Metrizamide CT cisternography in cases of traumatic subdural hygroma and chronic subdural hematoma

Subdural fluid collection and some cases of chronic subdural hematoma are observed by means of a CT scan as marginal low-density areas (m-LDA) in head-injured patients. It is thought that the cerebro-spinal fluid dynamics may play an important role in the pathogenesis and clinical course of such subdural pathology. We applied metrizamide CT cisternography to these cases. According to the findings of this metrizamide CT cisternography (M-CTC), the examples of subdural pathology can be classified into four types: Type I: Metrizamide filling is seen in both the cortical subarachnoid space and the m-LDA. Type II: Metrizamide filling is seen only in the cortical subarachnoid space, not in the m-LDA. Type III: Metrizamide filling is very poor in both the cortical subarachnoid space and the m-LDA. Type IV: Metrizamide filling extends well into the m-LDA, but only partially into the cortical subarachnoid space. Many of these cases studied had been operated on and the subdural pathology had been ascertained. From a comparison between the M-CTC and subdural types of pathology, subdural pathology of Types I, II, and III can all be classified as cases of a subdural hygroma (subdural fluid collection or subdural effusion), while Type IV is a chronic subdural hematoma. The characteristics and choice of treatment of each type may be briefly shown as follows: For Type I conservative therapy is recommended because of its tendency to decrease rapidly. For Type II a subduro-peritoneal shunt is recommended, for the m-LDA is long-standing and a simple burrhole evacuation sometimes results in an aggravation of the subdural hygroma. For Type III a burrhole evacuation is recommended; also, care must be taken against the development of a chronic subdural hematoma. For Type IV a burrhole evacuation is recommended became such cases are all chronic subdural hematoma. (J.P.N.)