, with possible involvement of the maxillary, frontal, and posterior ethmoid sinuses and eventually the sphenoid sinus. If these obstructive areas can be removed with an endoscopic approach with restoration of drainage and ventilation through the natural ostia can be established, then resolution of limited or extensive disease in the dependent sinus can be achieved and its mucosa preserved. This represents a revolutionary concept compared with the classical surgical techniques of paranasal sinus surgery, which preferred creation of radical cavities, sometimes with removal of the mucosal coverage, or even intranasal total ethmoidectomy when there was only limited disease. The development of functional endoscopic sinus surgery contributed tremendously by providing a means to remove localized disease obstructing the narrow ethmoid clefts and thereby restoring normal mucociliary drainage and ventilation. Spontaneous resolution of mucosal disease in the maxillary and frontal sinuses could occur without the need for radical mucosal removal. Unfortunately, Messerklinger’s surgical approach for treatment of paranasal sinus disease was not published in the English literature until 1978.⁵

The third reason is the development of the CT scan, which is considered an essential examination for the diagnosis of paranasal sinus disease. A CT scan can show the different anatomical structures of the paranasal sinuses (including the delicate bony leaflets), identify the anatomical variants that may compromise the ventilation of the sinus, and demonstrate extensive pathologic areas or discrete points of diseased mucosa that are responsible for recurrent disease.

The fifth reason is related to the contribution of many excellent specialists throughout the world practicing rhinology in different locations and teaching these new surgical techniques to the younger generation of doctors. In this regard, the contributions of (in historical order) Prades,6 Dixon,^7–9 and Park¹⁰ in microsurgery of the paranasal sinus are very valuable. The concept of functional endoscopic sinus surgery was popularized and disseminated throughout the world by Stammberger (1985)11–15 and Kennedy (1985).^16–21 Wigand,^22–27 Rice,^28–33 and Levine^34–39 also shared their experience to achieve widespread circulation of this procedure with numerous publications.

Today the concept of functional surgery can be applied to three basic surgical procedures: microscopic sinus surgery, endoscopic sinus surgery, or a combination of both techniques, which has been the author’s preference since 1986.^40–42 Other surgeons, including Draf,^43–44 Rudert,⁴⁵ and Stamm,⁴⁶ are using the same combined technique.

Surgical Principles

General Overview

Contemporary sinus surgery has made tremendous progress over the last three decades. This is the natural consequence of a clear understanding of the pathogenesis of sinus diseases, the improvement of imaging studies, and the development of new optical technologies for better diagnosis and surgical treatment. Also the concept of the ostiomeatal complex, pioneered by Messerklinger,⁴ has gained wide acceptance. A set of general surgical principles that are applicable to virtually any surgical procedure has been established (Table 11–1).

1. Sinus surgery should be performed after an accurate sinus diagnosis based on clinical history, endoscopic nasal findings, and imaging studies (the basic principle for surgical management of sinus patients). The pathology of the sinus should be clearly established by CT scan prior to any scheduled sinus procedure.

2. Surgical treatment of sinus disease should be performed after failure of appropriate medical management. This should be the general rule of contemporary sinus surgery, and conservative medical treatment should be the first choice for treating sinus problems. Even with massive nasal polyposis a significant decrease of the polyp mass is achieved after systemic administration of steroids. In this situation, preceding medical management will render the surgical procedure easier and less hazardous by decreasing the polyp mass.

3. Proper surgical planning should be the guideline for a comprehensive and accurate surgical plan supported by the clinical history, the nasal findings by endoscopy, and the preoperative CT scan, although it is possible to find unexpected pathology that should be taken care of during surgery.

4. The concept of one-stage integrated treatment of the nose and paranasal sinus is an adequate approach to treat combined nasal problems and sinus diseases during the same surgical procedure (Table 11–2). The importance of correcting local morphological alterations of the nasal cavity, such as septal deviations, septal perforations, concha bullosa, and hypertrophy of the inferior turbinates, during the same operative procedure should be emphasized. These alterations may decrease the nasal airflow and may affect their mucosal drainage and the ventilation of the sinus and, consequently, may cause sinus problems. On the contrary, an infected sinus may drain purulent material to the nasal cavity, adversely affecting the nasal mucosa, which aggravates sinusitis, particularly when there are nasal abnormalities. In this situation, a vicious circle is generated between the affected sinus and the pathologic mucosa of the nasal cavity.

This concept of integrated treatment of the nose and paranasal sinuses represents a great advantage for the patient and avoids a second-stage procedure with an acceptable operating time at no increased morbidity and with reduced costs.

It must be recognized that sinus surgery techniques do not provide a cure for all of the inflammatory sinus diseases because the underlying factors are multiple. Allergies, systemic diseases, genetic influences, and environmental pollution are associated with reactive airway disease. Surgical treatment may correct anatomical abnormalities of the nose and sinus, remove the diseased tissues, restore drainage and ventilation, and possibly control the nature of the disease. However, there are other factors including those mentioned before that should also be taken into consideration and may influence the final outcome of the treatment. Tobacco smoking and exposure to environmental tobacco smoke are also important factors implicated in chronic nasal irritation and other respiratory symptoms in children and adults.47–49 Children exposed to the parental smoking are also at higher risk to develop chronic middle ear effusions and allergic disorders, including allergic rhinitis. It might be expected that after chronic nasal irritation caused by active and passive smoking, such exposure may result in an increased incidence of respiratory disorders of the nose and paranasal sinus, and/or may potentiate the effects of allergies on nasal and sinus functions, and/or may induce the recurrence of sinus disorders after medical/surgical treatment.

6. A thorough knowledge of the nose and paranasal sinus anatomy is of paramount importance. Recognition of the anatomical landmarks that provide surgical guidance is crucial for an effective and safe surgery. The great variability of anatomical structures is a constant feature, and even in the same individual variability occurs from one side to another. Because of these anatomical variations, previous surgical dissections in cadaveric specimens of paranasal sinus should be mandatory before starting surgical treatment of patients with paranasal sinus pathology.

7. Excellent visualization and minimal bleeding are basic surgical requirements for a safe surgery. The use of optical instruments such as the microscope and endoscope allows the surgeon to have an excellent view of the surgical field, including clefts, recesses, niches, and even the inside of the sinus cavities. The contribution of local vasoconstriction to keep bleeding to a minimum is very important.

8. Removal of diseased tissue from the sinus with minimal surgical trauma is another principle of contemporary sinus surgery. One of the priorities of this surgical procedure is the complete and accurate resection of the diseased tissue with maximum preservation of normal-looking mucosa. This concept of functional surgery directed only to a limited removal of irreversibly damaged mucosa and the obstructing anatomy has gained wide acceptance. Even massive inflammatory changes in the sinus mucosa have the capacity to undergo spontaneous healing after restoration of drainage and ventilation. This concept of “reversibility” of mucosal disease has been debated in our specialty for many years, and the merits of aeration versus radical procedures have been discussed. At what point does mucosal disease become irreversible? It is probably better to remove questionable mucosa than to leave it behind and hope that it undergoes transition back to normal tissue, providing that such removal can be safely accomplished.

In severe cases of chronic sinusitis, it is important to remove osteitic bony partitions as thoroughly as possible from the areas of severe mucosal disease. It is possible that these sites have a low-grade chronic osteomyelitis that may be responsible for the recurrent focus of chronic sinusitis.⁵⁰ Although the concept of minimally invasive surgical therapy to remove obstructive areas to improve mucociliary clearance and restore normal sinus drainage and ventilation should be applied particularly in early and mild diseases, a more aggressive surgery should be performed with removal of bony partitions where there is more extensive pathology, while at the same time preserving the normal-looking mucosa. However, complete removal of mucosa from the bony surfaces should be avoided because this will increase the possibility of postoperative osteitis and scar formation (Fig. 11–1A and B).

9. Restoration of normal drainage and ventilation from the affected sinus is the concept introduced by Messerklinger.⁵ In the past it was believed that chronic inflammatory disorder of the paranasal sinuses was an infectious process arising primarily from the affected sinus itself. However, based on studies of mucociliary clearance, Messerklinger was able to demonstrate that the etiology in most patients with chronic or recurrent sinusitis in the ethmoid, maxillary, and frontal sinuses is related to anatomical abnormalities and/or mucosal pathology obstructing the drainage system of these sinuses. Classical surgical procedures for treatment of chronic infections of the sinuses and other disorders, such as nasal polyposis, direct the surgeon to remove diseased tissues in the nose and/or paranasal sinuses. The new surgical openings in the sinus caused by those conventional surgical techniques are in locations distant from the natural ostium, and so treatment of the disease interferes with the mechanism of drainage of secretions of the sinus already disturbed by the infection.

The mucus produced in the anterior ethmoid sinus, maxillary sinus, and frontal sinus drains into an anatomically complex region of the lateral nasal wall called the ostiomeatal complex. The ostiomeatal complex is a narrow anatomical region consisting of multiple bony structures (middle turbinate, uncinate process, ethmoid bulla), air spaces (frontal recess, ethmoid infundibulum, middle meatus), and the ostia of the anterior ethmoid, maxillary, and frontal sinuses. In this area the mucosal surfaces are very close or even in contact with each other, and mucous secretions can be removed easily from the sinus because of the ciliary sweeping motion, which keeps the drainage system functioning. If, however, the opposing mucosal surfaces in this cleft become inflamed and swollen, drainage and ventilation of the sinus may be seriously impaired because the ciliary sweeping motion decreases and eventually ceases. When edema develops, the ostium quickly becomes blocked because of its small diameter, and consequently mucus can no longer be excreted. Also, ventilation that ensures gaseous exchange can be affected, and any alteration of this mechanism can have deleterious consequences. Hypoxia, increasing edema, decreased ciliary motion, and transudate form a vicious circle that facilitates possible infection. Supuration then develops either as a result of aerobic bacterial infection that consumes large amounts of oxygen or by a gradual decrease in pO₂ pressure that makes phagocytosis less effective and permits colonization by anaerobic organisms.

The main and most frequent indications for paranasal sinus surgery are summarized in Table 11–3, but their range will continue to increase and expand with new sophisticated equipment and more refined surgical procedures. The surgeon must tailor the operation to the disease and its characteristics, location, and extent. However, the patient’s clinical condition, ability to withstand general anesthesia, prolonged postoperative care, and expectations must be considered.

The most common indication for performing paranasal sinus surgery is chronic sinusitis. However, if adequate medical therapy can control the patient’s symptoms and the evolution of the disease, then the benefit of surgery is difficult to justify, and it should be avoided. Most patients with acute sinusitis can be treated with appropriate medical management without the need for surgical intervention. In certain cases with threatening or established complications (e.g., abscess formation), surgery should be performed to achieve drainage of the involved sinuses. In cases of acute sinusitis with periorbital or intraorbital complications, sinus surgery can provide access to the medial orbital wall (lamina papyracea), and resecting the lamina will expose the periorbital fascia to drain the periorbital abscess or to incise the fascia to decompress orbital cellulitis.

Recurrent acute sinusitis is an uncommon indication, and the patient should be evaluated very carefully before the decision to undergo surgery is made. This condition is defined by the absence of significant mucosal disease during the intervals of acute sinusitis episodes. A variety of anatomical abnormalities may be visualized on CT scan in this type of sinusitis, including the concha bullosa and the paradoxical middle turbinate (Fig. 11–2).

Variations of the uncinate process (with either pneumatization or lateralization), excessive aeration of anterior ethmoid cells, enlarged Haller’s cells, and agger nasi cells may also be found. These alterations may decrease sinus drainage and ventilation and predispose the patient to recurrent acute sinusitis. An excessively deviated nasal septum may have the same effect by impinging upon the middle turbinate and narrowing the infundibulum. In these cases, medical management may help control the frequency and severity of the infections, but only surgery can solve the problem. Usually the maxillary sinus is the affected sinus, and a very limited approach to enlarge the natural ostium is the treatment of choice. The other abnormalities should be surgically treated also using techniques like septoplasty, resection of the lateral lamella of the concha bullosa and partial resection of the middle turbinate to remove the lateralized segment.

Sinonasal polyposis frequently requires both medical and surgical treatment to achieve clinical improvement. The goal of sinus surgery in these patients is to remove the polyps and restore sinus drainage and ventilation. In the presence of extensive polyposis, a complete surgical cure of this disease is unlikely. This situation is related to an underlying mucosal hyperreactivity and general tendency to form polyps. Sinonasal polyposis is a multi-factorial disorder, and it should be looked at as a non-specific local reaction of the mucosa to a great variety of inflammatory, allergic, thermal, toxic, and mechanical stimuli. Consequently, other treatment options should be considered for management of this entity such as adjuvant therapy.

The outcome of paranasal sinus surgery depends on a very careful preoperative evaluation, including a complete otorhinolaryngologic examination with special emphasis on the nose and paranasal sinuses, and a collection of general medical information about the clinical condition of the patient. The routine examination comprehends a clinical history, physical examination, and complementary testing considered necessary for an accurate diagnosis (Table 11–4).

The clinical history related with the nose and paranasal sinuses is directed to the most common symptoms: nasal obstruction, nasal stuffiness, anterior nasal discharge, postnasal drip, mucopurulent rhinorrhea, itchy nose, sneezing, disorders of smell, facial pain, pressure, and headaches. Questioning should be systematic and should also cover the symptoms of ear diseases (e.g., hearing loss, popping and itching in the ears, and sensations of pressure). Chronic throat symptoms, such as slight discomfort, pain, dry sensation, scratchy throat, and frequent throat clearing, are often due to discharge from an infected nasal region and/or chronic sinusitis flowing down the pharynx. Also, pulmonary symptoms (coughing, spitting, wheezing, etc.), diseases of the teeth and jaws, allergic symptoms, eye complaints (eye pressure, pain, watery eyes, etc.), dizziness, chronic fatigue, weight loss, inflammatory diseases of the joints, autonomic disorders, and skin and systemic diseases, such as diabetes and hypertension, should be inquired about. The clinical history should establish the timing of the symptoms, duration of the disease (acute, chronic, or recurrent), tobacco smoking, current medications, previous surgeries, and complications.

The nasal examination should be performed in a routine fashion looking for morphologic abnormalities and characteristics of the nasal mucosa and its secretions. Particular attention should be paid to the lateral nasal wall and the middle turbinate area, although often this cannot be accomplished until a nasal spray decongestant is applied. This nasal inspection can also be accomplished using the microscope as the light source instead of a headlight (Fig. 11–3). The author has used the microscope for routine otorhinolaryngologic examination for the past 20 years because it provides better illumination and amplification.

If the nasal abnormalities are detected by anterior or posterior microrhinoscopy, no further examination is necessary. However, if the nasal examination under the microscope needs further evaluation or is otherwise incomplete, it should be combined with nasal endoscopy. This diagnostic technique is best performed by spraying the nose with a vasoconstrictor (0.5% phenilephrine hydrochloride) and an anesthetic agent (10% lidocaine) and allowing them to work for a few minutes. Then the entire nasal cavity should be systematically examined (including the nasopharynx) with a rigid 0-degree, 4 mm endoscope, or, if it is difficult to pass between the middle turbinate and the lateral nasal wall, a 30-degree, 2.7 mm endoscope. The flexible 3.2 mm endoscope is preferable with children. Again, particular attention should be paid to the middle meatus, where it is likely that the main changes will be found. Using videoendoscopy, these findings can be stored on a digital videotape, and with a laser printer the resulting images can be printed for the patient’s chart.

Computed tomography has become the main radiological investigation for sinonasal pathology and is absolutely mandatory for sinus surgery. By presenting bone and soft tissue details, it defines structural abnormalities, as well as the location and extension of disease, and often indicates the diagnosis when certain characteristic features are present. A coronal CT scan and axial CT projections provide comprehensive and detailed information about the nose and the paranasal sinus anatomy, its variations, relationships of important surrounding structures, and pathologic findings.

Other tests, such as the rhinomanometry and acoustic rhinometry,51–60 are performed on patients complaining of nasal obstruction in the routine preoperative evaluation. The rhinomanometry is an objective nasal test that measures nasal airway resistance by making a quantitative measurement of nasal flow and pressure. Acoustic rhinometry is another nasal test based on sound reflection that provides an estimate of the cross-sectional area as a function of distance from the nostril. Both are indicated mainly for quantification of pre- and posttherapy (medical and/or surgical) for nasal obstruction, for exclusion of functional disorders, and for medicolegal purposes. Nasal respiration and paranasal sinus aeration are not always correlated. However, improvement of the nasal air passages will contribute to the recovery of the sinus from sinusitis. In this situation, surgical treatment of the deviated nasal septum and/or the hyperthrophic inferior turbinates together with paranasal sinus surgery is essential to correct the nose and paranasal sinus unit. All of these procedures can be performed during the same operation, which the author calls one-stage integrated surgical treatment.

If there are systemic allergic disorders such as asthma, dermatitis, conjunctivitis, or gastrointestinal disturbances, or an underlying allergy coupled with nasal symptoms, then allergy testing is requested. The skin prick test, IgE antibodies (RAST) test, and serum IgE (PRIST) test are very useful for identification of the allergens responsible for the symptoms.^61–66

Preoperative olfactometry is very valuable for assessing disturbances of the olfaction and the results of ethmoid procedures in diffuse polyposis. Dysosmia is often caused by inflammation of the olfactory mucosa, and it improves after careful endoscopic management of the polypoid mucosa of the olfactory cleft. Other tests, such as mucociliary testing and nasal cytology, may be useful for additional information, but they should not be considered routine tests for preoperative evaluation.^67–74

In children with chronic recurrent sinusitis, the sweat test should be used to rule out cystic fibrosis, and determination of immunoglobulins and immunoglobulin classes, along with nasal mucosa biopsy to establish the diagnosis of ciliary diskinesia.^75–78

After reviewing these tests for preoperative evaluation, it should be concluded that clinical examination of the patient together with the imaging studies is essential for an accurate diagnosis. Other tests should be performed according to the clinical judgment. Correct diagnosis and the establishment of a surgical plan can be achieved in most situations by combining clinical examination, endoscopic results, and imaging studies.

The author strongly advises having a protocol for sinus surgery to evaluate sinus symptoms and to describe the nasal endoscopic and CT scan findings, surgical planning, and the results of surgery. It is a great effort toward data standardization that can be stored in a computer for a better update and follow-up, analysis of long-term results, and interchange of medical information.

Surgical Planning

After a careful preoperative evaluation, an accurate diagnosis can be established, and a treatment plan must be developed and introduced to the patient. The surgical procedure should be defined by the clinical examination, and the objective findings encountered during the preoperative evaluation must follow the surgical principles already described and must be performed according to the surgeon’s experience. The age of the patient and his or her medical conditions, expectations should also be considered before a final decision is made and the patient is scheduled for surgery.

Preoperative medication should be recommended before surgery in patients who have suppurative sinusitis. They should receive an appropriate oral antibiotic for 10 to 12 days before the surgical procedure. Patients with massive polyposis should take a short treatment of oral corticosteroids immediately before surgical treatment with a “booster” dose intraoperatively. Hypertension and diabetes must be controlled before surgical intervention with the cooperation of an internist. Medications, such as aspirin and nonsteroidal anti-inflammatory drugs that prolong bleeding should be discontinued before the operation.

The majority of the surgical operation is performed with the Zeiss operating microscope OPMI ORL (Fig. 11–4) equipped with coaxial fiberoptic, cold-light illumination with a 12 V, 100 W halogen reflector lamp (cold light), spot illumination, 0-degree central illumination, 1:6 zoom magnification, 180-degree wide field tiltable tubes with eyepieces, and motorized internal fine focusing. A stereo co-observation tube with excellent ergonomic conditions is used for the assistant, and another arm with a video camera system is adapted to the microscope and fitted with a lens with a focal length of 300 mm.

Another optical aid is the endoscope. Several endoscopes are available for performing endoscopic procedures. A rigid telescope with a brighter illumination source provides an excellent clear field of vision. The improved telescopes incorporate wide views of the peripheral field along with magnified images of the anatomical structures. The built-in mechanism of angled vision in the rigid telescopes provides the further advantage of viewing deeper areas located in narrow clefts. Angled telescopes are therefore useful to see inside the sinuses, around corners, and into niches, recesses, or ducts.

Microscopes have been well-established magnifying equipment in practical use in otorhinolaryngology, and their sophistication has reached powerful limits with the current technologies. In 1923, Holmgren introduced the binocular operative microscope without coaxial light for ear surgery.79

Endonasal surgery and laryngeal microsurgery accompany the historical developments of ear surgery. In 1958, Heermann pioneered the use of the binocular Zeiss operating microscope with coaxial illumination in endonasal surgery.² Kleinsasser was the founder of modern laryngeal microsurgery in 1962, using a Zeiss operating microscope.⁸⁰

Since the beginning, the application of the operating microscope has been the standard method of optical aid in otorhinolaryngology. In 1972, Messerklinger developed the concept of endoscopic sinus surgery using nasal endoscopes. This has revolutionized, improved, and radically changed the techniques used for the diagnosis and treatment of patients with sinus disease.

Other surgeons, including this author, are continuing to use both instruments, combining microscopic and endoscopic techniques (COMET surgery).

Optical Performances

The two basic optical instruments used for sinus surgery are the microscope and the endoscope. It is absolutely necessary for technical knowledge and teaching purposes to describe the main parameters of any optical system⁸¹ and to compare the characteristics of these optical aids based on optical performance and ergonomic capabilities. Although there are several relationships between the main characteristic parameters of any optical system, for practical reasons, the most important and currently used ones are described here (Tables 11–5 and 11–6).

The focal distance (working distance) defines the clearance or distance between the object and the first surface of a lens system. It affects the user’s ability to image and manipulate the sample at the same time. The working distance increases with the objective focal length. For the microscope, the focal distance is variable and finely adjustable. The range is in the order of 300 mm, giving very ample volume for all surgical work. The head of the surgeon, once working on a region, remains steady behind the ocular, and the adjustment of the focus is simple by rotating the focusing knob.

For the endoscope, the focal distance is fixed, not adjustable. The range is in the order of a few millimeters. The working volume is very small. The head and one of the hands of the surgeon have to move to focus. The surgeon has to bow his or her head over the patient and remain at a close distance to see through the endoscope.

The depth of field (focus) is the distance by which the image (or object) may be shifted longitudinally with respect to a reference plane (retina of optical system) without introducing unacceptable blur. In practice, this represents the visible depth of the object.

The microscope presents a much larger depth of field, providing a deeper volume of visibility. Also, the depth of focus is much greater, and the surgeon can comfortably move his or her eyes behind the ocular lens. With the endoscope, the depth of field is shorter; therefore, the endoscope must be finely moved by hand to examine in depth. The depth of focus is short, and consequently the eyes of the surgeon have to move together with the endoscope to keep the image in focus.

The numerical aperture is related to the depth of field (focus), the luminance, and the resolution of the system. The illumination of an image is proportional to the square of the numerical aperture. The numerical aperture in the microscope is smaller, more light is required (illuminating a larger area), and resolution limit is smaller than in the endoscope. However, it can be varied and adjusted. In the endoscope, the numerical aperture is higher and the image looks brighter and has better fine details, although the image field extension is much smaller. The numerical aperture is fixed, and the endoscope must be moved.

The field of view is the volume within which there is image formation. In the microscope, the field of view is much more extended, as is the volume. The surgeon is able to follow the movement of almost the entire body of the surgical instruments. With the endoscope, the field of view is much smaller. The surgeon can see only the tip of the surgical tools and therefore follow the movement only within a short range (Fig. 11–5).

The resolution limit expresses the distance between two points that can be still separated at the image plane. With the microscope, the resolution limit is smaller, but only by less then an order of magnitude, which is very adequate. Resolution can be varied and adjusted.

With the endoscope, the resolution, in principle, is higher, giving finer details in a clear form. However, the resolution is fixed, and the endoscope must be changed whenever the numerical aperture and the resolution have to be adjusted.

The luminance (brightness of the image) is the quantity of light flux passing through a point on a specific surface, in a specified direction per unit of projected area, and per unit solid angle in the given direction. For the microscope, the luminance is smaller, but it can be adjusted, either by using a stronger light source or by increasing the numerical aperture. In practice, it does not represent a disadvantage. The luminance is uniform without bright spots. The endoscope intrinsically presents a higher luminance. However, due to the mechanism, if illumination is by fiber optics and the image forming process is fiber optics, the used light source has to be more intense. In practice, the problem is solved, and the luminance of the image is good. Nevertheless, as the tip of the endoscope acts as a light source very close to the surgical instruments with highly reflective surfaces, strong reflections occur during the procedure that saturate the image, and bright spots occur with frequency. This may cause temporary discomfort to the surgeon, but slight adjustments of light intensity during surgery can be performed.

The distortion is related to technical performance of the optical system, which has imperfections and does not handle perfect spherical waves. Distortion is one of the so-called primary aberrations Efforts are being made to design an optical system that minimizes aberrations and optimizes its performance for this application.

The design of the optical microscope leads to smaller distortion. In the endoscope, the number of optical elements for aberration correction generally causes a higher distortion.

Cleanliness and protection are relevant for preservation and operation purposes. Because the microscope has all optical systems far away from the surgical field, it presents as an ideal solution. The endoscope is placed within the area to be treated, and so is constantly affected by fogging, staining, and accidental scratching.

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Aug 1, 2016 | Posted by admin in OTOLARYNGOLOGY | Comments Off on Combined Microscopic and Endoscopic Technique (COMET Surgery)

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TABLE 11–7 Microscopic and Endoscopic Main Optical Performances

Optical characteristics	Microscope	Endoscope
Objective focal length	0.5–100 mm	0.2–5 mm
Magnification	5X–5000X	2X–26X
Numerical aperture	0.10–0.96	0.25–0.7
Resolution power	<430 I p/mm	250–400 I p/mm
Depth of field	Few μm	Mm to ∞