Are spinal or paraspinal anatomic markers helpful for vertebral numbering and diagnosing lumbosacral transitional vertebrae?

Abstract

Objective: To evaluate the value of spinal and paraspinal anatomic markers in both the diagnosis of lumbosacral transitional vertebrae (LSTVs) and identification of vertebral levels on lumbar MRI.

Materials and methods: Lumbar MRI from 1049 adult patients were studied. By comparing with the whole-spine localizer, the diagnostic errors in numbering vertebral segments on lumbar MRI were evaluated. The morphology of S1-2 disc, L5 and S1 body, and lumbar spinous processes (SPs) were evaluated by using sagittal MRI. The positions of right renal artery (RRA), superior mesenteric artery, aortic bifurcation (AB) and conus medullaris (CM) were described.

Results: The diagnostic error for evaluation of vertebral segmentation on lumbar MRI alone was 14.1%. In lumbarization, all patients revealed a well-formed S1-2 disc with squared S1 body. A rhombus-shaped L5 body in sacralization and a rectangular-shaped S1 body in lumbarization were found. The L3 had the longest SP. The most common sites of spinal and paraspinal structures were: RRA at L1 body (53.6%) and L1-2 disc (34.1%), superior mesenteric artery at L1 body (55.1%) and T12-L1 disc (31.6%), and AB at L4 body (71.1%). CM had variable locations, changing from the T12-L1 disc to L2 body. They were located at higher sacralization and lower lumbarization.

Conclusion: The spinal morphologic features and locations of the spinal and paraspinal structures on lumbar MRI are not completely reliable for the diagnosis of LSTVs and identification on the vertebral levels.

Keywords: Lumbosacral vertebrae; MRI; Spine; Transitional vertebrae.

Fig. 1

Example of sagittal whole-spine localizer image with half-Fourier acquisition single shot turbo spin-echo sequence for numbering lumbar vertebrae.

Fig. 2

Sagittal T2-weighted MRI of man with lumbarization of S1 vertebra (thick arrow). There is well-formed S1-2 disc (thin arrow) with squaring of S1 vertebral body (thick arrow).

Fig. 3

Sagittal T2-weighted MRI of woman demonstrates sacralization of L5 vertebra (arrow). L5 body shows rhombus shape similar to S1 vertebra.

Fig. 4

Sagittal T2-weighted images (A-C) of man with normal lumbar segmentation. A. Proximal right renal artery (arrow) is located at L1-2 disc space. B. Root of superior mesenteric artery (arrow) is positioned at L1 body. C. Aortic bifurcation (arrow) is located at L4 body.

Fig. 5

Sagittal T2-weighted MRI of woman with normal lumbar segmentation shows that conus medullaris (arrow) is located at L1 body.

Fig. 6

Comparison on locational distributions of spinal and paraspinal structures in study groups. RRA = right renal artery, RSMA = root of superior mesenteric artery, CM = conus medullaris, AB = aortic bifurcation