A Novel Radiographic Sign and a New Classifying System in Mastoiditis-Related Epidural Abscess

OBJECTIVETo describe a novel radiographic sign (“halo”) and a new classification method of an evolving perisigmoid epidural abscess and present its correlation with intraoperative findings. STUDY DESIGNRetrospective and prospective cohort study in a tertiary academic children’s hospital. METHODSThe retrospective arm (15 children) was conducted between 1998 and 2007 and the prospective arm (11 children) between 2008 and 2013. The computerized tomographic appearance of the perisigmoid region was classified into four groupsClass I, normal; Class II, smooth halo; Class III, nodular halo 4 mm or less in diameter; and Class IV, gross nodular halo more than 4 mm in diameter. Intraoperative findings of the perisigmoid region were compared with the preoperative scan results. RESULTSThe correlation between preoperative imaging and intraoperative findings of the retrospective arm was highly significant (p = 0.007). The correlation between the preoperative imaging studies and intraoperative findings of the prospective arm was also highly significant (p = 0.005). The interobserver agreement for the proposed classification method was high (Cohen kappa score, 0.76; weighted kappa score, 0.84). CONCLUSIONA novel radiographic sign (“halo”) and a new classification method for an evolving perisigmoid epidural abscess in acute mastoiditis are described. A thin and smooth halo sign is not indicative of a true abscess formation. Gross perisigmoid granular changes, however, are highly suggestive of an epidural abscess that warrants surgical intervention.