Diagnostic Significance of Fruiting Bodies in Pathology Specimens: A Series of 13 Patients

In pathology (surgical pathology/cytopathology) specimens, <i>Aspergillus</i> species can be challenging to differentiate from other fungi that produce hyaline septate hyphae by morphology alone. It has been suggested that fruiting bodies-if present-indicate <i>Aspergillus</i>. The aim of this study was to determine whether the presence of fruiting bodies in pathology specimens is specific for <i>Aspergillus</i>. Specimens containing fungal hyphae with fruiting bodies were identified and fungal culture and PCR results were reviewed to determine the identity of the fungi. To determine whether fruiting bodies can be formed in tissue by other fungi, non-<i>Aspergillus</i> fungi were included for analysis if cultures or PCR confirmed a non-<i>Aspergillus</i> fungus. Fruiting bodies were present in specimens from 13 patients (12 surgical pathology, 1 cytology). In 11/13, the identity of the fungus was confirmed (10 <i>Aspergillus fumigatus</i>, 1 <i>Rhizopus</i> species). In 6/13, <i>A. fumigatus</i> was confirmed by microbiologic cultures. In 4/13, <i>A. fumigatus</i> was confirmed by PCR on formalin-fixed paraffin-embedded tissue. In 2/13 specimens, cultures/PCR were not performed. The one <i>Rhizopus</i> sp. was confirmed by culture. In most (10/13) specimens, fruiting bodies of <i>Aspergillus</i> consisted of yellow vesicles containing a row of radiating phialides, occasional stalks/conidiophores and detached yellow conidia (spores) in the background. In contrast, fruiting bodies of the <i>Rhizopus</i> sp. were sporangia (large spore-containing sacs) lacking phialides. To evaluate fruiting bodies in non-<i>Aspergillus</i> fungi, 18 specimens were identified with hyphal structures in tissue with available microbiologic culture or PCR results. No fruiting bodies were identified in the 18 non-<i>Aspergillus</i> fungal infections (11 <i>Fusarium</i>, 6 Mucorales order genera, 1 <i>Acrophialophora</i>). In pathology specimens, fruiting bodies with the morphologic features described in this study (conidiophores with yellow-brown vesicles, attached phialides, detached yellow conidia) are specific for <i>Aspergillus</i> and can be differentiated from <i>Rhizopus</i>, whose fruiting bodies feature sporangia (large spore-containing sacs lacking phialides).