Subdural Hemorrhage and Posttraumatic Hygroma

Introduction

The accurate age determination of a subdural hemorrhage is one of the most common and basic assessments in the setting of head trauma. On computed tomography (CT), the classic descriptions of blood products within the subdural space relate to density changes which evolve over time. These changes reflect the evolution from acute blood to clot formation, clot retraction, clot lysis, and eventual resorption. Based on the density of the subdural collection, subdural hematomas (SDHs) are classically subdivided into acute, subacute, and chronic SDHs. Although the process of estimation is generally straightforward in everyday clinical practice, several variations must be taken into account to avoid confusion. This confusion may be ameliorated by focusing first on the relevant anatomy and then on the different types of subdural collections, including both SDHs and subdural hygromas.

An SDH is a typically crescent shaped extraaxial collection of blood within the innermost layer of the dura, designated the dural border cell layer ( Fig. 2.1 ).

The fact that SDHs form within the innermost layer of the dura is of crucial importance for a conceptual understanding of the different types of subdural collections. This is because there is a rich venous plexus within this layer ( Fig. 2.2 ). The small caliber of these vascular structures is beyond the resolution of our current imaging. Although there is still much that is unknown about its function, this venous plexus is thought to play a role in cerebrospinal fluid (CSF) resorption into the venous system.