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Year : 2019  |  Volume : 5  |  Issue : 3  |  Page : 145-149

“Dot in Circle” Sign in Actinomycotic Mycetoma on MRI and Ultrasound − A Case Series

Department of Radiodiagnosis, Maulana Azad Medical College, Bahadur Shah Zafar Road, New Delhi, India

Date of Submission30-Jul-2019
Date of Decision31-Jul-2019
Date of Acceptance01-Sep-2019
Date of Web Publication17-Dec-2019

Correspondence Address:
Dr, MD, DNB, MNAMS, Professor Jyoti Kumar
Department of Radiodiagnosis, Maulana Azad Medical College, Bahadur Shah Zafar Road, New Delhi-110002
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mamcjms.mamcjms_61_19

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Mycetoma, a chronic granulomatous disease more common in tropical countries such as India, has been conventionally diagnosed by invasive and time-consuming modalities like biopsy and microbiological culture. This case series aims to stress on the benefits of leveraging magnetic resonance imaging and ultrasonography in the early diagnosis of mycetoma, avoiding the invasive techniques and preventing debilitating complications that may develop from delay in diagnosis.

Keywords: Dot-in-circle, mycetoma, madura foot, MRI, ultrasound

How to cite this article:
Kumari A, Kumar J, Garg A, Gupta S. “Dot in Circle” Sign in Actinomycotic Mycetoma on MRI and Ultrasound − A Case Series. MAMC J Med Sci 2019;5:145-9

How to cite this URL:
Kumari A, Kumar J, Garg A, Gupta S. “Dot in Circle” Sign in Actinomycotic Mycetoma on MRI and Ultrasound − A Case Series. MAMC J Med Sci [serial online] 2019 [cited 2020 Apr 6];5:145-9. Available from: http://www.mamcjms.in/text.asp?2019/5/3/145/273286

  Introduction Top

Mycetoma is a chronic suppurative granulomatous infection involving the subcutaneous tissue wherein an exogenous etiological agent incites the production of pus and sulfur granules. The infection can involve the underlying muscles and bones, depending on the immune status of the patient, the causative agent, and duration of infection and can cause serious functional impairment. The defining clinical triad comprises localized mass-like soft tissue (tumefaction), draining sinuses, and grains of contagious material.[1],[2]

Mycetomas are subdivided by their causative agents into two categories: eumycetoma or eumycotic mycetoma and actinomycetoma or actinomycotic mycetoma. Eumycetoma is caused by fungi, most often Madurella mycetomatis (maduromycosis), and prevalent in tropical and subtropical regions including Indian subcontinent. Actinomycotic mycetoma is caused by filamentous bacteria most often Nocardia brasiliensis and Streptomyces somaliensis, and prevalent in Africa (where S. somaliensis dominates) and central and south America (where N. brasiliensis dominates).

We report two cases of actinomycotic mycetoma in the Indian subcontinent, affecting the leg, with characteristic ultrasound and magnetic resonance imaging (MRI) features.

  Case Report Top

Case 1

A 53-year-old male patient, a daily wage laborer, presented with complaints of multiple swellings (size approximately 20 × 10 cm) and sinuses discharging yellow grains [Figure 1] with on and off pain over right calf since last 6 years with rapid increase in size since last year. Initially, patient developed a small nodular swelling that gradually increased in number and size up to the present size. The patient did not have any difficulty in walking or standing. There was no history of trauma, fever, or bone pain. The patient was nondiabetic and immunocompetent. Multiple enlarged painless, mobile right inguinal lymph nodes were present on examination. From the history and local examination, a provisional clinical diagnosis of mycetoma was considered.
Figure 1 Photograph of the patient’s right leg showing soft tissue swelling with multiple discharging sinuses and scarring of the skin.

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High-resolution ultrasound of the local part [Figure 2] revealed a large heteroechoic swelling within the subcutaneous tissues of the calf with multiple discharging sinus tracts. There were distinct hypoechoic lesions surrounding a hyperchoic center giving the “dot-in-circle” appearance.
Figure 2 Ultrasound image reveals diffuse heterogenous soft tissue thickening with multiple distinct hypoechoic rounded lesions representing granulomata (thick white arrow) surrounding hyperechoic centers representing fungal grain (thin yellow arrow).

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MRI of the right leg [Figure 3] was performed to determine the extent of the disease. We performed MRI of the right leg on 3 Tesla magnet system (Magnetom Skyra, Siemens – 3T MRI). T1W, T2W, Short tau inversion recovery (STIR), and postcontrast images were obtained in different planes. MRI revealed diffuse subcutaneous soft tissue thickening with scarring on overlying skin at sites of discharging sinuses. Soft tissue thickening appeared predominantly hypointense on T1W and T2W images. Disease process was confined to skin and subcutaneous plane only without involvement of underlying muscles and bones. On T2W and STIR, characteristic multiple round hyperintense cystic lesions with central hypointense nodules were found, giving the characteristic “dot-in-circle” appearance. The postcontrast scans revealed heterogenous enhancement of the soft tissue with nonenhancing central nodule surrounded by heterogeneously enhancing granulation tissue.
Figure 3 Short tau inversion recovery (STIR) axial (A) and coronal (B) images reveal marked soft tissue thickening with multiple well-defined hyperintense lesions (solid yellow arrow) with central hypointense nodules within (dashed yellow arrow) giving a characteristic dot-in-circle appearance. Postcontrast axial (C) and coronal (D) images reveal heterogenous enhancement of soft tissue with enhancing rounded lesions with central nonenhancing nodule.

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Discharging grains were examined on potassium hydroxide preparation (KOH mount preparation) that was negative. On gram stain, the grains showed gram-positive filamentous bacilli. For confirmation of the diagnosis, grains were examined on fungal and bacterial culture. Fungal culture was negative whereas bacterial culture showed Acinetobacter spp. A diagnosis of actinomycotic mycetoma was made.

The patient was started on a multidrug regimen comprising gentamicin, cotrimoxazole, and doxycycline for a period of 8 months and showed marked improvement on follow-up. The follow-up ultrasound [Figure 4] showed significant resolution of the previous lesions.
Figure 4 (A) Photograph of the patient’s right leg after 8 months of treatment shows marked healing of sinuses that were now nondischarging. (B) Ultrasound image after 8 months of treatment shows significant resolution of the previous lesions.

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Case 2

A 27-year-old farmer with history of barefoot practice in the fields came with the history of painless progressive swelling with discharging sinuses extruding blackish grains in the lateral aspect of sole of the left foot for the past 7 years. There was no significant progress in the size of the swelling after the first 2 years and the patient underwent excision of the same without any further investigation. The swelling relapsed and then progressed to involve the entire sole and also the lateral aspect of the dorsum. With a provisional diagnosis of mycetoma based on history and clinical examination, ultrasound and MRI were performed.

On ultrasonography (USG), there was diffuse subcutaneous edema and heterogeneity with multiple hypoechoic lesions having hyperechoic centers giving a characteristic “dot-in-circle” appearance.

3 Tesla MRI evaluation of the left foot [Figure 5] to assess the soft tissue extent of the lesion revealed ill-defined soft tissue mass in the left foot (plantar aspect > dorsum) with multiple discrete T1 isointense and T2/STIR hyperintense lesions with hypointense central nodule. The mass showed heterogenous postcontrast enhancement with nonenhancing nodules surrounded by enhancing granulation tissue. The mass was seen to cause extensive involvement of the intrinsic muscles of the sole, tendons, and subcutaneous tissue producing an irregular surface over the plantar aspect of the foot. Marrow edema was seen in multiple tarsal and metatarsal bones.
Figure 5 STIR sagittal (A) reveals an ill-defined soft tissue mass in the sole of the left foot with multiple discrete hyperintense lesions (solid yellow arrow) with hypointense central focus. Postcontrast sagittal T1-weighted image (B) reveals heterogenous enhancement of soft tissue having nonenhancing central nodules (dashed yellow arrow) with surrounding enhancing granulation tissue. Note is made of a ganglion cyst in relation to the flexor hallucis longus tendon (solid white arrow).

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The grains were subsequently subjected to Gram staining and it yielded multiple filamentous gram-positive bacilli. They were negative on KOH mount, pointing to a bacterial etiology. On bacterial culture, it was found to be Actinomyces spp. A diagnosis of actinomycotic mycetoma was hence established. The patient was started on a combination of gentamicin, cotrimoxazole, and doxycycline. After 3 months of treatment, there was marked improvement in the symptomatology of the patient.

  Discussion Top

Mycetoma is typically an indolent infection of young adults with male preponderance, possibly due to outdoor and occupational exposure. It usually affects the foot, hands, and legs but may involve any part of the body. It generally presents as a localized painless tumefactive process with subsequent development of sinuses discharging the fungal elements or bacterial colonies surrounded by granulation tissue, loosely termed as “grains.”[3] If left untreated, it spreads to involve the underlying soft tissue and bones and may lead to morbid complications. In case of involvement of the extremities, it causes difficulty in daily activities and may require amputation in advanced cases. In the chest, neck, and face, it may cause mutilation of vital structures.[4]

Histologically, the diagnosis is based on the characterization of grains. Direct microscopy of the wet mount is performed and various differential stains such as Albert, Gram, Gomori methenamine silver, periodic acid Schiff, and lactophenol blue are used.[5] Cultures are made on brain heart infusion agar with aerobic and anaerobic incubation. Microscopy and culture is the gold standard for diagnosis but may be difficult to achieve in fastidious organisms.

The USG appearances were initially described by Fahal et al.,[6] in 1997, on in vitro imaging of the mycetoma lesions. They demonstrated that the hyperreflective echoes corresponded to the fungal grains, whereas eumycetoma grains produce sharp bright hyperechoic foci and actinomycetomas produce smaller, less-distinct hyperechoic foci that commonly settle at the bottom of the rounded lesions with raised vascularity on Doppler.[6]

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.” The “dot-in-circle” sign, seen as tiny hypointense foci within the hyperintense spherical lesions was initially described by Sarris et al.,[7] 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.[7] The USG “dot-in-circle” sign is similar to the MRI sign, with multiple hyperechoic foci within a hypoechoic mass. On multiple subsequent studies, it was established that the “dot-in-circle” is pathognomonic of mycetoma. In conclusion, this case report demonstrates that early detection of mycetoma, even before the development of sinuses or extrusion of grains, is possible by using of imaging modalities such as MRI and USG. Dot-in-circle sign comprising granulomatous tissue surrounding fungal elements/bacterial colonies is an easily recognizable sign with high degree of specificity, obviating the need for multiple surgical biopsies. The only constraint to this diagnostic approach is the limited availability of MRI facility and expertise. Microbiological investigations may still be required for confirmation of organism and drug sensitivity.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Jain V, Makwana GE, Bahri N, Mathur MK. The “dot in circle” sign on MRI in maduramycois: a characteristic finding. J Clin Imaging Sci 2012;2:66.  Back to cited text no. 1
Laohawiriyakamol T, Tanutit P, Kanjanapradit K, Hongsakul K, Ehara S. The “dot-in-circle” sign in musculoskeletal mycetoma on magnetic resonance imaging and ultrasonography. SpringerPlus 2014;3:671.  Back to cited text no. 2
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.  Back to cited text no. 3
[PUBMED]  [Full text]  
Zaias N, Taplin D, Rebell G. Mycetoma. Arch Dermatol 1969;99:215-25.  Back to cited text no. 4
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. 5
Fahal AH, Skeik HE, Homeida MMA, Arabi YE, Mahgoub ES. Ultrasonographic imaging of mycetoma. Br J Surg 1997;84:1120-22.  Back to cited text no. 6
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. 7


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


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