Subperiosteal abscess of the orbit: computed tomography and the clinical course.

In an earlier study, a trial of i.v. antibiotics, with surgical drainage reserved for failure to respond, was recommended for children aged < 9 years with medial subperiosteal abscesses (SPAs) of modest size and without compromised vision. Careful monitoring is mandatory in these cases, and comparison of serial computed tomography (CT) scans frequently guides therapy. The present study examines how the CT findings actually relate to the clinical course of SPA. Initial and subsequent CT scans in 37 cases were analyzed with respect to the subperiosteal material encountered at surgery and the response to treatment. The subperiosteal material could not be predicted from the size or relative radiodensity of the collections in CT scans. Initial scans were not predictive of the clinical course. Serial scans showed enlargement of abscesses during the first few days of i.v. antibiotic therapy, regardless of the ultimate response to treatment. It is concluded that expansion of an SPA in serial CT scans during the first few days of treatment should not be equated to failure of the infection to respond to antibiotics alone. In interpreting serial scans, the time-dependent pharmacokinetics of antibiotic therapy should be considered.