<P> Arachnoid villi, which are outgrowths of the arachnoid mater (the middle meningeal layer), extend into the venous sinuses to drain CSF . These villi act as one - way valves . Meningeal veins, which course through the dura mater, and bridging veins, which drain the underlying neural tissue and puncture the dura mater, empty into these dural sinuses . A rupture of a bridging vein causes a subdural hematoma . </P> <P> The supratentorial dura mater membrane is supplied by small meningeal branches of the trigeminal nerve (V1, V2 and V3). The innervation for the infratentorial dura mater are via upper cervical nerves . </P> <P> Many medical conditions involve the dura mater . A subdural hematoma occurs when there is an abnormal collection of blood between the dura and the arachnoid, usually as a result of torn bridging veins secondary to head trauma . An epidural hematoma is a collection of blood between the dura and the inner surface of the skull, and is usually due to arterial bleeding . Intradural procedures, such as removal of a brain tumour, or treatment of trigeminal neuralgia via a microvascular decompression require that an incision is made to the dura mater . To achieve a watertight repair and avoid potential post-operative complications the dura is typically closed with sutures . In the event that there is a dural deficiency, a dural substitute may be used to replace this membrane . Small gaps in the dura can be covered with a surgical sealant film . </P> <P> In 2011, researchers discovered a connective tissue bridge from the rectus capitis posterior major to the cervical dura mater . Various clinical manifestations may be linked to this anatomical relationship such as headaches, trigeminal neuralgia and other symptoms that involved the cervical dura . The rectus capitis posterior minor has a similar attachment . </P>

What is the term for a collection of blood located outside the dura mater