**3. Indications**

The first ever use of an optical tool to visualize the interior of the human body was performed by Bozzini in 1806 [1]. A hundred years later, Lespinasse used a cystoscope to visualize the ventricles of two hydrocephalic children [2]. In 1918, Dandy performed an endoscopic avulsion of the choroid plexus in five hydrocephalic children (where four died) [3]; he called his instrument a "ventriculoscope." In 1922, he opened the floor of the third ventricle by sacrificing an optic nerve [3, 4]. In 1923, Mixter performed a third ventriculocisternostomy through the anterior fontanelle [5], which is considered the first ever successful ETV. In 1947, McNickle was the first to introduce a percutaneous method of performing the third ventriculostomy that led to decline of the complication rate, thus improving the success rate [6]. Afterward the endoscopic technique progressively developed to reach the current modifications in the ventriculoscope for better, clear, and safe visualization of the intraventricular

There is still a detectable failure rate of all treatment modalities of hydrocephalus. However, ETV represents a convenient and easy mode of management. In the recent studies that evaluated the endoscopic third ventriculostomies performed for the treatment of obstructive hydrocephalus, success rates were found between 50 and 94% [8–11]. The type of hydrocephalus and age of the patient, in addition to the surgical technique, play an important role in the success of the ETV [11]. We will discuss comprehensively the surgical technique, indications, and current challenges regarding the increase of the success rate of

A preoperative MRI is almost always needed prior to surgery. From the frontal coronal burr hole, one reaches first the central part of the lateral ventricle near the frontal horn. The frontal horn is demarcated by the absence of choroid plexus. The lateral wall is formed by the nucleus with subependymal veins; medially is the septum pellucidum with septal veins. The choroid plexus and the foramen of Monro are very important landmarks for the central part of the lateral ventricle. The plexus is situated in the floor of the lateral ventricle, the thalamostriate vein lies laterally, and the septal vein's meeting point is on the medial wall; these three structures form the Y-shaped configuration necessary for orientation. The foramen of Monro is formed anterolaterally by the fornix, posteromedially by the anterior thalamic tubercle (**Figure 1**). On looking backwards with the endoscope, the body of the lateral ventricle back to the region of the trigone, with the body of the caudate laterally underlying the thalamostriate vein and the stria terminalis thalami. Adequate orientation of the morbid anatomy that can occur due to

By entering the foramen of Monro, the floor of the anterior part of the third ventricle is clearly identifiable, with the mammillary bodies and tuber cinereum as the two main structures

Liliequist's membrane is an arachnoid leaflet situated in the basal cisterns and is a very impor-

anatomical structures [7].

96 Hydrocephalus: Water on the Brain

**2. Endoscopic anatomy**

chronic hydrocephalus is needed [12–14].

needed for the anatomical orientation (**Figure 1**) [14].

tant anatomical structure in the postsellar region.

the ETV.

ETV is considered the first management option in adult patients with obstructive hydrocephalus by many neurosurgeons. It is a reliable management option in adults with aqueductal stenosis with a success rate that reach 88% [15]. Stenosis at the aqueduct of Sylvius can be congenital or acquired. In three quarters of cases, the root cause might be unknown [16]. It is not considered as a stable condition as it can be tolerated for years, where stenosis is aggravated by trauma, subarachnoid hemorrhage, viral infection, or gradual accumulation of the CSF proximal to the aqueduct in partial obstruction [16–18]. In a previous study, clinical improvement with identifiable success of the procedure was detected in 86.4% of cases [19], where the success rate was lower in secondary ETV after VP shunt (**Figure 2**). This would be better identified in patients with previous history of multiple VP shunt revisions where the ETV failure is relatively more encountered [19, 20]. ETV is also preferred as the first-line management of hydrocephalus due to obstruction of the aqueduct of Sylvius with pineal tumors or tectal gliomas [21–23].

ETV is less successful in pediatric age groups, with the lowest success rate in children younger than 6 months of age, even in aqueductal stenosis [24, 25].

The application of the ETV has been expanded to patients with hydrocephalus associated with fourth ventricular outlet obstruction, Dandy-Walker malformation [26], Chiari malformation [27–29], communicating hydrocephalus [30], and normal pressure hydrocephalus [31, 32].

widening, with subsequent opening of the liliquist membrane, is important for a direct visualization of a naked basilar artery (BA) [25]. A delicate surgical technique is required with experienced hands during the opening of the floor of the third ventricle till the BA is clearly

Endoscopic Third Ventriculostomy, Indications and Challenges

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The ETV Success Score (ETVSS) has been developed and validated to predict ETV success based on certain variables [34, 35]. It depends on predicting the success according to the age of the patient, cause of hydrocephalus, and presence of the previous shunt operation. The success rate can be predicted according to these variables. However, intraoperative factors "like the presence of excessive adhesions, mobility of the stoma, excessive bleeding, and opening of Liliequist's membrane" (**Figure 3**) should be taken into consideration in predicting the success of ETV [36]. In addition, the VP shunt independence is considered a generalized but competent method to measure the success of ETV after VP shunt failure

The change of the ventricular size with a deterioration of the clinical condition has been well known as one of the signs that identify hydrocephalus. In addition, the decrease of the ventricular size after management which accompanied improvement of the general condition has its additional value of success confirmation (**Figure 2**). However, the change of the ventricular size is not well supported as an accurate measurement of the effective treatment of hydrocephalus, especially when it is irrelevant to the clinical condition of the

Specific intraoperative factors are considered significant in addition to the associated morbidity. This would include the duration of surgery, type(s) of endoscope used, and degree of

**Figure 3.** Another patient during ETV where thick arachnoid membranes (arrow) surrounding the basilar artery (b)

visualized to avoid major vascular injury [33].

**5.1. Clinical evaluation and radiological evaluation**

**5. Outcome**

[37, 38].

patient [39].

intraoperative bleeding [33, 36].

denoting possibility of ETV failure.

**Figure 2.** CT of the brain of a previously shunted 12-year-old male with aqueductal stenosis that had signs of increased tension and VP shunt failure; the CT shows enlarged ventricles (A) where ETV was performed without removing the shunt. Follow-up CT of the brain 3 months afterward showed decline in the ventricular size (B) which was accompanied by clinical improvement of the patient.

However, in exclusion to adult-type obstructive hydrocephalus, there is still a lack of strong evidence that supports the procedure.
