We conducted a retrospective observational study to evaluate patients who underwent surgery or endovascular treatment at our neurosurgical-neuroradiological university centre in Dresden between 2002 and 2023 and suffered from SDAVF. Eighty-one patients with SDAVF were identified, of whom seventy were treated surgically and eleven endovascularly.

Patients with suspected SDAVF on MRI/MRA (vascular myelopathy and/or flow voids) and corresponding symptoms (disturbances of gait, sensory function, motor function, bowel or bladder function or pain) were included in the study. Patients without evidence of SDAVF in the DSA were excluded from the study (Figure 1).

The study was approved by our local ethics committee (Reference number BO-EK-437102023). After case identification, patients’ data were collected via the ORBIS system (ORBIS, Dedalus, Bonn, Germany) and neuroimaging studies through the IMPAX system (IMPAX, Impax Asset Management Group plc, London, UK). Radiological data, including MRI, MRA, and DSA of the spine were available for review.

Data collected included age, gender, duration of symptoms to diagnosis, time from diagnosis to surgery or intervention, history of comorbidity (vascular disease, coronary heart disease, stroke, hypertension, hyperlipidaemia, degenerative spine disease, vertebral fractures, rheumatic diseases, drugs that trigger bleeding, use of corticosteroids, and BMI), performance of a preoperative or postoperative MRI/MRA/DSA, number of incomplete or failed occlusions, number of secondary treatments performed (surgery or embolization), recording of treatment- or hospital-related complications, side of the fistula, location of the fistula site, type of surgical approach, duration of surgery, surgical strategy in the form of coagulation with transection or combined (clipping, coagulation, ligation, transection and clip removal), use of indocyanine green fluorescein angiography (ICGFA), use of intraoperative microvascular doppler sonography (IOMVDS), type of embolization materials (Histoacryl, Squid, Onyx), first symptom, neurological status pre-treatment, at the time of hospital discharge, first follow-up (3 months after discharge), second follow-up (6 months after discharge), third follow-up (12 months after discharge), American Spinal Injury Association motor score (ASIA-MS), and modified Aminoff-Logue scale of disability (mALS) (22).

Clinical symptoms such as pain, disturbances of gait, sensory function, motor function, bowel or bladder function associated with MRI/MRA signs of myelopathy and flow voids form the basis for the suspected diagnosis of SDAVF. The diagnosis is confirmed by digital subtraction angiography (DSA). Each case was discussed in a multidisciplinary board with neurointerventional radiologists and neurosurgeons. If two therapeutic options were considered, the patient was usually informed and educated about both treatment options. The decision on the procedure was left to the patient. Until 2012, endovascular treatment was preferred in our hospital as a less invasive procedure. At that time, surgical treatment was suggested if endovascular treatment failed or was not feasible (vertebral artery or adamkiewicz proximity with inadvertent risk of embolization). Since 2012, surgical treatment became the treatment of choice in our hospital and endovascular therapy was considered as an alternative. In all cases, DSA and MRI/MRA were carefully reviewed by the neurosurgeon and a neurointerventional radiologist prior to surgery to determine the exact location and side of the fistula.

The location of the fistula was precisely determined using conventional fluoroscopy prior to the surgical procedure. The patient is carefully positioned in a prone position. In high- or mid-thoracic DSAVF cases, radiopaque markers are useful for intraoperative identification of the target level. The procedure was achieved through a single-level hemilaminectomy or laminectomy. A single-level laminectomy allows for easier watertight closure of the dura, especially in older and overweight patients, but may result in spinal instability, although the facet joint is not removed. A median skin incision of 3 cm is made, followed by uni- or bilateral tendon muscle disinsertion to expose the targeted hemi-lamina or lamina, which is then carefully resected with a diamond drill or/and a Kerrison bone punch. In rare cases, a unilateral interlaminar fenestration is performed, here the median skin incision is 2 cm, and a unilateral tendon muscle dissection is performed to expose an interlaminar window. Fluoroscopic reconfirmation of the level is required before opening the dura. The upper hemilamina is narrowed with the bone punch or diamond drill without damaging the facet joints. The lower part of the upper pedicle including the target nerve root with the accompanying artery can be seen here. The bones are also narrowed on the contralateral side in order to see the midline of the dura and later to facilitate the watertight dural sutures. The flavum is now resected and the dura exposed.

Under microscopic magnification, the dura mater is opened along the midline. The arachnoid is left intact, and the dura tack-up sutures are placed to retract the dural edges to minimize epidural bleeding and increase the view field. The arachnoid is then opened and the arterialized vein is identified as it exits the dura and then dissected free of arachnoid adhesions and the adjacent nerve roots. The fistula is then clipped with a temporary aneurysm clip and a change in the colour and turgor of the distal part of the clipped arterialized vein can be seen immediately. Intraoperative ICGFA and/or IOMVDS can be performed to confirm closure of the fistula. The distal and proximal arterialized vein is coagulated, ligated on both sides, sharply incised and then the temporary clip is removed. As an alternative method, the fistula is coagulated and sharply divided. After removal of the clip, ICGFA and/or IOMVDS were repeated to assess complete closure. A watertight dural suture was created and then fibrin sealant or biological glue was used. No drainage was placed in either surgical technique.

A postoperative spinal DSA or MRI/MRA was performed within the first 3 days after treatment to assess fistula closure and any postoperative complications. MRI/MRA was performed 3, 6 and 12 months after surgical or endovascular treatment to assess the disappearance of myelopathy and the regression of abnormal flow voids.

All statistical analyses were carried out using the software package SPSS (SPSS Statistics 28, IBM, Armonk, New York, USA). Following the initial descriptive analysis of the variables, Kruskal-Wallis tests were used to determine statistically significant differences (p < 0.05) as a non-parametric method for comparing three or more variables (pre-treatment, at discharge, at first, second and third follow-up). Categorical variables were compared by the Chi-squared or Fisher exact tests, as appropriate. All statistical tests were two-tailed, and a p-value p < 0.05 was considered statistically significant.

The most common first symptom in the 81 patients was gait disturbance (36, 44.4%), followed by sensory disturbances such as paraesthesia, hypesthesia, and anaesthesia (24, 29.6%), pain (15, 18.5%), extremity paresis (5; 6.2%) and bowel or bladder dysfunction (1, 1.2%) (Figure 2).

The location of the fistula point was most common in the lower thoracic region (T6–T12; n = 36, 44.5%), followed by the lumbar region (L1–L5; n = 23, 28.4%), the upper thoracic region (T1–T6; n = 12, 14.8%), the sacral region (from S1, n = 6, 7.4%) and the cervical region (C1–C8; n = 4, 4.9%). Fistula point was on the right side in 46 patients (56.8%) and left in 33 patients (40.7%), with two patients having fistulas on both sides (2.5%) (Table 2).

Among the 70 patients treated surgically, single-level laminectomy was the most common approach performed by the surgeon in 31 patients (44.3%), followed by single-level hemilaminectomy in 28 patients (40.0%) and unilateral interlaminar fenestration in 11 patients (15.7%). The average duration of surgery was 138.6 ± 65.7 min. The most common surgical strategy was coagulation and transection (36, 51.4%), followed by a combined strategy of clipping, coagulation, ligation, transection, and clip removal (34, 48.6%). ICGFA was used in 21 patients (30.0%), while IOMVDS was used in 41 patients (58.6%) (Table 3).

The endovascular embolization was most frequently performed with Histoacryl (7, 63.6%), followed by Onyx (3, 27.3%), and Squid (1, 9.1%).

The monocentric, retrospective nature of our analysis, the long inclusion interval, and the limited number of SDAVF patients treated with embolization (11 patients) might reduce the external validity of our study. Furthermore, our analysis could be affected by a possible selection bias due to our treatment flow charts, as our experience has been to favor surgery over embolization. Nevertheless, our cohort analysis is based on a 20-year treatment period of SDAVF in a large university neurosurgery center, suggesting a high internal validity of our study. Therefore, our observations may be useful to understand the clinical and radiologic characteristics of SDAVF.