Gamma knife treatment of cerebrovascular malformations
Cerebrovascular malformation is a congenital abnormality on cerebral vasculogenesis. According to the pathological changes, it can be divided into four types: cerebral arteriovenous malformation, cavernous hemangioma, venous malformation, and capillary dilation. Among them, AVM is the most common. The main cerebral vascular malformations suitable for radiosurgery treatment are AVM and some cavernous hemangiomas and mixed types.
The lack of capillaries between cerebral arteries and cerebral veins at the lesion site results in direct communication between arteries and veins, forming a short circuit between cerebral arteries and veins and resulting in a series of pathological and cerebral hemodynamic changes, causing recurrent intracerebral spontaneous hemorrhage, convulsions, progressive neurological dysfunction and other clinical manifestations. Also, AVM is one of the most common causes of subarachnoid hemorrhage.
Although surgical resection of AVMs spares a significant proportion of patients from the risk of hemorrhage, a certain number of patients do have AVMs that cannot be completely removed surgically because they are located in important functional areas. Moreover, surgery can cause severe disability or even death. In order to eliminate the risk of preoperative and postoperative AVM bleeding and reduce surgical trauma and mortality, Professor Leksell of Sweden proposed the concept of stereotactic radiosurgery in 1951 based on the principle of stereotactic technique. After that, through more than 10 years of efforts, the world’s first gamma knife was finally developed in 1967, and in 1970, Drs. Steiner and Backlund successfully performed the first gamma knife treatment for an AVM case. As of the end of December 2002, more than 31,924 AVM patients worldwide have been treated with the Gamma Knife with excellent clinical results.
Basic knowledge about the development of AVM
1.Incidence There is no reliable information about the exact incidence and prevalence of AVM. A significant proportion of patients often do not have any clinical symptoms until bleeding or seizures occur. It is estimated that in the United States and Canada, about 500,000 people suffer from AVM, accounting for about 3.4%. In our country, the incidence of AVM is almost the same as intracranial aneurysm, which is much higher than that reported in foreign literature. In China, AVM is likewise one of the most common causes of subarachnoid hemorrhage.
The annual rate of bleeding in AVM and the relationship with lesion size have been reported in the literature, and the relationship between lesion size and bleeding rate has been reported in the literature. A retrospective study of 2262 cases of AVM, of which 1479 had bleeding as the first symptom, with complete data, was conducted. The results showed that the mean annual bleeding rate was 3.4% in the small AVM group (<2 cm3) and 3.7% in the medium to large AVM group (>2 cm3).
3. The relationship between the first bleeding of AVM and age The good age for the first bleeding of AVM is 10-40 years old, especially around 20 years old as the peak. It should be noted that this does not mean that the chance of AVM rupture decreases with age. As age increases, the chance of AVM rupture and bleeding increases accordingly. Therefore, appropriate treatment should be selected as early as possible for diagnosed AVM cases, regardless of age.
4. The relationship between AVM bleeding and gender The risk of AVM bleeding has been reported to be higher in men than in women, up to one times higher than in women. However, recent studies have shown that the peak bleeding period for female AVM patients is during the reproductive age.
Clinical manifestations and diagnosis of AVM
1.Clinical manifestations Except for a few insidious or small AVMs which can have no symptoms and signs, most AVMs will have corresponding clinical manifestations in the process of disease development. Some of the common ones are as follows.
(1) Bleeding The onset is sudden, often occurring during physical activity or mood swings. Patients may present with severe headache, vomiting, and varying degrees of altered consciousness. Hemorrhage can occur repeatedly, up to 10 times.
Epilepsy About 40%-50% of cases will have seizures at different times during the course of the disease, and some also appear as the first symptom. Mostly complex partial seizures are predominant and may also manifest as grand mal seizures. The cause of seizures is mainly related to the ischemia and hypoxia of the brain tissue around the AVM caused by “cerebral blood theft”, which can also be accompanied by convulsions when the AVM bleeds.
Progressive neurological dysfunction About half of the patients will develop progressive neurological deficits as the disease progresses. The manifestations are related to the location and size of AVM, the degree of blood theft, and whether there is bleeding. The common ones are motor or sensory impairment, and some have different degrees and types of aphasia or visual impairment.
④ Headache Chronic headache is a common symptom in AVM patients, with about 60% or more patients having this complaint. The cause of headache may be related to cerebral vasodilatation. If there is an increase in intracranial pressure or bleeding, the headache is aggravated and often accompanied by nausea and vomiting.
(5) Other symptoms Large or giant AVM may have severe blood theft and severe ischemia of the surrounding brain tissue, resulting in degeneration of brain cells or developmental disorders.
2.Diagnosis Young patients with the above symptoms, especially spontaneous SAH or intracerebral hemorrhage, should first think of the possibility of this disease. If the disease is accompanied by limited or generalized seizures, the disease should be considered.
MRI is uniquely superior in the diagnosis of intracranial AVM, showing the lesion itself and its surrounding brain tissue, and reflecting the blood flow within the malformed vessels. Magnetic resonance angiography (MRA) has a good demonstration of some of the larger AVMs. Since the resolution of MRA is still limited, there is still a possibility of missing the diagnosis for smaller AVMs using MRA alone.
Angiography is still the gold standard for AVM diagnosis, especially digital subtraction angiography (DSA) has an important reference value in determining the location, size, blood supplying arteries and draining veins, and whether other vascular lesions (such as aneurysms or venous tumors) are associated with AVM.
Preoperative evaluation
1.The size of AVM Traditional classification methods almost always describe the size of AVM by the maximum or average diameter of AVM. This method can be used as an objective indicator for cases undergoing microsurgery, both for preoperative preparation and postoperative outcome evaluation. In recent years, many scholars have used volume to describe the size of the AVM based on their own data. The volume <2cm3 is self-defined as small AVM, ≥2cm3 (2-50cm3, average 5.8cm3) as medium-sized AVM. Some scholars found that AVM not more than 4cm3, the rate of complete occlusion after 2-3 years of gamma knife treatment is greater than 80%; while the volume of AVM greater than 4cm3, with the increase in volume, the rate of complete occlusion has a tendency to gradually decrease.
2.The site of AVM The different sites of AVM will directly affect the treatment results, and the incidence of complications also differs significantly depending on the site of AVM.
3, AVM imaging typing In addition to the aforementioned international and domestic common classification of AVM, in order to meet the clinical needs and predict the prognosis of radiosurgery on AVM treatment, Inoue et al. divided AVM into cloudy, straight-through and mixed types according to the characteristics of hemodynamic changes based on neuroimaging performance. To compare the efficacy of different types of AVM after gamma knife treatment, it was found that the therapeutic effect of cloudy and homogeneous type AVM was much better than that of straight-through type and non-homogeneous type AVM.
4, the choice of treatment timing Generally speaking, once AVM is detected, appropriate treatment should be selected as early as possible. However, it is worth noting that patients with bleeding as the first symptom account for 67.8% of all AVM cases. This means that most patients have an acute onset, often with significant signs and symptoms due to intracranial hematoma or subarachnoid hemorrhage, and in some cases even life-threatening. Therefore, gamma knife treatment during the acute bleeding period of AVM is generally not recommended. In addition, intracerebral hematoma, intracerebroventricular hematoma, hydrocephalus and vasospasm caused by subarachnoid hemorrhage can cause deformation and displacement of the deformed vascular mass, and even incomplete or no visualization. If gamma knife treatment is used during this period, it may result in incomplete treatment of AVM vascular nests, thus affecting the treatment effect. Most scholars now choose the timing of gamma knife treatment for post-hemorrhagic AVM to be performed after the absorption of the hematoma, that is, 3 months after the hemorrhage. For AVM cases that remain after surgery or after hematoma removal only, gamma knife treatment is usually considered after the complete disappearance of cerebral edema, normal structure reset and systemic status stabilization. In cases of AVM that have been treated with embolization but not completely occluded, if combined treatment with gamma knife is needed, it should be arranged within 3 months after embolization treatment if possible to prevent recanalization of the malformed vessels.
Efficacy and follow-up
1, criteria for AVM occlusion The gold standard for complete occlusion after AVM gamma knife treatment should be assessed based on cerebral angiography at follow-up. The requirements for achieving complete occlusion should meet the following conditions: complete disappearance of AVM aberrant vascular nests, retraction of dilated blood supply arteries and drainage veins to normal diameter, and restoration of normal blood circulation time.
2, efficacy Compared with surgical treatment of AVM, the efficacy of gamma knife treatment of AVM appears as a slow and progressive process of occlusion of the malformed vessels. After the malformed vessel nest is treated by gamma knife, the vessel wall will be proliferated by radiation, the lumen will be progressively narrowed, the blood flow will be slowed down, and eventually the malformed vessel nest will be occluded by the formation of intravascular thrombus. This process can occur 6 months-3 years after gamma knife treatment. Therefore, the assessment of efficacy after Gamma Knife treatment is mostly chosen 2 years after treatment. According to most literature reports, the rate of complete occlusion of AVMs is 80-90% at 3 years after Gamma Knife treatment.