1995 Volume 4 Issue 2 Pages 121-127
The authors have investigated 8 cases of a traumatic subacute subdural hematoma by the following methods : computed tomography (CT), magnetic resonance imaging (MRI), the results of surgery, and the histological findings. Within a few days after each head injury, CT showed a highly dense subdural hematoma, but the volume of the hematoma then decreased in 3 to 7 days. However, CT at 7 to 14 days demonstrated a low or isodense area and enlargement of subdural hematoma. MRI findings showed that most of the subacute subdural hematomas visualized as an area of high intensity with only a small portion showing a low intensity, and that the shape of the hematomas over the cortical surface were irregular. For repair, 6 of the cases underwent a craniotomy and two received a burr hole evacuation in 7 to 27 days. The contents of these subdural hematomas consisted of clots and liquid. There was all outer neomembrane on the outer surface of each of the hematomas, but none had an inner membrane. In 3 cases, on removal of the subdural hematoma, blood was seen spurting from a tiny cortical artery rent, and in 5 cases, localized subarachnoid hemorrhage was found around the cortical arteries. These findings appear to indicate that the cortical arteries are a bleeding source of head traumas. In one subdural hematoma, MRI revealed that the cerebral cortex had attached to the dura mater within the hematoma in the shape of a tent (the "tenting"sign) , and the subsequent surgical and histological finding showed that a cortical artery had adhered to the outer neomembrane, and that there was a defect in the arachnoid membrane at the point of adhesion. Thus, this"tenting"sign can be considered a diagnostic sign that the cerebral cortex has adhered to the dura mater or to the outer neomembrane. In another case, a small tear ill the arachnoid membrane was found near localized subarachnoid hemorrhage. In 4 cases the results of the histological examination showed that the outer neomembrane consisted of fibrous connective tissue and many dilated capillaries, and in 3 cases new petechial hemorrhages around the capillaries were noted. Based on these findings, the mechanisms that cause a subacute subdural hematoma to develop may occur as follows : 1) On sustaining a mild head injury, an acute subdural hematoma may arise from a cortical artery rupture. Then, from 3 to 7 days later, the hematoma decreases in volume. Next, a neomembrane of granulous tissue forms between the hematoma and the dura mater, and, 2) An influx of cerebrospinal fluid enters the subdural space, and during the subacute stage, a transcapillary shift of blood plasma through dilated capillaries and petechial hemorrhaging in the neomembrane may cause the enlargement of the hematoma.
