- Email: [email protected]
Hydrocephalus
600
HYDROCEPHALUS
antidopaminergic drugs. Therefore, antidopaminergic drugs should be reserved for patients with disabling chorea or serious psychosis. Antidepressant drugs are often helpful in ameliorating the affective disorders, but jerky movements can be precipitated. Antiglutaminergic drugs (which block the activity of the neurochemical glutamate) are currently being tested in clinical trials. Psychological support, genetic counseling, long-term planning, and access to social service agencies are important elements of patient management. Neural transplantation with fetal striatal or other cell sources may become experimental options in the future. —Esther Cubo and Christopher G. Goetz See also–Basal Ganglia, Diseases of; Caudate Nucleus; Corpus Striatum; Degenerative Disorders; Dementia; Genetic Testing, Molecular; Movement Disorders, Overview; Trinucleotide Repeat Disorders Further Reading DiFiglia, M., Sapp, E., Chase, K. O., et al. (1997). Aggregation of huntingtin in neuronal intranuclear inclusions and dystrophic neurites in brain. Science 277, 1990–1993. Huntington’s Disease Collaboration Research Group (1993). A novel gene containing a trinucleotide repeat that is expanded and unstable on Huntington’s disease chromosomes. Cell 72, 971–983. Nance, M. A. (1996). Huntington’s disease—Another chapter rewritten. Am. J. Hum. Genet. 59, 1–6. Penney, J. B., and Young, A. B. (1998). Huntington’s disease. In Parkinson’s Disease and Other Movement Disorders (J. Jankovic and E. Tolosa, Eds.), 3rd ed., pp. 205–216. Williams & Wilkins, Baltimore. Ritchfield, E. K., Maguire-Zeiss, K. A., Vonkeman, H. E., et al. (1995). Preferential loss of preproenkeaphlin neurons from the striatum of Huntington’s disease patients. Ann. Neurol. 38, 852–861.
Understanding how CSF abnormally accumulates within the ventricular system depends on first understanding the basics of ventricular anatomy (Fig. 1) and CSF physiology (Fig. 2). The ventricles underlie the layers of cerebral cortex and white matter. CSF is produced and fills these cavities deep within the brain. The ventricles and CSF act as a natural shock-absorbing system for the brain. A considerable amount of CSF flowing into the ventricles is the result of fluid and waste flowing away from surrounding neural structures; in effect, the ventricular system and CSF may also function as the neurological equivalent of the lymphatic system. Within the ventricular system, specialized collections of tissue known as choroid plexus filter the specific molecular constituents of CSF from blood. CSF is produced at a constant rate of approximately three times the volume of the ventricular system every day. The CSF must flow from the lateral to the third and fourth ventricles before exiting the ventricular system at the base of the brain. From there, CSF can flow downward around the spinal cord or up around the base of the brain and over its convexities (Fig. 2).
Hydrocephalus Encyclopedia of the Neurological Sciences Copyright 2003, Elsevier Science (USA). All rights reserved.
THE WORD hydrocephalus derives from the Greek
roots for water (hydor) and head (kephale). When speaking to laypeople, neurosurgeons may refer to hydrocephalus as ‘‘water on the brain.’’ A more accurate description might be ‘‘water in the brain.’’ Hydrocephalus represents an abnormal collection of cerebrospinal fluid (CSF) within the ventricular system of the brain.
Figure 1 Ventricular anatomy. The ventricular system is composed of paired right and left lateral ventricles and midline third and fourth ventricles. Cerebrospinal fluid flows from the lateral ventricles into the third ventricle through the two foramina of Monro and proceeds to the fourth ventricle through the sylvian aqueduct. With permission from the Barrow Neurological Institute.
HYDROCEPHALUS
601
ventricle, the entry into the fourth ventricle otherwise known as the sylvian aqueduct, or the outflow foramina of the fourth ventricle). Downstream, scarring from an infection, inflammatory process,
Figure 2 Cerebrospinal fluid (CSF) circulation. CSF is produced by choroid plexus in the lateral, third, and fourth ventricles. It then flows out of the ventricular system to circulate around the brain and spinal cord surfaces before being reabsorbed into the bloodstream at the superior sagittal sinus. With permission from Williams and Wilkins.
CSF is resorbed through a specialized collection of cells in the large vein at the top of the brain known as the superior sagittal sinus. These specialized arrangements of cells are called arachnoid granulations. The granulations act as physiological valves between the subarachnoid space and blood within the superior sagittal sinus. An accumulation of CSF causes these valves to open if the pressure within the brain rises too high. Thus, a steady state is maintained between CSF production from the blood and its resorption back into the bloodstream. Hydrocephalus, an abnormal collection of CSF within the ventricular system, can result from abnormally elevated levels of CSF production, reduced CSF absorption, or obstruction to CSF flow anywhere within the ventricular system or subarachnoid space. Rare tumors, such as choroid plexus papillomas or choroid plexus carcinomas, can produce excessive CSF. Obstruction to CSF flow, however, is a more common cause of hydrocephalus (Fig. 3). A mass that compresses any part of the ventricular system can limit the flow of CSF. Upstream, the ventricular system will most likely dilate to accommodate the increased CSF. Tumors and cysts cause these types of obstructions, particularly where the ventricular system narrows (e.g., at the third
Figure 3 Coronal magnetic resonance imaging with contrast. A large cerebellar tumor (arrowhead) compresses the ventricular system causing blockage to cerebrospinal fluid flow. As a result, upstream from the obstruction the ventricles dilate (arrows). The image plane is at the junction of light and dark in the diagram of the head above the scan. With permission from the Barrow Neurological Institute.
602
HYDROCEPHALUS
or prior hemorrhage can cause obstructions to CSF flow around the base of the brain. Along the path of CSF circulation, the final site where flow can be obstructed is at the arachnoid granulations. Infection or hemorrhage into the CSF space can scar the arachnoid villi and limit the amount of CSF that can be resorbed into the bloodstream. Because the point of obstruction to CSF flow is outside the ventricular system, CSF accumulates diffusely throughout the ventricular system. Traditionally, hydrocephalus was classified as obstructive if CSF flow was obstructed in the ventricular system or as nonobstructive if the obstruction was outside the ventricular system. This distinction, however, is lost in some of the more diffuse disease processes. After a subarachnoid hemorrhage (SAH), for example, blood in the CSF scars the ventricles, the base of the brain, and the arachnoid granulations. When CSF accumulates within the ventricular system, the most likely response of the brain is to permit the ventricles to dilatate. Such dilatation, however, is limited because continued expansion of the ventricular space eventually displaces brain structures. Sometimes, the pressure caused by hydrocephalus acts on structures deep within the brain to produce the characteristic gaze paresis (i.e., an inability to look up). Headache, nausea, and vomiting may also be associated with progressive hydrocephalus. If untreated, hydrocephalus progresses until CSF production and resorption reach a new steady state or until vital brain structures such as the brainstem are displaced, consciousness is lost, and the individual dies. Because hydrocephalus develops for many reasons and obstructions can form at many sites along the path of CSF flow, the symptoms of hydrocephalus can vary among individuals. Normal pressure hydrocephalus (NPH) is a form of hydrocephalus in which the cerebral ventricles dilate even though intracranial pressure is normal. In addition, waves of intermittently increased intracranial pressure can be seen. This condition can reflect absorption abnormalities in the arachnoid granulations, but it most likely indicates a lack of stiffness or turgor (stiffness) in the brain tissue. Patients with NPH tend to be older and to exhibit memory deficits, balance and gait difficulties, and urinary incontinence. Lumbar puncture can be diagnostic if pressure elevations are noted. In addition, removal of 15–30 ml of CSF may provide some temporary symptomatic relief. If performed early enough, shunting procedures can halt or even reverse the
progression of symptoms. Shunts may be of greater benefit in those patients who showed improvement with serial lumbar puncture. Hydrocephalus is usually diagnosed from computed tomography scans or by magnetic resonance imaging (MRI). These studies often show dilated ventricles (Fig. 4) and the cause of obstruction if a tumor or cyst is responsible. A few patients, however, may not develop large ventricles in response to an obstruction to CSF flow. In such cases, abnormal brain turgor prevents ventricular expansion. Consequently, these
Figure 4 Axial magnetic resonance imaging. Significantly dilated lateral ventricles (arrows) are a hallmark of advanced hydrocephalus. The diagram above the scan depicts the image plane of the scan. With permission from the Barrow Neurological Institute.
HYDROCEPHALUS
patients may become symptomatic more rapidly than those whose ventricle dilatate. Ultrasonography can be used to estimate the size of the ventricles and to assess whether hydrocephalus is present in infants whose fontanels, or soft spots, on the skull have not yet closed. Until the mid-20th century, there was no effective treatment for hydrocephalus unless the direct cause of CSF flow obstruction could be addressed. For example, if a brain tumor causing an obstruction could be removed fully, hydrocephalus could sometimes be alleviated. This sort of surgical approach is still preferred for benign and resectable tumors. Some tumors are exquisitely sensitive to radiation or chemotherapy and may resolve completely in time. Before these therapies reach their full effect, however, patients may still need some form of CSF diversion. When CSF obstruction is diffuse or cannot be treated surgically (e.g., after SAH as described previously) or when hydrocephalus is congenital, a permanent device must be placed to divert CSF. Such devices are referred to as shunts because they shunt excess CSF from the ventricles to another body cavity, where it can be absorbed (Fig. 5). Shunts usually consist of a proximal catheter that is placed through the skull and brain into the ventricles. The proximal catheter is connected to a valve that limits the amount of CSF flow. The value prevents too much CSF from being siphoned away from the ventricles. Finally, CSF is diverted into a space such as the abdominal cavity where it can be absorbed easily. Shunt systems have been indispensable in the treatment of hydrocephalus, but they are not a perfect alternative to the body’s natural system. The failure rate for shunts within 5 years of placement is high. Consequently, patients with shunts must always look for symptoms that indicate their shunt has failed (i.e., hemorrhage and infection) and that CSF is again accumulating within their cerebral ventricles. Shunts fail for many reasons: They can become clogged with protein and brain debris; they can fracture, or shunt tubing or valve parts can break; or the distal shunt site may be unable to absorb CSF (e.g., excessive scarring in the abdominal cavity). Recent developments regarding endoscopic instruments and techniques allow neurosurgeons to place endoscopes into the ventricular system. Some obstructions to CSF flow within the ventricular system can then be viewed directly and potentially removed through this minimally invasive approach. Newer endoscopic techniques, such as endoscopic third ventriculostomy or aqueductoplasty, can sometimes
603
Figure 5 Ventriculoperitoneal shunt system. Cerebrospinal fluid is redirected from the ventricles through the shunt tubing and valve (arrow) under the skin to the peritoneum (abdomen), where it can be reabsorbed. With permission from the Barrow Neurological Institute.
be performed to reroute CSF flow from the ventricular system to the subarachnoid space around the brain. These techniques effectively bypass or directly dilatate the point of obstruction, but they cannot be applied to all forms of hydrocephalus. In the past few decades, the overall prognosis for patients with hydrocephalus has improved significantly. Improvements in surgical techniques and approaches allow neurosurgeons to access tumors previously considered unresectable. More sophisticated forms of delivering radiation (e.g., Gamma Knife) can target certain tumors while sparing other
604
HYPERACTIVITY
parts of the brain. Shunt systems have become more reliable, and a larger variety of valves are now available to fit the specific CSF outflow needs and characteristics of individual patients. Finally, newer endoscopic techniques enable CSF to be shunted within the skull, creating bypasses for CSF to flow around obstructions. Nonetheless, patients with a history of hydrocephalus must always monitor themselves or have others observe them closely for recurrent symptoms of hydrocephalus in case one of these interventions fails. —G. Michael Lemole, Jr., Ruth Lemole, and Harold L. Rekate See also–Bacterial Meningitis; Bypass Surgery; Cerebrospinal Fluid Rhinorrhoea; Fungal Meningitis; Mass Effect; Megalencephaly; Shunts, Neurosurgical Further Reading Albright, A. L. (1994). Hydrocephalus in children. In Principles of Neurosurgery (S. S. Rengachary and R. H. Wilkins, Eds.), pp. 6.1–6.23. Wolfe, London. Black, P. McL. (1996). Hydrocephalus in adults. In Neurological Surgery (J. R. Youmans, Ed.), 4th ed., pp. 927–944. Saunders, Philadelphia. Black, P. McL., and Matsumae, M. (1994). Hydrocephalus in adults. In Principles of Neurosurgery (S. S. Rengachary and R. H. Wilkins, Eds.), pp. 7.1–7.7. Wolfe, London. Carey, C. M., Tullous, M. W., and Walker, M. L. (1994). Hydrocephalus: etiology, pathologic effects, diagnosis, and natural history. In Pediatric Neurosurgery. Surgery of the Developing Nervous System (W. R. Cheek, A. E. Marlin, D. G. McLone, D. H. Reigel, and M. L. Walker, Eds.), pp. 185–201. Saunders, Philadelphia. Rekate, H. L. (1994). Treatment of hydrocephalus. In Pediatric Neurosurgery. Surgery of the Developing Nervous System (W. R. Cheek, A. E. Marlin, D. G. McLone, D. H. Reigel, and M. L. Walker, Eds.), pp. 202–220. Saunders, Philadelphia. Sainte-Rose, C. (1996). Hydrocephalus in childhood. In Neurological Surgery (J. R. Youmans, Ed.), 4th ed., pp. 890–926. Saunders, Philadelphia.
Hydroxybutyric Aciduria see Organic Acid Disorders
Hydroxyglutaric Aciduria see Organic Acid Disorders
Hyperactivity Encyclopedia of the Neurological Sciences Copyright 2003, Elsevier Science (USA). All rights reserved.
HYPERACTIVITY, also known as hyperkinesis, refers to
excessive or developmentally inappropriate levels of motor or vocal activity. Restlessness, fidgetiness, and generally unnecessary gross motor movements are frequent manifestations. In social interactions with others and self-talk during play and work, excessive speech and commentary may also be present. Hyperactivity is a common, nonspecific symptom of many etiologies. ‘‘Hyper’’ or ‘‘hyperactive’’ have been used as adjectives to describe almost any behavioral symptom in a child. Most commonly, hyperactivity is associated with attention deficit hyperactivity disorder (ADHD). In fact, ‘‘hyperactivity’’ and ‘‘ADHD’’ are often used interchangeably to describe the same disorder. Other less common presentations of hyperactivity may be related to medical conditions, other psychiatric disorders, family and psychosocial problems, speech and language problems, and academic/learning problems. ATTENTION DEFICIT HYPERACTIVITY DISORDER ADHD is one of the most common and controversial neurobehavioral disorders of childhood, affecting 3 or 4% of school-age children. The core features involve a persistent and pervasive pattern of inattention and/or hyperactivity and impulsivity that is more frequent and severe than seen in children of a comparable developmental level. The condition leads to significant functional impairment across multiple domains, including home, school, peer relationships, and work. The manifestations may change depending on the age and developmental level of the individual, but they are generally present by preschool age and may continue through adulthood. Children with ADHD are at high risk for other psychiatric disorders. In fact, coexisting conditions (known as comorbidity) tend to be the rule rather than the exception. As many as two-thirds of elementary school-age children with ADHD have at least one other diagnosable psychiatric disorder. Oppositional defiant disorder and conduct disorder occur in up to half of children with ADHD. Anxiety disorders are present in approximately 25%, with up to one-third experiencing depression. Approximately 20–25% have a learning disorder. The rate of
HYDROCEPHALUS
antidopaminergic drugs. Therefore, antidopaminergic drugs should be reserved for patients with disabling chorea or serious psychosis. Antidepressant drugs are often helpful in ameliorating the affective disorders, but jerky movements can be precipitated. Antiglutaminergic drugs (which block the activity of the neurochemical glutamate) are currently being tested in clinical trials. Psychological support, genetic counseling, long-term planning, and access to social service agencies are important elements of patient management. Neural transplantation with fetal striatal or other cell sources may become experimental options in the future. —Esther Cubo and Christopher G. Goetz See also–Basal Ganglia, Diseases of; Caudate Nucleus; Corpus Striatum; Degenerative Disorders; Dementia; Genetic Testing, Molecular; Movement Disorders, Overview; Trinucleotide Repeat Disorders Further Reading DiFiglia, M., Sapp, E., Chase, K. O., et al. (1997). Aggregation of huntingtin in neuronal intranuclear inclusions and dystrophic neurites in brain. Science 277, 1990–1993. Huntington’s Disease Collaboration Research Group (1993). A novel gene containing a trinucleotide repeat that is expanded and unstable on Huntington’s disease chromosomes. Cell 72, 971–983. Nance, M. A. (1996). Huntington’s disease—Another chapter rewritten. Am. J. Hum. Genet. 59, 1–6. Penney, J. B., and Young, A. B. (1998). Huntington’s disease. In Parkinson’s Disease and Other Movement Disorders (J. Jankovic and E. Tolosa, Eds.), 3rd ed., pp. 205–216. Williams & Wilkins, Baltimore. Ritchfield, E. K., Maguire-Zeiss, K. A., Vonkeman, H. E., et al. (1995). Preferential loss of preproenkeaphlin neurons from the striatum of Huntington’s disease patients. Ann. Neurol. 38, 852–861.
Understanding how CSF abnormally accumulates within the ventricular system depends on first understanding the basics of ventricular anatomy (Fig. 1) and CSF physiology (Fig. 2). The ventricles underlie the layers of cerebral cortex and white matter. CSF is produced and fills these cavities deep within the brain. The ventricles and CSF act as a natural shock-absorbing system for the brain. A considerable amount of CSF flowing into the ventricles is the result of fluid and waste flowing away from surrounding neural structures; in effect, the ventricular system and CSF may also function as the neurological equivalent of the lymphatic system. Within the ventricular system, specialized collections of tissue known as choroid plexus filter the specific molecular constituents of CSF from blood. CSF is produced at a constant rate of approximately three times the volume of the ventricular system every day. The CSF must flow from the lateral to the third and fourth ventricles before exiting the ventricular system at the base of the brain. From there, CSF can flow downward around the spinal cord or up around the base of the brain and over its convexities (Fig. 2).
Hydrocephalus Encyclopedia of the Neurological Sciences Copyright 2003, Elsevier Science (USA). All rights reserved.
THE WORD hydrocephalus derives from the Greek
roots for water (hydor) and head (kephale). When speaking to laypeople, neurosurgeons may refer to hydrocephalus as ‘‘water on the brain.’’ A more accurate description might be ‘‘water in the brain.’’ Hydrocephalus represents an abnormal collection of cerebrospinal fluid (CSF) within the ventricular system of the brain.
Figure 1 Ventricular anatomy. The ventricular system is composed of paired right and left lateral ventricles and midline third and fourth ventricles. Cerebrospinal fluid flows from the lateral ventricles into the third ventricle through the two foramina of Monro and proceeds to the fourth ventricle through the sylvian aqueduct. With permission from the Barrow Neurological Institute.
HYDROCEPHALUS
601
ventricle, the entry into the fourth ventricle otherwise known as the sylvian aqueduct, or the outflow foramina of the fourth ventricle). Downstream, scarring from an infection, inflammatory process,
Figure 2 Cerebrospinal fluid (CSF) circulation. CSF is produced by choroid plexus in the lateral, third, and fourth ventricles. It then flows out of the ventricular system to circulate around the brain and spinal cord surfaces before being reabsorbed into the bloodstream at the superior sagittal sinus. With permission from Williams and Wilkins.
CSF is resorbed through a specialized collection of cells in the large vein at the top of the brain known as the superior sagittal sinus. These specialized arrangements of cells are called arachnoid granulations. The granulations act as physiological valves between the subarachnoid space and blood within the superior sagittal sinus. An accumulation of CSF causes these valves to open if the pressure within the brain rises too high. Thus, a steady state is maintained between CSF production from the blood and its resorption back into the bloodstream. Hydrocephalus, an abnormal collection of CSF within the ventricular system, can result from abnormally elevated levels of CSF production, reduced CSF absorption, or obstruction to CSF flow anywhere within the ventricular system or subarachnoid space. Rare tumors, such as choroid plexus papillomas or choroid plexus carcinomas, can produce excessive CSF. Obstruction to CSF flow, however, is a more common cause of hydrocephalus (Fig. 3). A mass that compresses any part of the ventricular system can limit the flow of CSF. Upstream, the ventricular system will most likely dilate to accommodate the increased CSF. Tumors and cysts cause these types of obstructions, particularly where the ventricular system narrows (e.g., at the third
Figure 3 Coronal magnetic resonance imaging with contrast. A large cerebellar tumor (arrowhead) compresses the ventricular system causing blockage to cerebrospinal fluid flow. As a result, upstream from the obstruction the ventricles dilate (arrows). The image plane is at the junction of light and dark in the diagram of the head above the scan. With permission from the Barrow Neurological Institute.
602
HYDROCEPHALUS
or prior hemorrhage can cause obstructions to CSF flow around the base of the brain. Along the path of CSF circulation, the final site where flow can be obstructed is at the arachnoid granulations. Infection or hemorrhage into the CSF space can scar the arachnoid villi and limit the amount of CSF that can be resorbed into the bloodstream. Because the point of obstruction to CSF flow is outside the ventricular system, CSF accumulates diffusely throughout the ventricular system. Traditionally, hydrocephalus was classified as obstructive if CSF flow was obstructed in the ventricular system or as nonobstructive if the obstruction was outside the ventricular system. This distinction, however, is lost in some of the more diffuse disease processes. After a subarachnoid hemorrhage (SAH), for example, blood in the CSF scars the ventricles, the base of the brain, and the arachnoid granulations. When CSF accumulates within the ventricular system, the most likely response of the brain is to permit the ventricles to dilatate. Such dilatation, however, is limited because continued expansion of the ventricular space eventually displaces brain structures. Sometimes, the pressure caused by hydrocephalus acts on structures deep within the brain to produce the characteristic gaze paresis (i.e., an inability to look up). Headache, nausea, and vomiting may also be associated with progressive hydrocephalus. If untreated, hydrocephalus progresses until CSF production and resorption reach a new steady state or until vital brain structures such as the brainstem are displaced, consciousness is lost, and the individual dies. Because hydrocephalus develops for many reasons and obstructions can form at many sites along the path of CSF flow, the symptoms of hydrocephalus can vary among individuals. Normal pressure hydrocephalus (NPH) is a form of hydrocephalus in which the cerebral ventricles dilate even though intracranial pressure is normal. In addition, waves of intermittently increased intracranial pressure can be seen. This condition can reflect absorption abnormalities in the arachnoid granulations, but it most likely indicates a lack of stiffness or turgor (stiffness) in the brain tissue. Patients with NPH tend to be older and to exhibit memory deficits, balance and gait difficulties, and urinary incontinence. Lumbar puncture can be diagnostic if pressure elevations are noted. In addition, removal of 15–30 ml of CSF may provide some temporary symptomatic relief. If performed early enough, shunting procedures can halt or even reverse the
progression of symptoms. Shunts may be of greater benefit in those patients who showed improvement with serial lumbar puncture. Hydrocephalus is usually diagnosed from computed tomography scans or by magnetic resonance imaging (MRI). These studies often show dilated ventricles (Fig. 4) and the cause of obstruction if a tumor or cyst is responsible. A few patients, however, may not develop large ventricles in response to an obstruction to CSF flow. In such cases, abnormal brain turgor prevents ventricular expansion. Consequently, these
Figure 4 Axial magnetic resonance imaging. Significantly dilated lateral ventricles (arrows) are a hallmark of advanced hydrocephalus. The diagram above the scan depicts the image plane of the scan. With permission from the Barrow Neurological Institute.
HYDROCEPHALUS
patients may become symptomatic more rapidly than those whose ventricle dilatate. Ultrasonography can be used to estimate the size of the ventricles and to assess whether hydrocephalus is present in infants whose fontanels, or soft spots, on the skull have not yet closed. Until the mid-20th century, there was no effective treatment for hydrocephalus unless the direct cause of CSF flow obstruction could be addressed. For example, if a brain tumor causing an obstruction could be removed fully, hydrocephalus could sometimes be alleviated. This sort of surgical approach is still preferred for benign and resectable tumors. Some tumors are exquisitely sensitive to radiation or chemotherapy and may resolve completely in time. Before these therapies reach their full effect, however, patients may still need some form of CSF diversion. When CSF obstruction is diffuse or cannot be treated surgically (e.g., after SAH as described previously) or when hydrocephalus is congenital, a permanent device must be placed to divert CSF. Such devices are referred to as shunts because they shunt excess CSF from the ventricles to another body cavity, where it can be absorbed (Fig. 5). Shunts usually consist of a proximal catheter that is placed through the skull and brain into the ventricles. The proximal catheter is connected to a valve that limits the amount of CSF flow. The value prevents too much CSF from being siphoned away from the ventricles. Finally, CSF is diverted into a space such as the abdominal cavity where it can be absorbed easily. Shunt systems have been indispensable in the treatment of hydrocephalus, but they are not a perfect alternative to the body’s natural system. The failure rate for shunts within 5 years of placement is high. Consequently, patients with shunts must always look for symptoms that indicate their shunt has failed (i.e., hemorrhage and infection) and that CSF is again accumulating within their cerebral ventricles. Shunts fail for many reasons: They can become clogged with protein and brain debris; they can fracture, or shunt tubing or valve parts can break; or the distal shunt site may be unable to absorb CSF (e.g., excessive scarring in the abdominal cavity). Recent developments regarding endoscopic instruments and techniques allow neurosurgeons to place endoscopes into the ventricular system. Some obstructions to CSF flow within the ventricular system can then be viewed directly and potentially removed through this minimally invasive approach. Newer endoscopic techniques, such as endoscopic third ventriculostomy or aqueductoplasty, can sometimes
603
Figure 5 Ventriculoperitoneal shunt system. Cerebrospinal fluid is redirected from the ventricles through the shunt tubing and valve (arrow) under the skin to the peritoneum (abdomen), where it can be reabsorbed. With permission from the Barrow Neurological Institute.
be performed to reroute CSF flow from the ventricular system to the subarachnoid space around the brain. These techniques effectively bypass or directly dilatate the point of obstruction, but they cannot be applied to all forms of hydrocephalus. In the past few decades, the overall prognosis for patients with hydrocephalus has improved significantly. Improvements in surgical techniques and approaches allow neurosurgeons to access tumors previously considered unresectable. More sophisticated forms of delivering radiation (e.g., Gamma Knife) can target certain tumors while sparing other
604
HYPERACTIVITY
parts of the brain. Shunt systems have become more reliable, and a larger variety of valves are now available to fit the specific CSF outflow needs and characteristics of individual patients. Finally, newer endoscopic techniques enable CSF to be shunted within the skull, creating bypasses for CSF to flow around obstructions. Nonetheless, patients with a history of hydrocephalus must always monitor themselves or have others observe them closely for recurrent symptoms of hydrocephalus in case one of these interventions fails. —G. Michael Lemole, Jr., Ruth Lemole, and Harold L. Rekate See also–Bacterial Meningitis; Bypass Surgery; Cerebrospinal Fluid Rhinorrhoea; Fungal Meningitis; Mass Effect; Megalencephaly; Shunts, Neurosurgical Further Reading Albright, A. L. (1994). Hydrocephalus in children. In Principles of Neurosurgery (S. S. Rengachary and R. H. Wilkins, Eds.), pp. 6.1–6.23. Wolfe, London. Black, P. McL. (1996). Hydrocephalus in adults. In Neurological Surgery (J. R. Youmans, Ed.), 4th ed., pp. 927–944. Saunders, Philadelphia. Black, P. McL., and Matsumae, M. (1994). Hydrocephalus in adults. In Principles of Neurosurgery (S. S. Rengachary and R. H. Wilkins, Eds.), pp. 7.1–7.7. Wolfe, London. Carey, C. M., Tullous, M. W., and Walker, M. L. (1994). Hydrocephalus: etiology, pathologic effects, diagnosis, and natural history. In Pediatric Neurosurgery. Surgery of the Developing Nervous System (W. R. Cheek, A. E. Marlin, D. G. McLone, D. H. Reigel, and M. L. Walker, Eds.), pp. 185–201. Saunders, Philadelphia. Rekate, H. L. (1994). Treatment of hydrocephalus. In Pediatric Neurosurgery. Surgery of the Developing Nervous System (W. R. Cheek, A. E. Marlin, D. G. McLone, D. H. Reigel, and M. L. Walker, Eds.), pp. 202–220. Saunders, Philadelphia. Sainte-Rose, C. (1996). Hydrocephalus in childhood. In Neurological Surgery (J. R. Youmans, Ed.), 4th ed., pp. 890–926. Saunders, Philadelphia.
Hydroxybutyric Aciduria see Organic Acid Disorders
Hydroxyglutaric Aciduria see Organic Acid Disorders
Hyperactivity Encyclopedia of the Neurological Sciences Copyright 2003, Elsevier Science (USA). All rights reserved.
HYPERACTIVITY, also known as hyperkinesis, refers to
excessive or developmentally inappropriate levels of motor or vocal activity. Restlessness, fidgetiness, and generally unnecessary gross motor movements are frequent manifestations. In social interactions with others and self-talk during play and work, excessive speech and commentary may also be present. Hyperactivity is a common, nonspecific symptom of many etiologies. ‘‘Hyper’’ or ‘‘hyperactive’’ have been used as adjectives to describe almost any behavioral symptom in a child. Most commonly, hyperactivity is associated with attention deficit hyperactivity disorder (ADHD). In fact, ‘‘hyperactivity’’ and ‘‘ADHD’’ are often used interchangeably to describe the same disorder. Other less common presentations of hyperactivity may be related to medical conditions, other psychiatric disorders, family and psychosocial problems, speech and language problems, and academic/learning problems. ATTENTION DEFICIT HYPERACTIVITY DISORDER ADHD is one of the most common and controversial neurobehavioral disorders of childhood, affecting 3 or 4% of school-age children. The core features involve a persistent and pervasive pattern of inattention and/or hyperactivity and impulsivity that is more frequent and severe than seen in children of a comparable developmental level. The condition leads to significant functional impairment across multiple domains, including home, school, peer relationships, and work. The manifestations may change depending on the age and developmental level of the individual, but they are generally present by preschool age and may continue through adulthood. Children with ADHD are at high risk for other psychiatric disorders. In fact, coexisting conditions (known as comorbidity) tend to be the rule rather than the exception. As many as two-thirds of elementary school-age children with ADHD have at least one other diagnosable psychiatric disorder. Oppositional defiant disorder and conduct disorder occur in up to half of children with ADHD. Anxiety disorders are present in approximately 25%, with up to one-third experiencing depression. Approximately 20–25% have a learning disorder. The rate of