Contribution of imaging to the evaluation of pyomyositis

To analyse the fundamental features of each imaging modality with the aim of defining their contribution to the diagnosis of pyomyositis.

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.

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.

Since the clinical symptoms of pyomyositis are often insidious and delayed, an integrated imaging approach may be very useful for diagnosing this condition.