The “dot-in-circle” sign in musculoskeletal mycetoma on magnetic resonance imaging and ultrasonography

Abstract

This study aimed to present the ‘dot-in-circle’ sign, which indicates the typical magnetic resonance imaging (MRI) and ultrasonographic (USG) findings for mycetoma involving soft tissue and bone. A total of 8 cases with histopathological proof of mycetoma affecting the musculoskeletal system, and that were examined via MRI and/or coexistent diagnostic ultrasonography between 2004 and 2013 in Songklanagarind Hospital were included in this study. The ‘dot-in-circle’ sign on the MRI and USG images of all the patients was reviewed by two radiologists. The analytic method was descriptive. All cases of musculoskeletal mycetoma revealed the ‘dot-in-circle’ sign on MRI, which was seen as multiple, small, round- to oval-shaped hyperintense lesions separated and surrounded by a low-signal intensity rim (circle), and a tiny, central, low-signal focus (dot). An USG study was available in four patients, and all USG findings demonstrated the ‘dot-in-circle’ sign as a central hyperechoic area (dot) surrounded by hypoechoic tissue (circle). In conclusion, the ‘dot-in-circle’ sign is a typical feature on MRI and USG findings for the diagnosis of musculoskeletal mycetoma.

The importance of diagnostic imaging of mycetoma in the foot

“…The “dot‐in‐circle” sign found by MRI consists of small, rounded or oval hyperintense lesions between 2 and 5 mm in size, separated and surrounded by a low signal intensity border (the circle) and a small central focus of low signal intensity (the dot). This represents the only significant pathological finding in mycetoma infection in MRI studies, and it is highly specific for this pathology . It was proposed by Sarris et al ., who analyzed a case series using MRI in T1, STIR, and T2 contrasted with gadolinium.…”

“…This is characterized by a hyperechoic central area (the dot) surrounded by hypoechoic tissue (the circle) . Doppler US has also shown advantages by demonstrating affected blood vessels and hyperemia . Even though it is possible to distinguish between actinomycetoma and eumycetoma, it can be difficult…”

“…This represents the only significant pathological finding in mycetoma infection in MRI studies, and it is highly specific for this pathology. 12,13 It was proposed by Sarris et al, 14 who analyzed a case series using MRI in T1, STIR, and T2 contrasted with gadolinium. However, it cannot distinguish between mycetomas caused by eumycetes and actinomycetes.…”

“…20 Doppler US has also shown advantages by demonstrating affected blood vessels and hyperemia. 12 Even though it is possible to distinguish between actinomycetoma and eumycetoma, it can be difficult. 21 Another diagnostic imaging tool is helical computed tomography with multiplanar reconstruction.…”

Eumicetoma: actualidades y perspectivas

“…Los granos aparecen como lesiones de forma redonda, de baja intensidad, pequeñas, de 2 a 5 mm de diámetro (que recuerdan un punto), en conglomerados rodeados de un anillo de alta intensidad (semeja un círculo) que representa la reacción granulomatosa periférica. Esta imagen característica se denomina «punto en círcu-lo» [39][40][41][42] y se reconoció posteriormente en imágenes obtenidas por ultrasonido, donde se observa como un área hiperecoica (punto) rodeada por tejido hipoecoico (circulo) 43,44 . El Shamy, et al 45 propusieron una escala para valorar la gravedad del micetoma utilizando los hallazgos en la resonancia magnética.…”