Origin and Pathological Significance of Smooth Muscle Cells and Myofibroblasts in the Subdural Neomembrane

Abstract

The outer membranes of the subdural neomembranes (SNs) from 30 patients with chronic subdural hematoma were examined by light and electron microscopes. All the specimens were gained by “en bloc” resection together with the overlying dura mater. Seventeen cases had histories of head injury which varied from 10 to 90 days prior to the operation. Besides the cells known to occur in SN, there were many cells which had ultrastructural characteristics of both smooth muscle cell (SMC) and fibroblast, showing a wide range of transitional morphology between them. They are so-called “myofibroblasts” (MFs) and were observed abundantly in all the cases. In four SNs, typical SMCs were present. They were distributed in a layered fashion in the midzone of the SNs. Examination of the relationship between the incidence of MF and the histological stage of SN or post-traumatic interval revealed that the SMCs were found only in the SNs with fibrosis and after 8 weeks of post-traumatic interval. The SNs containing SMCs showed many MFs in them. It is not recorded in the literature that the presence of MFs in SNs is a common finding, or that SMCs appear in the early stage of SN formation. Although it could not be proven, the origin of SMCs was suggested to be fibroblasts. Considering the recent studies of MF in general pathology, it is conceivable that MFs and SMCs play a role in the contraction and organization of SNs.