Soft tissue pseudotumor following intramuscular injection of "DPT": a pitfall in magnetic resonance imaging.

We report the time-dependent magnetic resonance imaging (MRI) changes that resulted from an intramuscular injection of a commonly-used pediatric sedation regiment ("DPT"). These changes at the site of injection consist of a focal abnormality characterized by a slight increase in signal intensity on T1 weighted images and markedly increased signal intensity on T2 weighted images. Alterations in signal are detectable almost immediately after the injection and progress over the first 31 hours. This abnormality, which could be mistaken for real disease, persists up to 36 days following injection.