The origin of pure trichocephalic craniopharyngioma has been debated, and there are two main views [5]: the embryonic origin theory suggests that craniopharyngioma originates from the squamous cell nests of the remnant Rathke’s bursa; the tissue chemotaxis theory suggests that craniopharyngioma originates from the nodal part of the pituitary stalk or the chemotaxis of squamous epithelial cells of the adenohypophysis, rather than the remnant cells of the embryonic period. In 1953, Dobos et al [6] reported the first case of purely intra-trigeminal craniopharyngioma and observed that it originated from the funnel. It is suggested that intracerebroventricular craniopharyngioma originates from these nests of chemotaxic squamous cells. It is generally believed that during embryonic development, part of the cells of the Rathke’s bursal fissure (which develops into the pituitary stalk nodule) rotate upward to join the ventral neuroectoderm of the cerebral vesicle (which develops into the funnel and the base of the trichocephalon), and during the fifth week of gestation, before the rotation of the pituitary nodule, the mesoderm-derived molluscum contagiosum inserts normally between the primitive orifice recess and the cerebral vesicle. The site of origin depends on the degree of nodal rotation. If the developmentally delayed soft meninges do not insert properly between the primordial orifice and the cerebral vesicles, some of the nodal cells enter the soft meninges, leading to the development of pure intracerebroventricular craniopharyngiomas [6,7.8]. In our group, all eight cases originated from the base of the three ventricles, and the tumor was found intraoperatively to be separated from the base of the three ventricles by an oval plane, which can be confirmed as a pure intraventricular craniopharyngioma; two cases originated from around the gray nodes, three cases were located in the funnel (i.e., the root of the pituitary stalk), and the rest originated from the anterior part of the base of the three ventricles. The intraoperative findings in this group of cases provide new evidence for the embryologic origin of pure intraventricular craniopharyngioma. Clinical characteristics of pure intracerebroventricular craniopharyngioma The clinical characteristics of pure intracerebroventricular craniopharyngioma are significantly different from those of craniopharyngioma in other parts of the brain. The incidence of pure intracerebroventricular craniopharyngioma is extremely low, accounting for about 0.7-11% of all craniopharyngiomas [2-3], and the incidence is mostly in the adult group [9,11], and the incidence of pure intracerebroventricular craniopharyngioma in this group accounts for 7.3%, with only one patient younger than 15 years old and a mean age of 36 years, which is roughly consistent with the literature. The clinical symptoms of pure intracerebroventricular craniopharyngioma are late, and the first symptoms are mostly related to the increase of intracranial pressure due to hydrocephalus caused by the growth of pure intracerebroventricular craniopharyngioma, and the main clinical manifestations are bilateral frontotemporal headache and dizziness. In this group, three patients showed decreased visual acuity, three cases of bilateral temporal hemianopsia, and one case of bilateral visual field loss in most of the eyes. In this group, there were 4 cases of solid and cystic tumors (mainly solid) and no pure cystic tumors; most of the preoperative cranial sagittal MRI of pure intracerebroventricular craniopharyngioma could clearly find the complete base of the three ventricles, which is significantly different from the craniopharyngioma with suprasellar protrusion into the three ventricles [11]. 5 patients, all of them could clearly judge that the tumor was completely located in the three ventricles before surgery. The tumor was completely located within the tricentrium, and in three patients, due to the irregular growth of the tumor, it was difficult to discern whether the tumor was completely located within the tricentrium from MRI alone, which was only confirmed by the intraoperative finding of the plane of the intact tricentriolar floor and the tumor. Therefore, preoperative MRI images play an important role in the localization and diagnosis of intraventricular craniopharyngioma. Microsurgical treatment of pure intracerebroventricular craniopharyngioma 3.1 Selection of surgical approach Microsurgical treatment is preferred for pure intracerebroventricular craniopharyngioma. The choice of surgical approach should be based on the preoperative CT and MRI images, especially MRI examination, which can clearly show the location, size, cystic solidity and cerebrospinal fluid circulation pathway of the tumor in the three ventricles. In the literature, there are three common surgical approaches for pure intracerebroventricular craniopharyngioma [4,12,13]: trans-pterygoid endplate approach, trans-frontal cortical lateral ventricular approach and transcallosal approach. (1) Transcallosal approach: This approach is a short route, in which the lateral fissure is separated to release cerebrospinal fluid, and the end plate is exposed and incised to access the tricranial ventricles. Three cases in this group used this approach and had good intraoperative exposure. (2) The transfrontal cortical lateral ventricular approach [16] is suitable for tumors that reach the upper part of the three ventricles, especially for tumors that protrude into the lateral ventricles through the interventricular foramen, and the tumor obstructs the foramen of Monro, enlarges the lateral ventricles, and thins the frontal cortex, creating conditions for this approach. In our group, there are two cases in which the transfrontal cortical lateral ventricular approach was used and the tumor was completely resected. (3) Transcallosal approach [14,15], this approach is the same as the transcallosal lateral ventricular approach, which is a superior approach and does not require incision of the cortex, and when the lateral ventricles are not enlarged, the lateral ventricles can still be entered smoothly, and the bilateral lateral ventricles can also be entered through the transparent septum. In this group, this approach was used in three cases with good results. 3.2 Surgical technique The bottom of the three ventricles are the optic cross, optic tract, funnel and gray nodes, etc. The tumor mostly originates around the funnel, so when cutting off the tumor tip, the above structures should be prevented from being damaged. For cystic component tumor, intracapsular puncture can be performed to decompress the fluid. If the exposure is not sufficient, the anterior edge of interventricular foramen can be cut through the fornix column by 5 mm, and the tumor tip should be carefully dissected and separated to avoid forcible traction. After entering the lateral ventricle through the corpus callosum approach, the tumor is removed by entering the triventricular ventricle through the fornix foramen. If necessary, the fornix column on the anterior side of the fornix foramen is cut or the venous angle formed by the thalamic vein and anterior septal vein behind the fornix foramen is separated anteriorly to expand the exposure, or the layers of the fornix and the roof of the triventricular ventricle can be separated bilaterally to remove the posterior triventricular tumor. In the case of trans-pterygoid endplate approach, the endplate can be cut in ten pieces and the tumor can be resected from the anterior and inferior parts first, then from the posterior and superior parts and bilateral tumors, and the part that cannot be seen directly can be resected by changing the angle of the microscope or holding the tumor to the middle and anterior and inferior parts. Most of them can be fully resected. 3.3 Treatment of surgical complications Pure intracerebroventricular craniopharyngioma causes obstructive hydrocephalus due to obstruction of cerebrospinal fluid pathway, and cerebrospinal fluid pathway can be restored after tumor resection. Complications of surgery are mainly perioperative water and electrolyte disorders caused by hypothalamic injury and transient uremia are still common. 6 cases in this group showed changes in serum sodium ions and 5 cases showed transient uremia, which gradually returned to normal after applying hormones, rehydration adjustment and using other diffusion coagulation therapy.