The lounging position for posterior fossa surgery: anesthesiological considerations regarding air embolism

The safety and utility of the semi-sitting position for clipping of posterior circulation aneurysms

BACKGROUND

The semi-sitting position offers advantages for surgeries in the posterior cranial fossa. However, data on its safety and effectiveness for clipping aneurysms in the posterior cerebral circulation are limited. This retrospective cohort study evaluates the safety and effectiveness of using the semi-sitting position for these surgeries.

METHODS

We conducted a retrospective study of 17 patients with posterior cerebral circulation aneurysms who underwent surgical clipping in the semi-sitting position in the Department of Neurosurgery at Hannover Medical School over a 10-year period.

RESULTS

The mean age at surgery was 62 years (range, 31 to 75). Fourteen patients were admitted with subarachnoid hemorrhage and 3 patients had incidental aneurysmas. Fifteen patients had PICA aneurysms, and two had aneurysms of the vertebral artery and the superior cerebellar artery, respectively. The median diameter of the aneurysms was 5 mm (range 3-17 mm). Intraoperative venous air embolism (VAE) occurred in 4 patients, without affecting the surgical or clinical course. VAE was associated with a mild decrease of EtCO2 levels in 3 patients and in 2 patients a decrease of blood pressure occurred which was managed effectively. Surgical procedures proceeded as planned in all instances. There were no complications secondary to VAE. Two patients died secondary to respiratory problems (not related to VAE), and one patient was lost to follow-up. Eleven of fourteen patients were partially or completely independent (Barthel index between 60 and 100) at a median follow-up duration of 13.5 months (range, 3-103 months).

CONCLUSION

The semi-sitting position is a safe and effective technique for the surgical clipping of aneurysms in the posterior cerebral circulation. The incidence of VAE is comparable to that seen in tumor surgery. However, it is crucial for the surgical and anesthesiological team to be familiar with potential complications and to react immediately in case of an occurrence of VAE.

Semisitting position for cerebello-pontine angle surgery: Analysis of complications and how to avoid it

OBJECTIVE

To analyze the primary complications related to semisitting position in patients undergoing cerebelo-pontine angle surgery.

METHODS

Retrospective data analysis from patients undergoing elective tumoral cerebelo-pontine angle surgery in a semisitting position. The incidence, severity, occurrence moment, treatment, duration, and outcomes of venous air embolism (VAE), pneumocephalus, postural hypotension, and other complications were recorded. Neurointensive care unit (NICU), length of stay (LOS), hospital LOS, and modified Rankin scale scores were calculated six months after surgery.

RESULTS

Fifty patients were operated on. Eleven (22%) presented VAE (mean duration 8±4.5min): five (10%) during tumor resection, and four (8%) during dural opening. Ten (20%) were resolved by covering the surgical bed, air bubbles aspiration, jugular compression, and one (2%) tilted to a steep Trendelenburg position. One (2%) had intraoperative hemodynamic instability. The only variable associated with VAE was meningioma at histopathology OR=4.58, p=0.001. NICU was higher in patients with VAE (5.5±1.06 vs. 1.9±0.20 days, p=0.01). There were no differences in the Rankin scale. All patients presented postoperative pneumocephalus with a good level of consciousness, except one (2%) who required evacuation. Seven patients (14%) showed postural hypotension, three (6%) after positioning, and one (2%) after developing a VAE; all were reversed with usual vasoactive drugs. No other position-related complications or mortality were registered in this series.

CONCLUSIONS

The semisitting position is a safe option with the knowledge, prevention, detection, and early solution of all the possible complications. The development of VAE rarely implies hemodynamic instability or greater disability after surgery. Postoperative pneumocephalus is very common and rarely requires evacuation. Excellent cooperation between anesthesia, nursing, neurophysiology, and neurosurgery teams is essential to manage complications.

Medulloblastomas in Pediatric and Adults

Medulloblastoma is the primary malignant embryonic tumor of the cerebellum and the most common malignant tumor of childhood, accounting up to 25% of all CNS tumors in children, but is extremely rare in adults. Despite the fact that medulloblastomas are one of the most malignant human tumors, it is worthy to note that a great breakthrough has been achieved in our understanding of oncogenesis and the development of real methods of treatment. The main objective of surgical treatment is a maximum resection of tumor with minimal impairment of neurological functions, in order to reduce the volume, remove tumor tissue, get the biopsy, and restore the cerebrospinal fluid flow. The progress of surgical techniques (using a microscope, ultrasound suction), anesthesiology, and intensive care has significantly decreased surgical mortality and increased radicality of tumor removal. Postoperative mortality is less than one percent in most studies, while neurological complications have been reported between 5-10%. Radiotherapy is the main method of treatment in patients older than 3 years, which dramatically improved the recurrence-free survival. Nevertheless, the radiation therapy without systemic chemotherapy leads to a high risk of systemic metastases. After the role of chemotherapy was statistically proven, investigations of the optimal combination of different chemotherapy regimens continued around the world. Currently, 80% of patients can already be cured, however, the quality of life of patients in the long-term period remains quite low, which depends on many factors including endocrinological, cognitive, neurological, and otoneurologic aspects. Thus, the main strategic goal of the development of neuro-oncology is to reduce the doses of radiation therapy to the CNS and the main task of international research is to optimize existing protocols and develop fundamentally new ones based on molecular genetic research in order to improve the quality of life.

The semisitting position in pediatric neurosurgery: pearls and pitfalls of a 10-year experience

OBJECTIVE

The authors sought to investigate the pearls and pitfalls of using the semisitting position in pediatric neurosurgery, with special focus on related morbidity and surgical practicability.

METHODS

All pediatric cases at a single institution were evaluated retrospectively. Those patients who underwent procedures in the semisitting position between December 2010 and December 2020 were included in the final analysis. Results were compared with all children who underwent surgery in the prone position for posterior fossa lesions within the same time frame.

RESULTS

A total of 42 posterior fossa surgeries were performed in 38 children in the semisitting position between December 2010 and December 2020. The mean patient age at the time of surgery was 8.9 years (range 13 months-18 years). The data of 24 surgeries performed in the prone position in 22 children during the same time frame were analyzed in comparison. Three children (7.9%) were diagnosed with a persistent foramen ovale preoperatively. The surgery was completed in all cases. The incidence of venous air embolism (VAE) was 11.9%. There was no VAE-related hemodynamic instability, infarction, or death. Endoscopic techniques were applied safely in 14 cases (33.3%). Postoperative pneumocephalus occurred significantly more frequently in patients who had undergone procedures in the semisitting position (p < 0.05), but without the need for intervention. During 1 surgery (2.4%), the patient experienced a postoperative skull fracture and epidural bleeding due to the skull clamp application. Clinical status of the patients immediately after surgery was improved or stable in 33 of the 42 surgeries (78.6%) performed in the semisitting position.

CONCLUSIONS

With attentive performance and an experienced surgical team, the semisitting position is a safe option for posterior fossa surgery in the pediatric population. With a comparable complication profile, the semisitting position offers excellent anatomical exposure, which is ideal for the application of endoscopic visualization. Careful skull clamp application and appropriate monitoring are highly recommended.

Occurrence and management of postoperative pneumocephalus using the semi-sitting position in vestibular schwannoma surgery

Background

The semi-sitting position in neurosurgical procedures is still under debate due to possible complications such as venous air embolism (VAE) or postoperative pneumocephalus (PP). Studies reporting a high frequency of the latter raise the question about the clinical relevance (i.e., the incidence of tension pneumocephalus) and the efficacy of a treatment by an air replacement procedure.

Methods

This retrospective study enrolled 540 patients harboring vestibular schwannomas who underwent posterior fossa surgery in a supine (n = 111) or semi-sitting (n = 429) position. The extent of the PP was evaluated by voxel-based volumetry (VBV) and related to clinical predictive factors (i.e., age, gender, position, duration of surgery, and tumor size).

Results

PP with a mean volume of 32 ± 33 ml (range: 0–179.1 ml) was detected in 517/540 (96%) patients. The semi-sitting position was associated with a significantly higher PP volume than the supine position (40.3 ± 33.0 ml [0–179.1] and 0.8 ± 1.4 [0–10.2], p < 0.001). Tension pneumocephalus was observed in only 14/429 (3.3%) of the semi-sitting cases, while no tension pneumocephalus occurred in the supine position. Positive predictors for PP were higher age, male gender, and longer surgery duration, while large (T4) tumor size was established as a negative predictor. Air exchange via a twist-drill was only necessary in 14 cases with an intracranial air volume > 60 ml. Air replacement procedures did not add any complications or prolong the ICU stay.

Conclusion

Although pneumocephalus is frequently observed following posterior fossa surgery in semi-sitting position, relevant clinical symptoms (i.e., a tension pneumocephalus) occur in only very few cases. These cases are well-treated by an air evacuation procedure. This study indicates that the risk of postoperative pneumocephalus is not a contraindication for semi-sitting positioning.

Effect of the degree of head elevation on the incidence and severity of venous air embolism in cranial neurosurgical procedures with patients in the semisitting position

OBJECTIVE The semisitting position of a patient confers numerous advantages in various neurosurgical procedures, but venous air embolism is one of the associated complications of this position. To date, no prospective studies of the relationship between the degree of head elevation and the rate and severity of venous air embolism for patients undergoing a procedure in this position have been performed. In this study, the authors compared changes in the severity of venous air embolism according to the degree of head elevation (30° or 45°) in patients undergoing an elective cranial neurosurgical procedure in the semisitting position. METHODS One hundred patients undergoing an elective infratentorial craniotomy in the semisitting position were included, and each patient was assigned to 1 of 2 groups. In Group 1, each patient's head was elevated 30° during surgery, and in Group 2, each patient's head elevation was 45°. Patients were assigned to their group according to the location of their lesion. During surgery, the standard anesthetic protocol was used with total intravenous anesthesia, and transesophageal echocardiography was used to detect air in the blood circulation. Any air embolism seen on the echocardiography screen was classified as Grade 0 to 4. If multiple events occurred, the worst graded attack was used for statistical analysis. During hemodynamic changes caused by emboli, fluid and vasopressor requirements were recorded. Surgical and anesthetic complications were recorded also. All results were compared statistically, and a p value of < 0.05 was considered statistically significant. RESULTS There was a statistically significant difference between groups for the total rates of venous air emboli detected on transesophageal echocardiography (22.0% [n = 11] in Group 1 and 62.5% [n = 30] in Group 2; p < 0.0001). The rate and severity of air embolism were significantly lower in Group 1 than in Group 2 (p < 0.001). The rates of clinically important venous air embolism (Grade 2, 3, or 4, venous air embolism with decreased end-tidal carbon dioxide levels and/or hemodynamic changes) were 8.0% (n = 4) in Group 1 and 50.0% (n = 24) in Group 2 (p < 0.0001). There was no association between the rate and severity of venous air embolism with patient demographics (p > 0.05). An association was found, however, between the rate of venous air embolism and the type of surgical pathology (p < 0.001); venous embolism occurred more frequently in patients with a meningioma. There were no major surgical or anesthetic complications related to patient position during the postoperative period. CONCLUSIONS For patients in the semisitting position, an increase in the degree of head elevation is related directly to a higher rate of venous air embolism. With a 30° head elevation and our standardized technique of positioning, the semisitting position can be used safely in neurosurgical practice.

Comparison of outcomes following complex posterior fossa surgery performed in the sitting versus lateral position

The sitting position during surgery is thought to provide important advantages, yet it remains controversial. We compared surgical and neurological outcomes for patients operated on in the sitting versus lateral position. Technically difficult procedures performed from the years 2001-2008 for complex lesions in the posterior fossa (vestibular schwannomas, other cerebellopontine angle tumors, foramen magnum meningiomas, brainstem cavernomas, pineal region tumors) were included. Outcomes in the two surgical positions were compared for all 243 patients (93 sitting, 38.3%; 150 lateral, 61.7%) and for 130/243 patients with vestibular schwannomas (50 sitting, 38.5%; 80 lateral, 61.5%). Sitting and lateral patient subgroups were clinically comparable. There were no surgical mortalities. The extent of removal and surgical and neurological outcomes were comparable. We found no advantage in surgical or neurological outcomes for use of the sitting or lateral surgical positions in technically difficult posterior fossa procedures. In vestibular schwannoma surgeries facial nerve preservation (House-Brackmann score 1-2) was related to extent of resection but not to surgical position. The choice of operative position should be based on lesion characteristics and the patient's preoperative medical status as well as the experience and preferences of the surgeons performing the procedure.

Neurosurgical procedures in the semisitting position: evaluation of the risk of paradoxical venous air embolism in patients with a patent foramen ovale

OBJECTIVE

To analyze the actual risk for patients with a patent foramen ovale (PFO) to experience a clinically relevant venous air embolism (VAE) during surgery performed in the semisitting position.

METHODS

All procedures were performed between January 2008 and December 2009, under general anesthesia and in the semisitting position. Transesophageal echocardiography (TEE) and capnometry were used intraoperatively to monitor for air bubbles in the venous system.

RESULTS

Of 200 consecutive patients who all were operated on in the semisitting position, 52 patients (26%) had a diagnosis of PFO. Rates of VAE in patients were graded as follows: grade 0 (no air bubbles visible, no air embolism), 23 patients (44.2%); grade I (air bubbles on TEE), 22 patients (42.3%); grade II (air bubbles on TEE with decrease of end-tidal carbon dioxide [ETCO2] ≤ 3 mm Hg), 2 patients (3.8%); grade III, air bubbles on TEE with decrease of ETCO2 >3 mm Hg, 4 patients (7.7%); grade IV, air bubbles on TEE with decrease of ETCO2 >3 mm Hg and decrease of mean arterial pressure ≥ 20% or increase of heart rate ≥ 40% (or both), 1 patient (1.9%); and grade V, VAE causing arrhythmia with hemodynamic instability requiring cardiopulmonary resuscitation, 0 patients (0%). There were no deaths in this series, and no new or unexplained, mild or severe neurologic deficits were caused by a VAE.

CONCLUSIONS

Under standardized anesthesia and neurosurgical protocols, patients with a PFO can be operated on safely in the semisitting position.

[Questionnaire on the anaesthesiology treatment of patients subjected to posterior fossa neurosurgery]

OBJECTIVES

To find out, by means of a questionnaire, the procedures used by Spanish anaesthetists in peri-operative management of patients subjected to neurosurgery of the posterior cranial fossa.

MATERIAL AND METHODS

A closed-question type questionnaire was sent to Anaesthesiology Departments with a Neurosurgery Department on the participation of anaesthetists in the peri-operative treatment of patients subjected posterior fossa surgery.

RESULTS

The questionnaire was completed by 42 (57.5%) of the 73 national public hospitals with a Neurosurgery Department. The posterior fossa surgery was performed in the sitting position in 36 hospitals, although it was less frequently used than the lateral decubitus or prone decubitus position. There was little specific neurological monitoring, as well as little use of precordial and/or transcranial Doppler for detecting vascular air embolism. Nitrous oxide was used in less than 10% of the centres, and 15% avoided neuromuscular block when neurophysiological monitoring was used during the surgery. Cardiovascular problems were mentioned as being the most frequent in 29% of the centres, while in the post-operative period the most common complications were, cranial nerve déficit, airway oedema (23%), and post-operative vomiting (47%).

CONCLUSIONS

The results obtained from the questionnaire showed that the sitting position was less used than the prone position in posterior fossa surgery, and that neurophysiological monitoring is during surgery is hardly used.

The history of ependymoma management

INTRODUCTION

The ependymomas are relatively not a common tumor. However, most clinicians agree that the radical removal of the tumor is the most important prognostic factor.

MORBIDITY OF TREATMENT

Tumor removal was not sufficient before the era of magnetic resonance imaging (MRI) and resulted in a considerable operative morbidity and mortality. As the microneurosurgical techniques and microsurgical anatomy become popular and the MRI provide more detailed anatomical information preoperatively, radical removal of this complex and complicated tumor can be more feasible. In childhood ependymoma, the treatment-related morbidity and mortality can be the special issues, which can modify the policy of management safe tumor removal and minimal adjuvant treatment, which are extremely important.

RADIATION THERAPY

Radiation treatment has been the option for disseminated disease and residual tumor. With the advancement of detailed MR anatomical information, safer and more delicate radiation becomes possible with newer radiation modalities, three-dimensional conformal radiotherapy, intensity modulating radiotherapy, and tomotherapy.

PROGNOSTIC FACTORS

Although many clinicians believe that the ependymomas are inheritably chemoresistant, the new targets for the treatment are under investigation or clinically tried. Also, the genetic alterations of ependymoma are developing and might be a promising target.

CONCLUSION

The surgical techniques and assistant modalities for tumor removal are still advancing. So, the outcome of ependymoma is still improving. Unfortunately, newer treatment modalities, such as new chemotherapeutic agent and gene modification agent, are still not promising. The history of ependymoma management is still in progress.

A standardized protocol for the prevention of clinically relevant venous air embolism during neurosurgical interventions in the semisitting position

OBJECTIVE

We report the results and complications associated with standardized intraoperative management designed for the prevention of hemodynamically relevant venous air embolism during surgery performed in the semisitting position.

METHODS

A protocol for preoperative evaluation and intraoperative monitoring was developed and applied in 187 consecutive patients who underwent surgery in the semisitting position between 1999 and 2004. The protocol included preoperative transesophageal echocardiography examination (TEE), intraoperative TEE monitoring, catheterization of the right atrium and a combination of fluid input, positive end expiratory pressure, and standardized positioning aiming at a positive pressure in the transverse and sigmoid sinuses. Data were collected retrospectively from the charts and intraoperative anesthesiological protocols of the patients for the incidence of clinically relevant air embolism (i.e., TEE-diagnosed air embolism plus a decrease in end tidal CO2 or hemodynamic changes) and other complications related to the semisitting position.

RESULTS

Three cases (1.6%) of relevant venous air embolism occurred in 187 patients. Only 1 case (0.5%) was hemodynamically relevant, with temporary arterial blood pressure decrease and heart rate increase. Pneumatocephalus leading to lethargy was a frequent postoperative finding, which resolved spontaneously in all except 1 patient with epileptic seizure and oculomotor nerve palsy attributable to space-occupying subdurally trapped air, which had to be treated surgically. There was no permanent morbidity or mortality related to the semisitting position.

CONCLUSION

Fear of massive venous air embolism is one reason for dramatic decline in the use of the semisitting position in neurosurgical practice. We found that strict adherence to a standardized protocol using TEE monitoring before and during surgery; exclusion of patients with patent foramen ovale; and a combination of positive end expiratory pressure, fluid input, and a standardized position aiming a positive pressure in the transverse and sigmoid sinuses helped to greatly minimize this complication to a rate of 0.5% for hemodynamically relevant events.

Surgery of extra-axial tumors of the cerebral base

Because of the complex structure of the cranial base and its close proximity to cranial nerves and vessels, surgery in this area is associated with considerable risk of morbidity and mortality. Multiple approaches to each part of the cranial base have been developed over the past few decades, ranging from small modifications of more traditional approaches to complex and sophisticated new techniques. However, experience has shown that optimal outcome is achieved if the selected approach is not associated with significant approach-related morbidity. Furthermore, not all cranial base tumors can be cured by surgery. The selection of operative approach and the goal of surgery should be part of the whole treatment strategy. The attempt to achieve complete resection can, therefore, be justified only if the associated long-term morbidity is minimal. Refinements of the traditional retrosigmoid suboccipital approach have made it the most effective and safe approach, the "gold standard" for lesions in the cerebellopontine angle. On the other hand, in some basal tumors, e.g., chordomas and chondrosarcomas, the approach has to be selected individually and must always be tailored to the characteristics of the particular tumor, its location, and the patient's expectations. The expertise of the surgeon is not reflected in his or her ability to perform the most complex approaches but in the ability to select the approach that affords both removal of the tumor and preservation of patient's neurological function and quality of life.

Anatomy of the mastoid emissary vein and venous system of the posterior neck region: neurosurgical implications

OBJECTIVE

The superficial venous system of the posterior neck (suboccipital venous plexus) is a potential source of complications from bleeding and air embolism. Because there is little information available about this in the literature, an anatomic study of the superficial posterior neck venous system and a morphometric analysis of the mastoid emissary vein (MEV) complex were undertaken. Both surgical and endovascular implications were considered.

METHODS

The posterior craniocervical regions of 15 silicon-injected human cadaveric specimens were dissected. The patterns and variances of venous anatomy were observed. Distances between fixed bony landmarks were measured with a caliper.

RESULTS

The suboccipital venous plexus, which forms a complex venous network located between the posterior muscular layers of the neck, drains to the anterior vertebral vein and deep cervical vein. The MEV connects this plexus to the sigmoid sinus. Its average diameter was 2.15 mm, and it was located a mean of 21.14 mm from the asterion and a mean of 33.65 mm from the mastoid tip. However, the size of the MEV complex varied considerably.

CONCLUSION

The suboccipital venous plexus in the posterior neck region may be very large. The size of the veins in the plexus varies, but the drainage pattern remains consistent. The plexus is a potential source of intense bleeding and air embolism during posterior fossa approaches. The risks are greatest for lateral surgical approaches, as a result of the anatomic position of the venous system. The described measurements can be used to approach the MEV in endovascular procedures that involve the sigmoid sinus.

Management of skull based meningiomas in the elderly patient

BACKGROUND

The demographic evolution of Western society together with availability of modern imaging techniques leads to an increasing diagnosis of meningioma patients over 70 years of age. This raises the question of appropriate management of this histologically benign tumour in a geriatric population.

DESIGN

Forty-three patients aged over 70 years were analyzed and matched in a retrospective study with a younger group of 89 patients according to tumour size, histology, symptoms, recurrence and presence of neurofibromatosis II.

RESULTS

Changes in postoperative Karnofsky scores were not statistically different between the two age groups. Neurological outcome was worse among the younger group (12% vs. 7% deterioration). Regarding surgical complications we noted only a statistically significant higher infection rate in the geriatric age group. There was no peri-operative mortality.

CONCLUSIONS

Age alone is not a criterion to deny a priori skull base surgery, since well selected geriatric patients may benefit from a meningioma operation that may enhance future quality of life.

Auditory Midbrain Implant

HYPOTHESIS

The lateral suboccipital approach is a well-established route for safe removal of vestibular schwannomas in neurofibromatosis Type 2 (NF2) patients. The goal of this study was to assess if this approach can be extended to a lateral supracerebellar infratentorial approach to enable insertion of an auditory midbrain implant (AMI) penetrating array along the tonotopic gradient of the inferior colliculus central nucleus (ICC).

BACKGROUND

The AMI is a new auditory prosthesis designed for penetrating stimulation of the ICC in patients with neural deafness. The initial candidates are NF2 patients who, because of the growth and/or surgical removal of bilateral acoustic neuromas, develop neural deafness and are unable to benefit from cochlear implants. The ideal surgical approach in NF2 patients must first enable safe removal of vestibular schwannomas and then provide sufficient exposure of the midbrain for AMI implantation.

METHODS

This study was performed on formalin-fixed and fresh cadaver specimens. Computed tomography scan and magnetic resonance imaging were used to study the heads of the specimens and for surgical navigation.

RESULTS

The lateral suboccipital craniotomy enabled sufficient exposure of the cerebellopontine angle and internal auditory canal for tumor removal. It could then be extended to a lateral supracerebellar infratentorial approach that provided good exposure of the dorsolateral aspect of the tentorial hiatus and mesencephalon for implantation of the AMI along the tonotopic gradient of the ICC. This approach did not endanger the trochlear nerve or any major midline venous structures in the quadrigeminal cistern.

CONCLUSION

This modified lateral suboccipital approach ensures safe removal of large vestibular schwannomas and provides sufficient exposure of the inferior colliculus for ideal AMI implantation.

Perioperative management of complex skull base surgery: the anesthesiologist's point of view

The anesthetic management of complex skull base surgical procedures provides unique problems and concerns for the neuroanesthesiologist. Positioning to access the skull base could put the patient at risk for peripheral nerve injury and some of the positions may increase the risk for air emboli. In addition, tumor pathology and involvement with vital structures could increase the chances for substantive blood loss, destruction of associated nerves or vessels, and may require temporary occlusion of the carotid artery necessitating intraoperative neuroprotection. Neurophysiological monitors may also be used to safeguard nerve function and anesthetic techniques must be adjusted to accommodate their use. Finally, postoperative morbidity may be affected by surgical approach to the skull base and the anesthesiologist should be aware of which approach may produce a greater incidence of pain, nausea, and vomiting in the postoperative period.

The authors discuss the anesthetic concerns and management for complex cranial base surgery. Different approaches will be discussed and comparisons of perioperative parameters between these approaches will be made with data provided by retrospective chart review of more than 600 skull base procedures performed at the authors' institution over the last 10 years. This information should help guide decision making concerning anesthetic management for these skull base procedures.

The sitting position for neurosurgery in children: a review of 16 years' experience

BACKGROUND

Use of the sitting position for neurosurgery is controversial. The main concern is the risk of venous air embolus (VAE) and its sequelae.

METHODS

The paediatric neurosurgeons at our institution routinely use the sitting position for posterior fossa and pineal surgery, and a retrospective audit of the incidence of VAE from 1982 to 1998 has been performed.

RESULTS

Venous air embolism, defined as a fall in end-tidal carbon dioxide pressure >0.4 kPa, was detected in 38 of 407 operations (9.3%). A fall in systolic arterial pressure >10% accompanied the VAE in nine out of 43 episodes (20.9%); this represents 2% of all operations. All VAE episodes responded promptly to treatment and there was no perioperative morbidity or mortality directly attributed to it.

CONCLUSIONS

This is the largest study of the incidence of VAE in children undergoing neurosurgery. Our results suggest that the sitting position can be used safely for neurosurgery in children.

Management of 1000 vestibular schwannomas (acoustic neuromas): hearing function in 1000 tumor resections

OBJECTIVE

The realistic chances of hearing preservation and the comparability of international results on hearing preservation in complete microsurgical vestibular schwannoma resections were the focus of this study in a large patient population treated by uniform principles.

METHODS

One thousand vestibular schwannomas were operated on at Nordstadt Neurosurgical Department, from 1978 to 1993, by the senior surgeon (MS). There were 1000 tumors in 962 patients, i.e., 880 patients with unilateral tumors and 82 patients operated on for bilateral tumors in neurofibromatosis-2 (120 cases). Preservation of the cochlear nerve was attempted whenever possible. The audiometric data were analyzed by the Nordstadt classification system and graded in steps of 30 dB by audiometry and in steps of 10 to 30% by speech discrimination; for comparability, the data were also evaluated by the criteria of Gardner, Shelton, and House, and they were assessed in relation to the Hannover tumor extension grading system.

RESULTS

Anatomic cochlear nerve preservation was achieved in 682 of 1000 cases (68%), as well as in some preoperatively deaf patients, a very few of whom regained some hearing. Of a total of 732 cases with some preoperative hearing, anatomic cochlear nerve preservation was achieved in 580 cases (79%) and functional cochlear nerve preservation in 289 (39.5%); analysis over time revealed an actual preservation rate of 47% in the most recent 200 cases. Specific factors, such as gender, tumor extension, preoperative hearing quality, and symptom duration, were investigated for their predictive value for hearing preservation. Male gender, small to medium tumor size (mainly extending within the cerebellopontine cistern; Classes T2 and T3), good to moderate hearing (up to 40-dB loss), and short duration of hypoacusis (< 1.5 yr) or of vestibular disturbances (< 0.7 yr) were advantageous factors, with chances of hearing preservation between 47 and 88%.

CONCLUSION

Functional cochlear nerve preservation in complete microsurgical resection should belong to the contemporary standard of treatment goals.

Management of 1000 vestibular schwannomas (acoustic neuromas): surgical management and results with an emphasis on complications and how to avoid them

OBJECTIVE

To identify the actual benefits and persisting problems in treating vestibular schwannomas by the suboccipital approach, the results and complications in a consecutive series of 1000 tumors surgically treated by the senior author were analyzed and compared with experiences involving other treatment modalities.

METHODS

Pre- and postoperative clinical statuses were determined and radiological and surgical findings were collected and evaluated in a large database for 962 patients undergoing 1000 vestibular schwannoma operations at Nordstadt's neurosurgical department from 1978 to 1993.

RESULTS

By the suboccipital transmeatal approach, 979 tumors were completely removed; in 21 cases, deliberate partial removal was performed either in severely ill patients for decompression of the brain stem or in an attempt to preserve hearing in the last hearing ear. Anatomic preservation of the facial nerve was achieved in 93% of the patients and of the cochlear nerve in 68%. Major neurological complications included 1 case of tetraparesis, 10 cases of hemiparesis, and caudal cranial nerve palsies in 5.5% of the cases. Surgical complications included hematomas in 2.2% of the cases, cerebrospinal fluid fistulas in 9.2%, hydrocephalus in 2.3%, bacterial meningitis in 1.2%, and wound revisions in 1.1%. There were 11 deaths occurring at 2 to 69 days postoperatively (1.1%). The techniques that were developed for avoidance of complications are reported. The analysis identifies preexisting severe general and/or neurological morbidity, cystic tumor formation, and major caudal cranial nerve deficits as relevant risk factors.

CONCLUSION

The current treatment options of complete tumor resection with ongoing reduction of morbidity are well fulfilled by the suboccipital approach. By careful patient selection, the mortality rate should be further reduced to below 1%.

Surgical management of medulloblastoma

Recent technological aids and understanding of pathophysiology has made the surgery of medulloblastoma safer. The guiding principle for the neurosurgeon remains removal of bulky disease, but there is no justification for removal of small amounts of tumor from critical locations. Post-operative complications include hydrocephalus, hematoma, mutism, asceptic meningitis, gastroinstestinal hemorrhage, and cervical instability. Staging is best done preoperatively with MRI, and presence of dissemination remains the most important prognostic factor in this disease. Postoperative surveillance imaging is of questionable value.

Hearing preservation in acoustic tumour surgery

900 acoustic neurinomas were removed by the suboccipital approach at Nordstadt Neurosurgical Department from 1978 to 1992 by the same surgeon (M. S.). While 247 patients were deaf on the involved side before surgery, there were 653 patients ears with some preoperative hearing. Preservation of the cochlear nerve was always attempted, and the overall-rate of hearing preservation was 38% (249 of 653), regardless of pre- and postoperative quality of hearing or of tumour sizes. In small tumour sizes below 3 cm of diameter preservation rate was 51%, in large tumours above 3 cm of diameter it was 22%. A classification system of hearing quality was made up considering pure tone audiometric hearing losses (PTA HL) at 1 to 3 kHz, and individual maximum speech discrimination scores. The usefulness of the preserved hearing is further evaluated considering the quality of hearing in the contralateral ear, and by application of other classification schemes. Presentation of the surgical strategies and their refinements by personal experience provide the base for discussion questioning whether and how further progress may still be anticipated.

Surgical management of high jugular bulb in acoustic neurinoma via retrosigmoid approach

Of 200 patients with acoustic neurinoma undergoing an operation via the retrosigmoid transmeatal approach in the semisitting position, 18 patients had a high jugular bulb on the tumor side. The frequency was 9%. From a neurosurgical point of view, a jugular fossa above the low border of the internal auditory canal (IAC) is classified as a high one. All 200 patients were evaluated by computed tomography with bone window reconstruction of high-resolution thin axial slices (1.5 mm). High jugular bulbs were classified into three grades as follows: Grade I, jugular bulb situated less than 1.5 mm above the low border of IAC; Grade II, jugular bulb between 1.5 and 3.0 mm above the low border of the IAC; Grade III, jugular bulb > 3 mm above the low border of IAC. There were eight patients with Grade I, six patients with Grade II, and four patients with Grade III. In these patients, in order to open the IAC without concomitant injury of the jugular bulb, the superior posterior portion of the porus was drilled away. Opening the jugular fossa was unavoidable in Grade III cases. No difference was noted in functional preservation of facial or cochlear nerve between HJB cases and normal jugular bulb cases, but HJB cases had a higher frequency of air embolism during tumor removal than did normal cases (16 versus 5%), especially Grade III cases (two of four). There was no mortality or morbidity in the cases of air embolism. Details of the surgical procedure in such cases are discussed.