The "dot-in-circle" sign -- a characteristic MRI finding in mycetoma foot: a report of three cases.

Three patients referred for MRI of the foot were found to have imaging features characteristic of mycetoma. Two patients presented with recurrent soft tissue masses, which were operated on several times and not suspected to be of infective aetiology. The third patient had typical clinical features with a history of blackish granule discharge. In all three patients, MRI showed conglomerate areas of small round discrete T(2) weighted hyperintense lesions, representing granulation tissue surrounded by a low-signal-intensity rim representing intervening fibrous septa. Within many of these hyperintense lesions, there was a central low-signal-intensity dot, which gives rise to the "dot-in-circle" sign that has been very rarely described in the literature. This sign is an easily recognisable and unique appearance that is highly suggestive of mycetoma.