Hydrocephalus is an excessive accumulation of cerebrospinal fluid (CSF) within the cranial cavity—often within the ventricles of the brain—potentially leading to enlarged ventricles, an enlarged skull, cortical flattening, and atrophy of the brain. Hydrocephalus can occur at any age and is related to multiple conditions. As a result of its diverse etiology, the incidence and prevalence of hydrocephalus vary greatly. These figures are most readily available when the condition is present at the time of birth; the majority of studies report a rate of 0.5–0.9 per 1,000 births when there are no other associated defects (Leech, 1991).
The manner in which hydrocephalus arises and its anatomical features coincide with recognized subtypes of the presentation. It may be congenital or acquired in development. Furthermore, it may be described as communicating or noncommunicating (a.k.a. obstructive), which coincides with the nature of CSF flow disturbance. Based on these factors, an array of functional outcomes and deficits may be seen across neurological, cognitive, behavioral, and physical domains as well as others.
Hydrocephalus has a variety of etiologies. In fact, it is related to many neurologic diseases, and as a result is one of the most common disorders treated by neurosurgeons (Bergsneider, 2001). Hydrocephalus is typically classified by cause (i.e., congenital or acquired); however, the specific cause cannot always be determined (Leech & Goldstein, 1991).
Brain tumors, arachnoid cysts, congenital malformations, trauma, infection, metabolic disease, neoplasms, and vein thrombosis have all been associated with the development of acquired hydrocephalus (Batchelor & Dean, 1996; Leech & Goldstein, 1991). In terms of congenital hydrocephalus, the presentation arises in relation to other structural defects of the central nervous system. Hydrocephalus has been most commonly discussed in relation to spina bifida. In fact, approximately half of the patients with congenital hydrocephalus also present with spina bifida (Leech, 1991). An easy way of suggesting one or the other is that, in most instances, congenital hydrocephalus presents within the first year, and anything after that is far more likely to be acquired.
Regardless of the cause for hydrocephalus, at least one of four general pathophysiologic mechanisms is typically involved. One of these mechanisms is aqueductal stenosis, which entails the aqueduct being too small for the normal passage of CSF (Leech & Goldstein, 1991). Another general mechanism is mechanical blockage. Blockage of the ventricular pathway can occur as the result of tumors, blood, or other materials; in addition, tumors or tumor-like conditions can cause blockage by pressing on this pathway from the outside (Batchelor & Dean, 1996; Leech & Goldstein, 1991). The third general mechanism for hydrocephalus is the obliteration of the subarachnoid space; there is an obstruction to the CSF circulation in this area of the brain (Leech & Goldstein, 1991). Hemodynamic or physiologic causes comprise the fourth general mechanism. The dynamic balance between the production and absorption of CSF is modified by certain conditions, which could then lead to hydrocephalus (Leech & Goldstein, 1991).
Often hydrocephalus is discussed from a pathological standpoint as being either communicating or noncommunicating (a.k.a. obstructive). These terms are used to described whether there is “communication,” in other words flow, between the subarachnoid space and the ventricles. However, some have challenged the use of terminology (i.e., Adams & Victor, 1993). The basis of the challenge is that the original conceptualization of communicating hydrocephalus suggests that no blockage of the ventricular system exists and that the hydrocephalus is due to an overproduction of CSF in the choroid plexus, which in reality is quite rare and usually only noted in papillomas. Rather, blockage at some point along the CSF flow pathway, whether it is movement between ventricles, into the subarachnoid space, or at the point of reabsorption, accounts for almost every case (Golden & Bonnemann, 2007). What then becomes of clinical importance is where the blockage occurs and from what, which can delineate treatment approach.
The neuroanatomical presentation of hydrocephalus varies based on the age when the presentation first arises, the basis for its development (e.g., vascular, tumor, etc.), if it is treatable, when it is treated, and the rate and magnitude of ventricular enlargement (Brewer, Fletcher, Hiscock, & Davidson, 2001). In cases of congenital hydrocephalus, cortical gyri appear flattened with shallow and reduced sulci. Microgyria, polygyria, or stenogyria may be noted depending upon when the hydrocephalus began in utero (Golden & Bonnemann, 2007). The features are commonly seen in conjunction with enlarged lateral ventricles regardless of the site of blockage. White matter destruction is commonly noted (Rubin et al., 1976). In the case of blockage preventing CSF moving into the subarachnoid space, this causes enlargement of the lateral ventricles due to the CSF not being able to escape while more CSF is being produced. In the case of reabsorption blockage, this can cause backflow of CSF and eventual buildup in the lateral ventricles. Prior to age 2, when the cranial sutures have yet to begin to fuse, this can lead to an enlarged head with protruding fontanelles as a means of relieving pressure. Often, whether or not the cranial sutures have fused can correspond with the degree of ventricular enlargement. Prior to suture closing, ventricular enlargement can be quite prominent as there is no structural restriction in place as is the case in hydrocephalus developing in a fixed skull. Destruction of nerve fibers, the corpus callosum, and other cerebral commissures may be seen as a result of stretching and breaking (Loveday & Edginton, 2011).
When the condition is congenital, the main feature is an enlarged head that continues to grow at an abnormally fast rate (Gascon & Leech, 1991a,b). In severe cases, the forehead may bulge and the eyes may appear to have receded into their sockets. Percussion testing of the head can be characterized by a “cracked-pot” sound if the hydrocephalus has developed prior to cranial suture fusion (Golden & Bonnemann, 2007). Prognosis is least favorable when hydrocephalus is present at birth as an isolated condition. Of those infants who do survive, less than half have normal IQs, whereas the rest may exhibit mild to severe mental retardation. Enlargement of the head, greater than two standard deviations above the mean, is the usual presentation of hydrocephalus within the first year of life; however, description is best defined by tracking of head growth over time as opposed to single point measurement. Other symptoms sometimes observed in infants are irritability, lethargy, and delayed motor development (Gascon & Leech, 1991a,b).
Extraocular movements may be impeded causing an upgaze paresis with a “setting sun phenomenon” in infants, whereas unilateral or bilateral abducens and trochlear paresis can also occur (Golden & Bonnemann, 2007). Papilledema can present but over time give way to optic atrophy and further diminished visual acuity, sometimes being bad enough in infants that there is appearance of cortical blindness as the pupil and lens respond properly to visual stimuli, but the information is not “seen” neurologically.
Interestingly, increasing head size is not a part of the clinical presentation of hydrocephalus in childhood and adolescence. For this age group, signs of hydrocephalus may include behavioral changes, decreased school performance, headaches, nausea, vomiting, changes in vision, and poor coordination. Signs of dementia, gait disturbance, and urinary incontinence are possible symptoms for adults with hydrocephalus (Gascon & Leech, 1991a,b). Chronic hydrocephalus may lead to mental retardation and/or optic atrophy with permanent visual loss (Batchelor & Dean, 1996).
Intellectually, low average performance is commonly reported in conjunction with and as a result of slowed development (Jacobs, Northam, & Anderson, 2001; Lindquist, Carlsson, Persson, & Uvebrant, 2005). Domain-specific deficits have been reported in processing speed (Jacobs et al., 2001), cognitive set shifting, and activation–reactivation (Swartout et al., 2008). Visuospatial abilities are often an area of weakness (Baron & Goldberger, 1993) but have been argued as potentially a manifestation of combined visual and motor defects as opposed to a pure visuospatial issue (Baron & Goldberger, 1993; Hetherington & Dennis, 1999; Wills, 1993).
Language is often characterized by dysfluency of speech, “cocktail-party talk/syndrome” (i.e., articulate and coherent expression that is irrelevant and sometimes pointless or without real direction) and preserved syntax and lexicon in the face of disrupted text and discourse (Fletcher et al., 2002).
Memory and learning deficits are fairly prominent. Although some have suggested widespread deficits of this domain characterized by verbal and nonverbal memory deficits, including deficits in both free recall and recognition and memory of both noncontextual and contextual information (Scott et al., 1998), others have suggested a pattern consistent with a prefrontal/subcortical pattern of dysfunction (Yeates et al., 1995). In this regard, cueing and recognition aids performance suggesting retrieval-based and organization deficits.
Finally, executive functioning deficits have been commonly reported with deficits arising in problem solving, planning, abstraction, sequencing, and set shifting in the absence of perseveration, impulsivity, and rule breaking (Fletcher et al., 1995; Snow, 1999).
Infants with hydrocephalus typically undergo skull radiographs, MRI, or CT scan to determine separation of sutures, areas of thinning of the bones, or intracranial calcifications. A CT scan can show ventricular size and the location and nature of an obstruction if any (Gascon & Leech, 1991a,b); however, MRI is preferred and offers the most refined and accurate evaluation of potential blockage (Golden & Bonnemann, 2007). In cases involving intraventricular hemorrhage, sonography is probably the procedure of choice (Gascon & Leech, 1991a,b). In older patients and even children, in addition to MRI or CT scan, CSF pressure can be monitored by way of a lumbar puncture.
Neuropsychological evaluation should be undertaken in all cases to determine what if any deficits are present. Given the high prevalence of visual deficits, optometry consultation is recommended.
The primary method of treatment for hydrocephalus is the surgical placement of a shunt, a device that provides drainage of fluid from the brain into the abdominal cavity (Kanev & Park, 1993). Shunting CSF from the dilated ventricles usually results in clinical improvement. Particularly, it can improve potential cognitive development in children (Batchelor & Dean, 1996; Rachel, 1999). However, the longer the disease has been present, the less likely it is that shunting will be curative. Other neurosurgical treatments for hydrocephalus include removal of tumors or cysts, ventricular bypass, ventriculocisternostomy, third ventriculostomy, and coagulation of the choroid plexus (Batchelor & Dean, 1996; Rachel, 1999). In infants where the hydrocephalus appears as a potential acute feature that may resolve over time, such as in the case where it develops in relation to vascular events (e.g., hemorrhage—posthemorrhagic hydrocephalus), permanent shunt placement may not be sought. Rather, temporary treatments such as daily lumbar puncture alone or in combination with CSF-reducing pharmacological practices such as furosemide with acetazolamide may be employed.
For infants and children with hydrocephalus, early intervention or stimulation programs may be helpful when dealing with developmental delays. In older children and adults, when the skull is no longer flexible, treating the underlying cause and psychological symptoms of hydrocephalus may be most feasible. Supportive or group counseling may be beneficial for treating irritability and changes in mental functioning. For school-aged children, remedial classes and peer support may be beneficial in dealing with academic-related problems.
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