Intra-lateral ventricular cysts are less common, mostly congenital, and are closely related to the lateral ventricular choroid plexus, whose contents are cerebrospinal fluid-like fluid. Lateral ventricular cysts are mostly called arachnoid cysts, and other names include choroid plexus cysts, ventricular meningeal cysts, and glial cysts. Figure 1 Cyst in the left lateral ventricular triangle Figure 2 Cyst revealed by neuronavigation-assisted endoscopy The age of onset of congenital cysts in the lateral ventricles is usually less than 40 years old, with young adults predominating. MRI is the main diagnostic imaging method for intra-lateral ventricular cysts (Figure 1), and the cysts are low signal in T1-weighted phase, the same as cerebrospinal fluid, and the cyst wall is not easily distinguishable. The lateral ventricular triangle or occipital horn is mostly enlarged in a circle-like or oval shape, and the cyst contents are high-signal in the T2-weighted phase, and the isosignal cyst wall resides between the cyst contents and the cerebrospinal fluid and is therefore clearly displayed. The water-suppressed phase brings out the entire cyst pattern. The cyst is closely related to the choroid plexus in the body and triangle of the lateral ventricle, and MRI enhancement scans show an enhanced choroid plexus creeping over the surface of the cyst wall in the midline portion. Symptomatic lateral ventricular arachnoid cysts present mainly with symptoms of cranial hypertension, focal compression and irritation and require surgical treatment. Treatment includes: 1. cyst puncture; 2. cystic ventral shunt; 3. cystotomy; and 4. cystectomy. Cyst puncture has a high recurrence rate and is now mostly not used. Cystic ventral shunt is easier and more widely used, but long-term foreign body implantation and shunt blockage have been a concern for patients. Lateral intraventricular cysts are closely related to the choroid plexus and choroidal bulb and have adhesions to the adjacent ventricular canal and hyaline septum and its surface veins. Traditional craniotomy for cyst removal is not only more traumatic on the surgical pathway, but also has many surgical dead ends due to the limitation of the surgical microscope to expose the deep structures, so the surgical complications are more and more serious. In recent years, endoscopic surgery is mostly preferred, and it is believed that modern endoscopic surgery has many advantages such as clear images, high color reproduction, large surgical field of view, good performance of local anatomical details, and fine design of related surgical instruments, which can minimize the surgical trauma while ensuring good surgical results. The cyst usually occupies most of the space in the body of the lateral ventricle, the triangle and the occipital horn, and the cyst wall is close to the surrounding intracerebroventricular structures. Therefore, sufficient ventricular space should be left between the endoscopic entry point and the cyst to facilitate endoscopic observation of the whole cyst and the relationship between adjacent anatomical structures, fully estimate the difficulty of surgery, and choose a reasonable surgical plan. The cyst wall is adherent to important structures such as choroid plexus, ventricular canal, hyaline septum and its surface veins (especially septal vein and thalamic vein), and vault, etc. Ventricular canal adhesions are easier to separate, while choroid plexus adhesions are usually tighter, and total resection cannot be forced when separation is difficult to avoid unpredictable neurovascular injury. At present, many domestic and foreign operators use the cystotomy method, which is considered to have good results, low recurrence rate of cysts, and minimal risk of surgical bleeding and high safety factor. Cystotomy cystotomy includes craniotomy, stereotactic surgery, endoscopic cyst membrane opening and neuronavigation-assisted endoscopic membrane opening. Although stereotactic cystotomy can precisely design the surgical incision and surgical path to avoid brain function loss caused by the surgical path, the operation still has a great blindness and can easily lead to neurovascular injury. The author used an endoscopic surgical approach combined with neuronavigation-assisted technology to successfully treat 21 cases of lateral intracerebral cysts (Figure 2). The advantages of neuronavigation are reflected in the following aspects: 1. Precise design of the surgical approach and surgical trajectory, which can keep the cortical incision away from the functional area, but also enable the endoscopic surgical trajectory to penetrate the anterior and posterior walls of the cyst, facilitating the simultaneous opening of the anterior and posterior walls of the cyst if necessary; 2. Endoscopic intracerebroventricular surgery requires the interventricular foramen, septal vein, thalamic vein, choroid plexus and its course, transparent septum and other structures as reference marks However, intracerebroventricular cysts usually result in displacement of the above structures or are covered by membranes. The precise positioning by neuronavigation imaging anatomy improves the safety of surgery and avoids damage to important neurovascular vessels; 3. After completing the navigation registration and correction steps, the head end and the sheath rod of the endoscopic working sheath represent the positioning point and the surgical direction, respectively, and the real-time, interactive operation function of the workstation is utilized so that the operator conveniently knows “where” the endoscopic lens end is The head end of the endoscopic sheath and the sheath rod represent the positioning point and the surgical direction respectively, and the real-time, interactive operation function of the workstation makes it easy for the operator to know “where” the endoscopic end is and “where” the endoscopic sheath is pointing. The cyst wall windowing site is mostly chosen away from the choroid plexus, as the surface veins of the cyst wall near the plexus are more dense. The windowing instruments and methods are in the following order: electrocoagulation cautery of the cyst wall, balloon puncture expansion and micro shearing of the cyst wall. The window opening area should be at least 20 mm × 10 mm, and to prevent closure of the opening edges of the capsule wall, the window opening should be followed by routine bipolar electrocoagulation of the window edges. If the window opening area of a single window is small, or if the cyst has a large adhesion surface with the lateral ventricle, which may make a part of the lateral ventricle containing the choroid plexus isolated by the cyst and does not communicate with the interventricular foramen, another window should be opened in the contralateral wall. In the author’s opinion, neuronavigation-assisted endoscopic membrane windowing is a more reasonable and safe surgical method for the treatment of intraventricular cysts at present, with simple surgery, minimal trauma and short hospital stay. After follow-up, the patient’s symptoms improved significantly, and there was no case of cyst recurrence.