Description of the condition

A specialised fluid system circulates around the central nervous system, providing structural and nutritional support for the brain and spinal cord. The fluid is a modified filtrate of the blood called cerebrospinal fluid (CSF), and is produced by groups of ependymal cells, found in the brain and spinal cord, and concentrated in the four choroid plexuses situated in the cerebral ventricles (four normal cavities) of the brain (Champney 2016; Wolburg 2010). The total CSF volume at any time is approximately 150 mL, of which 125 mL is produced inside the brain. The rate of production is 0.35 mL to 0.40 mL per minute. CSF flows from the lateral ventricles to the third ventricle and then through the aqueduct to the fourth ventricle. After that, it leaves the ventricular system through three foramina: two laterally placed (foramina of Luschka) and one medially placed (foramen of Magendie) to circulate in the subarachnoid space (which is a layer of connective tissue between dura matter and the brain surface) and, finally, it is absorbed into the venous system, through the arachnoid villi (an absorption system in the layer covering the brain) (Mancall 2011).

Hydrocephalus, known colloquially as 'water on the brain' or 'dropsy on the brain', is a common neurological disorder, caused by a progressive accumulation of CSF within the intracranial space that can lead to increased intracranial pressure, enlargement of the ventricles (ventriculomegaly) and, consequently, to brain damage. It results from problems with CSF production, circulation or reabsorption. The incidence of hydrocephalus in the USA lies between one and 32 cases per 10,000 births, depending on the definition used and the population studied (Jeng 2011; Kahle 2015). The most recent estimate of incidence comes from a large, population‐based study of idiopathic (unknown cause) infantile hydrocephalus in Denmark over a 30‐year period, which documented 1.1 cases per 1000 births (Munch 2012; Tully 2014).

Hydrocephalus can be classified into communicating and non‐communicating types on the basis of its pathophysiology. The non‐communicating type, also called obstructive hydrocephalus, can appear in the early foetal stage as part of certain congenital malformations (such as aqueductal stenosis, Chiari malformation), or associated with a broad spectrum of brain malformations, which prevent the normal flow of CSF around the brain, and its subsequent reabsorption. Hydrocephalus may also occur secondary to an obstruction of the CSF circulation caused by a tumour located in the fluid‐producing cavities of the brain (ventriculi). By comparison, communicating hydrocephalus results from a deficit in CSF reabsorption, for example, in post‐meningitis hydrocephalus. Haemorrhage in preterm infants can cause hydrocephalus by two mechanisms: acute obstruction by a blood clot or a delayed reabsorption caused by thickening of arachnoids, the inner layer of the meninges (Petre 2010). Although infrequent, hydrocephalus can also be associated with an overproduction of CSF, as in the case of a choroid plexus papilloma, which is a type of benign intraventricular tumour.

Normal Pressure Hydrocephalus (NPH) is a condition first reported in adults that refers to a chronic symptomatic hydrocephalus with a normal CSF pressure (i.e. less than 18 mmHg) (Adams 1965). The condition is defined by a clinical triad of symptoms: dementia, gait difficulties, and urinary urge incontinence in the presence of ventriculomegaly documented by computed tomography (CT) or magnetic resonance imaging (MRI) (Ziebell 2013; Halperin 2015). There are signs in the magnetic resonance images that differentiate NPH from other types of hydrocephalus, specifically, the amount of interstitial oedema surrounding the lateral ventricles (which should be minimal or absent), and the presence of brain deep white matter ischaemia (inadequate blood flow) also known as small vessel ischaemia or leukoaraiosis (Bradley 2015). In order to avoid overlap with other Cochrane Reviews, this review did not include people with NPH (Esmonde 2002; Tudor 2015; Ziebell 2013).

Signs and symptoms of hydrocephalus depend on the cause of the condition and time of presentation. In congenital hydrocephalus, patients present at birth with macrocephaly (overly large head), scalp vein distension, a bulging fontanelle and diastasis of sutures (stretching of fibrous joints between bones in the skull). These can be correctly evaluated using reference tables developed by measuring the circumference of the head of many children at different ages that are considered to establish the normal parameters of head growth. Using this simple tool, rapid head growth as a result of hydrocephalus can be detected clinically (O'Neill 1961). Patients with hydrocephalus may also present with Parinaud´s phenomenon, which is an inability to raise the eyes upwards, also known as 'Sunset Sign', caused by an increased pressure on the tectal plate, which is the area of the midbrain where the oculomotor nerve originates. Symptoms in patients with acquired hydrocephalus (obstructive, post‐infectious, or post‐haemorrhagic) constitute the intracranial hypertension syndrome which includes headache, vomiting and drowsiness (Petre 2010). The appearance of these signs and symptoms of intracranial hypertension is what differentiates developing hydrocephalus from benign ventriculomegaly (dilation of the lateral ventricles in the brain without causing an increase in the CSF pressure and, therefore, without risk of brain damage).

In addition to physical examination and assessment of symptoms, confirmation of diagnosis occurs by means of imaging studies that show enlargement of ventricles. For newborns and infants, ultrasonography is frequently used because it can be done at the bedside and is radiation‐free. Nevertheless, it is an operator‐dependent technology and does not assess the posterior fossa (intracranial space occupied by the cerebellum and brain stem), which sometimes makes it difficult to establish the cause of the hydrocephalus. For older children and adults, CT or MRI of the brain is usually used (Carey 1994).

Since Hippocrates in the fifth century BC, a poor understanding of the pathophysiology of hydrocephalus contributed to the failure of the early, and occasional attempts at therapy (Whytt 1768). In 1908, Payr introduced the first ventriculo‐venous shunt for drainage, which consisted of a vein graft that led from the ventricles directly into the sagittal sinus (a vein that surrounds the top of the brain from front to back) and jugular veins (Mccullough 1990). In the same year, Kaush used a rubber conduit to drain the lateral ventricle into the peritoneal cavity (Kausch 1908), but the medical community received this innovation with little enthusiasm. Research for more effective treatments followed, and eventually the placement of intracranial shunts was tested. Efforts to drain the excess CSF into other body cavities have also been considered; for example, Matson and colleagues at Boston Children´s Hospital first reported a ureteral diversionary procedure (Matson 1949).

The early twentieth century was a period in which knowledge of hydrocephalus, its diagnosis, and strategies for treatment evolved. Between January 1938 and December 1957, an observational, case‐series study, documented the progress of 182 patients with congenital or acquired (early after birth, due to trauma or infection) hydrocephalus, who were not operated on. By the end of the study, only 81 patients were alive, and these had spontaneously arrested hydrocephalus, that is, a gradual slowing of the rate of head growth with a reduction in fontanelle tension and improvement in the patient's general condition. Patients with comorbidities, such as myelomeningocele or Chiari malformation, had the worst prognosis (Laurence 1962). Since the introduction of an effective therapy for the symptoms of hydrocephalus in 1956, when the first shunt system became available, mortality rates have fallen from around 45% to 53% ‐ depending on the case series concerned ‐ to 15% (Hagberg 1962; Jansen 1985; Laurence 1967; Yashon 1963). Morbidity rates have also significantly improved, with up to 42% of treated hydrocephalus patients enjoying a normal lifestyle after receiving shunts (Hirsch 1994).

The breakthrough that launched the modern era of surgical treatment for hydrocephalus was the introduction of valve‐regulated shunts and biocompatible synthetic materials in 1952 (Lifshutz 2001). That same year, Nulsen, Spitz and Holter, reported the successful use of a ventriculo‐jugular shunt regulated by a spring and ball valve (Drake 1995), and almost simultaneously, Pudenz and colleagues, created a silicone one‐way slit valve (Pudenz 1957). The development of the valve system and the availability of new biocompatible materials made it possible to divert CSF safely and reliably, and to avoid the many complications associated with unregulated CSF drainage.

Despite this degree of innovation, these devices were not exempt from shunt failure, which represents a serious complication. The most common causes of shunt malfunction include over‐ and under‐drainage, mechanical mismatch (Inadequate selection of the pressure in a programmable valve or inadequate selection of the valve in relation to the type of hydrocephalus), occlusion (blocking) of the shunt and valve failure. These problems are largely resolved by replacing the valve or parts of the shunt, and sometimes by finding alternative drainage locations (for example, using the circulatory system or the pleural cavity in patients in whom the peritoneal cavity can not be used because of peritoneal inflammatory diseases or surgical sequelae) as well as with innovations in valve designs (Stein 2008).

Although implant of ventriculo‐peritoneal shunts is the standard treatment for patients with hydrocephalus, in the 1990s, an additional method to treat hydrocephalus without the use of a prosthetic device became available. Endoscopic third ventriculostomy (ETV) is a minimally invasive procedure originally introduced by Dandy in 1922. During the procedure, a neuroendoscope is introduced, through a burr hole, into the lateral cerebral ventricles and a hole is made within the third ventricle to enable intracerebral ventricles to communicate with the subarachnoid spaces. This procedure leads to a more physiological circulation of CSF and is a well established treatment for non‐communicating hydrocephalus in some neurosurgical units (Schroeder 1999). Risk of harms related to treatment is always present, depending on the procedure. Shunts may have complications related to placement, such as brain haemorrhages, brain damage, infections, coma, and even exceptionally, death (Smith 2004). In addition, there is an important and permanent risk of shunt malfunction. On the other hand, ETV may also carry serious complications including vascular injuries, hypothalamic injury (brain damage), and occasional death, as has been reported (Drake 2006; Hader 2002). Due to the lack of clinical trials comparing both strategies, the decision about whether to use ETV or ventriculo‐peritoneal shunts remains a topic of considerable debate (Cheng 2015; Limbrick 2014,Texakalidis 2019).

Description of the intervention

This review focused on the placement of various types of ventriculo‐peritoneal shunts for the treatment of hydrocephalus. We define a ventriculo‐peritoneal shunt as a system composed of a ventricular catheter, which is usually inserted into one of the cerebral lateral ventricles and is attached to both a valve and a distal catheter (at the other end of the system), which is implanted within the peritoneal cavity (abdomen) where CSF is finally reabsorbed (ICD‐9‐CM 2004; Patwardhan 2005).

Ventriculo‐peritoneal shunting is a complex surgical intervention. This procedure is usually performed by an experienced neurosurgeon, in the sterile conditions of an operating theatre, and with the use of general anaesthesia. In the most commonly used surgical technique, the patient lies on the operating table in the supine position (lying on his back) with his head turned to one side. Using sterile instruments, the surgeon makes two incisions. One is made on the scalp in order to expose the posterior parietal part of the skull (above and behind the ear), followed by a burr hole through the skull and a small opening in the dura (membrane that covers the brain), to access the dilated lateral ventricle with a catheter. The second incision is made in the skin of the abdomen; from there a tunnel is formed under the skin towards the skull incision, and through this tunnel the distal catheter is passed. This catheter is subsequently connected to the valve part of the shunt. The ventricular catheter is also connected to the valve, which, in turn, is fixed to the periosteum (connective tissue around the skull). Finally, the distal end of the abdominal catheter is placed into the peritoneal cavity, into which the CSF is drained (Warf 2005).

Valves are the most important part of the system, and there are a variety of valve systems available that offer fixed pressures, anti‐siphon devices, and programmable and self‐adjusting CSF flow‐regulating capabilities (Ames 1967; Kaiser 1992; Lumenta 1990; Ojemann 1968).

Fixed differential pressure (DP) valves are considered to be the first generation of valves. When pressure builds up inside the tubing, a slit is forced to open and CSF is allowed to flow outwards. Only unidirectional flow is permitted since an increase in external pressure closes the slit. The opening pressure is determined by the thickness of tubing walls. They are commonly classified according to the opening and closure pressures: low pressure (20 mm H₂O to 40 mm H₂O), medium pressure (40 mm H₂O to 70 mm H₂O) and high pressure valves (80 mm H₂O to 100 mm H₂O) (Post 1985)

Second‐generation valves include DP valves with flow‐regulating devices, valves with anti‐siphon mechanisms and programmable DP valves. Flow‐regulating devices limit CSF flow through the valve by progressively narrowing its orifice in response to increasing intracranial pressure (ICP), as a pressure sensitive ring moves along a variable‐diameter rod. Its aim is to prevent both postural and vasogenic (mediated by blood vessels) over‐drainage occurring during rapid eye movement (REM) sleep, physical exertion, coughing, and other physiological conditions (Hanlo 2003).

Through an increase in flow resistance, anti‐siphon devices counteract the effect of hydrostatic negative pressure when the patient stands in a vertical position. The aim of this system is to provide performance characteristics that simulate those of normal CSF absorption, while allowing the regulation of ICP in a fashion similar to that seen in healthy individuals when they change their head position from horizontal to vertical (Baird 2014; Watson 1994).

Programmable variable pressure valves allow the selection of different opening pressures (between 30 mm H₂O and 200 mm H₂O in intervals of 10 mm H₂O). The opening pressure can be selected through a percutaneous noninvasive magnetic programmer that manages valve pressure according to the patient's clinical and radiological evolution in terms of ventricular size. This permits avoidance of over‐drainage and its consequences, which include slit (shaped) ventricles (accompanied by headaches) and retardation of cranial vault growth (secondary craniosynostosis) (Baird 2014; Miyake 2016; Xu 2013).

Finally, third‐generation valves include DP programmable and anti‐siphon or gravitational systems combined in the same device. The DP unit allows the selection of an opening pressure between 0 to 20 cm H₂O, with the possibility of a transcutaneous adjustment. Unlike anti‐siphon systems, which use a fixed pressure, the gravitational unit can be set to opening pressures of 15 cm H₂O, 20 cm H₂O, 25 cm H₂O, or 30 cm H₂O, which cannot be changed after placement. This kind of device increases the opening pressure of the shunt by blocking the inlet flow using a gravity‐assisted ball bearing. These devices must be placed vertically in order to counteract the siphoning effect of negative hydrostatic pressures when the patient is standing (Rohde 2009).

How the intervention might work

The balance in production, circulation, and reabsorption of the CSF has a key role in the Monro‐Kelly hypothesis (Champney 2016; Lee 2009). This states that a stable ICP is the result of a rigid sphere (cranium) occupied by a non‐compressible volume of brain tissue, blood and cerebrospinal fluid, which must remain constant. Although physiological fluctuations can occur, these are related to reciprocal changes in the amount of blood and CSF at a given time (Han 2005). ICP varies during the day; normal values are between 7 mmHg to 15 mmHg in a supine adult. Fluctuations are regulated primarily by cranial venous system blood volumes (CVSBV). As a result of gravity, CVSBV diminish when a person is upright. A drop in blood volume causes a retraction in brain tissues away from the normal CSF filled ventricles, causing a drop in ICP. Production of CSF also fluctuates during the day, but, as there is a balance between production and reabsorption, the ventricular size remains stable. There are also variations in CSF flow rate at night, with periods of highest flow rate occurring during REM sleep (Watson 1994).

Normally, CSF is produced, circulates, and is reabsorbed within the craniospinal space. Changes in body position between the horizontal and vertical entail transfer of the CSF and blood from the cranial compartment to the spinal compartment in a balanced fashion. When a ventriculo‐peritoneal shunt is in place in a person with hydrocephalus, this balance is broken and hydrostatic pressure plays an important role (Kurtom 2007). Valves provide a resistance mechanism within the shunt system, which serves to control ICP more than CSF flow in patients with hydrocephalus (Miyake 2016).

In the developmental stage, shunt systems were synonymous with CSF diversion to provide a rapid decrease in ICP, with very little attention given to the cause of hydrocephalus. This approach produced good early results in terms of resolution of ventricle enlargement and reduction of ICP, but complications related to over‐drainage such as subdural haematomas (a type of blood clot that forms surrounding the brain) shunt failures due to catheter obstruction, multiple shunt revisions and infections did appear (Symss 2015).

Valve technology has evolved to demonstrate a more adequate understanding of the physiological balance that needs to be achieved in the production, circulation and reabsorption of CSF. As a result, modern valves decrease ICP, as well as reducing brain damage and shunt‐related complications. Since the first fixed‐pressure shunts, like those of Holter and Pudenz (Drake 1995; Pudenz 1957), shunt systems, and especially valves, have evolved to incorporate flow‐regulating, anti‐siphon and gravitational components that are designed to avoid the over‐drainage that can be caused by changes in patient position (Czosnyka 1998).

Why it is important to do this review

Hydrocephalus is a common chronic neurological disease that places a significant burden both on individuals and society as a whole.The cost of its medical treatment is not completely understood, but appears to be increasing (Pikus 1997). The National Inpatient Sample (NIS) database, a nation‐wide survey in USA healthcare facilities, identified that in 2000 the three most common causes of admission for hydrocephalus were: shunt malfunction (40.7%), non‐communicating hydrocephalus (16.6%), and communicating hydrocephalus (13.2%). The most common procedures that resulted from these hospitalisations were the placement of a shunt (43.4%) and shunt replacement (42.8%). The total costs of shunt‐related procedures were estimated to be approximately one billion USD (Patwardhan 2005).

Additionaly, a longitudinal study between 1997 and 2003 found an increasing proportion of older children were admitted with shunt malfunctions, and, when hydrocephalus treatment and its complications were compared with other chronic illness, such as cystic fibrosis, the inpatient utilisation (admissions, length of stay and hospital charges) were higher for hydrocephalus (Shannon 2011).

In low‐ and middle‐income countries, the treatment of hydrocephalus may encounter additional challenges due to the economic constraints that patients and families face to afford the costs of acquisition, transportation and access to proper care (Warf 2005).

Although ventriculo‐peritoneal shunting has been the most widely used treatment for hydrocephalus in the twentieth century, it is unclear whether the outcomes of shunting have improved significantly over time, despite improvements in the understanding of CSF physiology and the technological advancements in valve design. The Hydrocephalus Clinical Research Network concluded that in comparison with patients treated in the 1990s, there has been a reduction in the risk of complications ‐ assessed as the time to first shunt failure ‐ by about 18% (Kulkarni 2013). However, the reasons for this improvement are not obvious, and thus, open to interpretation.

Despite this, long‐term health and quality of life (QoL) outcomes after shunt implant have been highly variable, and range from patients leading a near normal life to those with physical, cognitive, social and emotional impairments associated with disability. These outcomes rely not only on the cause of hydrocephalus, but also on treatment‐related complications such as infections, haemorrhages leading to brain haematomas, brain injury due to Inadequate positioning of the catheter, coma, and occasionally, death (Smith 2004). They may appear shortly after surgery, and generally within six months of shunt implantation or revision (Kulkarni 2007; Peters 2014; Sciubba 2007).

The main goal of physicians, researchers and engineers when developing a new valve technology is to improve clinical outcomes ‐ both physical and mental ‐ as well as reducing the likelihood of shunt failure. A Cochrane systematic review published in 2013, evaluated the effectiveness of flow‐regulated versus differential pressure‐regulated shunt valves for adults with normal pressure hydrocephalus (Ziebell 2013), but it was limited to two types of valves in a specific group of participants. These reasons, and the fast pace of technological progress, prompt the need for a high‐quality synthesis of the evidence for the effectiveness and safety of common, fixed‐pressure and other more complex ventriculo‐peritoneal shunt devices for people with hydrocephalus with different causes.