A craniotomy is a door which is fashioned in the skull bone to allow access to the brain. At the end of the procedure this bone is replaced and the wound closed to look natural again. A range of incisions are used and tailored to the needs of the individual case. The access is freuqently of a keyhole type and designed to disturb the brain itself as little as possible. It is also important to make the scar as cosmetically satisfactory as possible. In most cases it will be invisible to an untrained observer.
The aneurysm is secured by placing a metal clip around its base. This permanently prevents blood from entering the aneurysm and removes the risk of bleeding. Modern clips are non-magnetic and come in a range of shapes and sizes to allow complex reconstructions of the blood vessels. They do not have to prevent future MRI scans and will not lead to difficulty when passing through airports.
The surgery is carried out under general anesthesia to provide the controlled operating conditions necessary for operating on such delicate structures. The anaesthetist plays a crucial role in enabling the surgery to be safely conducted and also sees the patient can wake comfortably afterwards.
The decision as to what treatment is offered will be considered by specialist interventional neuroradioologists as well as neurosurgeons. It may be appropriate that you meet both neuroradiologist and neurosurgeon to discuss the pros and cons of each approach and have your questions answered. The details of your operation will be discussed with you in detail by your surgeon and the risks specific to your operation explained. We will endeavour to answer any questions you have and encourage you to ask them.
The risks of surgical repair can include:
- A risk to life usally <1%
- Stroke- the exact effects depending on the blood vessels affected
- Infection - 1% risk approximately and much more rarely requiring surgery to remove infected tissue
The cosmetic appearence after surgery is very important and we strive to make it difficult to detect that surgery has been carried out. The modern repair of aneurysms frequently can be accomplished out through small openings. The precise approach must be tailored to the needs of the indivudal case and your sugeon will be happy to discuss the appearence and location of any scar with you beforehand.
In the photos on the right present an example of what a surgeon sees through the operating microscope as they approach a cerebral aneurysm.
In this case the patient has suffered a subarachnoid haemorrhage from an anterior communicating artery aneurysm. The complex shape of this aneurysm meant microsurgical treatment was favored for it.
There are blood vessels emerging close to the neck of the aneurysm that quickly give origin to small branches which supply oxygen to important parts of the brain. Injuring vessels in this region can affect movement and sensation in the legs, behaviour, speech, memory, concentration and the ability to control body chemistry.
In the photo you wll also notice that part of the aneurysm appears a yellow colour. This is an atherosclerotic plaque. Atherosclerosis is a degenerative process of blood vessels.
The word derives form a Greek word Ather- meaning a type of gruel or porridge. As a result of atherosclerosis blood vessels are hardened by the deposition of plaques made up of fatty material and calcium in their walls. The process is accelerated by smoking.
An incision is made behind the hairline and the scalp reflected forward so that the surgeon has access to the area just above the eye.
A small opening (craniotomy) is fashioned and the blood vessels at the base of the brain approached using a powerful operating microscope. The blood vessels that allow blood into the aneurysm are carefully identified and controlled before approaching the aneurysm itself. Should the aneurysm rupture again the bloodflow may therefore be temporarily arrested while the surgeon completes the repair.
The aneurysm is made secure by placing a small titanium clip across its base. This will effectively prevent it from bleeding again. We use a variety of clips in different shapes and sizes to reconstruct the original blood vessel while attempting to preserving the flow through blood vessels some of which are the thickness of a human hair. Occasionally the wall of the aneurysm may be re-enforced by wrapping the aneurysm in a material designed to form a scar on the aneurysm wall. Typically treated cotton is used for this purpose.
Technology to enhance the safety and efficacy of surgical repairs has developed considerably in recent years. Tiny ultrasound probes allow demonstration of the flow in small vessels in real time. Indocyanine green videoangiography (ICG-VA) is a technology where an intravenous dye administered during surgery may bbe viewed passing through the blood vessel in real time under the operating microscope. Specialist centres for the repair of brain aneurysms will have access to such equipment.
ICG-VA continues to develop and now not only provides information on the patency of vessels but can make comparison between the amount of blood flow at various points in a procedure. Indocyanine green videoangiogram images from the surgery to repair this relatively complex aneurysm are shown below.
The tiny but vital branches arising around the aneurysm are seen to fill with blood and this patient woke up without any adverse consequences. If necessary the clips are replaced and adjusted to optimise the blood flow to the brain. Once surgery is completed the lining of the brain is sutured closed and the craniotomy replaced before closing the wound.
Rarely it is necessary to construct an alternative pathway for blood to reach the brain thus bypassing the aneurysm completely- a cerebrovascular bypass. This is accomplished by using a donor vessel to carry blood from the large arteries in the neck directly to those in the brain. This donor vessel may be an artery from the scalp itself or the radial artery in the arm may be used. Alternatively a vein may be taken from the leg, similar to the the procedure used in coronary artery bypass grafting.
For very complex or giant aneurysms microsurgical bypass techniques to reconstruct the circulation may be combined with endovascular techniques to then occlude the aneurysm.
Bypass techniques are also used to increase blood flow to the brain in conditions such as Moyamoya disease where the main arteries delivering blood to the brain have become narrowed.