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 relat ion to surrounding bony structures in normal subjects were investigate d using magnetic resonance imaging. Objectives. This study determined the normal anatomic parameters of the lumbosacral nerve root and dorsa l root ganglion, to which degenerative or pathologic changes may be co mpared. Summary of Background Data. In the previous literature, most a uthors have used various modalities in either cadavers or symptomatic patients tb study the anatomic details of the lumbar nerve roots and d orsal root ganglia. The data in the literature are conflicting, mainly because of individual variations and different degrees of degenerativ e change in the spine. Methods. Twenty male volunteers who had no back pain or radiculopathy underwent magnetic resonance imaging. Ages rang ed 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 thirt y-three nerve roots were examined, including 36 L1, 40 L2, 40 L3, 39 L 4, 40 L5, and 38 S1 nerve roots. Measurements were determined using a computer digitizer. Results. The nerve root origin was at a mote cepha lad level for the caudad nerve roots, particularly the S1. The take-of f angles acutely changed at ii and S1. The length of the nerve roots i ncreased progressively to a maximum at L5, and decreased at S1. The ce nter of the dorsal root ganglion was positioned more cephalad at S1. T he average dimension of the dorsal root ganglion gradually increased f rom L1 to S1. The most striking difference was in the S1 root, which t akes 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 als o unique in that it was the largest and more frequently located intras pinally. 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 radicul opathy may involve both the nerve root and dorsal root ganglion as a r esult of either disc herniation or degenerative L5-S1 facet changes. T he relatively larger dorsal root ganglia and the greater dorsal root g anglion/foramen height ratios in the lower lumbar region may explain t he higher incidence of L5 or S1 radiculopathy, particularly given the propensity to disc degeneration and intervertebral foraminal narrowing in the lower lumbar region.