What is the role of biopsy in the workup of mucormycosis (zygomycosis)?

Updated: Jul 06, 2021
  • Author: Avnish Sandhu, DO; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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Answer

Biopsy of the involved tissue is the most definitive means of establishing a diagnosis of mucormycosis. A rapid histologic assessment of a frozen tissue section should be performed to promptly institute surgical and medical management for the infection.

Biopsy of necrotic tissue

Biopsy of necrotic tissue may be obtained from nasal, palatine, lung, cutaneous, gastrointestinal (GI), or abscess wall site.

Stains of fixed tissues with hematoxylin and eosin (H&E) or specialized fungal stains, such as Grocott methenamine-silver (GMS) or periodic acid-Schiff (PAS) stains, show pathognomonic broad (typically 6- to 25-µm diameter), irregular, ribbonlike, nonseptate (or sparsely septate) hyphae with irregular branching occurring at 45-90º. [75]  Vascular invasion and necrosis are the characteristic consequences of the infective process. Thus, neutrophil infiltration, vessel invasion, and tissue infarction are often observed. A granulomatous reaction may also be seen.

Histologic findings from an immunocompetent man wh Histologic findings from an immunocompetent man who sustained a high-pressure water jet injury, resulting in rhinocerebral mucormycosis. Traumatic inoculation of Apophysomyces elegans was the pathogenetic mechanism. Findings show the typical Mucorales hyphae on Grocott methenamine-silver staining. The hyphae are the dark structures with budlike, right-angle hyphae. Courtesy of A Allworth, MD, Brisbane, Australia.

Culture of biopsy samples is generally required to determine the species of Mucorales. Do not crush or grind the specimen, because the nonseptate hyphae are prone to damage. Growth usually occurs in 2-3 days. The genus and species are determined via examination of the fungal morphology (ie, the presence and location of the rhizoids). Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) can also provide rapid and accurate identification at the species level but requires a reference database. 18s ribosomal RNA (rRNA) sequencing may provide genus-level identification, even if tissue damage precludes fungal growth. [28]


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