The development of posterior fossa tumor surgery remains Harvey Cushing’s hallmark contribution to pediatric neurosurgery [1] . He was first to publish a large series of 61 patients with cerebellar medulloblastomas [2] . Before the era of Cushing, posterior fossa tumors were considered as inoperable and only bony decompression used to be offered. Since then, the evolution of surgical technique reflects the maturation of modern neurosurgery. Majority of patients with posterior fossa tumors have hydrocephalus at the time of presentation [3] . The management of hydrocephalus with posterior fossa tumors remains controversial. In recent studies, permanent postoperative cerebrospinal fluid (CSF) diversion was required in 30% - 38.7% of the patients [4] [5] [6] . However, awareness regarding factors that predict the need for CSF diversion following posterior fossa tumor surgery are essential for the surgeons during counseling, surgical planning, postoperative course and radiological monitoring [7] . Such factors include age of the patient, duration of history, location of the tumor, type of the tumor (solid or cystic), severity of hydrocephalus, tumor resection, CSF infection, CSF leak and pseudomeningocele [3] [7] [8] [9] .

The different surgical options are used to treat hydrocephalus. Previously some surgeons used to do separate burr hole routinely at the time of posterior fossa tumor surgery. Currently surgeons prefer CSF diversion through shunts, external ventricular drainage (EVD) or endoscopic third ventriculostomy (ETV). Each of these has its own merits and demerits. Reliability of EVD as a predictor of permanent CSF diversion is debatable. Most of the authors believe that longer the postoperative duration of EVD means permanent CSF diversion [8] [10] . However, we did not find any study in the literature mentioning the preoperative duration of EVD effects shunt dependency. Therefore, we conducted this study to assess the duration of preoperative EVD in posterior fossa tumor surgery as a predictor for permanent CSF diversion.

The study was conducted in the Department of Pediatric Neurosurgery, National Neuroscience Institute, King Fahad Medical City, Riyadh, Saudi Arabia from January 2010 to December 2013. The patients were enrolled retrospectively. The data were collected and were registered on the proforma. All the data were reviewed. Data were generated from the clinical, operative and radiological records. Categorical data were summarized as number and percentage. Continuous data was summarized as mean and standard deviation. Comparison between the groups for categorical variable was done using chi-square test or Fisher’s exact test and for continuous data student-t test or Mann Whitney u was used. Any association with p-value of less than 0.05 was considered as statistically significant. All statistical analysis was performed using SAS version 9.2 (SAS Institute, Inc, Cary, NC).

The patients who had insertion of EVD before the definitive posterior fossa tumor surgery in pediatric age were included. All such patients presented in emergency due to severe hydrocephalus. These patients underwent emergency insertion of EVD after CT scan. Later, magnetic resonance imaging (MRI) of brain and spine were done before undergoing definitive posterior fossa tumor surgery in all patients. Most of the patients required MRI under general anesthesia. After tumor surgery, the patients were considered for challenging of EVD around on 7^th postoperative day. If there were no clinical and radiological signs of hydrocephalus, EVD was removed. Otherwise, insertion of ventriculoperitoneal (VP) shunt was done.

The patients who were managed without EVD or with intraoperative insertion of EVD, who had shunt insertion before posterior fossa tumor surgery and who had surgery for recurrence were excluded from the study.

The time interval between insertion of EVD and definite tumor surgery was considered in dividing the patients in two groups. Group A consists of those patients who had duration of preoperative EVD equal or less than 7 days. Group B includes those patients who had duration of preoperative EVD more than 7 days. Different factors were studied in each group including age and sex of the patient, duration of symptoms, clinical presentation, duration of MRI after admission, location of the tumor, CSF seeding, amount of surgical resection, type of the tumor on histopathology, duration of postoperative EVD, CSF leak, pseudomeningocele, EVD related infection and VP shunt insertion. Data were analyzed and the literature was reviewed.

The preoperative emergency insertion of EVD was done in 38 pediatric patients with posterior fossa tumor (Figure 1). Mean duration of preoperative EVD was 5.44 days in Group A and 13.72 days in Group B. Group A has 16 patients while Group B has 22 patients. In Group B, initially parents of three patients refused surgery and later they agreed. Mean age was 4.5 year in Group A and 5.5 year in Group B. Male to female ratio was 1:0.6 in Group A and 1:0.8 in Group B. The predominant clinical feature was symptoms an d signs of raised intracranial pressure (ICP) only (Figure 2). Those were seen exclusively in 81.25% of patients in Group A and 77.27% of patients in Group B. The most of the patients presented with short duration of symptoms in both groups and had midline tumor (Figure 3). CSF seedings were appreciated in five patients in Group A and four patients in Group B (p value = 0.81). Gross total resection was achieved in 81.25% and 81.82% in Group A and B respectively. Medulloblastoma was the prime histopathologic diagnosis in both groups. It was followed by pilocytic astrocytoma, anaplastic ependymoma, cavernous hemangioma and Ewing’s sarcoma. CSF leak was observed in total of five patients (13.16%). It was seen in three patients in Group A and two patients in Group B (p value = 0.63). Pseudomeningocele was noted in six patients overall. It was found in two patients in Group A and four patients in Group B (p value = 0.63). Postoperatively EVD was kept in for mean of 17.44 days in Group A and 16.59 days in Group B.

Seven patients had EVD related infection (Figure 4). Preoperative EVD re-

lated infection secondary to Klebsiella pneumoniae was seen in one patient in Group B. He did not require shunt. There were three patients in each group who had postoperative EVD related infection with 18.75% in Group A and 13.64% in Group B (p value = 0.64). In Group A, infection was caused by Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa. In Group B, Klebsiella pneumoniae, Staphylococcus epidermidis and Enterobacter aerogenes were cultured from CSF. Once the infection is clear, all patients in Group A with infection and in Group B with Klebsiella pneumoniae and Staphylococcus epidermidis infection required shunt surgery. Overall, infection was seen in 18.4% of the patients. However, six patients who had infection eventually required VP shunt. VP shunt (Figure 5) was required in 31.25% of Group A patients and 18.18% of Group B patients (p value = 0.35). In total, shunt insertion rate was 23.68%. All the patients were followed up closely for six months. Results are shown in Table 1.

The posterior fossa is a limited space in the cranium. The tumors in this region usually present earlier. Posterior fossa tumors are the most common primary neoplasms in children. Such tumors require prompt decision and quick action as the most of the patients have associated hydrocephalus at presentation [3] . Early treatment will eventually affect the morbidity and mortality. However, there is

no consensus on the management of hydrocephalus secondary to posterior fossa tumor [7] . It can be managed before, during and after posterior fossa tumor surgery [11] .

In 1963, Abraham and Chandy managed the hydrocephalus related to posterior fossa tumors with ventriculoatrial (VA) shunts [12] . This method of managing the hydrocephalus became popular. Many neurosurgeons adopted the policy of putting VP or VA shunts before the definitive posterior fossa tumor surgery to have a better operative field. It resulted in 100% of the patients having permanent shunt insertion or dependency [13] . In 1985, the American Society of Pediatric Neurosurgery commissioned a study to find out the best way to manage the dilemma of hydrocephalus secondary to posterior fossa tumors. Robert McLaurin made the conclusion after obtaining the data from different hospitals of North America that there was no clear evidence of having any advantage to do preoperative shunt insertion [14] . It is still a matter of discussion.

Management of hydrocephalus secondary to posterior fossa tumors includes insertion of EVD, ETV, shunt insertion and no treatment at all [11] . Some surgeons in the past preferred to place a separate burr hole routinely during the posterior fossa tumor surgery to drain the ventricles [15] . Ventricular tap was also used in infants with open fontanel [16] . Recently Ommaya reservoir was used as an alternate to EVD, VP shunt and ETV. It is associated with lesser trauma and fewer complications [17] . Relieving the hydrocephalus in the presence of posterior fossa tumor can cause sudden decompression. It may lead to the formation of extradural hematoma [18] . ETV and VP shunt are recommended as permanent treatment for hydrocephalus after posterior fossa tumor surgery [11] .

There are number of factors that can determine the need for CSF diversion after the surgery. All these factors are debatable. Most of the surgeons believe that age at surgery is related to postoperative CSF diversion. Younger the patient means more chance of having permanent CSF diversion after surgery [9] . However; some surgeons observed that mean age at diagnosis and extent of tumor resection do not affect the need for CSF diversion. It was also noted that the patients who presented with duration of symptoms less than 3 months had higher rate of postoperative CSF diversion [7] . It is believed that midline tumors require more shunts than laterally located tumors [7] [9] . Medulloblastoma and ependymoma are more associated with postoperative CSF diversion [3] . Patients with meningitis and pseudomeningocele have higher risk of shunt requirement [7] .

VP shunt is still an option to treat hydrocephalus preoperatively. It can be done in those patients who are in poor neurological state as a result of delayed diagnosis and advanced disease. Papilledema responds well to VP shunt. It significantly reduces the overall morbidity and mortality. It may result in shunt infection and malfunction [8] [19] . However, it can cause upward herniation, tumor hemorrhage and peritoneal seeding. It will be difficult to make a plane between the tumor and adjacent normal brain and brain stem during tumor surgery [19] [20] . Preoperative VP shunt requirement varied from 29% - 43.1% after using different surgical options for the treatment of hydrocephalus depending on the presentation [19] [21] . It also depends on the policy of the center.

The use of preoperative ETV is an effective, feasible and safe procedure [22] . It is helpful in immediate and long term control of hydrocephalus [10] . It eliminates the risk of CSF infection related to EVD and avoids the complications of VP shunt like infection and malfunction. In developing countries where the presentation is late, ETV is recommendable option due to large ventricles [22] . However, ETV cannot always prevent postoperative hydrocephalus in all cases of posterior fossa tumors. The use of postoperative VP shunt is the alternative [10] . VP shunt was required in 6% of the patients after ETV for hydrocephalus related to posterior fossa tumor [20] .

EVD placement is one of the most commonly performed neurosurgical procedures. It is an effective alternate method to insertion of preoperative shunts [23] . It can be inserted preoperatively or intraoperatively. Preoperative EVD insertion is indicated in those patients who present in emergency with symptoms and signs of raised ICP. Care should be taken not to drain CSF quickly. ICP is usually high and is more than 30 cm of water in most of the cases [24] . The goal is to do slow controlled sustained decompression of ICP. It is one of the advantages as compared to the shunt where pressure of the valve is predetermined. One can adjust the level of EVD depending on the ICP. It is a live saving emergency procedure. It controls ICP before, during and after surgery [25] . It allows the drainage of blood and debris from CSF after tumor surgery [19] . Moreover, it provides smooth postoperative course. It decreases the possibility of aseptic meningitis and postoperative shunts [23] . It also prevents CSF leak and helps in wound healing by keeping the surgical wound dry [19] . However, it may result in tumoral hemorrhage and upward herniation [10] . The main issue related to EVD is CSF infection. It can be left safely, as long as needed, provided that meticulous care is taken for EVD insertion and nursing. EVD duration seems to have no effect on incidence of infection [26] . Infection rate of 7% - 10% was noted per procedure [27] . More than five days of drainage seems to raise concern for infection risk, though the weight of evidence shows long term drainage is safe and the routine catheter changes have led to higher not lower infection rates [28] [29] . Tunneling the catheter from insertion site as far as possible is preferred. Prophylactic systemic antibiotic use for the duration of drainage has shown little benefit. Antibiotic-impregnated EVD reduces the chance of catheter related infections [30] . Overall, meticulous technique at the time of insertion, cautious wound care, and aseptic technique during CSF sampling are essential to reduce infection rates. In our study, EVD related CSF infection was seen postoperatively in three patients in both groups. Only one patient had infection preoperatively in group B. None of the patient had infection preoperatively in group A. Overall infection rate was 18.4%. Gopalakrishnan et al. stated that children who underwent intraoperative EVD insertion had shunt rate of 39.6% compared with 16.7% of those who did not have an EVD [7] . The postoperative VP shunt was required in 6.1-19% the patients who had intraoperative EVD [19] [23] [25] . Some advocate that there is no association of EVD with the need of postoperative CSF diversion [21] [24] . While others had concluded that EVD dependence is a reliable predictor for permanent CSF diversion [31] [32] . In one study, 95.2% of the patients had symptomatic hydrocephalus but postoperative VP shunt was required in 29.8% of the patients. These were managed with either intraoperative EVD or without CSF diversion [7] . Most of the surgeons believe that eventually one third of the patients will require postoperative CSF diversion. Rate of VP shunt insertion was 30% - 38.7% in different studies [5] [6] [9] [19] . Schmid inserted EVD 2 - 5 days before definitive posterior fossa tumor surgery. His shunt free rate in children was 83% and infection rate was 4.9%. A shunt was inserted only if the CSF pathways remained obstructed after tumor removal [24] . With this regimen, shunt insertion rate can be lowered down with the risk of infection. We did not find any study in the literature that suggests that duration of preoperative EVD has any effect on postoperative permanent CSF diversion. In our study, not only our patients were symptomatic as they presented with signs and symptoms of raised ICP and they all were in need for emergency EVD insertion to relieve the pressure. Eventually, VP shunt was required in nine patients with 31.25% of the patients in group A and 18.18% of the patients in group B. These numbers may suggest that the longer duration of preoperative EVD can reduce the need for permanent CSF diversion postoperatively. But statistically these numbers have no significance (p value = 0.35). Overall, our shunt free rate was 76.3%.

Still there is no agreement on the management of hydrocephalus due to posterior fossa tumors. It depends on surgeon’s preferences, case to case variations and departmental policies and guidelines. All patients had severe hydrocephalus at presentation in our study. While using single modality for the management of hydrocephalus, permanent shunt insertion rate was comparably low. However, there is no effect of preoperative duration of EVD in determining the requirement of postoperative VP shunt.

We are grateful to Mr. Anhar Ullah from department of cardiac sciences, College of Medicine, King Saud University, Riyadh, Saudi Arabia, for his support and work in analyzing the data.

Ghani, E., AlBanyan, A., Sabbagh, A. and Ahmad, M. (2017) Duration of Preoperative External Ventricular Drain in Pediatric Posterior Fossa Tumors―Does It Matter? Open Journal of Ped- iatrics, 7, 86-97. https://doi.org/10.4236/ojped.2017.72012