Endoscopic Intradural Subtemporal Keyhole Kawase Approach to the Petroclival and Ventrolateral Brainstem Regions

Purely Endoscopic Subtemporal Keyhole Approach for Trigeminal Schwannomas: Surgical Techniques and Early Results

BACKGROUND AND OBJECTIVES

In the past, microscopic transcranial approach was the mainstay of treatment of trigeminal schwannomas. In recent years, several endoscopic procedures have been reported for trigeminal schwannomas. For trigeminal schwannomas arising around the Meckel cave, we introduced a fully endoscopic procedure with a small temporal craniotomy in June 2020 and have performed radical tumor removal as in the conventional approach. This article describes the details of the purely endoscopic subtemporal keyhole approach (PESKA) surgical procedure and reports the initial surgical results.

METHODS

Between June 2020 and November 2023, 8 cases of trigeminal schwannoma were treated with PESKA. The mean tumor diameter was 33.1 mm. The surgical procedure for PESKA consists of a 7-cm linear skin incision made upward from the anterior to the auricle on the side of the lesion, followed by a 4-cm temporal craniotomy and then endoscopic manipulation. The intradural part of the middle cranial fossa is observed, and the Meckel cave is identified and opened. The tumor is removed with preserving most normal trigeminal nerve fibers. The site of the lesion, the extent of resection, complications, operative time, Karnofsky Performance Status, and intraoperative blood loss were evaluated.

RESULTS

All 8 patients underwent gross total resection. Only one patient had new temporal edema on the side of the lesion, which was asymptomatic. The mean operative time was 4 hours and 21 minutes.

CONCLUSION

We report on PESKA, a fully endoscopic procedure with a small temporal craniotomy for a trigeminal schwannoma arising around the Meckel cave. The use of an endoscope allowed for a wide field of view, even in a narrow operative field, reducing brain traction and allowing radical resection of the tumor while preserving normal trigeminal nerve fibers. This method may represent an effective surgical alternative for trigeminal schwannomas.

Anatomical Comparison of Endoscopic and Microscopic Exposure of the Petroclinal Core Area Through the Extended Middle Skull Base Approach

OBJECTIVE

To compare the range of endoscopic and microscopic exposure of the petroclival core area through the middle skull base and to observe the corresponding anatomical structures.

METHODS

Ten intact adult cadaveric head specimens fixed with formaldehyde were craniotomized through an expanded middle skull base epidural approach on 20 sides. The distance from the greater superficial petrosal nerve to the petrous ridge was measured. When different degrees (1-3 degrees) of the Kawase triangle bone were removed, the exposed anatomical structure was observed, and the exposed core area of the rock slope was measured under an endoscope and microscope.

RESULTS

The average distance from the greater superficial petrosal nerve to the petrous ridge was 14.26 mm. During 1 to 2 degrees of bone removal, the petrous segment of the internal carotid artery (ICA) was not exposed, whereas during 3 degrees of bone removal, the petrous segment of the ICA was exposed. At 1 degree of bone removal, 400.62 ± 15.73 mm2 of the area was exposed by endoscopy and 170.87 ± 8.93 mm2 by microscopy, and the abducens nerve was not exposed. However, there was a significant difference between the two areas (P < 0.001). During 2 degrees of bone removal, 689.30 ± 32.06 mm2 of the abducens nerve was exposed by endoscopy, but 366.84 ± 30.30 mm2 of the abducens nerve could not be exposed by microscopy; moreover, there was a significant difference in the area of exposure between the two (P < 0.001). At 3 degrees of bone removal, the endoscopic exposure area was 875.92 ± 31.87 mm2, the microscopic exposure area was 699.26 ± 48.00 mm2, and the abducens nerves were exposed. There were significant differences between the two areas (P < 0.001). However, the difference between the 2-degree endoscopic exposure area and the 3-degree microscopic exposure area was studied by using paired t tests, and there was no difference (P > 0.05).

CONCLUSION

When the same degree of the Kawase triangle bone was removed, the extent of endoscopic exposure of the petroclival core area was significantly greater than the extent of microscopic exposure. At 2 degrees of bone removal, an endoscopic application can maximally expose the petroclival core area, thus reducing the probability of exposure damage to the ICA and abductor nerve.

[Application of the "five-line division method" in selecting surgical approach for spaceoccupying lesions in the saddle area and the adjacent areas]

OBJECTIVE

To explore the application of the"five-line division method "in selecting the surgical approach for occupying lesions in the saddle area and its adjacent areas.

METHODS

Based on the natural anatomic structures, 5 lines (alpha, beta, theta line and lambda, epsilon line) were drawn on the images of the craniocerebral axial plane crossing the middle of the saddle area and the craniocerebral median sagittal plane, thus dividing the saddle area and its adjacent areas into 6 regions in the axial plane (1, 2, 3, 1', 2', and 3' regions) and into 4 regions in the sagittal plane (I, II, III, and IV regions). Based on these divisions, the large space-occupying lesions in the saddle area and adjacent areas were classified and their respective surgical approaches were determined after reviewing the commonly used approaches in the saddle area and clinical experiences. We collected the data of 116 patients undergoing surgeries for space-occupying lesions involving the saddle and the adjacent areas in our hospital between September, 2014 and August, 2017, and analyzed their classifications and the corresponding surgical approaches based on the "five- line division method " to compare the consistency between the hypothetic approaches and the approaches adopted in the actual surgeries.

RESULTS

The actual surgical approaches adopted in the 116 cases were all selected under the guidance of experts in our hospital. The hypothetic surgical approaches selected based on the"five- line division method "showed a good consistency with the actually adopted approaches.

CONCLUSIONS

The"five-line division method "can spatially classify the commonly seen space-occupying lesions involving the saddle area and its adjacent area to provide assistance in the selection of surgical approaches for such lesions.

Detailed anatomy knowledge: first step to approach petroclival meningiomas through the petrous apex. Anatomy lab experience and surgical series

Petroclival meningiomas are a challenge for neurosurgeons due to the complex anatomy of the region that is rich of vessels and nerves. A perfect and detailed knowledge of the anatomy is very demanding in neurosurgery, especially in skull base surgery. The authors describe the microsurgical anatomy to perform an anterior petrosectomy based on their anatomical and surgical experience and perform a literature review. The temporal bone is the most complex and fascinating bone of skull base. The apex is located in the angle between the greater wing of the sphenoid and the occipital bone. Removing the petrous apex exposes the clivus. The approach directed through the temporal bone in this anatomical area is referred to as an anterior petrosectomy. The area that must be drilled is the rhomboid fossa that is defined by the Kawase, premeatal, and postmeatal triangles. In Division of Neurosurgery - University of Turin, 130 patients, from August 2013 to September 2015, underwent surgical resection of intracranial meningiomas. In this group, we have operated 7 PCMs and 5 of these were approached performing an anterior petrosectomy with good results. In our conclusions, we feel that this surgery require an advanced knowledge of human anatomy and a specialized training in interpretation of radiological and microsurgical anatomy both in the dissection lab and in the operating room.