How often is a contrast-enhanced brain MRI truly normal in the setting of spontaneous intracranial hypotension?

In a paper by D'Antona et al., PMID 33393980:

"Of 6878 articles, 144 met the selection criteria and reported on average 53 patients with SIH each (range, 10-568 patients). The most common symptoms were orthostatic headache (92% [95% CI, 87%-96%]), nausea (54% [95% CI, 46%-62%]), and neck pain/stiffne...