Iatrogenic Complications of CSF Shunting

Fig. 5.1

(a) MRI showing benign external hydrocephalus in a 6-month-old boy. (b) Spontaneous resolution of the pericerebral collection and ventriculomegaly at age 3 years

5.2.8.2 Posttraumatic and Postinfectious Subdural Collections

Posttraumatic and postinfectious collections of fluid, with bloody or xanthochromic fluid (subdural effusions), may produce brain compression. They also evolve with macrocephaly and are accompanied by neurological symptoms and require surgical treatment as subdural taps, burr-hole drainage, temporary external derivation, or they may even necessitate a subduroperitoneal shunt. On MRI, the fluid appears more intense than normal CSF. The most often used treatment is subduroperitoneal shunting.

5.2.8.3 Initial Stages of Communicating Hydrocephalus

Initial communicating hydrocephalus may show up with dilatation of the subarachnoid spaces, the cerebral fissures and cisterns, and with slightly enlarged ventricles [55, 16]. In this context, serial neuroimaging studies, preferably MRI, are mandatory to not delay surgery of true hydrocephalus. Diagnostic methods for differentiating subdural hygroma from communicating hydrocephalus include neuroimaging studies and also measurements of the subdural pressure with a manometer during trephine drainage [55].

5.2.8.4 Brain Atrophy

Similarly, dilated arachnoid spaces at the convexities, cerebral fissures, and cisterns do occur in conditions associated with brain atrophy. Logically, shunting these ex vacuo fluid spaces triggers a number of iatrogenic complications and does not afford any clinical benefit.

5.2.8.5 Leptomeningeal Seeding of Tumors

Exceptionally, external hydrocephalus may result from occult leptomeningeal seeding of a benign or malignant brain tumor [134]. In this case, subdural postcontrast enhancement will reveal the true nature of the condition.

5.2.8.6 Arachnoid Cysts

Correct management of intracranial arachnoid cysts represents a difficult issue due to the lack of guidelines and to the many possible surgical options. Certain complications related to the treatment of intracranial arachnoid cysts are of iatrogenic nature and are due to overzealous surgical management based on wrong indications. Some arachnoid cysts merely represent a form of localized hydrocephalus associated with a certain degree of focal atrophy.

Indications for arachnoid cyst shunting must be established on clinical criteria as most diagnostic methods are unable to discriminate which cysts benefit from surgery [83]. Arachnoid pouches may produce clinical symptoms depending on the patient’s age, cyst size, focal cerebral compression, and brain shifts apart from symptoms of raised ICP. An arachnoid cyst discovered on neuroimaging studies in an otherwise asymptomatic patient needs only periodic observation [83]. Options for arachnoid cyst treatment include endoscopic fenestration, cyst excision or fenestration by craniotomy, and cyst shunting. Until recently, the preferred method of treatment was cystoperitoneal shunting, a procedure that is fraught with a multitude of complications as happens with VP shunts. Current trends favor the use of neuroendoscopic or open surgical fenestration for obviating shunt-related complications. In a recent paper from our institution we insisted on two facts [84]. First, many arachnoid cysts merely constitute incidental discoveries and need only clinical observation. Second, undue shunt placement usually leads to iatrogenic overdrainage manifestations such as orthostatic headaches in the short term, and to more serious complications such as shunt dependency, slit- ventricle syndrome, pseudotumor syndrome, posterior fossa overcrowding, or even to tonsillar herniation (acquired Chiari malformation) in the long term [7, 17, 50, 76, 83].

5.3 Iatrogenesis in Diagnostic Procedures

5.3.1 Reservoir Pumping

The neurosurgeon often assesses shunt patency by pumping the valve reservoir. This method is of limited utility but it can give an estimate of valve functioning in the appropriate clinical setting [106]. A reservoir that does not refill after a few flushing maneuvers probably indicates ventricular catheter block, but a slow replenishment of the flushing device may also indicate low ICP, partial catheter block, or ventricular collapse. The diagnosis of shunt block is more dependable if the reservoir remains umbilicated. On the contrary, a reservoir that is felt hard upon pumping represents valve or distal catheter block. Parents should be discouraged from pumping the valve as repeated flushing of the reservoir may precipitate an iatrogenic shunt block [13].

5.3.2 Shunt Tap

Puncture of the valve reservoir is also performed to test shunt function and to obtain CSF for biochemical and bacteriological examination [91, 96, 117, 129]. The technique includes meticulous skin preparation and disinfection and the use of a thin 23G or 25G needle (often a butterfly system) that can be connected to a manometer [96]. In normal conditions, the recorded pressure must be equal or slightly higher than the opening pressure of the valve and fluid must drip spontaneously. Slight aspiration with a small syringe can be applied if there is scanty spontaneous CSF flow. When no fluid comes out with these maneuvers, there likely exists a proximal obstruction. A higher recorded pressure than that of the opening pressure of the valve indicates distal obstruction. Equivocal readings may occur in the presence of a shunt block later demonstrated at surgery [150]. The technique is quite safe but it may cause several iatrogenic complications: (a) shunt infection; (b) breakage of the reservoir; and (c) superficial or cerebral hemorrhage when aspiration is applied [91].

5.3.3 ICP Measurement

Several methods are usually employed to assess ICP before first shunt implantation and also for evaluation of presumed shunt failure [35, 49, 122, 155]. Lumbar puncture manometry has significant inaccuracies. Continuous pressure recording via the valve reservoir is difficult to be maintained for a significant time and is almost impossible to perform in small children due to poor collaboration. Transfontanelar ICP recording represents a safe noninvasive method that provides useful information on ICP in patients with doubtful signs of progressive hydrocephalus or of shunt malfunction [49]. Intraventricular pressure recording has long been considered as the gold standard for ICP measurements but its use is limited due to: (a) the possibility of infection, (b) limited length of utilization, and (c) the difficulties for cannulating a compressed ventricle.

Subdural monitoring is another method for ICP recording but has not gained widespread acceptance. Epidural sensors give less exact readings than those of intraventricular devices and present measurement drifts over time. However, in daily practice, epidural monitoring represents a good method for ICP recording. Epidural sensors can be kept in place for a prolonged period and possess less risks due to the barrier that the dura mater offers against infection. The most frequently used monitoring systems at present are the intraparenchymal sensors. Their use in hydrocephalus has two main indications: hydrocephalus of chronic evolution and suspicion of gradual shunt failure. This method constitutes a minimally invasive procedure, although it may be fraught by brain damage, hemorrhage, or infection [155].

5.3.4 Iatrogenesis Related to Neuroimaging Studies

Three main aspects of neuroimaging studies deserve consideration: (a) the risk of misinterpretation of the tests [48, 59]; (b) the dangers associated with the repeated use of ionizing radiation, especially in children; and (c) the diagnostic yield of the study. At present, physicians other than neurosurgeons are often called on to evaluate complex cases of suspected shunt malfunction and they rely on neuroimaging reports that do not mention or diagnose shunt malfunction [59]. Of reported methods currently utilized for checking shunt function, ultrasonography doubtless constitutes the most innocuous one. US studies are dependable, cheap, noninvasive, can be repeated as needed, can be performed at the bedside and require no sedation. Drawbacks of US include the lack of definition of the convexities and the posterior fossa, and its impracticability in children with a closed skull.

The so-called shunt series are often performed as a routine procedure at emergency departments in suspected shunt failure. X-ray studies are necessary for assessment of shunt integrity, for example, when breakage or disconnection is suspected and for depicting the catheter position. Generally speaking, the diagnostic yield of the shunt series is low [31, 143]. Shunt tube integrity in children and thin individuals can also be explored by simple palpation of the subcutaneous trajectory of the shunt from its cranial to its abdominal ends. As many shunted patients (“difficult shunt patients”) repeatedly attend the emergency services, shunt series should be performed only when this study is strictly necessary and never for defensive medicine [31, 143, 141].

CT and MRI are more dependable than shunt series in the evaluation of shunt malfunction (Fig. 5.2) [71]. CT head scan constitutes the gold standard for emergency assessment of shunt malfunction. CT scans are also requested very often, accounting for a cumulative exposure to ionizing radiation. CT scanning usually takes a short time; in most cases it does not require sedation or general anesthesia; and CT machines are usually available 24 h a day. In addition, some radiology departments use a rapid-sequence, low-dose CT scanning technique that does not reduce image quality [93, 141]. Plain radiographs and CT scanning have low sensitivity for identifying shunt failure, indicating that neurosurgical consultation should be sought in cases of suspected shunt failure [59, 85].

Fig. 5.2

MR (a) and serial CT (b, c) scans depicting the development of subdural hygroma in a 52-year-old female patient having undergone ventriculoperitoneal shunting due to hydrocephalus (Courtesy of Recep Brohi MD, Ankara, Turkey)

The best method for imaging the cerebral ventricles is MRI, but this technique is not always accessible in many hospitals during the whole day, and it requires sedation or even anesthesia in children and in uncooperative patients. Data acquisition involves a longer time, which makes it impractical in the emergency setting. A rapid-sequence MRI protocol for evaluation of hydrocephalus in children has also been developed [8].

To determine shunt patency, a shuntogram can be obtained by injecting a contrast medium (or an isotope) in the valve reservoir obtaining skull and abdominal images. Isotopic shuntogram is now rarely used with the same indication and is of no use in emergent situations.

5.3.5 Miscellaneous Tests

Biomarkers of infection such as C-reactive protein and routine blood analyses are of utmost value for the diagnosis of shunt infection, although the most reliable test in suspected infection is culture of CSF obtained from the valve reservoir. Several other tests are also utilized for establishing the diagnosis, for indicating surgical treatment, and for assessing shunt function, for example, EEG, evoked potentials, and so on. Most of them are noninvasive and lack significant complications, but they are impractical in the acute setting although useful in the evaluation of chronic failure.

5.4 Technical Problems

Many technical problems related to shunt treatment derive from the lack of established criteria for selecting the most appropriate treatment as are (a) choosing between ETV or shunting, (b) deciding the technique for shunt insertion, and (c) choosing the type of valve. If iatrogenic complications are to be avoided, the philosophy underlying shunt insertion must no more be considered as a sophisticated “plumbing work.” Cerebral pulsatility, bulk CSF volume flow, and hydrodynamic properties of the whole craniospinal axis have also to be taken into account in the design and performance of novel devices and in the search of new biomaterials. Table 5.1 summarizes the steps for shunt surgery.

Table 5.1

Steps for shunt surgery

Summary of steps for shunt surgery
1	Surgery is necessary
2	Better treatment not indicated
3	Shunt placement is not contraindicated
4	General and skin conditions are adequate
5	Choose the type of surgery/ shunting
6	Careful planning
7	Meticulous surgical technique

5.4.1 Preparations for Surgery

In this section, a standard VP shunt insertion is described (especially as performed in our institution). The shunt we currently use consists of: (a) ventricular catheter, (b) a burr-hole-type reservoir, and (c) a programmable (Sophysa-Polaris®) valve with a unitized peritoneal catheter. Table 5.2 gives an account of common iatrogenic failures in VP shunting.

Table 5.2

Common iatrogenic causes of VP shunt failures

Part of shunt insertion	Complication/cause
Ventricular catheter	Wrong length
	Malposition of catheter tip
	Ventricular migration
	Bleeding at catheter replacement
Reservoir	Inadequate contour/size
Valve	Inadequate valve
Subcutaneous tunneling	Skin breakdown from superficial passage
	Intrathoracic penetration
	Liver, gallbladder, lung penetration
	Lung apex perforation
Abdominal catheter	Preperitoneal placement
	Viscus perforation
	Vascular perforation
	Urinary bladder perforation
Connections	Disconnections: avoid connectors in growing patients

(a)

The patients must be in their best general status. Infections, sepsis, and coagulation disorders should have been previously corrected. Prior medications are usually continued. Preoperative anesthetic assessment is highly desirable. In premature newborns, temporary measures to delay surgery till they achieve a satisfactory weight are also advisable (in our institution this limit is 1,300 g). If necessary, a latex-free operating room and latex-free accessory materials are prepared.

(b)

The medical records (including the signed informed consent form) and the neuroimaging studies are taken to the operating room with the patient.

(c)

The necessary equipment (including two sets of valves) must also be ready. Pressure settings of programmable valves are adjusted beforehand while the valve is still in the sterile package.

(d)

Prophylactic antibiotics are given preoperatively and repeated at 8–12 h intervals for 1 or 2 days.

(e)

The hair is washed with an antiseptic shampoo. Hair shaving is performed immediately before surgery to avoid contamination of small scalp erosions [12].

5.4.2 Patient Position, Local Anesthetics, and Skin Preparation

5.4.2.1 Position

The patient is usually positioned supine, the head rotated to the side opposite to that of the planned skin incision, placing the head, neck, thorax, and abdomen in a flat horizontal plane to facilitate the passage of the tunneling device.

5.4.2.2 Skin

The skin is disinfected with an iodine solution (or clorhexidine if the patient is allergic to iodine) applied for 10 min and dried with sterile towels. Surgical drapes are placed around the planned surgical field and covered with adhesive plastic transparent films. Importantly, in shunt revisions, all the skin overlying the shunt trajectory is prepared as described to have the opportunity of revising both proximal and distal ends of the shunt.

5.4.2.3 Local Anesthetic

A local anesthetic is injected in the planned surgical incision for analgesia, prevention of bleeding, and for separation of the skin layers.

5.4.3 Skin Incision, Burr Hole, and Dural Opening

5.4.3.1 Skin Incisions

The cranial incision is usually made curved or as a small skin flap. Lineal incisions are not recommended as they would contact with the shunt hardware in case of wound infection. Incisions should not be performed in the proximity of tracheostomy or gastrostomy wounds. Dissection of the galea aponeurotica and the pericranium are of great importance, especially in infants, to achieve a watertight closure at the end of the operation.

5.4.3.2 Burr Hole

A burr hole of sufficient size, placed on the desired point of catheter insertion (frontal, posterior parietal, or occipital), is performed. At present, there is no scientific evidence on the superiority between frontal and posterior catheter placements [3, 14]. When a burr-hole-type reservoir is used, the bone opening must be large enough to accommodate it, avoiding a too large orifice that would favor the intracranial migration of the reservoir (or valve).

5.4.3.3 Dural Opening

The dura mater and brain are coagulated with monopolar cautery to make an opening of the same size as the proximal catheter. A too large dural orifice will facilitate the escape of fluid around the tube. At the same time, any dural or cortical bleeding points are coagulated.

5.4.4 Ventricular Catheter Insertion-Related Pitfalls

5.4.4.1 Choice of the Ventricular Catheter

Ventricular catheter length is calculated from preoperative CT or MRI scans. The catheter tip is placed in front of the foramen of Monro to avoid the choroid plexus [3]. Placement is not problematic in patients with large ventricles but in instances with smaller ventricles, US, stereotaxy, or navigation may be used [157].

5.4.4.2 Ventricular Cannulation

The catheter with its stylet is then gently introduced. Entry within the ventricle is felt by the surgeon’s hands and confirmed by the spontaneous flow of CSF. A sample of CSF is sent for analysis and bacteriological study. Excessive escape of CSF is avoided to prevent pneumocephalus and early overdrainage. The ventricular catheter can be irrigated or replaced if fluid does not flow properly. Proximal shunt block is the most frequent cause of shunt malfunction; accordingly, emphasis must be placed in confirming a good flow of CSF. Several ventricular catheter models with different holes and diameters have been designed for avoiding (or retarding) obstruction [43]. Nonstraight catheters, and those with flanged tips, are not recommended because they do not prevent blockage and, on the contrary, they increase the risk for hemorrhage during revision surgery. During reoperations, the ventricular catheter is placed without the stylet using the previous tract.

5.4.4.3 Misplacement of Ventricular Catheters

The ventricular catheter tip may be involuntarily positioned within the ventricular wall, embedded in the brain parenchyma, within the septum, in the temporal horn, or even in the cisterns (Fig. 5.3). Planning of the length and trajectory prevents this complication. Catheter impaction within the brain parenchyma usually results in its block. Treatment consists of shunt revision and catheter replacement. Sudden death has been reported by brain stem impaction of a fourth ventricle catheter [75].

Fig. 5.3

Examples of iatrogenic malposition: (a) skull radiograph of a tightly adhered ventricular catheter that was initially placed in the temporal horn; (b) CT in shunt malfunction due to a misplaced proximal catheter within the septum; (c) MRI showing impaction of fourth ventricular catheter in the brain stem, (d) radiograph showing a peritoneal catheter placed in the preperitoneal space

5.4.4.4 Intracranial Migration and Retention of Ventricular Catheters

Proximal catheters may disconnect from the attached reservoir (or valve) due to a too-loose ligature, use of absorbable sutures ties, or by suction into the ventricle during catheter replacement. BioGlide proximal catheters seem to be more prone to disconnections making retrieval difficult or impossible [20]. One-piece shunts have also been reported to migrate within the ventricles due to their uniform diameter and to a faulty fixation to the pericranium. In the same manner, catheters may also be pulled out of the skull during the patients’ growth.

5.4.4.5 Intraventricular Hemorrhage in Shunt Revision

Problematic intraventricular hemorrhage happens more often in proximal catheter revision than in new insertions [67]. The reported incidence of ventricular hemorrhage during shunt revisions is approximately 30 % [14]. On removing the catheter, it will often come out easily, but not infrequently it is firmly attached to the choroid plexus, septum, or ventricular wall. Attempts at removal have to be made with great care. If the catheter still continues to be adhered, it is better to leave it in situ. Forceful maneuvers for removing the proximal catheter often are the cause of iatrogenic hemorrhages. Proposed maneuvers for safe catheter removal include gentle traction, delicate rotation of the tube, irrigation with saline, and intraluminal coagulation with the stylet or with a flexible neuroendoscopy electrode, or laser coagulation through a separate burr hole [14, 80, 130]. Unfortunately, none of these methods completely avoids bleeding. Intraventricular urokinase has been used for reducing the duration of the external drainage and to prevent a new catheter block [83]. Delayed hemorrhage from an iatrogenic aneurysm has been documented after removal of a long-standing VP shunt [62, 139].

5.4.4.6 Intraparenchymal Hemorrhage

Intracerebral bleeding from ventricular catheter insertion is quite rare, but some asymptomatic instances may escape detection if CT scans are not routinely performed after shunt placement or revision [89]. The origin of these hemorrhages may be at the cortical vessels (arteries or veins) or along the proximal catheter tract. Bleeding is more frequent in older patients and in individuals with cerebrovascular conditions, brain edema, unrecognized coagulopathies, and bleeding disorders. They may also occur after repeated maneuvers for ventricular cannulation. Intracerebral bleeding may happen early after shunt placement or in a delayed form. Many of these hemorrhages may give no clinical manifestations and require no surgery. However, instances with neurological involvement may necessitate revision for hemostasis or even craniotomy. Prevention consists of careful coagulation of dural and cortical vessels and of avoiding multiple attempts for ventricular cannulation. Hemorrhages may also occur at sites distant from the ventricular catheter (extradural or subdural spaces) and are usually related to sudden CSF depletion (Fig. 5.4) [2, 109].

Fig. 5.4

(a) Preoperative cranial CT scan of a 15-month-old boy who was operated because of a tumoral lesion in the posterior fossa with the histopathological diagnosis of grade 2 pilomyxoid astrocytoma. (b, c) CT scans showing the development of subdural hematoma in the same patient having undergone ventriculoperitoneal shunting because of a persistent hydrocephalus due to a malfunctioning ventriculocisternal (Torkildsen’s) shunt (Courtesy of Recep Brohi MD, Ankara, Turkey)

5.4.5 Peritoneal Access

The habitual abdominal skin incision is a transverse paraumbilical one. Skin incision should be away from gastrostomy or colostomy wounds. The peritoneum can be entered by one of the following three methods:

5.4.5.1 Open Surgery

The open technique we routinely perform is a mini-laparotomy. After skin incision, the subcutaneous layer is dissected, the fascia is opened horizontally, and the muscles split vertically to expose the peritoneum. This layer is pulled up, away from the bowel, with straight mosquito forceps, and opened with dural scissors. In this way, the neurosurgeon can inspect under direct vision the intestinal loops and prevent the inadvertent placement of the distal catheter in the preperitoneal space (one of the most common preventable causes of iatrogenic shunt failure at the abdominal end). A thin brain spatula may be used for introducing the distal tube within the peritoneum.

5.4.5.2 Trocar Insertion

A trocar may also be utilized to access the peritoneum. Although extremely rare, the aorta and the iliac arteries [29], the cava, the bladder, the stomach, or the bowel can be perforated accidentally by the trocar, a method that we have abandoned after having experienced some unfortunate accidents. The risk of perforation is higher in infants and undernourished patients and in those who have peritoneal adhesions from previous abdominal surgeries. Before trocar insertion, it is mandatory to empty the bladder (especially in spina bifida patients) and to stop muscle relaxants. In our view, trocar use does not offer substantial advantages and, on the contrary, it may cause extremely severe injuries. The collaboration of a general surgeon should be sought when technical abdominal problems are anticipated. Bowel perforation occurring early after shunt surgery is undoubtedly an iatrogenic complication. Late bowel perforation is unrelated to the technique. It was earlier reported with the use of spring-reinforced shunts [105, 126]. Intestinal perforation can give rise to severe complications caused by Gram negative or anaerobic organisms, for instance peritonitis, ventriculitis, septic pneumocephalus, and brain abscess [105, 126].

5.4.5.3 Endoscopic Laparoscopy

This technique is increasingly being used for new shunt insertions and for revisions. Indications include prior abdominal surgery, obesity, previous peritoneal infections, retained fragments of broken devices, and pseudocysts [77]. However, it has the inconvenience of requiring the collaboration of an endoscopic surgeon with the appropriate equipment. Laparoscopic surgery is not devoid of risks of visceral or vascular perforation [29].

Intraperitoneal parts of broken or disconnected distal catheters can be retrieved both by open surgery and by laparoscopy. Nevertheless, retained abdominal catheters that cannot be removed during shunt revision can be safely left within the peritoneal cavity, as they produce no harm. Detailed accounts of shunt-related abdominal complications have been published [30, 46] and will be also discussed in another chapter of this book.

5.4.6 Tunneling and Subcutaneous Passage of the Distal Catheter

Placing the patient in a flat position is essential for making shunt passage easier. The shunt-passer can be introduced from scalp to abdominal incision or in the opposite way (the one we prefer). Saline can be injected in the subcutaneous tissue of the planned shunt course to facilitate the tunneller passage especially in infants and children. Then, the shunt-passer is advanced carefully, controlling the displacement of its tip under the subcutaneous trajectory by digital palpation.

Three sites call for special attention during tunneling [123], the passage above the lower ribs (to not damage the liver, gallbladder, or lungs), the pleural apex (to not produce a pneumothorax), and the junction of the cranial and cervical aponeurosis to avoid intracranial penetration in children with open sutures [108, 135]. During tunneling, passing beneath the breast in female patients is avoided to prevent late complications should breast surgery be performed as mastectomy, breast implants, etc. [121]. Care should also be taken to not perforate the thin skin of infants all along the passage of the tunneling device. Most shunt-passers are malleable and permit molding to adapt best to the patient’s anatomy. In adults, one or more intermediate skin incisions may be required for passing the shunt.

In shunt revisions, the previous tract can be used to pass subcutaneously the new catheter by suturing with a 4/0 silk suture, the end of the new tube to the end of the catheter that is being removed and pulling from it slowly. This maneuver is usually successful in cases of malfunctions occurring early after initial shunt placement and in patients with spring-reinforced shunts, but not when the tubing has become hardened over time. The tubing may break into pieces at removal, making difficult the extraction of fragments that will have to be left in place to avoid multiple unsightly cutaneous incisions.

When the shunt has to be taken out of the abdomen because of peritoneal infection, the tube must be removed from the abdominal incision and not from the cranial one because pulling it out through the scalp incision would contaminate the whole subcutaneous tract of the shunt producing severe cellulitis.

Connectors should not be employed in children at the level of the chest or abdomen in cases of shunt rupture or disconnection because the tubing will become detached again. In this case, replacing the whole distal catheter at the cranial end seems to be preferable.

5.4.7 Rupture, Disconnection, and Migration

Innumerable adverse events related to biodegradation, rupture, disconnections, and migration with or without protrusion (or extrusion) of the distal catheter have been reported that are mainly unrelated to the surgical technique and that cannot be regarded as iatrogenic [10, 68]. These complications include hydrothorax, migration of the distal catheter into the chest [27, 135], bronchus, heart [64], subscalp coiling [53], retrograde subcutaneous migration [79], migration and/or extrusion in the subdural space, ventricles [125], stomach or bowel, bladder, vagina [103], scrotum [111], umbilicus [1], mouth [45], nose, anus, skin incisions [32, 154], etc. Most of them are noniatrogenic in nature and their appearance is unpredictable and, hence, unpreventable [10, 42, 68, 79]. Intraventricular migration has been reported with valveless and cylindrical or unitized shunts, which suggests the possible prevention by a tighter fixation of the tubes to the pericranium and by avoiding these types of shunts [53, 125].

5.4.8 Reservoirs, Valves, and Antisiphon Devices

5.4.8.1 Reservoirs

Most neurosurgeons consider essential using a reservoir for testing shunt patency and for CSF sampling [96, 106, 117, 129]. Reservoirs may be of burr-hole type or placed in-line with the valve. Fortunately, reservoirs and flushing devices cause few iatrogenic problems, skin necrosis and occlusion being the most frequent [78].

5.4.8.2 Valves

Most valves drain CSF when there is a gradient of pressure between the ventricles and the end of the distal catheter. There are basically two main types: differential pressure and flow-regulated valves. There are three basic models of standard valves: low, medium, and high pressure, which refer to their closing pressure. Flow-controlled valves as the Orbis Sigma I and II provide a more physiological drainage but due to their increased resistance to flow they may not work in NPH and in infants with open sutures. So-called programmable valves permit the transcutaneous adjustment of pressure settings by using a magnet. Closed-ended and distal slit valves are not recommended because they are more prone to distal obstruction [28]. Presently, new devices that include an antisiphon or an antigravitational mechanism are also employed. No notable differences have been reported to exist with the use of one of these shunting devices [37, 107, 140].

The valve may be implanted on the burr hole or on the adjacent skull. In Table 5.3, we summarize the currently accepted indications for each type of surgery and valve according to the patient’s characteristics and the etiology of hydrocephalus. Under- and overdrainage may occur in most types of shunts and will be dealt with in the corresponding chapters. For avoiding skin necrosis over the valve (or reservoir dome) one can: (a) place the burr hole away from the parietal zone; (b) make a subcutaneous pocket for the valve; (c) use low-profile devices and small reservoirs; (d) avoid laying the patient’s head on the side of the valve; and (e) in premature and newborn children, choose a low-pressure or a programmable valve adjusted at low-pressure setting to facilitate CSF drainage that would counteract the tension produced by the reservoir on a distended scalp. These measures are especially advised for small babies and for debilitated patients.

Table 5.3

Patient-specific treatments at our institution

Type of hydrocephalus	Procedure/valve
Standard size ventricles	Programmable or medium-pressure valve
Premature and newborn infants	Programmable set at low pressure, low-pressure valve, small-contoured valve
Large ventricles, chronic hydrocephalus, adult NPH	Programmable, flow-regulated (OS-II), gravity valve/antisiphon devices
Slitlike ventricles	Programmable flow-regulated gravity valve antisiphon devices
Overdrainage
Obstructive hydrocephalus	Endoscopic third ventriculostomy
Obstructive hydrocephalus	CSF shunt
Multiloculated hydrocephalus, arachnoid cysts, trapped fourth ventricle	Neuroendoscopy
	DVP with one or two catheters connected in Y

Electing the most adequate shunt requires expertise and scientific knowledge. Nevertheless, we agree with the general recommendation of implanting the valve to which one is accustomed to and is more confident with.

5.4.8.3 Antisiphon Devices

Antisiphon devices may be added to most valves. Their main value consists of decreasing the siphoning effect of differential-pressure shunts. Antisiphon valves are not recommended in infants given that they lead to underdrainage. Some antisiphon models fail to function owing to the fibrosis that forms on the antisiphon mechanism.

5.4.8.4 In-Line Filters

In-line filters were formerly used for preventing tumor cell seeding through the shunt although they are now rarely utilized given that they become blocked easily.

5.4.9 Connection of the Shunt Parts, Closure, and Wound Dressing

The components of the shunt are assembled together with a 2/0 silk ligature (thinner threads cut the silastic tubes as do nylon sutures). Reabsorbable sutures are not advised as they give rise to disconnections. The ligature knots are placed facing the skull to avoid skin necrosis from knot pressure. The reservoir is then fixed to the pericranium with 4/0 silk sutures. Before closure, the correct functioning of the valve is checked by observing the drip of CSF through the distal tube after placing the distal catheter tip below the level of the patient’s body, by pumping the reservoir, or by aspirating with a small syringe. Only then, the peritoneal catheter is introduced within the peritoneum and the abdominal and cranial incisions are closed in layers. The wound is again disinfected and a slightly compressive wound dressing is placed on the incisions.

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Tags: Complications of CSF Shunting in Hydrocephalus

Jun 22, 2017 | Posted by admin in NEUROSURGERY | Comments Off

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