Intraoperative electro-oculographic Monitoring for Skull Base Surgery

During surgery on the skull base, preservation of the integrity of the ocular motor nerves is vitally important. Intraoperative electrophysiological monitoring methods for protecting such functions have been reported by several investigators. However, these methods so far have not been popularized sufficiently, due to the difficulty and complexity of the procedures involved. The authors have developed an extremely simple but far more reliable method using electro-oculography under total intravenous anesthesia with propofol to preserve the integrity of the ocular motor nerves. The ocular motor nerves were stimulated with a monopolar electrode intracranially, and the polarity of the waves was recorded using surface electrodes placed around the eyeball, yielding precise information concerning the locations of the oculomotor nerve and/or abducent nerve. In addition, by performing continuous monitoring, invasive procedures affecting the ocular motor nerves could be detected as spontaneous ocular movements. In practice at our department, this method has been applied in 12 cases with tumors close to the ocular motor nerves, and has produced excellent results.     

Image-Guided Robotic Skull Base Surgery

Objectives To describe the potential uses of computed tomography image guidance in concert with the surgical robot for skull base surgery.Design An anatomical study was conducted.Setting Tertiary academic center.Participants Cadaveric skull.Main Outcome Measures The primary outcome measure was to measure the accuracy of robotic arm positioning to anatomical landmarks on a skull using image guidance and the surgical robot synchronously. Instruments with different angles of rotations were used. Estimated systematic error was calculated and compared with achieved errors. Clinical applications of metachronous image guidance and robotic system were discussed.Results The skull model approximated < 1 mm accuracy using standard image guidance instruments and the 0-degree robotic arm positioning. Increased angles of instruments from 20 to 60 degrees on the robotic system revealed more significant increases in error than estimated.Conclusions Image guidance may be useful for transoral robotic approaches. Precise movements are improved by limiting the angle of deviation. Future studies will help optimize the combined technologies before validating the study in clinical settings.     

Intraoperative electro-oculographic Monitoring for Skull Base Surgery

During surgery on the skull base, preservation of the integrity of the ocular motor nerves is vitally important. Intraoperative electrophysiological monitoring methods for protecting such functions have been reported by several investigators. However, these methods so far have not been popularized sufficiently, due to the difficulty and complexity of the procedures involved. The authors have developed an extremely simple but far more reliable method using electro-oculography under total intravenous anesthesia with propofol to preserve the integrity of the ocular motor nerves. The ocular motor nerves were stimulated with a monopolar electrode intracranially, and the polarity of the waves was recorded using surface electrodes placed around the eyeball, yielding precise information concerning the locations of the oculomotor nerve and/or abducent nerve. In addition, by performing continuous monitoring, invasive procedures affecting the ocular motor nerves could be detected as spontaneous ocular movements. In practice at our department, this method has been applied in 12 cases with tumors close to the ocular motor nerves, and has produced excellent results.     

Complications of Anterior Skull Base Surgery

The complications associated with anterior skull base surgery were reviewed in 49 consecutive patients treated between November 1986 and August 1993. All procedures involved a combined otolaryngologic and neurosurgical approach, and the senior otolaryngologist was the same. Fifty-two procedures were completed; 37 for malignant disease and 15 for benign disease. Twenty-one of the 52 procedures had postoperative complications, a 40% complication rate. One postoperative death occurred from a myocardial infarction, for a 2% mortality rate. Infections complications were the most common, occurring in 19% of cases. The one case of meningitis responded to antibiotic therapy, without neurologic sequelae. Seven cerebrospinal fluid leaks occurred (13%); five resolved with conservative management, and two required reoperation. There was no significant difference between complication rates for patients with previous craniotomy, radiation therapy, or chemotherany compared with those with no prior therapy (p > .05). More complications occurred in patients with malignant disease than in those with benign disease (46% vs 27%), but this was not statistically significant (p > .05). Anterior and anterolateral skull base resection as part of a multidisciplinary approach to diseases of this region may provide improved palliation and may offer possible improved survival with acceptable surgical mortality. Although only 6% of patients were left with permanent neurologic sequelse in this series, the risks of serious complications are considerable.     

Endoscopic Surgery of Skull Base Chordomas

Objective To assess our clinical experience in treating midline intracranial pathology using minimally invasive surgical techniques.Design Retrospective chart review of patients undergoing endoscopic endonasal resection of clival chordomas.Setting Two tertiary referral centers in Australia and New Zealand.Main Outcome Measures Patients were assessed by intraoperative findings (macroscopic resection rate, tumor size, and operative complications) and clinical outcomes (residual disease, postoperative complications, recurrence rate, and mortality).Results Fourteen patients underwent endoscopic resection of clival chordomas (seven primary, seven revision) with a mean follow-up of 41.45 months (3 to 104 months). Macroscopic resection rates were 71% and 29%, respectively. Mean operative time was 386 minutes. Overall cerebrospinal fluid (CSF) leak rate was 3/14 (21%) and, using the nasoseptal flap, it was 0/5 (0%). Two patients developed late recurrence; one died of disease and one was treated with intensity modulated radiation therapy. Overall mortality was 2/14 (14%).Conclusion Endoscopic resection of clival chordomas is a safe and viable alternative to the traditional open approach. The nasoseptal flap is an excellent method of obtaining a watertight skull base closure. Furthermore, this series highlighted the fact that the primary attempt at surgery offers the best chance to achieve a total resection.     

Cerebral Revascularization in Skull Base Tumors

Skull base tumors involving the carotid artery pose a difficult surgical challenge. The potential for bypass grafting for cerebral revascularization carries inherent risks but may aid in tumor resection and control in those who warrant carotid sacrifice but have inappropriate natural cerebrovascular reserve. We include a review of the literature discussing the indications for carotid resection as part of skull base tumor surgery, indications for cerebral revascularization, balloon test occlusion, graft types and operative technique, complications, and results.     

Virtual Reality Augmentation in Skull Base Surgery

Objective: Skull base anatomy is complex and subject to individual variation. Understanding the complexity of surgical anatomy is faster and easier with virtual models created from primary imaging data of the patient. This study was designed to investigate the usefulness of virtual reality in image guidance for skull base procedures. Design: Primary volumetric image data from 110 patients was acquired using magnetic resonance, computed tomography (CT), and CT angiography. Pathologies included lesions in the anterior, middle, and posterior skull base. The data were transferred to an infrared-based image-guidance system for creation of a virtual operating field (VOF) with translucent surface modulation and optional "fly-through" video mode. During surgery, the target registration error for anatomical landmarks was assessed and the VOF was compared with the patient's anatomy in the operative field. Results: Complex structures like the course of the sigmoid sinus, the carotid artery, and the outline of the paranasal sinuses were well visualized in the VOF and were recognized by the surgeon instantly. Perception was greatly facilitated as compared with routine mental reconstruction of triaxial images. Accurate assessment of the depth of field and very small objects was not possible in VOF images. Conclusion: Supported by sound anatomical knowledge, creation of a virtual operating field for a surgical approach in an individual patient offers a déjà vu experience that can enhance the capabilities of a surgical team in skull base approaches. In addition, application of this technique in image-guided procedures assists in targeting or avoiding hidden anatomical structures.     

Management of Inflammatory Complications of Skull Base Surgery

Because the contents of the intracranial cavity are exposed to the upper airway, inflammatory complications are the most frequent in skull base surgery. If dura has to be resected and reconstructed with a graft, the risk of inflammatory complications increases. An evaluation of 93 patients with skull base tumors who were operated on at the University of California, Davis Medical Center between July 1982 and March 1992 and had resection and reconstruction of dura is presented. Inflammatory complications developed in 33 (35%) patients. Local wound infection, cerebrospinal fluid leak, and meningitis are by far the most frequent complications. Patients with middle and combined fossae approaches have the highest incidence. Cause, treatment, and prophylaxis of inflammatory complications are discussed.     

Intraoperative Frozen Section Diagnosis in Skull Base Surgery

During January 1990 through June 1992, we performed 39 surgeries for base of skull tumors with extracranial and intracranial involvement on 33 patients. Intraoperative frozen section was requested on 581 of 904 specimens submitted (64%). There was a discrepancy between the frozen section diagnosis and final diagnosis in 15 specimens for an error rate of 3%. There were two false-positive diagnoses of malignancy and 13 false-negative diagnoses. The discrepancies were a result of sampling error in ten cases and of interpretive error in five cases. Four of the five interpretive errors involved intradural tissues. Only two of the discrepancies were clinically significant. One involved the evaluation of adequacy of surgical margins and a second involved the misinterpretation of metastatic renal cell carcinoma for hemangioblastoma. We recommend careful attention to cryostat sectioning and interpretive experience in head and neck pathology and neuropathology. The importance of vigilant communications between surgeon and pathologist before, during, and after surgery cannot be overstated. We are utilizing a video-linked microscopic network that allows the surgeon to view the frozen section histologic sections in the operating room. Future trends may include the use of monoclonal antibodies and morphometry to improve accuracy in frozen section diagnosis.     

Two-Stage Skull Base Surgery for Tumours Extending to the Sub- and Epidural Spaces

Summary  The surgical management of extensive skull base neoplasms, which often extend to both the sub- and epidural spaces, is still a great challenge with considerable risk. The authors report 12 cases in which a two-stage operation was performed for such nonmalignant tumours.  The series consisted of four cavernous sinus meningiomas, one sphenoid-ridge meningioma, one cerebello-pontine angle meningioma, three pituitary adenomas, two chordomas, and one fibroma. Our operative strategy involved removal of the epidural part of the tumour and extensive skull base reforming during the first stage. After approximately one month, the second stage operation was performed by removing the residual subdural parts and the affected dura, which were less vascular, with dural plasty and subsequent spinal drainage. No complications such as cerebrospinal fluid (CSF) leakage or infection were observed. During the long-term follow-up (1.4 to 4.6 years, with a mean of 2.7 years), tumour recurrence was observed in a single case.  In conclusion, the major advantages of this procedure were as follows: [1] improvement of the total removal rate, [2] prevention of postoperative CSF leak and infection, [3] residual tumours were avascular, necrotic, and dwindling, and also shifted outwards resulting in less adhesions to the brain. Although it may counter the trend toward less invasive procedures, the two-staged skull base surgery warrants serious consideration as an option for the management of patients with such extensive cranial base tumours.     

A New Concept for Classifying Skull Base Defects for Reconstructive Surgery

To classify the defects of the skull base, we present a new concept that is intuitive, simple to use, and consistent with subsequent reconstructive procedures. The centers of defects are determined in the anterior (I) or middle (II) skull base. The defects are classified as localized in the defect''s center (Ia, IIa) or extended horizontally (Ib, IIb) or vertically (Ic, IIc) from the defect''s center. Accompanying defects of the orbital contents and skin are indicated by “O” and “S,” respectively. An algorithm for selecting subsequent reconstructive procedures was based on the classification. Using the new system, we retrospectively reclassified 90 skull base defects and examined how the defect classifications were related to the reconstructive flaps used and postoperative complications. All defects were reclassified with the new system without difficulty or omission. The mean correlation rate was high (88%) between the flaps indicated by the new classification and the flaps that had actually been used. The rate of postoperative complications tended to be higher with Ia, Ic, and IIb defects and combined defects. Our new classification concept can be used to classify defects and to help select flaps used for subsequent reconstructive procedures.     

Perioperative Management of a Jehovah's Witness Presenting for Skull Base Surgery

A 22-year-old, otherwise healthy, female Jehovah's Witness underwent resection of a midline skull base chondrosarcoma which had been detected after a work-up for headache and diplopia. After bilateral maxillectomies, ethmoidectomies, and a sphenoidectomy, the patient's chondrosarcoma was resected. Despite proper anesthetic management and meticulous hemostasis, significant intraoperative blood loss occurred. The initial postoperative hemoglobin level was 2.3 gm/dL. The clinical concerns pertaining to the perioperative management of the Jehovah's Witness are discussed along with the patient's course and management.     

Perioperative Management of a Jehovah's Witness Presenting for Skull Base Surgery

A 22-year-old, otherwise healthy, female Jehovah's Witness underwent resection of a midline skull base chondrosarcoma which had been detected after a work-up for headache and diplopia. After bilateral maxillectomies, ethmoidectomies, and a sphenoidectomy, the patient's chondrosarcoma was resected. Despite proper anesthetic management and meticulous hemostasis, significant intraoperative blood loss occurred. The initial postoperative hemoglobin level was 2.3 gm/dL. The clinical concerns pertaining to the perioperative management of the Jehovah's Witness are discussed along with the patient's course and management.