The purpose of this study was to characterize an observation that the most severe lumbar stenosis is often displaced from the disc.
A retrospective magnetic resonance (MRI) review of displacement and causes of lumbar canal stenosis, was undertaken. Lumbar MRIs (n=3000) were reviewed for stenosis defined as a canal diameter of ≤8 mm. Displacement of maximal stenosis from the disc was measured; measurements inferior to the disc were assigned negative values. Defined causes were; ligamentous hypertrophy, facet hypertrophy, lipomatosis, spondylolisthesis, synovial cyst, or adjacent segment disease.
Lumbar stenosis levels (n=1,042) identified in 749 patients were; L1-2 (3.8%), L2-3(20.1%), L3-4 (35.3%), L4-5 (37.7%), and L5-S1 (3.2%). Of these levels 20.8% were attributed to facet hypertrophy, 29.8% ligamentous hypertrophy, 31.1% epidural lipomatosis, 11.2% spondylolisthesis, 5.6% adjacent segment disease, and 1.5% synovial cyst. Mean displacement stenosis (mm) was; synovial cyst (-0.3; range 7 to -5), epidural lipomatosis, (-1.1; 5 to -13), ligamentous hypertrophy (-3.5; 5 to -13); facet hypertrophy (-3.9; 7 to -11), adjacent segment disease (-4.7; 7 to -11), and spondylolisthesis (-4.9; 11 to -12). Sub-group analysis revealed a predominantly negative displacement for spondylolisthesis, adjacent segment disease, facet hypertrophy, and ligamentous hypertrophy.
The site of maximal lumbar stenosis is at or near the center of the disc with lipomatosis or synovial cyst, but significantly inferiorly displaced when ligamentous or facet hypertrophy, spondylolisthesis, or adjacent segment disease is the major cause. Lipomatosis as a cause of stenosis is more common than previously reported.
Lumbar spinal stenosis requiring surgical decompression is a very common spine condition [
A retrospective review was undertaken of 3,000 lumbar MRIs performed at a single institution in 2017 and 2018. Review was conducted by a neurosurgeon (DAR), a neuroradiologist (JMP), a radiology resident (MC and NPL) and 2 medical students (JE and MS). Only cases of routine spondylosis were included. Cases of trauma, neoplasm, or infectious conditions were excluded. Cases with disc protrusions as the major contributor to spondylotic stenosis were excluded as most surgeons are likely to be aware that disc fragments can migrate and routinely direct the surgery to the site of the imaged fragments. Levels previously operated upon were also excluded.
Sagittal and axial T2 weighted images were inspected looking for areas with a midline anterior posterior (AP) canal diameter of ≤8 mm [
To evaluate for factors potentially contributing to the amount displacement of the most severe lumbar stenosis from the corresponding disc space, univariate associations were first examined using Pearson’s correlation for continuous variables, Spearman correlation for ordinal variables, and Pearson Chi-Square for nominal variables. Factors with statistically significant associations were entered in the multi-variate model as well as their corresponding interaction terms. Iterative grouping of the categorical variables were also performed to maximize associations between the merged variable and the displacement measurements. Factors with significant contributions to displacement measurements in the multi-variate model underwent further ANOVA analysis followed by
Of the 3,000 original lumbar MRIs, 1,042 levels in 749 separate patients were identified as meeting inclusion criteria. Studies were excluded when there was no significant stenosis at any lumbar level, demonstrated recent trauma, infection, or neoplasm, showed a disc protrusion as the major cause of stenosis, were postoperative, were redundant, or were of poor quality. Age range was 40 to 89 years (mean 65.6±10.7 years). Of the 1,042 levels there were 474 females and 568 males, and 39 cases (3.8%) were at L1-2, 209 cases (20.1%) at L2-3, 368 cases (35.3%) at L3-4, 393 cases (37.7%) at L4-5, and 33 cases (3.2%) at L5-S1.
Of the 1,042 levels; 217 (20.8%) were classified as being due to facet hypertrophy, 310 (29.8%) to ligamentous hypertrophy, 324 (31.1%) levels to epidural lipomatosis, 117 (11.2%) levels to spondylolisthesis, 58 (5.6%) levels to adjacent segment disease, and 16 (1.5%) levels to a synovial cyst (
Mean displacement from the disc space at levels that were due to synovial cyst, epidural lipomatosis, ligamentous hypertrophy, facet hypertrophy, adjacent segment, and spondylolisthesis were -0.3 mm (range 7 to -5 mm), -1.1 mm (range 5 to -13 mm), -3.5 mm(range 5 to -13 mm), -3.9 mm(range 7 to -11 mm), -4.7 mm(range 7 to -11mm), and -4.9mm(range 11 to -12 mm), respectively (
Significant univariate associations were demonstrated between displacement measurement and patient age (p=0.009, more advanced age associated with more negative displacement), lumbar canal stenosis underlying cause (p<0.001), sex (p=0.049, female sex associated with more negative displacement) and level of disease (p<0.001, lower level associated with more negative displacement). Further evaluation with multi-variate linear regression adjusting for interaction terms among patient age, cause of lumbar stenosis, gender, and level of disease confirmed significant contributions to displacement measurements from cause of lumbar canal stenosis and level of disease (p<0.001 and p=0.003, respectively) but not patient age or sex (p=0.135 and p=0.537, respectively). Iterative grouping of the categorical variables suggested merging of adjacent segment disease, facet hypertrophy, and ligamentous hypertrophy into one group with a group mean contribution of -3.2 mm as well as merging disease at levels L1-2, L2-3, and L3-4 into one group with a group mean contribution of -2.0 mm (
Sub-group analysis showed a common trend of predominantly negative displacement measurements with spondylolisthesis, adjacent segment disease, facet hypertrophy (the synovial joints bilaterally), and ligamentous hypertrophy (the low T2 signal structures internal to the lamina consistent with ligamentum flavum). Epidural lipomatosis (the high T1 and T2 signal internal to the ligamentum flavum and external to the thecal sac) showed a different distribution of displacement values with a significantly higher percentage of stenoses at the level of the disc space (
The fastest increasing area of lumbar spine surgery in recent decades is in older patients with lumbar spinal stenosis [
There is little mention in the minimally invasive lumbar decompression literature of the need to carefully assess the location of maximal stenosis in planning the procedure. We have conducted a retrospective review of 3,000 lumbar MRIs over 2 years, and found 1,042 levels showing stenosis defined as an AP diameter of the lumbar canal ≤8mm [
Intra-operative planning is dependent upon obtaining a true lateral fluoroscopic image that is critical to correctly positioning the access tubular retractor. If the view is obliquely oriented, then the surgeon may misinterpret the relationship of the retractor to the area of most severe stenosis(
Recently, minimally invasive decompression without fusion has been shown to be effective at a non mobile spondylolisthesis [
Minimally invasive decompression is also effective in segments adjacent to an instrumented fusion [
It is of interest that almost one third of our cases were judged to be due in large part to epidural lipomatosis. This is becoming an increasing problem, likely in association with the obesity epidemic and steroid exposure [
The study is limited by its retrospective nature, by the precise definition of stenosis selected, and by some variability in assigning a major cause of the stenosis, which is often multifactorial. As this study was undertaken with all lumbar MRIs performed in a finite period of time and obtained for a wide variety of reasons, it is not known if any of the findings were symptomatic or if any patients had subsequent surgery of any kind. It was not the intention of this study to correlate the findings with clinical outcomes.
In summary, the site of maximal lumbar stenosis is at or near the center of the disc space when the major cause is lipomatosis or synovial cyst, but is often significantly inferiorly displaced from the disc space when ligamentous or facet hypertrophy, spondylolisthesis, or adjacent segment disease is the major cause. Lower lumbar levels and older patients may harbor larger displacements from the disc space. Correctly orienting the access tube for minimally invasive lumbar decompression will help to prevent leaving an undecompressed stenotic segment caudal or rostral to the field of view.
No potential conflict of interest relevant to this article.
Demonstration examples of the measuring technique and various kinds of stenosis. Ⓐ Maximum stenosis 8 mm distally displaced due to ligamentous hypertrophy. Ⓑ Maximum stenosis 10 mm distally displaced due to spondylolisthesis. Ⓒ Maximum stenosis 0 mm displaced due to epidural lipomatosis. Ⓓ Maximum stenosis 5 mm rostrally displaced due to facet hypertrophy.
Displacement directionality by cause of spinal canal stenosis.
Intraoperative fluoroscopic images showing the position of the operating tubular retractor based upon the location of the pathology. The two instruments show the rostral and caudal extent of the decompression. Ⓐ: Tube directed distal to the disc space for the patient shown in
Major cause of cenosis by lumbar level (n=1,042)
Level (n; %) |
||||||
---|---|---|---|---|---|---|
Cause | (n) | L1‐2 | L2‐3 | L3‐4 | L4‐5 | L5‐S1 |
Lipomatosis | 324 | 20; 6.2 | 85; 26.2 | 126; 38.9 | 86; 26.5 | 7; 2.2 |
Ligamentous | 310 | 4; 1.3 | 42; 13.5 | 111; 35.8 | 143; 46.1 | 10; 3.2 |
Facet Hypertrophy | 217 | 11; 5.1 | 54; 24.9 | 83; 38.2 | 61; 28.1 | 7; 3.2 |
Spondylolisthesis | 117 | 1; 0.9 | 5; 4.3 | 18; 15.4 | 86; 73.5 | 7; 6.0 |
Adjacent Segment | 58 | 3; 5.2 | 20; 34.5 | 26; 44.8 | 8; 13.8 | 1; 1.7 |
Synovial Cyst | 16 | 1; 6.3 | 2; 12.5 | 3; 18.8 | 9; 56.3 | 1; 6.3 |
Displacement of maximum stenosis from the disc space by major causative factor
Cause | Percent | Range of displacement (mm) | Mean displacement (mm) | Absolute displacement (mm) |
---|---|---|---|---|
Synovial Cyst | 1.5 | 7 to ‐5 | ‐0.3 | 2.8 |
Lipomatosis | 31.1 | 10 to ‐11 | ‐1.1 | 1.6 |
Ligamentous | 29.8 | 5 to ‐13 | ‐3.5 | 3.6 |
Facet Hypertrophy | 20.8 | 7 to ‐11 | ‐3.9 | 4.1 |
Adjacent Segment | 5.6 | 7 to ‐11 | ‐4.7 | 4 |
Spondylolisthesis | 11.2 | 11 to ‐12 | ‐4.9 | 5.2 |
A summary of statistical analysis results
Analysis | Displacement | p-value |
---|---|---|
Univariate | and age | 0.009 |
and cause | <0.001 | |
and sex (female) | 0.049 | |
and spine level | <0.001 | |
Multivariate | Cause | <0.001 |
Level | 0.003 |