Incidence of numerical variants and transitional lumbosacral vertebrae on whole-spine MRI

Abstract

Objectives: This study sets out to prospectively investigate the incidence of transitional vertebrae and numerical variants of the spine.

Materials and methods: Over a period of 28 months, MRIs of the whole spine were prospectively evaluated for the presence of transitional lumbosacral vertebrae and numerical variants of the spine.

Results: MRI of the whole spine was evaluated in 420 patients, comprising 211 female and 209 male subjects. Two patients had more complex anomalies. Lumbosacral transitional vertebrae were seen in 12 patients: eight sacralised L5 (3 male, 5 female) and four lumbarised S1 (3 male, 1 female). The incidence of transitional vertebrae was approximately 3.3. % (14/418). Thirty-two (7.7 %) of 418 patients had numerical variants of mobile vertebrae of the spine without transitional vertebrae. The number of mobile vertebrae was increased by one in 18 patients (12 male, 6 female), and the number was decreased by one in 14 patients (4 male, 10 female).

Conclusions: Numerical variants of the spine are common, and were found to be almost 2.5 times as frequent as transitional lumbosacral vertebrae in the study population. Only whole-spine imaging can identify numerical variants and the anatomical nature of transitional vertebrae. The tendency is toward an increased number of mobile vertebrae in men and a decreased number in women. Main messages • Numerical variants of the spine are more common than transitional vertebrae. • Spinal numerical variants can be reliably identified only with whole-spine imaging. • Increased numbers of vertebrae are more common in men than women. • Transitional lumbosacral vertebrae occurred in about 3.3 % of the study population. • The incidence of numerical variants of the spine was about 7.7 %.

Keywords: Incidence; Lumbar vertebrae; MRI; Spine.

Fig. 1

26-year-old woman with thoracic pain. MRI of the spine with sagittal T1-weighted images (a) and a coronal reformat of a sagittal SPACE sequence (b) demonstrates a transitional lumbosacral vertebra. Counting from the top, this is a sacralised L5 vertebra. The coronal reformats are very helpful in identifying the transitional nature of this vertebra. It is more easily appreciated on an anterior-posterior (AP) radiograph of the lumbar spine (c)

Fig. 2

15-year-old boy with back pain. Sagittal T1-weighted image (a) and coronal reformats of a sagittal SPACE sequence (b) demonstrate a transitional lumbosacral vertebra. Counting from the top, this is a lumbarised S1 vertebra. This can also be identified on an anterior-posterior (AP) radiograph (c) of the whole spine, better appreciated on a magnified view of the lumbar spine only (d). The only reliable method for determining the nature of a transitional vertebra is to count from the top

Fig. 3

55-year-old man with spinal injury in the past. Sagittal T1-weighted images (a) and coronal reformats of a 3D SPACE sequence (b) demonstrate old injuries, fusion of cervical vertebrae C4 to C6 (most easily appreciated when counting the posterior elements), and one supernumerary vertebra. Additional mobile vertebrae are more common in men than in women

Fig. 4

Sagittal T1-weighted MRI of the whole spine in a 63-year-old female patient with back pain. Block vertebra formation C3/4. The number of mobile vertebrae is reduced by one. Assuming seven cervical and 12 thoracic vertebrae, there are four morphological lumbar vertebrae, and there is no transitional vertebra as such