Journal Club

Spontaneous Intracranial Hypotension with Deep Brain Swelling

Savoiardo M, Minati L, Farina L, et al.
Brain 2007;130:1884–93

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 postcontrast 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 degrees ± 10.3 degrees, mean ± SD, range 49–80 degrees) when compared to controls (group C, 73.3 degrees ± 12.3 degrees, mean ± SD, range 56–95 degrees). It was, however, grossly decreased in patients with brain swelling (group D, 40.7 degrees ± 12.8 degrees, mean ± SD, range 22–61 degrees), 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.

Comment

Leakage of cerebrospinal fluid is considered the pathogenetic factor of spontaneous intracranial hypotension and explains the usual complaint of orthostatic headache, which is relieved by lying down, as well as the characteristic signs on MRI mentioned above. Even when the leakage point often remains undetermined, response to an epidural blood patch with reversal of the complaints and imaging findings suggest this disease to be understood and adequately treated.

Savoiardo et al. extend the spectrum of the disease by reporting on patients with severe brain sagging and scarce or even absent subdural hematomas and contrast enhancement. The upper brain stem and diencephalon appear swollen most likely due to a mild vasogenic edema as indicated by increased diffusivity. Vasogenic edema is considered to be caused by impaired drainage of the deep venous system due to functional stenosis of Galen’s vein entering the straight sinus. There is a wide range of neurologic impairment, some of these patients had impaired consciousness or even lapsed into coma.

The rapidity of evolution of brain sagging is likely related to the clinical syndrome. A relatively good neurologic state of some patients with severe brain sagging may be related to very slow evolution. In 2003, van Roost et al. [1] described a cohort of 17 patients from different institutions with a very early postoperative onset of clinical deterioration (clouded or lost consciousness and pupillary abnormalities) associated with bilateral signal changes in the basal ganglia and/or thalamus. What they called pseudohypoxic brain swelling was likely caused by rapidly evolved intracranial hypotension, induced by suction drainage.

References

1. Van Roost D, Thees C, Brenke C, et al. Pseudohypoxic brain swelling: a newly defined complication after uneventful brain surgery, probably related to suction drainage. Neurosurgery 2003;53:1315–26.

(submitted April 4, 2008)

Horst Urbach, Bonn, Germany