The dot-in-circle sign is a recently described sign reflecting the unique
pathological feature of mycetoma.
It is seen as a tiny hypointense focus within high-intensity spherical lesions.
This sign was proposed by Sarris et al.in 2003 on T2-weighted,
STIR,
and
T1-weighted fat-saturated gadolinium enhanced images.
Pathological Correlates of Dot in Circle Sign:
The disease usually begins as a painless swelling or thickening of the skin and subcutaneous tissue.
As the disease gradually progresses over months or years,
the initial lesion enlarges and eventually becomes tumorous.
The overlying skin may be smooth,
dyspigmented,
or shiny.
Abscesses and sinus tracts develop over time and may contain a serosanguineous or seropurulent discharge,
which may contain white-to-yellow or black granules.
Granules are firm 0.2- to 5-mm aggregates of organized vegetative,
septate hyphae,
which often are embedded in a matrix cement substance
These granules are usually macroscopic and are observed in the lesional tissue and in sinus tracts.
The color of the dark grains is thought to be due to melanin,
host protein,
and dark debris.
Regional lymphadenitis secondary to bacterial super infection of the lesion may be present
Mycetoma feet and The Madura foot:
radiographic bone changes have been described to distinguish between actinomycetoma and eumycetoma
(1).
Eumycotic lesions tend to form a few cavities in bone ≥1 cm in diameter,
while actinomycetes often form smaller,
but more numerous cavities.
In a study by Lewall et al.
a motheaten appearance caused by a combination of irregular periosteal reaction,
periosteal erosion,
and small cavities within bone were seen in 25% of cases
of actinomycetoma,
but in none of the patients with eumycetoma.
The distinction between the 2 forms of soft tissue mycetoma was not possible with MRI.
MRI and histological findings correlation indicates that the small central hypointense foci represented the fungal balls or grains,while the surrounding high-signal intensity foci represented the inflammatory granulomata .
Eumycetoma is a chronic cutaneous and subcutaneous infection caused by various genera of fungi.
Approximately 40% of mycetomas worldwide are eumycotic as opposed to actinomycotic (ie,
caused by bacterial actinomycetes).
The disease is marked by progressive destruction of soft tissue and nearby anatomic structures
Differential Diagnosis of Mycetoma
Cutaneous Tuberculosis
Sporotrichosis
Squamous Cell Carcinoma
Syphilis
Verrucous Carcinoma
Yaws
Kaposi’s sarcoma