The “Dot in Circle” Sign on MRI in Maduramycosis: A Characteristic Finding

Abstract

Mycetoma or Maduramycosis is a localized chronic suppurative infection characterized by exuberant granulation tissue, discharging sinuses, and bone involvement later in the course of the disease. Early clinical diagnosis before the appearance of sinuses and grains (aggregates of organism surrounded by granulation tissue, which are discharged from the draining sinuses) is difficult. Delay in diagnosis may lead to amputation of the affected part. Definitive diagnosis is through biopsy and microbiological examination. However, at times diagnosis may still be difficult. The recently described “dot in circle” sign on magnetic resonance imaging (MRI) is easy to recognize and highly specific. We present a case of mycetoma foot with characteristic MRI features.

Pedal Mycetoma Mimicking Plantar Fibroma

“…MRI Imaging can also be helpful in establishing the diagnosis with dot-in-circle appearance; high intensity lesion on T2 images with a tiny central low-signal focus representing fungal grains within inflammatory granulomata [9,10]. This sign has also been described as a highly specific MRI and Ultrasonographic sign of Mycetoma [7].…”

Nocardia transvalensis/wallacei hindfoot actinomycetoma

“…Osteomyelitis is a common complication, and plain X-ray assessment or CT scan is advisable to demonstrate bony osteolytic areas and eventual periosteal reaction [10,11] . The initial radiographic changes include periosteal reaction, new bone formation, and cortical erosions.…”

“…This then progresses to remarkable sclerosis, lytic lesions (geodes), and osteopenia secondary to disuse. [12,13] The "dot-in-circle" sign has been considered to be a highly specific early sign of mycetoma on magnetic resonance imaging (MRI) [10,11] . Pijper et al reported the first case of N. transvalensis infection in 1927 as a pathogen of foot mycetoma in a South African patient.…”

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.…”