Abstract
Modic type 1 degenerative signal changes can mimic/suggest infection, leading to additional costly and sometimes invasive investigations. This retrospective study analyzes the utility and accuracy of a novel, diffusion-weighted "claw sign" for distinguishing symptomatic type 1 degeneration from vertebral diskitis/osteomyelitis. Seventy-three patients with imaging features resembling type 1 degeneration were classified clinically into 3 groups: true degenerative type 1 changes (n = 33), confirmed diskitis/osteomyelitis (n = 20), and radiologically suspected infection later disproved clinically (n = 20). A claw sign was defined on DWI as well-marginated, linear, regions of high signal situated within the adjacent vertebral bodies at the interface of normal with abnormal marrow. Two blinded neuroradiologists independently rated the presence of the claw sign, along with T2 disk signal and disk and endplate enhancement to determine the utility of each for identifying degeneration versus infection. When the 2 neuroradiologists identified a definite claw, 38 of 39 patients (97%) and 29 of 29 patients (100%) proved to be infection-free. When the readers identified a probable claw, 14 of 14 patients (100%) and 16 of 19 patients (84%) proved to be infection-free. Conversely, when the readers identified the absence of claw sign (diffuse DWI pattern), there was proved infection in 17 of 17 cases (100%) and 13 of 14 cases (93%). In patients with type 1 signal changes of the vertebral disk space, a claw sign is highly suggestive of degeneration and its absence strongly suggests diskitis/osteomyelitis.
Highlights
BACKGROUND AND PURPOSEModic type 1 degenerative signal changes can mimic/suggest infection, leading to additional costly and sometimes invasive investigations
In patients with type 1 signal changes of the vertebral disk space, a claw sign is highly suggestive of degeneration and its absence strongly suggests diskitis/osteomyelitis
The apparent discordance of their results versus ours most likely stems from the following factors: 1) We studied only Modic type 1 endplate degeneration, whereas most of the endplate changes included in study of Eguchi et al were types 2 and 3: The degenerative disk illustrated in that study was stated to be Modic type 3
Summary
With prior approval by the institutional review board, the imaging studies and clinical data of patients referred for spinal MR imaging were retrospectively reviewed to select 73 patients with MR imaging features resembling Modic type 1 degeneration at a specific disk level. In the specific subgroup of 20 patients with radiologically suspected infection later disproved clinically, the diffusion claw sign was scored definite or probable in 19 of 20 (95%) and 16 of 20 (80%) of cases, respectively. Of 33 levels with simple type 1 degenerative endplate changes; 0 In this study, infected and degenerative disks could manifest high, of 20 and 1 of 20 patients with proved diskitis/osteomyelitis; and normal, or low T2 signal intensity. In the specific subgroup of 20 patients with radiologically suspected infection who proved infection-free, the diffusion claw sign was scored definite or probable in 19 of 20 (95%) and 16 of 20 (80%) cases, strongly indicating degeneration. In 11 patients with 20 levels of disk degeneration (7 Modic 1, 7 Modic 2, and 6 Modic 3), the authors reported no high-diffusion signal “at the site of endplate abnormalities in any patients with degenerative changes.”. 3) We focused on the changes at the interface between the normal marrow and vascularized bone marrow close to the affected disk, whereas Eguchi et al appear to have focused on the disks and the endplates themselves
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