Adult Lumbar Scoliosis: Underreported on Lumbar MR Scans

Prevalence of Scoliosis

Our study revealed a prevalence rate of 19.9% (259/1299) for adult lumbar scoliosis, which, as contended, is considerably higher than what has been reported in a number of studies on adult scoliosis, including a study on 5000 intravenous pyelograms imaged in the 1970s by Kostuik et al⁸ that suggested a prevalence of 2.5% for lumbar scoliosis, and an x-ray study by Robin et al,¹² also from patients imaged in the late 1970s, which reported a frequency of 15%. In 2 other comparable studies, Perennou et al¹³ demonstrated a rate of 7.5% for adult lumbar scoliosis in patients with low back pain, and Witt et al¹⁴ documented a figure of 9.1% in such a population as opposed to 4.6% in a control population. The increased prevalence of scoliosis demonstrated by our study could be explained by an increase in life expectancy in the United States on account of advanced medical care resulting in a shift toward the “gray society”^22,23 and an increased number of patients seeking medical care in pursuit of a higher quality of life rather than simply learning to live with their low back pain.^22,24,25

A significant increase seen in the prevalence of adult lumbar scoliosis among older age groups is a reiterated pattern that has previously been documented by 2 studies.^12,13 However, an increase from 2% to 6% to 15% in young, middle-aged, and older age groups reported by Perennou et al¹³ is noticeably less than 9.1% to 13.3% to 38.9% observed in our data. Robin et al¹² reported an increased prevalence rate of 32% among 50- to 84-year-old patients during a follow-up period of 4 years.

The difference in the prevalence of scoliosis between genders in our study (15.6% in all males versus 22.6% in all females) was no different from what has been reported by Robin et al,¹² who reported rates of 27.6% and 35.9% for older males and females, respectively. On a similar note, we observed a prevalence of 31.7% (45/142) and 42.7% (112/262) between older-age group males and females, respectively, again suggestive of an ever-increasing incidence.

An increased prevalence of scoliosis (42.2%) in patients with spondylolisthesis confirms previously documented association between the two.^28–32 Scoliosis occurring concomitantly with spondylolisthesis has been divided into 3 main categories.³⁰ First, it can simply be idiopathic scoliosis of the upper spine, likely unrelated to the olisthetic defect. Second, it can be of the sciatic type, in which irritation associated with the olisthetic defect induces scoliosis via muscle spasm. Third, it can be the result of an asymmetric olisthetic defect as first explained by Tojner.³² Highest prevalence of scoliosis (54%) with L4/L5-level listheses is also in conformity with what has been documented before.^29,33 This has been attributed to the absence of stabilizing ligaments, such as the iliolumbar ligament, at the L4–L5 level. The indications for a surgical approach to coexistent scoliosis and spondylolisthesis parallel the indications for either of the problems arising independently.²⁸

Severity of Scoliosis

In total, 84.2% (218/259) of scoliotic patients were mild in severity and 15.8% (41/259) were of the moderate and severe categories, which is in sharp contrast to figures recorded by Perennou et al,¹³ who reported 56% mild and 44% moderate and severe curves. This disparity could be a result of underestimation of scoliotic degrees on standard MR images^34–36 used in our study as opposed to standing radiographs used by Perennou et al. As a corollary to this distribution, the mean scoliotic angle recorded by Perennou et al was 21.2 ± 11.4° as compared with 15.8 ± 6.1° noticed by us. They, however, did not notice any difference in mean scoliotic angle between genders, while we observed such a difference (14.3° in males and 16.5° in females), which was statistically significant (P = .009). As for direction of curvature, our study recorded 63.8% (166) levoscoliotic, 35% (91) dextroscoliotic, and 1.2% (3) double curves, which contrasts with 56% levoscoliotic and 44% dextroscoliotic curves observed by Perennou et al.¹³ The difference would be explained by an increased proportion of rotatory listhesis (34%) and its significant (P < .01) association with dextroscoliosis, recorded by Perennou et al, or by the differences in the demographics of the study subjects. Statistically insignificant (P = .205) differences between genders in the direction of curvature is in line with findings documented by Perennou et al.

Reporting

We have demonstrated that lumbar scoliosis in adults with low back pain is underreported on MR imaging reports. This deficiency was especially observed for cases of mild severity, where 113 of 153 (73.9%) cases were not reported, whereas just 2 of 19 (10.5%) of moderate to severe cases were not reported. The finding that spondylolisthesis was noted in >99.5% (198/199) of cases suggests that the underreporting was not a matter of insufficient training or skill, but was more a reflection of not being attentive to the value of the coronal scout images. Neuroradiologists as a group have not considered the reporting of scoliosis, particularly mild scoliosis, as important to their reporting efforts or to their spine surgery colleagues.

Standard MR images are done in supine position and are known to have a diminutive effect on the extent of scoliotic curvature^34–36 unless they are axially loaded.³⁶ Our study used standard MR images for scoliotic angle measurements, leading to possible underestimation of the true extent of the curves. Furthermore, exclusive review of sagittal scans may lead to underreporting, hence the critical importance of either including clinical quality coronal sequences to supplement axial and sagittal scans or careful scrutiny of the multiplanar scout images, which include coronal sequences that better depict the scoliosis.

Implications for Care

Adult spinal deformity is an increasingly recognized entity that may significantly contribute to back pain, disability, and neurologic dysfunction. In particular, adult degenerative or de novo scoliosis patients typically present with symptoms of low back pain, often reporting extensive time periods before coming to the attention of a spine surgeon. In those patients with unrecognized spinal deformity/scoliosis, some surgeons perform minimal decompressions or short fusion procedures that do not adequately address the regional and global spine alignment. In doing so, such surgeries may, at the very least, inadequately address the cause of the patient's initial complaint and, at the very most, lead to iatrogenic worsening of the spine malalignment, neurologic decline, or severe pain. Such outcomes may also require additional surgeries, which by nature are often associated with greater procedure-related morbidity.³⁷ Ploumis et al have noted that though patients with minor scoliosis of <15° may be treated with decompression only, those with >15° and/or lateral subluxation and/or dynamic instability should have both decompression and fusion.³⁸ Extension of the fusion to the sacrum may also be recommended with coronal plane decompensation. Additionally, pseudoarthrosis in patients with degenerative scoliosis treated with posterior fusions occurs in 40% of cases, whereas those who have anteroposterior fusions have a <5% pseudoarthrosis rate.³⁹ Treatment of concomitant scoliosis with spondylosis therefore makes a difference in outcomes.

Additionally, given that radiologists may underreport the presence of such deformities on MR imaging, even when they are radiographically apparent, there may be inadequate preoperative evaluation of these patients with the criterion standard of upright plain films. With an improvement in the detection and reporting of scoliotic spinal deformity present on MR imaging, there may be a higher rate of referral to spine surgeons specializing in spine deformity. Such referrals would lead to the performance of appropriate work-up (that of standing, weight-bearing plain films) to determine the true extent of the scoliosis and how that would affect the surgical planning on the case. Furthermore, as discussed earlier, standard MR images (supine and nonloaded) have a diminutive effect on the true extent of scoliotic curves. Wessberg et al³⁶ have demonstrated a mean difference of 8° between nonloaded MR images and axially loaded ones or standing radiographs. Of the 218 cases of mild scoliosis in our study, 50.9% (111/218) fall between 13° and 20°. This, then, logically leads us to think that most of the borderline mild cases detected on standard MR images might convert to moderate severity if Wessberg's analysis were applied to our subjects. This is where it becomes imperative to meticulously detect and report mild cases.

The use of standing, weight-bearing views of the spine, a requirement for scoliosis evaluation, is not typically performed before lumbar spine disk surgery. The reporting by the radiologist of the presence of scoliosis on an MR imaging, even if mild in severity on a supine MR imaging study, may lead to such definitive studies being ordered. Because, in many cases, the lumbar spine MR imaging is requested by a primary care physician before referral to a spine surgeon, the reporting of scoliosis may expedite the work-up of the patient. By referring the patient for weight-bearing radiographs before the consultation by the spine surgeon, the surgeon will have adequate data to make a treatment decision at the initial consultation rather than having to return after those studies are performed. Scoliosis is a consideration that the spine surgeon must address when contemplating what surgery is appropriate.