The importance of diagnostic imaging of mycetoma in the foot.

Mycetoma is a chronic, localized infection caused by fungi and bacteria. It usually affects the skin, subcutaneous tissue, and bone of exposed areas with deformity of the affected limb, ulcers, and fistula; however, pain is not severe, therefore the patient comes late to hospital for care.To establish the diagnosis of mycetoma in the foot by imaging and identify the principal radiological signs.Six patients with foot mycetoma were evaluated with plain x-ray, ultrasound, and magnetic resonance (MR) after confirming the diagnosis by histopathology and culture.All patients presented the MR "dot-in-circle" sign; four presented "punched out" bone lesions on plain x-ray. The six patients had fistulas, ulceration, a seropurulent exudate, edema, and a foot deformity. Four patients had N. brasiliensis infection with positive anti-Nocardia IgG antibodies, and only half presented bone lesions.Characteristic findings were foot deformity, edema, bone lesions, ulcers, fistulas and the presence of the "dot-in-circle" sign. We recommend a comprehensive study of patients with plain x-ray and MR.