• Incidence,Evaluation and Classification of lumbar spine MR abnormalities in asymptomatic individuals

    27 December at 23:34 from atlas

    • Incidence,Evaluation and Classification of lumbar spine MR abnormalities in asymptomatic individuals.

         Share27 December at 20:39 from atlas

      It is important to clearly state that :(i) there is a high incidence of MR lumbar spine abnormalities ,including bulges, protrusions, herniations, pars defects etc in totally asymptomatic individuals,and (ii) there is at times poor description of lumbar disc abnormalities in radiological and spinal surgical reports.With respect to the latter point, the terms bulge, protrusion, prolapse,herniation are used interchangeably.This is not the correct application of terms. The terms protrusion, prolapse and herniation are often assumed ,and tagged to mean a traumatic causation when morphologically there is a desiccated broad based circumferential annular bulge the result of age related facet joint laxity, nuclear dessication and broad based symmetrical bulging developing over years.Further more a true focal protrusion or nuclear prolapse/ focal herniation is part of the spectrum of changes of lumbar spondylosis or degeneration.Similarly the terms annular fissure or annular tears are used interchangeably and are part of annular degeneration and the use of 'tear' over 'fissure' does not imply causation.The annular changes are part of the changes occurring in the annulus with degeneration.The descriptors themselves do not equate to causation or aetiology.

      In assessing causation a medical examiner MUST follow 4 assessments: (1) Is there a probable (>50%) CAUSE? ;( 2) Is there a probable(>50%)EFFECT ?; (3) Is there a BIOLOGICAL PLAUSIBILTY between the cause and effect? ,and (4) Determine if there is a PROBABLE (>50%) RELATIONSHIP between this cause and effect, in this case.In assessing questions of probable causation the examiner MUST recall the Criteria set down by epidemiologist Sir Austin Bradford Hill in 1965 .

      Sir Austin Bradford Hill Criteria:

      1.Strength, 2.Consistency, 3.Specificity, 4.Temporality,5.Biological Gradient, 6.Plausibility, 7.Coherence, 8.Experimental evidence ,and 9. Analogy.

      An epidemiologist views all records and data in reaching scientific conclusions on causation.An epidemiologist would be criticised for not viewing scientific notes or records made in close temporal relation to the causative factor or event under scrutiny.(Sir Austin Bradford Hill Criterion 4).This also applies to an Independent Medical Examiner.All medical records(contemporaneous and close temporal relationship to the subject causative factor under scrutinyMUST be  made available ,viewed and considered in accordance with the American Board of Independent Medical Examiners' goals.A medical examinee's history is certainly important but the viewing of contemporaneous medical records  of the actual event is a BASIC requirement to fulfil the scientific requirement of assessing probable causation medically.

      STUDIES /CITATIONS REGARDING THE  INCIDENCE  OF LUMBAR MRI CHANGES IN  TOTALLY ASYMPTOMATIC VOLUNTEERS.

      1. Jensen MC ,Modic MT et al ,"MRI imaging of the lumbar spine in people without back pain".N Eng J Med-1004;331:369-373.

      52% of the 98 totally asymptomatic people under the age of 60 years had a lumbar disc bulge on MRI and 27% had a protrusion.1% had an extrusion. Other findings: 14%facet joint degeneration,8% spondylolysis( pars defects),7% spondylolisthesis. 36% of the 98 asymptomatic subjects had normal discs at all levels.Of 98 volunteers, 64% had an abnormal disc on MRI (bulge, protrusion,and/or extrusion).38% had an abnormality of more than one level.The authors advised: given the high prevalence of these findings and of back pain,the discovery by MRI of bulges or protrusions in people with low back pain may frequently be coincidental...over 50% of asymptomatic individuals had disc bulges.

      2.Boden SD et al."Abnormal magnetic resonance scans of the lumbar spine in asymptomatic subjects:A prospective investigation".J Bone Joint Surg Am 1990;72A:403-408.

      MRI examination ,read independently by 3 neuroradiologists, on 67 people who had never had lower back pain or sciatica. Under the age of 60, 20% had lumbar herniated nucleus pulposus (HNP).Over 60 years- 36% HNP, 21% spinal stenosis.35% between 20 and 39 years had degenerative disc disease with or without a bulge.There was degeneration or bulging of a disc between 20 and 39 years old and in all, but one subject 60 to 80 year old subjects.

      3. Weishaupt  D and Boos et al : 1998."MRI of the lumbar spine:Prevalence of Intervertebral disc extrusion and sequestration,nerve root compression and plate abnormalities,and osteoarthritis of the facet joints in Asymptomatic Volunteers."Radiology-1998;209:661-666.

      Research led by Dr Weishaupt of Zurich's Orthopaedic University Clinic's Department of Diagnostic Radiology  studied 60 asymptomatic(no history of back pain)  hospital employees volunteers-20 in  age epoch 20s, 20 in 30s,20 in age 35 years.  24% disc bulge,40% confirmed disc protrusion,18% disc extrusion,23% nerve root contact without displacement,5% nerve root displacement and 2 % severe nerve root compression.

      4.Boos N, et al."1195 Volvo Award in clinical science:The diagnostic accuracy of MRI, work perception,and psychosocial factors in identifying symptomatic disc herniations." Spine-1995;20:2613-2625.

      76 % disc herniations (63% disc protrusion,13% disc extrusion),17% minor nerve root compromise(contact or mild deviation),4% major compromise(significant root compression) .85% of this asymptomatic group had confirmed disc degeneration at at least one level i.e. Grade 3,4 or 5 (Pearce et al). 76% of this group  had disc protrusion or extrusion(13%) yet none had any lumbar or leg pain.At least 75% of asymptomatic individuals had significant disc herniations.

      5.Stadnik TW, Lee RR. Annular tears and disc herniations:prevalence and contrast enhancement on MR images in the absence of lower back pain or sciatica. Radiology;1998:206:49-55.

      Stadnik and Lee found in totally asymptomatic  individuals:Annular tears 56% (contrast enhancement in 96%), High Intensity Zones(HIZs) 47%, Disc protrusions 33% (contrast enhancement in 85%),disc bulges 81%, Mild-moderate disc degeneration 72%, Severe disc degeneration 55%.All of the cohort were totally asymptomatic of lower back pain or sciatica.These are common findings of limited clinical direct significance.

      6. AMA Guides by American Board Independent Medical Examiners( Lumbar).

      (i) Spondylolysis (pars interarticularis defect) ,7% of adults

      (ii) Spondylolisthesis (translation or 'slip' due to spondylolysis), 3% of adults

      (iii) Disc protrusions without radiculopathy up to 30% in individuals up to the age of 40(AMA5,p.383).Their presence does not of itself mean that the individual has an impairment due to injury.

      CONCLUSIONS: The high incidence of lumbar disc abnormalities including protrusions,herniations, bulges and degeneration in asymptomatic individuals on MR examination requires careful and evidence-based assessment when considering the effects of an incident or injury. This particularly  is relevant when proposing/ performing high risk surgical interventions on what may well be a common and incidental finding based on the prevalence of the findings in the scientific literature.In proposing surgery a high degree of assessment is required to confirm both sciatica (radicular pain travelling below the knee) or femoralgia (anterior thigh radicular pain) and concordant neurological deficits in the radicular neurological distribution of a significantly compressed and displaced nerve root, on MR/CT myelogram examination involving :(i) dermatomal sensation,(ii) myotomal motor strength, (iii)reflex diminution and (iv)wasting of the lower extremity AND positive lumbar nerve tension signs.The onset of the painful radiculopathy is expected to be present in close proximity to the incident or event and of course, a patient MUST be examined in detail before surgery , unless there exists an emergency situation, or other satisfactory explanation.In the absence of;(i) true sciatica  or femoralgia ,(ii)neurological evidence of radiculopathy ,and  (iii) MR/ CT myelographic evidence of appropriate and significant nerve root compression surgery is contra-indicated unless for cauda equina syndrome, neoplasia, sepsis, progressing/advanced spondylolisthesis or  unstable fracture/subluxation.

      In relation to the reporting or descriptions of lumbar disc abnormalities : the terms ' herniation', 'prolapse', 'bulge' and 'herniation' are often loosely used, and furthermore the terms 'protrusion' and 'herniation' do NOT imply a traumatic causation,as true focal nuclear herniations,/prolapses and protrusions are most commonly due to lumbar spondylosis or degeneration.Similarly, the terms 'annular tears' and 'fissures' are interchangeably utilised.An annular fissure or tear is more commonly due to the process of lumbar degeneration or spondylosis ,not trauma.They are ubiquitous and usually asymptomatic.A broad based protrusion of the annulus is more properly termed an 'annular bulge'. A focal protrusion of the annulus with the length of the height exceeding that of the base is more properly termed a 'prolapse' or 'herniation'.The 'bulge' represents broad based annular laxity due to annular Sharpey fibre loss of lamellation and tearing or fissuring, due to degeneration with associated nuclear desiccation (dark disc on T2 MR sequences) and facet OA changes.The 'prolapse' or 'herniation' represents a full thickness annular defect with nucleus pulposus herniation into the annulus ,sub/intra- ligamentous or epidural spaces.It is also more commonly due to degeneration but can also have a traumatic aetiology.

      Terminology for lumbar disc protrusion is important.Unfortunately terms are applied interchangeably and are often misinterpreted in terms of aetiology.There are a number of conventions which are morphological and reproducible between examiners.

      Resnick and Niwayama Classification( Resnick D ,Niwayama G .Degenerative disease of the spine in Diagnosis of bone and joint disorders 1995:1424) Classification :(i) Annular bulge:Annular fibres are intact and the disc protrudes beyond the intervertebral interspace around the endplate; (ii) Protrusion:Nuclear material protrudes through torn annular fibres with the outermost fibres remaining intact; (iii)Extrusion:The nuclear material penetrates all of the fibres of the annulus and lies under the PLL;(iv) Sequestration: The nuclear material penetrates the PLL and lies within the epidural space not in continuity with the remaining nucleus. 

      Brant-Zawadzki Classification (Brant-Zawadzki MN , Jensen MC et al.Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities'Spine 1995;20:1257-1264):(i) Normal:No disc extension beyond the interspace;(ii) Bulge: Circumferential extension beyond the interspace: (iii) Herniation: Any focal extension beyond the interspace. Subclassification :(a) Protrusion: Focal or asymmetric extension beyond interspace into the canal and base is broader than any other diameter of the protrusion: and (b) Extrusion: Focal, obvious extension beyond the interspace and the base is narrower than the height of the extruding material itself, or there is no connection to the parent disc at all.Extrusions are further sub classified by Herzog as sub- ligamentous and trans-ligamentous(often only discernible by careful surgical examination only).

      There are also classification schemes for degeneration process using parameters including nuclear signal intensity,nuclear lamination morphology and vertical disc heights, such as Pfirrmann(Spine 2001) and  Battie(Spine 1995).

      In assessing lumbar disc pathology causation (medically to the level of 'probability' i.e. >50%), the Independent Medical Examiner should follow he scientific Sir Austin Bradford Hill Criteria(1965) and refer to science, epidemiological studies , view all temporally related scientific/ medical records and practise with  available accepted scientific  knowledge and publications,evidence based and logically valid assessment processes with biologically plausible and independent decision making.

      About the author: Dr Michael Coroneos is a senior Brisbane Neurosurgeon.He is an examination certified independent medical examiner( CIME) by the American Board of Independent Examiners(ABIME).He is a Member of the Academy of Surgical Educators(MASE) of the RACS.He is also a Surgical Mortality Assessor(QASM) and a senior Clinical Examiner for the RACS.He is an honorary adjunct Assistant Professor at Bond University,Qld. CIME MASE FACS FRACS FRCSI FRCS(EDIN)SN FAIM MB BS (HONS) MAPS MNSA MNSQ.

      Patients are advised to seek and follow the advice of their treating medical practitioner.All opinions stated in this paper are those of the author unless otherwise stated.