Morphometric analysis of the lumbosacral nerve roots and dorsal root ganglia by magnetic resonance imaging

Study Design. Lumbosacral nerve roots and dorsal root ganglia in relation to surrounding bony structures in normal subjects were investigated using magnetic resonance imaging. Objectives. This study determined the normal anatomic parameters of the lumbosacral nerve root and dorsal root ganglion, to which degenerative or pathologic changes may be compared. Summary of Background Data. In the previous literature, most authors have used various modalities in either cadavers or symptomatic patients tb study the anatomic details of the lumbar nerve roots and dorsal root ganglia. The data in the literature are conflicting, mainly because of individual variations and different degrees of degenerative change in the spine. Methods. Twenty male volunteers who had no back pain or radiculopathy underwent magnetic resonance imaging. Ages ranged from 22 to 38 years, with a mean of 30.4 years. T1-weighted coronal magnetic resonance images were taken from L1 to S1. Two hundred thirty-three nerve roots were examined, including 36 L1, 40 L2, 40 L3, 39 L4, 40 L5, and 38 S1 nerve roots. Measurements were determined using a computer digitizer. Results. The nerve root origin was at a mote cephalad level for the caudad nerve roots, particularly the S1. The take-off angles acutely changed at ii and S1. The length of the nerve roots increased progressively to a maximum at L5, and decreased at S1. The center of the dorsal root ganglion was positioned more cephalad at S1. The average dimension of the dorsal root ganglion gradually increased from L1 to S1. The most striking difference was in the S1 root, which takes off more cephalad, at a more Vertical angle, and has the shortest length of any of the nerve roots, The S1 dorsal root ganglion was also unique in that it was the largest and more frequently located intraspinally. Conclusions. The anatomy of the lumbar nerve roots and dorsal root ganglia and their relations to bony structures have been better defined in this study. Because of its more medial location, S1 radiculopathy may involve both the nerve root and dorsal root ganglion as a result of either disc herniation or degenerative L5-S1 facet changes. The relatively larger dorsal root ganglia and the greater dorsal root ganglion/foramen height ratios in the lower lumbar region may explain the higher incidence of L5 or S1 radiculopathy, particularly given the propensity to disc degeneration and intervertebral foraminal narrowing in the lower lumbar region.