Enhancing subdural effusions
Patient with spontaneous subdural collections found on CT and suspected intracranial hypotension
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Subdural effusions with progressive contrast enhancement over a 10-minute period demonstrated by dynamic contrast enhanced MRI .
Despite its name, the "subdural space" is not subdural and it is not a naturally occurring space. The classic view is that blood or fluid accumulates in a preexisting (or potential) space called "subdural space", however electron microscopy evaluation of the meninges 1 demonstrates that there is no naturally occurring space at the dura-arachnoid junction. The so-called "subdural space" appears within one of the dural layers (dural border cell layer) due to pathological/traumatic processes. The "subdural space" is therefore intradural and collections or hematomas in this location would be better described as "dural dissections".
When a "subdural" hematoma or effusion occurs, the newly created subdural space is in direct contact with the wide extracellular spaces that characterize the dural border cell layer. This configuration explains the free diffusion of contrast from the outer membrane into the collection seen on the T1 dynamic images presented. It is important to emphasize that the subdural space is not a potential space where two layers can be separated without tissue disruption like in the case of the pleura 1. The formation of a "subdural space" implies tissue damage. Some studies have investigated the rate of enhancement of chronic subdural hematomas and subdural effusions 2,3.
Subdural effusions (without old blood) seem to enhance faster than chronic subdural hematomas and recent subdural hematomas tend to enhance faster than older ones 3. These findings suggest that the etiology and chronology of the pathological processes disrupting the dural border cell layer have an impact in the vessel density, vessel size or vessel permeability of the dura resulting in different rates of enhancement of the "subdural collections".
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