Spinal dural arteriovenous fistula (SDAVF).
1. Overview.
It is the most common type of SCAVLs, accounting for about 70% to 80% of cases. According to incomplete statistics, the incidence is about 5-10 cases per million people per year. It predominates in men over 40 years of age, with a mean age of 60 years and a male to female ratio of 5 to 8:1.
The clinical features of SDAVF were first reported in detail by Foix and Alajouanine in 1926, so much of the literature also refers to SDAVF as Foix-Alajouanine disease, and its vascular pathological basis was first reported by Kendall in 1977 and later confirmed in the 1990s.
Its etiology is not well understood. It is now believed to be mostly an acquired disease, associated with a variety of factors such as infection, spinal cord cavitation, trauma and surgery.
Pathology: SDAVF is a traffic between the artery supplying the dura or nerve roots and the spinal drainage vein as it crosses the dura at the intervertebral foramen.
2. Clinical symptoms
The pathogenic mechanism is mainly spinal venous hypertension, spinal venous hypertension impedes spinal venous return, resulting in a decrease in spinal artery perfusion pressure, causing degeneration and necrosis of the spinal cord.
Clinical manifestations are often insidious onset, slow progression, progressive aggravation. It starts with a single sensory, motor or sphincter dysfunction, which may be accompanied by urinary and faecal and sexual dysfunction, and then progresses in an upward direction. Cone syndrome is the most common clinical condition, while simple localized nerve root pain is rare.
Acute subarachnoid hemorrhage (SAH) is the first symptom in about l% of patients; in SDAVF in the craniocervical junction, SAH is the first symptom in about 60% of patients.
Because of the atypical symptoms, early diagnosis is difficult, and the condition is often serious by the time of consultation, and the misdiagnosis rate is reported to be 60.7% in China. In the Department of Neurosurgery, Huashan Hospital, Fudan University, incomplete statistics, the average disease duration of patients at the time of diagnosis has reached 18 months. The literature reports that the average duration of disease reaches 23 months.
3. Diagnosis
(1) MRI and MRA: As the first screening tool, MRI scan reveals a worm-like vascular flow signal on the dorsal and ventral side of the spinal cord, with the T2 W1 image showing the most clearly, and enhanced MRI scan shows the enhanced signal of tortuous vessels on the surface of the spinal cord (Figure 3-9-10).
(2) DSA: The blood supply artery suddenly thickens to the draining vein in the spinal canal as its imaging feature (Figures 3-9-10 and 3-9-11). The draining veins are migrating, meandering, and dilated, and the blood flow is slowed down, and the circulation time of spinal veins is prolonged for 40-60 seconds (Figure 3-9-10).
The vascular architecture of SDAVF is characterized by.
(1) Small fistula (diameter about 150-200 microns (Figure 3-9-11))
(2) The blood supply artery is small and tortuous, originating from the dural vessels, and the ASA and PSA are not involved in the blood supply
(3) Root vein drainage
(4) The fistula is located in the dura mater, mostly posteriorly and laterally
(5) Most of the fistulae are single fistulae and single donor artery
Special attention is paid to:
The first clinical symptom of SDAVF in the craniocervical junction area and upper cervical segment may be spontaneous SAH if it drains toward the skull base, therefore, in patients with spontaneous SAH mainly in the posterior cranial fossa, if no abnormality is found in the routine DSA of the brain, additional angiogram including this bilateral thyroglossal trunk, cribriocervical trunk, cervical and lumbar segments, or even the whole spinal cord should be done to prevent missing.
The leakage rate of SDAVF in the craniocervical junction area and upper cervical segment: 40.9% were found when transferred from outside hospitals to Huashan Hospital of Fudan University, compared with 60.5% abroad.
4.Treatment
Aminoff et al. reported that if SDAVF patients are not treated in time, about 19% of patients are disabled 6 months after the onset of symptoms and 50% after 3 years. Behrens reported that about 2/3 of patients who could only live on wheelchairs before surgery could stand after active treatment. Early treatment is emphasized.
The ideal treatment is to permanently eliminate venous congestion of the spinal cord without affecting its blood supply and normal venous return. The current treatment of SDAVF includes surgery, embolization or a combination of the two.
(1) Surgery
The efficacy of surgery is well established and is a permanent treatment.
History: In 1969, Ommaya et al. used the method of occluding the arteriovenous fistula without stripping the coronary vein to treat SDAVF and achieved better results. Later, many people used the method of ligating the drainage vein, which can solve the venous stasis and improve the symptoms of myelopathy after simply clamping the drainage vein, and the effect is more durable.
Currently, clamping of the draining vein and electrocoagulation of the arteriovenous fistula are used.
The procedure: After preoperative localization, the fistula is centered on the vertebral plate at the location of the fistula and on the next segment of the vertebral plate, the dura mater is cut along the midline, and the dura mater is explored along the side of the lesion, and the arterialized medullary vein can be seen near the posterior spinal nerve root through the dura mater (Figures 3-9-12 and 3-9-13). To distinguish the medullary vein from the medullary artery, the venous phase image should be compared with the preoperative imaging, and the medullary vein should be carefully observed to see if it joins the abnormal coronary plexus through the subarachnoid space. The draining vein is separated from the nerve root, electrocoagulated, and severed. Only the section of the draining vein from the inner dural layer to the anterior subarachnoid space is electrocoagulated and excised, without damaging the coronary plexus on the spinal cord surface.
After blocking the medullary veins, pressure changes in the swollen veins can be detected, while Doppler ultrasound examinations of the coronary plexus mostly show no blood flow signal and venous stasis. It should be mentioned that after fistula blockade, the color of the draining veins does not change significantly, as stated in the literature, but usually becomes darker and redder, and a lower tension of the draining veins is observed than before the blockade.
In recent years, indole i green (ICG) has been widely used in the intraoperative evaluation of cerebrospinal vascular disease and can be observed to compare the change in blood flow velocity before and after clamping the fistula and the visualization to assess whether it is complete or residual (Figure 3-9-12).
Postoperatively, the dura mater of the vertebral body next above the lesion, as well as the contralateral dura mater, should be explored to avoid missing the
the fistula.
Surgical results.
In 1979 Logue studied the results of surgery in 24 patients with dural arteriovenous fistulas, of which 22 were successful and 2 had worsening symptoms postoperatively; 59 cases were followed up: 15 patients had improved spinal nerve function, 7 had stable disease, and 2 had worsening. Many authors who support surgery believe that: surgery is effective, with a first-time success rate of even 100%; surgical treatment is recommended in the presence of multiple supplying arteries; after embolization, frequent imaging is needed to understand embolization and the need for reembolization: Songn et al. had a 15% recurrence rate after embolization with liquid material. Jelleman et al. followed up over a 6-year period and found that after embolization Jelleman et al. found that 46% of patients required re-treatment after embolization. Therefore, surgery should be the treatment of choice.
The short-term efficacy of surgery is positive, but the long-term studies are less reported and need to be further confirmed.
(2) Embolization
In 1968, Doppman et al. started to use endovascular embolization to treat SDAVF, which was considered as a non-invasive treatment method. Subsequently more and more people are using this method. Authors who support embolization believe that: embolization should be attempted at the first imaging, with a 30% success rate and no side effects, and even if embolization fails, it helps to locate the supply artery and drainage vein intraoperatively; therefore it should be the first-line treatment, and surgery should be considered only when embolization techniques are limited or unsuitable.
There is a wide variety of embolization materials: granules (PVA), spring coils, liquid gels (NBCA, Onyx, Glubran), etc. Due to the high rate of embolization recurrence of the first two, they are now rarely used and are now mostly treated with NBCA, Glubran or Onyx.
Embolization procedure: The microcatheter is superselected to the fistula and the embolic agent is injected 2 mm from the fistula and the beginning of the draining vein (Figure 3-9-14), taking care not to embolize the distal end of the draining vein and the perimedullary vein, as this may aggravate the condition. In case of arteriovenous fistulas where the supplying artery and the root medullary artery are co-operating, surgical treatment should be performed.
Effectiveness: In 1997, Niimi et al. retrospectively summarized the results of 47 patients with SDAVF after embolization with NBCA, with a first-time success rate of 87%. In 1998, Ling Feng et al. reported that NBCA is currently the most suitable embolization material for the treatment of SDAVF. Recently, it has been reported that the use of Onyx as embolization material has good effect, and it is considered that it is easier to control during embolization and it is not necessary to withdraw the catheter soon after embolization.
(3) Choice of treatment method
At present, it is recognized that surgery is the first choice because of its positive efficacy and low recurrence rate. Disadvantages of surgery: compared with embolization treatment, it is more traumatic, and the diagnosis and treatment should be completed twice.
If there is a suitable vascular construct for embolization, embolization can be attempted at the first imaging, especially for those who cannot tolerate surgery, those with more complicated surgery in the sacrococcygeal or craniocervical junction area, and those with multiple fistulas, because embolization treatment is less traumatic, diagnosis and treatment can be completed at once, and patients recover faster after treatment. Disadvantages of embolization: the efficacy is still uncertain and the recurrence rate is relatively high.
For high flow or multiple fistulas, combined therapy is advocated to overcome the disadvantages of surgery or embolization alone and is the mainstay of treatment: embolization should be attempted at the first angiogram if possible, or partial embolization in preparation for surgery, which can immediately reduce the patient’s symptoms. If embolization fails or is inappropriate, surgical treatment can be used without repeated embolization.
Increasing attention is being paid to whether to anticoagulate after surgery. After the DAVF is blocked, the pressure in the peri-medullary coronary plexus decreases by an average of 38.3%, and the dysfunction caused by venous hypertension is quickly restored, while most of the coronary plexus has slow or no blood flow signal on Doppler ultrasound, resulting in “venous stasis”. This predisposes to intravenous thrombosis. The lower the location of the fistula, the higher the probability of thrombosis.
Anticoagulation is performed within 24-48 h after embolization or surgery, usually with oral warfarin, to maintain prothrombin time at 2 to 3 times normal and activity at 30% of normal. To avoid postoperative bleeding, close attention should be paid to changes in the condition, and anticoagulation should be discontinued if bleeding occurs. The duration of anticoagulation is usually 1 to 3 months.
(4) Overall efficacy.
In 1997, Tacconi et al. found that 84% of patients’ symptoms improved or stabilized after surgery, however, the average follow-up of 147 months showed that only 35% of patients’ symptoms improved and the rest were significantly worse. 2003, China reported that 55% of symptoms completely disappeared, 35% improved and 10% did not change. 2007, China reported that the effect of surgery: 2/3 of In 2007, it was reported that 2/3 of the patients with impaired motor function had improved Amino row scores of 1 to 2, and nearly half of the patients had improved pain and sensory impairment.
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