Abstract】Objective To provide an applied anatomical basis for the clinical development of neuroendoscopic lateral ventricle and third ventricle surgery. Methods: Ten adult cadaveric specimens were observed under neuroendoscopic observation of the lateral ventricle and third ventricle structures and data were measured via a longitudinal callosal anterior lateral ventricular approach. Results (1) The thickness of corpus callosum was (6.1±1.2)mm, the length and width of interventricular foramen were (5.6±1.4)mm and (3.0±1.6)mm in diameter, and the length and width of intermediate block were (6.3±1.8)mm and (3.4±1.2)mm in diameter; (2) there were few draining veins 5 cm before the coronal suture; (3) the anterior horn of the lateral ventricle, the body of the lateral ventricle and the interventricular foramen were observed with different angles of neuroendoscopy (3) The Y-shaped structure of the anterior horn of the lateral ventricle, the body of the lateral ventricle and the interventricular foramen could be observed with different angles of the neuroendoscope, and the third ventricle could be accessed through the interventricular foramen for better exposure and observation. Conclusion The lateral ventricular approach through the anterior part of the longitudinal corpus callosum was entered according to the physiological gap, and the operating distance was short, and the endoscope pointed directly to the interventricular foramen, which could reveal the contralateral ventricles at the same time. Wu Chunfu, Department of Surgery, Wuxi Hospital of Traditional Chinese Medicine
With the development of microinvasive neurosurgery, neuroendoscopy has increasingly played an important role in the diagnosis and treatment of diseases of the ventricular system. However, due to the shortcomings of neuroendoscopy, such as small field of view, deformation of microscopic structures, and poor sense of hierarchy, this study was conducted to observe the ventricular system through the longitudinal corpus callosum lateral ventricular approach under neuroendoscopy, to grasp the anatomical features and important anatomical landmarks of the ventricular system under endoscopy, and to provide a local anatomical basis for the application of the longitudinal corpus callosum anterior lateral ventricular approach in the treatment of ventricular lesions.
1.Materials and methods
1.1 Materials
Eight old wet adult cadaveric heads fixed with 10% formalin, seven males and one female, and two fresh cadaveric heads, one male and one female. All cadaveric heads had no obvious ventricular enlargement or shrinkage, no obvious malformation or occupying lesions. All cadavers were perfused with red and blue latex via the bilateral internal carotid artery, vertebral artery and internal jugular vein, respectively.
1.2 Dissection tools
German Snake rigid ventriculoscope with accessories such as cold light source, color TV monitor, video recording system, etc., equipment for cadaveric head perfusion and measurement, and conventional microsurgical instruments.
1.3 Methods
The cadaveric head specimen was fixed on the head frame according to the surgical approach, and the incision was marked with nail violet. In this group, the medial margin of the incision was made along the sagittal line, the posterior margin was 1-1.5 cm after the coronal suture, and the lateral margin was at the top of the temporal area, with the flap turned toward the frontal area. Medially, 2 holes were drilled on the midline, part of the sagittal sinus was exposed in the midline, the bone flap was opened and turned toward the temporal side, the size was about 5 cm × 7 cm, the dura was not completely cut and the base was turned toward the sagittal sinus (Figure 1), and the number of draining veins in front of the coronal suture was recorded. The following steps were performed neuroendoscopically to cut the reflux vein anterior to the coronary sagittal point and to distract the right cerebral hemisphere. The pericallosal arteries on both sides are freed, i.e., the white corpus callosum is seen. The corpus callosum was incised longitudinally strictly along the intersection of the hypothetical line between the external auditory canal and the coronal suture and the corpus callosum, and the corpus callosum was incised 1.5 cm and 2 cm, respectively, to enter the left and right ventricles and the third ventricle via the interventricular foramen.
The skull cap, dura mater and cerebral falx were removed by sawing along the 1 cm line between the brow arch and the superior occipital ridge; the third ventricle was exposed with a blade along the midline, and the anatomical structures within the ventricles were observed anatomically.
2 Results
2.1 General observation
After the dural flap was incised (Figure 1A), the superior cerebral vein flowing back to the superior sagittal sinus was seen in 5 cm before the coronal suture, with one branch in 5 cases, two branches in 1 case, and no venous flow in 4 cases.
2.2 Neuroendoscopic anatomical observation
The reflux vein in front of the coronal sagittal point was cut, and the right cerebral hemisphere was retracted, and the callosal artery was seen to travel in the cingulate sulcus, below which was the cingulate gyrus, which was close to the cerebral falx. In 7 of the 10 cases, the pericallosal artery was symmetrically developed bilaterally, in 3 cases the pericallosal artery was well developed on one side, and the pericallosal artery on the other side was thinly developed, and in 4 cases there were transverse branches of communication between the pericallosal arteries on both sides. These branches were dissected, and the corpus callosum was incised longitudinally in the middle of the pericallosal artery on both sides, along the hypothetical line between the external auditory canal and the coronal suture and the intersection of the corpus callosum, with incisions of 1.5 cm and 2.0 cm, respectively, to understand the scope of neuroendoscopic observation. The corpus callosum was retracted to the side with a brain press and then fixed (Figure 1C), and four of the ten cases entered the transparent compartment cavity (fifth ventricle), two cases entered the left ventricle, and four cases entered the right ventricle (Figure 2A). When entering the hyaline septal cavity, both sides were seen to be thin tissue membranes, and the ventricles on both sides were entered by cutting to the left and right. If one side of the ventricle was entered, only the septum pellucidum had to be cut to enter the contralateral ventricle. With a 1.5 cm incision of the corpus callosum, a rigid endoscope can be used to enter one ventricle, and a septum can be used to enter the contralateral ventricle, both of which can be observed in the anterior horn and body of the lateral ventricle (Figure 2B). The corpus callosum was cut 2.0 cm, and the endoscope entered the third ventricle through the interventricular foramen, and the anterior margin of the middle block and the anterior union were observed in turn, and the end plate, optic cross crypt, funnel crypt, papillary body, and superior port of the aqueduct could be observed by cutting the middle block (Figure 2C). In this group, 8 specimens out of 10 cases showed intermediate blocks, and in one case, it was more difficult to advance endoscopically with a larger intermediate block.
2.3 Measurement of anatomical data of corpus callosum, intermediate mass and interventricular foramen
Based on the characteristics of the neuroendoscopic lateral ventricular approach through the anterior part of the longitudinal corpus callosum, anatomical measurements of the corpus callosum, intermediate mass and interventricular foramen were performed to provide clinical assistance. The thickness of corpus callosum was 6.1±1.2mm, the length diameter of interventricular foramen was 5.6±1.4mm, the width diameter of interventricular foramen was 3.0±1.6mm, the length diameter of middle block was 6.3±1.8mm, and the width diameter of middle block was 3.4±1.2mm.
3 Discussion
Yasargil [1] concluded that this approach has the advantages of avoiding brain injury and epileptic foci by eliminating the need for cortical dissection, clear anatomical landmarks, short pathway, and independent of ventricular size, and taking into account both sides of the ventricular lesion.Asgari et al [2] made a cursory study of the bone window, corpus callosum incision location and size of the transcallosal approach, Zhu Yuhui et al [3] made a detailed analysis of the scope of application and characteristics of the standard transcallosal lateral ventricular locking foramen approach, which provided a basis for the clinical development of transcallosal lateral ventricular locking foramen surgery, but with high individualization requirements. The unique advantages of the neuroendoscopic transversal longitudinal corpus callosum anterior lateral ventricular approach in the management of bilateral ventricular lesions require the endoscopist to master the anatomy of this approach, and a superb foundation in endoscopic local anatomy is one of the key factors to ensure the success of the procedure. By simulating the anterior lateral ventricular approach to the longitudinal fissure of the corpus callosum with a simple neuroendoscope, the size of the anterior incision of the corpus callosum was changed and important anatomical data were measured to compare the scope of operation of the neuroendoscope in the lateral ventricles, especially in the third ventricle, and to provide an anatomical basis for this surgical approach.
3.1 Influence of anterior coronal suture draining veins and pericallosal artery on neuroendoscopic operation
The number and thickness of the anterior coronary suture draining veins are an important factor influencing the lateral ventricular approach via the anterior corpus callosum. In our group, there were few draining veins in the first 5 cm of the coronal suture, which is consistent with the report of Winkler et al [4] that there were almost no draining veins in the first 5 cm of the coronal suture. However, if there are anterior and thick draining veins, which affect the retraction of the cerebral hemispheres and the exposure of the surgical field, the incision should be adjusted accordingly, and if necessary, the surgical operation should be performed with a contralateral bone window to avoid the obstruction of important draining veins. In the case of interventricular foramen or bilateral ventricular tumors, preoperative MRI-enhanced sagittal scans were performed to clarify the number and size of the draining vessels in order to develop the most appropriate surgical incision. The dissection results were similar. In our group, we found that 40% of the peri-callosal arteries had traffic branches. In our clinical work, the traffic branches were cut off by simple neuroendoscopy and the variant peri-callosal arteries were separated by careful dissection.
3.2 Effect of anterior callosal incision size, interventricular foramen and intermediate block size on the scope of neuroendoscopic operation
With the size of the bone window relatively fixed, the endoscope was advanced after entering the lateral ventricle, and the anatomical structure of the lateral ventricle, the position of the interventricular foramen, and the course of the choroid plexus and the thalamic vein were carefully identified to determine the site of endoscopic entry. During the operation, the relationship between the thalamic vein and the choroid plexus was used to determine whether to enter the left or the right ventricle, and if the thalamic vein was located on the right side of the choroid plexus, the endoscope entered the right ventricle. To enter one side of the ventricle, only the septum pellucidum needs to be cut to enter the contralateral ventricle. In clinical surgery, the septum pellucidum should be cut or fistula should be performed in a non-vascular area [6]. The significant difference between anterior endoscopic surgery of the corpus callosum and microsurgery is that the size of the bone window has little influence on the surgical operation. However, endoscopic access to the third ventricle is greatly influenced by the site and size of the corpus callosum incision and the size of the interventricular foramen, and the size of the middle block significantly affects the extent of endoscopic manipulation within the third ventricle. In our group, intermediate masses were present in 8 specimens out of 10 cases, and intermediate masses are present in 76% of normal adults[7] .
With a 1.5 cm incision of the corpus callosum, the rigid endoscope allowed access to one lateral ventricle and incision of the hyaline septum allowed access to the contralateral ventricle, both of which allowed observation of the anterior horn and body of the lateral ventricle. The interventricular foramen measurement in this group is highly variable, so the size of the interventricular foramen has a significant effect on neuroendoscopic surgery. When the interventricular foramen is large, the third ventricle can still be accessed through the interventricular foramen by changing the angle of the endoscope; when the interventricular foramen is small, it is often necessary to cut the ipsilateral vault column, but the size of the middle block often affects the exposure of the posterior structures of the third ventricle. The interventricular foramen can also be enlarged by opening the ventricular canal and choroidal tissue between the vault and choroid plexus without cutting the vault column to facilitate endoscopic access to the third ventricle [8].
With a 2.0 cm incision of the corpus callosum, the endoscope can be operated at a greater angle and the endoscope can be directed to the interventricular foramen. When the interventricular foramen is large and the middle block is small or absent, the neuroendoscope can mostly reveal the lower part of the third ventricle and the posterior part of the middle block through different angles of the mirror and perform the corresponding surgical operation; if the middle block is large, its distance from the anterior union and the roof of the third ventricle is often small, and even if the ipsilateral vault column is cut, it is more difficult for the endoscope to reveal the lower part of the third ventricle and the posterior part of the middle block, which to some extent restricts the endoscopic operation in the third ventricle in clinical surgery. In clinical surgery, the endoscope is to some extent limited in the operation of the third ventricle. Therefore, a 1.5 cm corpus callosum incision allows bilateral ventricular surgery, but endoscopic operation in the third ventricle is significantly limited. With a 2.0 cm incision of the corpus callosum, the space for neuroendoscopic manipulation was significantly improved, and Winkler et al [9] concluded that a 2.0 cm longitudinal incision of the corpus callosum did not have a significant effect on bilateral hemispheric information transfer. The corpus callosum thickness of (6.1±1.2) mm measured by anatomy in our group was consistent with the corpus callosum thickness measured on normal adult cadaveric specimens [9].
3.3 Clinical significance of the neuroendoscopic lateral ventricular approach through the anterior part of the longitudinal fissure of the corpus callosum
The anterior lateral ventricular approach through the longitudinal fissure of the corpus callosum utilizes the natural fissure of the brain and allows access to the lateral ventricles by incising the corpus callosum, allowing observation of the bilateral interventricular foramina.
Fig. 1 A: operation incision B: pericallosal artery C: both ventricles
Fig.1 A:operation incision; B:pericallosa artery; C: double lateral ventricles
Fig.2 Related anatomical structures under neuroscopy A:Intraventricular structures, interventricular foramen, septum pellucidum, thalamic striatal vein and choroid plexus of the lateral ventricle B:Body of the lateral ventricle, choroid plexus C:Third ventricular floor structures
Fig.2 Related anatomical structures by neuroendoscropy A:Structures in lateral ventricle, Monro foramen, septum pellucidum,vena thalamostriata, choroids plexus; B: The body of the lateral ventricle, choroids plexus; C: The floor of the third ventricle