Clinical History: A 66 year-old male presents to his doctor’s office with a longstanding history of low back and leg pain. On physical exam he demonstrates a left L5 radiculopathy. The patient is referred for an MRI of the lumbar spine. (1a,b) T2-weighted coronal and T1-weighted axial images are provided. What are the findings? What is your diagnosis?
Bertolotti’s Syndrome related to a transitional lumbosacral junction. The findings are present bilaterally consistent with a Type IIb transition according to the Castellvi classification.
The relationship between low back pain and lumbosacral transitional vertebra (LSTV) has been debated since Bertolotti, an Italian surgeon first described it in 19171. His initial description postulated low back pain caused by arthritic changes occurring at the site where an enlarged transverse process articulated with the sacrum, termed a pseudarthrosis. Over time the syndrome however has been enveloped in controversy and has come to represent a variety of pain syndromes related to adjacent pathologies associated with developmental variations in segmentation referred to as transitional lumbosacral junctions.
In 1984 Castellvi reported an imaging classification system for LSTV. His system is summarized in Figure 4. Type I is simply an enlarged L5 transverse process which is not felt to be clinically significant. Type II includes formation of either a unilateral or bilateral diarthroidal joint between the enlarged transverse process and the sacrum. Type III is a solid fusion either unilaterally or bilaterally and type IV is mixed with a pseudarthrosis on one side2.
Clinical Significance and Pathology
Although the prevalence of transitional segments varies in reports between 4% and over 35%, Bron et al. in 2007 found an average incidence of 12.3% in their review of the literature3. LSTV is a common finding at imaging but may be overlooked. Most patients with this find are asymptomatic. Part of the importance of its observation is to improve communication about vertebral body numbering to help prevent wrong level surgery. It is interesting to note that McCulloch and Waddell demonstrated that the functional L5 nerve root originates at the most caudal “mobile” segment4. This work was confirmed by Chang and Nakagawa5. This observation would suggest that LSVT which are of Type I or II should be labeled L5-S1 and LSTV which are Type III or IV should be labeled S1-2 on MR imaging. However there is no consensus on this matter.
Clinical and imaging studies conflict as to the importance of the presence of a LSTV as it relates to symptoms and imaging findings. There are many case reports and reviews which include a variable number of patients which advocate the existence of Bertolotti’s Syndrome6-19. However many studies and commentaries do not. Brohn reported that about half of observational studies found a positive correlation between a LSTV and low back pain3. In looking at diverse studies over a long period of time, it is important to consider how a LSTV was established in the patient population as some types of imaging are more sensitive to transitional segments than others. Certainly, MRI with coronal series, a CT scan with coronal reconstructions, and a Ferguson radiographic view of the lumbar spine are more sensitive than a standard AP radiograph of the spine.
The original description of Bertolotti’s syndrome referenced arthritis of the “transverse-sacral pseudarthrosis” as a source of back pain. This arthritis or “stress reaction” may be observed as edema within this structure on MRI, isotope avidity on bone scan particularly on SPECT, or as marginal spurring, hypertrophy and sclerosis on MR, CT or radiographs (Figure 5). Pain related to this “stress reaction” may respond with relief of symptoms following fluoroscopic or CT guided injection of anesthetics6,7,9,12,14,15,17,19.
Hypertrophic changes can also compress or displace the ventral spinal root in the paravertebral gutter, so called extraforaminal stenosis (Figure 7). This may be obvious on ‘routine’ MR or CT depending on slice selection and angulation but may require specific coronal sequences or reconstructions to highlight the finding10.
There is an increased incidence of disc degeneration, disc herniation and facet degeneration at vertebral levels just cephalad to the transitional vertebral body. Aihara et al. reported in cadavers that the iliolumbar ligaments were thinner and weaker at the level above the LSTV20. In some circumstances the transitional segment is postulated to act as a “blocked” or fused segment leading to hypermobility at the segment above. Therefore discogenic or facetogenic pain can arise indirectly from a subjacent LSTV. Disc herniation is much more likely at the level immediately above the transitional disc as well21 (Figure 8). Relative stability or lack of mobility of the transitional segment is felt to be responsible for the observation of reduced degeneration of discs subjacent to a transitional vertebral body.
Contralateral facet arthrosis and hypertrophy are also commonly found in relation to LSVT, and could theoretically create facetogenic pain. (Figure 10)
Although the literature lacks a consensus on the causal relationship between low back pain and LSTV, there is evidence that biomechanical function and load bearing are altered. This potentially impacts those involved in athletics or physical labor more than those with sedentary lifestyles. Connolly found abnormal isotope uptake at LSTV in some young athletes with low back pain11. Back et al. described two avid golfers felt to have Bertolotti’s Syndrome who had negative responses to medial branch RF denervation and discography but responded to diagnostic anesthetic injections into what they referred to as the “sacrotransverse pseudoarticulation” and subsequently responded to radiofrequency ablation of that joint7 (Figure 13). Dougherty also reported results of a small number of patients who failed to respond to CT-guided SI joint injection and epidural steroid injection but did respond to CT guided injection of the pseudarthrosis12.
In a review of 769 consecutive patients with low back pain and an MRI, Quinlan found 35 or 4.6% with Bertolotti’s Syndrome, More than half of their patients with this syndrome were under 30 years old and 11.4% of their patients less than 30 years old had Bertolotti’s Syndrome. The authors felt that Bertolotti’s Syndrome must be considered in younger patients with back pain16.
Since there is controversy about the existence of Bertolotti’s Syndrome and the significance of LSTV, one would expect a lack of consensus as to the best way to treat these patients. Various approaches include: percutaneous injection of anesthetic and steroids, radiofrequency ablation of the anomalous diarthroidal joint, posterior surgical fusion of the pseudarthrosis, and resection of the enlarged transverse process3,6,7,8,9,13,14,15,17. Cox in his classic textbook on chiropractic care stated that low back pain associated with a transitional segment requires the greatest number of therapeutic sessions to obtain maximal results22.
Lumbosacral transitional vertebral bodies are a commonly encountered abnormality on MR Imaging. Recognition and description of these anomalies are important as the transitional segments and their related pathologies may account for the patient’s pain. In addition, proper communication of vertebral body numbering in cases of transitional segments is necessary to reduce the risk of intervention at an incorrect lumbosacral level.
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17 Santavirta S, et al. Surgical Treatment of Bertolotti’s syndrome. Follow up of 16 patients. Arch OrthopTrauma Surg 1993, 112:82-87.
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22 Cox, James M. Low Back Pain: Mechanism, Diagnosis and Treatment 7th ed. Lippincott Williams & Wilkins, 2011, Chapter 12: Transitional Segment.