The timing of MRI determines the presence or absence of diffuse pachymeningeal enhancement in patients with spontaneous intracranial hypotension.

The timing and clinical relevance of diffuse pachymeningeal enhancement (DPE) in the magnetic resonance imaging (MRI) examination of patients with spontaneous intracranial hypotension (SIH) remain undetermined. We reviewed 53 consecutive SIH patients (30 F/23 M, mean age of onset 41.7 +/- 11.3 years) in a tertiary hospital. Thirteen (24.5%) patients did not have DPE on their initial cranial MRIs. They had significantly shorter latency between the time of MRI examinations and the time of headache onset compared with those with DPE (6.5 +/- 4.4 vs. 20.4 +/- 16.3 days, t-test, P < 0.001). Eight of these 13 patients received a follow-up MRI (mean duration 30.3 +/- 16.6 days, range 6-59 days) and six of them revealed DPE. Among patients with DPE, the enhancement disappeared as early as 25 days after headache onset. The outcome did not differ between patients with and without DPE. The presence of DPE was associated with the timing of the MRI examination.