CLASSIFICAÇÃO POR RESSONÂNCIA MAGNÉTICA DA DEGENERAÇÃO DO DISCO INTERVERTEBRAL CLASSIFICATION OF INTERVERTEBRAL DISC DEGENERATION BY MAGNETIC RESONANCE

As bases biológicas para o funcionamento de um disco intervertebral saudável baseiam-se na função celular, a qual inclui a expressão genética para produção da matriz extracelular. Sobre esta produção ocorre a manutenção e reparo do disco para que este mantenha a capacidade de suporte de carga exigida pela coluna. A perda das funções e reparos do disco intervertebral podem ser consideradas como doença degenerativa do disco intervertebral (DDD). A produção do colágeno varia conforme a idade. Estudos realizados por Bernick e Cailliet1 mostraram a redução gradual da formação de cartilagem na placa de crescimento desde os 16 anos de idade. Antoniou et al.2,3 em um amplo estudo, mostrou que o disco passa por três fases diferentes de produção de colágeno, sendo uma inicial com grande produção de colágeno, uma fase de maturação com manutenção da renovação de colágeno ;e uma terceira fase degenerativa, onde ocorre queda da produção de colágeno. Gruber e Hanley4 relacionaram as alterações do colágeno com a placa terminal e estudaram as imagens de morte celular (apoptose), procurando um paralelo entre a expressão gênica e a degeneração discal. Roberts et al.5 já havia demonstrado a degeneração progressiva do disco com rupturas da placa terminal gerando hérnias e hérnia de Schmorl. O mesmo autor, em 1996, demonstrou a importância das proteoglicanas na manutenção da nutrição do disco e sua perda progressiva resultando em redução das funções da placa terminal6. RESUMO


INtroDuCtIoN
Biological rationale for a healthy intervertebral disc functioning is based on cell function, which includes genetic expression for producing extracellular matrix.Over this production disc maintenance and repair occur so that it can keep the ability to hold loads required by spine.Intervertebral disc function and repair loss may be regarded as a degenerative disease of the intervertebral disc (DDD).Collagen production varies according to age.Studies conducted by Bernick and Cailliet 1 showed a gradual reduction of cartilage formation on the growth plate from 16 years old.Antoniou et al. 2,3 , in a large study, showed that the disc goes through three different phases to produce collagen: an early phase, with intense collagen production, a maturation phase with he maintenance of collagen renewal, and a third degenerative phase, when a reduced collagen production is seen.Gruber and Hanley 4 correlated collagen changes with terminal plate and studied cell death (apoptosis) images, searching for a parallel between genetic expression and progressive disc degeneration.Roberts et al. 5 had previously demonstrated the progressive disc degeneration with terminal plate ruptures causing herniations and the Schmorl's herniation.The same author, in 1996, demonstrated the importance of proteoglycans in maintaining disc nutrition and its progressive loss resulting in a reduction of terminal plate functions. 6lassifications of lumbar spine degeneration by imaging methods were first provided by Modic et al. 7 In that study, Modic followed type III and 18% type IV-a.However, the investigators disagreed with the conclusions in 4,5% of the disks.The authors found that the progressive signal lost in the T2-weighted images may be correlated to disk degeneration.Changes found in the magnetic resonance images must be standardized and classified for providing a better understanding.
up, by magnetic resonance, the evolution of patients submitted to treatment for disc conditions with chemopapayne, classifying these changes as grade I, II or III.Kim et al. 8 were the first ones to describe changes on disc herniation in magnetic resonance images, reporting a series of 28 patients with an accuracy of 80.6%.One year later, Kim et al. 9 published an article with a broader approach with 242 patients, showing that magnetic resonance has 92% of sensitivity, 91% specificity, and 92% accuracy, showing even better results when disc fragment sequestration was present.In 1995, Kramer 10 described a more complex classification for lumbar disc herniation, not only mentioning the size of the herniation but also its location compared to neural structures.Adding to the studies by Kim and Kramer [8][9][10] , Militte 11 provided a new classification, recommending the use of tomography and discography.At total, these three papers represented the initial discussion about the anatomopathology of disc diseases in magnetic resonance studies.Thompson et al. 12 were the first ones to suggest a classification for intervertebral disc degeneration disease (DDD) using a histological study.Thompson listed five assessment points ranging from age to degeneration degree.Southern et al. 13 classified intervertebral disc degenerative disease (DDD) by magnetic resonance using human cadavers and correlating resonance finings with quantitative DICONOMETRY, a method consisting of injecting fluid into the intradiscal space and measuring intradiscal pressure, with subsequent evaluation of images change.In 2001, Pfirrmann et al. 14   Southern with a morphological study of the disc with resonance, using a scale of 5 types, producing a good reliability.The priority in this study is to develop a classification system for disc degenerative disease (DDD) on lumbar spine.Based on magnetic resonance images at sagittal planes weighted in T2, analyses of progressive changes on disc degeneration have been made.We know that a degenerating disc shows hyposignal on T2, thus being called black disc.The authors followed the parameters described by Pfirrmann et al. 14 , such as disc structure, nucleus color, signal intensity, and disc height.This study seeks to reproduce the methods by Pfirrmann et al. 14 and Southern et al. 13 , but the authors made some changes in the classification by introducing an additional type, subdividing type IV into IV-a and IV-b, considering that disc height plays a key role in its classification.

objECtIvES
The objective f this study is to provide assistance to clinical practice and to standardize the treatment approach for degenerative diseases of the disc by using an intervertebral disc classification with magnetic resonance imaging.

mAtErIAlS AND mEthoDS
For this study, intervertebral discs removed from cadavers of people dead for less than 24 hours sourced by the Death Examination Center of University of São Paulo Hospital das Clínicas.The procedure was made with authorization by the UNIFESP committee of medical ethics and with the approval of FMUSP's discipline of anatomy (letter attached).The pieces were removed as blocks of lumbar spine, from L1 to S1.Those anatomical pieces were then submitted to magnetic resonance test at Unifesp-EPM Imaging Department, for assessing lumbar intervertebral discs.Magnetic resonance images were taken on T1 (spin echo [tr] 700) and T2 (spin-echo[tr] 5000) at axial and sagittal planes.We collected ten spines with five discs assessed per piece.Intervertebral discs were then classified on slides weighted in T2.We assessed disc structure for image homogeneity.Nucleus was also checked for clarity and/ or obscurity.Signal intensity found in the nucleus was regarded as hyper-or hypointense.Disc height was regarded as very important, so we subdivided, in this analysis group, Pfirrmann's type IV into IV-a and IV-b, because, in this parameter, an intermediate-intensity disc may already have a reduced height compared to others.We regarded type I as a homogenous-structure disc, with light nucleus, in which signal intensity is hyperintense and with normal height.(Figure 1) Type II shows structural changes with heterogeneous aspect characterized by a horizontal line; nucleus is light an with hyperintense signal; height is normal.(Figure 2) Type III has a grey heterogeneous structure, dark nucleus, with intermediate signal, but height remains normal.(Figure 3) Type IVa has a heterogeneous grey structure, with dark intermediate-signal nucleus, height is reduced, leading to a differentiation from type III.(Figure 4) Type IVb has a black heterogeneous aspect, with lost hypointense signal nucleus and reduced height.(Figure 5) Type V is distinguished from the others for being collapsed, keeping a black heterogeneous structure with lost hypointense-signal nucleus.(Figure 6) Classification grade was standardized as shown on Table 1.A classification model was prepared for assisting on images analysis.(Figure 7) All images were assessed by the radiology team and by the orthopaedics team in different days, and then conjunctively, in order to provide an agreed final classification.

rESultS
After assessing 44 discs, we set up a table with he classification of the changes found per disc.(Table 2) The authors considered 4.5% type I (2 discs), 40.9% type II (18 discs), 32% type III (14 discs), 18.1% type IVa (8 discs).There were 2 discs (4.5%) for which we reached to no consensus.In this study, the authors did not find discs with expected degeneration in IVb and V due to the random nature of the cadavers selected.

Figure 1 -
Figure 1 -Type-I disc, with light and high, well-defined nucleus.

Figure 3 -
Figure 3 -Type-III disc, grey nucleus and height maintained.

Figure 7 -
Figure 7 -Disc classification, visual classification model for intervertebral disc as I to V.

Figure 6 -
Figure 6 -Type-V disc, with black nucleus and collapsed height.

Table 2 -
Distribution of vertebral discs and their classifications.Analysis of findings of intervertebral disc classification in the different anatomical pieces studied.