What is Adult Aqueductal Stenosis?
Adult Aqueductal Stenosis is a pathological condition of the brain in which there is narrowing of the aqueduct of Sylvius resulting in blockage of the cerebrospinal fluid in the ventricular system. As a result of this blockage, the affected individual can develop hydrocephalus which is quite a serious medical condition.
Anatomically speaking, the aqueduct of Sylvius is a channel connecting the third ventricle to the fourth ventricle in the brain. This area is the narrowest path through which the cerebrospinal fluid passes through in the brain. Due to the small size of the aqueduct even a small obstruction can lead to complete blockage of the cerebrospinal fluid and affect its normal flow through the brain.
As a result of this blockage the volume of the ventricle increases due to accumulation of the cerebrospinal fluid causing increased pressure within the ventricles. This in turn causes increased pressure in the cortex and it gets pushed into the skull. This is what is termed as Adult Aqueductal Stenosis.
An individual may have Adult Aqueductal Stenosis and have no symptoms pertaining to it for years but due to a sudden trauma to the head or an infection may trigger the symptoms and worsen Adult Aqueductal Stenosis.
What are the Causes of Adult Aqueductal Stenosis?
Some of the causes of Adult Aqueductal Stenosis are:
Compression of Aqueduct Due to Tumor: In some cases, there is a brain tumor which develops in the midbrain which as it grows and progresses results in compression of the Aqueduct of Sylvius resulting in complete obstruction of the aqueduct and causing Adult Aqueductal Stenosis.
Narrow Aqueduct: Another cause for Adult Aqueductal Stenosis can be a congenitally narrowed aqueduct of Sylvius. This results in the aqueduct to be easily obstructed with time causing Adult Aqueductal Stenosis
Aqueduct Splitting: In some cases, the aqueduct gets split into multiple small channels. This happens when there is incomplete fusion of the median fissure. These separate channels may eventually come back together and form a single aqueduct or they may remain separated. In both the cases, the normal flow of the cerebrospinal fluid gets affected through the ventricular system ultimately resulting in Adult Aqueductal Stenosis.
Septum Formation: In these cases, there is growth of an abnormal membrane of glial cells that form lower portion of the aqueduct resulting in complete obstruction of the aqueduct causing Adult Aqueductal Stenosis.
Gliosis: This is a condition which causes the aqueduct to get blocked partially. In order for the cerebrospinal fluid to flow through this partially blocked channel the pressure in the third ventricle is increased and also the speed with which the cerebrospinal fluid flows through this region. This results in the epithelial cells within the lining of the ventricle to get damaged causing Adult Aqueductal Stenosis.
There are also certain other medical conditions which can cause Adult Aqueductal Stenosis. The most common among those conditions are X-linked Hydrocephalus which leads to development of Adult Aqueductal Stenosis. It is an inherited condition and the affected individual gets the defaulted gene from the mother which causes Adult Aqueductal Stenosis. In some cases, bacterial meningitis has also shown to cause Adult Aqueductal Stenosis.
What are the Symptoms of Adult Aqueductal Stenosis?
The symptoms of Adult Aqueductal Stenosis are quite similar to that of hydrocephalus and include:
- Persistent headaches
- Nausea with vomiting
- Cognitive problems
- Excessive sleepiness
- Balance and dexterity issues
- Gait abnormalities
- Problems with vision
- In some cases incontinence.
How is Adult Aqueductal Stenosis Treated?
The main aim of treatment of Adult Aqueductal Stenosis is to divert the flow of cerebrospinal fluid away from the blocked aqueduct so that the fluid does not get accumulated and there is smooth flow of the cerebrospinal fluid through the brain.
The treatment also aims at reducing the excessive stress that is being put on the ventricles due to Adult Aqueductal Stenosis. These treatments may not in any way increase the intellectual ability of the patient or improve the quality of life but definitely there will be an improvement of symptoms.
In cases of a brain tumor causing Adult Aqueductal Stenosis then surgical removal of the tumor is done to free up the blocked Aqueduct causing Adult Aqueductal Stenosis and allow free passage to the cerebrospinal fluid.
Apart from this the procedures done for treatment of Adult Aqueductal Stenosis are:
Extracranial Shunt Procedure: This is a procedure which is done to drain the excess cerebrospinal fluid accumulated within the third ventricle. This shunt contains a valve which allows only one way flow of the fluid and the other end of the shunt is connected to the peritoneal cavity where the excess CSF is drained and then reabsorbed by the tissues there.
This is quite a simple procedure and has a very good success rate. This procedure is done endoscopically. The valve present on the shunt is adjusted to regulate the pressure and flow of the cerebrospinal fluid and observe if the symptoms experienced by the patient become less with time post treatment of Adult Aqueductal Stenosis. This may be a straightforward treatment for Adult Aqueductal Stenosis but it carries with it the risk for malfunction of the shunt and the need to revise the shunt after approximately every two years. There are also certain other complications that arise due to this procedure like infections or inappropriate valve pressure which may be potentially serious.
An inappropriate valve pressure may result in more than normal draining or less than normal draining of the cerebrospinal fluid which may lead to potential serious complications.
Endoscopic Third Ventriculostomy: This is the second procedure which is used to treat Adult Aqueductal Stenosis. In this procedure, an incision is made at the bottom of the third ventricle to allow drainage of the excess cerebrospinal fluid.
This is a minimally invasive procedure and also has a high success rate in improving the symptoms of patients suffering from Adult Aqueductal Stenosis. This procedure creates a channel of communication between the third ventricle and the subarachnoid space where the excess cerebrospinal fluid is drained out and resorbed.
The risk of failure of this procedure is quite high during the first two months of the procedure but then the failure rate drastically drops. Also, since there is no device being put inside the patient the chances of infection are also very less and also the risk of device malfunction is not there which is always an issue with the shunt procedure.
This procedure also requires very little hospital stay as this is a minimally invasive procedure. In case if this procedure does not drain the fluid completely then surgeons resort to the shunt procedure to completely drain the fluid from the third ventricle in order to free up the aqueduct and treat Adult Aqueductal Stenosis.
- MedlinePlus (from the National Library of Medicine): https://medlineplus.gov/hydrocephalus.html
- Mayo Clinic: https://www.mayoclinic.org/diseases-conditions/hydrocephalus/symptoms-causes/syc-20373604
- National Institute of Neurological Disorders and Stroke: https://www.ninds.nih.gov/Disorders/All-Disorders/Hydrocephalus-Information-Page
- Johns Hopkins Medicine: https://www.hopkinsmedicine.org/health/conditions-and-diseases/hydrocephalus