Imaging features suggestive of a conjoined nerve root on routine axial MRI.

Objective: The purpose of our study is to evaluate imaging features suggestive of a conjoined nerve root on routine axial MRI.

Methods: Two radiologists and two surgeons retrospectively reviewed the MRI of three cases in which a conjoined nerve root was discovered during operation and found three suggestive signs on routine axial MR images: "corner" (asymmetric morphology of the anterolateral corner of the dural sac), "fat crescent" (intervening extradural fat between the asymmetric dura and the nerve root), and "parallel" signs (visualization of the entire parallel course of the nerve root at the disc level). Two radiologists prospectively found these signs during routine MRI interpretation sessions over a period of 6 months. If one or a combination of signs were noted on axial MR images, contiguous axial scans were additionally obtained. Three cases that were previously found during operations were also included. Prevalence and confidence scores for each sign were assessed on axial T1- and T2-weighted images.

Results: Twelve patients showed one or a combination of the three signs, 9 had contiguous axial MR scans. Five cases were confirmed by operation. The prevalence of the corner, fat crescent, and parallel signs were 12 out of 12 (100%), 6 out of 12 (50%), and 8 out of 12 (67.7%) on axial T1-weighted images. The overall diagnostic confidence was higher on T1- than on T2-weighted images (P<0.05).

Conclusion: On routine axial L-spine MRI, corner, fat crescent, and parallel signs are suggestive of and assist in the recognition of a conjoined nerve root.