Myelographic identification of the dentate ligament.

Abstract

The dentate ligament is a thin fibrous band situated on either side of the spinal cord. It separates the anterior from the posterior nerve roots. Its inner border is continuous with the pia mater and its lateral border is fixed at intervals to the dura mater by 21 triangular processes on each side. The first of these is attached to the dura mater opposite the margin of the foramen magnum, between the vertebral artery and the hypoglossal nerve, and the last near the lower end of the spinal cord at the level of D-12 or L-1. The lower end of the dentate ligament terminates in a two-pronged fork, the lateral prong forming the last dentate digit and the medial prong being prolonged along the side of the conus medullaris. The ligament is thicker in its cervical than dorsal section (1). The dentate ligament can be visualized in the lateral projection of a Pantopaque myelogram as a linear radiolucent shadow, its anterior and posterior surfaces being outlined by the opaque substance. Its visualization is facilitated by the use of at least 10 c.c. of the medium and a lateral projection. Because of its greater thickness, the cervical dentate ligament is more readily visualized than the dorsal portion. At times, the dentate ligament is not visualized as a linear radiolucent shadow (Figs. 1 and 2) but is indicated by a dense radiopaque column (Fig. 3), the posterior border of which outlines the dentate ligament as a result of collection of Pantopaque under its ventral surface. The dentate ligament has been visualized in 10 out of 23 lateral projections in 36 cervical myelograms, and 4 dorsal myelographic studies. The above interpretation of the linear radiolucent shadow on the lateral myelogram as the dentate ligament has been proved on cervical myelograms of fresh cadavers. In 5 fresh cadavers a laminectomy of the cervicodorsal spine was performed in prone position. The dura was opened along its midline posterior aspect from C-5 to D-2. The dentate ligaments were identified and silver clips were applied to the edge. In 2 instances, the clips were applied to the dentate ligament on both sides. A No. 14 rubber catheter was passed into the subarachnoid space with its tip placed at C-3. The dura was closed with interrupted stitches and water was injected through the catheter to refill the subarachnoid space in order to reproduce a condition simulating “normal” anatomical circumstance. After the arachnoid space had been filled with water, 10 c.c. of Pantopaque was instilled through the catheter. Air bubbles were led out from the subarachnoid space by manipulation of the neck and during the slow withdrawal of the catheter. The neck of the cadaver was placed in hyperextension and a roentgenogram was obtained in lateral projection. The silver clips were visualized in each instance in line with the radiolucent streak, the dentate ligament (Fig. 4).