Electron microscopic study of the median structure of the posterior column of the spinal cord of the adult rat with a special reference to the posterior median septum.

In neuroanatomy textbooks on humans, the posterior median septum is commonly depicted along the midline of the posterior column of the spinal cord. For intramedullary spinal cord tumors, the standard surgical treatment is posterior midline myelotomy. However, its anatomical basis is still unclear. Therefore, in this study we focused on the ultrastructural characterization of the median structure of the posterior column in an adult rat. In the median part of the fasciculi gracilis, a fine lineal tissue continued from the posterior median sulcus to the 3/4th depth of the fasciculi. At higher magnification, this fine lineal tissue consisted of bundles of astrocytes, which are often disrupted and eventually disappeared. At the junction of the ventral part of the fasciculi cuneatus and the gray commissure, short lineal figures of glial tissues extended dorsally. These lineal figures of glial tissues were morphologically similar to other lineal figures of glial tissues found in the posterior column; bundles of astrocytes extending along the axons that entered the gray commissure and the perivascular lineal figures of glial tissues. In conclusion, this study revealed that the posterior median septum is composed of very fine lineal figures of glial tissues that are often disrupted and eventually disappear. We consider these basic structures to be similar in humans. Therefore, during posterior midline myelotomy, accurately separating along the posterior median septum in the posterior column is extremely difficult.

[Description of the Microsurgical Anatomy and Intramedullary Tumor Resection in the Anterior Part of the Spinal Cord].

During resection of an intramedullary spinal cord tumor, dissection of the ventro-central part of the tumor is most difficult because of the close anatomical relationship between the spinal branches of central vessels to be preserved and the tumor feeding arteries. The central vessels run anteroposteriorly through the anterior median septum(AMS), and a pair comprising a central artery and vein forms a vascular bundle that runs into the spinal cord from the tip of the AMS. These vascular bundles are covered with thin folds of the AMS, named septal sleeves, until they enter the spinal cords. Furthermore, the feeding arteries of the tumor arising from the spinal branches of the central arteries at the tip of the AMS are contained in thick septal sleeves; these thick sleeves indicate the position of the feeding arteries to be excised. To control brisk bleeding from the stump of the feeding artery at the top of the AMS, pinpoint coagulation of the arterial stump under direct vision after debulking the tumor is desirable. When pinpoint hemostasis cannot be achieved, coagulation of the AMS including the bleeding artery to a depth of 1-2 mm is advisable. As central arteries run tortuously in the AMS, the direction of the coagulation should be inclined craniocaudally, although this may increase the risk of damaging the adjacent central vessels. Surgeons should be aware of the anatomical relationship between the AMS, the central vessels, and the tumor feeding arteries to perform safe detachment of the tumors in the ventral region.