Arteriovenous malformations (AVMs) are vascular masses formed by direct anastomosis of arteries and veins due to abnormal development of the vascular system during embryonic life, containing immature arteries and veins, with varying degrees of direct traffic between arteries and veins and no capillaries. Among the hemangiomas and vascular malformations, arteriovenous malformations are relatively rare, accounting for only about 1.5%, with the oral and maxillofacial regions being the most frequent sites, accounting for 50% of all arteriovenous malformations, followed by the extremities and trunk. Although arteriovenous malformations are congenital, only about 60% are detected at birth, with the remainder becoming apparent in adolescence or adulthood. The lesion usually grows proportionally with body development and can remain stable for a long time or increase rapidly in a short period of time. This usually occurs after trauma, hormonal changes in the body during pregnancy or conception and inappropriate treatment such as subtotal resection of the lesion, ligation or blockage of the blood supply artery. Interventional embolization is currently the main treatment. The key to successful interventional embolization is access to the center of the abnormal vascular mass and the selection of an embolic agent that can destroy the endothelium of the vessel. In this paper, with reference to the relevant literature and treatment experience at home and abroad, we formulate a guideline for the treatment of oral and maxillofacial arteriovenous malformations in the hope of guiding the standardized treatment of oral and maxillofacial arteriovenous malformations. This guideline will be updated in time to reflect and incorporate the latest research findings and provide the latest treatment options for patients. Arteriovenous malformations (AVMs), formerly known as trabecular hemangiomas, are vascular masses that contain immature arteries and veins with varying degrees of direct arteriovenous communication and no capillaries due to abnormal development of the vascular system during embryonic life. If the arteriovenous fistula is formed in the malformed vascular mass, especially if the fistula is large, the resistance to blood flow in the lesion decreases and the blood flow increases, resulting in thickening, increasing and distorting the blood supply arteries and stealing a large amount of blood from the adjacent normal tissues (i.e., the phenomenon of “blood theft”) to meet the high flow of blood supply to the lesion. The returning veins, mainly the external and internal jugular veins, increase in pressure and flow velocity, followed by gradual expansion and arterialization of the veins. In the International Society for the Study of Vascular Anomalies (ISSVA) classification system, arteriovenous malformations are classified as high-flow vascular malformations, along with arteriovenous malformations (AV) and arteriovenous fistulas (AVF). They can be found in various parts of the body, such as brain, spinal cord, internal organs, bone, skin and subcutaneous soft tissues. The oral and maxillofacial region is the most common site, accounting for 50% of all AVFs, followed by the extremities and trunk. Craniofacial arteriovenous malformations are mostly located in the middle of the face, nearly 70%, and can involve the cheeks, nose, ears and upper lip, etc. Scalp arteriovenous malformations are also not uncommon. Among angiomas and vascular malformations, arteriovenous malformations are relatively rare, accounting for only about 1.5%. In addition to the above common sites, arteriovenous malformations can also involve some rare sites, such as iris, tongue and mandible. It can also occur in conjunction with other body surface tumors, but is extremely rare. In type I neurofibromatosis, for example, a more typical arteriovenous malformation may be associated with functional changes in the neurofibromatosis protein. There is no evidence that arteriovenous malformations are hereditary or that food, drugs, or radiation can cause them, but they are present in some genetic disorders. For example, hereditary hemorrhagic telangiectasia (HHT), or Rendu-Osler-Weber syndrome, is an autosomal dominant disorder that usually presents with dilated skin and mucosal capillaries, nasal and gastrointestinal bleeding, and arteriovenous malformations of the lungs, brain, and liver. Another example is capillary malformation-arteriovenous malformation (CM-AVM), a newly discovered vascular lesion first described and named by Eerola et al. It presents as familial oval capillary erythema and arteriovenous malformation or arteriovenous fistula in 10% of the family members. In addition, arteriovenous malformations are also a manifestation of various other syndromes, such as ParkesCWeber syndrome, Cobb syndrome, BonnetCDechaumeCBlanc syndrome, and WyburnCMason syndrome. In these syndromes, arteriovenous malformations can be located in the brain, spinal cord, gastrointestinal tract, head and neck, and extremities. 1, clinical manifestations of arteriovenous malformations The head and neck region accounts for about 14% of the body surface area, but 50% of soft tissue arteriovenous malformations occur in this region. Although arteriovenous malformations are congenital disorders, only about 60% are detected at birth, and the rest gradually appear in childhood or adulthood. The lesion usually grows proportionally with physical development and may remain stable for a long time or may increase rapidly in a short period of time. This usually occurs after trauma, hormonal changes in the body during puberty or pregnancy and inappropriate treatment such as subtotal resection of the lesion, ligation or blockage of the blood supplying artery. Craniofacial soft tissue arteriovenous malformations present primarily as ill-defined soft tissue bulges with normal surface skin color, or with capillary dilation, or dark red. The lesion and the surrounding area may be characterized by large, pulsating blood vessels in the form of rosettes or cords, with surface temperature significantly higher than normal skin, persistent tremors, and a continuous blowing murmur. In a few patients, the volume of the focal tissues may increase gradually after the involvement of the ear, nose, lips or extremities, even expanding several times the original size, and the appearance is completely destroyed. In the later stages of the lesion, especially after ligation of the external carotid artery, the surface may become ulcerated or necrotic due to significant blood theft, jugular venous anger, increased pressure in the superior vena cava and widening of the cardiac border, leading to heart failure. The clinical manifestations of arteriovenous malformations and arteriovenous fistulas are similar, but the pathophysiological features and clinical course of the two are completely different and need to be distinguished. Most arteriovenous fistulas are acquired lesions, most often from trauma and chronic erosion, and are single arteriovenous fistulas in which arterial blood flows directly into the vein through the fistula hole, resulting in increased pressure in the returning vein. Arteriovenous malformations differ from arteriovenous fistulas in that they are congenital lesions with multiple tiny fistulae connecting the arteries and veins and foci of intercellular stroma embedded between the vessels. Both are associated with dilated and distorted blood supply arteries and return veins. Intramaxillary arteriovenous malformations are central lesions that occur in the bone marrow of the jaws and were previously referred to as central angiomas of the jaws. They are more common in women and are mostly congenital lesions or can occur secondary to trauma to the jaws. The main risk is recurrent, spontaneous bleeding in small amounts or acute bleeding that is difficult to control. Acute bleeding occurs mainly in children during the teething period, especially around the age of 10 years, mostly due to extraction of loose teeth, alternation of permanent teeth or misdiagnosed surgery; it can also occur after completion of jawbone and tooth development. Acute bleeding is often preceded by recurrent periodontal bleeding and can also be preceded by hemorrhage and accompanied by the loosening of the bleeding tooth. Intra-maxillary arteriovenous malformation mainly occurs in the molar or premolar region, mostly accompanied by root resorption; lesions occurring in the mandible may also cause numbness in the mandibular region. The lesions may be limited to the jaw bone or may be associated with peripheral soft tissue arteriovenous malformations. The development of arteriovenous malformation and bleeding in the jaw is associated with endocrine hormonal changes in women. Before the monthly menstrual period, soreness and discomfort may occur in the jaw lesion area; during the first menstrual period, pregnancy and childbirth in women, which may lead to accelerated lesion growth and bleeding. 2.Diagnosis of arteriovenous malformation Most of the craniofacial soft tissue arteriovenous malformations are located on the surface of the body, and the diagnosis can often be made according to their clinical manifestations. For deep lesions, imaging is often required to clarify the nature and extent of the lesion. On plain CT, the soft tissue arteriovenous malformation appears as an abnormal soft tissue bulge of equal density; after injection of enhancer, the abnormal soft tissue bulge is significantly enhanced, approximating the density of adjacent vessels, and the refluxing veins are shown in advance. On MRI, the abnormal soft tissue signal was shown as an iso-signal shadow on T1WI and an increased signal intensity on T2WI, with a clear flow-void signal within. After injection of enhancer, the abnormal soft tissue signal shadow was significantly enhanced. Digital subtraction angiography (DSA) can clearly show the vascular architecture of arteriovenous malformations and is a necessary test to develop treatment measures. However, due to the high invasiveness and cost of the test, it is not usually used as a routine test and is only used in combination with interventional therapy. The examination includes both sides of the external carotid artery, both sides of the internal carotid artery and both sides of the vertebral artery. Patients with recurrence of arteriovenous malformation after external carotid artery ligation also need to undergo imaging of the thyroglossal trunk. The characteristic DSA findings of craniofacial soft tissue arteriovenous malformations include massed, nodular nests of malformed vessels (nidus); thickened, increased supply arteries; and prematurely present, dilated draining veins. Due to increased blood flow and flow within the nidus, the supply arteries supplying the nidus are thickened and may be single or multiple branches, and the source of the supply arteries is related to the location of the nidus. For arteriovenous malformations located in the cranial surface 1/3 and the soft tissues of the nasal dorsum, the blood supply comes from the internal carotid artery, and the rest generally comes from the external carotid artery. The draining veins of the aberrant vascular nests are significantly thickened and tortuous and are visualized in the arterial phase along with the aberrant vascular nests. In arteriovenous malformations with high-flow arteriovenous fistulas and large arteriovenous malformations, a large amount of blood enters the arteriovenous malformation nest, causing the distal vessels of the lesion to be poorly visualized, which is the phenomenon of “blood theft”. The course of arteriovenous malformations can be divided into four stages according to the Schobinger clinical staging recommended by the ISSVA in 1990. stage I is the resting stage, which is asymptomatic, usually from birth to adolescence, with lesions that are inconspicuous or simply have the appearance of wine-colored spots or receding hemangiomas. In some patients, the lesions remain in the quiescent stage and do not worsen throughout life. Increased skin temperature, murmurs, and tremors suggest a high-flow nature of the lesion. Stage II is progressive, with most lesions beginning in adolescence, increasing in size, darkening in color, and invading the surface skin and deeper tissue structures. Histologically, it shows arterial and venous dilatation and fibrosis. Examination may reveal increased local skin temperature, palpable pulsations and tremors, and audible murmurs on auscultation. The skin appearance changes resemble Kaposi’s sarcoma, which is easily misdiagnosed. In addition, incorrect treatment such as ligation of the supply artery, partial resection, proximal arterial embolization, and laser may lead to progression from stage I to stage II; stage III is the destructive stage with progressive expansion and spontaneous skin or mucosal rupture, recurrent bleeding, or progressive dysfunction; stage IV is the decompensated stage where high flow of the giant arteriovenous malformation may lead to cardiac failure. This staging method still does not reflect the full picture of the clinical features of the complex disease of arteriovenous malformations, such as the fact that progressive arteriovenous malformations vary greatly from case to case, even at the same site, and it remains unclear how these differences relate to the pathological anatomy of arteriovenous malformations. Therefore, the establishment of a more in-depth classification system is still one of the important topics worthy of study. Arteriovenous malformations of the jaws are more prevalent in the mandible. CT shows enlarged bone marrow cavity, disappearance of bone trabeculae, single or multi-capsular hypodense foci, and chisel-like changes in the bone cortex if soft tissue is involved; if no soft tissue changes are present, the bone cortex is intact. If soft tissue is not involved, the bone cortex is intact. DSA of arteriovenous malformation of the jaws shows an abnormal vascular mass (also called “venous pool”) in the posterior part of the alveolar bone in the early and mid-arterial phase, which persists into the late venous phase. This anomalous vascular mass communicates with the refluxing veins and appears as a cystic expansion of the alveolar bone on CT. In the maxilla, the supplying artery is the posterior superior alveolar artery of the maxillary artery; in the mandible, the supplying artery is primarily the inferior alveolar artery of the maxillary artery. Ultrasonography of the supplying artery reveals that it supplies the anomalous vascular mass in the form of multiple slender branches. The arteriovenous malformation of the jaws has a more specific presentation on MRI, with loss of fatty signal in the marrow cavity of the jaws and a low signal shadow on T1WI and T2WI-weighted images. In case of peripheral soft tissue arteriovenous malformation, MRI shows irregular nests of foveal flow vessels and varicose nutrient vessels. CT by itself is not sufficient to make a definitive diagnosis of arteriovenous malformation of the jaws, but DSA has specific diagnostic value and remains the gold standard for the diagnosis of arteriovenous malformation of the jaws. CT is more visual and clearer than DSA in showing the extent, location, borders and size of lesions in the jaws. In addition, special attention should be paid to the fact that cases of periapical bleeding, high bleeding during tooth extraction or surgery, and blood seen in intra-maxillary puncture are not always jaw arteriovenous malformations and require careful differential diagnosis. Clinical experience shows that bleeding around teeth, bleeding during tooth extraction or surgery can be seen in cases of hemophilic pseudotumors, extravasated bone cysts and chondrosarcomas of the jaws; fresh blood on puncture of intra-maxillary lesions can be seen in cases of myeloma, extravasated bone cysts, aneurysmal bone cysts, synovial sarcomas and enamel cell tumors, in addition to arteriovenous malformations of the jaws. In addition, arteriovenous malformations of the mandible may be associated with daylight radiating new bone formation, which requires careful differentiation from osteosarcoma. Unfortunately, DSA often does not provide a definitive diagnosis in differentiating arteriovenous malformations of the jaws from hyperemic occupations in the jaws. Careful screening is required in conjunction with history, clinical presentation, and imaging features, and in some cases, close follow-up after urgent hemostasis is required. For example, arteriovenous malformations of the jaws are most often seen between the ages of 10 and 20 years, with posterior dentition, often with bleeding or hemorrhage, and if they occur in the mandible, they should be accompanied by thickening of the mandibular canal [18]. 3, Treatment of arteriovenous malformations Historically, there have been numerous treatment options for arteriovenous malformations, but the treatment strategy developed so far has been mainly based on interventional embolization, supplemented by surgical treatment. Surgical treatment is limited to the improvement of appearance even after interventional embolization and the debridement of post-embolization infection. Incomplete excision of the lesion can promote its development. The key to interventional embolization is the direct elimination of the abnormal vascular mass, and ligation or blockage of the blood supply artery is contraindicated, which not only fails to treat the lesion, but also further promotes the development of the lesion. The objectives of interventional embolization of craniofacial soft tissue arteriovenous malformation include: (1) complete cure of arteriovenous malformation; (2) embolization to reduce the lesion and control the occurrence of complications; (3) embolization to reduce the lesion to facilitate surgical resection. According to the purpose of interventional embolization, different embolization materials need to be selected clinically. The commonly used embolization materials for craniofacial soft tissue arteriovenous malformations are PVA (polyvinyl alcohol) particles, n-butyl dicyanoacrylate (NBCA) and anhydrous ethanol. PVA pellets are a medium-term embolic material with high recanalization rate, and the diameter of PVA pellets commonly used for craniofacial embolization is generally 150-250 μm. NBCA is a liquid embolic agent that polymerizes after entering the body and contacting with blood, and the polymerization time is related to the concentration of NBCA. NBCA is a liquid embolic agent, and the polymerization time is related to the concentration of NBCA, and the recanalization rate of NBCA embolization is lower than that of PVA. NBCA operation is demanding and difficult, and the risk of mucous tubing requires specialized physicians with certain interventional experience and familiarity with the properties of NBCA and microcatheter operation techniques. Recently, Onyx, introduced by American scholars, can overcome the shortcomings of NBCA with sticky tubes and is expected to be a new type of embolic agent. Since NBCA, PVA and Onyx cannot destroy the endothelial cells within the abnormal vascular mass, even with adequate embolization, there is still a possibility of regenerating the abnormal lumen and leading to lesion recanalization. Anhydrous ethanol is currently the only liquid embolic agent that can achieve the goal of healing arteriovenous malformation treatment. It not only cures arteriovenous malformations, but also improves their appearance by eliminating the occupying effect of the lesion on top of curing the arteriovenous malformation. Anhydrous ethanol directly destroys vascular endothelial cells through cell dehydration and demyelination changes, rapid denaturation of blood proteins, rapid necrosis and thrombosis of vascular malformation tissues, thus achieving the therapeutic purpose of arteriovenous malformations. PVA, liquid tissue glue and spring coils can also be used for embolization of oral and maxillofacial arteriovenous malformations, limited to physical occlusion, to reduce the flow rate of the lesion, to control complications and as an adjunctive embolization before surgery. In the past, maxillofacial arteriovenous malformations were mainly treated surgically, mostly by maxillectomy or scraping of the jaw lesion. This procedure is not only risky and bleeding, but also causes serious cosmetic damage and reduced masticatory function to the child. Secondly, even after jaw removal, the soft tissue lesions around the jaw continue to develop, resulting in new bleeding, ulcers, and jugular hypertension. The ideal outcome of treatment of jaw arteriovenous malformation is to preserve the integrity of the jaws and dentition while controlling acute bleeding and preventing the potential for major bleeding. The treatment of arteriovenous malformations of the jaws by interventional embolization dates back to 1986 and has been accomplished primarily through the injection of granular embolic material or liquid tissue gel into the blood supply artery. Although arterial embolization with tissue glue is more effective than granular embolization, it is difficult to completely fill the lesion with embolic agent through the donor artery alone due to the large size of the lesion in the jaw and the slender mesh between the donor artery and the anomalous vascular mass, which results in recurrence of the lesion or bleeding. Some scholars have recognized this deficiency, and after granular embolization of the blood supply artery, embolization was performed by local transosseous puncture of the anomalous vascular mass in the jaw bone, which achieved better results. Because of the hard mandibular cortex, local puncture for embolization bleeds more. In 2007, Yakes reported a successful case of anhydrous ethanol embolization for mandibular arteriovenous malformation at the Oral and Maxillofacial Vasculopathy Conference in Hangzhou. Subsequently, anhydrous ethanol was substituted for tissue glue, and the embolization of anhydrous ethanol in combination with spring coils for the treatment of intra-arteriovenous malformations in the jaws was successful in stages. The main advantages of anhydrous ethanol embolization over tissue glue in the treatment of intra-maxillary arteriovenous malformations are: it is less likely to cause foreign body reactions and infections; it is easier to achieve adequate dispersion within the abnormal vascular mass and destroy its endothelial cells, resulting in a more permanent embolization effect; and it can significantly improve the adjacent soft tissues that have been invaded, including decreased skin temperature, darkening of skin color, and recovery of dilated reflux veins. In conclusion, since the interventional embolization of arteriovenous malformations of the jaws was carried out in the late 1980s, better treatment results have been achieved. It has not only completely controlled the occurrence of bleeding in the disease, but also preserved the integrity of the jawbone and dental row and maintained the appearance. At present, interventional embolization has become the preferred treatment for this disease, and surgical resection or scraping is only used as a supplementary means to interventional embolization. 4.The main complications of arteriovenous malformation intervention and its prevention and control 1.Tissue necrosis The causes are: ① anhydrous ethanol injection into the normal tissue space; ② after the injection of anhydrous ethanol, failed to wait patiently for 10-15 minutes after imaging, then started to inject again, injecting too much and overflowing outside the lesion; ③ using the method of compression of reflux veins to reduce the lesion flow rate is too fast, anhydrous ethanol overflow occurred. In order to prevent tissue necrosis, the puncture needle must be placed in the center of the lesion during the operation; each treatment should not be rushed and should be performed in stages; the injection volume of anhydrous ethanol should be strictly controlled, and after each injection, we need to wait 10-15 minutes for imaging before deciding whether to inject again. Once tissue necrosis occurs, the color of the necrotic area first becomes dark, then black, and finally falls off. At this point, local heat and vasodilators can be applied to reduce the area of necrosis. When the time is appropriate, perform local debridement and second-stage repair. 2, cardiopulmonary function accident When anhydrous ethanol embolizes the arteriovenous malformation, part of the anhydrous alcohol flows into the pulmonary artery, and the capillaries of the pulmonary artery spasm, and causes the pulmonary artery pressure to rise. At this time, the right ventricular pressure and load are subsequently increased, the left heart output is reduced, and the systemic blood pressure and coronary perfusion are also reduced. If this condition is not corrected in a timely manner and deteriorates further, cardiogenic arrhythmias and cardiopulmonary accidents can occur. In cases of local anesthesia, this is manifested by severe coughing and dyspnea, and in cases of general anesthesia, by a sudden increase in airway resistance, which may be accompanied by varying degrees of decreased oxygen saturation. Mild symptoms can be automatically relieved by suspending the injection, oxygen and other treatments; heavy symptoms require intravenous nitroglycerin, nitroglycerin is a strong dilator of smooth muscle, the effect on the veins is obvious, the pulmonary vascular bed dilates, and the pulmonary artery pressure decreases. The method of use is sublingual 0.3mg/time or 5mg added to 5% glucose 250ml intravenous drip. During high-dose anhydrous ethanol embolization, dynamic detection of pulmonary artery pressure using the Swan-Ganz catheter is an effective way to control the occurrence of this complication. Once elevated pulmonary artery pressure occurs, the anhydrous ethanol injection is immediately stopped; if the pulmonary artery pressure still does not recover, nitroglycerin can be administered via the Swan-Ganz catheter, which can effectively relieve pulmonary artery pressure. Experience shows that pulmonary hypertension is often caused by a one-time high dose of anhydrous ethanol flowing through the pulmonary artery, so a divided, small push of anhydrous ethanol should be taken. 3. Transient hemoglobinuria is mainly seen in cases of high-dose anhydrous ethanol embolization. Anhydrous ethanol directly destroys red blood cells and platelets after entering the blood circulation system. It leads to a large amount of hemoglobin into the blood and is excreted through the kidneys. A dark red or soy sauce color of urine is observed in clinical practice. The literature reports that the probability of hemoglobinuria occurring at injected doses of anhydrous ethanol above 0.8 mg/kg is almost 100%. Generally, care should be taken to increase rehydration and alkalinize the urine after injection of larger doses of anhydrous ethanol.