Endoscopic sinus surgery using intraoperative computed tomography imaging for updating a three-dimensional navigation system

Identifying Best Practices for Managing Internal Carotid Artery Injury During Endoscopic Endonasal Surgery by Consensus of Expert Opinion

BACKGROUND

Injury to the internal carotid artery (ICA) is a potentially devastating complication of endoscopic endonasal surgery (EES) that as many as 20% of skull base surgeons will experience at least once during their careers. Managing these injuries is difficult given the small operative field and poor visibility created by high-flow hemorrhage, and, at present, there is no consensus regarding best practices.

OBJECTIVE

This study seeks to consolidate the practices and opinions of experienced skull base surgeons from high-volume tertiary care centers into a single consensus statement regarding the best practices for managing ICA injuries during EES.

METHODS

A panel of 23 skull base surgeons (15 neurosurgeons and 8 otolaryngologists) completed a 3-round Delphi survey that assessed experiences and opinions regarding various aspects of ICA injury management. Mean (SD) years since fellowship completion was 15.6 (8.1) and all but 3 surgeons had experienced an ICA injury at least once.

RESULTS

The final consensus statement included 36 guidelines all of which were grouped under 1 of 4 categories: 11 statements concerned preoperative management and equipment for high-risk patients; 14 statements concerned hemorrhage control; 4 statements concerned definitive management; 7 statements concerned pharmacologic treatment, blood pressure, and neurophysiologic monitoring.

CONCLUSIONS

There are numerous decisions that a surgeon must make when facing a carotid artery injury. In our estimation, many questions can be grouped under 1 of the 4 categories outlined in our consensus statement and can be addressed by these findings.

Tissue Structure Updating for In Situ Augmented Reality Navigation Using Calibrated Ultrasound and Two-Level Surface Warping

OBJECTIVE

In minimally invasive surgery (MIS), in situ augmented reality (AR) navigation systems are usually implemented using a glasses-free 3D display to represent the preoperative tissue structure, and can provide intuitive see-through guidance information. However, due to changes in intraoperative tissue, the preoperative tissue structure is not able to exactly correspond to reality, which influences the precision of in situ AR navigation. To solve this problem, we propose a method to update the tissue structure for in situ AR navigation in such way to reflect changes in intraoperative tissue.

METHODS

The proposed method to update the tissue structure is based on the calibrated ultrasound and two-level surface warping technologies. Firstly, the particle filter-based calibration is implemented to perform ultrasound calibration and obtain intraoperative position of anatomical points. Secondly, intraoperative positions of anatomical points are inputted in the two-level surface warping method to update the preoperative tissue structure. Finally, the glasses-free real 3-D display of the updated tissue structure is finished, and is superimposed onto a patient by a translucent mirror for in situ AR navigation.

RESULTS

we validated the proposed method by simulating liver tissue intervention, and achieved the tissue updating accuracy of 92.86%. Furthermore, the targeting error of AR navigation based on the proposed method was also evaluated through minimally invasive liver surgery, and the acquired mean targeting error was 1.92 mm.

CONCLUSION

The results demonstrate that the proposed AR navigation method is effective.

SIGNIFICANCE

The proposed method can facilitate MIS, as it provides accurate 3D navigation.

Template-based registration for image-guided skull base surgery

Objectives

To evaluate whether patient-to-image registration with the use of a maxillary template is sufficiently accurate for image guided skull base surgery.

Study Design and Setting

In an experimental phantom study, pair-point registration of a skull phantom to its CT image data was performed with 243 different configurations of a maxillary template with markers. Then artificial skull mounted target markers were located with an infrared tracking device as used in navigation systems.

Results

The average target registration error was 1.57 mm in the anterior skull base (95% confidence interval, 1.53 to 1.61 mm), but 3.31 mm in the lateral skull base (95% confidence interval, 3.26 to 3.37 mm).

Conclusions

Fiducial marker registration based on a maxillary template is sufficiently accurate for image-guided surgery in the anterior skull base, but not for the lateral skull base.

Significance

Template-based registration is an accurate yet noninvasive registration method for frontal skull base surgery.

Prospects and limitations of different registration modalities in electromagnetic ENT navigation

The present study examined electromagnetic tracking technology for ENT navigation. Five different registration modalities were compared and navigation accuracy was assessed. Four skull models were individually fabricated with a three-dimensional printer, based on patients' computer tomography datasets. Individual silicone masks were fitted for skin and soft tissue simulation. Five registration modalities were examined: (1) invasive marker, (2) automatic, (3) surface matching (AccuMatch), (4) anatomic landmarks, and (5) oral splint registration. Overall navigation accuracy and accuracy on selected anatomic locations were assessed by targeting 26 titanium screws previously placed over the skull. Overall navigation accuracy differed significantly between all registration modalities. The target registration error was 0.94 ± 0.06 mm (quadratic mean ± standard deviation) for the invasive marker registration, 1.41 ± 0.04 mm for the automatic registration, 1.59 ± 0.14 mm for the surface matching registration, and 5.15 ± 0.66 mm (four landmarks) and 4.37 ± 0.73 mm (five landmarks) for the anatomic landmark registration. Oral splint registration proved itself to be inapplicable to this navigation system. Invasive marker registration was superior on most selected anatomic locations. However, on the ethmoid and sphenoid sinus the automatic registration process revealed significantly lower target registration error values. Only automatic and surface registration met the accuracy requirements for noninvasive registration. Particularly, the automatic image-to-world registration reaches target registration error values on the anterior skull base which are comparable with the gold standard of invasive screw registration.

Intraoperative CT-guided cochlear implantation in congenital ear deformity

CONCLUSIONS

Intraoperative computed tomography (iCT)-guided cochlear implantation is practical and effective for correct electrode placement in the cochlea of patients with congenital inner ear and/or complex middle ear malformation.

OBJECTIVES

The operation in patients with inner ear and/or complex middle ear malformation including abnormal facial nerve course is difficult. This study evaluated the efficacy of cochlear implantation under the guidance of iCT to insure correct electrode placement.

METHODS

This was a prospective interventional case series. Ten patients with severe to profound sensorineural hearing loss due to ear malformations were enrolled, and iCT was used to confirm the right placement of electrodes.

RESULTS

Intraoperative CT was performed three times in one patient, twice in two, and once in the others. Interruption of the surgical process for each iCT until resumption of surgery was 9.64 ± 0.63 min. iCT revealed incorrectly positioned cochlear implants in two patients, which were immediately corrected. There were no reoperations due to misplacement of electrodes. iCT helped locate the cochlea in the middle ear of one patient with an abnormal facial nerve course. The overall intervention rate based on iCT findings was 30%.

LEVEL OF EVIDENCE

level 4.

Influence of different registration modalities on navigation accuracy in ear, nose, and throat surgery depending on the surgical field

OBJECTIVES/HYPOTHESIS

Various invasive and noninvasive registration methods have been established in the past for intraoperative navigation. The present study compared the registration and navigation accuracy of three different registration modalities in anatomical locations of special interest for ear, nose, and throat surgery.

STUDY DESIGN

Prospective experimental phantom study.

METHODS

Four skull models were individually fabricated with a three-dimensional printer based on the patient's computed tomography data sets and fitted with an individual customized silicone skin. Three different registration modalities were examined: 1) invasive marker (IM), 2) oral splint (OS), and 3) laser scan (L). Accuracy measurements were assessed by targeting 26 titanium screws placed over the skull. The overall accuracy and the target registration error for eight selected anatomical locations were measured.

RESULTS

Mean accuracy was 0.67 + or - 0.1 mm (quadratic mean + or - standard deviation) for IM, 0.98 + or - 0.16 mm for OS, and 1.3 + or - 0.12 mm for L. The greatest differences in accuracy were found on the mastoid with best accuracy for IM (0.59 + or - 0.2 mm; P < .05 vs. OS and L), followed by OS (1.23 + or - 0.41 mm; P < .05 vs. L), and L (1.88 + or - 0.45 mm). In contrast, only small differences in accuracy were detected in the anterior skull base between the registration modalities (IM 0.75 + or - 0.21 mm, OS 0.71 + or - 0.27 mm, L 0.93 + or - 0.34 mm).

CONCLUSIONS

L and OS meet accuracy requirements in the midface and anterior skull base. OS is superior to L with navigation accuracies comparable to marker registration. However, neither method meets the high precision requirements for lateral skull base surgery. Laryngoscope, 2010.

Intraoperative use of cone-beam computed tomography in a cadaveric ossified cochlea model

OBJECTIVES

To describe a cadaveric temporal bone model of labyrinthitis ossificans and investigate the utility of intraoperative cone-beam computed tomography (CBCT) in the facilitating cochlear implantation.

DESIGN

Cadaveric temporal bone study.

METHODS

Five cadaveric heads had cement introduced into the 10 cochleas. CBCT and a conventional CT scan were compared to assess the extent of cochlear obliteration. The cement was drilled-out (under CBCT guidance, if required) and cochlear implant electrode arrays (from 3 different manufacturers) inserted.

RESULTS

CBCT images demonstrated temporal bone anatomy and the extent of cochlear obliteration as clearly as conventional CT in all cases. Intraoperative CBCT guided drilling and facilitated electrode placement in two of five heads (3 of 10 ears). Streak-artifact from the electrodes of two devices partially obscured image clarity.

CONCLUSIONS

The obliterated cochlear model reproduced a disease-ossified cochlear both radiographically and surgically. CBCT is useful for intraoperative imaging to facilitate electrode array placement in the obliterated or congenitally abnormal cochlea.

Use of real‐time magnetic resonance image guidance in endoscopic sinus surgery

We evaluated the effectiveness of magnetic resonance image (MRI) guidance using an optical tracking system (MRI-guided therapy: MRT) in performing endoscopic sinus surgery (ESS). The profiles of the fourteen patients in the present study were as follows: eleven with mucocele in the paranasal sinus, one with recurrent chronic sinusitis, one with maxillary cancer, and one with Graves' ophthalmopathy. Preparation of the MRT system required an additional 54 min in cases involving general anesthesia, and an additional 17 min in cases involving local anesthesia, in comparison with corresponding control groups undergoing ESS in a traditional operating room. We developed nonmetal probes that were visualized in a real-time mode and assistive devices for the optical tracking system that were equipped to avoid obstruction caused by surgical instruments as well as by the hands of surgeons. Using these unique devices, anatomic landmarks were visualized using the present MRT system. The prognosis of patients was favorable, and in particular, no patients with sinus mucocele showed a recurrence of their lesions. We concluded that the MRT system used here for performing ESS was beneficial, especially in terms of the intranasal marsupialization of sinus mucoceles and for the verification of orbital contents.

Three-dimensional tomosynthesis and cone-beam computed tomography: an experimental study for fast, low-dose intraoperative imaging technology for guidance of sinus and skull base surgery

OBJECTIVES

To describe three-dimension (3-D) tomosynthesis and cone beam computed tomography (CBCT) as an intraoperative imaging system to guide both sinus and skull-base surgery in a cadaveric model.

METHODS

Five cadaveric heads underwent baseline CBCT imaging. Surgical targets were resected from each head (uncinectomy, ethmoidectomy, medial maxillectomy, pituitary gland resection, and clivus ablation). Intraoperative imaging was provided so that for a given task, the acquisition arc (theta(tot) = 20 degrees , 45 degrees , 60 degrees , 90 degrees , 178 degrees ) of the tomosynthesis scan was fixed. Different heads and tasks were allocated different acquisition angles. There was no limit to the number of scans that could be requested. Residual target was highlighted with 3-D visualization software.

RESULTS

The larger the image acquisition angle, the better the image. Only CBCT (theta(tot) approximately 178 degrees ) provided nearly isotropic 3-D spatial resolution and soft-tissue visibility in all three views. The volume of residual tissue remaining and the volume of adjacent-normal tissue that was resected were calculated as a function of tomosynthesis angle. For the easier surgical tasks (uncinectomy, ethmoidectomy) the residual tissue was not related to the tomosynthesis angle. However, for the difficult ablative tasks, the image quality became more important and tomosynthesis angle was related to the residual tissue.

CONCLUSIONS

We describe an intraoperative imaging platform that can deliver near-real-time images of the target and related structures with low radiation dose. Tomosynthesis scanning angles higher than 60 degrees provided quantifiable benefits to the surgeon and facilitated total target ablation while helping to spare surrounding structures.

Intraoperative computed tomography and automated registration for image-guided cranial surgery

OBJECTIVES

Two key problems for the use of navigation systems in image-guided surgery are accurate patient-to-image registration and the fact that with ongoing surgery the patient's anatomy is altered while the image data remains unchanged. A system for intraoperative CT imaging and fully automated registration of this image addresses both problems. It had been evaluated successfully in phantom studies. In this clinical study, we assessed the impact of the system on intraoperative workflow and registration accuracy in everyday patient care.

METHODS

In ten patients who underwent image-guided surgery, CT image data were acquired intraoperatively and were automatically registered in the navigation system. Registration accuracy and surgical outcome were assessed clinically. In six of these patients, a maxillary splint with markers had been inserted to cross-check registration accuracy. The target registration error of these markers was measured.

RESULTS

In all cases, registration accuracy was clinically sufficient and the surgical task could be performed successfully. In those cases where a maxillary template with target markers was attached for additional control of the registration accuracy, the target registration error was always better than 2 mm. Automated registration reduced the intraoperative registration time considerably and partially compensated for the time needed to perform the image data acquisition.

CONCLUSIONS

Intraoperative CT imaging and automated registration successfully address the two key problems of image-guided surgery. The method is robust and accurate and proved its usability in everyday patient care.

Intraoperative cone-beam computed tomography in oral and maxillofacial surgery using a C-arm prototype: first clinical experiences after treatment of zygomaticomaxillary complex fractures

PURPOSE

To describe the first clinical applications of intraoperative cone-beam computed tomography with an integrated flat-panel detector in oral and maxillofacial surgery after surgical treatment of zygomaticomaxillary complex fractures

PATIENTS AND METHODS

Nine cone-beam computed tomography datasets of patients with zygomaticomaxillary complex fractures were intraoperatively acquired using a mobile isocentric C-arm (PowerMobil; Siemens Medical Solutions, Erlangen, Germany), including a flat-panel detector. Datasets based on 400, 200, and 100 fluoroscopic images were performed with different tube currents (4.6 mA, 3.3 mA, 2.3 mA, 1.2 mA, and 0.5 mA) and a current tube voltage of 100 kV. Postprocessing resulted in 15 different datasets available for comparison with corresponding preoperative computed tomography datasets. Four oral and maxillofacial surgeons and 2 experienced radiologists evaluated each dataset regarding noise, transition, and the delimitation of landmarks.

RESULTS

All examinations were successfully performed. Reconstructed datasets showed high-resolution images of all midfacial osseous structures in near-computed tomography quality. Regarding high-contrast structures, detailed analyses of datasets acquired in this study suggest that the parameters 400 projections, 1.2 mA, and 100 kV are sufficient. In terms of soft-tissue visualization, a higher level of mA seems preferable.

CONCLUSIONS

The tested prototype predicts a new era in cone-beam computed tomography imaging. The integration of a flat-panel detector will overcome the limitations of current available systems. The size of the field of view is increased allowing regularly the visualization of the whole facial skeleton. Particularly in cases of open reduction of unilateral fractures, the assessment of symmetry is of clinical value.

Indications for image-guidance in pediatric sinonasal surgery

OBJECTIVES

To determine the indications and safety of image-guidance for pediatric sinonasal surgery.

METHODS

A retrospective review was carried out of all patients undergoing image-guided sinus surgery using a single electromagnetic navigation system. All patients less than 18 years who underwent image-guided endoscopic sinus surgery over a 5-year period at a tertiary children's hospital were included. The means and ranges of age, preoperative setup time, gender distribution, and indications for surgery were determined. Operative time, anatomic regions explored, and intraoperative complications were also analyzed.

RESULTS

Thirty-three patients underwent image-guided surgery over a 5-year period. The mean age was 12 years, with 23 males and 10 females. Mean operative time and preoperative setup time was 128 and 43 min, respectively. Indications for surgery included chronic (30.3%) and acute (12.1%) rhinosinusitis, nasopharyngeal angiofibroma (9.1%), allergic rhinosinusitis (9.1%) and allergic fungal sinusitis (9.1%).

CONCLUSIONS

This series represents the largest collection of pediatric image-guided sinus surgery. In our population, image-guidance was only used for advanced sinonasal procedures where there was an anatomic abnormality or disease that extended to the sphenoid sinus, frontal sinus, orbit, or skull base. No complications were noted.

The accuracy of image guided surgery based on cone beam computer tomography image data

OBJECTIVE

The objective of this study was to verify if accurate patient-to-image registration for precision navigation in maxillofacial surgery is possible based on cone beam computed tomography (CBCT) image data.

STUDY DESIGN

A maxillary registration template was placed on a standard plastic skull phantom that was equipped with a custom made model of the maxilla and with target markers. Imaging was performed with a CBCT device (Newtom 9000 Digital Volume Tomograph (DVT), QR s.r.l., Verona, Italy) and a computed tomography (CT) scanner (Somatom 4, Siemens, Forchheim, Germany). Using an infrared navigation system (Polaris, NDI, Waterloo, Ontario), multiple pair-point registration of both image data sets and the phantom were performed. The target registration error (TRE) was evaluated.

RESULTS

A total of 243 registrations were performed for either image data set. The spatial distribution of TRE on the skull showed increasing inaccuracy with growing distance from the registration markers. The average target registration error was 1.50 +/- 0.82 mm with CBCT and 1.57 +/- 0.84 mm with CT image data and did not differ significantly. Error distribution correlated strongly between CT- and CBCT-based registration.

CONCLUSIONS

The overall registration accuracy based on CBCT image data was similar to CT. The strong correlation of the geometric distribution of TRE between CT- and CBCT-based measurements proves that CBCT can be equivalent to CT in image-guided maxillofacial surgery.

Image quality and localization accuracy in C-arm tomosynthesis-guided head and neck surgery

The image quality and localization accuracy for C-arm tomosynthesis and cone-beam computed tomography (CBCT) guidance of head and neck surgery were investigated. A continuum in image acquisition was explored, ranging from a single exposure (radiograph) to multiple projections acquired over a limited arc (tomosynthesis) to a full semicircular trajectory (CBCT). Experiments were performed using a prototype mobile C-arm modified to perform 3D image acquisition (a modified Siemens PowerMobil). The tradeoffs in image quality associated with the extent of the source-detector arc (theta(tot)), the number of projection views, and the total imaging dose were evaluated in phantom and cadaver studies. Surgical localization performance was evaluated using three cadaver heads imaged as a function of theta(tot). Six localization tasks were considered, ranging from high-contrast feature identification (e.g., tip of a K-wire pointer) to more challenging soft-tissue delineation (e.g., junction of the hard and soft palate). Five head and neck surgeons and one radiologist participated as observers. For each localization task, the 3D coordinates of landmarks pinpointed by each observer were analyzed as a function of theta(tot). For all tomosynthesis angles, image quality was highest in the coronal plane, whereas sagittal and axial planes exhibited a substantial decrease in spatial resolution associated with out-of-plane blur and distortion. Tasks involving complex, lower-contrast features demonstrated steeper degradation with smaller tomosynthetic arc. Localization accuracy in the coronal plane was correspondingly high, maintained to < 3 mm down to theta(tot) approximately 30 degrees, whereas sagittal and axial localization degraded rapidly below theta(tot) approximately 60 degrees. Similarly, localization precision was better than approximately 1 mm within the coronal plane, compared to approximately 2-3 mm out-of-plane for tomosynthesis angles below theta(tot) approximately 45 degrees. An overall 3D localization accuracy of approximately 2.5 mm was achieved with theta(tot) approximately 90 degrees for most tasks. The high in-plane spatial resolution, short scanning time, and low radiation dose characteristic of tomosynthesis may enable the surgeon to collect near real-time images throughout the procedure with minimal interference to surgical workflow. Therefore, tomosynthesis could provide a useful addition to the image-guided surgery arsenal, providing on-demand, high quality image updates, complemented by CBCT at critical milestones in the surgical procedure.

Real-time computed tomography image update for endoscopic skull base surgery

INTRODUCTION

The development of computer-aided systems for endoscopic sinus surgery has enabled surgical navigation through diseased or surgically altered sinus anatomy with increased confidence. However, conventional computer-aided systems do not provide intra-operative updated computed tomography imaging. We describe the technical aspects of the xCAT, a new intra-operative mobile volume computed tomography scanner.

TECHNICAL REPORT

A patient with a malignant melanoma unwittingly removed at another hospital underwent surgery for removal of the lateral nasal wall and directed biopsies, in an attempt to identify the site of tumour origin. The procedure was performed with the GE InstaTrak 3500 Plus computer-aided system, updated with intra-operative computed tomography images. Intra-operative, updated images were integrated successfully into the InstaTrak system, and these images were consistent with the observed endoscopic anatomy.

CONCLUSION

The xCAT intra-operative mobile volume computed tomography scanner is a technological advancement that can assist the endoscopic sinus surgeon when performing complex rhinological and skull base procedures.

Image-to-patient registration techniques in head surgery

Frame-based stereotaxy was developed in neurosurgery at the beginning of the last century, evolving from atlas-based stereotaxy to stereotaxy based on the individual patient's image data. This established method is still in use in neurosurgery and radiotherapy. There have since been two main developments based on this concept: frameless stereotaxy and markerless registration. Frameless stereotactic systems ('navigation systems') replaced the cumbersome stereotactic frame by mechanically and later also optically or magnetically tracked instruments. Stereotaxy based on the individual patient's image data introduced the problem of patient-to-image data registration. The development of navigation systems based on frameless stereotaxy has dramatically increased its use in surgical disciplines other than neurosurgery, but image-guided surgery based on fiducial marker registration needs dedicated imaging for registration purposes, in addition to the diagnostic imaging that might have been performed. Markerless registration techniques can overcome the resulting additional cost and effort, and result in more widespread use of image-guided surgery techniques. In this review paper, the developments that led to today's navigation systems are outlined, and the applications and possibilities of these methods in the field of maxillofacial surgery are presented.

Advances in imaging of the paranasal sinuses

Imaging technology has played a significant role in the diagnosis and management of sinonasal disorders. Plain sinus films are almost exclusively replaced by CT in the work-up for inflammatory sinus disease. MRI provides complementary information to CT in cases of sinonasal and skull-base neoplasms. The evolution of endoscopic surgical techniques for the paranasal sinuses and skull base is made possible by the parallel advancement of imaging technologies. Recent advances that are currently in clinical use have included multidetector row CT scanners and computer image-guidance systems for surgery. Three-dimensional CT angiography, image-guided CT-MR fusion, and intraoperative image-guidance are new techniques that are currently being evaluated. As imaging technology continues to advance, so does the capability to treat diseases beyond the sinuses and skull base with minimally invasive, endoscopic approaches.

Intraoperative cone-beam CT for guidance of head and neck surgery: Assessment of dose and image quality using a C-arm prototype

Cone-beam computed tomography (CBCT) with a flat-panel detector represents a promising modality for intraoperative imaging in interventional procedures, demonstrating sub-mm three-dimensional (3D) spatial resolution and soft-tissue visibility. Measurements of patient dose and in-room exposure for CBCT-guided head and neck surgery are reported, and the 3D imaging performance as a function of dose and other acquisition/reconstruction parameters is investigated. Measurements were performed on a mobile isocentric C-arm (Siemens PowerMobil) modified in collaboration with Siemens Medical Solutions (Erlangen, Germany) to provide flat-panel CBCT. Imaging dose was measured in a custom-built 16 cm cylindrical head phantom at four positions (isocenter, anterior, posterior, and lateral) as a function of kVp (80-120 kVp) and C-arm trajectory ("tube-under" and "tube-over" half-rotation orbits). At 100 kVp, for example ("tube-under" orbit), the imaging dose was 0.059 (isocenter), 0.022 (anterior), 0.10 (posterior), and 0.056 (lateral) mGy/ mAs, with scans at approximately 50 and approximately 170 mAs typical for visualization of bony and soft-tissue structures, respectively. Dose to radiosensitive structures (viz., the eyes and thyroid) were considered in particular: significant dose sparing to the eyes (a factor of 5) was achieved using a "tube-under" (rather than "tube-over") half-rotation orbit; a thyroid shield (0.5 mm Pb-equivalent) gave moderate reduction in thyroid dose due to x-ray scatter outside the primary field of view. In-room exposure was measured at positions around the operating table and up to 2 m from isocenter. A typical CBCT scan (10 mGy to isocenter) gave in-air exposure ranging from 29 mR (0.26 mSv) at 35 cm from isocenter, to <0.5 mR (<0.005 mSv) at 2 m from isocenter. Three-dimensional (3D) image quality was assessed in CBCT reconstructions of an anthropomorphic head phantom containing contrast-detail spheres (11-103 HU; 1.6-12.7 mm) and a natural human skeleton. The contrast-to-noise ratio (CNR) was evaluated across a broad range of dose (0.6-23.3 mGy). CNR increased as the square root of dose, with excellent visualization of bony and soft-tissue structures achieved at approximately 3 mGy (0.10 mSv) and approximately 10 mGy (0.35 mSv), respectively. The prototype C-arm demonstrates CBCT image quality sufficient for guidance of head and neck procedures based on soft-tissue and bony anatomy at dose levels low enough for repeat intraoperative imaging, with total dose over the course of the procedure comparable to or less than the effective dose of a typical (2 mSv) diagnostic CT of the head.

Computer-aided surgery of the paranasal sinuses and skull base

Endoscopic sinus surgery is one of the most common surgical procedures in otolaryngology. However, the location of the orbit and intracranial contents in close proximity to the paranasal sinuses makes endoscopic sinus surgery potentially hazardous. Otolaryngologists have employed computer-aided surgery, or image-guided surgery, over the past two decades to enhance surgeon confidence, allow more thorough surgical dissections and possibly reduce the complication rate of endoscopic sinus surgery. Computer-aided surgery utilizes preoperative imaging to provide real-time localization of surgical instruments in the surgical field. Although computer-aided surgery originated in the neurosurgical realm, otolaryngologists soon appreciated that this technology could assist in identifying critical orbital or intracranial structures surrounding the paranasal sinuses, and potentially aid in decreasing complications. In this article, the history of image-guidance systems and their application to surgery of the paranasal sinuses and skull base will be reviewed. The components of computer-aided surgery systems and the currently available technologies for surgical instrument tracking are discussed, as well as the advantages and disadvantages of each of the tracking technologies. In addition, issues relating to the accuracy of image-guidance systems are examined. A number of institutional series noting surgeon experience with computer-aided surgery in the domain of paranasal sinus surgery are reviewed. Furthermore, the authors evaluate the utility of image-guidance technology beyond the paranasal sinuses and skull base, such as its use in surgery of the pituitary gland and pterygopalatine fossa, research and resident education. Finally, potential future applications of computer-aided surgery technology are discussed.

The next generation of navigational technology

Registration for image guidance has become significantly simplified and will continue to improve in accuracy. Unparalleled visualization of target tissues has been made possible through advances in imaging technologies,some of which have been modified to be employed directly in the operating room. With the advent of functional imaging techniques, the promise of functional rather than structural imaging suggests potentially fascinating interventions based on functional disturbances in tissue. Given the aggressive nature of the technology industry, some of the issues in surgical navigation discussed in this article have probably already been resolved and may be on their way to market. Undoubtedly, other points will also soon be addressed in novel and imaginative ways. As a result, the authors hope, the practice of rhinology will continue to evolve to improve the standard of care for patients. The future of many therapeutic interventions seems to be tied to the information infrastructure provided by information-guided therapy. Only through the innovative use of information-guided technology will further minimization of risks and maximization of benefit be achieved.

The Use of the Neuronavigator in the Orbital Surgery of a Rare Case of Rosai-Dorfman Disease

Neuronavigators are robotic devices that can help to bridge the gap between the data of three-dimensional images and the object by means of interactive computerized programs. A rare case of Rosai-Dorfman disease with prevalent bilateral endo-orbital interest is reported, in which an assisting neuronavigation system was used. The navigation system used is a stereotaxic system without the use of supporting mechanical arms, permitting bi-dimensional and tridimensional reconstruction through the data that are obtained from diagnostic equipment such as computed tomography, magnetic resonance imaging, single photon emission computed tomography, and positron emission tomography. This system has given an accurate localization of the pathological findings and has permitted a precise evaluation of the relation between the lesion and intraconical structures, which are fundamental requisites to optimize the treatment and reduce the postsurgical complications. The exciting results achieved in cerebral parenchyma surgery motivate extension of the use of neuronavigator systems to the splanchnocranial complex.

The Utility of Radiologic Studies in the Diagnosis and Management of Rhinosinusitis

The past two decades have seen the development of computed tomography scanning as the principal investigation for paranasal sinus disease. This article describes the benefits and limitations of computed tomography scanning in the assessment of rhinosinusitis. It also discusses the role of magnetic resonance imaging as a further diagnostic tool in the assessment of rhinosinusitis and in particular its complications. Other imaging modalities such as plain radiographs and ultrasound have limited use in this field. The introduction of image guidance techniques as an aid to surgical treatment and possible future developments are outlined.

Cirurgia Endoscópica Nasossinusal e da Base do Crânio Guiada por Computador

Introdução: Apesar de nas últimas décadas, as cirurgias dos seios paranasais e base de crânio terem apresentado grande progresso, principalmente com o advento dos novos instrumentais, visualização endoscópica e estudos por imagem, ainda apresentam complicações de graus variáveis. A cirurgia guiada por computador (CGC), tecnologia introduzida há poucos anos, foi idealizada para auxiliar o cirurgião na localização precisa de estruturas anatômicas durante o ato cirúrgico, proporcionando mais segurança para o paciente e para o médico. Objetivo: O objetivo deste estudo foi fazer uma avaliação global da utilidade, indicações e segurança desta tecnologia, apresentando a nossa experiência com este sistema. Forma de estudo: Clínico retrospectivo. Material e Método: Foram estudados 20 pacientes portadores de doenças nasossinusais e base de crânio, submetidos à cirurgia endoscópica dos seios paranasais e base de crânio, utilizando o sistema de navegação no período de novembro de 2000 a setembro de 2001 no Centro de Otorrinolaringologia e Fonoaudiologia de São Paulo. Dos 20 pacientes operados, onze (55%) eram do sexo feminino e 9 (45%), do sexo masculino, idades entre 16 e 74 anos, sendo a idade média de 46 anos. As avaliações da utilidade, indicações e segurança, foram baseadas em critérios subjetivos e objetivos. 1. Utilidade: foi avaliada segundo a necessidade ou não do auxílio do sistema pelo cirurgião durante as cirurgias - nenhuma, pouca, moderada, muita. 2. Indicações mais importantes: baseadas nas cirurgias ou nas áreas cirúrgicas onde o cirurgião mais necessitou do sistema. 3. Segurança: avaliada pela ocorrência ou não de complicações intra e pós-operatórias. Resultados: O sistema foi utilizado em todas as cirurgias, embora não com a mesma freqüência ou necessidade. As cirurgias que tiveram maior necessidade do sistema foram as de base de crânio, poliposes revisionais com anatomia alterada e na região do recesso frontal. Não houve nenhuma complicação intra ou pós-operatória nos pacientes operados referentes ao método empregado. Conclusão: O sistema de navegação associado à cirurgia video-endoscópica mostrou-se bastante útil e seguro nas cirurgias de base de crânio e nasossinusais, mas não essencial. O sistema se mostrou particularmente útil nas doenças do recesso e seio frontal, seio esfenoidal, doenças extensas, pacientes com alterações anatômicas, cirurgias revisionais e lesões de base de crânio.

Image-guided endoscopic transnasal removal of recurrent pituitary adenomas

OBJECTIVE

To assess the role that neuronavigation plays in assisting endoscopic transsphenoidal reoperations for recurrent pituitary adenomas.

METHODS

During a 45-month period, 19 endoscopic endonasal transsphenoidal reoperations were performed for recurrent pituitary adenomas. In 11 of 19 patients, the procedure was performed with the aid of an optically guided system. Clinical records were reviewed retrospectively, with attention to the following: comparison of baseline clinical data, the duration of surgery, and the postoperative course and complications of both image-guided and non-image-guided endoscopic reoperations. In addition, to test the reliability of the neuronavigation system, we made measurements of intraoperative accuracy in five additional transnasal endoscopic procedures in "virgin" noses and sphenoidal sinuses.

RESULTS

In both groups studied, we found no difference with regard to either morbidity or mortality, which were null. The mean setup time was 13 minutes shorter in non-image-guided procedures (P = 0.021), and the operative time was 36 minutes shorter in image-guided procedures (P = 0.038). No other statistically significant differences were found between the two groups. In all cases, we found that the system performed without malfunction. Continuous information regarding instrument location and trajectory was provided to the surgeon. Measurements of the intraoperative accuracy in the axial, coronal, and sagittal planes indicated a mean intraoperatively verified system error of 1.6 +/- 0.6 mm.

CONCLUSION

Neuronavigation can be applied during endonasal transsphenoidal endoscopic surgery and requires a minimal amount of time. It makes reoperation easier, faster, and probably safer.

A computed tomographic guide to endoscopic sinus surgery: axial and coronal views

SUMMARY

The purpose of this article is to correlate endoscopic surgical procedures in the sinuses with computer tomographic (CT) scans. Twelve commonly performed procedures were color-coded on a set of normal coronal and axial CT scans. The illustrated procedures are uncinectomy/antrostomy, anterior ethmoidectomy, posterior ethmoidectomy, sphenoidotomy, partial inferior turbinectomy, partial middle turbinectomy, septoplasty, frontal recess approach, dacrocystorhinostomy, orbital decompression, optic nerve decompression, and medial maxillectomy. Drainage of a medial orbital abscess is discussed but not illustrated. A brief description of the indications, surgical approach, and complications of each procedure is also provided.