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Table of Contents 
Year : 2022  |  Volume : 67  |  Issue : 4  |  Page : 459-463
Magnetic resonance imaging in the diagnosis of mycetoma with equivocal clinical and laboratory features

1 From the Department of Radio-Diagnosis, Jawaharlal Institute of Postgraduate Medical Education and Research JIPMER, Pondicherry, India
2 Department of Dermatology and STD, Jawaharlal Institute of Postgraduate Medical Education and Research JIPMER, Pondicherry, India

Date of Web Publication2-Nov-2022

Correspondence Address:
Krishnan Nagarajan
From the Department of Radio-Diagnosis, Jawaharlal Institute of Postgraduate Medical Education and Research JIPMER, Pondicherry
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijd.ijd_124_21

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How to cite this article:
Tarafdar S, Kanimozhi P, Sabarish S, Nagarajan K, Thappa DM, Laxmisha C. Magnetic resonance imaging in the diagnosis of mycetoma with equivocal clinical and laboratory features. Indian J Dermatol 2022;67:459-63

How to cite this URL:
Tarafdar S, Kanimozhi P, Sabarish S, Nagarajan K, Thappa DM, Laxmisha C. Magnetic resonance imaging in the diagnosis of mycetoma with equivocal clinical and laboratory features. Indian J Dermatol [serial online] 2022 [cited 2022 Dec 4];67:459-63. Available from:


Mycetoma are localised chronic granulomatous infection of fungal origin, which can affect skin, subcutaneous tissue and even bones if untreated.[1] It commonly affects people between age group 20 and 40 years and involves feet, legs and hand which are in direct contact with the soil.[2],[3] Typically there is a history of minor trauma with sharp object like thorn.[1],[4] The deep soft tissue structures and bones are infiltrated if neglected. The typical clinical triad consists of 'subcutaneous soft tissue mass with draining sinus and discharging grains'.[5] Mycetoma can be misdiagnosed as chronic pyogenic or tubercular infection, neuropathic foot or vascular malformation or neoplasm.[6] Biopsy and microbiological cultures provide a definitive diagnosis which are time consuming and susceptible to contamination.[7] The treatment is usually for a prolonged duration and some cases may require radical surgery like amputation in advanced cases.[1] There is a risk of recurrence of mycetoma even after complete treatment.[8] Early diagnosis is therefore necessary to prevent further mortality and morbidity. The 'dot-in-circle' sign in magnetic resonance imaging (MRI) is described as pathognomonic to this disease.[5],[9] The sign represents bright signal lesion on T2W/STIR sequence representing inflammatory granulation tissue with central low-signal intensity foci which may be due to metabolic products in fungal grain causing susceptibility effect.[10]

Seven patients, who presented with clinical suspicion of mycetoma and had subsequent histopathological examination or fungal culture, were retrospectively reviewed for their radiographic, computed tomography (CT, in one) and MRI findings. MRI was performed in 1.5 T (Avanto Siemens) MRI machine and the protocol was that of standard musculoskeletal part including post-contrast T1-weighted sequence. Our patients consisted of six male (five with foot and one with hand involvement) and one female patient with hand involvement, in age group 18–50 years. Five males were agriculturalists and one was a factory worker. The female patient was not working. One of the male was diabetic. They presented with the swelling of the foot or hand of many months duration (6 months to 15 years) and having pain since the past few months. Discharging sinuses were present in four male patients with foot involvement and one female patient had hand lesion. None of them gave a history of thorn prick or any penetrating trauma. The imaging findings, final biopsy or positive culture reports of all cases are summarized in [Table 1]. Mycetoma was confirmed by biopsy in six cases and one patient's biopsy showed nonspecific chronic granulomatous infection, which was confirmed by positive fungal culture, presence of discharging grains and response to treatment.
Table 1: Imaging (x-ray and MRI) findings and diagnosis in cases of Mycetoma

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The clinical diagnosis for mycetoma may sometimes be difficult unless a clinical history of penetrating trauma or thorn prick or signs and symptoms of painless swelling and/or discharging sinuses with grains are present. There was no typical history of thorn prick in any of our patients. Mycetoma is reported to present usually with painless subcutaneous mass, but our patients had pain at the time of initial presentation though swelling and sinuses were present months before the onset of pain. The colour of the grains was black in three cases of eumyecetoma and white or yellow in another three cases of actinomycetoma and one patient with foot involvement did not have grains in discharge.[11] Five of our patients were farmers by occupation as reported in the previous series with male predominance.[4],[12] Previous studies shows no significant correlation between duration of symptoms and bony involvement or MRI findings.[7],[13]

MRI is a preferred noninvasive modality with superior soft tissue characterization in diagnosis of myecetoma and provides valuable information regarding both soft tissue and bony involvement.[12],[13] However, except the 'dot-in-circle' sign, the other imaging features of myecetoma on MRI may mimic tubercular or pyogenic infective etiology, or even vascular malformation and malignancy. Hence, the 'dot-in-circle' sign is a very reliable and pathognomonic indicator of myecetoma and can be used for diagnosis even when clinical, imaging features, fungal cultures and biopsy are inconclusive.[1],[4],[8],[14],[15]

Staging of mycetoma has been postulated by Abd El Bagi et al.[16] which is a seven-stage classification from zero bone damage as stage 1 to stage 7 denoting extensive bone damage based on radiographic bony involvement of foot. This classification was based only on mycetoma manifestations in foot. One case which was showing stage 0 (no bony oedema) on radiograph, MRI showed bony oedema [Figure 6]. Early bony changes like mild oedema may be missed on both plain radiograph and CT but can be detected on MRI.[17]
Figure 1: (a) Plain radiograph (left) showed involvement of tarsal, metatarsal bones and first phalanx with destruction of intervening joints. Extensive soft tissue and bony involvement in T2 sequence (right) especially in the region of tarso-metatarsal joint, metatarso-phalyngeal joint and base of metatarsal mimicking neuroarthropathy. (b) 'Dot in circle' sign (arrow) in T2 coronal image

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Figure 2: (a) Both plain radiograph and sagittal image of CT shows punched out lytic areas in tarsal bones with cortical defect (arrow). (b) Sinus tract (arrows) seen through bony cortical defect in proton density (PD) fat saturation (FS) sagittal and coronal images (left and middle image). T1 post contrast image (right) shows 'dot-in-circle' sign (arrow)

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Figure 3: Plain radiograph (top left image) showing extensive periosteal with lytic areas within periosteal reaction mainly in metacarpal and carpal bones. Short tau inversion recovery (STIR) axial (top right and bottom left) shows marrow oedema with cortical defect, subperiosteal collection and sinus tracts (arrows). T2 coronal sequence (bottom right) showed 'dot-in-circle' sign

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Figure 4: Plain radiograph (top left) showed periosteal reaction with sclerosis in fourth and fifth metacarpal with erosion in fourth metacarpal. T2 axial images (top right and bottom left) show suspicious defect in cortex of fourth metacarpal mimicking cloaca with periosteal elevation and subperiosteal collection (arrows). T2-gradient sagittal image (bottom middle) showed 'dot-in-circle' sign (arrow). Follow-up post-operative radiograph shows fibular graft (bottom right)

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Figure 5: Plain radiograph (top left) shows soft tissue mass with involvement of mainly metatarsal with aggressive periosteal reaction and sclerosis. T2 sagittal image (top right) shows large soft tissue mass with adjacent bony involvement and oedema. Diffusion weighted images (DWI) shows areas of patchy diffusion restriction with corresponding areas showing reduction in apparent diffusion coefficient (ADC) values (bottom left and middle). T1 coronal post-contrast image (bottom right) shows homogenous enhancement of the mass with 'dot-in-circle' sign (arrow)

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Figure 6: (a) Plain radiograph (left) showed vague soft tissue mass without any obvious bony involvement. STIR axial image (right) showed serpiginous high signal masses with hypointense foci within resembling pheboliths. There is marrow oedema in fourth metatarsal. (b) Post contrast T1W FS sagittal image (left) showed diffuse enhancement. T2 coronal image (middle) shows 'dot-in-circle' sign (arrow). The STIR axial image (right) showed discharging sinus (arrow) contradicting haemangioma

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Another grading system has also been given by El Shamy et al.[13] using MRI which includes involvement of skin, subcutaneous tissue, muscle and bone.[7] Using this grading system, mycetoma lesion can be classified as mild (1–3), moderate (4–7) and severe (8–10). They studied 42 cases of mycetoma in MRI, out of which 24 cases were eumyecetoma and 18 patients were actinomyecetoma. They reported sinus tracts with grains in 33 patients and mentioned that 6 patients did not show grains. In our case series four out of seven cases were showing severe form of disease and rest all have moderate disease. This could be partly that it was not only neglected and patients presented in advanced stage, but also due to the fact that mycetoma was not considered as a possibility in the early stages of swelling, and imaging work-up was done late after the patient did not respond to initial management. In one of our case where MRI score was 9 (severe), medical management failed and amputation of metacarpal was done finally. There are no imaging criteria in differentiating actinomycetoma and eumycetoma.[13]

Cultures and biopsy are time-consuming and invasive procedure.[7],[18] In one of our cases, biopsy was that of nonspecific chronic granulomatous lesion. Hence using 'dot-in-circle' sign is a reliable imaging diagnostic criterion for diagnosis. Bone changes like periosteal reaction, cortical erosions, cortical hyperostosis, bone destruction and coarse trabeculation are definitely better seen on CT.[16] However, mycetoma affects extensively soft tissue apart from bones where MRI is superior in characterisation. The 'dot-in-circle' sign has also been described on ultrasonography, however it is inferior to MRI in showing bony and soft tissue involvement. The 'dot-in-circle' sign has not been described as a feature of chronic pyogenic osteomyelitis, tubercular osteomyelitis, neuroarthropathy, bone tumour and vascular malformation. In our series, all the cases showed positive 'dot-in-circle' sign.

Mycetoma may be the only other infective disease where an imaging criteria may be definitive and absolute like the 'scolex sign' of cysticercosis.[19] However this may have to be verified by a larger series to see whether any cases of mycetoma can present without the 'dot-in-circle' sign as mentioned in the series by El Shamy et al.[13] or alternately the sign not being visible throughout the entire course of the disease.

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]

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