Morphometric evaluation of the sacral dorsal root ganglia. A cadaveric study.

An anatomic study of the sacral dorsal root ganglia (DRG) was performed to determine the location and dimensions of the S1-4 DRGs and to correlate this information to sacral nerve root ganglion lesions. S1 DRGs were located in the intraforaminal region in 55-60% and in the intracanalar region in 40-45%. S2 DRGs were in the intraforaminal region in 15-50% and in the intracanalar region in 50-85%. All the S3 and S4 DRGs were located in the intracanalar region. None of the sacral DRGs was located in the extraforaminal region. The intraforaminal position of the S1 and S2 ganglia renders them vulnerable to compression caused by sacral fractures involving the sacral foramina because of the little space available for these ganglia in the foraminal region. The S1 DRG, with its its relatively larger dimensions and its intracanalar position relative to the other sacral DRGs, may be susceptible to compression by the L5-S1 disk herniation. Its intraforaminal position may predispose it to injury during S1 or S2 pedicle screw placement.