Brain Advance Access published online on May 29, 2007
Brain, doi:10.1093/brain/awm101
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Spontaneous intracranial hypotension with deep brain swelling
1Departments of Neuroradiology and 2Neurology and 3Scientific Direction Unit, Istituto Nazionale Neurologico Carlo Besta, Milano, Italy
Correspondence to:
Dr Mario Savoiardo, Department of Neuroradiology, Istituto Nazionale Neurologico "C. Besta", Via Celoria 11, 20133 Milano, Italy E-mail: msavoiardo{at}istituto-besta.it
Spontaneous intracranial hypotension (SIH) is caused by leakage of CSF, and characterized on MRI by brain sagging, dilatation of veins and dural sinuses, subdural fluid collections and post-contrast enhancement of the thickened dura. A few cases may present a very severe brain sagging through the tentorial notch and swelling of the diencephalic–mesencephalic structures, with absent or scarce subdural collections and post-contrast enhancement. These patients may have surprisingly few neurological signs or may become drowsy and even lapse into coma due to central herniation. We retrospectively examined the diffusion studies obtained in five patients with these MRI findings, in seven patients with SIH without brain swellings and in ten controls. Mean diffusivity was increased in SIH patients with brain swelling in areas draining into the deep venous system, collected by the vein of Galen (vG) and straight sinus (SS). In the hypothesis that central herniation might be responsible for venous stagnation because of impaired flow of the vG into the SS, the vG/SS angle was measured. The angle formed by the vG entering the SS was not altered in patients without brain swelling (group E, 67.8° ± 10.3°, mean ± SD, range 49–80°) when compared to controls (group C, 73.3° ± 12.3°, mean ± SD, range 56–95°). It was, however, grossly decreased in patients with brain swelling (group D, 40.7° ± 12.8°, mean ± SD, range 22–61°), P < 0.001 for comparison with groups E and C. As suggested by previous studies, downward stretching of the vG and narrowing of the vG/SS angle may cause a functional stenosis at the vG–SS junction. We suggest that in the application of the Monro–Kellie doctrine to SIH, the brain volume should not be considered as always invariable.
Key Words: spontaneous intracranial hypotension; diffusion imaging; vasogenic oedema; venous stagnation; Monro–Kellie doctrine
Abbreviations: ADC, apparent diffusion coefficient; DWI, diffusion-weighted imaging; ROI, region of interest; SIH, spontaneous intracranial hypotension; SS, straight sinus; vG, vein of Galen
Received December 1, 2006. Revised March 26, 2007. Accepted April 4, 2007.
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