The removal of an arteriovenous malformation of the brain was probably first successfully accomplished by the French Surgeon Jean Pean in 1897 in an age without operating microscopes, blood transfusion, angiography or critical care support. The development of microneurosurgery through the 1950s to 70s steadily increased the efficacy and safety of treatment and it remains the most consistently effective treatment for suitable AVMs.
Approaching The AVM
A decision to operate will be based on the careful study of a digital subtraction catheter angiogram as well as CT and MR scans. All these will be reviewed by a multidisciplinary team consisting of neurovascular surgeons, interventional
Image Guidance
MR, CT scans and digital subtraction angiogram images are transferred to an image guidance system to assist with navigation during the surgery. Once asleep the topography of the patients head is scanned and referenced to these images so that the position of surgical instruments during the procedure are indicated on these images. This facilitates the planning of surgical incisions ensuring the approach is efficient and that there is minimal disturbance to normal healthy tissue.
Access to the surface of the brain is gained through a door fashioned in the bone which will be securely closed again at the end. This is termed a craniotomy. As the operation progresses the anatomy will start to alter meaning the reference to pre-operative scans becomes less reliable. Real time images may then be conveniently obtained using ultrasound. Doppler ultrasound allows one to image and track the direction of blood flow within blood vessels.
Neurophysiological Monitoring
Once the patient is under anaesthesia small needles may be placed In muscle to record electrical signals during the procedure that may give early warning of nerves cells that are being disturbed- Intraoperative neurophysiological monitoring. This monitoring may be augmented by placing contact electrodes on the surface of the brain later in the surgery or by mapping the cortex close to the AVM to determine if motor function is nearby. It is also useful when cranial nerves such as the facial nerve pass nearby or their blood supply in affected by the arteriovenous shunt.
Extirpation of the Nidus
Extirpation of an AVM refers to its being completely removed from the body. This is usually the correct strategy for arteriovenous malformations.
Under the illumination and magnification afforded by the operating microscope the surgeon begin identifying and occluding the arteries carrying blood into the AVM. The venous drainage of the AVM is preserved until towards the end of the procedure to avoid congestion and swelling. The nidus is carefully separated from the surrounding brain before removal and any bleeding meticulously controlled. Although cross-matching of blood is standard practice, blood transfusion is not required in most cases.
The craniotomy is repaired with titanium discs fixing it firmly in place. An angiogram is then required to confirm complete removal.
Various tools may be deployed during the procedure if helpful. Image navigation is described above. Real-time images of the AVM and surrounding brain may be obtained using ultrasound and occasionally intraoperative CT, MRI or digital subtraction angiography are helpful. Indocyanine-Green videoangiography allows for a real time angiogram to be carried out under microscope illumination but is limited to vessels at the surface of the operative field. The video below shows some of these techniques combining in the removal of an AVM close to primary motor cortex:
In-situ Disconnection
In-situ disconnection is sometimes referred to as pial resection. It offers a curative surgical option for very selected AVMs usually in highly sensitive locations such as the brainstem or spinal cord.
AVMs for which this technique is appropriate are usually relatively small in volume. The strategy is to disconnect arteries entering the nidus and veins exiting without circumferentially dissecting the nidus, leaving it in place. This requires that all the associated arteries and veins need to be accessible on the pial surface of the brain. All of the tools described above may be deployed to assist and we have used it very successfully for such AVMs when other treatments have proven unsuccessful. The video to the right illustrates in-stu disconnection for a thalamic AVM.
Recovery From Surgery
Recovery from surgery following rupture will usually be determined by the impact any initial brain haemorrhage had on the individual. Rehabilitation requirements may need to be factored in as with any other form of stroke.
For the scheduled removal of unruptured AVMs recovery varies according the individual circumstances and your surgeon will be happy to discuss that with you in advance of an admission. The average person spends 3 to 5 days in hospital. A period of recuperation at home before returning to full activity is usually advisable even if you feel at your pre-operative baseline in neurological terms. It is not unusual to feel more easily fatigued for a period of time than one might be used to.
If not carried out intra-operatively a digital subtraction angiogram will be carried out to ensure complete extirpation of the AVM. For adult patients if the angiogram is clear then a follow-up MR is suggested at about one year after which discharge may be offered if all is well. For children who have had AVMs removed a further digital subtraction angiogram is recommended after the age of 18 years. This is because of uncommon but well-documented incidences of AVM recurrence in that age group. The brain continues developing into the early twenties providing an environment where AVM might recur even after documented complete removal in childhood.
Often the wound is closed with adhesive and there are no sutures sitiches removal. Staples may be used for closure and will usually be removed 5-7 days post-operatively. Although such surgery may involve the implantation of clips to secure blood vessels these are MRI compatible and will not set off security alarms.
