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The multidisciplinary task force on lumbar disk nomenclature to which Dr. Khalatbari refers tried to devise a practical and simple classification of disk herniations, with the fewest categories, so that substantial interobserver agreement could be achieved (1). This is the main reason why the proposed system does not require observers to grade compromise of nerve roots by displaced disk material, an unreliable exercise in frequent situations (eg, suboptimal technical quality images, spinal stenosis, postoperative changes). In this system, the impact of a disk herniation on the thecal sac and individual nerve roots is suggested by assessing volume of displaced disk material with respect to available space. Thus, herniations are graded as mild, moderate, or severe, depending on extension of displaced disk material in the proximal, middle, or distal third of the available spinal lumen, in a specific anatomical zone, and at a specific anatomical level. In the example provided by Dr. Khalatbari (Fig 4), the right subarticular zone is completely obliterated by disk material at the suprapedicular level, and the term mild is inappropriate to classify such a herniation according to the system proposed by the multidisciplinary task force: this lesion qualifies as a severe herniation. This is an interesting case because it illustrates an important concept; that is, in the subarticular zone, displacement of a relatively small amount of disk material can cause severe nerve root compression. However, I can well understand the reluctance to use the term severe to describe such a localized herniation and, in retrospect, a numerical grading system (grades 1, 2, 3) would have been a better choice to describe the volume of herniated disk material. Radiologists who report on lumbar spine imaging studies according to the classification and definitions proposed by the task force are of course welcome to provide referring physicians all additional anatomical details that they feel may be clinically relevant, such as those discussed by Dr. Khalatbari. A grading system for nerve root compromise (0, normal; 1, contact; 2, deviation; 3, compression) has been recently proposed (2) and might be considered as a complement.

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