Eumycetoma (Fungal Mycetoma) Workup

Updated: Jun 17, 2022
  • Author: George Turiansky, MD; Chief Editor: Dirk M Elston, MD  more...
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Laboratory Studies

Identification of the etiologic agent of eumycetoma is based on direct microscopic examination of the granules, culture isolation of the agent, colonial features and fungal microscopic morphology. [12, 13]

Eumycetoma granules can be crushed and examined at microscopy with direct wet mounts after treatment with 10-20% potassium hydroxide, lactophenol cotton blue, Albert stain, or physiologic saline solution.

Eumycetoma agents appear as broad, septate, branching hyphae 2-5 µm in diameter or, as in the case of E jeanselmei, as a compact mass of rounded cells.

Fresh granules can be teased from lesional tissue or biopsy specimens. These cells can be washed in saline solution or saline solution containing antibiotics prior to culturing on fungal media such as Sabouraud dextrose agar, blood agar, or a brain-heart infusion containing antibiotics.

Granules from draining sinus tracts may not be optimal for culturing because of bacterial contamination.

Ahmed et al reported two cases of leg eumycetoma due to M mycetomatis that were successfully identified by species-specific polymerase chain reaction and DNA sequencing.

Fine-needle aspiration cytology of lesional tissue with the use of special stains may be useful in diagnosis. [14]


Imaging Studies

Radiographs, CT scans, and MRIs demonstrate the presence and extent of bone or organ involvement. [15] Changes of underlying bony structures may include the following:

  • Osteoporosis

  • Bony destruction

  • Loss of cortical margin with bony erosion

  • Punched-out lytic lesions

  • Osteophyte formation

  • Osteomyelitis

  • Periosteal elevation

  • Marrow infiltration

  • Coarse trabecular pattern

  • Bony expansion

Dot in circle sign

The "dot in circle" sign is highly specific for mycetoma and is seen on MRI and ultrasound. The "dot" consists of a dense ball of fungal grains. The hyperechoic wall surrounding the central lesion consists of inflammatory granulomata. The "circle" is fibrous matrix. [16]


Histologic Findings

A biopsy specimen should be obtained from a small abscess or from the sinus tract. Hematoxylin-eosin stained sections reveal extensive granulation tissue containing abscesses. Granules of 0.2-5.0 mm in diameter may be found in abscesses or sinuses. Eumycotic granules have positive results with periodic acid–Schiff and Gomori methenamine silver stains. They contain gram-negative septate hyphae that are 2-5 µm in diameter. Eosinophilic material may be seen deposited around the granule; this material represents an immunologic response, the Splendore-Hoeppli reaction.