Image-guided Surgery of the Anterior Skull Base

The Role of Augmented Reality Neuronavigation in Transsphenoidal Surgery: A Systematic Review

In the field of minimally invasive neurosurgery, microscopic transsphenoidal surgery (MTS) and endoscopic transsphenoidal surgery (ETS) have been widely accepted as a safe approach for pituitary lesions and, more recently, their indications have been extended to lesions at various skull base regions. It is mandatory during transsphenoidal surgery (TS) to identify key anatomical landmarks in the sphenoid sinus and distinguish them from the lesion. Over the years, many intraoperative tools have been introduced to improve the neuronavigation systems aiming to achieve safer and more accurate neurosurgical interventions. However, traditional neuronavigation systems may lose the accuracy of real-time location due to the discrepancy between the actual surgical field and the preoperative 2D images. To deal with this, augmented reality (AR)-a new sophisticated 3D technology that superimposes computer-generated virtual objects onto the user's view of the real world-has been considered a promising tool. Particularly, in the field of TS, AR can minimize the anatomic challenges of traditional endoscopic or microscopic surgery, aiding in surgical training, preoperative planning and intra-operative orientation. The aim of this systematic review is to analyze the potential future role of augmented reality, both in endoscopic and microscopic transsphenoidal surgeries.

[Use of navigation in skull base surgery]

The review briefly presents the history of development of navigation systems in neurosurgery. The idea of the existing principles underlying the navigation systems used in neurosurgery is given. Currently, the basic principles of navigation are optical and electromagnetic. Studies are presented comparing the accuracy of various navigation systems. Optical navigation demonstrates greater accuracy compared to electromagnetic, but both methods demonstrate a submillimeter error in the experiment. The history of use of navigation in the surgery of the skull base is analyzed in detail, the most relevant areas of use of navigation within the surgery of the skull base are considered: craniofacial reconstruction, endoscopic endonasal surgery, surgery of common tumors of the skull base affecting the infratemporal, pterygopalatine fossa, temporomandibular joint. Indications for the use of navigation, limitations of the methodology are explained.

Severe Cerebral Complications Secondary to Perforation Injury of the Anterior Skull Base During Sinonasal Surgery: An Underappreciated Problem?

OBJECTIVE

Functional endonasal sinus surgery (FESS) is widely practiced and is considered a generally safe procedure. Skull base injuries occur in <1% of procedures and are typically associated with cerebrospinal fluid leaks. Rarely, skull base injuries might result in cerebral lesions. Here we present a series of 4 patients with iatrogenic perforating injuries of the anterior skull base and cerebral lesions after routine FESS.

METHODS

Four patients with iatrogenic perforating cerebral lesions after routine FESS, performed at other institutions, were referred to a tertiary neurosurgery department. Within a 10-year period these procedures were performed in 3 patients as endoscopic FESS and as a microscopic FESS in 1 patient.

RESULTS

There were 3 men and 1 woman. Mean age at the time of surgery was 50 years. In 3 instances (in which an endoscope was used), the ear, nose, and throat physician had noted perforation of the skull base during surgery, but it went unnoticed in 1 patient operated with the microscope. Frontal lobe hematoma occurred in all patients, and in 3 of them cerebral infarction developed secondary to injury of branches of the anterior cerebral artery. Three patients developed acute hydrocephalus. Two had rapid global brain swelling and they succumbed within days. The other 2 patients survived without apparent neurological deficits.

CONCLUSIONS

Cerebral lesions during FESS still occur in contemporary surgery and they are possibly underreported. Even with prompt conservative and surgical measures, these lesions may result in catastrophic outcome. Associated vascular injuries have a worse prognosis. The only risk factor associated with lethal outcome in our series was younger age.

Real-time continuous image-guided surgery: Preclinical investigation in glossectomy

OBJECTIVES/HYPOTHESIS

To develop, validate, and study the efficacy of an intraoperative real-time continuous image-guided surgery (RTC-IGS) system for glossectomy.

STUDY DESIGN

Prospective study.

METHODS

We created a RTC-IGS system and surgical simulator for glossectomy, enabling definition of a surgical target preoperatively, real-time cautery tracking, and display of a surgical plan intraoperatively. System performance was evaluated by a group of otolaryngology residents, fellows, medical students, and staff under a reproducible setting by using realistic tongue phantoms. Evaluators were grouped into a senior and a junior group based on surgical experience, and guided and unguided tumor resections were performed. National Aeronautics and Space Administration Task Load Index (NASA-TLX) scores and a Likert scale were used to measure workloads and impressions of the system, respectively. Efficacy was studied by comparing surgical accuracy, time, collateral damage, and workload between RTC-IGS and non-navigated resections.

RESULTS

The senior group performed more accurately (80.9% ± 3.7% vs. 75.2% ± 5.5%, P = .28), required less time (5.0 ± 1.3 minutes vs. 7.3 ± 1.2 minutes, P = .17), and experienced lower workload (43 ± 2.0 vs. 64.4 ± 1.3 NASA-TLX score, P = .08), suggesting a trend of construct validity. Impressions were favorable, with participants reporting the system is a valuable practice tool (4.0/5 ± 0.3) and increases confidence (3.9/5 ± 0.4). Use of RTC-IGS improved both groups' accuracy, with the junior group improving from 64.4% ± 5.4% to 75.2% ± 5.5% (P = .01) and the senior group improving from 76.1% ± 4.5% to 80.9% ± 3.7% (P = .16).

CONCLUSIONS

We created an RTC-IGS system and surgical simulator and demonstrated a trend of construct validity. Our navigated simulator allows junior trainees to practice glossectomies outside the operating room. In all evaluators, navigation assistance resulted in increased surgical accuracy.

LEVEL OF EVIDENCE

NA Laryngoscope, 127:E347-E353, 2017.

Implementation of a miniaturised navigation system in head and neck surgery for the detection and removal of foreign bodies

The removal of embedded blast-generated fragments from soft tissue is very difficult, especially in the head and neck regions. First, because many retained foreign materials are non-metallic and can, therefore, not be detected by fluoroscopy, and second, because a broad exploration of the soft tissue is not possible in the facial area for functional and cosmetic reasons. Intraoperative navigation computer-assisted surgery (CAS) may facilitate the retrieval of foreign bodies and reduce exploration trauma. In a blind trial, five test specimens of different materials (glass, metal, wood, plastic, and stone) were inserted on the left and right sides of the head and neck of ten body donors through an intraoral incision. A second physician then detected and removed the foreign bodies from one side of the body without and from the other side of the body with navigation. We measured the duration of surgery, the extent of tissue trauma caused during surgery, the time it took to remove the foreign bodies, and the subjective evaluation of the usefulness of navigation. With the aid of the navigation system, the various foreign bodies were detected after an average of 26.7 (±35.1) s (p < 0.0001) and removed after an average of 79.1 (±66.2) s (p = 0.0239), with an average incision length of 10.0 (±3.5) mm. Without the navigation system, the foreign bodies were located after an average of 86.5 (±77.7) s and removed after an average of 74.1 (±45.9) s, with an average incision length of 13.0 mm (±3.6) mm (=0.0007). Intraoperative navigation systems are a valuable tool for removing foreign bodies from the soft tissue of the face and neck. Both the duration of surgery and the incision length can be reduced using navigation systems. Depending on the material of the foreign bodies and the signal intensity in the CT/MRI scanner, however, the detection reliability varies. All in all, navigation is considered to be a useful tool.

Evaluation of a system for high-accuracy 3D image-based registration of endoscopic video to C-arm cone-beam CT for image-guided skull base surgery

The safety of endoscopic skull base surgery can be enhanced by accurate navigation in preoperative computed tomography (CT) or, more recently, intraoperative cone-beam CT (CBCT). The ability to register real-time endoscopic video with CBCT offers an additional advantage by rendering information directly within the visual scene to account for intraoperative anatomical change. However, tracker localization error (  ∼ 1-2 mm ) limits the accuracy with which video and tomographic images can be registered. This paper reports the first implementation of image-based video-CBCT registration, conducts a detailed quantitation of the dependence of registration accuracy on system parameters, and demonstrates improvement in registration accuracy achieved by the image-based approach. Performance was evaluated as a function of parameters intrinsic to the image-based approach, including system geometry, CBCT image quality, and computational runtime. Overall system performance was evaluated in a cadaver study simulating transsphenoidal skull base tumor excision. Results demonstrated significant improvement in registration accuracy with a mean reprojection distance error of 1.28 mm for the image-based approach versus 1.82 mm for the conventional tracker-based method. Image-based registration was highly robust against CBCT image quality factors of noise and resolution, permitting integration with low-dose intraoperative CBCT.

Real-time tracking and virtual endoscopy in cone-beam CT-guided surgery of the sinuses and skull base in a cadaver model

BACKGROUND

Custom software was developed to integrate intraoperative cone-beam computed tomography (CBCT) images with endoscopic video for surgical navigation and guidance. A cadaveric head was used to assess the accuracy and potential clinical utility of the following functionality: (1) real-time tracking of the endoscope in intraoperative 3-dimensional (3D) CBCT; (2) projecting an orthogonal reconstructed CBCT image, at or beyond the endoscope, which is parallel to the tip of the endoscope corresponding to the surgical plane; (3) virtual reality fusion of endoscopic video and 3D CBCT surface rendering; and (4) overlay of preoperatively defined contours of anatomical structures of interest.

METHODS

Anatomical landmarks were contoured in CBCT of a cadaveric head. An experienced endoscopic surgeon was oriented to the software and asked to rate the utility of the navigation software in carrying out predefined surgical tasks. Utility was evaluated using a rating scale for: (1) safely completing the task; and (2) potential for surgical training. Surgical tasks included: (1) uncinectomy; (2) ethmoidectomy; (3) sphenoidectomy/pituitary resection; and (4) clival resection. CBCT images were updated following each ablative task.

RESULTS

As a teaching tool, the software was evaluated as "very useful" for all surgical tasks. Regarding safety and task completion, the software was evaluated as "no advantage" for task (1), "minimal" for task (2), and "very useful" for tasks (3) and (4). Landmark identification for structures behind bone was "very useful" for both categories.

CONCLUSION

The software increased surgical confidence in safely completing challenging ablative tasks by presenting real-time image guidance for highly complex ablative procedures. In addition, such technology offers a valuable teaching aid to surgeons in training.

[New developments in computer-assisted surgery (CAS). From intraoperative imaging to ultrasound-based navigation]

Ever faster processor capacity is having an impact on computer-assisted or computer-aided surgery (CAS). The fusion of different imaging modalities enables functional data such as PET-CT, for example, to be available in image-guided surgery. Referencing of image data is the key to precise navigation. Intraoperative data acquisition is a new approach to improving accuracy. Thus, intraoperative CT conducted under navigational support enables automatic referencing of up-to-date image data. Alternatively, intraoperative magnetic resonance imaging or intraoperative sonography can be performed. Ultrasound systems have already been successfully integrated in existing navigational systems to compensate for intraoperative tissue shifting. Ultrasound systems may play a role in the future as a single modality in image-guided surgery in soft tissue of the neck and skull bone.

Neuronavigational guidance in craniofacial approaches for large (para)nasal tumors involving the anterior skull base and upper clival lesions

OBJECTIVE

Due to the destruction of osseous landmarks of the skull base or paranasal sinuses, the anatomical orientation during surgery of frontobasal or clival tumors with (para)nasal extension is often challenging. In this relation computer assisted surgical (CAS) guidance might be a useful tool. Here, we explored the use of CAS in an interdisciplinary setting.

METHODS

The surgical series consists of 13 patients who underwent a lateral rhinotomy combined with a subfrontal craniotomy in case of significant intracranial tumor extension. The procedures were planned and assisted by advanced CAS techniques with image fusion of CT and MRI. Tumors included carcinomas (one case associated with an olfactory groove meningioma), esthesioneuroblastoma, chordoma, chondrosarcoma and ganglioglioma.

RESULTS

The application of CAS in the combined approaches was both safe and reliable for delineation of tumors and identification of vital structures hidden or encased by the tumors. There was no perioperative 30-day mortality; however two patients died 5 weeks and 5 months after craniofacial tumor resection due to worsening medical conditions. The most common perioperative morbidity was postoperative wound complication in two cases. Tumors were either removed completely, or subtotal resection was achieved allowing targeted postoperative radiotherapy.

CONCLUSION

Craniofacial approaches with intraoperative neuronavigational guidance in a multidisciplinary setting allow safe resection of large tumors of the upper clivus and the paranasal sinuses involving the anterior skull base. Complex skull base surgery with the involvement of bony structures appears to be an ideal field for advanced navigation techniques given the lack of intraoperative shift of relevant structures.

[Computer-aided surgery of the paranasal sinuses and the anterior skull base]

Endoscopic or microscopic surgery for chronic rhinosinusitis with or without nasal polyps is a routine intervention in daily practice. It is often a delicate and difficult minimally invasive intervention in a narrow space, with a tunnel view of 4 mm in the case of endoscopy and frequent bleeding in chronically inflamed tissue. Therefore, orientation in such a "labyrinth" is often difficult. In the case of polyp recurrence or tumors, the normal anatomical landmarks are often missing, which renders orientation even more difficult. In such cases, computer-aided navigation together with images such as those from computed tomography or magnetic resonance imaging can support the surgeon to make the operation more accurate and, in some cases, faster. Computer-aided surgery also has great potential for education.

Verification of clinical precision after computer-aided reconstruction in craniomaxillofacial surgery

OBJECTIVE

Computer-aided surgery (CAS) has proved to be useful in reconstructive craniomaxillofacial surgery. Preoperative creation of virtual models by segmentation of the computerized tomography (CT) dataset and mirroring of the unaffected side allows for precise planning of complex reconstructive procedures. The aim of this study was to evaluate the accuracy of the preoperative planning and the postoperative result regarding the skeletal reconstruction.

STUDY DESIGN

In a first step, the symmetry of unaffected human skulls and faces were evaluated by 20 midface CT data of skulls and 20 surface-scan data of healthy individuals. By mirroring and adjusting the original and mirrored datasets using a 3-dimensional modeling software, an automatic measurement procedure could evaluate the mean and the maximal modulus of the distances between both datasets. In a second step, 18 consecutive cases were selected which had been treated with CAS support. Group 1 consisted of orbital floor and/or medial wall fractures (n = 12), group 2 consisted of zygomatic bone fractures (n = 4), and group 3 included 2 patients who were treated by secondary orbital reconstruction including reosteotomy of the zygomatic bone (n = 2). To verify the surgical result, the preoperative CT dataset including the virtual planning and the postoperative CT dataset were compared by using image fusion. Additionally, postoperative surface scans and the clinical symptoms of the patients were evaluated.

RESULTS

No differences between the skull and face symmetry were found. Mean values for distances considering the skull symmetry were 0.83 mm for male and 0.71 mm for female and for the face symmetry 0.65 mm for male and 0.76 mm for female. Comparing the preoperative planning with the postoperative outcome, a mean accuracy of 1.49-4.12 mm with maximum modulus of 2.49-6.00 mm was achieved. Orbital true-to-original reconstructions and the secondary reconstructions were more precise than the reposition of the zygomatic bones. The postoperative acquired surface scans resulted in mean distances from 0.89 to 1.784 mm. Despite these deviations, all patients demonstrated satisfying clinical outcome.

CONCLUSION

The natural asymmetry in humans influences the accuracy of preoperative planning procedure, when the mirroring tool is used. The accuracy transforming the preoperative planning to the surgical reconstruction using CAS depends on location, surgical approach, and matter of reconstruction.

Navigationsunterstützte tumorfokussierte Chirurgie bei Schädelbasismalignomen

BACKGROUND

Multimodal strategies are required due to the poor prognosis for locally advanced frontal skull base tumors staged as T4. Therefore, a further increase in the degree of invalidity caused by therapy should be avoided, if possible, to preserve the quality of life. As the incidence of these tumors is low, there are no evidence-based, generally accepted therapeutic strategies.

METHODS

We evaluated the clinical results of three patients with extended frontal skull base malignomas staged as T4 tumors. The clinical course as well as the surgical technique were analyzed.

RESULTS

High dose neoadjuvant therapy for tumor downsizing was performed in all three patients within a multimodal therapy concept. The additional space for surgical manipulation close to the tumor borders, non-traumatically produced by tumor remission, permitted a safely navigated, controlled resection of the tumor under endoscopic or microscopic viewing using an approach associated with reduced trauma as "targeted surgery".

CONCLUSIONS

Surgical radicality is limited by the direct vicinity of locally progressive T4 tumors to the frontal brain and other vital structures. A controlled tumor downsizing allows the resection of such tumors using a minimally invasive approach assisted by instrumental navigation leading to less traumatization.

Endoscopic pituitary surgery with and without image guidance: an experimental comparison

BACKGROUND

The combination of image guidance and endoscopy is the newest trend in pituitary surgery. To assess the impact of image guidance on EPS, we measured and calculated the accuracy of the system and compared some critical surgical steps with and without image guidance under experimental conditions in terms of surgical time and precision.

METHODS

Twenty cadaver heads were explored by standard endoscopic transsphenoidal surgical technique. Optic-radiologic correlations of topographic landmarks were photographed, and the system accuracy and actual visual accuracy were recorded. Some important anatomical parameters were measured in surgical field and on navigation system, and the differences were calculated and analyzed. Some critical surgical steps were recorded and compared between with and without image guidance.

RESULTS

The system accuracy (root mean square), calculated by the computer automatically, showed a mean value of 0.28 +/- 0.06 mm. In some cases, there was a small discrepancy between the visible position of the pointer and its counterpart on the navigation system; we coined this actual visual accuracy. The average value was 1.53 +/- 0.49 mm. The maximum difference between the measurements from the navigation system and from their actual visual counterparts was less than 7%. With and without image guidance, in normal anatomical conditioning, there was no statistically significant difference between the duration of ostium sphenoidale exposure and sellar window creation; however, in anatomical variations, the surgical time was shown to be significantly shorter when navigation was used.

CONCLUSION

We have demonstrated in this experimental setting that the electromagnetic tracking image guidance possesses a high accuracy at millimetric level and therefore provides precise localization and orientation in EPS. With the assistance of neuronavigation system, it is advantageous not only in saving operating time, but also, more importantly, in enhancing the orientation, thus, rendering surgeries safer and more efficient. During the in vivo pituitary surgery, EPS with image guidance can provide accurate and reliable stereoinformation to achieve better results with lesser risks, particularly in complex cases or in reoperations, even in the hands of experienced surgeons.

Investigation of C-arm cone-beam CT-guided surgery of the frontal recess

OBJECTIVE/HYPOTHESIS

A cone-beam CT (CBCT) imaging system based on a mobile C-arm (Siemens PowerMobil) incorporating a high-performance flat-panel detector (Varian PaxScan) has been developed in our laboratory. We hypothesize that intraoperative C-arm CBCT provides image quality and guidance performance sufficient to assist surgical approach to the frontal recess.

STUDY DESIGN

A preclinical prospective study was conducted using six cadaver heads to assess the performance characteristics and the potential clinical utility of this imaging system.

METHODS

The mobile C-arm was employed for intraoperative CBCT guidance of the endoscopic approach to twelve frontal recesses.

RESULTS

The imaging system is capable of sub-mm 3D spatial resolution with bone and soft-tissue visibility and a field of view sufficient for guidance of head and neck surgery. The system can generate intraoperative, volumetric CT images rapidly with an acceptably low radiation exposure to the patient and with image quality sufficient for most surgical tasks. Moreover, the system is portable and compatible with the surgical setup, providing excellent access to the patient. Finally, the accuracy of the system is not bound to a registration process.

CONCLUSIONS

The ability to create updated images as surgery progresses introduces the concept of 'near-real-time' CT guidance for head and neck surgery. We found that the use of CBCT increased surgical confidence in accessing the frontal recess, resolved ambiguities with anatomical variations, and provided valuable teaching information to surgeons in training in both preoperative planning and correlation between tri-planar CT scans and intraoperative endoscopic findings.

Intraoperative computed tomography in otorhinolaryngology

CONCLUSIONS

Intraoperative CT surgery provides the surgeon with additional information about the altered surgical site in difficult anatomical situations. The skull base and lamina papyracea may be revealed by means of intraoperative CT, which may be beneficial in endonasal sinus surgery involving difficult surgical sites, although individual ethmoid cells cannot be assessed owing to blood artefacts. This provides the surgeon with valuable information that may facilitate the procedure considerably. In soft-tissue surgery it is advisable to apply a contrast agent in order to achieve good soft-tissue contrast, thus allowing the tumour to be adequately distinguished from benign tissue. The intraoperative application of CT is a fairly time-consuming procedure, partly owing to the preparation time (set-up of the appliance; 10-min warming-up phase) and partly due to the length of time required to calculate each image (15 s).

OBJECTIVE

CT is a well-established imaging method for the assessment of osseous and soft-tissue structures in the head and neck region. Saving information and transferring it to the intraoperative site may, however, be problematic. Computer-assisted navigation systems are now able to assist difficult surgical procedures in the field of otolaryngology. To investigate the indications for intraoperative CT, we used it in various surgical procedures in the head and neck region.

MATERIAL AND METHODS

Intraoperative CT was applied using the Tomoscan M in 46 cases in order to demonstrate the surgical benefit of the following procedures: endonasal surgical procedures on the paranasal sinuses (maxillary and ethmoidal sinusitis, anterior fracture of the sphenoidal sinus); tumour removal by means of laser surgery (carcinomas of the hypopharynx and larynx); and cochlear implantation (to verify the electrode position). After positioning the patient on the CT table, the workstation was set up in the operating theatre. If necessary, the gantry could be moved over the patient's head without repositioning the patient.

RESULTS

Intraoperative CT was used to assist in the exposure of the skull base and lamina papyracea in endonasal surgery of the paranasal sinuses. Individual ethmoidal sinuses could not be evaluated owing to blood artefacts. Intraoperative imaging proved particularly helpful in revision surgery for chronic sinusitis in cases with missing anatomical landmarks owing to previous surgeries, where there is an increased risk of inflicting damage to the skull base or orbita. The resection margins can be determined in craniofacial resections. In soft-tissue procedures, such as tumour removal by means of laser surgery, it proved possible to visualize the resection borders of malignant tumours. Assessment of the electrode position in cochlear implantation is particularly useful in revision cases and in cases of cochlear obliteration.

[Computer assisted methods in reconstructive and function-preserving orbital surgery. New capabilities of computer assisted preoperative surgical planning (CAPP) and computer assisted surgery (CAS)]

BACKGROUND

Orbital reconstruction after tumor or trauma makes high demands on the surgeon when restoring the optic axis and cosmetic features. Computer-assisted preoperative planning surgery (CAPP) and computer-assisted surgery (CAS) allow calculation of the form of the orbital cavity to be reconstructed preoperatively as well as the process of its realization intraoperatively.

METHODS

We developed new planning software methods for this surgical procedure. For validation the deviation of accuracy was assessed between the virtual and the real model in eight patients with surgical reconstruction of the orbit.

RESULTS

The check of accuracy of the reconstructions compared to the planning of the surgery by fusion of preoperative and postoperative data resulted in a mean deviation of 1.74 mm. The volumetric measurements presented a mean deviation of 0.2 cm(3) with an accuracy of >99%. The accuracy of linear measurements with the techniques of image fusion of the "feature-based" method was 0.38 mm and thus close to the technical threshold of effective data accuracy of 0.35 mm. The enophthalmus could be assessed more objectively with this method compared to using the Hertel index.

CONCLUSIONS

CAPP and CAS are helpful in reconstructive orbital surgery to verify the position of the optic axis and the cosmetic result intraoperatively.

Image-Guided Procedures of the Skull Base

The primary factor in determining the surgical approach to skull base pathology should not be the presence or absence of IGS. The knowledge and experience of the surgeon is far more important than any technology or instrumentation. As with any computerized system, IGS is susceptible to numerous human and technical errors that can lead a surgeon astray. IGS must be used solely as a preoperative planning instrument and an intraoperative confirmatory tool. Under no circumstances should a surgeon proceed with a procedure using only information obtained from an IGS system, nor should a surgeon feel compelled to perform operations for which they have not had adequate training simply because IGS is now widely available. Continued advances in endoscopic equipment, radio-graphic techniques, and IGS systems will permit the rhinologist to continue to stretch the minimally invasive boundaries in treating skull base pathology.

Endoscopic Surgery of the Anterior Skull Base

OBJECTIVES/HYPOTHESIS

Traditional surgical approaches to the anterior skull base often involve craniotomy, facial incisions, disruption of skeletal framework, tracheotomy, and an extended hospital stay. As experience with endoscopic sinus surgery has grown, the techniques and equipment have been found to be adaptable to treatment of lesions of the anterior and central skull base. A minimally invasive endoscopic approach theoretically offers the advantages of avoiding facial incisions, osteotomies, and tracheotomy; surgery should be less painful, recovery quicker, and hospital stays should be shorter. The study attempted to assess endoscopic approaches to the anterior and central skull base for its ability to achieve those goals.

STUDY DESIGN

Retrospective review of 72 cases performed at a single institution from November 1996 to July 2003. A subgroup of 15 patients who underwent endoscopic approach to their pituitary tumors was compared with a similar group of 15 patients who underwent traditional open trans-sphenoidal surgery for their pituitary tumors.

METHODS

Patient records were analyzed and information tabulated for age, sex, disease, location of lesion, operative time, use of image-guided surgical systems, blood loss, length of intensive care unit stay, duration of operative pain, length of postoperative hospitalization, complications, and completeness of resection.

RESULTS

Of the cases, 86.1% were performed exclusively endoscopically, and 13.9% used a combination of endoscopic and open techniques. An image-guided surgical system was used in 83% of cases. Hospital length of stay was 2.3 days for the exclusively endoscopic group as opposed to 8 days for the combined group. With the patients with pituitary tumors, operative times were similar between the two groups (255.13 vs. 245.73 min), blood loss was less in the endoscopic group (125.33 vs. 243.33 mL), pain duration was shorter in the endoscopic group (10 of 15 patients pain free on postoperative day 1 vs. 2 of 15 patients pain free in the open group), and intensive care unit stay and hospital length of stay were both shorter in the endoscopic group. Complication rates and completeness of resection was similar in both groups, although the open group had a higher rate of complications related to the approach to the sella.

CONCLUSION

The study demonstrated the safety and efficacy of judicious endoscopic approaches to anterior skull base lesions. An outcomes assessment in pituitary surgery demonstrates advantages of an endoscopic approach in appropriate cases.

Combined modeling and experimental approach for the development of dual-release polymer millirods

This paper describes a combined modeling and experimental approach for the design and development of a polymer device to provide local drug therapy to thermally ablated solid tumors. The polymer device, in the shape of cylindrical millirod, will be implanted via image-guided procedures into the center of the ablated tumor. Drug released from the millirod aims to eliminate residual cancer cells at the boundary of the normal and ablated tissue following thermal ablation to provide an effective treatment of the total tumor volume. The design of the millirod release kinetics is based on a mathematical model of drug transport in the ablated tumor and the surrounding normal tissue. The optimal release kinetics consists of a dual-release process-a burst release followed by sustained release-to provide the most optimal drug pharmacokinetics at the ablation boundary. Model analysis leads to a quantitative correlation of burst dose and release rates to the ablation size and the drug concentration at the ablation boundary. A three-layer polymer millirod is produced by a dip-coating method, and in vitro study demonstrates the dual-release kinetics in which a burst release occurs within 2 h followed by a sustained release over 7 -10 days. Independent control of the burst and sustained release rates is achieved by varying the structural composition of the outer and middle layers of the millirods, respectively. Results from this study provide the rational basis and experimental feasibility of dual-release millirods for further efficacy studies in solid tumors.