The ‘‘dot-in-circle’’ sign — a characteristic MRI finding in mycetoma foot: a report of three cases 1 R S CHERIAN, DMRD, DNB, 1 M BETTY, MBBS, 2 M T MANIPADAM, MD, 3 V M CHERIAN, MS, 3 P M POONNOOSE, MS, 3 A T OOMMEN, MS and 1 R A CHERIAN, DMRD, DNB, FRCR Departments of 1 Radiology, 2 General Pathology and 3 Orthopaedics, Christian Medical College, Vellore-632004, Tamil- Nadu, India ABSTRACT. 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. Received 9 April 2008 Revised 29 May 2008 Accepted 7 July 2008 DOI: 10.1259/bjr/62386689 ’ 2009 The British Institute of Radiology Mycetoma is a localised chronic suppurative infection characterised by exuberant granulation tissue formation involving the subcutaneous tissues, which can extend to involve the deeper tissues [1]. It is caused by different species of fungi or by filamentous bacteria known as actinomycetes. Mycetomas caused by fungi are known as eumycetoma, whereas those caused by aerobic actinomy- cetes are called actinomycetomas. Clinically, the disease follows an indolent but progressive course after initially presenting as a firm, painless nodule. Eventually, the lesions communicate via sinuses onto the skin surface or involve the adjacent bone to cause a form of osteomyelitis [2]. Early diagnosis before the sinuses and fungal grain discharge occurs is sometimes difficult. If untreated, however, mycetomas can lead to significant destruction and deformity. Biopsy or microbiological culture can provide the diagnosis, but this may not always be possible, especially if the organism is fastidious [3]. The purpose of this study is to describe the character- istic MRI appearances of mycetoma foot. With the increasing availability of MRI, especially in areas of the dry tropics where organisms causing mycetomas are endemic, this would aid in the early diagnosis of this condition and facilitate appropriate management. Methods and materials Three patients were referred for evaluation of soft tissue masses involving the foot during the period 2006 to 2007. Plain radiographs were available for all patients. MRI was performed for the first two patients using a 3T MRI scanner (Intera Achieva, Philips Medical Systems, The Netherlands) and for the third patient using a 1.5T MRI scanner (Siemens Avanto, Erlangen, Germany). The sequences were obtained using a phased-array surface coil and included fat suppressed T 2 weighted, proton density (PD) and T 1 weighted images. Intravenous gadolinium contrast was not administered. The studies were read by radiologists with MRI experience of 3–7 years. All three lesions underwent histopathological examination and were proven to be eumycetoma. Results Patient 1 A 30-year-old male soldier presented with a recurrent soft tissue mass in the left foot, which had been operated on elsewhere four times. Reports of previous surgery and histopathology were not available. Examination revealed a swelling in the dorsum and medial aspect of the foot. The tibialis anterior tendon was non-function- ing. Plain radiograph revealed a soft tissue mass in the dorsum of the foot with no calcification. MRI showed a soft tissue mass in the subcutaneous plane of the dorsum of the foot, anterior to the tibialis anterior tendon (Figure 1a–d). The mass showed con- glomerate areas of multiple, discrete, small 2–5 mm round hyperintense lesions, which were separated by a low-signal-intensity rim in the subcutaneous plane of the dorsum of the foot. Within many of these hyperintense lesions, there was a central low-signal-intensity dot. A separate focus of involvement was seen in the medial aspect of the foot. At this time, fungal aetiology was not suspected and the patient underwent wide excision of the lesion, with skin grafting. The tibialis anterior tendon was sacrificed. The tissue was sent for histopathology, which showed eumycetoma. Address correspondence to: Rekha S. Cherian, Radiology Department, Christian Medical College, Vellore-632004, Tamil- Nadu, India. E-mail: [email protected] The British Journal of Radiology, 82 (2009), 662–665 662 The British Journal of Radiology, August 2009
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