SIH is commonly caused by spinal CSF leakage. Brain neuroimaging findings in SIH can be used not only to make a diagnosis but to predict outcomes. The Monro-Kellie doctrine has been widely adopted to explain brain neuroimaging abnormalities in SIH. According to this theory, the sum of brain tissue, CSF, and intracranial blood volume is constant. To the current knowledge, intracranial veins tend to dilate to compensate for the decreased CSF volume. However, the brain volume change in SIH remains unknown.

The present study aimed to measure the brain volume in spontaneous intracranial hypotension (SIH).

We retrospectively reviewed the brain and spinal MR neuroimaging findings as well as demographics and clinical profiles of consecutive patients with SIH in Taipei Veterans General Hospital. The follow-up neuroimaging studies were performed within three years after recovery. The brain structure volume was analyzed using SPM12 and FSL.

Between January 2007 and July 2015, 188 patients with SIH were recruited.  Of them, 61 had qualified initial and follow-up neuroimaging studies and of note, their SIH was successfully treated by epidural blood patching. Compared to follow-up stage, the whole brain volume decreased during SIH (before treatment vs. follow-up: 1185.8 mL: 1197. 2 mL, p=0.005). Meanwhile, the CSF volume in the ventricles also decreased during SIH (before treatment vs. follow-up: 92.8 mL: 129.4 mL, p=0.0002). Regarding brain volume change, the length of anterior epidural CSF collections were associated with a greater reduction of brain volume (< 7 segments (of the vertebrae) vs. ≥ 7 segments: 4.7mL vs. 20.2mL, p=0.047). 

Our study showed the brain volume decreased during SIH, which challenges the conventional assumption that brain volume is constant in SIH. The decreased brain volume may be related to reduced glymphatic CSF flow through the brain parenchyma.