CT/MR spectrum of far lateral and anterior lumbosacral disk herniations.

Forty-eight patients had 50 extraforaminal disk herniations (EFDHs) demonstrated on CT and/or MR by (1) presence of disk density or disk signal material lateral to the neural foramen, (2) displacement or obliteration of paravertebral fat, and (3) nerve root or ganglion compression or displacement. Forty-one of 50 EFDHs had a coexisting intraforaminal component; nine of 50 had an isolated far lateral herniated nucleus pulposus. EFDHs typically occurred in the absence of a coexisting intraspinal disk herniation. Migratory fragments were seen in 50% of all cases and were at or cephalad to the interspace of origin in all cases. Forty-six percent of EFDHs were at L2-L3 or L3-L4, although the most commonly affected level was L4-L5 (38%). EFDHs, which were often overlooked (15/50 scans reviewed), are an important preventable cause of failed intraspinal diskectomy. EFDHs can be readily identified on both CT and MR if appropriate scans are obtained from L2 through S1 and if the neural foramina and paravertebral spaces are carefully examined.