MRI-Based Classification of the Morphology and Pathology of the Annulus Fibrosus of the Intervertebral Disc

Abstract

Introduction The high rate of recurrent disc herniation after discectomy is a prevalent problem. An effective biological annular repair could improve the surgical outcome in patients with contained disc herniation but otherwise minor degenerative changes. To estimate the integrity of the annulus fibrosus (AF) and judge different repair options a better understanding of disc morphology and pathology is crucial.1 Axial- and sagittal T2*-mapping are effective to detect early stages of degenerative disc disease and are especially suited to evaluate the interface between the proton-rich nucleus pulposus and the fibers of the annulus fibrosus.2,3 So far there is no classification of AF morphology or pathology as current classifications only describe localization and extend of the hernia itself. Materials and Methods Prospective consecutive case study of 100 patients requiring MRI diagnostic for suspected lumbar disc herniation. Beside the clinical standard MRI protocol with sagittal T1- and T2-weighted images, axial and sagittal T2*-mapping sequences of the affected and adjacent discs were performed using 3T MRI. Three observers used established classification schemes to assess the grade of degeneration (Pfirrmann, Benneker, Watanabe) and herniation (Carragee, Rajaserakan) and also developed a new classification protocol specific for the annulus fibrosus. Results In the preliminary data four types of annulus morphology/pathology could be found: type 1: healthy, uniform thickness of AF, clear demarcation between nucleus pulposus (NP) and AF. Type 2: concentric thinning with bulge, concentric tears, demarcation between NP and AF unclear. Type 3: nonconcentric thinning, ±radial fissures, ±protrusion, and type 4: herniations with further subgroups. Conclusion Based on preliminary axial and sagittal T2* images a new classification system for AF morphology and pathology could be established. Inter- and intraobserver liability is high. Disclosure of Interest None declared References Guterl CC, See EY, Blanquer SB, et al. Challenges and strategies in the repair of ruptured annulus fibrosus. Eur Cell Mater 2013;25:1–21 Stelzeneder D, Welsch GH, Kovács BK, et al. Quantitative T2 evaluation at 3.0T compared to morphological grading of the lumbar intervertebral disc: a standardized evaluation approach in patients with low back pain. Eur J Radiol 2012;81(2):324–330 Hoppe S, Quirbach S, Mamisch TC, Krause FG, Werlen S, Benneker LM. Axial T2 mapping in intervertebral discs: a new technique for assessment of intervertebral disc degeneration. Eur Radiol 2012;22(9):2013–2019