Ultrastructure of collagen fibers in the outer membrane of recurrent chronic subdural hematoma.

The three-dimensional structure of the collagen fibers in the outer membrane of recurrent chronic subdural hematoma was studied by scanning electron microscopy (SEM). Specimens obtained at surgery were treated with NaOH at room temperature to digest away all cellular components and expose the collagen fibers. SEM observation of the dural side of the outer membrane showed the collagen fibers were woven into a compact feltwork with a dense arrangement. The fiber bundles had a honeycomb structure framed by the collagen fibers. Observation of the hematoma side found the collagen bundles had a sparse wavy appearance. The arrangement of the collagen fibers on the dural side is different from that on the hematoma side. The thick outer membrane may be formed by granulation resulting from inflammatory reaction. Collagen fibrillar networks are not fragile, and may reinforce the outer membrane of the recurrent hematoma.