Influence of nomenclature in the interpretation of lumbar disk contour on MR imaging: a comparison of the agreement using the combined task force and the nordic nomenclatures

Normative Measurements of L1-S1 Segmental Angulation, Disk Space Height, and Neuroforaminal Dimensions Using Computed Tomography

BACKGROUND AND OBJECTIVES

To establish normative anatomic measurements of lumbar segmental angulation (SA) and disk space height (DSH) in relation to neuroforaminal dimensions (NFDs), and to uncover the influence of patient demographic and anthropometric characteristics on SA, DSH, and NFDs.

METHODS

NFDs, SA, and anterior, middle, and posterior DSH were measured using computed tomography of 969 patients. NFDs were defined as sagittal anterior-to-posterior width, foraminal height, and area. Statistical analyses were performed to assess associations among SA, DSH, NFDs, and patient height, weight, body mass index, sex, and ethnicity.

RESULTS

SA and DSH measurements increased moving caudally from L1 to S1. Foraminal width decreased moving caudally from L1 to S1. Foraminal height and area demonstrated unimodal distribution patterns with the largest values clustered at L2-L3 on the right side and L3-L4 on the left. Significant differences in SA, DSH, and NFD measurements were observed based on the disk level. Inconsistent, marginal NFD differences were observed based on laterality. Across all disk levels, only weak-to-moderate correlations were observed between SA and DSH in relation to NFDs. Patient height, weight, and body mass index were only weakly associated with SA, DSH, and NFDs. Based on patient sex, significant differences were observed for SA, DSH, and NFD measurements from L1 to S1, with males demonstrating consistently larger values compared with females. Based on patient race and ethnicity, significant differences in SA and NFD measurements were observed from L1 to S1.

CONCLUSION

This study describes 48 450 normative measurements of L1-S1 SA, DSH, and NFDs. These measurements serve as representative models of normal anatomic dimensions necessary for several applications including surgical planning and diagnosis of foraminal stenosis. Normative values of SA and DSH are not moderately or strongly associated with NFDs. SA, DSH, and NFDs are influenced by sex and ethnicity, but are not strongly or moderately influenced by patient anthropometric factors.

Correlation between lumbar spinal canal magnetic resonance imaging grading systems and parameters in lumbar spinal canal compromise

Background

There is a need to assess how commonly used classification systems of intervertebral disc degeneration reflect the compromise of neural elements. This study aims to explore the relationship between lumbar discs degenerative diseases using the Pfirrmann and the Combined Task Forces (CTF) of the North American Spine Society (NASS) grading systems as well as qualitative and quantitative grades of lumbar spinal stenosis. This retrospective cohort study included adult patients undergoing non-contrast MR imaging of lumbosacral spine. The radiological assessment included the Pfirrmann grading system, Van Rijn classification, Combined Task Force (CTF) classification, measurement of the cross-sectional area of the dural sac, mid-sagittal antero-posterior diameter of the thecal sac, the degree of dural sac compression at disc level, lateral recesses heights, and intervertebral foramina diameters. The degree of stenosis of the spinal canal and intervertebral foramina was assessed.

Results

One hundred patients were included in the study. At all levels, Pfirrmann grades had a moderate, significant, positive correlation with the severity of stenosis of the central and lateral spinal canals as well as foraminal stenosis. The grades of lumbar spinal canal and foraminal stenosis had a significant positive correlation with degree of disc displacement as assessed by CTF classification and had a significant negative correlation with the quantitative lumbar spinal canal and foraminal measures.

Conclusions

There is a good correlation between Pfirrmann classification, CTF classification of NASS, qualitative grading and quantitative measures of lumbar spinal canal that reflects the severity of lumbar spinal canal stenosis and nerve root compression.

Deep Learning Model for Automated Detection and Classification of Central Canal, Lateral Recess, and Neural Foraminal Stenosis at Lumbar Spine MRI

Background Assessment of lumbar spinal stenosis at MRI is repetitive and time consuming. Deep learning (DL) could improve -productivity and the consistency of reporting. Purpose To develop a DL model for automated detection and classification of lumbar central canal, lateral recess, and neural -foraminal stenosis. Materials and Methods In this retrospective study, lumbar spine MRI scans obtained from September 2015 to September 2018 were included. Studies of patients with spinal instrumentation or studies with suboptimal image quality, as well as postgadolinium studies and studies of patients with scoliosis, were excluded. Axial T2-weighted and sagittal T1-weighted images were used. Studies were split into an internal training set (80%), validation set (9%), and test set (11%). Training data were labeled by four radiologists using predefined gradings (normal, mild, moderate, and severe). A two-component DL model was developed. First, a convolutional neural network (CNN) was trained to detect the region of interest (ROI), with a second CNN for classification. An internal test set was labeled by a musculoskeletal radiologist with 31 years of experience (reference standard) and two subspecialist radiologists (radiologist 1: A.M., 5 years of experience; radiologist 2: J.T.P.D.H., 9 years of experience). DL model performance on an external test set was evaluated. Detection recall (in percentage), interrater agreement (Gwet κ), sensitivity, and specificity were calculated. Results Overall, 446 MRI lumbar spine studies were analyzed (446 patients; mean age ± standard deviation, 52 years ± 19; 240 women), with 396 patients in the training (80%) and validation (9%) sets and 50 (11%) in the internal test set. For internal testing, DL model and radiologist central canal recall were greater than 99%, with reduced neural foramina recall for the DL model (84.5%) and radiologist 1 (83.9%) compared with radiologist 2 (97.1%) (P < .001). For internal testing, dichotomous classification (normal or mild vs moderate or severe) showed almost-perfect agreement for both radiologists and the DL model, with respective κ values of 0.98, 0.98, and 0.96 for the central canal; 0.92, 0.95, and 0.92 for lateral recesses; and 0.94, 0.95, and 0.89 for neural foramina (P < .001). External testing with 100 MRI scans of lumbar spines showed almost perfect agreement for the DL model for dichotomous classification of all ROIs (κ, 0.95-0.96; P < .001). Conclusion A deep learning model showed comparable agreement with subspecialist radiologists for detection and classification of central canal and lateral recess stenosis, with slightly lower agreement for neural foraminal stenosis at lumbar spine MRI. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Hayashi in this issue.

How should we grade lumbar disc herniation and nerve root compression? A systematic review

BACKGROUND

MRI is the gold standard for evaluating the relationship of disc material to soft tissue and neural structures. However, terminologies used to describe lumbar disc herniation and nerve root compression have always been a source of confusion. A clear understanding of lumbar disc terminology among clinicians, radiologists, and researchers is vital for patient care and future research.

QUESTIONS/PURPOSES

Through a systematic review of the literature, the purpose of this article is to describe lumbar disc terminology and comment on the reliability of various nomenclature systems and their application to clinical practice.

METHODS

PubMed was used for our literature search using the following MeSH headings: "Magnetic Resonance Imaging and Intervertebral Disc Displacement" and "Lumbar Vertebrae" and terms "nomenclature" or "grading" or "classification". Ten papers evaluating lumbar disc herniation/nerve root compression using different grading criteria and providing information regarding intraobserver and interobserver agreement were identified.

RESULTS

To date, the Combined Task Force (CTF) and van Rijn classification systems are the most reliable methods for describing lumbar disc herniation and nerve root compression, respectively. van Rijn dichotomized nerve roots from "definitely no root compression, possibly no root compression, indeterminate root compression, possible root compression, and definite root compression" into no root compression (first three categories) and root compression (last two categories). The CTF classification defines lumbar discs as normal, focal protrusion, broad-based protrusion, or extrusion. The CTF classification system excludes "disc bulges," which is a source of confusion and disagreement among many practitioners. This potentially accounts for its improved reliability compared with other proposed nomenclature systems.

CONCLUSIONS

The main issue in the management of patients with lumbar disc disease and nerve root compression is correlation of imaging findings with clinical presentation and symptomatology to guide treatment and intervention. Although it appears that the most commonly supported nomenclatures have strong interobserver reliability, the classification term "disc bulges" is a source of confusion and disagreement among many practitioners. Additional research should focus on the clinical application of the various nomenclatures.

Validation of multisociety combined task force definitions of abnormal disk morphology

BACKGROUND AND PURPOSE

The multisociety task force descriptively defined abnormal lumbar disk morphology. We aimed to use their definitions to provide a higher level of evidence for the validation of MR imaging in the evaluation of this pathology in patients who have undergone diskectomy by retrospectively classifying their preoperative MRI.

MATERIALS AND METHODS

This retrospective, institutional review board-approved study included 54 of 86 consecutive patients (47 men; average age, 44 years) enrolled in an ongoing prospective trial of surgically treated lumbar disk herniation who had preoperative MRI and documented intraoperative classification of the abnormal disk as protrusion, extrusion, or sequestration by the treating surgeon. Preoperative MRI was classified by 2 blinded radiologists; discrepancies were resolved by a third reader. Statistical analysis of interobserver agreement and imaging compared with surgical findings was performed.

RESULTS

The readers disagreed on only 1 of the 54 cases. The third reader resolved the disagreement. Eight protrusions and 46 extrusions were found on imaging, with no sequestrations. At surgery, there were 13 protrusions and 40 extrusions, with 2 of the extrusions also containing sequestrations; the remaining case had only sequestration. There were 16 discrepancies between imaging and surgery, resulting in 70% agreement.

CONCLUSIONS

This study, which was intended to validate the multisociety combined task force definitions of abnormal disk morphology by using MR imaging with a surgical criterion standard, found 70% agreement between imaging diagnosis and surgical findings. Although reasonable, this finding highlights differences that often exist between intraoperative and preoperative imaging findings of lumbar disk herniation.

[Critical reading of articles about diagnostic tests (part I): Are the results of the study valid?]

In the era of evidence-based medicine, one of the most important skills a radiologist should have is the ability to analyze the diagnostic literature critically. This tutorial aims to present guidelines for determining whether primary diagnostic articles are valid for clinical practice. The following elements should be evaluated: whether the study can be applied to clinical practice, whether the technique was compared to the reference test, whether an appropriate spectrum of patients was included, whether expectation bias and verification bias were limited, the reproducibility of the study, the practical consequences of the study, the confidence intervals for the parameters analyzed, the normal range for continuous variables, and the placement of the test in the context of other diagnostic tests. We use elementary practical examples to illustrate how to select and interpret the literature on diagnostic imaging and specific references to provide more details.

Systematic literature review of imaging features of spinal degeneration in asymptomatic populations

BACKGROUND AND PURPOSE

Degenerative changes are commonly found in spine imaging but often occur in pain-free individuals as well as those with back pain. We sought to estimate the prevalence, by age, of common degenerative spine conditions by performing a systematic review studying the prevalence of spine degeneration on imaging in asymptomatic individuals.

MATERIALS AND METHODS

We performed a systematic review of articles reporting the prevalence of imaging findings (CT or MR imaging) in asymptomatic individuals from published English literature through April 2014. Two reviewers evaluated each manuscript. We selected age groupings by decade (20, 30, 40, 50, 60, 70, 80 years), determining age-specific prevalence estimates. For each imaging finding, we fit a generalized linear mixed-effects model for the age-specific prevalence estimate clustering in the study, adjusting for the midpoint of the reported age interval.

RESULTS

Thirty-three articles reporting imaging findings for 3110 asymptomatic individuals met our study inclusion criteria. The prevalence of disk degeneration in asymptomatic individuals increased from 37% of 20-year-old individuals to 96% of 80-year-old individuals. Disk bulge prevalence increased from 30% of those 20 years of age to 84% of those 80 years of age. Disk protrusion prevalence increased from 29% of those 20 years of age to 43% of those 80 years of age. The prevalence of annular fissure increased from 19% of those 20 years of age to 29% of those 80 years of age.

CONCLUSIONS

Imaging findings of spine degeneration are present in high proportions of asymptomatic individuals, increasing with age. Many imaging-based degenerative features are likely part of normal aging and unassociated with pain. These imaging findings must be interpreted in the context of the patient's clinical condition.

Magnetic resonance imaging predictors of surgical outcome in patients with lumbar intervertebral disc herniation

STUDY DESIGN

A retrospective cohort design.

OBJECTIVE

To determine whether baseline magnetic resonance imaging findings, including central/foraminal stenosis, Modic change, disc morphology, facet arthropathy, disc degeneration, nerve root impingement, and thecal sac compression, are associated with differential surgical treatment effect.

SUMMARY OF BACKGROUND DATA

Intervertebral disc herniation remains the most common source of lumbar radiculopathy treated either with discectomy or nonoperative intervention. Although magnetic resonance imaging remains the reliable "gold standard" for diagnosis, uncertainty surrounds the relationship between magnetic resonance imaging findings and treatment outcomes.

METHODS

Three hundred seven "complete" images from patients enrolled in a previous trial were de-identified and evaluated by 1 of 4 independent readers. Findings were compared with outcome measures including the Oswestry Disability Index. Differences in surgery and nonoperative treatment outcomes were evaluated between image characteristic subgroups and TE determined by the difference in Oswestry Disability Index scores.

RESULTS

The cohort comprised 40% females with an average age of 41.5 (±11.6) years, 61% of whom underwent discectomy for intervertebral disc herniation. Patients undergoing surgery with Modic type I endplate changes had worse outcomes (-26.4 vs. -39.7 for none and -39.2 for type 2, P = 0.002) and smaller treatment effect (-3.5 vs. -19.3 for none and -15.7 for type 2, P = 0.003). Those with compression of ≥1/3 showed the greatest improvement within the surgical group (-41.9 for ≥1/3 vs. -31.6 for none and -38.1 for <1/3, P = 0.007) and the highest TE (-23 compared with -11.7 for none and -15.2 for <1/3, P = 0.015). Furthermore, patients with minimal nerve root impingement demonstrated worse surgical outcomes (-26.5 vs. -41.1 for "displaced" and -38.9 for "compressed," P = 0.016).

CONCLUSION

Among patients with intervertebral disc herniation, those with thecal sac compression of 1/3 or more had greater surgical treatment effect than those with small disc herniations and Modic type I changes. In addition, patients with nerve root "compression" and "displacement" benefit more from surgery than those with minimal nerve root impingement.

LEVEL OF EVIDENCE

2.

Appropriateness of lumbar spine magnetic resonance imaging in Spain

OBJECTIVES

To determine the minimum percentage of lumbar spine magnetic resonance imaging (LSMRI) which are inappropriately prescribed in routine practice.

METHODS

LSMRI performed prospectively on 602 patients in 12 Radiology Services across 6 regions in Spain, were classified as "appropriate", "uncertain" or "inappropriate" based on the indication criteria established by the National Institute for Clinical Excellence, the American College of Physicians and Radiology, and current evidence-based clinical guidelines. Studies on patients reporting at least one "red flag" were classified as "appropriate". A logistic regression model was developed to identify factors associated with a higher likelihood of inappropriate LSMRI, including gender, reporting of referred pain, health care setting (private/public), and specialty of prescribing physician. Before performing the LSMRI, the radiologists also assessed the appropriateness of the prescription.

RESULTS

Eighty-eight percent of LSMRI were appropriate, 1.3% uncertain and 10.6% inappropriate. The agreement of radiologists' assessment with this classification was substantial (k=0.62). The odds that LSMRI prescriptions were inappropriate were higher for patients without referred pain [OR (CI 95%): 13.75 (6.72; 28.16)], seen in private practice [2.25 (1.20; 4.22)], by orthopedic surgeons, neurosurgeons or primary care physicians [2.50 (1.15; 5.56)].

CONCLUSION

Efficiency of LSMRI could be improved in routine practice, without worsening clinical outcomes.

Vertebral endplate changes are not associated with chronic low back pain among Southern European subjects: a case control study

BACKGROUND AND PURPOSE

Data on the association between vertebral endplate changes and low back pain are contradictory. This study was designed to assess whether this association exists among Southern European subjects.

MATERIALS AND METHODS

Patients in this study serving as cases were 35-50 years of age with low back pain lasting >90 days, for whom a lumbar MR imaging had been prescribed. Controls were subjects 35-50 years of age, having a cranial MR imaging for headache with normal findings, and no history of clinically relevant LBP. Two hundred forty cases and 64 controls were recruited consecutively in the radiology services across 6 cities in Spain. Imaging findings and subject characteristics were gathered through previously validated instruments. Radiologists who interpreted MRI were blinded to the subject characteristics. A multivariate logistic regression model was developed to assess the association of vertebral endplate changes with LBP, adjusting for sex, age, body mass index, lifetime exposure to smoking, physical activity, disk degeneration, and the interaction between disk degeneration and vertebral endplate changes.

RESULTS

Vertebral endplate changes were found in 80.4% of the cases and in 87.5% of the controls. In the regression model, disk degeneration was the only variable showing a confounding effect. Results showed that after adjusting for disk degeneration, the presence of vertebral endplate changes is associated with the absence of chronic LBP (OR for LBP: 0.31; 95% CI, 0.10-0.95).

CONCLUSIONS

In Southern European subjects, vertebral endplate changes are not associated with chronic LBP.

Modic changes and associated features in Southern European chronic low back pain patients

BACKGROUND CONTEXT

Conflicting reports exist regarding the prevalence of Modic changes among low back pain (LBP) patients and factors associated with their existence.

PURPOSE

To assess the prevalence of Modic changes and other findings on lumbar magnetic resonance imaging (MRI) among Spanish adult chronic LBP patients and the patient characteristics and radiological findings associated with Modic changes.

STUDY DESIGN

A cross-sectional imaging study among chronic LBP patients.

PATIENT SAMPLE

Four hundred eighty-seven patients (263 women and 224 men) undergoing lumbar spine MRI examination for chronic LBP.

OUTCOME MEASURES

Gender, age, body mass index (BMI), lifetime smoking exposure, degree of physical activity, and image features (disc degeneration, type and extension of Modic changes, disc contour, annular tears, spinal stenosis, and spondylolisthesis).

METHODS

Ten radiologists from six hospitals across six cities in Spain consecutively recruited adult patients in whom lumbar MRI had been prescribed for LBP lasting ≥3 months. Patients' characteristics and imaging findings were assessed through previously validated instruments. A multivariate logistic regression model was developed to assess the features associated with Modic changes.

RESULTS

Modic changes were found in 81% of the patients. The most common was Type II (51.3%), affecting only the end plate. Variables associated with Type I changes were disc contour abnormalities, spondylolisthesis, and disc degeneration. The same variables were associated with a higher risk of Type II or any type of Modic changes, as well as being male, and having a higher BMI.

CONCLUSIONS

Modic changes are found in 81% (95% confidence interval, 77-85) of adult Spanish patients in whom an MRI is prescribed for chronic LBP. Modic changes are more likely to be found in males with a high BMI, who also show disc contour abnormalities, spondylolisthesis, or disc degeneration.