Contribution of imaging to the evaluation of pyomyositis.

Abstract

PURPOSE: To analyse the fundamental features of each imaging modality with the aim of defining their contribution to the diagnosis of pyomyositis. MATERIALS AND METHODS: We retrospectively reviewed 10 observations collected between 1997 and 2004, 5 of paravertebral muscles and 5 of the muscles of the limbs. Imaging was carried out with US (8/10 observations) and/or CT (9/10 observations), and/or MRI (6/10 observations). The pathogen was isolated in 6/10 observations. RESULTS: The imaging criteria for the detection and characterization of pyomyositis are based on three pathological phases: an invasive phase characterized by inflammatory oedema, a suppurative phase characterised by abscess development, and a late phase featuring the distant spread of the infection. Based on these interpretation criteria, pyomyositis was correctly diagnosed with US in 5/8 observations, with CT in 9/9 observations and with MR in 5/6 observations. Four false-negative cases were found. CONCLUSIONS: Since the clinical symptoms of pyomyositis are often insidious and delayed, an integrated imaging approach may be very useful for diagnosing this condition.