**4. Success rate of distinct indications**

30°, 45°, and/or 70° optics to view the anterior and posterior parts of the ventricles if applicable. It can be useful in case of obstruction of the aqueduct or tumor. In the midline between the mammillary bodies and the infundibular recess, the perforation is performed. For fenestration, there are several possibilities. The perforation can be performed by sharp perforation with semisharp probe [54], by blunt perforation with the endoscope itself, the balloon catheter itself [8], by coagulation with monopolar or bipolar diathermy [7, 8, 54], and by laser perforation [54, 55], waterjet dissection [55], ventriculostomy forceps [7], or ultrasonic probe [56]. It is recommended to use a blunt perforation to avoid vascular injury [8, 55]. In case of thick ventricle floor, it is recommended to use cauterization with bipolar diathermy at low energy [7, 8], sharp perforation with semisharp catheter [54], or waterjet dissection [55]. However, laser perforation and monopolar diathermy should be avoided [8]. After the perforation by a rigid instrument, enlarging ventriculostomy is initially performed by a perforation forceps and subsequently by inflation of a Fogarty balloon catheter (4–7 mm). After ventriculostomy, an inspection is performed with the 0° diagnostic optic to identify the dorsum sellae and the tip of the basilar artery to ensure free CSF flow. If a Liliequist membrane or subarachnoid adhesions are present, they also should be perforated (**Figure 8**). While withdrawing the operating sheath, an active bleeding at the foramen of Monro or at the corticotomy should be ruled out. After removal of instruments, a gelatin sponge is inserted in the burr hole and the galea is tightly closed to avoid a subgaleal CSF accumulation and leakage. The skin is sutured with

**Figure 10.** (Left) Landmarks on the MRI scan TRUFI sequence, (L) lateral ventricle, (III.) third ventricle. Infundibular recess (grey arrow), mammillary body (wavy arrow), and interpeduncular and prepontine cistern (dotted arrow).

In case of infants up to 2 years of age, the procedure is performed in the same way; the only

In addition, a flexible endoscope can be used for transaqueductal inspection. Following ETV, the work sheath should be moved posteriorly to achieve a straight approach to the Sylvian aqueduct. If the size of diameter of the aqueduct allows it, the working optic can be withdrawn and

exception is that the head is fixed with bandages running over the forehead [57].

clamp or thread. As standard, no EVD is inserted (**Figure 1**) [7, 9].

(Right) Entry point.

138 Hydrocephalus: Water on the Brain

In case of a successful third ventriculostomy, the symptoms mostly improve soon after surgery. Most of the patients, who suffered from deterioration of consciousness because of obstructive hydrocephalus, show a rapid improvement after the surgery [6]. Of course, it requires an adequate indication and it depends considerably on the underlying pathology [6, 7, 12] (**Table 1**).

Postoperative CT scan is routinely performed; however, the radiological findings alone do not count as an indicator of ETV success. It must be assessed in all cases with the clinical findings [6, 10, 58, 59]. After ETV, the intraventricular pressure does not decrease immediately in certain cases [10]. The ventricle size can increase, decrease, and remain unchanged after ventriculostomy [6]. In most cases, the ventricle size might correlate with the clinical outcome as early as 1 month after the surgery. In successful cases, a significant decrease can be seen, while it is not observable or not significant in ETV failures [58, 60]. Especially, decreasing of the third ventricle size is


**Table 1.** Success rate of ETV in distinct indication cases.

reliable [60]. The ventricle size decreases to smaller size as measured preoperatively but remains still bigger than in healthy patients. It shows presumably that the absorptive mechanisms do not work as well as in healthy patients and the successful ventriculostomy provides a compensated communicating hydrocephalus [61]. The postoperative examination can be supplemented by MRI scan. The presence of CSF flow void, which refers to signal loss in the MRI occurring with CSF, may indicate the success [58]. It is important to emphasize that even without any changes in the ventricle size, the patient can improve clinically as a result of successful ventriculostomy.

choice is ETV. Nevertheless, the success rate in each case depends on the etiology, age, clinical findings, and radiological characteristics [13]. The presence of aqueduct obstruction with free prepontine cistern is associated with significantly better outcome of ETV [66]. Regarding the etiology, the acquired stenosis has a better success result than the congenital form [67]. The clinical manifestation of the congenital form appears earlier than the acquired one, which contributes to the lower success rate. In infants, the success of the procedure seems to depend on the age as well as on the etiology. Under the age of 1 year, ETV also has higher success rate in case of aqueduct stenosis than in case of other etiology, although significantly less than in older children [9, 68]. Regarding age, the success seems to be related not only to the age at the time of the surgery but also to the age at onset of the pathological changes [13]. The different range of success rate derives from the fact that the studies examine mixed population

Presentation of the Success Rate of ETV in Distinct Indication Cases of Hydrocephalus

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141

Obstruction distal to the fourth ventricle is a rare cause of HC, but in any case, ETV might be

The intraventricular, pineal region, infratentorial tumor- and cyst-related obstructive hydrocephalus has a high success rate after third ventriculostomy (56–81%, in cysts over 90%) [6, 7, 9–11, 63]. The best candidates seem to be patients with aqueduct obstruction in case of tectal tumors, pineal region tumors or cysts, and third ventricle tumors [11, 15, 27]. Simultaneously performing tumor mass resection or biopsy is also possible in certain cases. The success of ventriculostomy with simultaneous tumor removal or biopsy is reported [7, 69]. Another option is to perform ventriculostomy before or after the tumor surgery. There are diverging opinions on the timing [14]. The preceding ventriculostomy may reduce the chance for postoperative hydrocephalus in case of posterior fossa tumors [70, 71]. In case of cysts, a cyst resection or a fenestration between the cyst and the ventricle simultaneously may be performed to ETV. The success rate in these cases reaches 56–95% [6, 7, 11, 14, 27, 69]. After tumor removal, the cause of obstruction can be eliminated restoring the normal CSF flow. Therefore, performing ETV routinely is not necessary [32]. In case of posterior fossa tumors, higher success is established if hydrocephalus persists after tumor resection [72]. On the other hand, there are studies where the rate in case of tumors is significantly lower (56%) [6]. The different data can be explained by the fact that many studies do not differentiate between benign space-occupying lesions and progressive tumors; however, there is a significant difference between the two groups regarding the outcome [11]. The success of ETV depends on the localization and the growth pattern of the tumor. A progressive tumor is more likely to close the ventriculostoma earlier than a benign lesion or cysts. The same applies to a lesion in the third ventricle compared to an infratentorial tumor, which has no direct connection to the new CSF flow diversion. Likewise, the duration of the symptoms seems to be an influencing factor [7]. Regarding the surgical technique, it can be performed in a relatively uncomplicated way, but the obscuration of the ventricle anatomy by the tumor

a successful treatment with 72–76% of postoperative success [19, 26, 47].

regarding age and pathology [16] .

**4.2. Far distal obstruction**

**4.3. Tumor and cystic lesions**

might cause difficulties [10, 14].

The overall success rate of ETV is reported at 60–90% [6–12, 62] (**Table 2**). The initial success rate in the early postoperative evaluation is higher than during long-term follow-ups [6, 63]. Different data regarding the success rate can be explained by the different definitions of ETV success and with the fact that lots of studies examined mixed population regarding the age, the underlying pathology, the time course of the follow-up, and the strategy of patient selection [6–8]. Based on the experience and on the data, it is recommended to define the clinical success of third ventriculostomy as needless of re-ETV or shunt placement 3 months after the surgery [6, 63]. However, there is no common agreement regarding the point of time when a ventriculostomy is considered completely functional. In contrast, according to a Canadian experience, the success strictly means "no further CSF diversion procedures" [64].

As many studies have established, the success rate of the procedure depends highly on the underlying pathology and the age of the patients [6, 7]. Furthermore, the outcome is influenced by the indications and the performing neurosurgeon [12]. An ETV Success Score (ETVSS) was developed by Kulkarni et al. to estimate a 6-month outcome taking age and etiology into account. The success score is recommended to be used while selecting the optimal candidate for ETV. Even though ETVSS was initially developed to predict the short-term success, the score likewise correlates with the long-term outcome. The score ranges between 0 and 90, where 0 means extremely poor chance for success and 90 means very good chance for success. Regarding the success rate, the patients might be divided into three groups: high ETVSS-Group ≥80, moderate ETVSS-Group 50–70, and Low ETVSS-Group ≤40. The optimal candidate for ETV seems to be the patient over 10 years of age with obstructive hydrocephalus as aqueduct stenosis or tectal tumor and without infection, cerebral hemorrhage, or previous shunting in case history [5].

#### **4.1. Aqueduct stenosis**

Endoscopic ventriculostomy has the most favorable outcome in case of benign aqueduct stenosis (67–93.5%) [6, 7, 9–11, 14, 63, 65]. This fact supports the assumption that the therapy of


**Table 2.** Overall success rate considering the age groups.

choice is ETV. Nevertheless, the success rate in each case depends on the etiology, age, clinical findings, and radiological characteristics [13]. The presence of aqueduct obstruction with free prepontine cistern is associated with significantly better outcome of ETV [66]. Regarding the etiology, the acquired stenosis has a better success result than the congenital form [67]. The clinical manifestation of the congenital form appears earlier than the acquired one, which contributes to the lower success rate. In infants, the success of the procedure seems to depend on the age as well as on the etiology. Under the age of 1 year, ETV also has higher success rate in case of aqueduct stenosis than in case of other etiology, although significantly less than in older children [9, 68]. Regarding age, the success seems to be related not only to the age at the time of the surgery but also to the age at onset of the pathological changes [13]. The different range of success rate derives from the fact that the studies examine mixed population regarding age and pathology [16] .

#### **4.2. Far distal obstruction**

reliable [60]. The ventricle size decreases to smaller size as measured preoperatively but remains still bigger than in healthy patients. It shows presumably that the absorptive mechanisms do not work as well as in healthy patients and the successful ventriculostomy provides a compensated communicating hydrocephalus [61]. The postoperative examination can be supplemented by MRI scan. The presence of CSF flow void, which refers to signal loss in the MRI occurring with CSF, may indicate the success [58]. It is important to emphasize that even without any changes in the ventricle size, the patient can improve clinically as a result of successful ventriculostomy. The overall success rate of ETV is reported at 60–90% [6–12, 62] (**Table 2**). The initial success rate in the early postoperative evaluation is higher than during long-term follow-ups [6, 63]. Different data regarding the success rate can be explained by the different definitions of ETV success and with the fact that lots of studies examined mixed population regarding the age, the underlying pathology, the time course of the follow-up, and the strategy of patient selection [6–8]. Based on the experience and on the data, it is recommended to define the clinical success of third ventriculostomy as needless of re-ETV or shunt placement 3 months after the surgery [6, 63]. However, there is no common agreement regarding the point of time when a ventriculostomy is considered completely functional. In contrast, according to a Canadian

experience, the success strictly means "no further CSF diversion procedures" [64].

**4.1. Aqueduct stenosis**

140 Hydrocephalus: Water on the Brain

**Age group Overall success** 

**Table 2.** Overall success rate considering the age groups.

**rate (%)**

As many studies have established, the success rate of the procedure depends highly on the underlying pathology and the age of the patients [6, 7]. Furthermore, the outcome is influenced by the indications and the performing neurosurgeon [12]. An ETV Success Score (ETVSS) was developed by Kulkarni et al. to estimate a 6-month outcome taking age and etiology into account. The success score is recommended to be used while selecting the optimal candidate for ETV. Even though ETVSS was initially developed to predict the short-term success, the score likewise correlates with the long-term outcome. The score ranges between 0 and 90, where 0 means extremely poor chance for success and 90 means very good chance for success. Regarding the success rate, the patients might be divided into three groups: high ETVSS-Group ≥80, moderate ETVSS-Group 50–70, and Low ETVSS-Group ≤40. The optimal candidate for ETV seems to be the patient over 10 years of age with obstructive hydrocephalus as aqueduct stenosis or tectal tumor and without infection, cerebral hemorrhage, or previous shunting in case history [5].

Endoscopic ventriculostomy has the most favorable outcome in case of benign aqueduct stenosis (67–93.5%) [6, 7, 9–11, 14, 63, 65]. This fact supports the assumption that the therapy of

Adults 60–90 Vulcu et al. [6], Schroeder et al. [8], Grunert et al. [9],

Children > 2 years 66–71 Vulcu et al. [6], Grunert et al. [9], Baldauf et al. [80], Oertel et al. [81], Beems and Grothenius [82], Etus et al. [83] Children < 2 years 22–67

**References**

Siomin et al. [62]

Hellwig et al. [10], Hopf et al. [11], Sacko et al. [12],

Obstruction distal to the fourth ventricle is a rare cause of HC, but in any case, ETV might be a successful treatment with 72–76% of postoperative success [19, 26, 47].

#### **4.3. Tumor and cystic lesions**

The intraventricular, pineal region, infratentorial tumor- and cyst-related obstructive hydrocephalus has a high success rate after third ventriculostomy (56–81%, in cysts over 90%) [6, 7, 9–11, 63]. The best candidates seem to be patients with aqueduct obstruction in case of tectal tumors, pineal region tumors or cysts, and third ventricle tumors [11, 15, 27]. Simultaneously performing tumor mass resection or biopsy is also possible in certain cases. The success of ventriculostomy with simultaneous tumor removal or biopsy is reported [7, 69]. Another option is to perform ventriculostomy before or after the tumor surgery. There are diverging opinions on the timing [14]. The preceding ventriculostomy may reduce the chance for postoperative hydrocephalus in case of posterior fossa tumors [70, 71]. In case of cysts, a cyst resection or a fenestration between the cyst and the ventricle simultaneously may be performed to ETV. The success rate in these cases reaches 56–95% [6, 7, 11, 14, 27, 69]. After tumor removal, the cause of obstruction can be eliminated restoring the normal CSF flow. Therefore, performing ETV routinely is not necessary [32]. In case of posterior fossa tumors, higher success is established if hydrocephalus persists after tumor resection [72]. On the other hand, there are studies where the rate in case of tumors is significantly lower (56%) [6]. The different data can be explained by the fact that many studies do not differentiate between benign space-occupying lesions and progressive tumors; however, there is a significant difference between the two groups regarding the outcome [11]. The success of ETV depends on the localization and the growth pattern of the tumor. A progressive tumor is more likely to close the ventriculostoma earlier than a benign lesion or cysts. The same applies to a lesion in the third ventricle compared to an infratentorial tumor, which has no direct connection to the new CSF flow diversion. Likewise, the duration of the symptoms seems to be an influencing factor [7]. Regarding the surgical technique, it can be performed in a relatively uncomplicated way, but the obscuration of the ventricle anatomy by the tumor might cause difficulties [10, 14].

### **4.4. Cerebellar infarction**

A cerebellar ischemic stroke might lead to obstruction of CSF pathway through the parenchymal edema. The occlusion can be treated with EVD or ETV depending on the endoscopic experiences of the surgeon. The ideal management is still controversial. An endoscopic ventriculostomy might be recommended if no brainstem compression exists [37]. The overall success of ETV in this case is about 86% [7]. Under certain circumstances, this etiology seems to be ideal for ETV, probably because of the acute onset and the pure obstructive origin [7]. The main indicator for successful ETV seems to be the level of consciousness. In case of no improvement of deteriorated consciousness despite ventriculostomy or in case of brainstem compression, a suboccipital decompression is required [37].

overall has a higher ETV success rate compared with noncommunicating hydrocephalus. In patients with meningomyelocele, the success may be higher if ETV is combined with choroid plexus cauterization [47]. In case of Chiari malformation type I and syringomyelia-related hydrocephalus, a shunt independency with a high rate of causing a high ETV success may achieved

Presentation of the Success Rate of ETV in Distinct Indication Cases of Hydrocephalus

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143

Successful endoscopic ventriculostomy was reported in some giant aneurysm–related obstruction [49, 50]. The most feared complications are related to vascular injury leading to infarction, hemorrhage, or pseudoaneurysm development [49]. Although, as mentioned above, some successful ETV was reported, where the procedure seemed to be a good option for treatment

In case of normal- and low-pressure hydrocephalus and malabsorptive hydrocephalus, the success rate amounts about 65–72% [10, 14, 75]. In patients less than 65 years of age and with communicating hydrocephalus, with only minimal cognitive deficits, where the dominant symptom is gait disturbance, the success rate is comparable with the rate after shunt placement [14].

The success in case of shunt malfunction or infection was observed in similar percentage of 67–80% [14, 76]. An exact indication for ETV in communicating hydrocephalus and shunt malfunction has not been defined yet, but as it can be seen, it may be an alternative in certain cases. As mentioned earlier, patients with shunt malfunction might be treated successfully with ETV in certain cases as well. It is clear that a patient with aqueduct stenosis benefits more from ventriculostomy following shunt malfunction than patients with other etiologies. Consequently, ventriculostomy can be recommended in case of shunt malfunction if an obstruction exits in the CSF pathway. In contrast, patients without obstruction should be treated with shunt revision [77]. Following ventriculostomy, it is recommended to remove the shunt system to avoid

The debate is still open, whether the etiology or the age is the determining factor of ETV success in children. The overall success rate reaches about 66–71% in children [6, 7, 9]. In children under 2 years of age, having the chance for a success is significantly lower (22–67%), and infants under 6 months have the worst chance for restoration of the CSF circulation [6, 7, 9, 78–81]. While trying to predict the success using ETVSS, the age plays an important role [5]. The outcome has been examined in several studies regarding the underlying pathology in children, and the difference was also conspicuous between the various etiology groups [9, 78, 80, 81]. The final results correlate with data in adults. Patients with aqueduct stenosis overall have very favorable outcome [9, 78, 81]. Despite all these data, there are studies where no difference regarding the age [4] or etiology [82] was found. Nevertheless, based on the experiences and studies, the

outcome seems to depend both on the underlying pathology and on the age [78, 83, 84].

[14]. The reduction of the caliber, even a resolution of the syrinx, was observed [13, 14].

of obstructive hydrocephalus, the experiences and reports in these cases are wanting.

**4.8. Obstruction due to giant aneurysm**

**4.9. Success in cases of further indications for ETV**

the intermittent CSF diversion through the shunt [14].

**4.10. Children**

#### **4.5. Hemorrhage-related obstructive hydrocephalus**

The optimal management in case of hemorrhage-related obstructive hydrocephalus is still controversial. The overall success rate is 43–73% [6, 9, 39, 40, 63, 73], which is significantly lower than in other etiologies mentioned above. In this case, a difference was also established regarding the outcome in various age groups. The younger population has a lower success rate than the adult group. Moreover, in combination with infection, the rate is about 23% [40]. Evaluating the success of ETV remains difficult in any case, because of the adverse prognoses and clinical status in case of extensive intraparenchymal or intraventricular hemorrhage [39].

#### **4.6. Infection-related hydrocephalus**

The overall success rate amounts for about 60–64% in case of obstructive hydrocephalus caused by infection [13, 40, 63], even though adults benefit more from the procedure than children [13, 40]. The success of ventriculostomy depends on whether a prepontine scarring exits. In many case, ETV cannot be performed, because of intraventricular, ependymal scarring and anatomical distortion. In contrast, an obstruction, especially of the Sylvian aqueduct in postinfectious hydrocephalus, promises a better outcome [45]. As mentioned above, infection combined with hemorrhage has a lower success rate [40].

In tuberculous meningitis, the exudate is deposited in basal cisterns leading to an obstruction at the level of Sylvian aqueduct, at the outlet of fourth ventricle, or in the subarachnoid space [14]. ETV success amounts for about 60–83% in this case [43, 74]. The difference of the success depends highly on the thickness of the ventricle floor and the presence of the exudate. In acute phase, the tuberculous exudates in ventricle system and subarachnoid space and the inflammation of ependyma may impede the surgery and lead to lower success rate [14].

#### **4.7. Congenital malformation–related hydrocephalus**

Although opinions vary widely about the role of ventriculostomy in congenital CNS malformation–related hydrocephalus, it may be a successful option in certain cases [13, 26, 46, 47]. The overall success rate in case of brain malformation–related hydrocephalus amounts to 21–80% [25, 26, 46, 47]. These various rates may be explained by the fact that most surgeries are performed in infancy, which considerably influences the outcome. Moreover, obstructive hydrocephalus overall has a higher ETV success rate compared with noncommunicating hydrocephalus. In patients with meningomyelocele, the success may be higher if ETV is combined with choroid plexus cauterization [47]. In case of Chiari malformation type I and syringomyelia-related hydrocephalus, a shunt independency with a high rate of causing a high ETV success may achieved [14]. The reduction of the caliber, even a resolution of the syrinx, was observed [13, 14].

#### **4.8. Obstruction due to giant aneurysm**

**4.4. Cerebellar infarction**

142 Hydrocephalus: Water on the Brain

suboccipital decompression is required [37].

**4.6. Infection-related hydrocephalus**

**4.5. Hemorrhage-related obstructive hydrocephalus**

tion combined with hemorrhage has a lower success rate [40].

**4.7. Congenital malformation–related hydrocephalus**

A cerebellar ischemic stroke might lead to obstruction of CSF pathway through the parenchymal edema. The occlusion can be treated with EVD or ETV depending on the endoscopic experiences of the surgeon. The ideal management is still controversial. An endoscopic ventriculostomy might be recommended if no brainstem compression exists [37]. The overall success of ETV in this case is about 86% [7]. Under certain circumstances, this etiology seems to be ideal for ETV, probably because of the acute onset and the pure obstructive origin [7]. The main indicator for successful ETV seems to be the level of consciousness. In case of no improvement of deteriorated consciousness despite ventriculostomy or in case of brainstem compression, a

The optimal management in case of hemorrhage-related obstructive hydrocephalus is still controversial. The overall success rate is 43–73% [6, 9, 39, 40, 63, 73], which is significantly lower than in other etiologies mentioned above. In this case, a difference was also established regarding the outcome in various age groups. The younger population has a lower success rate than the adult group. Moreover, in combination with infection, the rate is about 23% [40]. Evaluating the success of ETV remains difficult in any case, because of the adverse prognoses and clinical status in case of extensive intraparenchymal or intraventricular hemorrhage [39].

The overall success rate amounts for about 60–64% in case of obstructive hydrocephalus caused by infection [13, 40, 63], even though adults benefit more from the procedure than children [13, 40]. The success of ventriculostomy depends on whether a prepontine scarring exits. In many case, ETV cannot be performed, because of intraventricular, ependymal scarring and anatomical distortion. In contrast, an obstruction, especially of the Sylvian aqueduct in postinfectious hydrocephalus, promises a better outcome [45]. As mentioned above, infec-

In tuberculous meningitis, the exudate is deposited in basal cisterns leading to an obstruction at the level of Sylvian aqueduct, at the outlet of fourth ventricle, or in the subarachnoid space [14]. ETV success amounts for about 60–83% in this case [43, 74]. The difference of the success depends highly on the thickness of the ventricle floor and the presence of the exudate. In acute phase, the tuberculous exudates in ventricle system and subarachnoid space and the inflam-

Although opinions vary widely about the role of ventriculostomy in congenital CNS malformation–related hydrocephalus, it may be a successful option in certain cases [13, 26, 46, 47]. The overall success rate in case of brain malformation–related hydrocephalus amounts to 21–80% [25, 26, 46, 47]. These various rates may be explained by the fact that most surgeries are performed in infancy, which considerably influences the outcome. Moreover, obstructive hydrocephalus

mation of ependyma may impede the surgery and lead to lower success rate [14].

Successful endoscopic ventriculostomy was reported in some giant aneurysm–related obstruction [49, 50]. The most feared complications are related to vascular injury leading to infarction, hemorrhage, or pseudoaneurysm development [49]. Although, as mentioned above, some successful ETV was reported, where the procedure seemed to be a good option for treatment of obstructive hydrocephalus, the experiences and reports in these cases are wanting.

### **4.9. Success in cases of further indications for ETV**

In case of normal- and low-pressure hydrocephalus and malabsorptive hydrocephalus, the success rate amounts about 65–72% [10, 14, 75]. In patients less than 65 years of age and with communicating hydrocephalus, with only minimal cognitive deficits, where the dominant symptom is gait disturbance, the success rate is comparable with the rate after shunt placement [14].

The success in case of shunt malfunction or infection was observed in similar percentage of 67–80% [14, 76]. An exact indication for ETV in communicating hydrocephalus and shunt malfunction has not been defined yet, but as it can be seen, it may be an alternative in certain cases.

As mentioned earlier, patients with shunt malfunction might be treated successfully with ETV in certain cases as well. It is clear that a patient with aqueduct stenosis benefits more from ventriculostomy following shunt malfunction than patients with other etiologies. Consequently, ventriculostomy can be recommended in case of shunt malfunction if an obstruction exits in the CSF pathway. In contrast, patients without obstruction should be treated with shunt revision [77]. Following ventriculostomy, it is recommended to remove the shunt system to avoid the intermittent CSF diversion through the shunt [14].

#### **4.10. Children**

The debate is still open, whether the etiology or the age is the determining factor of ETV success in children. The overall success rate reaches about 66–71% in children [6, 7, 9]. In children under 2 years of age, having the chance for a success is significantly lower (22–67%), and infants under 6 months have the worst chance for restoration of the CSF circulation [6, 7, 9, 78–81]. While trying to predict the success using ETVSS, the age plays an important role [5]. The outcome has been examined in several studies regarding the underlying pathology in children, and the difference was also conspicuous between the various etiology groups [9, 78, 80, 81]. The final results correlate with data in adults. Patients with aqueduct stenosis overall have very favorable outcome [9, 78, 81]. Despite all these data, there are studies where no difference regarding the age [4] or etiology [82] was found. Nevertheless, based on the experiences and studies, the outcome seems to depend both on the underlying pathology and on the age [78, 83, 84].
