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

In pathology (surgical pathology/cytopathology) specimens, Aspergillus 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 Aspergillus. The aim of this study was to determine whether the presence of fruiting bodies in pathology specimens is specific for Aspergillus. 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-Aspergillus fungi were included for analysis if cultures or PCR confirmed a non-Aspergillus 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 Aspergillus fumigatus, 1 Rhizopus species). In 6/13, A. fumigatus was confirmed by microbiologic cultures. In 4/13, A. fumigatus was confirmed by PCR on formalin-fixed paraffin-embedded tissue. In 2/13 specimens, cultures/PCR were not performed. The one Rhizopus sp. was confirmed by culture. In most (10/13) specimens, fruiting bodies of Aspergillus 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 Rhizopus sp. were sporangia (large spore-containing sacs) lacking phialides. To evaluate fruiting bodies in non-Aspergillus 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-Aspergillus fungal infections (11 Fusarium, 6 Mucorales order genera, 1 Acrophialophora). 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 Aspergillus and can be differentiated from Rhizopus, whose fruiting bodies feature sporangia (large spore-containing sacs lacking phialides).