Operations for arterial aneurysms and arteriovenous malformations of the brain

Surgical treatment of arterial aneurysms

There are two fundamentally different approaches to surgical treatment of aneurysms:

1. Traditional intracranial access with isolation of the carrier arteries and exclusion of the aneurysm from the general blood flow by clipping its neck or forced occlusion of the aneurysm-carrying artery (trapping). In rare, particularly complex cases, wrapping of the aneurysmal sac with muscle or special synthetic materials (surgigel, tachocomb) is used.
2. Endovascular method, the essence of which is to perform all manipulations aimed at turning off the aneurysm inside the vessel under the control of X-ray images. Permanent occlusion of the aneurysm is achieved by introducing either a detachable balloon catheter or special microspirals (coils).

The intracranial method of aneurysm exclusion is technically more complex and traumatic for the patient, but in terms of reliability it occupies a leading place.

The operation involves performing an osteoplastic craniotomy, wide opening of the basal cisterns with aspiration of cerebrospinal fluid, which allows to reduce the brain in volume and improve access to the arteries of the base of the brain. Using an operating microscope and microsurgical equipment, the carrier artery is first isolated, then one or two efferent arteries are isolated. This is done to be able to apply temporary clips in case of intraoperative rupture of the aneurysm. The main stage is the isolation of the aneurysm neck. The body of the aneurysm, with the exception of giant ones, is usually not excised. It is enough to apply a clip to the neck of the aneurysm, reliably disconnecting it from the blood flow. Self-compressing removable spring clips developed in the 70s of the 20th century by S. Drake and M. Yasargil are used all over the world.

Intracranial surgeries can be reconstructive and deconstructive. All surgeons strive to perform reconstructive surgeries that allow the aneurysm to be switched off while preserving all the afferent and efferent arteries. In cases where, due to the peculiarities of the anatomical location and shape of the aneurysmal sac, it is impossible to switch it off reconstructively, trapping is performed, i.e. switching off the aneurysm together with the carrying artery. Most often, such an operation ends with a cerebral infarction and the development of a severe neurological deficit in the patient. Sometimes, in such situations, neurosurgeons prefer not to switch off the artery, but to wrap the aneurysm with muscle or special synthetic materials in order to strengthen the wall from the outside with the developing fibrosis in response to the foreign body.

Endovascular surgeries are performed by introducing a detachable balloon catheter into the aneurysm cavity through the common carotid artery (aneurysms of the carotid basin) or through the femoral artery (aneurysms of the vertebrobasilar basin). Special balloon catheters designed by F.A. Serbinenko are used to exclude the aneurysm from the bloodstream. The balloon is inserted into the aneurysm cavity under X-ray control and filled with a fast-hardening silicone mass. The volume of silicone injected must exactly match the volume of the internal cavity of the aneurysm. Exceeding this volume may lead to rupture of the aneurysmal sac. Injecting a smaller volume will not ensure reliable occlusion of the aneurysm. In some cases, it is not possible to exclude the aneurysm with a balloon while maintaining the patency of the arteries. In these cases, it is necessary to sacrifice the carrier artery, excluding it together with the aneurysm. Before turning off the aneurysm, a trial occlusion is performed by introducing a saline solution into the balloon. If the neurological deficit does not worsen within 25-30 minutes, the balloon is filled with silicone and left permanently in the cavity of the parent artery, turning it off together with the aneurysm. In the last decade, detachable microspirals have replaced balloons in most clinics. The most progressive product of new technologies has become electrolytically separable platinum microspirals. By August 2000, more than 60,000 patients worldwide had been operated on using this method. The probability of performing a reconstructive operation using a spiral is significantly higher, and the probability of intraoperative rupture of the aneurysm is lower than with a balloon.

Assessing both methods, it is necessary to note that the intracranial method has been the leading method to date. And this method, as more reliable and controllable, should be used for most operations. Only those aneurysms whose direct exclusion is associated with significant brain trauma should be subjected to endovascular operations.

Features of surgical technique in the extirpation of arteriovenous malformations

Extirpation, or removal of arteriovenous malformation, is one of the most complex operations in neurosurgery. It requires not only high surgical technique of the surgeon and good technical equipment of the operating room (microscope, microinstruments), but also knowledge of the features of extirpation. AVM cannot be treated as a tumor, it cannot be removed in parts, it is necessary to accurately distinguish the afferent arterial vessels from the draining veins, be able to consistently isolate, coagulate and cross them. Bleeding that occurs during the operation from the AVM vessels can confuse an untrained surgeon, and any panic during such an operation is fraught with serious consequences, including death. Therefore, a surgeon going to such a complex operation needs to know about all its features, possible complications and methods of dealing with them.

The first condition is that you cannot go to surgery without having a full idea of the size of the malformation, its location and all sources of blood supply. A mistake can lead to the surgeon inevitably bumping into the walls of the AVM during the surgery and damaging them. An insufficient trepanation window greatly complicates the surgeon's actions and allows for an atraumatically performed surgery. The trepanation window should be 1.5-2 times larger than the maximum size of the AVM.

The dura mater is opened with an arc-shaped incision, bordering the AVM on all sides and exceeding its dimensions by 1.5-2 cm. In case of convexital location of the AVM, it is very important not to damage the draining veins, which often outline and shine through the thinned membrane. Turning back the dura mater is also an important and responsible moment. On the one hand, the membrane can be soldered to the draining veins and vessels of the AVM, and on the other hand, the vessels of the membrane can participate in the blood supply of the AVM. This stage should be performed using optics and, if it is not possible to easily separate the membrane from the AVM vessels, it should be cut off with a bordering incision and left.

It is important to correctly assess the borders of the malformation and the arachnoid and pia mater are coagulated and dissected along the perimeter above the expected border. The draining veins are preserved. The main feeding arteries are located in the subarachnoid cisterns or deep in the grooves, so they can be isolated with minimal trauma.

When determining the sources of blood supply, it is necessary to identify the main and secondary ones. The arteriovenous malformation should be isolated near the main sources of blood supply, but the draining veins should not be damaged or disconnected. In AVM, there is a certain balance between the inflowing and outflowing blood, the slightest obstruction of the blood outflow inevitably leads to a sharp increase in the volume of the AVM, overstretching of its venous vessels and simultaneous rupture of several of them. If not the superficial vessels are damaged, but the intracerebral ones, then the blood rushes into the brain and subarachnoid spaces, causing a sharp prolapse of the brain. To avoid this, you should know the following rules:

1. The AVM and the afferent arteries are isolated at a distance from the main draining veins.
2. If the afferent arteries and draining veins are located close to each other, using microtechnique, the draining vein is isolated and fenced off with cotton strips.
3. If the vein wall is damaged during the extraction and severe bleeding occurs, it cannot be wedged or coagulated. It is necessary to apply a cotton strip soaked in hydrogen peroxide to the rupture site and press it with a spatula so that the bleeding decreases, but the blood flow through the vein is maintained.
4. Coagulation or clipping of the vein will reduce the blood outflow and lead to the complications described above, so it is better to wait longer and achieve complete hemostasis without turning off the vein. Even if the blood leaks past the padded jacket at first, do not rush. After 5-10 minutes, the bleeding usually stops. It is even better to perform hemostasis with a hemostatic sponge such as "Spongostan".
5. Before coagulating the afferent artery, it is necessary to make sure that it is not a vein, since the vein also carries scarlet blood. But since the venous wall is thinner than the arterial wall, it is also redder in color than the artery. Sometimes, a turbulent blood flow through it is visible under a microscope. Arteries have a duller pink color. During coagulation with a weak current, the venous wall contracts easily, and a large artery is difficult to coagulate. But this is not enough to accurately identify the artery and vein. In case of doubt, a removable vascular clip can be placed on the suspected artery. If there is no reaction, then it is an arterial vessel. If, literally before your eyes, the AVM begins to increase in volume and the pulsation increases, then a vein was clipped, and the clip should be removed immediately.
6. The malformation must be isolated from all sides, but first of all from the side of the blood supply sources. In this case, the brain tissue adjacent to the body of the malformation is resected with a fine suction, but in such a way as not to injure its vessels. All secondary arteries and veins encountered along the way are successively coagulated and crossed. There may be several dozen such vessels. If bleeding occurs not from the body of the malformation, but from the afferent or efferent vessels up to 1.5-2 mm in diameter, they should be coagulated with bipolar tweezers.
7. As the main feeding arteries are turned off, the malformation may decrease in size and become darker in color. However, one should not rest until the AVM is completely removed, as the secondary arteries that can cause serious bleeding if the malformation wall is damaged are not yet turned off.
8. When removing an AVM, the surgeon may leave its areas in the brain matter unnoticed. This is especially dangerous if the arterial inflow to them is preserved, but the outflow is impaired. In these cases, immediately after the removal of the arteriovenous malformation, the brain may begin to “swell” and bleed from the walls of the brain wound. There may be several sources of bleeding. Bleeding areas should be covered with cotton strips, lightly pressed with a spatula and quickly begin to resect the brain matter with suction around each source of bleeding, and, having found the leading arterial vessel, coagulate or clip it.
9. Before closing the wound, it is necessary to ensure the reliability of hemostasis, for which the anesthesiologist artificially creates moderate arterial hypertension. It is impossible to suture the membrane against the background of low arterial pressure. A number of authors try to explain the acute swelling of the brain after AVM removal by its acute hyperemia, due to the elimination of the source of "radiation". This is especially dangerous in cases where the main afferent arteries are more than 8 cm long. However, Yashargil is convinced that acute "swelling" is only a consequence of non-radical extirpation of AVM.
10. If, despite all precautions, you still prematurely turn off the draining vein and the AVM has increased in volume, you should urgently reduce the arterial pressure to 70-80 mm Hg. This can prevent multiple ruptures of its vessels and allow you to find the feeding arteries and turn them off sequentially.
11. If multiple ruptures of AVM vessels do occur, do not rush to coagulate them, this will only increase bleeding. Press them with cotton strips soaked in hydrogen peroxide, and as quickly as possible look for feeding arteries and turn them off. Only such tactics will save the patient's life.
12. If the surgeon overestimates his abilities and during the operation realizes that he will not be able to perform a radical extirpation, he can stop the operation if:
    • a) the outflow from the AVM is not impaired;
    • b) arterial flow to it is reduced;
    • c) hemostasis is ideal even against the background of artificial arterial hypertension.
13. Partial removal of an arteriovenous malformation should not be attempted intentionally.
14. When going for surgery, you should always think about possible blood transfusion. The larger the size of the AVM, the more blood will be needed during the surgery.
15. Blood loss of up to 1 liter can be compensated by plasma-substituting solutions, but large blood loss requires blood transfusion. We recommend taking 200 ml of blood from the patient 1-2 times before the operation and reinfusing during the operation. This allows in most cases to do without donor blood.
16. The radicality of the AVM extirpation is indicated by a change in the color of all draining veins: they become dark cherry in color. The preservation of at least one bright red vein indicates that the operation is not radical.

Along with radical extirpation of arteriovenous malformation, in recent years the endovascular method of AVM occlusion has been introduced. For this purpose, various thrombosing substances are introduced into the malformation vessels. Previously, these were compositions based on adhesive compounds - cyanoacrylates. Now the most promising is embolin, which is a 10% solution of low-molecular linear polyurethane in anhydrous dimethyl sulfoxide. Embolin, when in contact with blood, causes rapid development of a thrombus of fibril-elastic consistency. In most cases, AVM can be excluded subtotally (90-95%), which is sufficient to prevent its repeated rupture. Endovascular occlusion is most indicated for patients with AVM of the basal ganglia and pons, as well as for giant AVMs of any localization. In some cases, endovascular embolization of AVM is performed as the first stage before its radical extirpation. This achieves a reduction in blood loss during open surgery.

Small and medium-sized malformations can also be coagulated with a directed proton beam, but this method can only be used in clinics equipped with a linear accelerator. For this reason, the method is not yet widely used.

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