Arterial and venous malformations due to congenital abnormalities are encountered infrequently in everyday practice. These malformations represent a heterogeneous group of isolated or multiple congenital abnormalities sometimes associated with complex congenital syndromes. Relatively few basic experiments have addressed the problem of congenital arteriovenous malformations (AVMs). Correct recognition and classification of these rare abnormalities may sometimes be difficult. No systematic classification of arterial and/or venous vascular malformations due to congenital abnormalities is currently available. For the student and the diagnostician, a classification based on the etiology of communication is helpful. The congenital AVMs are primarily divided into 4 categories: (1) hemangiomas, (2) predominantly venous malformations, (3) multifistulous AVMs, and (4) single fistula. Hemangiomas are either neoplastic or nonneoplastic. Predominantly venous malformations are further divided as those with demonstrable shunting (Parkes-Weber Syndrome) and those with no shunting, which are usually cavernous lesions (Klippel-Trenaunay syndrome). Multifistulous AVMs can be macrofistulous communications, which are demonstrable on angiography, or microfistulous communications, which are not demonstrable on angiography. A single fistula is a patent ductus, septal defect, peripheral arteriovenous fistulas (AVFs), or another anomaly of the great vessels. Vascular malformations, as opposed to hemangiomas, are not neoplastic. These lesions have no endothelial proliferation and show no growth on tissue cultures. In general, congenital AVMs, like other congenital anomalies, remain incompletely understood in terms of pathogenesis. From a clinical standpoint, these are malformations and not neoplasms. As generally isolated anomalies, they are rarely genetically transmitted, they are often stable, and they require no treatment. Congenital vascular malformations may involve arterial, venous, and lymphatic structures. They can appear in a variety of forms and present many diagnostic and therapeutic challenges. Two-thirds of all congenital vascular malformations are predominantly venous. Most of the venous malformations are asymptomatic and should be managed conservatively. However, the clinical presentation of patients with venous malformations associated with lymphatic anomalies is variable, and treatment may be challenging. The early work of Woodlard on the embryology of the vascular system shed light on our understanding of these congenital anomalies. In the early stages of development, the vascular system consists of interlacing blood spaces in the primitive mesenchyma. Because of a genetic factor in the capillary endothelium, these interlacing networks differentiate into arteries and veins. Focal persistence of the primitive vascular elements constitutes the congenital vascular malformations. According to Woodlard, the 3 stages of development are (1) the stage of undifferentiated capillary network (Hemangiomas result from arrest of development during this stage.), (2) the retiform stage (AVM results from arrest of development during this stage.), and (3) the vascular maturation stage (A port-wine stain is an example.). The overall incidence of congenital vascular malformations in the general population is 1.5%. Approximately two thirds are malformations of venous predominance. Abnormalities of the deep venous trunks have been observed in association with large superficial compensatory varices in these types of malformations. Knowledge of the integrity of the deep venous system is important for management of these malformations because excision of the enlarged superficial veins may be deleterious if aplasia or hypoplasia of the deep venous trunks exists. Patients with congenital vascular malformations were evaluated at Children's Hospital of Mexico City (1963-1983, 223 children) and the Walter Reed Army and National Naval Medical Centers (1984-1998, 169 children). Of the 392 patients, 257 (65.6%) had malformations of venous predominance. Prevalences of phlebectasia, aplasia or hypoplasia of venous trunks, aneurysms, and avalvulia were recorded. Pathologists differentiate vascular malformations into 4 categories, as follows: In terms of pathophysiology, congenital AVMs are always due to 3 separate and distinct phenomena: (1) the local effect of the fistula (warmth, aneurysmal dilatation of the veins), (2) central and distal effects (distal ischemia depending on the amount of shunting), and (3) high-output cardiac failure. The frequency and severity of the symptoms and signs depends on the magnitude and location of the fistulas. Congenital AVFs can occur almost anywhere in the body. They most commonly involve the extremities, lower more than upper. Among fistulas of the extremities, those involving the femoral vessels are most common. Congenital AVFs have also been described in the head and neck, where they contribute to major clinical deformities. Patients with an AVM of the brain have a dramatic presentation. Pelvic AVMs are usually extensive and manifest with vaginal bleeding or compressive symptoms on other pelvic organs. Congenital visceral fistulas are seen in lung, kidney, and alimentary tract. Alimentary-tract AVMs are usually a part of congenital telangiectatic syndromes. Congenital AVMs can sometimes result in portal hypertension. Patients are usually asymptomatic. Bruits may be audible. Other congenital anomalies can coexist. Some coexisting anomalies occur in response to abnormal local blood flow (eg, overgrowth, undergrowth, and focal gigantism). The observed association of hyperhidrosis and café au lait spots suggests connections between abnormal vascular and neurologic anomalies. No sex predominance is observed except in infantile hemangiomas. Gradual growth occurs in proportion to the growth of the individual. Clinical detection is variable. The lesion sometimes manifests as a local skin discoloration, a local bruit or thrill, or a local pulsatile mass. Detection can be based on the effects on adjacent structures or on secondary complications, such as hemorrhage, venous ulceration, or ischemia of the regional tissues due to steal phenomenon. Local trauma may direct attention to the congenital malformation. Some believe that trauma activates congenital AVMs to open new channels as they enlarge or become symptomatic. The enlargement is due to enlargement of vascular channels and not cellular proliferation. High-output cardiac failure can be an initial manifestation; this usually occurs in lesions in infancy and extremely large pelvic or intra-abdominal lesions in adults. Vague local pain is sometimes the presenting symptom. Local varicosities can also be seen in some patients. Local gigantism is another clinical manifestation. Vascular malformations can occur anywhere in the body, though certain anatomic sites, such as the pelvis, extremities, and intracranial circulation, seem to be most commonly affected. Pelvic lesions can manifest in multiple ways: Bleeding from cranial lesions could cause a subarachnoid, intracerebral, or intraventricular hemorrhage. AVMs usually appear with an intracranial bleed, but patients may have a variety of symptoms and signs, including headache, cranial bruit, convulsive seizure, mental deterioration, or hemispheric neurologic deficit. If large enough, these malformations can be diagnosed by using CT and MRI of the brain. The final diagnosis is made by means of 4-vessel cerebral angiography, with which all the feeding arteries, nidus, and venous drainage can be demonstrated. AVMs tend to bleed earlier in life than aneurysms; the peak incidence is in individuals aged 30-40 years. Available data suggest that, subsequent to diagnosis, the annual cumulative risk of rebleeding in intraparenchymal AVMs is 3-4%. The risk might be slightly increased in the first year after an initial hemorrhage, but it appears to remain relatively constant from that point for the remainder of the patient's life. Techniques for management of AVMs include microsurgical excision, embolization with glue or thrombogenic particles, and focused radiation. Depending on the clinical condition of the patient and the characteristics of the AVM (size, location, arterial supply, venous drainage), a decision is made regarding which of the 3 modalities should be used. Venous angiomas are characterized by an extensive network of veins separated by normal parenchyma. These lesions seldom bleed or give rise to clinical symptoms. Telangiectasis lesions (ie, capillary angiomas) are generally benign lesions of the brainstem. Cavernous angiomas are typically developmental malformations in the brain substance that can be demonstrated by means of brain CT or MRI. They may clinically manifest as growing masses, intracerebral hemorrhage, or intractable seizures. Symptomatic lesions that are accessible are usually removed surgically. AVMs are usually larger than the other types of lesions, but they can vary in size. AVMs consist of a feeding artery or arteries, a nidus, and draining veins. The superficial portion of a malformation may cover part of the cerebral surface, but the lesion frequently extends like a cone down to the ventricular surface Vascular malformations Hemangiomas are congenital lesions that rarely pulsate or that have an associated bruit. Moreover, they have several small feeding arterial vessels that can be seen by means of angiography. They are histologically composed of numerous thin-walled but normal-appearing blood vessels. AVMs are also congenital, but they pulsate and have associated bruits. Furthermore, they have a number of large arterial feeding vessels that can be seen by means of angiography. They are histologically composed of abnormal dysplastic vessels. Surgical management of all lesions should be carefully planned and executed. AVMs and skeletal-muscle hemangiomas tend to recur if they are not completely excised. Venous anomalies Anomalies of the deep venous system occur in almost one half of congenital vascular malformations of venous predominance. The most common is the relatively innocuous phlebectasias, which occur in more than one third of cases. Aplasia and/or hypoplasia, venous aneurysms, and avalvulia are relatively rare, with a frequency of <10%. Failure to detect these anomalies may lead to serious therapeutic errors.
Treatment primarily includes observation and careful follow-up. The series by Szilagyi showed no worsening of symptoms in 20 of 23 patients. Because most infantile hemangiomas spontaneously resolve, expectant treatment is the rule. Corticosteroids and radiation therapy are also used to treat this condition. Absolute indications for surgery are hemorrhage, ischemic complications, and congestive heart failure due to shunting. Relative indications include pain (from a nonhealing ulcer), functional impairment, and cosmetic deformity. Contraindications to surgery include bleeding disorders and an asymptomatic status.
Selective catheter-directed embolization Selective catheter-directed embolization of the feeding arteries, occasionally followed by tumor excision, is the treatment of choice. Three techniques are available for the management of AVMs: (1) microsurgical excision, (2) embolization with glue or thrombogenic particles, and (3) focused radiation. Depending on the patient's clinical condition and on the characteristics of the AVM (size, location, arterial supply, and venous drainage), a decision is made regarding which of the 3 modalities should be used. Since 1980, great strides have been made in selective catheter embolization. Numerous embolic materials have been developed, ranging from simple Gelfoam pledgets to complex systems employing microcatheters and detachable balloons. Temporary embolic materials are not suitable because permanent occlusion is needed. Permanent embolic materials include stainless-steel coils, detachable balloons, polyvinyl alcohol particles, liquid silicone, and acrylic tissue adhesives. Proximal occlusion should be avoided as the lesions always recur after initial regression due to formation of collaterals. New coaxial catheter systems enable the embolization of small branches. Ethanol embolization Ethanol embolization was used to treat symptomatic vascular malformations in 20 patients who were not candidates for surgery or in whom previous surgery or standard embolotherapy failed. Symptomatic vascular malformations include venous malformations, AVMs, and congenital and posttraumatic AVFs. All large complex lesions required multiple embolizations as staged procedures. Immediate thrombosis was achieved in all patients. Complications occurred in 13% of patients; the events were generally minor and treated conservatively. Follow-up studies performed in 19 of 20 patients showed persistent occlusion of the symptomatic vascular malformation in all cases. Ethanol embolization of symptomatic vascular malformations, performed according to strict techniques, has proved to be effective in managing symptomatic vascular malformations, and it is emerging as a definitive form of therapy. Complications of the procedure include tissue necrosis, inadvertent embolization of normal tissues, and passage of embolic materials through arteriovenous communications resulting in pulmonary embolization. The literature reports a complication rate of 6%. The recurrence rate after successful embolization is 75%, but 55% of patients have an improvement in symptoms. Sclerotherapy Sclerotherapy is effective in managing venous malformations. Embolization of feeding arteries is not effective in treating venous malformations. Direct injections of sclerosants and surgical excision are 2 effective modalities to treat this condition. Hemangiomas and AVMs are distinct, congenital, benign, vascular lesions. Differentiation of the two is important because AVMs are amenable to embolization techniques and because patients with hemangiomas can be given a prognosis more favorable than those of patients with AVMs. A major error in management is to ligate the proximal arterial blood supply to an AVM because the lesion continues to grow, additional collateral vessels develop, and future angioaccess for purposes of evaluation or embolization is denied. With care and prudence, many of these lesions can be successfully excised or at least managed so that their effects can be ameliorated. Total surgical excision offers the best cure. The lesions most suitable for surgical treatment are those of the superficial trunk, scalp, face, and extremities. Surgical techniques for cranial lesions include gamma-knife irradiation or linear-accelerator radiosurgery, endovascular embolization of AVMs, and microsurgical resection with or without embolization. Preoperative details include discussion of the risks and benefits of surgery, assessment of indications, and consideration of various surgical techniques. The surgical techniques require intraoperative blood transfusion and intraoperative use of cell-saver techniques. A team approach is often required. The fundamental principle is obtaining proximal and distal vascular control. Gamma-knife irradiation or linear-accelerator radiosurgery is especially well suited for small and deep cortical AVMs that have not bled and that otherwise are not treatable. Large, inoperable AVMs in the eloquent cortex can be candidates for focused irradiation if embolization can diminish their size or divide them into small sections that can then be individually irradiated. Microsurgical resection with or without embolization is still the modality most commonly used to treat AVMs, whether they hemorrhage or cause seizures. If an AVM is suspected to be the cause of an intracerebral hematoma, angiography is always indicated to define the exact anatomy of the malformation. With microsurgical techniques, the feeding arterial supply is sacrificed, and total resection of the nidus is performed. Postoperative angiography must be used to document resection of the entire nidus because even small residual pieces of malformation can lead to catastrophic hemorrhages if left untreated. Postoperative details include routine follow-up care and careful monitoring for late complications and recurrence. Short-term follow-up consists of wound care. Long-term follow-up consists of surveillance. Possible complications include hemorrhage and rethrombosis. Endovascular embolization of AVMs effectively reduces the amount and rate of blood flow through the malformation. However, few malformations can be totally obliterated by using this technique, and either surgery or focused radiation should be used in combination. Microsurgical resection with or without embolization is still the modality most commonly used to treat AVMs. It is usually associated with excellent outcome if the feeding arterial supply is sacrificed and if the nidus is totally resected. Postoperative angiography must be used to document resection of the entire nidus because even small residual pieces of malformation can lead to catastrophic hemorrhages if left untreated. After treatment with a gamma knife, the patient is not immediately protected from repeat hemorrhage. In about 60-80% of patients, 3-cm AVMs are obliterated after 2 years. The smaller the AVM, the higher the likelihood of total obliteration. Gamma-knife irradiation or linear-accelerator radiosurgery is currently reserved for surgically inaccessible lesions. Further work in this area is needed.Introduction
Frequency
Pathophysiology
Presentation
Indications
Relevant Anatomy
Workup
Laboratory Studies
Imaging Studies
Other Tests
Treatment
Medical Therapy
Principles of Treatment
Medical Therapy
Interventional therapies
Surgical Therapy
Preoperative Details
Intraoperative Details
Postoperative Details
Follow-up
Complications
Outcome and Prognosis
Future and Controversies
Saturday, March 27, 2010
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