II. LESIONS IN MENINGES AND VENTRICULAR SYSTEM

A. Epidural Hemorrhage

1. Epidural hemorrhage results in most cases from tearing of the middle meningeal artery (less often may occur from tearing of other vascular branches or venous sinuses). This event is usually associated with skull fracture, often of the temporal bone

2. Epidural hemorrhage is a rapidly expanding space occupying lesion and death may occur 2-12 hours after injury (bleeding is slower if the middle meningeal artery is not involved). The hematoma often causes uncal herniation and/or downward displacement of brainstem structures.

3. The classical clinical picture involves initial unconsciousness due to concussion, a lucid interval (seconds to hours) and progression to coma. However, the lucid interval does not occur in many cases and patients remian unconsious from the time of injury. Symptoms may include focal signs and/or indications of increased intracranial pressure.

4. Pathological examination shows a fresh epidural clot at autopsy.

B. Subdural Hemorrhage

1. Blood accumulates between the dura and arachnoid as a result of shearing of bridging veins. Subdural hemorrhage is often associated with blunt trauma without skull fracture and results from rotation of brain.

2. The rate of progression is variable - subdural hemorrhage may be classified as acute or chronic and (and sometimes subacute) depending on the rate of accumulation of blood and thus rate of progression of symptoms. Acute and chronic conditions will be discussed separately.

3. Acute subdural hemorrhage is associated with obvious trauma and is usually accompanied by contusion and cerebral artery tearing (leading to subarachnoid hemorrhage and bloody CSF). Symptoms develop within a few days (the onset of symptoms is slower than for epidural hemorrhage). The hemorrhage acts as a space-occupying lesion and symptoms may be focal and/or those of increased intracranial pressure. Consequences depend on the rapidity of surgical drainage and severity of concomitant damage to the brain.

This coronal section illustrates compression of one cerebral hemisphere by an acute subdural hemmorage.

4. Chronic subdural hemorrhage is common in infants, the elderly, alcoholics, epileptics and demented individuals. Contributing factors include frequent head trauma and an enlarged subdural space (due to cerebral atrophy), providing less support for veins traversing this space. Chronic subdural hemorrhage follows mild trauma (sometimes forgotten by the patient) and symptoms may not occur for weeks to months after the trauma due to the slow rate of blood accumulation. Symptoms include seizures, headaches, confusion, behavioral changes, and signs of increased intracranial pressure; neurological signs may mimic those of degenerative disorders or neoplasms. CSF may or may not show evidence of concomitant old subarachnoid hemorrhage or of reactive meningitis. Among diagnostic tests, CT scan or MRI is the most useful.

5. Pathology. For chronic subdural hematoma, the hematoma is encapsulated after several weeks, by a pseudomembrane composed of granulation tissue derived from the inflammatory reaction in the dura. The membrane forms initially at the clot surface facing the dura and is called the outer membrane. It extends around the clot to the surface facing the arachnoid, to form the thinner inner membrane. Subsequent episodes of rebleeding may occur, expanding the mass, followed by reorganization with a decrease in size. (Waxing and waning of neurological signs may correspond to the changes in hematoma size).