Anatomy of the human spinal cord arachnoid cisterns: applications for spinal cord surgery

OBJECTIVEThe goal in this study was to describe the overall organization of the spinal arachnoid mater and spinal subarachnoid space (SSAS) as well as its relationship with surrounding structures, in order to highlight spinal cord arachnoid cisterns.METHODSFifteen spinal cords were extracted from embalmed adult cadavers. The organization of the spinal cord arachnoid and SSAS was described via macroscopic observations, optical microscopic views, and scanning electron microscope (SEM) studies. Gelatin injections were also performed to study separated dorsal subarachnoid compartments.RESULTSCompartmentalization of SSAS was studied on 3 levels of axial sections. On an axial section passing through the tips of the denticulate ligament anchored to the dura, 3 subarachnoid cisterns were observed: 2 dorsolateral and 1 ventral. On an axial section passing through dural exit/entrance of rootlets, 5 subarachnoid cisterns were observed: 2 dorsolateral, 2 lateral formed by dorsal and ventral rootlets, and 1 ventral. On an axial section passing between the two previous ones, only 1 subarachnoid cistern was observed around the spinal cord. This compartmentalization resulted in the anatomical description of 3 elements: the median dorsal septum, the arachnoid anchorage to the tip of the denticulate ligament, and the arachnoid anchorage to the dural exit/entrance of rootlets. The median dorsal septum already separated dorsal left and right subarachnoid spaces and was described from C1 level to 3 cm above the conus medullaris. This septum was anchored to the dorsal septal vein. No discontinuation was observed in the median dorsal arachnoid septum. At the entrance point of dorsal rootlets in the spinal cord, arachnoid trabeculations were described. Using the SEM, numerous arachnoid adhesions between the ventral surface of the dorsal rootlets and the pia mater over the spinal cord were observed. At the ventral part of the SSAS, no septum was found, but some arachnoid trabeculations between the arachnoid and the pia mater were present and more frequent than in the dorsal part. Laterally, arachnoid was firmly anchored to the denticulate ligaments’ fixation at dural points, and dural exit/entrance of rootlets made a fibrous ring of arachnoidodural adhesions. At the level of the cauda equina, the arachnoid mater surrounded all rootlets together—as a sac and not individually.CONCLUSIONSArachnoid cisterns are organized on each side of a median dorsal septum and compartmentalized in relation with the attachments of denticulate ligament and exit/entrance of rootlets.

Arachnoiditis

Arachnoiditis is a rare debilitating condition characterized by back pain, paresthesias, decreased truncal movement, lower extremity weakness, and decreased reflexes. The arachnoid mater is the middle layer of the meninges that envelope the spinal cord and brain. The dura mater lies on the outer layer of the meninges, arachnoid mater in between, and the pia mater lying closest to the neural tissue. These three layers provide protection and blood supply to the areas they surround. Arachnoiditis is the inflammation of the arachnoid layer that can occur after an insult is encountered to this layer. It causes swelling of the arachnoid layer, which eventually leads to scarring from collagen deposition over time. Arachnoiditis may become a chronic condition that can be difficult to treat.

On the Trabecular Morphologies and Load Transfer to the Brain

The human brain trabeculae contain strands of collagen tissues connecting the arachnoid to the pia mater. In this paper the mechanotransductions of the external loads to the head passing through different trabecular architectures of the subarachnoid space were investigated. This has been accomplished by creating several local 2-D models consist of skull, dura mater, arachnoid, trabecular architecture and the brain. Different orientations of several architectures of the trabeculae were also analyzed. All models were subjected to the same loading and constraints. The strains in the brain for each model of the architecture and morphology were determined and compared to other corresponding models. It is concluded that the strain in the brain is less where the tree-shape trabeculae are upright, where the branches are attached to the arachnoid mater and the stems are attached to the pia mater. In addition, in the case of other morphologies the strain in the brain is less when the ratio of the trabecular area to the CSF space is less.

Subarachnoid–subarachnoid bypass: a new surgical technique for posttraumatic syringomyelia

Object The origin of posttraumatic syringomyelia is not completely understood. With respect to posttraumatic syringomyelia, the optimum management strategy for patients with spinal cord injury has also not been established. The authors hypothesized that reconstruction of the subarachnoid channels would reestablish CSF flow, thereby addressing the underlying cause of the syrinx formation. The authors performed a new type of surgery, subarachnoid–subarachnoid bypass (S–S bypass), in which an attempt was made to reestablish normal CSF circulation around the spinal cord. The purpose of this study was to evaluate the effectiveness of S–S bypass for posttraumatic syringomyelia. Methods Twenty consecutive patients with symptomatic posttraumatic syringomyelia who had progressive neurological symptoms and underwent S–S bypass were included in the study. The surgical procedure was as follows: a laminectomy was performed at the level of trauma, and a midline dural opening was made under a microscope. The arachnoid was exposed up to the area of normal arachnoid mater with normal CSF circulation. After dissection of the normal arachnoid mater at the cephalic and caudal sites, 1 or 2 tubes made of medical-grade silicone were inserted into the cephalic and caudal ends of the normal subarachnoid space. Bypass tubes were laid in the subdural space, and a watertight dural closure was accomplished using running sutures. The mean follow-up period was 48.2 months (range 12–93 months). The preoperative status and postoperative clinical course were assessed according to 3 grading systems: the Frankel grading system for global neurological status, the American Spinal Injury Association motor score for motor weakness, and the Klekamp system for bladder function. The major presenting symptoms or signs were assessed in terms of symptom improvement, stabilization, or deterioration. Preoperative and postoperative MRI was used to analyze the size and craniocaudal extension of the cavity. Results Twelve patients showed clinical improvement, 4 were stable, and 4 showed deterioration. The mean length of the syrinx observed on preoperative MRI was 9.9 spinal levels, and the mean Vaquero index was 62.3%. The mean length of the syrinx observed on postoperative MRI was 5.3 spinal levels, and the mean Vaquero index was 28.4%. These values were significantly lower than the preoperative values (p = 0.01 and p < 0.01, respectively). Conclusions This study showed that interference with CSF flow was the major cause of syrinx development and that reconstruction of CSF flow is the most important treatment strategy based on the cause of the syrinx. Subarachnoid–subarachnoid bypass, which can be performed without myelotomy, was not only a safe and effective surgical technique, but may also be a more physiological way of treating posttraumatic syringomyelia.