Lateral split arachnoid cysts can produce headaches, seizures, etc. If the patient’s clinical symptoms are only headache, it is difficult to determine definitively that a lateral split arachnoid cyst is the cause. The patient is placed in the supine position with the head turned to the opposite side. Depending on the size of the cyst, the location of the surgical incision on the anterior zygomatic arch is determined. Neuronavigation facilitates the determination of the ideal cranial drilling location and the best path to guide the basal pool. Once the dura is incised, the cyst wall of the arachnoid cyst is revealed. The vessels in the cyst wall are electrocoagulated to avoid possible bleeding during movement of the neuroendoscope. Immediately after dissection of the cyst wall, a neuroendoscopic sheath is introduced into the cystic cavity to avoid excessive loss of cerebrospinal fluid. A cotton pad is also placed around the sheath to avoid blood flow into the cystic cavity, which may lead to blurring of the surgical view. Once inside the arachnoid cyst, the first step is to visualize the landmark anatomic structures within the cystic cavity: the internal carotid artery, middle cerebral artery, optic nerve, and arteriolar nerve. The ideal location for the fistula – the space between the internal carotid artery and the optic nerve – is the space between the internal carotid artery and the optic nerve. If the internal carotid artery-actinic nerve space is too narrow, then the fistula may also be located lateral to the actinic nerve. Occasionally, a fistula may be made medial to the internal carotid artery. In adults, the arachnoid membrane is thicker, so it needs to be cut with microscissors and then enlarged with biopsy forceps. Once the arachnoid cyst wall fistula is complete, the Liliequist membrane can be seen through this fistula. This membrane must be opened so that traffic can be established between the arachnoid cyst and the anterior pontine pool. The key anatomical structure to determine if the anterior pontine pool has been entered is the basilar artery (once the basilar artery is seen, it can be determined that the anterior pontine pool has been entered.) Below, we illustrate this in detail with a case. This is an 8-year-old boy with a headache as his primary clinical symptom. MRI suggests the presence of a large arachnoid cyst in the right lateral fissure and has led to displacement of midline structures and compression of the lateral ventricles. Neuronavigation was used to determine the optimal cranial drilling location and neuroendoscopic pathway. A 0° endoscope is first used to probe into the cystic cavity and observe the landmark anatomic structures: internal carotid artery, middle cerebral artery, posterior communicating artery, arteriolar nerve, and optic nerve. Then, the endoscope is advanced forward and the anatomical structures can be observed as shown Then, the endoscope is turned backward and the optic nerve, actinic nerve, internal carotid artery, posterior communicating artery, and anterior choroidal artery can be observed. Between the internal carotid artery and the arteriolar nerve, the thinnest wall of the arachnoid cyst as well as the Liliequist membrane is cut with microscissors. The fistula opening was then enlarged with Decq forceps. The pituitary stalk can be visualized by probing the interpeduncular pool with a 30° endoscope through the fistula. The 30° endoscope was then probed into the anterior pontine pool, allowing observation of the contralateral actinomycete nerve, posterior cerebral artery, and superior cerebellar artery. Finally, the stoma is observed again as the endoscope is gradually withdrawn. Immediately after surgery, the child’s headache was relieved. A repeat brain MRI 2 years after surgery showed a significant reduction in the volume of the lateral fissure arachnoid cyst and visualization of a patent cyst-pool fistula (shown by arrows).