Limited dilatation of the temporal horn of the lateral ventricle can sometimes be encountered in clinical work. Why does this happen? Post-brain tumor resection, cerebral hemorrhage or ventriculitis can lead to limited dilatation of the temporal horn of the lateral ventricle, resulting in clinical symptoms such as headache, dizziness, epilepsy, and memory loss. What is the least invasive and most effective treatment option chosen by Zhou Yan, Department of Neurosurgery, Air Force General Hospital? An intuitive treatment option would be to open up the abnormal temporal horn to the lateral ventricle, but this is not advisable because scar tissue or anatomical variations in the area can complicate the procedure and increase the risk of surgery. If the interpeduncular pool is spacious and the wall of the capsule in the proximal midline of the temporal horn is thin, only the two conditions mentioned above give us another option – lateral ventriculotemporal horn fistula – a minimally invasive procedure using neuroendoscopic techniques. Let’s first understand the general principles of this procedure and then describe the whole procedure of lateral ventriculotemporal horn fistula in detail with a case study. What is the most important thing before the surgery starts? –surgical position–this determines whether the entire procedure will go smoothly. The head is deflected to the opposite side. The ideal puncture tract is determined with the help of neuronavigation. Usually the cranial drill is positioned in the temporoparietal region, which allows the puncture tract to go straight to the top of the temporal horn. Once the endoscope has entered the temporal horn of the lateral ventricle under neuroguidance, the main anatomical landmark, the choroid plexus, needs to be identified. This allows the guidance of the choroid plexus to be followed to the tip of the temporal horn. Sometimes the hippocampal head can also be identified. At the tip of the temporal horn, the proximal midline lateral wall near the choroidal fissure is usually the thinnest. The ideal site for fistulae is usually the proximal midline lateral wall located near the interpeduncular pool. Percussion-like perfusion helps to identify the thinnest point on the proximal midline lateral wall. A blunt fistula is first created using a Decq micro clamp and then a 2 mm diameter endoscope is introduced through this initial fistula opening to confirm that the interpeduncular pool is reached. The fistula was then further dilated using a 3-Fr Fogarty balloon catheter. Subsequently, brain tissue around the circumference of the fistula is removed using microscopic scissors and forceps to further expand the fistula to avoid postoperative scarring leading to closure of the fistula. It is most important and paramount to identify and protect the arteriovenous nerve and the penetrating branches of the posterior communicating and posterior cerebral arteries. The endoscope is introduced through the fistula into the interpeduncular pool and the pituitary stalk and the arteriolar nerve are clearly identified. This minimally invasive procedure is described in detail in a typical case. This is a 15-year-old female patient who recovered well after temporal lobe triangle tumor resection but was found to have progressive dilatation of the temporal horn of the lateral ventricle after periodic review. A neuroendoscopic technique, lateral ventriculotemporal horn fistulotomy, was chosen for treatment. The procedure was started as described above. After introducing the endoscope into the lateral ventriculotemporal horn, its tip is reached and the hippocampal head can be observed. The thinnest area on the proximal midline lateral wall is then identified under the guidance of neuronavigation. The fistula is bluntly detached using a Decq micro clamp. A 2-mm diameter 30° endoscope was introduced through the fistula to identify the posterior communicating artery and the arteriolar nerve. These two important anatomical landmarks indicate that the temporal horn of the lateral ventricle and the interpeduncular pool have been opened. The brain tissue around the perimeter of the fistula was then further excised with biopsy forceps. The fistula was further dilated using a 3-Fr Fogarty balloon catheter. The interpeduncular pool was then accessed using a 3.3mm 30° endoscope to identify the pituitary stalk. The arteriolar nerve, posterior communicating artery, and superior cerebellar artery were then further explored. A repeat MR 1 year after surgery showed a narrowing of the temporal angle of the lateral ventricle and confirmed patency of the lateral ventriculostomy.