The syndrome of spontaneous intracranial hypotension (SIH) represents a significant recent challenge for neuroradiology because it relies heavily on imaging for diagnosis and management. Since the imaging findings of SIH were first described on MRI,¹ there have been many articles on the intracranial imaging findings associated with SIH. Although an empiric nondirected epidural blood patch (EBP) can have success in treating the condition, it is clear that in patients who fail an initial EBP, the most effective treatment and cure of SIH can only come about with definitive localization of the CSF leak.

The challenge of leak localization again falls squarely upon the neuroradiologist. Our article shows that a systematic approach to leak localization with MR imaging of the brain and spine as well as dynamic myelography provides a high-yield pathway to leak localization. Having localized the leak, the neuroradiologist may again be called upon to provide EBP or focal fibrin patching. Eventually, many patients will go on to surgery.

For patients who demonstrate spinal longitudinal extradural collections (SLECs) on MR imaging of the spine (SLEC-positive), the work-up is straightforward and leads to leak localization in almost 100% of cases.

Two vexing problems remain to be addressed. First, what can we offer the 10% of patients with SIH who are head MRI-positive, SLEC-negative, and whose leak cannot be localized despite a full battery of dynamic myelography (be it digital subtraction myelography [DSM], dynamic CT myelogram, or both)? Simply put, we know that they have a leak but cannot find it. Is there a new, as-yet-undiscovered type of leak?

The reader is reminded that it was only 4 years ago that the entity of CSF venous fistula (CVF) was discovered²; we now know that CVF accounts for over 20% of leaks. I suspect that these missing leaks are simply due to slow or intermittent CVF. How do we intelligently move forward? What modifications to our current dynamic myelographic techniques are needed to visualize these missing leaks? Improved MR imaging with higher spatial and temporal resolution may play a role in further evaluating these head MRI-positive, SLEC-negative, DSM-negative patients who may harbor an intermittent CVF.

Second, what are we to do with patients who present clinically with symptoms suggestive of SIH but in whom MR imaging is persistently negative for all signs of SIH? It is commonly stated that a percentage of these patients do actually suffer from SIH and harbor a cryptic leak.³ Should all these “headache patients” undergo EBP as well as a full battery of DSM? That would entail a somewhat invasive effort with a significant radiation dose to find a small number of leaks. Instead, a highly sensitive and specific diagnostic test for SIH is required. This may already exist with current MR imaging and may simply require validation. Perhaps a marker for CSF leak (ie, a CNS-specific compound that can be easily quantified in the serum and can be shown to be elevated in patients with CSF leak due to higher-than-normal turnover of CSF) will be elucidated in the future.

The growing awareness of the methods of diagnosis, along with increasing identification of patients who suffer from SIH and multicenter collaboration, will help us answer these questions.

References

1. Fishman RA, Dillon WP. Dural enhancement and cerebral displacement secondary to intracranial hypotension. Neurology 1993;43:609–11, 10.1212/wnl.43.3_part_1.609
2. Schievink WI, Moser FG, Maya MM. CSF–venous fistula in spontaneous intracranial hypotension. Neurology 2014;83:472–73, 10.1212/WNL.0000000000000639
3. Kranz PG, Gray L, Amrhein TJ. Spontaneous intracranial hypotension: 10 myths and misperceptions. Headache 2018;58:948–59, 10.1111/head.13328

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