Role of Anatomical Landmarks in Identifying Normal and Transitional Vertebra in Lumbar Spine Magnetic Resonance Imaging

Abstract

Study design: Retrospective study.

Purpose: Identification of transitional vertebra is important in spine imaging, especially in presurgical planning. Pasted images of the whole spine obtained using high-field magnetic resonance imaging (MRI) are helpful in counting vertebrae and identifying transitional vertebrae. Counting vertebrae and identifying transitional vertebrae is challenging in isolated studies of lumbar spine and in studies conducted in low-field MRI. An incorrect evaluation may lead to wrong-level treatment. Here, we identify the location of different anatomical structures that can help in counting and identifying vertebrae.

Overview of literature: Many studies have assessed the vertebral segments using various anatomical structures such as costal facets (CF), aortic bifurcation (AB), inferior vena cava confluence (IC), right renal artery (RRA), celiac trunk (CT), superior mesenteric artery root (SR), iliolumbar ligament (ILL) psoas muscle (PM) origin, and conus medullaris. However, none have yielded any consistent results.

Methods: We studied the locations of the anatomical structures CF, AB, IC, RRA, CT, SR, ILL, and PM in patients who underwent whole spine MRI at our department.

Results: In our study, 81.4% patients had normal spinal segmentation, 14.7% had sacralization, and 3.8% had lumbarization. Vascular landmarks had variable origin. There were caudal and cranial shifts with respect to lumbarization and sacralization. In 93.8% of cases in the normal group, ILL emerged from either L5 alone or the adjacent disc. In the sacralization group, ILL was commonly seen in L5. In the lumbarization group, ILL emerged from L5 and the adjacent disc (66.6%). CFs were identified at D12 in 96.9% and 91.7% of patients in the normal and lumbarization groups, respectively. The PM origin was observed from D12 or D12-L1 in most patients in the normal and sacralization groups.

Conclusions: CF, PM, and ILL were good identification markers for D12 and L5, but none were 100% accurate.

Keywords: Costal; Ligaments; Lumbar vertebrae; Magnetic resonance imaging.

Fig. 1. (A) Magnetic resonance imaging parasagittal T2 sequence shows normal costal facet at D12 vertebra (white arrow). (B) The costal facet appears rudimentary (white arrow).

Fig. 2. Parasagittal T2 sequence showing the last costal facet at D11 (white arrow).

Fig. 3. (A) Magnetic resonance imaging sagittal T2 sequence shows the origin of the celiac trunk at D12 vertebral level (white arrow) and superior mesenteric artery root at D12–L1 intervertebral disc level (curved arrow). (B) Origin of the right renal artery observed at the end of L1 (double-headed white arrow).

Fig. 4. (A) Magnetic resonance imaging sagittal T2 sequence bifurcation of aorta observed at L4 vertebral level, right and left illiac arteries (white arrows). (B) Confluence of inferior vena cava observed at L4–L5 intervertebral disc level (wavy arrows).

Fig. 5. (A) Magnetic resonance imaging axial T2 sequence shows partial sacralization of L5 with a thick posterior band of illiolumbar ligament (ILL) on the right side (white arrow). (B) L5 with thick anterior and posterior band ILLs on the right side (white arrow) and thin multiple fine bands on the left side (wavy arrow). (C) Thick ILL on the left side in the partial sacralized L5 (white arrow). (D) L5 showing thin ILL bilaterally, except for a posterior band on the left side (squiggly arrow).

Fig. 6. Magnetic resonance imaging axial T2 sequence shows thick illiolumbar ligament clearly visualized at the intervertebral disk level bilaterally (white arrows).

Fig. 7. (A) Coronal short tau inversion recovery sequence showing origin of the bilateral psoas clearly visualized at D12–L1 intervertebral disc level (white arrow). (B) Edema around the psoas major well delineates the psoas fibers arising from D12 (white arrow).

Fig. 8. (A–C) Axial T2 sections (arrow) showing the origin of the psoas muscle from D12 on the right side clearly visualized below D12–L1 intervertebral disc level and L1 levels (arrow).