MRI of mycetoma of the foot: two cases demonstrating the dot-in-circle sign.
Sarris I., Berendt AR., Athanasous N., Ostlere SJ., OSIRIS collaborative study group None.
Radiological and histological findings of two patients with fungal mycetoma of the foot are presented. MRI revealed multiple 2-5 mm lesions of high signal intensity interspersed within a low-intensity matrix. Within many of the lesions a minute low-intensity focus was identified. Ultrasound showed distinct hyperechoic foci within a hypoechoic mass. We speculate that the low-signal matrix represents fibrous tissue, the high-intensity lesions correspond to granulomata and the central low-signal focus to the characteristic organised fungal elements (grains) present in this condition. This "dot-in-circle sign" on MRI reflects the unique pathological features of mycetoma and is likely to be a highly specific sign for this lesion.