Preparation for Surgery
Surgery may be combined with other therapies, most commonly endovascular treatment of the malformation but radiosurgery has also been used to target very large AVMs to render them safer surgical prospects. Endovascular embolisation is described in more detail elsewhere on the site. It use as an adjunct to surgery is usually reserved for larger lesions with a high blood flow.
It is usually the case that a patient undergoing microsurgery for an AVM will undego a pre-operative CT or MR scan which is fed into a computer guidance system that helps to precisely direct the surgeon to the area in the brain being targetted. Advanced MR neuroimaging techniques can now estimate the projections of whitematter pathways within the brain and how they relate to the AVM. During the procedure various tools may be deployed to demonstrate the architecture of the malformation and ultimately to help demonstrate that the malformation has been completely removed. These tools include ultrasound scans of the brain, indocyanine green videoangiography and intraoperative digital subtraction angiography.
Admission to the intensive care or high dependency units will be planned ahead of surgery. Larger AVMs will sometimes require long procedures and during general anaesthesia great care is given to control of the patients blood pressure and this control is maintained on the intensive care unit in the immediate post-operative period. Anti-epileptic medication may be prescribed for a period of time after the surgery even if seizures have not occurred up to that point. Blood will be taken for cross matching in case blood transfusion is required during the operation as is occasionally required.
The surgeon will discuss the risks of the procedure and try to address any questions a patient or their carers have before . They will complete a consent form with you documenting the reasons the procedure is being undertaken, the estimated risks of the operation and outlining what the folow up will be afterwards. Signing of the form is a necessary formality which does not mean more questions cannot be posed or indeed that a patient may not change their mind. You will be provided a copy of the consent form and with copies of clinical correspondence.
During the Operation
The surgical strategy is to sequentially disconnect the arteries supplying blood to the nidus of the AVM. Gradually the blood flow is abolished throughout the nidus and the veins draining blood away from it collapse. This is illustrated in the series of images on the right. This patient has an arteriovenous malformation in the temporal lobe. The nidus is gently dissected away from the normal cerebral cortex. The arteries are then sequentially disconnected. There are a few large arteries which are closed with the aid of clips and many tiny blood vessels joining the nidus from the surrounding brain. Not until all arteries are disconnected do the nidus, and the veins draining blood from it, change from engorged pink vessels to soft, blue ones. This indicates the abnormal connection from arterial circulation to venous has been abolished and that the nidus may be safely lifted away from the brain with division of the last vein. A further angiogram is carried out to confirm complete removal of the AVM.
For large, AVMs with a high blood flow routine admission to high dependency or intensive care per-operatively is arranged. Very strict control is maintained over the patients blood pressure until an angiogram has confirmed the absence of any residual arteriovenous shunting of blood. The successful treatment of larger AVMs involves multidisciplinary, staged procedures on occasion. The various members of the multidiciplinary team will be happy to answer questions on its various parts. Successful treatment of larger AVMs involves multidiciplinary, staged procedures on occasion. The various members of the multidiciplinary team will be happy to answer questions on its various parts.