Prevention of complications

Proper surgical indication

In general, there is more risk associated with ETV compared to shunting in terms of neural injury. Good preoperative planning, avoidance of multiple ETV trials and prediction of ETV success are essential prerequisites for a successful ETV [8].

Proper selection of the entry point of ventricular entry

Entry point should be based on the size and configuration of the ventricles of the patient. Typical location is at or just in front of the coronal suture in the midpapillary line, more or less, similar to that of Kocher’s point. It is important to maintain straight trajectory as much as possible to the foramen of Monro and floor of the third ventricle [8, 24].

Modification of entry point is particularly important in cases where ETV and biopsy are simultaneously required such as in cases of pineal region tumors that extend into the 3rd ventricle. Advancement in neuroendoscopy has allowed safe procedures to be done with flexible working angles; the availability of neuronavigation is particularly important in helping to select the appropriate and safe trajectory [24]. Likewise, flexible endoscope is especially helpful for tumors in the posterior third of 3rd ventricle. Either single or double burr holes are acceptable options [25]. We prefer biportal trajectory with rigid endoscopy to perform the two procedures (Fig. 1). Because of possible bleeding from the tumor, we perform the ETV first and then perform the biopsy later [26].

Fig. 1
figure 1

Preoperative sagittal T1 MRI with contrast showing the trajectory for an ETV (yellow arrow) and the trajectory for pineal region tumor biopsy (white dotted arrow)

Proper insertion of the endoscope

Nowadays, endoscopes have become smaller in diameter compared to the past; despite their small diameter, they are still larger than a shunt catheter and may cause significant neuronal injury if not placed correctly. Preoperative ventricular measurement is important to gauge the feasibility of ventricular cannulation. If the ventricular size is relatively small, intraoperative image guidance or intraoperative ultrasound as an alternatively is fundamental tools for a proper ventricular access. If ventricular size is moderate or large, ventricular puncture can usually be done safely with careful aiming of the endoscope based on preoperative images [27].

Accurate anatomical orientation for steering of endoscopes

A common mistake encountered is entering too anteriorly in the frontal horn where it becomes difficult to find the choroid plexus which emanate from foramen of Monro and run posteriorly; in such cases, the endoscope should steered posteriorly. Septal defects are not unusual particularly in chronic or congenital hydrocephalus [28].

It is important to identify anatomical landmarks early to make a proper orientation. Such anatomical structures include Monro, septal veins, thalamostriate veins and the choroid plexus. The dorsum sella and at times tip of basilar artery can be seen through the relatively thin and transparent floor of the 3rd ventricle. However, in cases where there were a chronic inflammation and congenital anomalies as is seen in myelomeningocele, these easy landmarks can be distorted. It is important to step back and appreciate the surrounding anatomical structures to orient oneself before advancing further [6].

Meticulous preoperative inspection of magnetic resonance images to evaluate the position of the basilar artery in relation to the floor of the third ventricle is important given the anatomical variations [29, 30].

Skillful passing of an endoscope through the foramen of Monro

Passage through the foramen of Monro is a very critical step and requires care as it is common to injure the fornix at this step of the procedure. In most circumstances, the injury is unilateral and minor which does not cause memory disturbance. However, if the injury is bilateral significant, postoperative memory disturbance can ensue.

If the ETV is to be done for a second time, it is important to choose the same entry through the foramen of Monro especially in cases where there has been a previous injury to the fornix [4].

The choroid plexus exiting the foramen of Monro can sometimes be large enough to obliterate the foramen of Monro. In this case, it is reasonable to coagulate the choroid plexus before passing the endoscope. In cases where the foramen of Monro is small, using fluid irrigation near the foramen may help to enlarge the foramen Monro [31]. Proper selection of the size of endoscope should be based on the assessment of the size of foramen of Monro in the preoperative MRI.

Proper insertion of instruments through the endoscopic port

It is important to note that there is 180° visual angle available. The ventricular outlet of the endoscope is at the same level as the optic fiber. Therefore, when passing instrument in and out of the endoscope, the endoscope must be retracted back for a short distance in order for the surgeon to see the tip of the instrument being inserted. Indiscriminate passing of instruments through the endoscope especially when the tip of the endoscope is near important neuronal structures will cause injury and bleeding. Although injury to the lateral ventricular wall is mostly benign, it may be a source of bleeding and may cause prolonged operative time. It is prudent to orient the tip of the endoscope slightly away from important structures until the tip of the inserted instrument is seen at which time then the endoscope can be advanced with the instrument as one piece [22].

Skillful penetration of the floor of the third ventricle

The point of perforation of the floor is in the midline and just anterior to the mammillary bodies (Fig. 2).

Fig. 2
figure 2

Floor of 3rd ventricle showing the anatomical landmark for an ETV ostium (dotted white line). BA; basilar artery, IS; infundibulum stalk, MB; mammillary body

Technical note

Multiple techniques can be used for perforating the floor of third ventricle. We use endoscopic grasping forceps to make the initial perforation. After perforation, the hole can be enlarged either by a Fogarty balloon catheter or endoscopic grasping forceps which should be inserted and then spread in the stoma. It is crucial to avoid closing the grasping forceps after the floor has been breached so that a penetrating vessel on the other side is not inadvertently grabbed; the forceps should be inserted through the hole, opened, and then withdrawn without closing them until the tips are directly visualized (Fig. 3). The stoma should be widened as much as possible without encroaching on the mammillary bodies, infundibular recess, or walls of the third ventricle. It is vital to confirm that the prepontine cistern has been entered. We should make sure that two layers have been penetrated, the tuber cinereum and the membrane of Liliequist. One source of procedure failure is penetrating the floor (tuber cinereum) but not adequately traversing the membrane. The surgeon should avoid endoscopic tourism after accomplishing the procedures to avoid any unexpected complication at the end of the procedure.

Fig. 3
figure 3

A: Techniques of widening the stoma, B: the stoma after being widened by grasping forceps

Thick and opaque membrane

It is not unusual to encounter a thick and opaque membrane. This causes a challenge and requires high level of expertise. Water jet dissection technique has been described to reduce risk of bleeding and neurological deficits when thick and cloudy membranes are encountered [14].

It is always prudent to remember the ethical principle of “do no harm”; therefore, in such circumstances where the surgeon faces tough 3rd ventricular floor membrane, it is wise to abandon the procedure especially when there is disorientation or a higher risk of complications. Attempting to pass through such membranes will cause unnecessary bleeding, stretching of adjacent critical neuronal structures, or may simply not be amenable to perforation. Other CSF diversion techniques may be sought such as ventriculoperitoneal shunt.

Adequate control of bleeding

Bleeding sources inside ventricles usually come from small capillaries, choroid plexus, veins which are commonly encountered during ventricular endoscopic access. The most common way of controlling bleeding from these vessels is by using continuous saline irrigation, which not only will clear the operative field but also will stop the bleeding. Although washing itself is less effective in controlling the bleeding, the pressure component exerted by the fluid of the saline irrigation is what allows bleeding to stop. This fluid column pressure effect can be augmented effectively by closing the drainage port for as long as 4–5 min while alerting the anesthetic staff to be vigilant for any hemodynamic changes and to avoid the unwanted high pressure that may cause ischemic damage [11]. Major bleeding is a rare occurrence and usually occurs from basilar perforators at the stoma site [32], and the tear in the arterial wall is thought to be small; however, it takes much longer time to control, wash-out with large amount of saline irrigation is required, and follow-up angiography is important to rule out pseudoaneurysm which may require neurointerventional procedures [12, 13]. Some authors described the small-chamber irrigation technique as a simple maneuver for managing intraoperative hemorrhage during endoscopic intraventricular surgery [33]. Nagasaki et al. reported a balanced irrigation–suction technique with a multifunctional suction cannula for intraoperative hemorrhage during ventricular endoscopy [34]. The dry field technique was described by many authors as a last resort to deal with intraoperative hemorrhage during ventricular endoscopy [35].

Precaution to prevent postoperative CSF leakage in infants

Underdevelopment of CSF absorption pathways in infants as compared to older children increases the failure rate of ETV, leading to a major surgical concern and conversion to shunting procedures [36]. Moreover, the dura and galea are weaker and thin in small children which adds another challenge to getting a watertight closure. The most important step is to plug the tract of the endoscope with piece of tapered Gelfoam fashioned in a way that it does not slip into the ventricle. Enforcement of the wound is another way to prevent CSF leak and pseudomeningocele formation. If possible and in case where a large burr hole was created, closure of the dura can be attempted. It is important to make use of the pericranium as well that overlies the burr hole. In addition, using dural sealants or bone dust to plug the burr hole with the addition a titanium burr hole cover as a support will also help facilitate tight closure [37, 38].

Reclosure of the stoma

Early reclosure of the stoma is not common if the procedure was done correctly. Careful postoperative monitoring of the patient is required with a focus on ICP signs and symptoms. Early reclosure may be caused by low CSF pressure through the stoma which would in turn allow the stoma to fold on itself and close, or it may be due to incomplete opening of the floor of the third ventricle and or Liliequist’s membrane. As a general rule of thumb, if the endoscope can pass through the ostium, the ostium is probably wide enough. Difficulty with fenestration of the Liliequist’s membrane arises when the membrane itself is deep and pushed up against the clivus by the basilar artery making small corridor for the endoscope or the instruments to pass, or where there are perforators running through or adjacent to the Liliequist’s membrane making its perforation risky. In such circumstances, the goal of the procedure would have not been established and it is wise to convert to other CSF diversion techniques such as ventriculoperitoneal shunting. A successful ETV indicator is to see the floor of the third ventricle flapping in synchrony with the diastolic and systolic waves. Parikh et al. [39] advocated placement of CSF reservoir following ETV for direct ventricular access in case early failure was anticipated and also for direct ICP measurement; however, we think that this defeats the purpose of ETV where the main purpose is avoiding implantable devices. Others have also performed stented ETV to maintain the patency of the created stoma in patients with a high likelihood of reclosure; however, more research is needed to establish its use [40,41,42].

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