What is dural arteriovenous fistula?
Dural arteriovenous fistula or dural fistula is an uncommon disease affecting the blood vessels of the brain.
There will be communication between arteries (that carry oxygen rich blood) and veins (carry deoxygenated blood) on the surface of the brain called dura matter.
In the spinal canal, it will be located on the surface of nerve root. The blood flow will bypass normal capillaries and hence the arterial pressure is directly transmitted into the veins,
which normally has very low pressure. The result would be high flow of blood in the veins, causing its enlargement, or ballooning out. It will increase the pressure on the veins of the brain as well,
which could rupture and cause bleeding. It can also resist normal blood flow from brain into the heart, causing increase in pressure inside the brain. This elevation of pressure can lead to a variety of symptoms.
In the spinal dural fistula, the pressure is transmitted into the veins of spinal cord, affecting its function.
What are the symptoms?
In some, dural fistula can remain without symptoms for a long time. Patients may experience headache, whooshing sound in the ear (tinnitus), fits (seizures),
memory disturbances of varying severity (cognitive impairment). If bleeding occurs, severe headache, vomiting, loss of consciousness or limb paralysis, threat to life could result.
Spinal dural fistula present with slow and progressive weakness of Bothe lower limbs, difficult to pass urine or motion, reduction or loss of sensation such as touch and pain in both limbs. Sudden symptoms listed above can also occur.
How is it investigated?
CT scan or MRI scan is usually obtained as a part of investigation. MRI coupled with angiogram using MRI can reveal the diagnosis and most of the information needed for planning further management. A dye (contrast agent) injected into the veins of the hand (intravenous) is usually not needed for diagnosis, but may be obtained depending on the findings. For evaluation of spinal dural fistula, dye is usually administered in case of diagnostic doubt and to find the exact level of the disease.
Angiogram of the brain or spine is definitive test for diagnosis and plan treatment. The test usually done through a small nick in the groin after giving anesthesia locally. Through the nick a small tube (arterial sheath) is placed, and using long tubes ( catheters), angiogram of the neck and brain vessels are obtained. The procedure is painless and it may take 45 minutes to an hour to complete. Following the procedure, the tube placed in the groin is removed and the hole in the artery is compressed to stop bleeding. Limb movement is restricted to avoid delayed bleeding. Ambulation is possible next day.
For spinal dural fistula, the blood vessels(arteries) supplying the vertebra is obtained. The procedure can be lengthy as there are many arteries that supply the vertebra. In our hospital, we try to a limited angiogram after confirming the possible location through MRI.
The clinical symptoms can be sometimes vague and nonspecific. Since the disease is very uncommon, other likely causes may be present for your symptoms, it is better to consult physician/neurologist for evaluation initially. If imaging investigations confirms or suspects DAVF, further assessment is needed.
What is the treatment?
Effective treatment is possible in most situations. Usually minimally invasive approaches such as endovascular treatment is considered. In endovascular treatment, the procedure is carried out through a small nick in one or both the groins. A short tube (sheath) is placed and through this tube,small and fine tubes are taken into the blood vessel (artery) and the entire network of abnormal vessels are blocked by injecting appropriate drug. The procedure is performed under the guidance of X-rays on an angiography suite. The drug a polymer called ethylene vinyl alcohol (Onyx, Squid etc ) or acrylate (n-butyl cyanoacrylate) called glue and it is injected until entire fistula is disappeared.
Sometimes, the fistula is blocked using coils and this decision is made based on the location of fistula. The number coils needed is variable and depends on the size of the fistula. In case of spinal dural fistula, the fistula is blocked using a drug called glue.
The procedure may take 3-4 hours depending on complexity and it is performed under general anaesthesia. Blood thinning agents may be initiated to prevent clotting of veins in the brain or spinal cord. The patient is discharged after 4-5 days of uneventful procedure.
Follow up and outcome
Routine follow up intervals are 1,3,6 and 12 months and yearly thereafter. Blood thinning agents are needed usually for one month, but it is decided on patient to patient basis. Physiotherapy or speech therapy is advised in case of limb weakness or difficulty in speech respectively.
The outcome is generally good after complete occlusion of the fistula. Follow up imaging using MRI or angiogram would be needed to confirm occlusion or to detect recurrence. The fistula can occur at the same site (recurrence) or different site and it needs further evaluation.
Spinal dural fistula can recur if the drug penetration into the fistula is inadequate. In such situations, if feasible additional embolisation can be attempted. Alternatively, surgical options can be explored.