Hydrocephalus Research – Promise and Innovation
By Tina Popov, Clinical Nurse Specialist/Nurse Practitioner,
Hospital for Sick Children, Division of Neurosurgery
Hydrocephalus is a disorder of the cerebral spinal fluid (CSF) circulation that causes CSF to build up inside the brain. It affects both the pediatric and adult population although the cause of hydrocephalus differs between the two populations. The most common treatment for hydrocephalus has been insertion of a ventriculoperitoneal shunt. This is a small, valved tube tunneled from the ventricle inside the brain, to the peritoneal (abdominal) cavity, traveling under the skin. It provides an alternate path for CSF to flow and be absorbed. Shunts by their nature are imperfect. Complications related to shunt functioning include infection, blockage, and over/under drainage. Exciting advances in new procedures and the development of new technologies to help deal with the shunt’s inadequacies have recently been reported. This article will provide a brief overview of these reports.
Diversionary Procedures: Subgaleal Shunt and Endoscope Third Ventriculostomies
Subgaleal shunts are a temporary diversionary procedure for CSF flow particularly in premature infants with intraventricular hemorrhage. This allows for continuous decompression of the ventricle into the subgaleal space, a potential space between the skull and the skin, which has excellent absorptive capacity. A typical ventricular catheter is placed into the ventricle but is left open to drain into the subgaleal pocket where CSF is reabsorbed. It is only a temporary measure but has been found to be effective for up to 35 days(Tubbs et al. 2003). Most commonly this procedure has been used in the premature infant due to their small size, infection risk from a standard VP shunt, or when the abdomen is not usable due to necrotizing enterocolitis (Savitz et al. 1999). It allows time for the infant to grow, and resolve any serious medical problems. Infection rate for this procedure is low - 5.9 %(Tubbs et al. 2005). Other possible complications include CSF leak, the subgaleal space becoming full and tense, or the subgaleal space resealing. Neurosurgeons are expanding the use of subgaleal shunts for people with hydrocephalus due to intraventricular abscesses and for palliation of hydrocephalus related to malignant tumors (Tubbs et al. 2003).
Endoscopic third ventriculostomy (ETV) is another diversionary procedure used to maintain flow for obstructive hydrocephalus. No implanted hardware is used. Instead an opening is made in the floor of the third ventricle to bypass the block. A small incision is made in the scalp and a small hole is made in the skull. A ventriculoscope (small camera) is used to view the ventricle and the block. A small hole is created in the floor of the third ventricle and dilated. A follow up MRI is done to confirm the CSF flow through the opening. This procedure has been found to be most effective in the treatment of aqueductal stenosis and space occupying lesions of the third ventricle (mainly tumors)(Feng, 2004, Brockmeyer, 1998). Aside from the absence of any implanted hardware, the infection risk is less than that of a traditional VP shunt. However patients who undergo third ventriculostomies have comparable failure rates to that of VP shunts. Children less than one year of age tend to have a higher failure rate, although there is ongoing debate about whether age or the cause of the hydrocephalus is the most important factor for failure. It is imperative that patients with third ventriculostomies have long term follow up. Parents and patients need to be educated and familiar with the signs and symptoms of increased intracranial pressure if the third ventriculostomy fails. These patients treated with a third ventriculostomy do not have the physical reminder of a shunt to alert themselves and other health care professionals of their risk of developing increased intracranial pressure.
Recent Innovation: Antibiotic Impregnated Shunts and EVD’s and Programmable valves
The most distressing complication related to shunt insertions and extraventricular drains is infection. Although the reported shunt infection rates vary, the commonly accepted infection rate is 10 %. Shunt infection causes shunt failure, which puts people at increased risk for morbidity and mortality. Shunt infections have been linked to increases risk of seizures, shunt malfunction, reduced IQ’s and impaired school performance. The literature regarding shunt infection shows that the infection begins at the time of shunt insertion. The most common bacteria causing infection is gram positive cocci. These are bacteria that are normally present on the skin. Antibiotic impregnated catheters were first reported in the 1990’s and the efficacy in the shunted hydrocephalic population in the early 2000’s. These catheters are impregnated with antibiotics, typically rifampin and minocycline, so that organisms will not be able to grow on the shunt tubing. The antibiotics slowly diffuse out of the tubing over a one-month period. Studies have shown that coating of the catheters with antibioitics decreases colonization and catheter related infection at 2 and 6 months(Gavender, 2003, Zambraski, 2003).
Most shunts respond to the differences between the pressure in the ventricular cavity and the cavity to which the shunt drains into. Shunts are generally categorized as low, medium and high pressure depending on the pressure at which they open. Surgeons will choose a shunt most applicable for their patient and presenting symptoms. Unfortunately individual responses to shunt systems cannot always be predicted. Some people may develop problems in regards to under and over drainage and require further surgical intervention. The opening pressure of programmable shunts can be altered using a magnetic field external to the skin, and allows for non invasive management of complications and symptoms of shunt pressure mismatch, particularly shunt dependent patients who are extremely sensitive to pressure changes. It has been shown to be most advantageous for individuals with normal pressure hydrocephalus (Zemack, 1999 and Zemack, 2000). For this population the adjustable valves been said to decrease revision rates and the complications related to over and under drainage. Further patient populations have yet to be defined.
Hydrocephalus Outcome Measure
The majority of the literature in regards to hydrocephalus focuses on diagnosis, management and treatment of the condition. There has been no research looking at the impact of hydrocephalus and quality of life. However, Dr. Abhaya Kulkarni, a staff neurosurgeon at the Hospital for Sick Children has developed the Hydrocephalus Outcome Questionnaire (Kulkarni et al. 2004). This is a tool that measures the health status of children with hydrocephalus. It is an important tool because it recognizes that hydrocephalus involves more than just the shunt and has the potential to affect all aspects of a Child’s health and life. It provides a systematic way of assessing relevant aspects of health in a quick and easy fashion. It contains statements pertaining to all aspects of the child’s life from activity of daily living, socialization, child’s self confidence, and organizational abilities and asks the child to rate each statement according to a defined scale. It truly is a comprehensive measure that will provide a wealth of information and further understanding of the child with hydrocephalus. The tool has been applied to a small group of hydrocephalic children and is presently being tested in a larger population.
Normal Pressure Hydrocephalus Guidelines
Normal Pressure Hydrocephalus (NPH) is a condition that occurs in adults. The concept of NPH was first introduced in the 1960’s. These patients would present with gait disturbances, incontinence and dementia. Depending on who saw the patients the diagnosis and management of this condition was quite controversial. The presenting symptoms were very similar to that of Alzheimer’s and Parkinson’s disease, which potentially caused misdiagnosis of many patients. NPH is a treatable condition. Making the diagnosis is key. In 2005 an independent study group attempted to set out guidelines for the diagnosis and management of idiopathic NPH (Marmou et al. 2005). Based on the present literature they made recommendations regarding the diagnosis, tests required for the diagnosis, surgical management and outcomes of shunting this patient population. These guidelines have provided defined areas where further research needs to be focused in order to provide optimal care to this patient population.
The diagnosis of Hydrocephalus is not new. As illustrated in this article there have been many advances made in the treatment, management and understanding of hydrocephalus. It is a very exciting time. Many clinicians are working hard to better serve the hydrocephalic patient population. As evidenced in the literature presented, the future holds promise. Promise to provide optimal care, management and understanding to patients and families with hydrocephalus.
References for this article are available from SB&H upon request.