The injury occurs typically after a high-speed motor vehicle collision. ASDH, however, is being increasingly seen in elderly patients after same-height falls, and especially in patients on anticoagulant or antiplatelet medication. Bleeding is typically venous in nature, resulting from shearing of cortical veins, bridging veins, or veins from one of the cerebral venous sinuses.
A computed tomography (CT) scan typically shows a hyperdense crescent of blood between the dura and the brain. Despite a relatively small amount of blood, there is typically significant underlying hemispheric cerebral edema with associated midline shift. An entity known as a hyperacute ASDH has been described on CT: the presence of mixed hyperdensity indicates ongoing active bleeding. Contusions are also frequent and typically will worsen after surgical evacuation of the ASDH.
The decision to operate is based on a number of factors, but increasing, age is an extremely strong independent factor indicating a poor prognosis.
The following recommendations by the Brain Trauma Foundation (New York) have been proposed for surgical management:
• An ASDH with a thickness greater than 10 mm or a midline shift greater than 5 mm should be surgically evacuated regardless of the patient’s GCS.
• All patients with ASDH with GCS less than 9 should undergo intracranial pressure monitoring.
• A patient with a GCS less than 9 and with an ASDH less than 10 mm thick and a midline shift less than 5 mm should undergo surgical evacuation of the lesion if the GCS decreases by 2 or more points between injury and hospital admission and/or the patient presents with asymmetric or fixed and dilated pupils and/or the intracranial pressure (ICP) exceeds 20 mm Hg.
• Patients with ASDH and indications for surgery should have evacuation performed as soon as possible.
The issue of “as soon as possible” for surgical intervention has been widely studied. In a landmark paper in 1981, it was found that patients undergoing surgery within 4 hours of injury had a lower (30%) mortality rate than those undergoing surgery at later than 4 hours (90%). A subsequent paper in 1991 did not find any significant difference in mortality for patients undergoing surgery within or after 4 hours. It has been suggested that the degree and extent of underlying brain injury is probably the more important determinant of recovery than is the absolute timing of surgery.
The goal of surgery is the most complete evacuation of the ASDH as is possible through a large “trauma craniotomy” flap. Attention should be directed to coagulating any bleeding cortical veins or bridging veins. If there appears to have been avulsion of a vein from one of the venous sinuses, unless there has been adequate exposure of the area, such is best controlled by packing with hemostatic agents. If there is significant brain swelling, it is often best not to replace the craniotomy flap.
Unfortunately, despite the most aggressive neurocritical care, the mortality rate from ASDH remains high, ranging from 40% to 60% across all GCS categories and greater than 70% in patients presenting in coma.
CONTUSIONS
Contusions are parenchymal mass lesions that occur in up to 35% of patients with severe TBI. Approximately 30% will enlarge progressively or become associated with significant surrounding edema. Although most can be managed medically, it has been recommended that surgery be considered in the following setting: patients with GCS scores of 6 to 8 with frontal or temporal contusions greater than 20 cm3 in volume, with midline shift of at least 5 mm and/or cisternal compression on CT scan, and any patients with any lesion greater than 50 cm3 in volume should be treated operatively.
DIFFUSE AXONAL INJURY
Diffuse axonal injury (DAI) or shear injury, as the name implies, results from stretching and tearing of axons throughout the brain. Although the injury is diffuse, two of the most common areas of involvement are the corpus callosum and the posterolateral quadrants of the upper brainstem. CT scans may show discrete punctuate hemorrhages in these and other white matter tracts. Magnetic resonance imaging (MRI) is very sensitive to DAI lesions, which appear hyperintense on T2-weighted images. Severe DAI is unfortunately associated with a poor outcome.
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