Introduction
An active distension of the ventricular system of the brain resulting from the inadequate passage of CSF from its point of production from the choroid plexus within the cerebral ventricles to its point of absorption into the systemic circulation through the arachnoid granulations (1) (Figure 1). Depending on the pathology, the treatment options may vary. Endoscopic third ventriculostomy (ETV) has been a well-known technique for over a century and gained its popularity over the last 3 decades and became one of the primary treatment modalities of internal CSF (cerebrospinal fluid) diversion (2). ETV is a minimally invasive neurosurgical procedure aimed at treating predominantly obstructive hydrocephalus secondary to aqueductal stenosis either congenital or acquired. People have tried this procedure in a few selected cases of communicating hydrocephalus with limited success (3, 4). Conventional ETV (Video 1) aimed at creating an alternate CSF pathway through the floor of the third ventricle (tuber cinereum) to the basal cisterns into interpeduncular space using the channeled neuroendoscope. In a few difficult cases, like thickened floor, distorted anatomy of floor of the third ventricle or high arched basilar artery with very limited space in prepontine cisterns, an alternative ETV technique called lamina terminalis ETV (LTETV) can be done using a flexible endoscope (Video 2).
Figure 1. Illustrated diagram showing the normal CSF circulation with possible causes of CSF circulation abnormalities causing hydrocephalus and their modes of management. CPC, choroid plexus coagulation; VSG, ventriculo subgaleal shunt; VPS, ventriculo peritoneal shunt; ETV, endoscopic third ventriculostomy; TPS, thecoperitoneal shunt.
| Video 1. https://youtu.be/G95SH-f_1Gc |
| Video 2. https://youtu.be/3C0HIyzW49c |
This chapter is structured to provide comprehensive insights into the ETV procedure, its indications, technique, and post-operative care.
Selection of cases for ETV
Selecting an ideal case for ETV depends on the patient’s age, etiology and previous treatment. Neonatal or early infantile hydrocephalus poses a major challenge and has high failure rates with ETV or shunt surgery. Kulkarni et al. (5, 6) proposed ETV success score to select an appropriate case for ETV with reasonably high success rates of surgery. There are other independent radiological parameters like the third ventricular bowing sign which will predict the ETV success (7, 8). Down bowing of the third ventricular floor by more than 5 mm has been associated with high success rates. In older children and adults the indications are relatively clear and ETV is the first option in obstructive hydrocephalus. Post-haemorrhagic and post-infective hydrocephalus in pediatric or adult cases are associated with very low success rates with ETV. I follow this flow chart for the selection of different treatment options (Figure 2). For this chapter, I will limit myself to ETV and discuss the technical nuances, post-operative complications and outcomes of this technique.
Figure 2. Flow chart showing the hydrocephalus management algorithm and role of ETV in the management of hydrocephalus. EVD, external ventricular drainage; obt. HC, obstructive hydrocephalus; comm. HC, communicating hydrocephalus; FU, follow up.
Endoscopic third ventriculostomy (ETV) technique
The procedure is performed under general anaesthesia (GA). Pre-operative evaluation of the imaging is very crucial in planning the head position and placement of the burr hole. The patient is positioned supine with 10–150 flexion and the head is turned to the opposite side by 20–300 so that it brings the burr hole point to the highest position (9). The exact entry point can be measured on CT or MRI images. The best point is accessed by two point technique, where we draw a line connecting the stoma site in the floor of the third ventricle to the midpoint of the foramen Monroe and is extended onto the scalp. This line will be straight and without damage to the fornix one can advance the scope into the third ventricle in sizable dilated foramen Monroe (Figure 4). This line has to be adjusted both in sagittal and coronal planes. Usually, this point will match with Kocher’s point. Occasionally when one is planning for biopsy along with the ETV in posterior third ventricular lesions, one needs two different burr holes separately for biopsy and ETV (10). To avoid this one can use a single burr hole in the centre of both or use a flexible neuroendoscope to do the biopsy through the standard precoronal burr hole (Figure 4). Once the patient is positioned, the head can be strapped to the horseshoe headrest to avoid any movement during the surgery, especially in neonatal and pediatric populations. I routinely use the endoscope holder which is attached to the table on the side of the burr hole. Neuronavigation is used in planning and marking in selected cases with narrow ventricles, small foramen Monroe or multiseptated hydrocephalus. With the navigation, proper entry point, the direction of the trocar and cannula to advance into the ventricle can be planned precisely (11).
Figure 3. Figures showing the channeled endoscopes. (A,C) Lotta system (Karl Storz) depicting the arrangement of working channels (B) Fiber optic flexible neuroendoscope (Karl Storz). (D) Flexible video endoscope: Chip on tip new generation flexible endoscope (Karl Storz).
Figure 4. MR images of a hydrocephalus patient showing pre-operative planning marking the entry point in coronal (A) and Sagittal (B) view for a standard ETV. (C) MR image of a patient with posterior third ventricular tumor with hydrocephalus showing different trajectories for the doing ETV and biopsy of the tumor.
The endoscopic equipment is the surgeon’s preference and two companies that supply these channel neuro endoscopes are Storz® and Aesculap®. Both these systems have three working channels (Figure 3). Two channels are used for instruments and one for irrigation. Once the trocar, cannula assembly is introduced into the lateral ventricle, it’s fixed to the holding arm and CSF is collected for analysis. Later the channel endoscope is introduced through the cannula and locked in position. Subsequently, the scope is advanced into the third ventricle through the foramen Monroe. Anatomy is inspected and the stoma point in the floor of the third ventricle is identified anterior to the mamillary bodies. In uncomplicated cases, the floor is thin and transparent where one can inspect the pulsating basilar vessel or its branches. In the case of the opaque floor, one can feel the dorsum Sella with the help of a blunt bipolar electrode and puncture the floor just posterior to that. After the puncture through the floor, the stoma is enlarged using a 2F or 3F Fogarty catheter to achieve a stoma size of approximately 5mm or more. The Fogarty catheter dilatation should be very smooth and the balloon is engaged at the stoma orifice to enlarge it in a better way. It needs a bit of practice and coordination among the surgeon and the assistant. Just below the tuber cinereum, there will be a second layer called the membrane of Lilliquist. Both these layers need to be opened to have an effective functioning stoma (12–14). The endpoint of a successful ETV surgery is
• Adequate size stoma (≥5 mm).
• Flip-flop movement of the membrane at the free edge of the stoma.
• Visible basilar vessels in the prepontine cisterns.
The ventriculostomy process may encounter minimal bleeding through the margins of the stoma in a few cases. This bleeding will stop with the irrigation. As much as possible all kinds of electrocoagulation to be avoided in that area to avoid injury to the perforators or hypothalamic damage. Any amount of blood collected in the ventricle can be irrigated and cleared. In difficult cases and unfavorable anatomy at the floor of the third ventricle, one can do the lamina terminalis ETV (LT ETV) using a flexible scope (Video 2). In cases of the narrow foramen of Monroe (FM), where it becomes difficult to advance the scope across the FM, a flexible scope can be used to do the conventional ETV (Video 3) or the conventional scope be fixed at the FM level and complete the ETV procedure. After securing adequate hemostasis, the scope and cannula are withdrawn. The wound is closed in layers.
| Video 3. https://youtu.be/Fap-ovz1xHk |
Post-operative care
Following extubation, the patient is observed in the ICU for a few hours or a day depending upon the team’s preference. Most of these patients can be discharged on the second day in uncomplicated hydrocephalus. Post-operative check CT or MRI is good to have an assessment of the ventricles. Post-operatively infants are monitored with clinical parameters, head circumference and anterior fontanelles. In older children and adults, clinical parameters are to be monitored. In case of any clinical deterioration, brain imaging is warranted. Follow-up MRI brain after 6–8 weeks gives a better appreciation of post-operative radiological changes.
Outcome
In uncomplicated cases, ETV has success rates ranging between 70 and 90%. The results can be ranged between 30 and 90% depending on the pathology and age group. Proper pre-operative evaluation and case selection using ETVSS can aim for high success rates (14). Most of the failures are seen in the first 1–2 months. A successful ETV beyond 5 years has the least chance of failure rates.
Conclusion
Endoscopic third ventriculostomy (ETV) is a minimal invasive CSF diversion procedure in hydrocephalus.
It can be performed safely in most of the uncomplicated cases. Lower success rates are seen in the infantile age group below 6 months and post-infective or post-haemorrhagic hydrocephalus. Proper case selection and pre-operative evaluation are associated with better long-term results.
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