CT-Guided Epidural Contrast Injection for the Identification of Dural Defects

DISCUSSION

PDPH is underreported and can be debilitating. Prior work has used DSM to diagnose dural defects in PDPH, but this technique requires an extra dural puncture. Our technique of injecting contrast into the dorsal epidural space is different in that it does not require another puncture to be made in the dura. We present this technique for consideration in patients with suspected PDPH.

Performing myelography, be it DSM or CT myelography, for PDPH is problematic for several reasons. First, this requires a dural puncture that carries additional risk of PDPH. Second, contrast injection for a myelogram can cause leakage into the epidural space (Fig 4) that obscures the site of a pre-existing dural defect. Contrast injection into the epidural space does not have either of these limitations.

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FIG 4.

Two examples of extradural contrast after intrathecal injection that limit the ability of myelography to detect a dural defect. A, Image from a lateral decubitus photon-counting detector CT myelogram that shows contrast extending posteriorly along the needle tract (white arrow). B, CT imaging after DSM, after the needle was removed, shows extradural contrast at the site of prior needle placement (black arrow). Both findings would obscure the detection of contrast leakage through a dural defect present before myelography.

A case report from Callen et al¹² described a similar contrast jet after epidural contrast in a postpartum patient with PDPH. Their patient had a focal dural outpouching on the lumbar spine MRI by using a 3D T2-weighted sequence. Although our patients had MR imaging only before the lumbar puncture, this MRI finding has not been described outside of this case report. Their patient did not have an adequate response to epidural fibrin and required surgical repair. An empiric lumbar epidural blood patch is standard practice for PDPH. In equivocal cases, treatment without diagnosis becomes complicated if the patient has atypical symptoms or has incomplete response to the blood patch that could potentially require surgery, as highlighted by the case from Callen et al.¹²

This technical report mimics the technique that we have recently described to diagnose spinal postoperative pseudomeningoceles by injecting extrathecal contrast to detect a dural defect.¹³ That report describes injecting contrast directly into a postoperative paraspinal fluid collection for the purposes of visualizing a contrast jet into the subarachnoid space to confirm and localize the leak site. Additionally, we separately described the injection of epidural contrast to propose an alternative mechanism for intrathecal hematoma after epidural blood patch, where epidural blood traverses from the epidural space to the subarachnoid space via a dural defect.¹⁴ If a contrast jet is seen, our practice tends to inject a smaller amount of blood, with the thought that high pressure of larger volumes could lead to more egress of blood into the subarachnoid space. The technique described in the present study is limited in that we only assess the dorsal dura, and a ventral dural defect caused by inadvertent deep needle position would not be evaluated.

Our technique, while it would remain the same for subacute versus chronic PDPH, was only demonstrated after recent lumbar puncture. This reflects our procedural practice, which performs multilevel blood patches after negative myelography work-up and does not see as many patients for chronic PDPH. Future work should be done to confirm this finding in subacute and chronic PDPH. Membrane formation has been described in the setting of spinal CSF leaks,¹⁵ and could occur at the site of dural defects in PDPH, particularly when long-standing. Our described technique could be specific but lacks sensitivity if obstructive membranes prevent the visualization of contrast jets. Even in the setting of potentially limited sensitivity, we favor epidural contrast injection rather than a new dural puncture and myelography to evaluate for persistent dural defects from a prior lumbar puncture. Our case examples had prior image-guided lumbar puncture with known puncture levels. If the prior puncture site is unknown secondary to absent records or nonimage guided technique, epidural contrast could be injected at multiple levels. Further study of this technique could also evaluate treatment outcomes related to the epidural blood patch. This CT fluoroscopy–guided procedure does require radiation exposure, but with only minimal increased dose when compared with an isolated CT fluoroscopy–guided epidural blood patch.

PDPH is increasingly recognized as an important cause of chronic debilitating headache. When the diagnosis is not recognized promptly after the spinal procedure, or when there are atypical symptoms, additional tests are often required to establish the diagnosis. Injecting contrast into the dorsal epidural space is a technique that can help to identify dural defects that cause PDPH.