Paraspinal Edema Is the Most Sensitive Feature of Lumbar Spinal Epidural Abscess on Unenhanced MRI.

OBJECTIVE: Spinal epidural abscess (SEA) is a serious infection requiring prompt treatment and potential neurosurgical intervention. Although contrast-enhanced spine MRI is the mainstay for diagnosis of SEA, unenhanced MRI is typically performed for patients with nonspecific symptoms or insufficient clinical information. We evaluated the sensitivity and specificity of imaging features suggestive of SEA at unenhanced spine MRI. MATERIALS AND METHODS: We searched our database for contrast-enhanced lumbar spine MRI examinations from January 1, 2000, through August 1, 2014, with "epidural abscess" in the report. We included 68 patients older than 18 years with an enhancing epidural collection at MRI and surgical (60%), microbiologic (15%), or clinical (25%) confirmation of SEA. Sixty-eight age- and sex-matched control subjects without SEA were also selected. Three readers scored unenhanced MR images on the degree of psoas and paraspinal muscle edema, extent of bone marrow edema, and abnormal disk signal. RESULTS: Paraspinal edema was highly sensitive (97%) for SEA, with lower sensitivities for psoas (54%), bone marrow (65%), and disk edema (66%). Each of these markers was highly significant in univariate analysis (p < 0.001). A multivariate logistic regression model adjusting for age and sex found that paraspinal (p < 0.001) and bone marrow edema (p = 0.006) were significant independent predictors of SEA (odds ratio, 58; p < 0.001), with a trend toward significance for psoas edema and abnormal disk signal. Psoas muscle edema was the most specific (96%) finding for the presence of SEA. CONCLUSION: Paraspinal edema is highly sensitive for SEA. Familiarity with the findings for SEA at unenhanced MRI could help expedite further definitive evaluation when contrast agent is not administered.