Surgical Correction of Hydrocephalus

The most common surgery for the treatment of hydrocephalus is the insertion of a shunt - a device that diverts fluid from the brain into the abdominal cavity where it is safely absorbed into the blood stream. Though a shunt may be inserted in infants, children and adults, the procedure is essentially the same regardless of the size of the patient. Anatomy and Physiology  In a normal brain there are four fluid filled spaces called ventricles (Figure 1) There are two large ventricles (lateral ventricles) located on either side of the brain Two other ventricles (the third and fourth ventricles) are placed along the midline Within the ventricles are tufts of vascular tissue called the choroid plexus. As blood flows through the choroid plexus it distills a clear watery fluid into the ventricles called cerebrospinal fluid, or CSF CSF flows from the ventricles towards the surface of the brain and returns to the blood (Figure 2) From the lateral ventricles the CSF flows into the centrally placed third ventricle and then through a narrow channel called the aqueduct, into the fourth ventricle CSF then flows over the surface of the brain in the subarachnoid space, an area between the brain and the membrane (dura) lining the inside of the skull  The CSF then returns to the blood by passing into the large veins that drain the brain called sinuses Figure 1 - Anatomy of the ventricles. Figure 2 - CSF flows from the lateral ventricles into the third ventricle, through the aqueduct of Sylvius, to the fourth ventricle and finally over the surface of the brain to the dural sinuses where it is absorbed into the blood. Pathology Hydrocephalus occurs when there is an obstruction to the flow of CSF resulting in pressure on the brain and causing the ventricles to enlarge In infants and young children, the expanding brain causes the skull to enlarge. In older children and adults, the skull, which is now fixed in size, does not enlarge  The causes of hydrocephalus are numerous and can include: Birth defects Hemorrhage  Infection Tumor  A block of the aqueduct History and Examination The findings of hydrocephalus are age related. In infants:  Enlarged head and prominent scalp veins. Sometimes serial measurements (measurements of the head over a period of days or months that record growth) may be necessary  The soft spot on the head may be tense and the spaces between the bones of the head may be spread  An associated birth defect such as a myelomeningocoele (an abnormality seen over the spine)  Abnormal skull shape  The child may be listless and feed poorly In the older child and adult, enlargement of the head is usually not seen. When hydrocephalus develops rapidly there may be:  Lethargy, nausea and vomiting associated with headaches  Difficulty with thinking, loss of memory or confusion  Difficulty in walking  Loss of bowel or bladder control Diagnostic Tests In the infant, enlargement of the ventricles may be diagnosed by ultrasound through the soft spot (Figure 3 and 4) Computerized Tomography (CT) or Magnetic Resonance Imaging (MRI) can make the diagnosis when the soft spot is closed (Figure 5 and 6) The CT or MRI films show the enlarged ventricles and frequently point out the cause of the obstruction to the flow of CSF  Under certain circumstances, the doctor may order special tests that are used more infrequently such as an isotope cisternogram or intracranial pressure monitoring Figure 3 - Normal infant ultrasound of the head. Courtesy J. Bender, MD Figure 4 - Ultrasound showing hydrocephalus in an infant. Note the large ventricles compared to the normal. Figure 5 - Normal CT scan of the head in an adult. Figure 6 - CT scan of an adult with Normal Pressure Hydrocephalus. Alternative Therapy Hydrocephalus may not have to be treated if the flow of CSF is restored on its own and there are no symptoms or enlarging ventricles  However, when there are symptoms or enlarging ventricles, hydrocephalus must be treated in order to prevent further deterioration of the patient  Rarely, medication that affects the formation of CSF or a diuretic may be of benefit Surgical Treatment The treatment of hydrocephalus consists of creating a connection between the enlarged ventricles or the spinal subarachnoid space and a place where cerebrospinal fluid can be returned to the bloodstream. Ventriculo-peritoneal (VP) Shunt. This is the most common procedure for the treatment of hydrocephalus. CSF is channeled through an implant called a shunt, which directs flow of CSF from a lateral or third ventricle into the abdominal cavity where it is absorbed into the bloodstream. (Figure 7) The basic ventriculo-peritoneal shunt consists of three components:  Ventricular catheter- A small tube made of silicone rubber, a material well tolerated by the body, with several small holes at its tip. It is placed through the brain into the ventricle  Valve- A special mechanism for regulating the flow of CSF through the shunt that is designed to simulate normal CSF drainage. The valve is either made of silicone rubber or covered with silicone rubber. The valve sits between the skull and scalp  Peritoneal (Abdominal) catheter- This catheter is also made of silicone rubber. It leads from the valve to the abdominal cavity Figure 7 - A ventriculo-peritoneal shunt between the lateral ventricle and peritoneum. At times a shunt may overdrain and produce too low an intracranial pressure. A siphon limiting device or specially designed valves may be added to minimize this excess drainage The procedure is as follows: An incision is made in the scalp Then a small hole is made in the skull. The position of the hole in the skull may vary depending on the choice of the surgeon The catheter is then inserted through the brain tissue into the enlarged lateral ventricle  A valve is attached to the ventricular catheter. The valve lies between the skull and scalp The peritoneal (abdominal) catheter is then inserted beneath the skin of the neck, chest and abdomen and attached to the valve. Finally, the peritoneal catheter is inserted into the abdominal cavity that surrounds the stomach and bowel  CSF entering the shunt in the ventricle is conducted through the regulating valve and passes into the abdominal cavity where the fluid is absorbed back into the bloodstream  Animation An animation showing the placement of a ventriculo-peritoneal shunt. Click on Image Ventriculo-atrial (VA) Shunt This shunt channels CSF from the ventricle of the brain to the right atrium of the heart (The chamber of the heart that collects blood from the body) The ventricular catheter and valve are placed as in a VP shunt  The catheter from the valve is inserted into the jugular vein in the neck and guided into the right atrium of the heart (the chamber that collects blood from the body) Lumbo-peritoneal (LP) Shunt  The shunt is placed between the lumbar (spinal) subarachnoid space, which contains the nerve roots to the legs, and the peritoneum  The shunt is composed of a thin silicone rubber catheter. Usually the proximal end of the catheter is inserted into the spine through a needle The catheter is tunneled beneath the skin to the abdomen and then inserted into the peritoneal cavity  A valve may or may not be used Ventriculo-cisternal shunt (Torkildsen procedure) This procedure can only be used when there is a block between the ventricles and the subarachnoid space around the brain A burr hole is placed in the parietal area, the dura opened and one end of a silicone catheter is inserted through the brain into the lateral ventricle (Figure 9) The other end of the catheter is passed beneath the scalp to the junction of the brain and spinal cord. Some bone is removed from the lower aspect of the occipital bone. The suboccipital dura is opened and the lower end of the catheter is inserted into subarachnoid space around the junction of the brainstem and spinal cord Though more difficult to insert this procedure avoids the complications of shunts related to overdrainage Figure 9 - Ventriculo-cisternal (Torkildsen) shunt. A catheter is placed from the lateral ventricle into the subarachnoid space at the back of the skull. © T. Graves Third Ventriculostomy This procedure does not insert a shunt. It can only be used when there is a block between the ventricles and the subarachnoid space around the brain A new channel is created between the ventricles and the subarachnoid space restoring the flow of CSF  An endoscope, an optically guided tube through which the surgeon can operate, is inserted into a dilated lateral ventricle and guided to the floor of the dilated third ventricle  The thinned out floor is punctured producing a communication between the third ventricle and the subarachnoid space This procedure, when successful, obviates the necessity of a shunt and thus the problems that may occur with shunt failure Frames from video of third ventriculostomy procedure. Left, thinned out floor of third ventricle just in front of two small bumps of tissue in the hypothalamus called the mammillary bodies. Middle, A small tool is passed through the thinned floor into the underlying subarachnoid space. Right, hole produced in the floor of the third ventricle. Courtesy R. Jones, M.D Ventriculo-subgaleal shunt This shunt connects the ventricles to the subgaleal space - the space between the scalp and the skull This shunt is most frequently used as a temporizing measure in the premature infant with hydrocephalus caused by a hemorrhage within the ventricle. It usually functions for only 4 - 6 weeks  The shunt allows blood to clear from the ventricles before a permanent shunt is inserted, since shunts tend to malfunction in the presence of blood. It also allows the premature infant to mature A catheter is placed in the ventricle and connected to a low pressure valve. The valve is placed under the scalp and the incision closed. The shunt is allowed to drain under the scalp. Fluid under the scalp indicates the shunt is functioning  Subdural-peritoneal shunt This is a specialized shunt that is not used for the treatment of hydrocephalus. It is used for the treatment of subdural hygroma or liquefied subdural hematoma. These are collections of fluid between the brain and the dura that may increase in size and cause pressure on the brain (Figure 10) A catheter is placed through the skull and dura into the hygroma. This is attached to a low pressure valve and peritoneal catheter The hygroma gradually drains into the peritoneal cavity thus allowing the brain to expand into its normal position beneath the dura Figure 10 - CT scan of an elderly male with a liquefied subdural hematoma. Complications No surgery is absolutely safe and free of complications. Some of the possible complications of shunt placement are:  Effects of anesthesia,  Bleeding or hemorrhage  Infection  Injury to the brain causing paralysis, loss of sensation, speech loss or abnormality, visual loss or disturbance, seizures, memory loss or other loss of brain function  Malfunction of the shunt including obstruction, separation of the catheters, valve failure or failure of any of the shunt components  Fracture of the peritoneal catheter with obstruction of shunt and lower end of the catheter falling loose into the peritoneal cavity. The loose catheter is usually removed at time of shunt revision. (Figure 11) Overdrainage of cerebrospinal fluid causing headaches or shunt malfunction  Formation of blood clots over the brain surface  A ventriculo-peritoneal, lumbo-peritoneal or subdural-peritoneal shunt may cause abdominal complications including hernia, fluid collection in the abdomen, bowel twisting or perforation of bowel or bladder  A ventriculo-atrial shunt may cause blood clots in the heart and lungs or infection of the blood, heart or kidneys  A lumbo-peritoneal shunt may cause irritation of the nerve roots in the spinal canal A third ventriculostomy may cause injury to the brain around the third ventricle. Occasionally, injury to the basilar artery may occur with severe hemorrhage and even death  Figure 11a - Lower end of peritoneal catheter loose in abdomen as seen through laparoscope.  Figure 11b - grasping forceps removing catheter. Figure 11c - New catheter inserted through trocar into peritoneal cavity. Care After Surgery After discharge, instructions are given for home care In particular, the doctor should be called if there is:  Any redness or discharge from the wound Fever Weakness Change in level of consciousness  Persistent headache or  Any other symptom that concerns the patient or caregiver  Note: You must remember that hydrocephalus is a life-long disease and a shunt is a mechanical device that is subject to failure at any time. It is therefore, imperative to maintain continued follow-ups with your doctor.