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II. Lesions in Meninges and Ventricular System

C. Subarachnoid Hemorrhage

Accumulation of blood in the subarachnoid space to a greater or lesser degree is a consistent accompaniment of cerebral contusions. Upon lumbar puncture, grossly bloody CSF may be detected. In some cases in which a medium-sized superficial vessel is torn, subarachnoid hemorrhage may be the direct cause of symptoms; in most cases, bleeding arises from small vessels and is part of the surface bruising associated with fracture of the skull. Hydrocephalus may result if the subarachnoid bleeding or subsequent fibrosis obstructs CSF flow in the subarachnoid space.

This diagram shows the subarachnoid space (lavendar) containing an artery (red).  The arachnoid is shown as gray, with the pia as a black line adjacent to the gold brain parenchyma.
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