[Natural course of non-operative cases of acute subdural hematoma: sequential computed tomographic study in the acute and subacute stages].

We have studied 20 non-operative cases of traumatic acute subdural hematoma in the acute and subacute stages by sequential computed tomography (CT). 20 patients were divided into three groups as is shown below; 8 patients with rapid complete resolution within 24 hours (rapid resolution group), 10 patients with slow resolution beyond 24 hours, mainly in the subacute stage (slow resolution group), and 2 patients worsening clinically due to the increase of subdural fluid collection in the subacute stage (subacute worsening group, what is called, "subacute subdural hematoma"). In the rapid resolution group, CT showed mixed density thin subdural hematoma in 6 patients; delayed subdural effusion in 3 patients; cerebral contusion in 2 patients; and diffuse brain swelling in 2 patients. We reviewed 8 of our cases and 13 reported cases. As a result, we consider that the main pathological mechanisms of rapid resolution types were, in the elderly, the washout of the hematoma by the leakage of cerebrospinal fluid (CSF) and, in the young, the compression of the hematoma by brain swelling. In the subacute worsening group, CT showed, in the acute stage, mixed density thick subdural hematoma with brain atrophy and no intraaxial lesions and, in the subacute stage, the increase of low density subdural fluid collection with marked mass effect. We reviewed 2 of our cases and 19 reported cases. As a result, we related the increase of subdural fluid collection in the subacute stage with the CSF leakage into the subdural space due to the tearing of arachnoid membrane. However, massive CSF leakage into the subdural space, producing marked mass effect, may be joined by other factors such as osmotic pressure gradient or oozing from the outer membrane of the hematoma.