Magnetic resonance imaging in adults presenting with severe acute infectious cellulitis

Early categorization of some acute soft-tissue infections, such as severe infectious cellulitis (IC) without or with secondary abscess formation, necrotizing fasciitis (NF) or pyomyositis, is frequently difficult. The first one requires only medical treatment, the remaining ones require either surgery or closed drainage. To determine the presence and the extent of these infections early, we have prospectively studied the value of magnetic resonance imaging in patients admitted for IC with local or general criteria of severity. Images were analyzed on a blind basis. Definite diagnosis was obtained by reviewing clinical records and, in most patients, the results of an invasive procedure.

Twenty-six patients (56 +/- 23 years old) were included in this study. Among them, 13 received gadolinium-diethylene-triaminepenta-acetic acid intravenously. The final diagnosis was pyomyositis (five patients), NF (three patients), or IC with (seven patients) or without (11 patients) subcutaneous abscess. Images specific for these diseases were best outlined with T2-weighted sequences. In patients with pyomyositis or subcutaneous abscess(es), we observed spindle-shaped or round, well-defined areas of high signal intensity within the muscles or subcutis, respectively. Patients with NF exhibited numerous homogeneous, well-defined dome-shaped areas of hypersignal in the deep hypodermis. In patients with uncomplicated IC, these dome-shaped areas of hypersignal appeared ill-defined, heterogeneous, smaller, thinner, and less numerous than those in patients with NF.

In patients presenting severe IC, magnetic resonance imaging provided an early clue in the diagnosis of pyomyositis, NF, and abscess-complicated IC. By precisely defining the extent of these infections, it helped to plan surgical treatment.