Spinal arteriovenous malformations are congenital vascular formations of spinal localization. They consist of abnormally altered vessels shunting blood from the arterial network into the venous one, bypassing the capillaries. They are latent. Manifest symptoms of spinal hemorrhage, radicular pain, progressive motor disorders. Diagnosis is based on clinical, tomographic and angiographic data. Neurosurgical treatment: endovascular obliteration, open microsurgical resection, radiosurgical removal.
Q27 Other congenital anomalies [malformations] of the peripheral vascular system
Spinal arteriovenous malformations (SAVMs) are a section of an abnormal vascular network with direct communication of arteries and veins without connecting capillaries. Arteriovenous malformations of the spinal cord include SAVMs of vessels located inside the medulla (intramedullary), in the membranes (intradural) and on the surface of the spinal cord (extramedullary). Spinal vascular malformations are a rare pathology. In the structure of volumetric spinal formations, they occupy 6-10%. Extramedullary SAVMs of the lumbar and thoracic sections are the most common. The disease is congenital, manifests itself more often in young and middle-aged people. In 40% of cases it is combined with other malformations.
Vascular anomalies are formed during intrauterine development as a result of a local failure in the formation of vessels of medium and small caliber. There is no hereditary link. The factors provoking dysgenesis are diseases and intoxication of the mother during pregnancy, intrauterine infections, fetal hypoxia, adverse environmental effects, taking pregnant pharmaceuticals with a side teratogenic effect. Separately, there are triggers that provoke clinical manifestation: excessive physical exertion, weight lifting, pregnancy, childbirth, spinal injury, visiting a bath, sometimes hypothermia.
Arteriovenous malformations are characterized by a long latent course. The vascular system in the area of the anomaly adapts to work in the created conditions. Over time, it is possible to thin the walls of the vessels entering the formation, the occurrence of aneurysms (protrusions of the vascular wall). Spinal cord tissues in the area of the anomaly may suffer from chronic ischemia and hypoxia as a result of the stealing mechanism, when blood does not flow through the capillary network, but is discharged through arteriovenous shunts. Therefore, several pathogenetic mechanisms that determine the clinic of the disease are being considered.
Provoking triggers (stress, pregnancy, injuries) cause increased metabolism of spinal cells, which exacerbates their hypoxia and causes dysfunction. There are symptoms of vascular myelopathy. On the other hand, under the influence of triggers, there is an increase in blood flow, including in the spinal arteriovenous malformations. If the blood does not have time to be discharged from the arteries into the veins, there is an increased blood filling of the malformation with an increase in its volume. The increasing formation squeezes the roots or brain matter — a picture of the root syndrome or myelopathy develops. With thinning of the vascular wall, increased blood flow leads to its rupture with the clinic of intramedullary or subarachnoid hemorrhage.
Spinal arteriovenous malformations are a group of quite variable vascular anomalies. In clinical practice, the determining importance in choosing the optimal method of surgical treatment belongs to their morphology and location. The following classification has found the greatest practical application:
By structure — examines the morphology of the spinal arteriovenous malformations, the number of adducting (afferent) arteries and diverting (efferent) veins, their mutual position. Allows to separate arteriovenous malformations according to their hemodynamic characteristics:
- Type I is a bundle of altered vessels with 1-2 hypertrophied adductor arteries and an efferent vein. In some cases, the outflow goes through several veins. It is clearly visible on angiograms, blood flow is slowed down.
- Type II (glomus) is a compact vascular tangle with looped vessels, often convoluted afferent arteries. It has several arteriovenous shunts, the location of which is difficult to determine with X-ray contrast examination. The blood flow is increased, slows down in the drainage vein.
- Type III (juvenile) is a rare form of large immature vessels. Several adducting arteries and draining veins of different caliber. Blood flow is accelerated throughout the malformation. Gives a systolic noise, audible auscultatively.
- Type IV — has no small vessels. The artery is directly connected to the vein by the “end to side” or “end to end” type. In the latter version, it looks like a serpentine path on angiograms.
By localization — takes into account the location of the spinal arteriovenous malformations in relation to the spinal cord. It is important for understanding the degree of invasiveness of the upcoming surgical intervention:
- Intramedullary — located in the spinal cord in whole or in part. Blood is supplied exclusively by spinal vessels.
- Extraperimedullary — localized on the surface of the brain, do not penetrate intramedullary. Blood flow and drainage occurs through the root vessels.
- Extrarethromedullary — located on the posterior surface of the brain. The posterior spinal artery acts as an afferent vessel. A rare option.
- Intradural — located in the cerebrospinal (dural) membrane. The inflow is provided by the radicular arteries, the outflow is provided by the spinal veins.
Spinal arteriovenous malformations have a long latent period, sometimes lasting a lifetime. In some patients, it is detected during angiographic examination for another pathology. The onset, symptoms, and course of the disease differ greatly depending on the pathogenetic mechanism being implemented. Accordingly, apoplexy and paralytic variants of the clinical picture are distinguished.
Apoplexy is observed in 15-20% of patients, more often at a young age. It is caused by the rupture of the wall of one of the abnormal vessels with the outpouring of blood into the subarachnoid space or the substance of the spinal cord. It is characterized by a sudden acute onset with intense pain in the spine, weakness in the extremities. Subarachnoid bleeding is accompanied by hypertonicity of the occipital muscles, other meningeal signs. When the spinal arteriovenous malformations is located in the thoracic and lumbar spinal cord, weakness in the legs (lower paraparesis) occurs. Arteriovenous malformations in the cervical region are manifested by weakness of all limbs (tetraparesis). Motor disorders are combined with a disorder of sensitivity and muscle tone. Pelvic organ dysfunction is possible.
The paralytic form is characterized by gradual development. It proceeds with a steady aggravation of symptoms (progressive variant) or with periods of improvement / deterioration (intermittent variant). A progressive course is observed in 40% of patients. It may begin with radicular syndrome — severe pain in the spine, spreading to the arm, leg or chest (in accordance with the affected part of the spinal cord). Then muscle weakness and sensitive disorders are added. Weakness of the leg muscles causes increased fatigue when walking. Over time, the gait takes on a spastic character. There are convulsions, twitching of the muscles of the lower extremities. The next stage of the disease is a spastic increase in tone in the legs, aggravation of weakness, violation of urination, defecation. The symptoms progress up to a complete transverse lesion of the spinal cord. The involvement of the lower spinal thickening is manifested by a decrease in muscle tone, loss of reflexes.
Difficulties in diagnosis, late initiation of treatment contribute to the transition of clinical manifestations from the stage of reversible neurological deficit to a state of persistent pathological changes. Severe paresis and paralysis occur, self-care becomes difficult, the patient loses the ability to walk. With the development of severe tetraparesis, the patient is constantly in bed, which contributes to the occurrence of bedsores, congestive pneumonia, etc. complications.
The possibility to diagnose arteriovenous malformations of the spinal cord appeared in clinical neurology in the 60s of the XX century, when spinal angiography began to be introduced into medical practice. Prior to this, vascular malformations were detected during myelography as volumetric formations and were reliably diagnosed only intraoperatively. Now the modern diagnosis of spinal AVMs includes:
- Neurological examination. During the examination, paresis, sensitive disorders, changes in reflexes and tone are detected. The obtained data will help the neurologist to determine the approximate localization of the pathological process.
- Lumbar puncture and analysis of cerebrospinal fluid are performed in the apoplexy variant of the disease. The presence of blood in the spinal fluid indicates hemorrhage.
- MRI of the spinal cord. Allows you to visualize arteriovenous malformation, diagnose spinal hemorrhage, determine its volume and location.
- Angiography. It can be carried out using radiography with the introduction of a contrast agent. MRI of spinal cord vessels is more informative. Gives an idea of the type, location, extent, hemodynamics of the vascular anomaly. The results of spinal MR angiography help to choose an adequate method of treatment, plan the course of the operation.
Differential diagnosis is performed with spinal cord tumors, infectious myelopathy, multiple sclerosis, Strumpel’s disease, ALS. The apoplexy variant of the spinal cord AVM clinic is differentiated from hemorrhagic spinal stroke.
Spinal arteriovenous malformations that do not give clinical symptoms, are an accidental finding and have small sizes, do not require treatment, but need regular supervision by a neurosurgeon. If there is a clinic, surgical treatment is necessary. The following techniques are used:
Endovascular embolization is the introduction of an embolizing substance into an afferent vessel. It is performed under the control of angiography. Allows to achieve partial obliteration of the lumen of the adductor artery. It is used independently and as a preparation for surgical removal.
Open removal is a surgical operation during which microsurgical isolation, ligation and intersection of the arteries feeding the malformation is performed, followed by resection of the vascular conglomerate. An important point is the preservation of blood supply to the spinal cord.
Stereotactic radiosurgery is used when the formation is small, located in a hard-to-reach place, if endovascular obliteration is impossible. It acts as an additional treatment for incomplete excision of the formation as a result of open surgery, partial obliteration after endovascular intervention. Targeted irradiation causes aseptic inflammation, leads to gradual sclerosis. The disadvantage of the method is the gradual “closure” of the vascular lumen after surgery. During this period (up to 2 years), the probability of bleeding persists.
Restorative postoperative treatment is carried out by rehabilitologists. A control MRI and angiography are required. The combination of these studies makes it possible to identify the remnants of the anomaly, possibly preserved after removal, to determine the degree of obliteration after embolization and radiosurgery.
Prognosis and prevention
Proper diagnosis and timely treatment can prevent bleeding from the spinal arteriovenous malformations, the development of compression myelopathy, persistent motor disorders. In most patients, there is a significant recovery of lost functions up to a complete regression of the neurological deficit that has arisen. In the future, a relapse is possible, associated with incomplete shutdown of vicious vessels from the bloodstream. For several years after neurosurgical treatment, patients need to be monitored by a neurosurgeon. Prevention of the occurrence of spinal arteriovenous malformations is the exclusion of adverse effects on the fetus during pregnancy.