| Background:The view of the neurovascular structures located in the deep side in the operating field are often obscured by the overhanging tissues and prominence in the superficial field in an axial illumination at 0° microscopic visualization. What is more, the microscope lack the ability to provide a satisfactory view around corners which is located outside in the center operation field. To expose and operate on the tissues in the corners and structures located in the deep side, operators often have to distract the brain tissue with extension, which may lead cerebral ischemic, infarction and contusion. The endoscope, with its ability to see around corners and behind structures, facilitated exposure of the operation field. The advantages of the endoscopic approach compared with the microscopic approach are that it allows for a smaller craniotomy, less dissection, minimal retraction, and more highly magnified focal exposures. The high magnification and enhanced illumination provided by the endoscope have led to its increasing use in neurosurgery. However, several drawbacks prevent its popular. Firstly, unlike three-dimensional images provided by the microscope, the endoscopic images are two-dimensional and lack a depth perception. Secondly, the endoscope provides vision only at its tip. The inability of the endoscope to look sideways or backward when positioned in the main operative field, which means that any movement may have a possibility of injury to adjacent structures by the shaft of the endoscope. Thirdly, holding devices for the endoscope are still suboptimal, especially for use in the narrow confines of the subarachnoid space. The surgeon often has to hold the endoscope in one hand, thereby limiting simultaneously work with the other hand, which inabilities the surgeons to treat complex situation during the operation. Last, even a mild discoloration of the cerebrospinal fluid tinged by blood product drastically reduces the quality of the endoscopic images and renders them unavailing. The disadvantages mentioned above limited the pure endoscope technology, which is mainly used for lesions in the cerebral ventricle and for pituitary tumor by transsphenoidal approach. Endoscope-assisted microsurgery, which combine the both advantage of the microscope and the endoscope by inserting an endoscope into the operation filed under the surveillance of a microscope, provides the surgeons with a three-dimensional view, while keeping an eye on structure in the corners. What is more, like all routine microsurgical procedures, is performed with both hands; the endoscope is fixed in its desired position via a mechanical arm to the headholder. However, for an indeed approach, whether an endoscope-assisted microsurgery still have these advantages is still not that clear, and a defined study is necessary.The retrochiasmatic region, especially the retroinfundibular area is one of most difficult area to access in the neurosurgery. Its anatomical boundaries are the optic apparatus and anterior recess of the third ventricle superiorly, the mammillary bodies with the basilar artery and posterior cerebral arteries posteriorly, and the posterior communicating artery and its perforators along with the oculomotor nerve bracketing the region laterally, contains vital neural structures such as the posterior diencephalon, the posterior perforated substance, and the basis of the cerebral peduncles and of the upper pons. Accessing this region presents a challenge no matter what surgical approach is used. Several approaches have been proposed for treating the retrochiasmatic lesions. Although transcranial access via various cranial base approaches, such as midline transcranial (bifrontal transbasal, subfrontal, bifrontal), midline transnasal (transsphenoidal), anterolateral (pterional, orbitozygomatic), and posterior petrosal approaches, has been described, most of these approaches provide only limited exposure of the interpeduncular cistern. The optimal surgical approach remains controversial, what is more, there were few articles focused on the endoscope-assisted microsurgery. In our study, we used subfrontal and transpetrosal approaches to access this area combined with an endoscope-assisted microsurgery, and compared it with the microscopic microsurgery.The cerebellopontine angle is complex and contains numerous neurovascular structures. The anatomic knowledge is essential for a surgeon to operate on this region. To access this area, the retrosigmoid approach was most frequently used. In this approach, surgeons have to pass though the narrow passage between the petrosal bone and the cerebella. There were a lot of articles focused on the endoscopic and microscopic anatomy in this area; however, there were few articles compared the difference with them. In our study, we used retrosigmoid and retrolabyrinthine-retrosigmoid approaches to access this area by an endoscope-assisted microsurgery, and compared it with the microscopic microsurgery.Methods:1, To investigate and evaluate the exposure and maneuverability of the retrochiasmatic region by using an endoscope-assisted subfrontal approach and to compare that to a microscopic subfrontal approach. Four formalin fixed cadaver head specimens were used in this study. Surgical procedures were carried out as follows:(1) perform the subfrontal craniotomies. Create a 5 x 3 bone flap; (2) flatten the orbital roof extradurally; (3) perform an intradural anterior clinoidectomy; (4) mobilize the clinoid process; (5) drilled the tuberculum sellae to optimize the infrachiasmatic window. We defined each grade by the site-specific visibility and the maneuverability. The visibility was determined by viewing our selected key structures, including diaphragma sellae, dorsum sellae, posterior clinoid process, pituitary stalk, mamillary bodies, tuber cinereum, oculomotor nerves, basal pons, upper trunk of the basilar artery, superior cerebellar arteries, posterior cerebral arteries, posterior communicating arteries, and basilar bifurcation.We evaluated the maneuverability by executing simulated surgical maneuvers on the selected structures. Maneuvers included peeling arachnoid membrane, coagulating vessel, the possibility of manipulating a surgical needle on a neurovascular structure and mocked tumor resection. Exposure and surgical maneuverability score defined as follows:0 target is not visible; 1 target visible, but maneuvers are not possible; 2 target visible, maneuvers are difficult; 3 target visible, maneuvers are possible; 4 target visible, maneuvers are facilitated. Visibility and maneuverability were assessed using the microscope or the endoscope-assisted mode.2, Comparison of surgical exposure and maneuverability associated with microscopy and endoscopy in the retrolabyrinthine and transcrusal approaches to the retrochiasmatic region:a cadaveric study. Four formalin fixed cadaver head specimens were used in this study. Surgical procedures were carried out as follows:(1) a "?" shaped skin incision was performed around the ear. The skin incision was started from preauricular crease, approximately 1 cm in front of the ear at the zygomatic arch level, and extended upward,3 cm above the ear, then downward,2 cm posterior of the ear, and ending approximately 1 cm posterior to the mastoid tip; (2) bone craniotomy, consisting of a mastoidectomy and a temporal craniotomy. The partial mastoid bone and air cells were removed using a high-speed drill. The sigmoid, superior petrosal sinuses and sinodural angle were skeletonized. Drilling was continued into the petrosal bone until anatomical landmarks such as the three semicircular canals, fallopian canal, and tympanic antrum were exposed. Before skeletonization of the three semicircular canals, the bone between the sigmoid sinus and the posterior semicircular canal was also removed, leaving only a thin shell on the dura; (3) the superior and posterior semicircular canals as well as partial petrosal apex were removed by using a diamond drill. The resection of the partial petrosal apex should be carried out superior to Donaldson’s line, which is an imaginary line along the lateral semicircular canal, back to the sigmoid sinus, and ending at the Meckel’s cave. The temporal bone resection was carried out in a Kawase approach manner. After bone resection, the dura was opened in a "T" fashion. The superior petrosal sinus was cut after the supratentorial and presigmoid dura were opened; (4) to combine the bilateral space of the tentorium into a larger corridor, the tentorium was split in a lateral-medial direction along the inner side of the superior petrosal sinus, with great care to preserve the trochlear nerve at the tentorial incisura. To accurately describe the different surgical areas of the retrochiasmatic region exposed by the two approaches, we divided the region into four areas:the area before the infundibular, which was further divided into the (1) ipsilateral and the (2) contralateral areas; the (3) retroinfudibular area; the (4) third ventricle. The visibility was determined by viewing our selected key structures in each department. Maneuvers included peeling arachnoid membrane, coagulating vessel, the possibility of manipulating a surgical needle on a neurovascular structure and mocked tumor resection. Exposure and surgical maneuverability score defined as follows:0 target is not visible; 1 target visible, but maneuvers are not possible; 2 target visible, maneuvers are difficult; 3 target visible, maneuvers are possible; 4 target visible, maneuvers are facilitated. Visibility and maneuverability were assessed using the microscope or the endoscope-assisted mode.3, Comparison of surgical exposure and maneuverability associated with microscopy and endoscopy in neurovascular decompression of the trigeminal nerve:a cadaveric study. Four formalin fixed cadaver head specimens were used in this study. Surgical procedures were carried out as follows:(1) skin incision was started from 3cm above the asterion, and ended at 2cm inferior of the digastric groove; (2) perform the retrosigmoid craniotomies, create a bone flap, with its front to the sigmoid, up to inferior surface of the transverse sinus,3 cm inferior to the inferior nuchal line, the bone flap is 4 x 4cm; (3) open the dural alongside the sigmoid sinus and the transverse sinus; (4) we divided the CNV into three segments:the portion at the entry to Meckel’s cave, the cisternal portion, and the root entry zone and divided it into four quadrants; (5) we assess the exposure and maneuverability of the CNV under the following four conditions, that is, the microscopic approach without cutting superior petrosal vein (SPV), endoscope-assisted approach without cutting the SPV, microscopic approach with cutting of the SPV, and endoscope-assisted approach with cutting of the SPV. The score is defined as follows:0, CNV not visible; 1, CN V visible but no maneuverability; 2, CN V visible and limited maneuverability; 3, CN V visible and full maneuverability. The maneuverability is defined as the ability to separate and redirect neurovascular structures contained in the surgical space at different quadrants.4, Comparison of surgical exposure and maneuverability associated with microscopy and endoscopy in the retrosigmoid and retrolabyrinthine-retrosigmoid approaches to the cerebellopontine angle:a cadaveric study. Four formalin fixed cadaver head specimens were used in this study. Surgical procedures:(1) access to the cerebellopontine angle by retrosigmoid approach; (2) divided the cerebellopontine angle into nine compartments; (3) we evaluated the maneuverability by executing simulated surgical maneuvers on the structures contained in each compartment; (4) a combined retrolabyrinthine and retrosigmoid approach was performed; (5) insert the endoscope into the cerebellopontine angle, and reevaluate the exposure and maneuverability. Maneuvers included peeling arachnoid membrane, coagulating vessel, the possibility of manipulating a surgical needle on a neurovascular structure and mocked tumor resection. Exposure score defined as follows:0 target is not exposure; 1 target limited exposure; 2 target multiangled exposure; 3 circumferential exposure. Maneuverability score defined as follows:1 surgical maneuvers are not possible; 2 surgical maneuvers are difficult; 3 surgical maneuvers are possible; 4 surgical maneuvers are facilitate. Visibility and maneuverability were assessed using the microscope or the endoscope-assisted mode.Result:1, The maximum absolute score achievable is 52. This maximum absolute score represents the score achievable when full maneuvers are possible on all the structures targeted. Combining the scores of all targeted structures, the average overall combined score of the pure microscopic approach was 8 ±1.20, in which six targeted structures (mamillary bodies, tuber cinereum, root entry zone of the oculomotor nerve, the basal pons, posterior cerebral artery, and posterior communicating artery) were not visible, and obviously no maneuver were possible on these structures. In contrast, the overall combined score of the endoscope-assisted approach was 48.88±1.46 because all the targeted structures could be viewed with varied maneuverability. The endoscope was able to reach some of the blind spots not reachable by the microscope. Statistical evaluation showed a statistically significant difference (P<0.05) in maneuverability of retroinfundibular targets between the microscopic and endoscope-assisted mode favoring the endoscope-assisted mode.2, The endoscope-assisted transcrusal approach had the highest score (82.13±3.40), followed by the endoscope-assisted retrolabyrinthine approach (43.75±1.67). The pure microscopic transcrusal approach and retrolabyrinthine approach scored 39.75±2.12 and 32.38±2.56, respectively. The overall exposure and maneuvers afforded by transcrusal approach is superior to that of retrolabyrinthine approach in both microscopic (p<0.05) and endoscope-assisted methods (p<0.05). The transcrusal approach is better than the retrolabyrinthine approach at offering exposure and manipulation to structures in the retrochiasmatic region. Endoscopes may be helpful in transcrusal approach in terms of exposing and maneuvering structures in the contralateral and interpeduncle fossa areas. However, in retrolabyrinthine approach, not enough room is available for simultaneously maneuvering an endoscope and a surgical instrument.3, The endoscope-assisted mode with SPV cutting had the highest score(11.25± 0.71) followed by the endoscopic mode without SPV cutting (10.75±1.04). The pure microscopic mode scored 7.88±1.64 and 9.37±1.30, respectively, without and with cutting of the SPV. The overall maneuverability using the endoscopic assistance is better than the one afforded by the microscopic mode alone (p<0.05) irrespective of SPV status. The sacrifice of the SPV significantly increases the individual maneuverability only in pure microscopic approaches (p= 0.02). However, when we looked at the endoscope-assisted maneuverability, cutting SPV had no improvement.4, The overall maneuvers afford by the endoscope-assisted combined approach had the highest score(62.25±1.28), which is much higher than the followed endoscope-assisted retrosigmoid approach (45.50±2.62) (p< 0.05), and the pure microscopic retrosigmoid approach, which is scored 45.75±1.49 (p< 0.05). The maneuvers afforded by The overall maneuvers afforded by endoscope-assisted and the pure microscopic had no difference (p= 0.79). The overall exposure score afford by the endoscope-assisted in the combined approach is 46.00±0.93, and the overall exposure score afford by the endoscope-assisted in the retrosigmoid approach is 45.38 ±1.06. The exposure afforded by these two methods had no difference (p= 0.55), however, when compared the score afforded by the microscopic in the retrosigmoid approach, which is 27.75±1.28, the exposure afforded by these two methods is much higher (p< 0.05).Conclusion:1, Based on our study, in the endoscope-assisted subfrontal approach is associated with larger exposure and maneuverability than the pure microscopic approach to the retrochiasmatic region, especially in the retroinfundibular region.2, With partial petrosectomy and removal of the posterior and superior semicircular canals, the endoscope-assisted transcrusal approach is better than endoscope-assisted retrolabyrinthine approach in terms of offering exposure and manipulation to structures in the retrochiasmatic region, especially in patients whose lesion is located high into the third ventricle and/or is expanded into the contralateral part. An endoscope may be helpful in transcrusal at exposing and maneuvering structures in the contralateral and interpeduncle fossa areas. However, in retrolabyrinthine approach, no enough room is available for simultaneously maneuvering an endoscope and a surgical instrument.3, Based on our study, the endoscope helps in visualization and maneuverability of vascular conflict associated with microvascular decompression of the trigeminal never. Cutting of the SPV may improve maneuverability only in microscopic microvascular decompression only at the superior quadrant of the nerve is concerned. Special attention should be given to the trigeminal never at the entry to Meckel’s cave where most of the conflicts missed by microscopic microvascular decompression were located; and we found the endoscope-assisted method is helpful at finding out the conflicts in this entry to Meckel’s cave area. We suggest perform an endoscopic inspection of the nerve even when a vascular conflict is identified using the microscope because other conflicts may be visualized by using the endoscope. When using the endoscopic-assisted method, cutting SPV may be unnecessary for most of patients, thus we suggest that surgeons should try his/her best to preserve the SPV during microscopic microvascular decompression.4, The microscope in the retrosigmoid approach provided good visualization of the structures in the posterolateral and middle compartments, whereas poor visualization was offered to the structures in the anteromedial compartment. The combined endoscopic-assisted approach dramatically improved visualization and surgical maneuverability of the neurovascular structures in the anteromedial compartments. This approach allowed for full realization of the benefits of endoscopic-assisted technique by improving surgical access and maneuverability. The endoscopic-assisted retrosigmoid approach improved the visualization of the structures in the anteromedial compartment; however, the manipulation associated with it was still poor. We found that the endoscopic probe is still too large, which may inhibit surgical maneuverability when using the same surgical corridor with the surgical instruments. We propose a combined dual-port endoscope-assisted retrolabyrinthine-retrosigmoid approach that provides enhanced visualization of the cerebellopontine with decreased field depth and increased surgical maneuverability of the neurovascular structures, especially for the neurovascular structures in the anteromedial compartments. |
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