Idiopathic Intracranial Hypertension: Glymphedema of the Brain

Abstract

Background : During the last decade, our understanding of cerebrospinal fluid (CSF) physiology has dramatically improved thanks to the discoveries of both the glymphatic system and of lymphatic vessels lining the dura mater in human brains. Evidence acquisition :We detail the recent basic science findings in the field of CSF physiology and connect them with our current understanding of the pathophysiology of idiopathic intracranial hypertension (IIH).Results : Transverse sinus stenoses appear to play a major causative role in the symptoms of IIH, as a result of a decrease in the pressure gradient between the venous system and the subarachnoid space. However, the intracranial pressure (ICP) can be highly variable amongst different patients, depending on the efficiency of the lymphatic system to resorb the CSF as well as on the severity of transverse sinus stenoses. It is likely that there is a sub-clinical form of IIH and that IIH without papilledema is probably under-diagnosed among patients with chronic migraines or isolated tinnitus.Conclusions : IIH can be summarized in the following pathological triad: Restriction of the venous CSF outflow pathway -Overflow of the lymphatic CSF outflow pathway -Congestion of the glymphatic system. In order to better encompass all the stages of IIH, it is likely that the Dandy's criteria need to be updated, and that perhaps renaming IIH should be considered.

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“…CSF withdrawal not only lowers CSF pressure, but also promotes the turnover of CSF, and I believe that CSF drainage may favorably affect the fluid dynamics of the glymphatic system, and that this could be an alternative explanation as to why CSF withdrawal may be beneficial in a subgroup of CFS patients [29] . As discussed below, this latter view [29] is now supported by very recent observations confirming that a significant proportion of CFS patients represent a variant of IIH [30] and that IIH may be considered as a manifestation of “glymphedema” of the brain [31] .…”

“…In a very recent state-of-the art review, Nicholson et al [31] detailed the new discoveries of both the glymphatic system and lymphatic vessels lining the dura mater in human brains, and connected them with our current understanding of the pathophysiology of IIH. The authors concluded that IIH can be summarized in the following pathological triad: restriction of the venous CSF outflow pathway, overflow of the compensating lymphatic CSF outflow pathway, and congestion of the glymphatic system.…”

“…As further noted by the authors, the ICP may be highly variable amongst different patients, depending on the efficiency of the lymphatic system to resorb the CSF and on the severity of transverse sinus stenoses. It is likely that there is a subclinical form of IIH in patients with a degree of CSF outflow impairment but in whom the signs and symptoms do not yet meet the criteria for IIH [31] . It is therefore likely that IIH without papilledema (i.e., with normal or near-normal ICP) is probably underdiagnosed among patients with chronic migraines or isolated tinnitus [31] .…”

“…It is likely that there is a subclinical form of IIH in patients with a degree of CSF outflow impairment but in whom the signs and symptoms do not yet meet the criteria for IIH [31] . It is therefore likely that IIH without papilledema (i.e., with normal or near-normal ICP) is probably underdiagnosed among patients with chronic migraines or isolated tinnitus [31] . Papilledema and raised ICP could probably therefore be considered as the most severe stage of the disease, whereas headache and pulsatile tinnitus with normal ICP (and without papilledema) could be considered as benign stages of IIH [31] .…”

“…It is therefore likely that IIH without papilledema (i.e., with normal or near-normal ICP) is probably underdiagnosed among patients with chronic migraines or isolated tinnitus [31] . Papilledema and raised ICP could probably therefore be considered as the most severe stage of the disease, whereas headache and pulsatile tinnitus with normal ICP (and without papilledema) could be considered as benign stages of IIH [31] . This may explain why the radiological signs of IIH are frequently found in patients with chronic headache or isolated pulsatile tinnitus without papilledema or raised ICP [31] .…”