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Significance of spinal canal and dural sac dimensions in predicting treatment of lumbar disc herniation
Abstract
This retrospective study was performed to investigate the significance of quantitative MRI measurements of spinal canal and dural sac dimensions for treatment decisions and clinical outcome of lumbar disc herniation. 182 patients (111 nonsurgical patients and 71 surgical patients) were included, while 78 nonsurgical patients and 50 surgical patients were enrolled in the final follow-up. The initial JOA score in nonsurgical patients was significantly superior to surgical patients (t-test: p < 0.001), whereas the final JOA score and the rate of improvement were not significantly different between the two groups of patients (t-test: p > 0.05). 88.46% of nonsurgical patients and 90.00% of surgical patients had a good or excellent outcome (chi-square test: p > 0.05). However, if the 16 recurrent cases were included, the proportions dropped to 75.82% and 84.90% for nonsurgical and surgical patients, respectively. Compared with nonsurgical patients, quantitative parameters, such as midsagittal diameter and available diameter of spinal canal, lateral recess width and cross-sectional areas of spinal canal and dural sac, were significantly smaller in surgical patients (t-test: p < 0.001), and was reflected in the initial JOA score (128 cases; Spearman rank correlation coefficient: r 0.01 = 0.486, 0.499, 0.493, 0.507, 0.484; p < 0.001). The spinal canal and dural sac dimensions were important predictive factors for treatment selection of lumbar disc herniation.
... Higher PCR on initial MRI was found to be an important predictive factor for failure of conservative treatment and the need for surgery. 27 Karppinen et al, 28 on contrary, found that the degree of disk displacement in MRI did not correlate with any subjective symptoms in patients operated for sciatica. Also, the correlation between higher PCR and good outcome after surgery remains controversial. ...
... It was reported that spinal canal volume size differs among patients with lumbar disc herniation with or without clinical symptoms, and that patients with severe symptoms have a smaller spinal canal volume, which indicates that spinal canal diameter is an important factor determining the severity of patients' symptoms [11]. Yuan et al. [12] studied the spinal canal morphology of 182 patients whose symptoms were signi cantly relieved after conservative or surgical treatment, and found that the spinal canal volume in the patients in the conservative treatment group was signi cantly greater than of the patients in the surgery group. On the basis of the different signal characteristics of protrusions on ordinary MRI, Iwabuchi et al. [13] speculated that most type 1 protrusions were composed of nucleus pulposus. ...
Background: The phenomenon of lumbar disc herniation resorption is increasingly being reported, but the occurrence of this phenomenon cannot currently be accurately predicted.
Methods: We acquired magnetic resonance imaging (MRI) of patients with giant lumbar disc herniation from January 2018 to December 2019, and analyzed the prognostic value of measurements performed on the images. The patients underwent conservative treatment according to the doctor’s decision. The imaging assessments included Komori points, MSU type, Iwabuchi type, the presence of a “bull’s eye” sign on contrast-enhanced MRI, Modic type classification, initial imaging prominence rate, and maximum level projection area. Post-treatment MRI was reviewed to evaluate the outstanding prominence rate and the maximum level projection area, thereby allowing calculation of the intervertebral disc absorption rate after treatment. The rate of patients undergoing later surgery was also recorded.
Results: Seventy-six patients (46 males and 30 females, aged 14–65 years [mean 37.79 ± 10.60]) were included in this study, 12 of whom underwent surgery, giving a surgical rate of 15.79%. All patients were followed up for more than 9 months. The outburst rate was 84.41% ± 14.72%. The absorptivity rate of the 64 patients under conservative treatment was 38.35% ± 40.64%, with the absorptivity of the patients with Iwabuchi type 1 and a bull’s eye sign being significantly higher than the average rate (P < 0.01).
Conclusions: The resorption of giant lumbar disc herniation is a natural process. Imaging findings showed Iwabuchi type 1 and a positive bull’s eye sign on contrast-enhanced MRI to be associated with an increased probability of resorption.
... 47 Smaller sagittal and cross-sectional spinal canal dimensions are significant factors in predicting outcomes of surgery for symptomatic disc herniations. [50][51][52] Although the vertebral body and spinal canal are correspondingly smaller at higher levels, the laminar thickness is increased in the upper lumbar spine of L1-3 compared with L4 and L5. 53 In addition to the narrower spinal canal and thicker lamina at the upper lumbar levels, there is a higher number of nerve roots and often the conus medullaris behind L1. ...
Study Design
Systematic review and meta-analysis.
Objective
To conduct a literature review on outcomes of discectomy for upper lumbar disc herniations (ULDH), estimate pooled rates of satisfactory outcomes, compare open laminectomy/microdiscectomy (OLM) versus minimally invasive surgical (MIS) techniques, and compare results of disc herniations at L1-3 versus L3-4.
Methods
A systematic review of articles reporting outcomes of nonfusion surgical treatment of L1-2, L2-3, and/or L3-4 disc herniations was performed. The inclusion and exclusion of studies was performed according to the latest version of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement.
Results
A total of 20 articles were included in the quantitative meta-analysis. Pooled proportion of satisfactory outcome (95% CI) was 0.77 (0.70, 0.83) for MIS and 0.82 (0.78, 0.84) for OLM. There was no significant improvement with MIS techniques compared with standard OLM, odds ratio (OR) = 0.86, 95% CI (0.42, 1.74), P = .66. Separating results by levels revealed a trend of higher satisfaction with L3-4 versus L1-3 with OLM surgery, OR = 0.46, 95% CI (0.19, 1.12), P = .08.
Conclusion
Our analysis reveals that discectomy for ULDH has an overall success rate of approximately 80% and has not improved with MIS. Discectomy for herniations at L3-4 trends toward better outcomes compared with L1-2 and L2-3, but was not significant.
... 25 Higher PCR on initial MRI was found to be an important predictive factor for failure of conservative treatment and the need for surgery. 27 Karppinen et al, 28 on contrary, found that the degree of disk displacement in MRI did not correlate with any subjective symptoms in patients operated for sciatica. Also, the correlation between higher PCR and good outcome after surgery remains controversial. ...
Objective
Risk factors for developing cauda equina syndrome (CES) caused by lumbar disc herniation (LDH) remain controversial and have not been yet established. The aim of the study was to investigate whether there is a relationship between age, sex, body mass index (BMI) or the degree of spinal canal compromise and the presence of CES in patients undergoing lumbar microdiscectomy.
Methods
Between 2015-2019, 506 patients were prospectively identified who had an operation for LDH compressing the dural sac. The “Prolapse:Canal ratio” (PCR) was calculated as a proportion of the cross-sectional area (CSA) of the disc prolapse compared to the total CSA of the spinal canal.
Results
In total, 35 CES (6.9%) patients were identified. Multivariate logistic regression, adjusted for age, gender, BMI and PCR shows that only PCR was associated with the presence of CES (p<0.001,AUC 0.7431). BMI was not associated with an increased risk of CES.
Conclusions
This study demonstrates a significant correlation between the size of LDH relative to size of the spinal canal and the presence of CES. A finding of LDH causing more than 60% obstruction of spinal canal should be considered a red flag and such patients need to be watched more closely.
... Still other studies reported that Pfirrmann's grade [14], more laterally located discs, extrusion and protrusion herniation types, and larger fragments [15] could predict the risk of conservative treatment failure in patients with LDH. Yuan et al. showed that the spinal canal and dural sac dimensions were important predictive factors for treatment selection of lumbar disc herniation [16]. In addition, psychosocial issues, personal Table 4. Two-by-two matrices of the relationship between the estimated dissatisfied and the actual dissatisfied (sensitivity analysis). ...
Does the Finneson-Cooper score reflect the true value of predicting surgical success before discectomy? The aim of this study was to identify reliable predictors for surgical success two year after surgery for patients with LDH. Prospective analysis of 154 patients with LDH who underwent single-level lumbar discectomy was performed. Pre- and post-surgical success was assessed by the Oswestry Disability Index (ODI) over a 2-year period. The Finneson-Cooper score also was used for evaluation of the clinical results. Using the ODI, surgical success was defined as a 30% (or more) improvement on the ODI score from the baseline. The ODI was considered the gold standard in this study. Finally, the sensitivity, specificity, and positive and negative predictive power of the Finneson-Cooper score in predicting surgical success were calculated. The mean age of the patients was 49.6 (SD = 9.3) years and 47.4% were male. Significant improvement from the pre- to post-operative ODI scores was observed (P < 0.001). Post-surgical success was 76.0% (n = 117). The patients' rating on surgical success assessments by the ODI discriminated well between sub-groups of patients who differed with respect to the Finneson-Cooper score. Regarding patients' surgical success, the sensitivity, specificity, and accuracy of the Finneson-Cooper ratings correlated with success rate. The findings indicated that the Finneson-Cooper score was reflective of surgical success before discectomy.
Introduction:
There is conflicting data on the risk factors for recurrent lumbar disc herniation (rLDH). Most of the predictors for rLDH identified so far are acquired risk factors or radiological factors at the level of the herniation. Whole lumbar spine (WLS) morphometry has not been evaluated as a possible predictor of rLDH.
Objectives:
We aimed to evaluate if preoperative spinal morphometry can predict the occurrence of rLDH requiring revision surgery.
Methods:
This retrospective case-control study on 250 patients included 45 patients operated for rLDH, 180 controls without rLDH who had previously undergone microdiscectomy for a single level lumbar disc prolapse, and a holdout validation set of 25 patients. Morphometric variables related to the WLS were recorded in addition to previously identified predictors of rLDH. Logistic regression (LR) analysis was performed to identify independent predictors of rLDH.
Results:
LR yielded four predictors of which two were WLS morphometric variables. While increasing age and smoking positively predicted rLDH, increasing WLS interfacet distance and WLS dural-sac circumference negatively predicted rLDH. The LR model was statistically significant, χ2 (4) =15.98, P = 0.003, and correctly classified 80.3% of cases. On validation, the model demonstrated a fair accuracy in predicting rLDH (accuracy: 0.80, AUC: 0.70).
Conclusions:
Larger mean lumbar bony canals and dural sacs protect from the occurrence of symptomatic rLDH. These WLS morphometric variables should be included in future risk stratification algorithms for lumbar disc disease. In addition to the previously recognized risk factors, our study points to an underlying developmental predisposition for rLDH.
BACKGROUND: Timing of surgery and the importance of the size of disc prolapse in cauda equina syndrome (CES) remain controversial.
OBJECTIVE: To investigate whether there is a relationship between postoperative urinary function, preoperative duration of neurogenic lower urinary tract dysfunction (NLUTD), and the level of canal compromise.
METHODS: Seventy-one patients operated for CES were prospectively identified between 2010 and 2013. Fifty-two cases with preoperative NLUTD were included. The "Prolapse: Canal ratio" (PCR) was calculated as a proportion of cross-sectional area of disc prolapse on total cross-sectional area of spinal canal.
RESULTS: Median of preoperative duration of NLUTD was 72 h (48; 132) and period from first assessment to surgery 10.5 h (7; 18.5). Urinary incontinence was seen in 46.2% of patients, 38.4% had painless retention and 15.4% had painful retention. In 38.5% of cases, urinary symptoms persisted for more than 20 mo postoperatively. There was no correlation between duration of preoperative NLUTD and urinary dysfunction persistence (P = .921). The outcome was not significantly influenced by having surgery more than the 48 h after presentation (P = .135). Preoperative incontinence persisted in 58% and painless retention in 30% of cases. The mean PCR was 0.6 ± 0.18. There was no correlation between PCR and outcome (P = .537) even after adjusting for duration of preoperative NLUTD (P = .7264).
CONCLUSION: No significant correlation was demonstrated between the preoperative duration of urinary dysfunction, the size of disc herniation relative to size of spinal canal, and postoperative urinary function in a large consecutive series of patients with CES.
Centrally located lumbar disc herniations have been reported to be of predictive value for poor post-operative clinical outcome. One hundred and fifty patients undergoing lumbar disc herniation surgery were prospectively included. Herniation-related parameters, including the grading of contours, were assessed from pre-operative computed tomography (CT) and magnetic resonance imaging (MRI) images using a new three-dimensional grading system. The radiological findings were compared with outcome parameters two years post-operatively (patient-assessed pain, function/health scores and evaluation by an independent observer). An intra- and inter-observer validation of the classification was performed in a subgroup of patients. High intra-observer and good inter-observer reliability for both CT and MRI was seen. In the study population, no relation between the distribution or size of the herniations and outcome at 2-year follow-up were found. The distribution and size of the lumbar disc herniations with the three-dimensional classification were not found to be of importance for the clinical outcome.
To evaluate the effects of early lumbar disc surgery compared with prolonged conservative care for patients with sciatica over two years of follow-up.
Randomised controlled trial.
Nine Dutch hospitals.
283 patients with 6-12 weeks of sciatica.
Early surgery or an intended six months of continued conservative treatment, with delayed surgery if needed.
Scores from Roland disability questionnaire for sciatica, visual analogue scale for leg pain, and Likert self rating scale of global perceived recovery.
Of the 141 patients assigned to undergo early surgery, 125 (89%) underwent microdiscectomy. Of the 142 patients assigned to conservative treatment, 62 (44%) eventually required surgery, seven doing so in the second year of follow-up. There was no significant overall difference between treatment arms in disability scores during the first two years (P=0.25). Improvement in leg pain was faster for patients randomised to early surgery, with a significant difference between "areas under the curves" over two years (P=0.05). This short term benefit of early surgery was no longer significant by six months and continued to narrow between six months and 24 months. Patient satisfaction decreased slightly between one and two years for both groups. At two years 20% of all patients reported an unsatisfactory outcome.
Early surgery achieved more rapid relief of sciatica than conservative care, but outcomes were similar by one year and these did not change during the second year.
ISRCT No 26872154.
Study design:
Concurrent prospective randomized and observational cohort studies.
Objective:
To assess the 8-year outcomes of surgery versus nonoperative care.
Summary of background data:
Although randomized trials have demonstrated small short-term differences in favor of surgery, long-term outcomes comparing surgical with nonoperative treatment remain controversial.
Methods:
Surgical candidates with imaging-confirmed lumbar intervertebral disc herniation meeting Spine Patient Outcomes Research Trial eligibility criteria enrolled into prospective randomized (501 participants) and observational cohorts (743 participants) at 13 spine clinics in 11 US states. Interventions were standard open discectomy versus usual nonoperative care. Main outcome measures were changes from baseline in the SF-36 Bodily Pain and Physical Function scales and the modified Oswestry Disability Index-AAOS/Modems version assessed at 6 weeks, 3 months, and 6 months, and annually thereafter.
Results:
Advantages were seen for surgery in intent-to-treat analyses for the randomized cohort for all primary and secondary outcomes other than work status; however, with extensive nonadherence to treatment assignment (49% patients assigned to nonoperative therapy receiving surgery versus 60% of patients assigned to surgery) these observed effects were relatively small and not statistically significant for primary outcomes (bodily pain, physical function, Oswestry Disability Index). Importantly, the overall comparison of secondary outcomes was significantly greater with surgery in the intent-to-treat analysis (sciatica bothersomeness [P > 0.005], satisfaction with symptoms [P > 0.013], and self-rated improvement [P > 0.013]) in long-term follow-up. An as-treated analysis showed significant surgical treatment effects for primary outcome measures (mean change, surgery vs. nonoperative care; treatment effect; 95% confidence interval): bodily pain (45.3 vs. 34.4; 10.9; 7.7 to 14); PF (42.2 vs. 31.5; 10.6; 7.7 to 13.5); and Oswestry Disability Index (-36.2 vs. -24.8; -11.3; -13.6 to -9.1).
Conclusion:
Carefully selected patients who underwent surgery for a lumbar disc herniation achieved greater improvement than nonoperatively treated patients; there was little to no degradation of outcomes in either group (operative and nonoperative) from 4 to 8 years.
Level of evidence:
2.
Two hundred eighty patients with herniated lumbar discs, verified by radiculography, were divided into three groups. One group, which mainly will be dealt with in this paper, consisted of 126 patients with uncertain indication for surgical treatment, who had their therapy decided by randomization which permitted comparison between the results of surgical and conservative treatment. Another group comprising 67 patients had symptoms and signs that beyond doubt, required surgical therapy. The third group of 87 patients was treated conservatively because there was no indication for operative intervention. Follow-up examinations in the first group were performed after one, four, and ten years. The controlled trial showed a statistically significant better result in the surgically treated group at the one-year follow-up examination. After four years the operated patients still showed better results, but the difference was no longer statistically significant. Only minor changes took place during the last six years of observation.
The study compared different methods to measure the absolute and relative size of lumbar disc herniations on computed tomography scans and their relation to sciatica.
Computed tomography (CT) examinations were done before and at 3 and 24 months after nonoperative treatment in 30 patients with lumbar disc herniations. The size of the herniation was described by different indexes and related to the degree of sciatica. One index was formed by the area of the herniation in relation to the spinal canal (A-index), whereas two indexes were formed by linear measurements of the herniation in relation to the spinal canal in either two (ST-index) or one direction (S-index).
Each index was correlated significantly to the degree of sciatica. The area of the herniations decreased markedly over time.
Linear measurements of the herniation in two perpendicular directions provide a practical and accurate way of describing the size of lumbar disc herniations.
A two-part observational study. In Part 1, consecutive lumbar magnetic resonance imaging scans in patients with sciatica meeting enrollment criteria were prospectively and blindly analyzed by a set protocol. In Part 2, further clinical findings at the time of the magnetic resonance imaging were obtained by retrospective chart review and outcome assessment done at follow-up of more than 2 years.
To determine the quantitative magnetic resonance findings of disc and canal measures in patients with sciatica and to analyze the predictive values of these magnetic resonance imaging and clinical variables on outcomes.
Part 1: Consecutive patients with a primary diagnosis of sciatica who came to lumbar magnetic resonance imaging were enrolled, and magnetic resonance imaging dimensions of discs and canal at the herniated level were collected. Part 2: Of 186 patients in Part 1, 135 were followed for more than 2 years; 87 were treated conservatively, and 48 were treated surgically. Outcomes were judged on satisfaction, activity level, medication intake, and reported pain at follow-up (mean, 2.6 years).
Part 1: Wide ranges of disc and canal measurements were seen in all parameters. Significant differences in all magnetic resonance parameters were noted between male and female patients. Men had proportionately greater canal compromise by the affected disc than women. Positive sciatic tension signs and short duration of symptoms correlated with large disc herniation. Right-sided symptomatic herniations were usually larger than left. Part 2: At follow-up, predictors of outcome were determined independently for the surgery and the nonoperative groups. In the nonoperative group, a shorter duration of sciatica was the most significant predictor of a good outcome (P = 0.0018). Moreover, a duration of symptoms less than 6 months, no involvement with litigation, and younger age were also correlated with a favorable outcome. The only magnetic resonance parameter associated with good outcome was a small ratio of disc hemiarea to remaining canal hemiarea (P = 0.045). For the surgical group, a larger anteroposterior disc length was the most significant independent predictor of a positive outcome (P < 0.0001). Larger ratios of disc area to canal area are also significantly associated with good outcomes (P < 0.0001), as are large disc areas and small remaining canal areas. Large right-left canal widths and small disc widths are also identified as predictors of a favorable outcome. Of the clinical parameters, concurrent medical illness, workers' compensation involvement, and female gender appear to be the most significantly correlated with poor outcome. All fair or poor surgical outcomes were in patients with smaller (< 6 mm) disc herniations.
Quantitative measurements by magnetic resonance imaging of disc and canal morphology of 188 patients with sciatica indicate a wide range of herniation and canal sizes, with significant differences between men and women. In a cohort of 135 patients followed for more than 2 years, demographic and clinical features appeared to predict outcomes of nonoperative treatment, whereas morphometric features of disc herniation and the spinal canal seen on magnetic resonance imaging were much more powerful predictors of surgical outcomes.
Narrow spinal canals or herniated discs can be associated with leg pain. However, it is not known whether quantitative measurements of the spinal canal or herniated disc are sensitive and specific for low back-related leg pain. The size and cross-sectional area of the dural sac and any herniated discs were measured from magnetic resonance imaging examinations of 22 asymptomatic individuals and 44 patients with sciatica. The sensitivity and specificity of these measurements were determined. In this small population of patients, a dural sac anteroposterior (AP) diameter of 10.2 mm at the L3-4, L4-5, or L5-S1 vertebral levels was 74% sensitive and 74% specific for leg pain. Based on measurements in symptomatic patients, a herniated disc with an AP diameter of approximately 3 mm was over 95% sensitive and 95% specific. However, if the AP diameters of herniated discs in symptomatic patients were compared with similar measurements in asymptomatic controls, the most sensitive and specific threshold value was 6.8 mm. These findings must be confirmed in a larger population before they are applied clinically. J. Magn. Reson. Imaging 2000;12:439-443.
Spinal canal dimensions are assumed to play a significant role with regard to the development of symptoms in individuals with disc herniations. The literature is inconclusive on the significance of spinal canal size as a risk factor for sciatica, mainly because of study design problems. The objective of this study, therefore, was to test the hypothesis that spinal canal dimensions are a significant risk factor for the development of sciatica, comparing symptomatic and asymptomatic individuals. Thirty symptomatic patients undergoing lumbar discectomy and 45 asymptomatic volunteers were investigated by clinical and MRI examination. The size of the spinal canal and thecal sac as well as the midsagittal spinal canal diameter were measured using a point counting method and scanner software, respectively. Differences between the groups were compared separately for each level L3/4 to L5/S1. The intra- and inter-observer error ranged between 0.95 and 0.99 for all measurements. In symptomatic patients, the dimensions of the spinal canal and thecal sac as well as the midsagittal spinal canal diameter were smaller at all disc levels. Unpaired t-test demonstrated a significant difference, ranging from P<0.05 to P<0.001. When controlled for age, sex and body height, the odds ratio for a symptomatic disc herniation increased to as high as 35, depending on the spinal level, when the size of the spinal canal was smaller than the mean for controls by two standard deviations or more. In symptomatic patients, spinal canal dimensions are significantly smaller than those in asymptomatic individuals. Spinal canal dimension is an important factor discriminating patients from control subjects. A clinically relevant grading system for disc herniation should therefore be based on the spatial relationship between herniated disc material and neurogenic structures.
There is limited information describing the correlation between the initial quantitative measurements on magnetic resonance imaging (MRI) scans of disc herniation area, canal cross-section areas, percent canal compromise, and disc herniation location to the need for surgery.
Our aim is to determine if the size of disc herniation area, canal cross-section area, percent canal compromise, and disc herniation location taken from MRI images of patients with symptomatic single-level lumbar herniated intervertebral discs upon initial presentation to a spine surgeon, were predictive of the need for surgical treatment.
This is a retrospective case matched study of patient MRI images in the senior author's private practice.
From a pool of 332 patients with sciatica caused by lumbar intervertebral disc herniations at our institution, 65 patients had surgery, of which MRI images were available and analyzed on 44 patients. Forty-four additional patients were randomly selected from the remaining 267 original group as nonoperative controls.
The axial MRI image showing the largest canal compromise by the herniated disc was selected for measurements. Using T1- and T2-weighted images, the areas of interest were digitally scanned at high resolution. The canal area and disc herniation area measurement were calculated from the total number of pixels per cross-sectional area, multiplied by a scan correction factor, mm(2) /pixel. Disc herniation locations were classified into either central or paracentral. The percent canal compromise was obtained by disc herniation area divided by canal cross-section area and multiplied by 100.
The surgical group's overall mean herniated disc area was 219.6 square millimeter (mm(2)), 179.8 at L4-5, and 267.4 at L5-S1. The nonoperative group's overall mean herniated disc area was 178.4 mm(2), 135.1 at L2-3, 160.3 at L4-5, and 207.4 at L5-S1. The surgical group's overall mean canal cross-sectional area was 471.8 mm(2), 418.6 at L4-5, and 535.6 at L5-S1. The nonoperative group's overall mean canal cross-sectional area was 541.3 mm(2), 518.1 at L2-3, 446.8 at L4-5, and 669.9 at L5-S1. The overall percent canal compromise ratio in the surgery group was 46.7%, 44.1% at L4-5, and 49.8% at L5-S1. The overall percent canal compromise in the nonoperative group was 34.2%, 34.1% at L2-3, 36.1% at L4-5, and 31.8% at L5-S1. The percent canal compromise in central herniations at L4-5 level was 53.0% in the surgical group, and 32.8% in the nonoperative group; at the L5-S1 level surgical group percent canal compromise was 64.1% and in the nonoperative group canal compromise was 27%. L4-L5 level paracentral herniations canal compromise was 36.7% in the surgical group compared with 42.5% canal compromise in the nonoperative group. At the L5-S1 level the canal compromise was 45% in the surgical group and 34.8% in the nonoperative group.
Our findings show a trend for patients treated with surgery to have larger disc herniation areas and smaller canal cross-section areas, corresponding to larger percent canal compromise than the nonoperative group. Centrally located herniations followed this trend closely at all levels studied. However, the paracentral herniation at the L4-5 level does not follow this trend, possibly because paracentral disc herniation clinical course is determined more by herniation location rather than the overall herniation size.