Evolution from Acute Subdural Hematomas to Chronic Subdural Hematomas

Summary

We analyzed 52 patients of acute subdural hematoma treated conservatively because of mild clinical symptoms and/or thin subdural hematoma to elucidate the evolution from acute subdural hematomas to chronic subdural hematomas. Based on the follow-up CT findings, these patients were classified into two groups: subdural hematomas increased in size gradually with or without deterioration of clinical manifestations(group 1) and subdural hematomas disappeared spontaneously(group 2). Group 1 included 23 patients. In most patients, CT showed the increase in size with a decrease in hematoma density 8 to 14 days after the insult. Fifteen patients were treated with a burr hole craniectomy and the evacuation of liquid hematoma content because of a deterioration of signs and symptoms. Average time elapsed to be operated was 26 days. The neomembrane similar to the outer membrane of chronic subdural hematomas was verified in 11 out of 15 operated patients. These neomembrane could not be differentiated from that of ordinary chronic subdural hematomas pathohistologically. The average age in 29 patients of group 2 was younger than that of group 1. Despite variable changes in hematoma density, subdural hematomas in group 2 decreased in size gradually or rapidly, and eventually disappeared. Average time elapsed to disappear was 25 days. When chronic subdural hematomas are defined as chronically enlarged and encapsulated subdural hematomas, a part of group 1 is considered to be chronic subdural hematomas and the evolution from acute subdural hematomas to chronic subdural hematomas can be present.