Spinal Enumeration by Morphologic Analysis of Spinal Variants: Comparison to Counting in a Cranial-To-Caudal Manner

Abstract

Objective: To compare the spinal enumeration methods that establish the first lumbar vertebra in patients with spinal variants.

Materials and methods: Of the 1446 consecutive patients who had undergone computed tomography of the spine from March 2012 to July 2016, 100 patients (62 men, 38 women; mean age, 47.9 years; age range, 19-88 years) with spinal variants were included. Two radiologists (readers 1 and 2) established the first lumbar vertebra through morphologic analysis of the thoracolumbar junction, and labeled the vertebra by counting in a cranial-to-caudal manner. Inter-observer agreement was established. Additionally, reader 1 detected the 20th vertebra under the assumption that there are 12 thoracic vertebra, and then classified it as a thoracic vertebra, lumbar vertebra, or thoracolumbar transitional vertebra (TLTV), on the basis of morphologic analysis.

Results: The first lumbar vertebra, as established by morphologic analysis, was labeled by each reader as the 21st segment in 65.0% of the patients, as the 20th segment in 31.0%, and as the 19th segment in 4.0%. Inter-observer agreement between the two readers in determining the first lumbar vertebra, based on morphologic analysis, was nearly perfect (κ value: 1.00). The 20th vertebra was morphologically classified as a TLTV in 60.0% of the patients, as the first lumbar segment in 31.0%, as the second lumbar segment in 4.0%, and as a thoracic segment in 5.0%.

Conclusion: The establishment of the first lumbar vertebra using morphologic characteristics of the thoracolumbar junction in patients with spinal variants was consistent with the morphologic traits of vertebral segmentation.

Keywords: Anatomic variation; Computed tomography; Enumeration; Lumbar vertebra; Spine; Thoracolumbar transitional vertebra.

Fig. 1. 47-year-old woman with anomalous total number of vertebra.

A. Sagittal T2-weighted fast spin-echo magnetic resonance image of whole spine shows 25 presacral mobile vertebra. B, C. Coronal CT image (B) showing 20th vertebra, with paired ribs that are 3.8 cm or greater in length. Paired ribs originate from facet at pedicle of 20th vertebra on axial CT image (C). Therefore, 20th vertebra is morphologically thoracic vertebra. D. On axial CT image, 21st vertebra morphologically appears to be first lumbar vertebra. Thus, this patient has 25 presacral mobile vertebra with seven cervical, 13 thoracic, and five lumbar vertebra. CT = computed tomography

Fig. 2. 38-year-old man with TLTV.

A, B. Posteroanterior chest radiograph (A) and supine abdominal radiograph (B) demonstrate 24 presacral mobile vertebra. C. Axial CT image showing 19th vertebra, with paired ribs that are 3.8 cm or greater in length and originate from facet at pedicle. Therefore, 19th vertebra is morphologically thoracic vertebra. D. On axial CT image, 20th vertebra, which has short rib on left side and accessory ossification center on right side, is TLTV. E. On curved planar reformatted image of left rib of 20th vertebra, rib length is measured by drawing line at midpoint of rib width from proximal head of rib to distal body. Rib measures 30.4 mm and is classified as short rib. F. On axial CT image, 21st vertebra, exhibiting both fused transverse processes without articulating ribs, is identified as first lumbar vertebra. Thus, this patient has 24 presacral mobile vertebra with seven cervical, 12 thoracic, one TLTV, and four lumbar vertebra. TLTV = thoracolumbar transitional vertebra

Fig. 3. 74-year-old woman with anomalous distribution of vertebra.

A, B. Posteroanterior chest radiograph (A) and supine abdominal radiograph (B) indicate presence of 24 presacral mobile vertebra. C. Axial CT image showing 18th vertebra, with paired ribs that are 3.8 cm or greater in length and originate from facet at pedicle. Therefore, 18th vertebra is morphologically thoracic vertebra. D. On axial CT image, 19th vertebra has both fused transverse processes and morphologically appears to be first lumbar vertebra. Thus, this patient has anomalous distribution of 24 presacral mobile vertebra with seven cervical, 11 thoracic, and six lumbar vertebra.

Fig. 4. Labeling of morphologic first lumbar vertebra by counting in cranial-to-caudal manner.

Fig. 5. Morphologic analysis of 20th vertebra.