Etiology and pathology
Intracranial vascular malformation is a developmental malformation of the intracranial vascular bed; it manifests as an abnormal increase in blood vessels in a region of the skull.
Currently, they are generally classified into 4 types.
1, arteriovenous malformation ;
2.Capillary dilation;
3.Venous hemangioma and varicose vein Z
4, cavernous hemangioma. Among them, arteriovenous malformations are the most common, accounting for more than half of them. This section describes the arteriovenous malformations. Cerebral arteriovenous malformations are mostly seen in young people, with the highest incidence in young adults between the ages of 20 and 40, and are more common in men than women. In the embryonic period, if some factors affect the normal development of the primitive cerebrovascular network, the capillaries are incomplete and the arterioles and veins are directly connected to form a short circuit, which develops into cerebral arteriovenous malformation.
Clinical manifestations
Cerebral arteriovenous malformations are associated with no discomfort or occasional seizures. The most common symptom of cerebral arteriovenous malformation is the rupture and bleeding of the malformed blood vessel, forming an intracerebral hematoma or subarachnoid hemorrhage. Sudden onset of severe headache, stiff neck, accompanied by nausea, vomiting and some degree of impaired consciousness, lesions and hemorrhage at different sites, localization signs such as hemiparesis, hemianopia, aphasia and hemianopic sensory impairment and oculomotor disorders, ataxia and other manifestations of posterior cranial fossa arteriovenous hemorrhage. This is followed by epilepsy and headache.
Imaging manifestations
1.Brain arteriogram
Cerebral arteriovenous malformation has the following typical manifestations.
(1) Showing malformed vessels. This is a characteristic manifestation of a mass of tortuous and dilated vessels with similar diameter entangled with each other. The extent of the malformation can be as small as a fingernail or as large as the palm of a hand, mostly in the cerebral hemisphere cortex.
(2) Abnormally large feeding arteries and draining veins with accelerated local circulation. This is a manifestation of local blood flow short circuit.
(3) Blood flow shunt phenomenon: the contrast agent flows into the vein with the blood flow through the short circuit of the malformed vessel, so that the malformed part of the vessel is very clearly visualized due to the increased blood flow.
(4) The performance of hematoma: The main performance of hematoma is local occupying sign when the blood vessel ruptures and bleeds to cause intracerebral hematoma, a brain arteriovenous malformation without hematoma, cerebral vessels do not appear occupying sign, cerebral vessels are not displaced.
2.CT performance.
There are more typical CT manifestations before the cerebral arteriovenous malformation is ruptured and bleeding. In plain scan, focal high-low or low-mixed density shadow is seen in the form of speckles, clusters or cords with unclear edges. The high-density shadow is due to focal gliosis, thrombus, calcification, new hemorrhage or slow blood flow within the malformation and iron-containing hemosiderin deposition, while the low-density shadow is due to small infarcts or old hemorrhage with limited cerebral atrophy around the lesion, no obvious occupying effect and no peripheral cerebral edema. In some patients, arteriovenous malformations cannot be detected on plain scan, but contrast is injected to reveal the lesion. After contrast injection, the arteriovenous malformations in the brain show mass-like enhancement, and even tortuous vascular shadow, blood supply arteries and draining veins are visible.
In post-hemorrhagic cerebral arteriovenous malformations, intracerebral hematomas, subarachnoid and ventricular system hemorrhages are seen. Depending on the duration of the hemorrhage, high-density, mixed-density and low-density shadows are seen, and the hematoma is surrounded by a low-density edema area. There are also occupational effects such as ventricular compression and deformation and midline shift. After contrast injection, some of the hematoma edges may show tortuous reinforcement of malformed vessels, while the mixed dense shadow hematoma often has ring reinforcement.
3.MRI performance
The diagnostic value of MRI is greater than that of CT in the diagnosis of cerebral arteriovenous malformations, especially in posterior cranial fossa lesions, so MRI is the preferred imaging method when patients are suspected of having cerebrovascular malformations.
(1) The vascular component of cerebral arteriovenous malformation is shown as a signal-free flow-void vascular shadow distributed in clusters and networks. The blood supplying arteries appear as low signal or no signal on T1 and T2-weighted images due to flow-void phenomenon. The draining veins show low signal on T1-weighted images and high signal on T2-weighted images due to slow flow. Calcification of the vessel appears as a low or no signal dark area. The thrombus in arteriovenous malformation shows low signal interspersed with iso-signal or high signal interspersed with high signal within high signal and low signal in both T1 and T2-weighted images.
(2) Hematoma formed by bleeding from arteriovenous malformation shows T1 and T2-weighted image changes similar to other causes of hematoma. In the subacute stage, the hematoma is high signal on both T1 and T2-weighted images. With time, the hematoma gradually changes to iso- or low-signal on T1-weighted images and remains high signal on T2-weighted images.
Surgical treatment
Indications
1.Patients with one of the following conditions, and the angiography determines that the malformed vessels can be removed.
(1) History of spontaneous subarachnoid hemorrhage.
(2) Frequent epilepsy with poor results of drug therapy.
(3) Those with symptoms of progressive localized neurological damage or mental retardation (blood-stealing syndrome).
(4) Those with combined intracranial hematoma or intracranial hypertension.
2. Those who can be treated by the following surgical methods.
(1) Hematoma removal, applicable to patients with hematoma after bleeding. If the patient is in good condition, cerebral angiography can be performed before surgery, and malformation angiography can be performed at the same time. If the patient is in critical condition, the hematoma can be removed first, and cerebral angiography can be performed after recovery, and then secondary surgery can be performed for lesion removal.
(2) Deformed vascular resection is suitable for those who have had bleeding, especially repeated bleeding; those who have progressive cerebral dysfunction such as progressive light hemiparesis and those who have intractable seizures that are difficult to control by medication due to cerebral blood theft.
(3) Ligation of the supply artery is suitable for deep lesions involving important structures such as the brainstem and deep large veins. However, there are multiple supply arteries, and ligation of only 1-2 of them may not be therapeutic.
(4) Artificial embolization, which is suitable for those with extensive or multiple lesions that cannot be resected or used as a preparatory procedure before resection of extensive vascular malformations.
In this article, arteriovenous malformation resection is used as an example.
Contraindications
All are relative contraindications, with the improvement of technology, some of these cases can still be treated surgically.
1, arteriovenous malformations in the deep brain, internal capsule, basal ganglia, brainstem, etc.
2.Widespread or multiple arteriovenous malformations.
3.Asymptomatic people.
4.Older people over 60 years old with serious diseases of heart, kidney and respiratory system.
Pre-operative preparation
1.Because of the possibility of multiple, preoperative whole brain angiography or bilateral carotid angiography should be made, or vertebral arteriogram should be added according to the presumed site of malformed vessels. The typical cerebral arteriovenous malformation includes three parts: supply artery, malformation foci and drainage veins. The source of the supply artery and the direction of the draining vein, the site and scope of the malformation, the presence of hematoma and other comorbidities, as well as the presence of other malformations in the patient, should be identified by the angiogram in order to formulate a perfect surgical plan, which is also the key to successful surgery.
2, for complex arteriovenous malformation, in order to deal with intraoperative hemorrhage, blood preparation should be sufficient (1500-2000ml of blood should be prepared for larger cerebral arteriovenous malformation), hemostatic instruments and drugs should also be complete, and two sets of suction devices can be prepared. Preoperatively, two intravenous infusions should be done, and arterial transfusion instruments should be prepared. Give drugs according to general anesthesia before surgery.
3, if available, the operation should be performed on the operating table where imaging is possible, so that intraoperative imaging can be performed if necessary.
Anesthesia
If the lesion is shallow and small, it is estimated that it is easy to handle intraoperatively, local anesthesia can be used. For more complex cerebral arteriovenous malformations, surgery is best performed under general anesthesia. For complex and difficult cerebral arteriovenous malformations, the pressure can be lowered at the beginning when the malformed vessels are revealed, and the systolic pressure can be stabilized at 10.7-12.0 kPa (80-90 mmHg) throughout the main procedure.
Surgical steps
1.Preparative surgery For surgery in which the carotid artery and its branch trunks are the arteries supplying the cerebral arteriovenous malformation, the carotid artery blood supply should be controlled intraoperatively in a supine position with the head turned to the healthy side. After local anesthesia, a longitudinal incision is made along the anterior border of the sternocleidomastoid muscle in the plane of the thyroid cartilage. The broad carotid muscle is incised, the sternocleidomastoid muscle is pulled outward, the carotid sheath is incised, and the internal carotid artery is isolated and bypassed with a rubber band, but its blood flow is not blocked for the time being. The incision was protected by stuffing dry gauze for temporary control of bleeding if necessary during the operation.
2.Position and incision (take the more common frontoparietal lesion of the cerebral hemisphere as an example) The patient lies on his side, and a large horseshoe-shaped incision is made at the top of the frontal area, which should reveal the precentral gyrus in front and include the whole lesion in the surgical field, with the midline of the incision in the sagittal line in order to reveal the longitudinal fissure of the cerebral hemisphere.
3.Craniotomy The craniotomy is handled conventionally according to the scalp-cranial flap, but the following points should be noted.
(1) Scalp and skull bleeding is often more, sometimes like meningioma, so the scalp should be sectioned and carefully stop bleeding; scalp and bone flap can be turned over separately.
(2) If the thick blood vessels in the anterior central gyrus are obviously adherent to the dura mater, do not forcefully lift it, but leave a small piece of dura mater.
(3) If the blood vessels are torn when the bone flap is lifted, a small piece of muscle or gelatin sponge can be used to compress them and suture them to the dura mater, without ligating the blood vessels, otherwise postoperative hemiparesis or epilepsy may occur.
(4) After the formation of the scalp bone flap, the bleeding at the edge of the bone window is coated with bone wax, and the bleeding veins and arachnoid granules are covered with brain cotton to stop bleeding and prevent air embolism.
4.Identification of the central gyrus and blood supply arteries The anatomical position alone to determine the motor area is not accurate enough, and an electrical stimulator can be used to identify it. The diameter of the main blood supply artery is thicker than normal artery, the wall of the vessel is slightly thicker than the wall of the deformed vessel, and the blood in the vessel is mainly arterial blood, which is in line with the positioning on the film, and can be determined according to the above conditions. However, sometimes the arterial blood and venous blood are mixed and the vessel wall itself is defective, so if it cannot be determined, small forceps or aneurysm clips can be used to hold the vessel and observe it for a moment. If it is an artery, its distal end will change to blue venous blood; on the contrary, if it is a vein, there will be no such change.
5.Ligation of the blood supply artery After determining the extent of arteriovenous malformation in the cerebral cortex and the blood supply artery, the blood supply artery should be ligated with silver clips or silk threads, but the blood vessel supplying the anterior central gyrus should be preserved. If the main blood supplying artery is from the middle cerebral artery, the lateral fissure can be carefully separated first to reveal the middle cerebral artery, and the blood flow can be temporarily controlled with a vascular clip for 6-8 minutes, then the branch supplying the hemangioma can be quickly separated, cut off with a silver clip, and then the small vascular clip can be released. In short, the main blood supply artery should be ligated as much as possible, and the closer to the hemangioma, the better. If it is not deflated, we should consider that there is still a main blood supply artery in the deep part, so we should pay attention to reveal and deal with it when separating.
6.Separate the hemangioma In the immediate vicinity of the hemangioma, electrocoagulate and cut the cortex 3~4mm deep (the artery with silver clip should be cut off). Use brain pressure plate (deeper part should use brain pressure plate with light or cold light source) and suction device to carefully separate the side under direct vision, but never blindly pull out, so as not to cause raging bleeding. In case of larger vessels, the aneurysm needle with thread is often used for double ligation and then cut off. However, the silver clip must be longer than the diameter of the vessel, and if there is no large silver clip, the cerebral aneurysm clip can be used. Then the malformation foci are gradually separated and turned over, and the deep main blood supply vessels are found, firmly ligated and cut off, and the brain arteriovenous malformation foci can be removed.
After removing the hemangioma, the active bleeding point will be stopped by bipolar electrocoagulation or silver clips [Figure (11)]. Then put in a ball of wet brain cotton with thread and attract with suction device to make the brain cotton attached to the wall of tumor cavity, and after a few minutes, lift up the brain cotton carefully and slowly, and stop the bleeding with bipolar electrocoagulation patiently and carefully respectively. The bleeding will be stopped by repeated treatment. Before closing the cranium, fill the tumor cavity with saline and observe again whether there is any blood seepage; if there is, continue the treatment until the saline placed in the tumor cavity remains clarified and does not bleed even after withdrawing the hypotensive drug and re-pressurizing or compressing the jugular vein.
8.Cranial closure Tightly suture the dural brain and suspend the dural suture at the edge of the cranial window. If the dura is excessively relaxed in the cranial window, a dural suspension line can be drilled from the corresponding part of the cranial flap, and the suspension line is led to the outside of the skull and ligated with the periosteal suture to eliminate the extra-dural space as much as possible and reduce the chance of postoperative hematoma formation. A drainage tube is placed under the dura mater and another one is placed outside the dura mater and a separate incision is made for drainage.
Intraoperative precautions
The general principle is to try to find out the supply artery after craniotomy and ligate it, and then deal with the vein after removing the deformity. If the patient’s condition deteriorates, the operation can be stopped and the symptoms can be reduced after the operation. The veins of cerebral vein malformation are filled with arterial blood and turn red, sometimes it is not easy to distinguish them from arteries, at this time the veins are mistakenly ligated, which will inevitably cause the hemangioma to be more congested, and even make the veins with thin walls swell and bleed.
If bleeding occurs, the main reason is that the blood-supplying artery is not properly treated. Control.
In order to reduce continued bleeding during the process of revealing the trunk of the blood supply artery, the assistant can be asked to tighten the fat skin ring around the internal carotid artery to temporarily block the blood flow of the internal carotid artery, but the shorter the time the better, if the problem cannot be solved for a while, the rubber skin ring can be relaxed intermittently so as not to take too long and make the brain tissue ischemic; or the blood pressure can be lowered to 10.7-12.0 kPa (80-90 mmHg systolic pressure). If the blood supply artery is poorly revealed, the operator can pinch the separated hemangioma tightly with the fingers and continue to separate along the hemangioma calmly and quickly, while separating and stopping the bleeding with silver clips or bipolar electrocoagulation and cautery; the assistant can clean the surgical field with the suction device. After ligating the main blood supply artery, bleeding can be mostly stopped, while blood transfusion should be accelerated according to the estimated blood loss. However, this is a measure of last resort.
Another type of hemorrhage is caused by “normal perfusion pressure breakthrough syndrome”, which is rare but often leads to surgical failure if not handled properly. When the artery supplying the hemangioma is thick, the arterial blood is directly introduced into the vein through the deformed focal vessel, which results in the decrease of the intra-arterial pressure and the increase of the intra-venous pressure, and the cerebral vessels near the lesion are in a state of extreme dilatation and low pressure for a long time, causing the loss of cerebral vascular autoregulation. After the lesion is removed, the cerebrovascular flow in the area will increase with the rise of cerebral perfusion pressure, resulting in normal perfusion pressure breakthrough syndrome, which is manifested as acute swelling of brain tissue, oozing blood and even extensive hemorrhage. The treatment is to prolong the duration of blood pressure lowering and increase the magnitude of blood pressure lowering. If the hemangioma is located in the frontal pole, temporal pole and other non-important functional parts, a more extensive lobectomy can also be performed until the brain tissue no longer oozes blood or bleeds.
3. Shock is mainly due to hemorrhage. Reducing blood loss and equal amount of blood transfusion during surgery is the fundamental prevention method. However, if the shock has been serious, and the rapid improvement is not seen even after the input of sufficient amount of whole blood, the following measures should be taken.
(1) Input equilibrium fluid 1000ml, then input low molecular (molecular weight 10000-40000) dextrose 500-1000ml, in order to expand blood volume; recently, fluorocarbon artificial blood is used, each time can input 500-1000ml, but there is a class of allergic reaction, allergic people generally should not input;
(2) Increase the effect of cardiac contraction (available isopropyl adrenaline or dopamine, etc.);
(3) Adequate oxygen administration;
(4) Appropriate cooling;
(5) Apply a large amount of hormone (such as intravenous dexamethasone, etc.);
(6) Pay attention to the possibility of diffuse intravascular coagulation and give the necessary examination and treatment.
(4) Intraoperative failure to find the lesion Deep or small hemangiomas are sometimes not easy to find, therefore, preoperative analysis and positioning should be carefully done to choose the correct surgical approach, and intraoperative patient and meticulous tracking should be done along the supply artery. If a small lesion is a major supply artery, sometimes a simple ligation of the artery can also yield satisfactory results. If necessary, a brain cotton piece with silver clip (black silk thread is needed to prevent missing in the incision) can be inserted into the vicinity of the lesion, and a frontal and lateral cerebral angiogram can be made on the operating table to determine the distance between the lesion and the silver clip to help the search.
5. For patients with hemangioma who undergo emergency craniotomy due to intracranial hemorrhage causing brain herniation, the main goal should be to remove the hematoma, release the brain herniation compression and save life. If the hemangioma can be found intraoperatively, it will be treated according to the above required steps. If the hemangioma is extensive and the source of the supplying artery is unclear, the hemangioma should not be removed blindly to prevent hemorrhage and endanger the patient’s life. After the patient’s condition is stabilized, cerebral angiography will be performed to clarify the diagnosis, and a second elective surgery will be performed to remove the hemangioma.
Postoperative treatment
Observe the vital signs closely, pay attention to the occurrence of intracranial hematoma, shock and cerebral edema, and deal with them accordingly; for those who continue to lower the blood pressure to treat the “normal perfusion pressure breakthrough syndrome” after surgery, special treatment and care should be provided until the blood pressure returns to normal.