European Annals of Otorhinolaryngology, Head and Neck diseases (2010) 127, 33—39

REVIEW ARTICLE

Image-guided sinus surgery

V. Prulière-Escabassea,b,∗,c,d, A. Costea,b,c,d

a Hôpital intercommunal, Créteil Hospital, 40, avenue de Verdun, 94000 Créteil, Franceb Service d’otorhinolaryngologie et de chirurgie cervicofaciale, hôpital intercommunal, 51, avenue duMaréchal-de-Lattre-de-Tassigny, 94000 Créteil, Francec Paris-Est University, 61, avenue du Général-de-Gaulle, 94000 Créteil, Franced Inserm Unit 955, Créteil Medical School, 8, rue du Général-Sarrail, 94000 Créteil, France

Available online 24 March 2010

KEYWORDSCAN;Sinus;Endoscopic surgery

Summary Image-guided surgery (IGS) is extremely useful for anatomic location in at-risk sinussurgery: extensive inflammatory disease, sinus cavity revision, and frontal sinus, posterior eth-moid, sphenoid or nasosinal tumor surgery. There are two systems on the market, based onelectromagnetic and infrared detection, respectively; optimal functioning depends on calibra-

tion. IGS is only a location aid, complementary to and not a substitute for endoscopy. It enablesthe experienced endonasal surgeon to check the endoscopic location at any time, and providesappreciable ‘‘psychological’’ comfort in what are difficult and sometimes stressful operations,the limits of which are being forever pushed back.

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Introduction

Endoscopic endonasal surgery was developed to treat at-risk chronic sinusitis. Although morbidity is low in endonasalsurgery, there is a risk of serious complication due tothe anatomic proximity of the sinus cavities, optic nerve,carotid artery, dura mater and brain. It therefore seemedinteresting, alongside endoscopic guidance, to provide sur-

geons with a medical imaging-assisted mapping aid. Variouscomputer-assisted navigation or image-guided surgery (IGS)systems have been developed in endonasal surgery over thelast 10 years, and several are now on the market, based

∗ Corresponding author. Tel.: +33 1 45 17 54 60;fax: +33 1 45 17 54 40.

E-mail address: virginie.escabasse@chicreteil.fr(V. Prulière-Escabasse).

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n electromagnetic or infrared detection technology. Allf these systems have millimetric precision. In endonasalurgery, image-guidance supplements endoscopic informa-ion, improving anatomic location. IGS systems, however,hould not be used in isolation but only in combinationith endoscopy. Surgeons furthermore need to learn theasic principles of IGS before being able to use suchystems appropriately. Such basic knowledge teaches theimitations inherent to the technology, enabling secondaryomplications to be minimized.

istory

he first navigation aids were developed by neurosurgeons,or whom precise anatomic location is primordial. As ofhe 1970s, CT-assisted location systems were tried outor focal destruction in stereotactic brain surgery [1—3],sing reference frames solidly attached to the patient’s

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Figure 1 Image guidance equipped with an optical system.The spatial repository is acquired from a battery of threeinfrared cameras which determine the position of an instrumentfitted with infrared emitters or infrared-reflecting sensors.Image guidance equipped with an electromagnetic system. Thespatial repository is derived from an electromagnetic fieldincluding the surgical field, in which the position of an instru-ment connected up to an electromagnetic support can bed

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ead and positioning of fiducial markers which made therocedure cumbersome for ENT surgery. During the 1980snd 1990s, various systems were developed to bypass these of reference frames, using localization by acoustic orltrasound triangulation or else articulated arms, alwayseferenced according to fiducial markers [4—9]. These sys-ems achieved a precision of 2 mm.

Localization systems more specifically dedicated tondonasal surgery progressed during the 1990s, especiallyn Germany. A surgical planning system was developed by aeam at Aachen University [10], then a localization systemsing opaque radio-markers positioned on the patient’s facehead of the peroperative scan then located at the begin-ing of surgery by a pointer mounted on an articulated arm,equiring the markers not to move in the meantime [11].he same team later used an infrared diode location system12]. In the USA, the first report of an endonasal surgeryeries using computer-assisted localization with articulatedrm was in 1994 [13].

Finally, the late 1990s saw the advent of infrared andlectromagnetic localization systems which avoided theeed for fiducial points and articulated arms and left theurgeon free to operate [14—19]. The endoscopic endonasalurgery systems currently on the market use one or other ofhese localization techniques.

rinciples of electromagnetic and opticalystems

lectromagnetic and optical localization systems bothnable real-time detection of instrument position in a 3Dmaging repository. At present, such repositories are exclu-ively based on CT acquisitions reformatted to obtain aeries of slices in three dimensions. A software interfaceatches the imaging repository to a peroperative spatial

epository in which the instrument can be located.In electromagnetic systems, the spatial repository is

erived from an electromagnetic field including the surgicaleld, in which the position of an instrument connected upo an electromagnetic support can be determined. Matchingmaging and spatial repositories initially required fitting theatient with a helmet equipped with magnetic landmarksuring preoperative CT scanning and during surgery itself.he helmet is now no longer needed during CT acquisitionut only during surgery, the spatial and imaging reposito-ies being matched by surface scanning as in the infraredethod.In optical systems, the spatial repository is produced by

battery of two or three infrared cameras which can deter-ine the position of an instrument fitted either with infrared

mitters, in what are known as ‘‘active’’ systems (elec-roluminescent diodes), or with sensors reflecting infraredmitted by a source coupled to the camera, in so-called‘passive’’ systems. Localization uses triangulation fromlectroluminescent or reflecting landmarks which are fixedith respect to the patient’s head (usually by means of a

elmet). Matching is based on computerized mathematicalnalysis of the geometrical concordance between virtual andeal anatomic points. This step requires CT images to be pro-essed to obtain a 3D mask of the surface of the patient’sace, on which the surgeon can choose virtual landmarks. At

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he beginning of surgery, a locatable instrument is used toark the anatomically corresponding real points as precisely

s possible (‘‘surface matching’’).It is noteworthy that surgery room installation and

urgical procedure are unchanged by the use of anlectromagnetic system, whereas optical systems require

particular arrangement in the surgery room, avoid-ng any human or material obstacle between instru-ents and cameras. The necessary instrument visibil-

ty also makes certain demands on surgical proce-ure.

In conclusion, these two systems, with their very differ-nt concepts, both enable constant real-time location of

oupled instruments on scan images in three dimensions,hroughout surgery (Fig. 1).

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Image-guided sinus surgery

Calibration

Calibration is the process by which the navigation systemmatches the surgeon’s reference points on the patient withthose on the scan, registered in the navigator. Each point ineach volume has specific coordinates, xyz. Calibration alignsthe two sets of points. During surgery, the navigation sys-tem deduces the position of the operator’s instrument byextrapolating the calibration points.

Whichever navigation system is being used, there are afew rules to be followed in order to optimize calibration.Points should be relatively fixed and reproducible: mobilepoints on the face should be avoided, in favor of the tragus,external canthus and nasal root.

Calibration systems involving surface scanning of thepatient’s face need to take account of soft tissue mal-leability. Clinically, hydration and tension differences infacial tissue between image acquisition when the patient isawake and surgery under general anesthesia can cause sig-nificant differences (up to 2 mm) in the position of points.Face contour point selection designs, however, get roundthis problem by the large number (500—600) of pointsemployed. The surface of the face should be brushed withthe instrument held at 90◦, avoiding both pressure andloss of contact. Preoperative imaging is thus essential: thescan should be taken with millimetric slices and a 512X512pixel matrix. Reconstruction should enable facial contoursto be defined, and initial CT acquisition should take thisinto account, including the entire face up to the outer ears(Fig. 2).

Instrumentation

The first navigation systems used rectilinear pointers whichwere hard to manipulate in the nasal fossae. A range ofinstruments has now been adapted for computer-assistedsurgery: straight or angled aspirators, coagulating forceps,rasps and microdebriders.

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Figure 2 Calibration. Facial surface scanning calibration systemssurface of the face should be brushed with the instrument held atbe relatively fixed and reproducible. Thus, mobile points on the facenasal root (left). Each endonasal surgical instrument connected up toband (right).

35

ole of IGS in sinus surgery

he main contribution of IGS is the possibility of 3D visual-zation of the sinonasal cavities, compared to the 2D viewf endoscopy. The 3D information provided by comparisonith the preoperative scans adds depth to the endoscopic

mages, minimizing localization error. The risk of majoromplications in endoscopic sinus surgery is low (0—3%), buthe potential morbidity and mortality associated with per-nd postoperative complications are severe, including blind-ess, double vision, brain lesion, CSF leakage, epistaxis andeath [20—23].

Indications for IGS are under debate worldwide, but it isnanimously indicated in sinus surgery neighboring the skullase, the orbit or the optic or carotid nerves. Consensus ismerging for indications in surgery for extensive inflamma-ory disease, sinus cavity revision, frontal sinus, posteriorthmoid and sphenoid surgery, sinonasal tumor surgery andn sinus surgery with associated congenital facial deformityr post-traumatic facial bone remodeling [17,24—26].

GS in ethmoid surgery

GS is of great interest in primary surgery for extensiveinonasal polyposis, allergic fungal sinusitis or invertedapilloma or malignant tumor, when the indispensablenatomic landmarks (medial concha, orbital wall, cranialase) are masked by the polyps or tumor volume or in casef surgical hemorrhage in inflammatory tissue [27,28].

In ethmoid cavity revision, IGS may be indicated as pre-ious surgery may have obliterated anatomic landmarks:ynechia, hyperstosis, absence of medial concha, papyra-eous lamina breakage [29,30]. Kacker’s team reported no

omplications in a cohort of 85 patients undergoing eth-oid cavity revision under image-guidance, whereas Jiang,

n a series of 142 cavity revisions without image-guidance,eported periorbital exposure or lachrymal pathway woundsn 9.9% of cases: they conclude that IGS affords improved

require soft-tissue malleability to be taken into account. The90◦, avoiding both pressure and loss of contact. Points shouldshould be avoided, in favor of the tragus, external canthus orthe IG system is then calibrated by contact with the reference

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ocalization of anatomic landmarks and reassurance for theurgeon [25].

Functional failure following cavity revision under image-uidance, at 11%, is no more frequent than in primarythmoid surgery (2 to 24%), but significantly less frequenthan in endoscopic revision without image-guidance [25,29].n conclusion, cavity revision seems to be more completend thus potentially more functionally beneficial when per-ormed under image-guidance.

GS in frontal sinus surgery

GS is of special interest in frontal sinus surgery, due to thenatomic complexity. The nasofrontal canal is of variableength and diameter, depending on the adjacent sinal struc-ures. Localization depends on the pneumatization of thethmoid bulla, the agger nasi and medial concha lateraliza-ion, which may combine to narrow frontal sinus drainage31,32].

Endoscopic repermeabilization of the frontal sinus is indi-ated in frontal sinusitis resistant to medication, to enablerainage and efficient ventilation. Frontal sinus obliterationy an external approach is indicated only in persistent sinusi-is following failure of endoscopy. IGS may be of use in bothhese indications.

GS in frontal sinus endoscopyn frontal recess pathology, the nasofrontal canal can easilye localized by IGS after anterior ethmoidectomy. IGS serveslso to differentiate supraorbital cells of the frontal sinusstium. It can improve the surgeon’s confidence by help-ng locate the nasofrontal canal and avoid false trajectories33]. Reardon, in a series of 800 frontal sinus operations,ound a higher rate of repermeabilization associated withhe use of IGS. Maxillary sinus, ethmoid and sphenoid open-ng, on the other hand, do not benefit from the use of IGS34] (Fig. 3).

GS in Draf 3rontal sinus surgery is a challenge for rhinologists, due torequent recurrence of nasofrontal canal stenosis followinginusotomy. Recently, the Draf-3 modified Lothrop tech-ique, has offered a surgical alternative to sinus obliterationy an external approach, with the benefit of reduced mor-idity. The technique consists in nasalizing the frontal sinusy exeresis of the floor of both frontal sinuses, the intersinuseptum and part of the superior nasal septum. The opera-ion is often made difficult by the narrowness of the region,he limited angle of view and anatomic alterations followingrevious surgery. These factors combine to increase the riskf false trajectory and defective orientation, even for theost experienced surgeon. IGS enables localization of the

rontal sinus ostium, to keep rasping in the canal axis. With-ut IGS, rasping often begins blindly up to the frontal sinus.nce the sinus is open, bone resection is pursued anteri-rly, under direct endoscopy. The sagittal IGS slice enables

asy location of the frontal sinus beak, which is to be low-red to enlarge drainage. During bone resection, IGS affordshe surgeon reassurance with regard to the cranial base,rbit and skin. At end of surgery, IGS ensures frontal sinusompartment opening, including supraorbital ethmoid cells.

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V. Prulière-Escabasse, A. Coste

unctional success in Draf-3 does not significantly differ withr without IGS (83.1% versus 74.3%), although there is a slightrend to better results with IGS [35].

GS in endoscopic frontal sinus fillingfter repeated failure of endoscopic frontal sinus reper-eabilization, sinus filling may be indicated. Although

unctional results are excellent, the peroperative compli-ation rate is high (20%) [36]. Complications include duralxposure, dural wounds with CSF leakage, and papyra-eous lamina breakage with orbital fat extrusion. Theseomplications are mainly due to rasping beyond the frontalinus walls. IGS may be the optimal means of assessingrontal sinus size ahead of bone flail. The technique involvesositioning the band on the vertex. Endoscopic frontal sinuslling under IGS was recently assessed by Matson’s team

n unilateral sinus pathology associated with small frontalinus. This innovative technique employs a supraorbital inci-ion to insert the endoscope and an instrument (rasp orspirator) so as to fill the sinus with fat [37]. The authorseport lower morbidity than with the classical externalpproach, but the results are to be interpreted with caution,iven the small number of cases (10) and lack of follow-up.

GS in external frontal sinus approacharrau’s team was the first to report on IGS in frontal sinuslling surgery, showing it to be more effective than classictandard X-ray for analyzing frontal sinus size and especiallyhe posterior and lateral borders [38]. A recent case-controltudy found less peroperative complications with the use ofGS in this indication [39].

GS in CSF rhinorrhea surgery

ndoscopic closure of post-traumatic or spontaneous cra-ial base cracks has given satisfactory results for morehan 20 years [40—42]. IGS may be useful for localizingracks with dangerous locations due to the proximity ofhe optic or carotid nerve (sphenoid sinus) or with difficultccess (frontal sinus). In a recent retrospective study, IGSvoided intrathecal fluorescein injection or lumbar drainagen difficult-to-locate cracks with non-negligible associatedorbidity [43].

GS in sinonasal tumor surgery

urgical management of benign tumor or pseudotumor (boneumor, inverted papilloma, mucus retention cyst) underndoscopy is now consensual [44—46]. Coupling to IGSnables the position of structures hidden or destroyed byhe tumor to be ascertained (papyraceous lamina, cribiformlate, cranial base, anterior ethmoid artery, optic nerve,

arotid artery) and can help to achieve complete resec-ion in case of difficult location such as the frontal sinus47]. Endoscopic malignant sinus tumor surgery remains con-roversial and there are as yet no reports of IGS in thisndication.

Image-guided sinus surgery 37

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IGS, complication risk in sinonasal surgery,and improved surgical management

Lanza’s team recently published a meta-analysis of 105articles (1990—2006) to assess (i) the contribution ofIGS to reducing severe (orbital and cerebral) or moder-ate complications (peroperative hemorrhage) in sinonasalsurgery; and (ii) whether IGS improves clinical results [26].On the first point, most of the studies analyzed concerned aseries of some hundred patients with varying surgical indi-cations: analysis suggested a reduced risk of complicationor no significant difference, without the possibility of sta-tistical demonstration even in the larger cohorts [48,49]:as Lanza points out, demonstrating significant reduction inthe risk of a rare complication (1—2%) would require ana-lyzing 3000 patients per group; orbital and cerebral risksare even smaller (∼0,25%) and would need a cohort of35,000 patients to demonstrate a halving in risk. The sec-ond question — whether IGS improves clinical results — goesunanswered, there being no randomized studies of the clin-ical benefit of IGS in sinus surgery. Randomization wouldimply not using IGS in a group of patients in whom it is indi-cated, which no physician would find ethically acceptable.

New generation IGS: real-time imagereconstruction in sinus surgery

Present-day IGS uses preoperative images for 3D recon-struction, and can thus not be updated during surgery.Unciformectomy, ethmoid cell opening and mucus or tumortissue exeresis, however, can alter the position of anatomiclandmarks. Kennedy’s team recently assessed peroperativeCT with transfer to IGS in ethmoid cavity revision and sinustumor surgery [50]. Images were acquired in less than 40 s

and transferred to IGS in a matter of minutes. This develop-ment impacted surgical strategy for 30% of patients in theirstudy. The same team reported considerable benefit fromperoperative CT transferred to IGS in a case of frontal sinusrepermeabilization [51]. Peroperative MRI (used by some

t nasofrontal canal localization during endoscopic repermeabi-

eurosurgery teams) may likewise be coupled up to IGS, butemains costly and has yet to be assessed in sinus surgery.eroperative imaging in IGS is thus a promising developmentor sinus surgery and for tumor surgery in particular.

onclusion

GS is of definite use in sinus surgery. The experiencedndonasal surgeon can at any time check the exacti-ude of the endoscopic localization, acquiring a welcome‘psychological’’ reassurance in difficult, and sometimes,tressful surgery. However, IGS is no more than a localizationid, complementary to and not a substitute for endoscopy.he various systems available enable the indications forndonasal surgery to be extended; perfect endoscopicwareness of anatomy and procedure, however, remainandatory, but can be more easily obtained using neuron-

vigation.

onflict of interest statement

he authors declared no conflict of interest.

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