MR appearances of the temporal evolution and resolution of infectious spondylitis

OBJECTIVE. We undertook this study to document the MR appearances of evolving or resolving infectious spondylitis. MATERIALS AND METHODS. A retrospective review was carried out of all patients with infectious spondylitis who had undergone MR imaging from 1991-1993 at Boston University Hospital and Boston City Hospital Imaging Foundation. The study population consisted of 25 patients (seven females and 18 males). There was a bimodal age distribution with peaks at 34 and 59 years old (age range, 25-81 years old). The causative organism was isolated in 20. Sixteen had Staphylococcus aureus, two had mycobacterium tuberculosis, and two had gram-negative bacilli. Follow-up MR imaging was performed in 20. Nine had two studies, three had three, five had four, two had five, and one had six. The median length of follow-up was 8 weeks (range, 2-104 weeks). Follow-up MR appearances were correlated with clinical outcome. RESULTS. Early imaging revealed atypical appearances. Fourteen of 20 (70%) improved; the first sign of response to treatment was a reduction in the inflammatory soft tissue (8/14, 57%). Changes in the bones or discs concurrently progressed in six of eight patients (75%) including involvement of a new disc level in four (50%). A definitive sign of healing was a peripheral rim of high T1 signal in bone (5/14, 36%). Gadolinium enhancement persisted long after resolution of changes in the soft tissues, for up to a median of 17.5 weeks (range, 8-80 weeks). A subgroup of six IV drug users showed unique radiologic features. CONCLUSION. The early appearances of infectious spondylitis may be atypical. Resolution of soft-tissue change and fat deposition in the bone marrow are reliable signs of healing. Bone or disc changes can progress despite clinical improvement. Gadolinium enhancement can increase and persist after symptom resolution.