The problem of cauda equina nerve root identification.

Ventral and dorsal nerve roots can be identified in the cauda equina partly by a combined anatomical-electrical method. The cross-section of dorsal and ventral roots in the lower thoracic and lumbo-sacral range are somewhat spherical with the exception that the large roots are more elliptically shaped. Ventral roots consist mainly of one subgroup, dorsal roots normally of several. The larger diameter of ventral and dorsal roots are about 1 mm in the lower thoracic region. It rises to about 2 mm between L 3 and S 1 and then reduces again. The dorsal roots are always slightly bigger than the ventral ones. Nerve roots can be easily identified by their rootlets. More ventral roots can be identified without having access to the rootlets by continued counting from the last distinguished rootlet, knowing that the last thick root is the S 1 root. The reduction in size from the first ventral sacral root (2 mm) to the second (1.2 mm) is so pronounced that it can normally be recognized. Dorsal roots also reduce in size in the sacral range. But because each dorsal root consists of several subgroups they cannot be counted up and identified. Of some anatomical help is the following: the dorsal roots emerging from the conus medullaris form on each side a bulk, and the top of this bulk consists mostly of the S 1 root and the medial falling phase of the S 2 root. In the liquor free cauda equina about 5 cm away from the medullaend the two bulks fall to the middle and touch each other.(ABSTRACT TRUNCATED AT 250 WORDS)