Letter: Microsurgery of Spinal Dural Arteriovenous Fistula Using Indocyanine Green Video Angiography: 2-Dimensional Operative Video.

To the Editor: Yokoyama et al1 present a video of resection of a spinal dural arteriovenous fistula (SDAVF) in microsurgery, with the aid of intraoperative indocyanine green (ICG) microangiography. The surgery was performed according to routine. The operation is anatomically successful and the video presented is therefore a useful educational tool for young neurosurgeons and for neurosurgeons approaching spinal and vascular vertebral surgery. The video also demonstrates the usefulness of using ICG combined with microscopy. This video provides us the message that even a standard surgical treatment is approachable with different operative techniques. At our department, the SDAVF removal technique is also a standard technique. However, in addition to the use of ICG, we use a protocol that includes a multimodal consensus of multiple experts present in the neurosurgical operating room. We believe that the neurosurgeon alone is sometimes not critical enough to be able to uniquely decide which is the best therapeutic strategy, and for this reason, we collaborate with other experts. In addition to the help of the neurophysiologist, with his intraoperative monitoring, the neuroradiologist is also present in the operating room during the operation, helping the neurosurgeon to identify the arterial axes through his preoperative angiographic evaluation through the visualization, inside the operating room, of the images previously acquired by him. We believe that neuroradiologists remain, in most cases, the maximum experts in spinal vascular anatomy. Because we believe that surgery remains the best possible strategy, the last 6 patients with SDAV admitted at our department were treated surgically. All patients underwent neurophysiological preoperative test to obtain starting data to confront; moreover, modified Aminoff and Logue2 Score (mALS) was adopted to evaluate the motor function of the lower extremities and sphincter. The patient underwent laminectomy for microsurgical clip occlusion. With the constant help and consultation of the neuroradiologist during the procedure, intraoperative micro-Doppler (IMD) and indocyanine green (ICG) video-angiography were used both before placing the clip to locate the arterialized veins of the fistula and, after clip placement, to confirm that the fistulous connection had been obliterated and normal blood flow had been restored. During the procedure, intraoperative neurophysiological monitoring (IONM) was performed, evaluating somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) with electrical transcranial stimulation. Both multipulse technique with multiple myomeric registration of limb responses and single-pulse technique were used, with D-wave registration by epidural and intradural recording.3 Moreover were constantly monitored free-running (frEMG) and evoked electromyography (eEMG) with bilateral segmental recording from target muscles. In the hands of the most skilled surgeon, as well, spinal surgery carries an inherent risk of damaging critical nerve structures, which can result in the development of a postoperative neurological deficit. To make surgery as safe as possible, many of the neurosurgeons use intraoperative neurological monitoring. However, although this tool cannot directly prevent intraoperative damage, it has the potential to provide the surgeon with real-time feedback of the neurological pathways. In certain circumstances, this feedback can prevent or reduce neurological damage.4 It is important, even beyond the intraoperative monitoring, to have a competent neuroradiologist (skilled), with deep knowledge of spinal vascular neuroanatomy, and a DVAF hemodynamics expert, who can be the same neuroradiologist or neurophysiologist present there. The concomitant presence of these figures and their constant collaboration are key points in the success of the surgical treatment. We believe that the preoperative discussion between the neurosurgeon, the anesthetist, the electrophysiologist, and the neuroradiologist is the primary and essential component for the definition of an intraoperative monitoring protocol and for the definition of the alarm criteria to be used and the possible steps to be followed in case of a negative accidental event.4 Multimodal monitoring has the potential to compensate for the limitations of each individual monitoring and has therefore become standard practice for a variety of spinal-type procedures. Some studies have documented how the sensitivity and specificity of multimodal monitoring is approximately 100%.5-7 In our small case series, the use of multiple techniques and the union of multiple minds have allowed us to ensure a better outcome of the surgery. However, there is a lack of standardization in risk criteria during neurophysiological monitoring. Moreover, the scientific literature on the preoperative checklist, and therefore on the choice of which monitoring methods to use, remains incomplete. It would be useful to define a specific protocol to create a new scenario, a standardized and reproducible approach in all clinics. In conclusion, on the day of discharge, mALS was decreased in 4 patients and remained unchanged in 2 patients. No worsening of mALS was observed. The neurological status improved or remained stable in 100% of patients on the day of discharge. Postoperative DSA showed complete removal of sDAVF. We conclude that the presence in the operating room of an expert neuroradiologist and neurophysiologist makes this multimodal approach simple, and it is important to understand intraoperative vascular and functional anatomy and choose the best surgical strategy.