Ultrasound detection of a subperiosteal abscess secondary to coalescent otomastoiditis.

We report the unusual ultrasound appearance of coalescent otomastoiditis with subperiosteal abscess in a 3-month-old boy with a 1-week history of an enlarging lump behind the left ear. Ultrasound examination of the lump revealed subcutaneous oedema with an abscess extending from a defect in the cranial vault as a result of extension of the inflammatory process. We believe that this sonographic appearance has not been previously described in the published literature.