Human spinal arachnoid septa, trabeculae, and "rogue strands".

This study was undertaken because of confusion arising from a diversity of names, descriptions, and drawings of the human spinal subarachnoid septa and trabeculae in the standard texts and dictionaries. Sixty-two complete human cords were examined under the dissecting scope. The finely "woven" adult arachnoid membrane was two-layered, and there were essentially no connecting septa or trabeculae between the cord and the arachnoid membrane anteriorly. Posteriorly, in the upper cervical region there is a scanty series of connecting fibers and fenestrated sheets 1 or 2 mm on either side of the midline; these become progressively more extensive in the lower cervical region, remain extensive to the lumbar enlargement, beyond which they progressively dwindle to end abruptly at the filum terminale origin. Throughout the cauda equina, strands are haphazardly arranged connecting the roots and supporting blood vessels. These occasionally become tangentially adherent to the arachnoid membrane. Throughout the length there are many unexplained, redundant, nonbranching, beaded, thicker "rogue strands". All of the above are of a different character from the right-angle fiber arrangement of the denticulate ligament, the two leaves of which are often separated form segmental longitudinal tunnels. The nerve rootlets (fila radicularia) for each dermatome are joined by strands and webs to each other. There was no evidence of change in number or type of connection with age.