Surgical management of petroclival meningiomas: factors determining the choice of approach

Application accuracy of computed tomography-based, image-guided navigation of temporal bone

OBJECTIVE

Although frameless stereotactic techniques have become indispensable in neurosurgery, their technical complexity requires careful definition and evaluation. Navigation is of particular concern when it is applied to approach a complex, tight surgical area like the temporal bone, where every millimeter is important. Theoretically, the temporal bone is an ideal location in which to use image-guided navigation because its bony construct precludes pre- and intraoperative shift. In this context, the feasibility of using a navigational system is determined by the system's accuracy and by the spatial characteristics of the targets. Literature addressing the accuracy of image guidance techniques in temporal bone surgery is relatively sparse. Accuracy of these systems within the temporal bone is still under investigation. We investigated the application accuracy of computed tomography-based, frameless, image-guided navigation to identify various bony structures in the temporal bone via a retrosigmoid approach.

METHODS

In a total of 10 operations, we performed a retrosigmoid approach simulating operative conditions on either side of 5 whole, fresh cadaveric heads. Six titanium microscrews were implanted around the planned craniotomy site as permanent bone reference markers before the surgical procedure. High-resolution computed tomographic scans were obtained (slice thickness, 0.6-mm, contiguous non-overlapping slices; gantry setting, 0 degrees; scan window diameter, 225 mm; pixel size, >0.44 x 0.44). We used a Stryker navigation system (Stryker Instruments, Kalamazoo, MI) for intraoperative navigation. External and internal targets were selected for calculation of navigation accuracy.

RESULTS

The system calculated target registration error to be 0.48 +/- 0.21 mm, and the global accuracies (navigation accuracies) were calculated using external over-the-skull and internal targets within the temporal bone. Overall navigation accuracy was 0.91 +/- 0.28 mm; for reaching internal targets within temporal bone, accuracy was 0.94 +/- 0.22 mm; and for external targets, accuracy was 0.83 +/- 0.11 mm. Ninety-five percent of targets could be reached within 1.4 mm of their actual position.

CONCLUSION

Using high-resolution computed tomography and bone-implanted reference markers, frameless navigation can be as accurate as frame-based stereotaxy in providing a guide to maximize safe surgical approaches to the temporal bone. Although error-free navigation is not possible with the submillimetric accuracy required by direct anatomic contouring of tiny structures within temporal bone, it still provides a road map to maximize safe surgical exposure.

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.

Evolution of surgical approaches in the treatment of petroclival meningiomas: a retrospective review

OBJECTIVE

We examined the surgical approaches used at a single institution to treat petroclival meningioma and evaluated changes in method utilization over time.

METHODS

Craniotomies performed to treat petroclival meningioma between September of 1994 and July of 2005 were examined retrospectively. We reviewed 46 patients (mean follow-up, 3.6 yr). Techniques included combined petrosal or transcochlear approaches (15% of patients), retrosigmoid craniotomies with or without some degree of petrosectomy (59% of patients), orbitozygomatic craniotomies (7% of patients), and combined orbitozygomatic-retrosigmoid approaches (19% of patients). In 18 patients, the tumor extended supratentorially. Overall, the rate of gross total resection was 43%. Seven patients demonstrated progression over a mean of 5.9 years. No patients died. At 36 months, the progression-free survival rate for patients treated without petrosal approaches was 96%. Of 14 patients treated with stereotactic radiosurgery, none developed progression.

CONCLUSION

Over the study period, a diminishing proportion of patients with petroclival meningioma were treated using petrosal approaches. Utilization of the orbitozygomatic and retrosigmoid approaches alone or in combination provided a viable alternative to petrosal approaches for treatment of petroclival meningioma. Regardless of approach, progression-free survival rates were excellent over short-term follow-up period.

Significance of the tentorial alignment in approaching the trigeminal nerve and the ventral petrous region through the suboccipital retrosigmoid technique

Object

In this study, the authors aimed to identify the factors that would predict the operative distance between the trigeminal nerve (fifth cranial nerve) and the acousticofacial nerve complex (seventh–eighth cranial nerves) preoperatively when approaching the cerebellopontine angle (CPA) through the suboccipital retrosigmoid approach.

Methods

In 40 consecutive patients who underwent microvascular decompression of the trigeminal nerve via a sub-occipital retrosigmoid approach for trigeminal neuralgia, the following three parameters were assessed on preoperative magnetic resonance images: 1) the angle between the tentorium and the line drawn from the hard palate (tentorial angle); 2) the angle between the lines drawn along the petrous bones ventral to the internal auditory canals (petrous angle); and 3) the angle between the tentorium and the line connecting the opisthion to the inion (occipital angle). The distance between the trigeminal nerve and the acousticofacial nerve complex (referred to as “distance”) was measured intraoperatively. Statistical analysis was performed using the Pearson correlation test.

Results

The mean values were 50.9 ± 11.5° for the tentorial angle, 102.5 ± 13.1° for the petrous angle, 83.4 ± 9.7° for the occipital angle, and 3.1 ± 1.5 mm for distance. There was a strong inverse correlation between the tentorial angle and distance (r = −0.228, p = 0.08). The mean distance was 3.5 ± 1.9 mm for a tentorial angle less than 51° and 2.7 ± 1.1 mm for a tentorial angle of at least 51°. No correlation existed between either the petrous or occipital angles and distance.

Conclusions

The distance between the trigeminal nerve and acousticofacial nerve complex decreases in the presence of a steep tentorial angle. This limits the operating field between these cranial nerves when reaching the petroclival or the superior CPA regions through the retrosigmoid approach. Awareness of such anatomical features at the time of pre-operative planning is of paramount importance in selecting the optimum surgical approach and minimizing operative complications.

Petroclival meningiomas: multimodality treatment and outcomes at long-term follow-up

OBJECTIVE

To evaluate patients' clinical outcome, survival, and performance status, at the long-term follow-up evaluation after aggressive microsurgical resection of petroclival meningiomas.

METHODS

During a 13-year period (1991-2004), 150 patients underwent 207 operative procedures for resection of petroclival meningiomas. The tumor size was large in 79% of the patients, with a mean tumor diameter of 3.44 cm. Tumors extended into adjoining regions in 57% of the patients. Thirty patients (20%) previously underwent operation or irradiation. One hundred patients (66%) had a single operation, 43 patients (29%) had two operations, and seven patients (5%) had three operations. Gross tumor resection was accomplished in 48 patients (32%), subtotal resection in 65 patients (43%), and partial resection in 37 patients (25%). There were no operative deaths. Postoperative complications (cerebrospinal fluid leakage, quadriparesis, infections, cranial nerve palsies, etc.) were observed in 33 patients (22%). Postoperative radiation or radiosurgery was administered to 47 of the 102 patients who had residual tumors. The outcome and survival of patients were evaluated by questionnaires, telephone calls, and review of their recent radiological images.

RESULTS

At the conclusion of the study, 87 patients (58%) were alive with disease and 45 patients (30%) were alive without disease. The mean follow-up period was 102 months (range, 15-180 mo). Seven patients (5%; five of the subtotal and partially resected patients and two of the total resection patients) had recurrence; of these patients, two underwent repeat resection and four were treated with gamma knife radiosurgery. One of the patients died of tumor progression with no response to gamma knife radiosurgery. The recurrence-free survival rate was 100% at 3 years, 92.7% at 7 years, and 85% at 12 years; the progression-free survival rate was 96% at 3 years, 86.8% at 7 years, and 79.5% at 12 years. The Karnofsky Performance Scale score was 78 +/- 11 preoperatively, 76 +/- 11 at 1 year postoperatively, and 84 +/- 9 at the time of the latest follow-up evaluation. Common disabilities at the time of the follow-up evaluation included diplopia, loss of hearing, balance problems, and loss of sensation in the V1 and V2 cranial nerve distribution. Most patients developed coping mechanisms.

CONCLUSION

This series has the largest number of patients with the longest follow-up period, to our knowledge, reported in the literature to date. The excellent quality of life at the time of the long-term follow-up examination for these patients warrants aggressive but judicious tumor resection, with or without radiosurgical treatment of tumor remnants.