CT Fluoroscopy–Guided Blood Patching of Ventral CSF Leaks by Direct Needle Placement in the Ventral Epidural Space Using a Transforaminal Approach

Discussion

CT fluoroscopy–guided EBP via direct needle placement in the VES by using a transforaminal approach has an excellent technical success rate. In 72 needle placements, 95.8% were technically successful, and nearly half (47.2%) resulted in an optimal epidurogram. Given these findings, we conclude that this technique can result in substantial spread of patching material throughout the ventral epidural space.

This technique should be considered when treating patients with a CSF leak arising from the ventral dural surface, particularly in cases refractory to conventional blood patch methods. In these patients, surgery is often the only remaining possibility for treatment. Though potentially curative, such surgical interventions carry with them the risk of significant morbidity as well as higher costs and longer recovery times, all of which could be avoided with a successful ventral EBP.^14,15

Previously described methods for imaging-guided EBPs typically involve either a posterior interlaminar epidural approach or a posterior transforaminal approach, analogous to those used with corticosteroid injections.^16,17 These techniques result in needle-tip placement within the dorsal epidural space of the spinal canal or the dorsal epidural space of the neuroforamen, respectively. In either case, the needle tip remains far removed from the dural defect responsible for a ventral CSF leak. Prior studies investigating the spread of epidurographic contrast by using a posterior interlaminar approach during corticosteroid injections have consistently demonstrated relatively poor spread to the VES.^5,7 For example, Botwin et al⁵ found that only 36% of interlaminar injections resulted in ventral epidural spread despite using 5 mL of contrast (significantly more than used in this study). Prior studies of transforaminal approaches have demonstrated slightly better rates of success, ranging from 61.4%–88%.^6,18,19 However, it is important to note that in all of these studies, “ventral” was defined as the anterior aspect of the neuroforamen. This was because the investigators were interested in the efficacy of corticosteroid injections for nerve origin pain. Furthermore, these investigations all involved procedures guided by conventional fluoroscopy, which limited their ability to assess for contrast spread into the spinal canal VES rather than simply the neuroforaminal VES. Therefore, it is impossible to know what percentage of these cases would be considered as either technically successful or optimal epidurograms according to the metrics defined in our study; presumably, it would be considerably less than the percentages previously reported. Achieving contrast spread into the spinal canal VES is important when treating a ventral CSF leak because an inability to deliver patching material to the site of the dural tear will preclude successful treatment.

Importantly, there were no complications in any of our cases. A potential risk of this procedure might include injection into a radiculomedullary artery, given the transforaminal approach used. Transforaminal epidural needle placement, performed during corticosteroid injections for pain, has been associated with rare but serious reported complications, including paralysis, stroke, and death.^{20⇓⇓⇓–24} These events are thought to be the result of either embolic injection into, or direct vascular injury to, a radiculomedullary artery supplying the spinal cord. Embolic injection is the more likely mechanism, considering that no catastrophic events have been reported with nonparticulate corticosteroids.²⁵ We performed 72 needle placements without a complication. Furthermore, we found no cases of intra-arterial contrast injection. We did identify an inadvertent intravascular injection rate of 29.3%, which is slightly higher than the reported rates in the literature for posterior interlaminar and transforaminal needle placements.^{13,26⇓–28} The rich epidural venous plexus within the spinal canal is presumably responsible for the relatively increased incidence of vascular cannulation in our study. The fact that all of these incidents were classified as either “definitely venous” or “probably venous” supports this supposition. We recommend an approach through the inferior third of the neuroforamen, where possible, for 2 reasons. First, there was a relatively increased incidence of inadvertent venous injection when the needle traversed the middle third of the foramen. Second, a radiculomedullary artery will usually be located anterior to the nerve root within the superior third of the neuroforamen within the thoracic spine.^29,30 Therefore, an inferior approach will help to avoid it. Of course, any potential risk associated with placement of a needle in the ventral epidural space via a posterior transforaminal approach should be considered in the context of the available alternative treatment options. For patients with ventral CSF leaks that have failed conventional treatments, it is often the case that the sole remaining option is a complex and challenging surgical intervention with significant morbidity and potential mortality.

In limited case reports, prior investigators have recognized the potential benefit of direct, targeted placement of patching material within the ventral epidural space. Park and Villablanca⁸ published a single-case report of an anterior approach through the C5–6 intervertebral disc under conventional fluoroscopic guidance. This anterior needle approach courses between the pretracheal fascia and the carotid sheath and is commonly used during cervical discography and disc biopsy.³¹ Given the presence of the mediastinal structures and the lungs, this technique would not be feasible in the thoracic spine, which is where most ventral CSF leaks occur. Furthermore, the technique is not without significant risk because of the need to displace the carotid artery as well as avoid the vertebral artery. In fact, multiple complications have been previously reported, including hemorrhage, vertebral artery injury, damage to the spinal cord, and injury to the trachea and carotid artery.³² Zaw et al⁹ reported a single case of successful epidural blood patch achieved by placement of the needle tip in a ventral epidural collection at T6 via a posterior transforaminal approach. This procedure was performed after several failed conventional blood patch attempts. Similarly, most of our cases also were performed after failure to achieve a durable treatment with more conventional methods. Our study is the first to investigate this transforaminal approach to the ventral epidural space in a large series of patients. Furthermore, it includes new information about the extent of ventral epidural spread of patching material and provides insight into the safety profile of this approach.

There are several limitations to our investigation. First, this was a retrospective study of a relatively limited number of procedures performed by highly experienced interventionalists. We recommend caution for proceduralists with limited experience. In addition, rare complications could have been missed given the number of patients. However, 72 consecutive needle placements without a complication suggests that the incidence of such adverse events is likely very low. Second, we did not perform a direct comparison of the contrast epidurograms achieved by using conventional CT fluoroscopy–guided patching methods (ie, interlaminar and traditional transforaminal approaches) with the experimental technique outlined in this manuscript. There might be a different and more efficacious mechanism for achieving an optimal epidurogram in the VES. However, prior studies suggested that conventional interlaminar and transforaminal approaches under fluoroscopic guidance do not result in adequate spread to the ventral epidural space of the spinal canal.^{5⇓–7,18,33} Finally, though we noted that 41% of patches resulted in successful resolution of patient symptoms for at least 2 months, prospective patient outcomes were not assessed in this investigation. A more structured evaluation with validated headache outcome measures could be included in a future prospective investigation. Furthermore, a study comparing patient outcomes for interlaminar epidural, transforaminal epidural, and ventral epidural approaches is needed to justify more widespread adoption of this technique in patients with ventral CSF leaks.