Cysts of the septum pellucidum (CSPs) are considered a normal variant of the human brain with an incidence of 10% in adults and 82% in newborns and generally do not require surgical intervention, although a very small number of CSPs develop clinical symptoms. Its surgical treatment includes: craniotomy, cyst-abdominal shunt, stereotactic cystocentesis and endoscopic cyst ventriculotomy. During the period from December 2007 to December 2010, the Department of Neurosurgery of the Naval General Hospital applied neuroendoscopy combined with stereotactic treatment to 18 cases of symptomatic hyaline septal cysts with satisfactory results, which are reported below. Zhao Hulin, Department of Neurosurgery, Naval General Hospital Data and methods 1. General data: Of the 18 cases in this group, 10 were male and 8 were female. Age ranged from 12 to 28 years, with an average of 20 years, and the duration of the disease ranged from 4 months to 3 years. All cases had headache and dizziness, nausea and vomiting in 4 cases, depression, insomnia and anxiety in 2 cases, memory loss and regression in academic performance in 1 case, mild edema of the optic disc in 3 cases, and epileptic disorientation in 1 case. The cranial CT showed: oval cystic hypodensity in the midline septal area, with a maximum width of 1.5-2.3 cm, similar to the signal of cerebrospinal fluid, and no significant enhancement after drug injection. EEG showed that there were localized spike-tip waves. 2. Surgery method: intravenous anesthesia, supine position for transfrontal approach, lateral position for transoccipital approach, frameless brain stereotactic surgery system with the aid of German Snake Ascular neuroendoscope and domestic CSA-R series robotic system. During the operation, four marker points are placed on the patient’s head, and a cranial MRI localization scan is performed (the scope of the scan includes all markers). The skin incision for the transfrontal approach was 1 cm in front of the coronal suture, 5 cm in front of the midline, and about 3 cm in the direct skin incision; the skin incision for the transoccipital approach was 4 cm behind and 4 cm above the external auditory canal, and about 3 cm in the direct skin incision. The dura is opened, and the channel-dilating needle core is safely introduced into the lateral ventricle under the guidance of the frameless stereotactic robot arm. The robotic arm is moved aside and the freehand endoscope is passed into the lateral ventricle along the dilated puncture tract of the channel-dilating needle core. The flow rate was adjusted at any time to maintain a clear operative field by continuous flushing with 37 ℃ equilibrium fluid. The fistula was first cauterized with an electrocoagulator, and the endoscopic scissors were used to enlarge the fistula to more than 10 mm, and the bleeding was stopped by electrocautery. The interventricular foramen and the three ventricles were observed endoscopically without obstruction, and after confirming that there was no bleeding, the endoscope was slowly withdrawn. A Expansive bowl dilatation of Septum pellucidum Cyst seen in the operation B fenestrated hole of the cyst A Intraoperative dilated hyaline septal cyst B Fistula made by the cyst wall Results Two patients in this group developed fever after the operation and were treated symptomatically. They were treated symptomatically and returned to normal after 2 days. In the rest of the patients, there were no postoperative complications. 16 patients had their cysts significantly reduced on cranial CT 1 week after surgery, and all patients were followed up for 1 month to 5 years. The follow-up imaging data were as follows: A T1-weighted axial MRI scans obtained before surgery showing septum nepellucidum cyst with laterally bowed walls. B T1-weighted axial MRI B T1-weighted axial MRI scans obtained 6 months after endoscopic surgery showing a significant decrease in the size of the cyst. A Preoperative B Postoperative Discussion The hyaline septum is located between the lateral ventricles on both sides and consists of two vertically divided laminae. The middle is a narrow lumen (septal cavity). The septum pellucidum is a normal variant and is usually asymptomatic. 15% of adults have a septum pellucidum [1]. If the distance between the lateral walls of the septal cavity is greater than or equal to 10 mm, the diagnosis of septal cyst is established [2-4]. Some septal cysts are asymptomatic [5-7], while others cause significant neurological deficits. The most common symptoms in our group of 18 patients were episodic headache and dizziness, and a few were accompanied by nausea and vomiting, which were thought to be related to intermittent obstruction of the interventricular foramen by the cyst; one patient had an aphasic seizure, which disappeared after surgery, and epilepsy was considered to be related to the cyst, and the exact mechanism was unknown. There are several treatment options for hyaline septal cysts, including: open hyaline septal cyst penetration surgery, cyst-ventricular or cyst-abdominal shunt surgery, stereotactic cyst penetration surgery [8-10], and endoscopic windowing surgery [11-12]. Compared with endoscopic surgery, the first three methods have disadvantages such as high trauma, permanent implantation of foreign body in vivo and high failure rate. In 1995, Jakowaski et al. first reported the use of neuroendoscopic techniques for endoscopic windowing of hyaloid septal cysts [13]. To date, an increasing number of scholars have adopted endoscopic treatment of septal cysts [1, 12,14-19]. Nevertheless, the correct determination of endoscopic orientation and accurate localization of the lesion may be affected by anatomical changes and small ventricles during hyaline septal cyst stoma, and even serious complications may arise. In order to solve these conflicts, we applied the stereotactic technique to endoscopic hyaloid septal cyst stoma surgery to improve the accuracy of the procedure. The purpose of endoscopic septal cyst surgery is to open a large enough window in a safe area without important blood vessels in the lateral wall of the cyst under direct endoscopic view to ensure permanent free traffic between the fluid in the cyst and the cerebrospinal fluid in the lateral ventricle, eliminate the pressure gradient between the cyst cavity and the lateral ventricle cavity, release the tension of the cyst wall, remove the occupying effect of the cyst, relieve hydrocephalus and restore the neurological function of the hypothalamic septum. Because of the narrowing of the ventricles due to the encroachment of the hyaline septal cyst into the lateral ventricles, endoscopic puncture of the frontal or occipital horn is difficult and may cause damage to the vault, thalamus, internal capsule, caudate nucleus, septal vein, and thalamic vein during endoscopic insertion. This makes precise endoscopic access to the lateral ventricles critical. The optimal entry point and surgical pathway may be difficult to determine and achieve without the use of localization techniques. This risk can be mitigated with the aid of a directional system. The use of stereotactic techniques allows the perfect combination of the precision of the orientation technique and the advantages of the visualization of the endoscopic technique. Stereotactic guidance is particularly valuable in cases of anatomical abnormalities and small ventricles. Recently, neuronavigation-assisted endoscopic treatment of hyaline septal cysts has been reported [20,21], but the application of navigation will undoubtedly increase medical costs significantly. We successfully performed a single opening of the cyst [22], which allowed full communication between the cyst and the lateral ventricle on one side, and the patient recovered completely after the operation without sequelae. The surgery has the following experiences: 1. For patients who are young or uncooperative, in order to avoid intraoperative head movement which affects the accuracy of surgery, framed stereotactic; or frameless stereotactic, but the head needs to be fixed by Mayfeid head frame and under general anesthesia; for those who use frameless stereotactic technique under local anesthesia, the head needs to be fixed by plastic pillow. The cranial drilling should be done gently, and offstage assistants should help support the head to prevent displacement.2. The surgical entry point is generally chosen to be located in the frontal region, 1 to 2 cm before the coronal suture and 3 to 5 cm next to the midline.3. When choosing the target point for endoscopic entry, it should be located in the ventricular cavity near the wall of the hyaloid septum cyst.4. The endoscope should first reach the target point carefully under the guidance of the directional instrument guide clip, and then be removed after confirming entry into the ventricle. After confirming the entry into the ventricle, the guiding clip can be removed, the robotic arm or the directional bow can be removed, and the endoscope can be operated manually. 5. When opening the window in the wall of the septal cyst, the area with relatively few blood vessels should be selected, usually 5-10 mm above the posterior interventricular foramen, between the fornix and the corpus callosum, where the cyst fluctuates significantly, and two fistulas are first cauterized with bipolar cautery and created, and then the two fistulas are enlarged into a large window (diameter >1 cm) with scissors. The burr at the edge of the fistula was smoothed with bipolar cautery.6 A unilateral opening of the cyst wall can achieve satisfactory surgical results. Because the second window is operated in the anterior part of the cyst wall from the cyst cavity to the lateral ventricular cavity, it is difficult to see the course of the contralateral septal vein, which is easily damaged. Moreover, the unilateral wall opening is large enough and the chance of reclosure is rare. In this group of patients, a single window was performed to achieve satisfactory results.7. After the fistula is completed, the interventricular foramen should be inspected endoscopically for adhesions and obstruction to ensure unobstructed cerebrospinal fluid circulation.8. Because the image quality of the bendable soft fiber endoscope is not as good as that of the rigid mirror, and the reliability and operability of the accompanying scissors, biopsy forceps, bipolar electrocoagulation and other operating instruments are not as good as that of the rigid mirror system, the authors have used the neuroendoscope in clinical openings and fistulas. Therefore, the neuroendoscope used in clinical openings and fistulas was mainly rigid. The combination of stereotactic and neuroendoscopy, the characteristics of endoscopic operation under direct vision, and the accuracy of stereotactic, makes the operation simple, safe and effective, and reduces side injuries and complications, which is an ideal surgical method for hyaline septal cysts and is worthy of clinical promotion and application.