ABSTRACT
Introduction and Aims:
Grade 1 spondylolisthesis can be challenging to detect on magnetic resonance imaging (MRI), particularly for spinal surgeons and radiologists with limited experience interpreting spinal MRIs. This study aims to describe a unique sign described as a “mustache sign,” which may assist in detecting subtle Grade I spondylolisthesis on sagittal sequences on MRI of the spine.
Patients and Methods:
A retrospective review of 50 lumbar spine MRI scans of patients with Grade I spondylolisthesis of L5/S1 performed over 3 years was conducted at a tertiary orthopedic spinal center in the United Kingdom. The scans were assessed for the presence of the “mustache sign” and findings were independently recorded by one musculoskeletal radiology registrar and one fellowship trained musculoskeletal radiologist with over 10 years of experience.
Results:
There were 35 females (70%) and 15 males (30%). The patient’s mean age was 54.3 years (13–82). The “mustache sign” was present in 13 (26%) of these patients. Twelve of 13 scans (92%) positive for the sign also demonstrated pars interarticularis defects (P < 0.001, Fisher’s Exact test), compared to those without the sign. There was excellent interobserver reliability with a kappa of 1.
Conclusion:
The “mustache sign” on MRI spine correlates well with the presence of Grade I spondylolisthesis. This ancillary sign can complement other previously described radiological findings on sagittal MRI sequences to confirm Grade I spondylolisthesis.
Keywords: Lumbar spine, magnetic resonance imaging, mustache sign, radiology, spondylolisthesis
INTRODUCTION
Spondylolisthesis is defined as the anterior displacement of a vertebral body relative to the vertebra below.[1] Spondylolisthesis was a term first used by Killian in 1853.[2] Once spondylolisthesis is identified on imaging, the etiology, degree, and associated degree of foraminal narrowing should be made. However, it is also a common incidental finding in asymptomatic patients. Spondylolisthesis could be classified into five main etiologies, including degenerative, traumatic, isthmic, dysplastic, or pathological.[3] Degenerative spondylolisthesis is due to the degenerative changes in the spine, usually related to the facet joint and disc degeneration, leading to instability and forward displacement of the vertebral body relative to the one below, without any defect in the pars interarticularis.[4]
Spondylolisthesis has the highest incidence in the lumbar spine but may also happen in the cervical spine and rarely in the thoracic spine. Degenerative spondylolisthesis has the highest prevalence in adulthood and is more common in females and those with higher body mass index. Isthmic spondylolisthesis is more common in the adolescent and young males.[5] Dysplastic spondylolisthesis is more common in pediatric patients, with females commonly more affected than males.[6]
From the radiological perspective, spondylolisthesis is graded according to the Meyerding classification, based on the degree of vertebral body slippage over the body beneath it, with Grade 1 being the least advanced and Grade V being the most advanced.[7] Grade 1 involves the slippage of 25% of the vertebra forward, Grade II involves 50%, Grade III constitutes 75% of slippage, Grade IV with 100%, and Grade V involves a vertebra completely which is fallen off (also known as spondyloptosis). Understanding the course of history of this disorder is essential in counseling patients and determining the course of action in the future. Grade I spondylolisthesis accounts for almost 75% of all cases, with the highest prevalence at the L5–S1 level, followed by at the L4–L5 level.[8]
Magnetic resonance imaging (MRI) is a commonly performed imaging test for the investigation of back pain, and spondylolisthesis is a common finding on these studies. While Grade II and higher grades of spondylolisthesis be identified on MRI with a high degree of confidence, more subtle forms of Grade I spondylolisthesis can be challenging to identify, particularly for spinal surgeons and radiologists with limited experience with reading spinal MRI. Nonetheless, this is an important finding that may have management implications for the patient.
This study aims to describe the utility of a novel ancillary sign described as the “mustache sign,” which may be helpful in recognizing the presence of a Grade I spondylolisthesis at the L5–S1 level. We also aim to describe its prevalence in our patient cohort who were referred to our tertiary orthopedic and spinal center.
Description of the “mustache sign” on sagittal magnetic resonance imaging sequences
The “mustache sign” is assessed on the sagittal MRI spine sequences in patients with Grade 1 spondylolisthesis, ideally on a T2-weighted sagittal sequence, which is a routinely performed sequence in spine MRI. The “mustache sign” comprises the L5–S1 intervertebral disc which is superiorly and posteriorly displaced and compressed between the inferior endplate of L5 and the superior endplate of S1, resembling the appearance of a handlebar mustache [Figure 1a and b].
Figure 1.
Sagittal T2 magnetic resonance imaging images showing Grade 1 anterolisthesis of L5/S1 with mustache sign (arrow) (a). Schematic of mustache sign (b)
PATIENTS AND METHODS
Following local ethical committee approval according to the local trust guidelines, a retrospective review of the Radiology Information System and Picture Archiving and Communication System (PACS) of 50 patients with Grade 1, L5–S1 spondylolisthesis based on the Meyerding classification was conducted. The scans were performed over 3 years at a tertiary orthopedic spinal center in the UK. The MRI scans were performed using either a 1.5 or 3 Tesla MRI scanner comprising of a minimum of sagittal T1, T2, and short tau inversion recovery sequences and axial T1- and T2-weighted images from L3 to L5 level.
All images were reviewed independently and interpreted on a standard PACS workstation by one musculoskeletal radiology registrar and one fellowship-trained musculoskeletal radiologist with over 10 years of experience. The data were analyzed independently with a subsequent consensus discussion.
Patients with Grade 1 L5–S1 spondylolisthesis were included in the study. Patients with spondylolisthesis grading above Grade 1 were excluded. Patients’ demographics including gender, age, and the presence of pars defect were quantified and analyzed using a statistical analysis software (SPSS Version 24) SPSS: Statistical Package for Social Sciences, IBM, SPSS Inc. New York, USA.
RESULTS
All participants in this study (n = 50) had Grade 1 spondylolisthesis. There were 35 females (70%) and 15 males (30%). The mean age of the patients was 54.3 years (13–82). The patient demographics are summarized in Table 1.
Table 1.
Patient demographics
| Number of patients (n=50) | n (%) |
|---|---|
| Female | 35 (70) |
| Male | 15 (30) |
| Age, mean (range) | 54.3 (13–82) |
| Presence of mustache sign | |
| Yes | 13 (26) |
| No | 37 (74) |
| Presence of pars defect | |
| Yes | 16 (32) |
| No | 34 (68) |
The “mustache sign” was present in 13 patients (26%). Pars defects of L5 were present in 16 patients (32%). Among the 13 patients with the presence of the “mustache sign,” 12 (92.3%) of them also had pars defects of L5. In 37 patients without the presence of mustache sign, only four patients (11%) had pars defects of L5. The difference in these two groups were statistically significant, reporting higher number of patients with pars defect in patients with the presence of the “mustache sign” (P < 0.001, Fishers’ Exact test) [Table 2]. There was excellent interobservor reliability with kappa of 1.
Table 2.
Mustache sign versus pars defect
| Presence of pars defect | Presence of mustache sign | Total | P | |
|---|---|---|---|---|
| Yes | No | |||
| Yes | 12 | 4 | 16 | <0.001 |
| No | 1 | 33 | 34 | |
| Total | 13 | 37 | ||
DISCUSSION
Findings from this study reported that approximately a quarter of patients (26%) in our cohort who had Grade 1 L5–S1 spondylolisthesis demonstrated the “mustache sign.” This sign was also shown to have a higher prevalence in patients with pars defects (P < 0.001). Therefore, the presence of this sign may not only help in identifying spondylolisthesis but also help to point toward the presence of pars interarticularis defect, noting the latter can also be challenging to identify on standard MRI sequences. We believe that having this sign as an adjunct would improve the ability to identify this pathology on lumbar spine MRI.
One of the hallmark signs of Grade 1 spondylolisthesis is the subtle translation or displacement (<25% of the superior vertebral endplate’s width in relation to the adjacent one) on the sagittal MRI sequences. This anterior shift is a critical diagnostic feature and based on the Meyerding grading system as previously discussed. However, in addition to the vertebral body displacement, radiologists may also examine the pars interarticularis for any disruption or irregularity, a common underlying cause of spondylolisthesis.
Furthermore, other associated signs may also provide valuable diagnostic clues for radiologists, including facet joint degeneration or enlargement due to the altered biomechanics associated with spondylolisthesis.[9] The altered alignment and biomechanics can also lead to degenerative changes of the facet joints. Hence, radiological evidence of facet joint degeneration, including sclerosis, enlargement, joint space narrowing, can serve as an indicator of the presence of spondylolisthesis. Besides, there may be changes in intervertebral disc height, reflecting the biomechanical stress, and load redistribution affecting the spinal segment. Over time, the discs may show signs of compression or reduced height, which can be visualized on imaging such as an MRI scan.[10]
In addition, there are also other studies providing insights into the radiological signs of Grade I spondylolisthesis. For instance, Ravichandran described radiological sign of isolated lateral deviation and rotation of spinous process due to pathology in the pars interarticularis and spondylolisthesis.[11] Besides, Appleby and Stabler had also introduced a malalignment sign involving the superior articular facets of the slipped vertebra, useful in diagnosing mild spondylolisthesis.[12] Takagi et al. also discussed the morphological features of spondylotic spondylolisthesis such as decreased lumbar index, increased lordosis, laminar angle, and lumbosacral angle.[13]
Radiological evaluation of Grade 1 spondylolisthesis encompasses a constellation of signs and associated findings, including assessment of pars interarticularis, facet joint changes, and intervertebral disc heights as mentioned before. One of the limitations is its inability to detect subtle abnormality and the interobserver variability in recognizing Grade 1 spondylolisthesis. We believe that including the “mustache sign” in conjunction with these other features may help radiologists and spinal surgeons in making an accurate diagnosis of Grade 1 spondylolisthesis, formulate appropriate treatment plans, which may involve conservative measures, physiotherapy, and, in advanced cases, surgical intervention to alleviate the symptoms and prevent further progression of this condition.
There are several limitations in this study, including its relatively smaller sample size. In addition, this study was conducted at a single institution with a high volume of referrals for investigation for the presence of spinal pathology in symptomatic patients, which may skew some of the results. Besides, we only focused on the utility of the “mustache sign” without assessing and comparing its specificity and sensitivity against different radiological signs. Further multicenter studies with larger patient cohorts may be required to further extrapolate the findings of this study.
CONCLUSION
The “mustache sign” on the MRI spine correlates well with the presence of Grade 1 spondylolisthesis. This ancillary sign can complement other previously described radiological findings on MRI to confirm the presence of Grade I spondylolisthesis.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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