CT Myelography for the Planning and Guidance of Targeted Epidural Blood Patches in Patients with Persistent Spinal CSF Leakage

Discussion

IHS as a cause of persistent daily headaches has been shown not to be as rare as was previously thought. The annual incidence has been estimated as 5 per 100,000.¹⁶ Orthostatic headache is the most common, but not mandatory, manifestation of IHS, accompanied by a wide variety of other symptoms such as neck pain or stiffness, nausea, hearing loss, visual blurring, facial numbness, Parkinsonism, ataxia, or dementia.^2,9,17 It seems plausible that a low CSF volume due to a persistent CSF leak is the cause of this syndrome. Most often, such a leak is due to dural puncture for diagnostic LP or spinal anesthesia.¹⁸ Nevertheless, a dural leak could also be associated with dural injury in the course of spinal surgery or craniospinal trauma. In 2 of our patients, lumbar facet joint injections were practiced before the symptoms of IHS occurred. There are no reports that document facet injection as a potential cause of CSF leakage. However, in both patients with facet joint injection, CT myelography revealed diffuse extradural spreading of contrast medium at the levels treated. We had no data that documented whether the facet joint injection was performed by using palpation or fluoroscopic guidance. A violation of the dural sac during a blind procedure is rare but should be taken into consideration. In 4 patients, no cause for the existence of a CSF leakage could be found. In these cases, CSF leaks were suspected to have occurred spontaneously. There is strong clinical evidence that a significant number of these spontaneous dural leaks are related to connective tissue disorders, as seen in hereditary syndromes like Marfan syndrome and Ehlers-Danlos syndrome.^19,20 In these patients, a great variety of structural abnormalities causing spontaneous spinal CSF leaks may be found during surgery. Meningeal diverticula, dural holes, dural tears, or missing nerve root sleeves have been reported.^1,18

The standard procedure for the diagnosis of IHS includes imaging of the brain and spine. As far as brain imaging is concerned, MR imaging is the preferred technique, showing pachymeningeal thickening and gadolinium enhancement, engorgement of venous structures, pituitary hyperaemia, and sagging of the brain.^2,21,22 These findings seem to be part of the compensation mechanism related to the loss of CSF volume.²³ MR imaging of the spine has attracted less interest, mainly because of the limited ability to localize a dural leakage site.⁹ MR myelography, in particular, has revealed promising results,^24,25 but only some institutions are performing it for diagnostic purposes; thus, the safety of intrathecal gadolinium application is yet unclear.²⁶ Therefore, CT myelography is still the diagnostic tool of choice, as it can show the location and extent of CSF leaks with high accuracy.^9,11 The de facto complication rate associated with lumbar puncture is very low and includes pain, paresthesias, meningitis, cauda equina syndrome, and persistent leakage of CSF.²⁷ On the other hand, an untreated, persistent CSF leak may have severe consequences such as subdural hematoma, downward displacement of the brain, and nerve injury.²

Consistent with other studies, we could not detect the CSF leak conclusively by MR imaging in any of our patients. However, CT myelography revealed a dural leak in all 7 patients, with cervical localization for 3 patients and lumbar localization for 4 patients. Two patients with a lumbar leak showed nerve-root-associated spreading of contrast-enhanced CSF, thus implicating a lacking or damaged nerve root sleeve at this level.

It is believed that most dural leaks occlude spontaneously within a few weeks. Therefore, conservative measures should be sought at first, including bed rest, oral hydration, caffeine intake, and the use of an abdominal binder. If symptoms persist or even aggravate, then further, more invasive therapeutic options should be taken into account.

EBP is the most common therapy in patients with a persistent CSF leak, though it has been questioned, as a systematic review has revealed less favorable results than initial reports suggested.²⁸

Although CSF leaks occur most often in the cervical or thoracic spine, an EBP is commonly applied without visual control at the lumbar level and is not performed at the suspected site of the leak. However, to ascertain distribution of blood to the upper spine, the patient needs to be seated in a Trendelenburg position after the injection.^9,29 There are a few reports that observed a minor upward spread of a lumbar blood injection by up to 4–6 spinal segments.^3,8,29 However, when blood is injected at a site distant from the CSF leak, it is difficult to conceive how the blood can traverse to the desired, remote location, with clotting commencing immediately after injection. Despite some reports of successfully treated CSF leaks with this method, animal experiments have shown that an EBP performed directly at the site of the leak will seal the dural defect more effectively than a blind epidural patch in the lumbar region.¹⁰ This suggests that, for therapeutic purposes, the local sealing effect of the epidural tamponade is the predominant effect.⁹ Some reports state a mean injected blood volume of about 30 mL, and up to 100 mL in certain cases.^9,29 Conversely, a targeted blood patch requires much lower amounts of blood (mean 15 mL) and thereby reduces the chance of complications.

Despite these facts, the blind lumbar patch is still preferred due to a higher risk of spinal cord violation during cervical EBP. To minimize this risk and to decrease the rate of symptom relapse, we performed CT myelography followed immediately by a targeted EBP. This way, the contrast enhancement of the spinal intra- and extradural space is used to initially diagnose and to subsequently guide the EBP safely, due to the positively identified epidural space (as seen in Fig 1). Recently, Kranz et al¹⁴ also reported a series of 8 patients who were treated with targeted epidural blood patches by using a similar procedure with promising results. In contrast to our method, in which only a single EBP is applied, they used several blood patches in each patient, ranging from 1–10 in the initial treatment session.

The loss of resistance puncture technique is usually applied to inject medication into the epidural space, in particular by anesthesiologists.³⁰ However, the loss of resistance due to loosely packed tissue in the epidural space (containing fat, veins, and emerging nerve roots of the spinal cord) cannot be detected reliably if the epidural space is filled with CSF caused by a dural leak.²⁷ Therefore, contrast-enhanced CT images could help to place the needle tip in the epidural space exactly, without the risk of damaging the spinal cord. Furthermore, our method could improve EBPs, even in case of a lumbar leak, because the injected amount of blood could consequently be minimized without reduction of the tamponade effect.¹³ In addition, the risk of subarachnoid blood injection resulting in an intrathecal hematoma, accompanied by severe back pain and radicular symptoms, could be reduced.²⁹

For the 7 patients who we have reviewed in this study, there were no complications or adverse events. Six out of the 7 patients experienced a considerable relief of symptoms within 24 hours after the procedure. The one remaining patient went into remission after a repeat EBP at an additional suspected leakage site.

We are well aware of the limitations of this study. First, as already criticized in other studies and as per definition of this kind of study, there is no control for spontaneous remission in our patients.

Second, the inclusion of more patients would yield better data, in particular, regarding efficacy and safety of our procedures. However, the extra radiation dose that is incurred by doing a large CT myelogram study is a limiting factor because the reduction of radiation is an important aim. Although a CT myelography-guided, targeted EBP seems effective and low risk, it might not be necessary if medical history and diagnostic findings clearly indicate a spinal CSF leakage. In this case, an initial blind lumbar EBP may reduce radiation dose. If this fails, a CT myelography-guided targeted EBP could be the next step of escalation.

In the case of lumbar CSF leaks, a blind EBP is certainly a possible treatment option. However, if myelography is performed for diagnostic purposes, an immediate targeted patch can probably seal the leak more effectively and safely.