Treatment options vary depending on the symptoms, type, and extent of the collection. Mainly three options have been proposed for this purpose. First, it may be possible to manage these collections conservatively if they are small (≤8 mm) with no accompanying brain compression or herniation. Second option is to treat the overdrainage by raising the opening pressure of the shunt’s valve. This can be achieved by substituting the valve with a higher resistance one or raise the opening pressure if the valve is adjustable (Fig. 7.3). Alternatively, inserting an antisiphon device can be considered (Fig. 7.4). Finally, the drainage of the extra-axial fluid collection either alone or in combination with second option can be applied as the third alternative [3].

Bergsneider et al. reported their clinical experience in shunted iNPH patients with adjustable valves in some different scenarios [12]. Briefly, they performed the follow-up of the asymptomatic and relatively small effusions (≤8 mm), conservatively. In the presence of moderate effusions (8–15 mm) in asymptomatic patients, it was recommended to raise the initial opening pressure and perform the follow-up with computed tomography (CT). If the patient is symptomatic (headache or focal neurological deficit), it was recommended to act depending on the degree of morbidity. In this regard, it was recommended to raise the initial opening pressure and perform the follow-up with CT in cases with minimal morbidity. If morbidity is moderate/severe, on the other hand, it was recommended to raise the initial opening pressure for smaller subdural effusions. Finally, the placement of a temporary subdural drain or a subdural-peritoneal shunt is reserved for large (>15 mm) or moderate/severe symptomatic collections.

Drainage may be accomplished by a burr hole and a temporary drain or via a subdural catheter that is spliced into the existing shunt system below the valve. This latter system (i.e., combination intraventricular catheter and spliced subdural catheter) commonly results in reexpansion of the brain with resolution of the extra-axial fluid collections. Reexpansion occurs due to relative pressure gradient from the ventricular system to the extra-axial fluid space resulting in brain expansion and obliteration of the subdural space [3].

In the case of a subdural hematoma whether it is primary or associated with the hemorrhagic conversion of subdural effusion, patients should be treated urgently. Accordingly, previous anticoagulation should be reversed and/or antiplatelet medication interrupted. Besides, the application of prophylactic anticonvulsants should be considered. Smaller, asymptomatic subdural hematoma collections can often be resolved after increasing the valve pressure. On the other hand, larger and/or symptomatic subdural hematoma collections typically require surgical evacuation in addition to valve pressure adjustments [12].

This complication is best prevented by avoiding overdrainage through selection of appropriate valve systems. Albeit previous studies showed a reduction of overdrainage by using high-pressure valves or flow-controlled shunts, clinical outcomes were disappointing due to insufficient CSF drainage in the horizontal position [3].

Although the exact definition of the slit ventricle syndrome (SVS) is unclear in the pediatric neurosurgery literature, the characteristic finding of the syndrome is symptomatic small ventricles. SVS is a condition in which the clinical picture is one of acute or semiacute headache, nausea, vomiting, and/or lethargy. The headache could be episodic, typically presenting as pressure waves, often terminating in vomiting or hyperventilation, and is sometimes associated with bradycardia and systemic hypertension [14]. Browd et al. defined this condition as shunt malfunction in spite of the presence of a patent shunt system [3]. SVS can be seen in both pediatric and adult patients. Clinically, symptomatic, shunted patient with “slit” or collapsed ventricles or intracranial hypertension syndrome without any neuroradiological findings can be seen during the course [3, 12, 14].

Patients with SVS often have a patent shunt system which was inserted several years ago and radiographic studies (CT or MRI) revealed small in size ventricles (Fig. 7.5). Recently, Larysz et al. indicated the importance of appreciating the existence of small ventricles after placement of a ventriculoperitoneal shunt with proper positioning of ventricular catheter for exclusion of intracranial hypertension [14]. Although the incidence of slit ventricle syndrome is low, it accounts for a disproportionate number of shunt revisions and is a common problem in the pediatric neurosurgery literature. Di Rocco et al. reported excessive drainage in less than 1 % of all newly shunted patients [15].

The common complaints of the patients are body position-dependent symptoms such as headaches, nausea, and/or vomiting in the vertical position. These symptoms generally improve quickly by lying down. Orthostatic headaches, dizziness, and/or lack of concentration in school children can be also encountered. This group also showed clinically unclassifiable symptoms such as orthostatic whole body pain or a feeling of heaviness in the legs immediately after standing up [1].

Intermittent proximal catheter obstruction during the course of SVS can lead to intermittent headaches due to fluctuated ICP. An acute presentation with loss of appetite and lethargy can be rarely seen. Augmented fatigue, restlessness, and/or constant weeping in patients younger than 5 years are reported as other symptoms [1].

The patients with SVS has been classified by Rekate into five subgroups: those with (1) extreme low pressure headaches, probably from siphoning of CSF from the brain by the shunt, (2) intermittent obstruction of the proximal shunt catheter, (3) normal volume hydrocephalus with diminished buffering capacity of the CSF, (4) intracranial hypertension associated with working shunts, and (5) headaches (in shunted children) unrelated to intracranial pressure or shunt function [16, 17].

The underlying pathophysiological events leading to SVS have been proposed as overdrainage caused by siphoning at the distal catheter, either by gravity alone or, in the case of atrial or pleural shunts, by negative pressure at the distal end of the catheter tubing [3].

If overdrainage occurs during the period of brain growth, the brain fills the intracranial space completely and the ventricles remain collapsed consequently. This leads to an impairment in brain compliance and intermittent obstruction of the ventricular catheter by the collapsed ventricular system. Obstruction may be symptomatic without a measurable change in ventricle size because of poor compensatory mechanisms. Occasionally this obstruction leads to severe life-threatening complications [3].

The incidence of the SVS is variable among different studies. The Shunt Design Trial demonstrated SVS in only one case out of the 344 patients included to the study (follow-up 1.0–5.5 years, median 3 years) [18]. In a series of 120 patients with ventriculoatrial shunts with a long-term follow-up (average 11 years) an incidence of 1.8 % was reported [19]. It is a well-known phenomenon that SVS occurs generally several years after shunt insertion [20]. Thus, the lower incidence documented in some studies may be related to insufficient follow-up period [3]. Long ago, Sgouros et al. reported a SVS incidence of 10 % among 70 patients with 16-year follow-up [21]. On the contrary, Serlo et al. noted that slit ventricles occurred in 75 of 141 (53 %) patients in their series [22].

Although relatively few shunted patients develop SVS, Browd et al. made a point of the disproportionate number of shunt-related consultations and procedures among these patients [3].