[A morphological study of the peri- and epineurium in the compression zone of the median nerve in carpal tunnel syndrome].

The structure of the peri- and epineurium of the median nerve in the carpal tunnel syndrome was studied by light and transmission electron microscopy. Electron microscopy confirms the flattened lamellar arrangement of the perineurial cells, but in contrast to the normal architecture the perineurial component of the median nerve in carpal tunnel syndrome consists of 20-25 layers of ramified squamous-type cells, each layer being separated from the adjacent one by a wide space containing thick bundles of collagen fibrils. The perineurial cells are bounded on both sides by a basement membrane which is of substantial thickness. A prominent feature is the occurrence of multiple pinocytotic vesicles and caveolae opening on both the internal and external aspects of the flattened cells. They also contain bundles of closely aggregated filaments. In the spaces between the perineurial cells we find, in some places, extremely disoriented and individually abnormal fibrils and fine filaments arranged in form of a spider web. Matrix vesicles can also be seen. The epineurium of the median nerve in the carpal tunnel syndrome is also considerably thickened, and the attachment is solid, so that the median nerve is relatively immobile constricted like an hourglass. The thick collagen fibers are orientated predominantly parallel to the axis of the nerve, but circular fibers can also be seen. Apart from fibroblasts, the outer layer of the epineurium contains mast cells and vasa nervorum as well as myelinated nervi nervorum. Variable quantities of fat are also present, particularly in the surrounding loose connective tissue.