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MUSCULOSKELETAL RADIOLOGY  
Year : 2011  |  Volume : 21  |  Issue : 4  |  Page : 264-266
Case report: Dot-in-circle sign - An MRI and USG sign for "Madura foot"


1 Department of Radiodiagnosis, Devi Scans, Medical College, Thiruvananthapuram, India
2 Department of Rheumatology, Kerala Institute of Medical Sciences, Thiruvananthapuram, Kerala, India

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Date of Web Publication8-Dec-2011
 

   Abstract 

Mycetoma is a chronic granulomatous disease that is more common in tropical than in temperate regions. Early diagnosis is important due to the therapeutic implications. Although biopsy and microbiological culture provide definitive diagnosis, they are time-consuming procedures and may not be able to provide a definite diagnosis in cases of fastidious organisms. The "dot-in-circle" sign has recently been proposed as a highly specific magnetic resonance imaging (MRI) and ultrasonography (USG) sign of mycetoma, which may allow a noninvasive as well as early diagnosis. We present a case of histologically proven mycetoma that demonstrated this sign.

Keywords: Dot-in-circle; magnetic resonance imaging; mycetoma; ultrasonography

How to cite this article:
Sen A, Pillay RS. Case report: Dot-in-circle sign - An MRI and USG sign for "Madura foot". Indian J Radiol Imaging 2011;21:264-6

How to cite this URL:
Sen A, Pillay RS. Case report: Dot-in-circle sign - An MRI and USG sign for "Madura foot". Indian J Radiol Imaging [serial online] 2011 [cited 2014 Sep 2];21:264-6. Available from: http://www.ijri.org/text.asp?2011/21/4/264/90684

   Introduction Top


Mycetoma is a chronic granulomatous disease affecting mainly the feet, which are more prone to trauma, and hence more likely[1] to get infected, as compared to other organs in the body such as the lower legs, hands, head, neck, chest, shoulders and arms. It is more common in males between the ages of 20 and 50 years.[2] Although mainly a disease of the tropics, patients residing in temperate regions may also be affected. A noninvasive and early diagnosis may be possible with USG[3],[4] and MRI.[3],[5],[6],[7],[8]


   Case Report Top


A 50-year-old male from Tamil Nadu presented with a soft tissue swelling of his ankle and foot. Workup included punch biopsy, from which a diagnosis of eumycetoma was made.

MRI showed extensive soft tissue edema in the foot and ankle region with tibial and talar involvement [Figure 1]A and multiple small cystic areas with central hypointensity, suggestive of the "dot-in-circle sign" [Figure 1]A, C, D. CT scan confirmed bony osteolytic areas and showed periosteal reaction [Figure 1]B. USG demonstrated hypoechoiec areas with central hyperechoiec foci [Figure 2].
Figure 1: (A-D) Sagittal short-Tau inversion recovery (STIR) MRI image (A) shows osteolytic areas in the tibia (grey arrow) and talus (white arrowhead); "dot-in-circle" lesions (white arrows) are seen in the soft tissue. Sagittal CT scan (B) shows osteolytic areas (black arrowhead) and periosteal reaction (white arrow) in the tibia. Axial T2W MRI image through the sole of the foot (C) and sagittal T2W MRI image (D) show multiple T2-bright round lesions (white arrow) with a central dot (white arrowheads), seen clearly in some lesions and faintly in others

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Figure 2: USG image shows hypoechoic lesions with hyperechoic centers (white arrows)

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   Discussion Top


Mycetoma or Madura foot is a chronic granulomatous infection of the dermis and epidermis caused by the bacteria Actinomyces (Actinomycetoma) or by true fungi (eumycetoma). [9] It was first described in the Indian district of Madura in 1846, hence the eponym Madura foot. [10] Endemic in Africa, Mexico and India, it is also found in Central and South America and the Middle and the Far East. [11] Eumycetoma is more common in areas with scarce rainfall and actinomycetoma in areas of abundant rainfall. [12]

The infecting organism is presumed to be directly inoculated after penetration of the skin with a sharp object,[13] e.g., a thorn. Patients present with painless subcutaneous nodules and fistulae, from which a purulent exudate may be discharged. The process is usually indolent but with a potential for abscess formation, draining sinus tracts, osteomyelitis, and fistula formation,[14] with severe deformity and disability ensuing if treatment is not provided. Although antifungal medication is successful in almost 90% of cases, lesions not arising in the foot or due to fungus tend to have a worse prognosis and require surgery.[13]

Histologically, the lesion consists of "grains" of fungal hyphae or bacteria in microabscesses within a granulomatous fibrous-tissue reaction.[15] Gram stain, Gomori methenamine silver, periodic acid-Schiff and lactophenol blue stains are useful to differentiate actinomycetoma and eumycetoma.[16] Early laboratory diagnosis, before the appearance of the sinuses and grains, is difficult. Though biopsy (with demonstration of the characteristic features) or staining and microbiological culture of the discharge from the lesion usually gives the definitive diagnosis, both are time-consuming procedures and diagnosis may be difficult to achieve, especially with fastidious organisms.

Radiographs may be normal, demonstrate soft tissue enlargement, bone sclerosis, bone cavities, periosteal reaction, bone expansion, extrinsic cortical scalloping, fanning of the rays or osteoporosis. [17] The bones are almost always attacked from the outside, in contrast to bacterial osteomyelitis. [18] Radiographic classification of bone involvement (stages 0-6) has been suggested. [18] A few radiographic bone changes have been described that help distinguish between actinomycetoma and eumycetoma. [14]

Eumycotic lesions tend to form a few cavities in bone that are ≥1 cm in diameter, while actinomycetes often form smaller but more numerous cavities, leading to a moth-eaten appearance. [14] CT scan provides better delineation of the bone changes than radiographs. [19]

Initial reports of the MRI findings of mycetoma described lesions with low signal on T1W and T2W images, which were assumed to be due to susceptibility from the metabolic products of the 'grains'. [20] The "dot-in-circle" sign, seen as tiny hypointense foci within the hyperintense spherical lesions, was initially described by Sarris et al., [3] in 2003 on T2W, STIR, and T1W fat-saturated gadolinium-enhanced images. Correlating the MRI and histological findings, they suggested that the high-signal areas seen on MRI represented inflammatory granulomata, the low-intensity tissue seen surrounding these lesions represented the fibrous matrix, and the small central hypointense foci within the granulomata represented the fungal balls or grains. They proposed that it is likely to be a highly specific sign for mycetoma. It was also later reported in 2007, [5] 2009 [6],[7] and 2010. [8] The last (2010) case was misdiagnosed as a soft tissue hemangioma on MRI due to the presence of serpiginous enhancing masses with the "dot-in-circle" sign (the "dots" were mistaken for phleboliths). Another differential for the "dots" is rice bodies - hypointense foci seen in the synovial fluid of patients with articular or tendon tuberculosis. [21]

The USG appearances were initially described by Fahal et al., [4] who demonstrated on in vitro imaging of the mycetoma lesions that the hyper-reflective echoes corresponded to the grains; eumycetoma grains produce sharp hyperechoiec foci, while actinomycetomas produce fine hyperechoiec foci that commonly settle at the bottom of the rounded lesions. The USG "dot-in-circle" sign is similar to the MRI sign, with multiple round hypoechoiec lesions containing hyperechoiec foci. [3].[4] et al. had predicted that with the increasing availability of MRI in the metropolitan centers of countries where mycetoma is endemic, the sensitivity and specificity of this sign could be determined. This case from Tamil Nadu, the land of the Madura foot (Madura being a district in the Indian state of Tamil Nadu), reiterates the specificity of the "dot-in-circle" sign.

 
   References Top

1.Lichon V, Khachemoune A. Mycetoma: A review. Am J Clin Dermatol 2006;7:315-21.  Back to cited text no. 1
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2.Magana M. Mycetoma. Int J Dermatol 1984;23:221-36.  Back to cited text no. 2
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3.Sarris I, Berendt AR, Athanasous N, Ostlere SJ. MRI of mycetoma of the foot: Two cases demonstrating the dot-in-circle sign. Skeletal Radiol 2003;32:179-83.  Back to cited text no. 3
    
4.Fahal AH, Skeik HE, Homeida MM, Arabi Y, Mahgoub ES. Ultrasonographic imaging of mycetoma. Br J Surg 1997;84:1120-2.   Back to cited text no. 4
    
5.Kumar J, Kumar A, Sethy P, Gupta S. The dot-in-circle sign of mycetoma on MRI. Diagn Interv Radiol 2007;13:193-5.  Back to cited text no. 5
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6.Lee Parker BM, Singh D, Biz C. The dot-in-circle sign in Madura foot. J Foot Ankle Surg 2009;48:690.e1-690.e5.  Back to cited text no. 6
    
7.Cherian RS, Betty M, Manipadam MT, Cherian VM, Poonnoose PM, Oommen AT, et al. The 'dot-in-circle' sign-a characteristic MRI finding in mycetoma foot: A report of three cases. Br J Radiol 2009;82:662-5.  Back to cited text no. 7
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8.Petscavage J, Richardson ML, Jonelle M. Madura foot masquerading as a hemangioma. Radiol Case Rep 2010;5:355.  Back to cited text no. 8
    
9.Negroni R, Lopez Daneri G, Arechavala A, Bianchi MH, Robles AM. Clinical and microbiological study of mycetomas at the Muniz Hospital of Buenos Aires between 1989 and 2004. Rev Argent Microbiol 2006;38:13-8.   Back to cited text no. 9
    
10.Carter HV. On a new and striking form of fungus disease principally affecting the foot and prevailing endemically in many parts of India. Trans Med Phys Soc Bombay 1860;6:104-42.   Back to cited text no. 10
    
11.Welsh O. Mycetoma. Semin Dermatol 1993;12:290-5.  Back to cited text no. 11
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12.Bakshi R, Mathur DR. Incidence and changing pattern of mycetoma in western Rajasthan. Indian J Pathol Microbiol 2008;51:154-5.  Back to cited text no. 12
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13.McGinnis MR, Fader RC. Mycetoma: A contemporary concept. Infect Dis Clin North Am 1988;2:939-54.  Back to cited text no. 13
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14.Lewall DB, Ofole S, Bendl B. Mycetoma. Skeletal Radiol 1985;14:257-62.  Back to cited text no. 14
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15.Magana M. Mycetoma, some clinical and histopathological features. Turk J Dermatopathol 1994;3:94.  Back to cited text no. 15
    
16.Pilsczek FH, Augenbraun M. Mycetoma fungal infection: Multiple organisms as colonizers or pathogens. Rev Soc Bras Med Trop 2004;40:463-5.  Back to cited text no. 16
    
17.Abd El-Bagi ME, Fahal AH. Mycetoma revisited. Incidence of various radiographic signs. Saudi Med J 2009;30:529-33.   Back to cited text no. 17
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18.Abd El, Bagi ME. New radiographic classification of bone involvement in pedal mycetoma. AJR Am J Roentgenol 2003;180:665-8.  Back to cited text no. 18
    
19.Al-Ali AA, Kashgari TQ, Nathani PG, Moawad MK. Radiological manifestations of madura foot in the Eastern Province of Saudi Arabia. Ann Saudi Med 1997;17:298-301.  Back to cited text no. 19
    
20.Czechowski J, Nork M, Haas D, Lestringant G, Ekelund L. MR and other imaging methods in the investigation of mycetomas. Acta Radiol 2001;42:24-6.  Back to cited text no. 20
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21.Hsu CY, Lu HC, Shih TT. Tuberculous infection of the wrist: MRI features. AJR Am J Roentgenol 2004;183:623-8.  Back to cited text no. 21
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Correspondence Address:
Anitha Sen
Devi Scans, Medical College PO, Thiruvananthapuram, Kerala
India
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DOI: 10.4103/0971-3026.90684

PMID: 22223936

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    Figures

  [Figure 1], [Figure 2]

This article has been cited by
1 Mycetoma of foot: MR imaging demonstrated the "dot-in-circle" sign
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[Pubmed]



 

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