In a study published last month in the American Journal of Clinical Pathology, Dekio et al 1 reported on the performance and clinical impact of histologic examination of surgical pathology tissues for fungi from immunocompromised pediatric patients at risk for invasive fungal infections (IFIs). IFIs are associated with high morbidity and mortality in immunocompromised pediatric patients. 2-4 Thus, rapid and accurate laboratory diagnosis is of the utmost importance. 5,6 This is one of few reports of histologic examination in pediatric immunocompromised patients, and the results of this study emphasize the important diagnostic role of histology in providing clinically actionable information.The purpose of histologic examination of tissue for fungi is twofold: (1) to alert clinicians to the presence of fungi and (2) to guide clinicians in the choice of antifungal therapy through provision of an inclusive but targeted differential diagnosis. This study highlights these points while also underscoring the importance of communication among pathologists, microbiologists, and clinicians in the care of immunocompromised pediatric patients.In the study by Dekio et al, 1 two surgical pathologists and one clinical microbiologist retrospectively reviewed histologic slides from 47 pediatric patients with IFI collected over an 11-year period. The aims of their study were to evaluate the predictive accuracy of histologic examination and to investigate the impact of histologic results on clinical decision making. Correlation between histologic appearance and culture was available for 27 patients, while the impact of histologic results on clinical decision making was evaluable in 36 patients for whom medical records were accessible.Several important findings resulted from this study. First, the authors demonstrated that histology correlated with culture for all cases in which growth was obtained. Concordance in their study was broadly defined as the following: yeast on histology with yeast in culture, septate hyphae on histology with septate hyphae in culture, and broad nonseptate hyphae on histology with the same in culture. This definition of concordance may be too broad, however, for the purposes of individual patient care, since many organisms that display septate hyphae with acute angle branching mimic each other on histopathology but show widely divergent behavior and antifungal resistance profiles. 7,8 Examples of organisms that mimic Aspergillus by histologic appearance include Fusarium spp, which is highly resistant to multiple antifungal agents ❚Image 1❚; Scedosporium spp, Pseudallescheria spp, and Lomentospora spp, which may be multiply resistant; and dematiaceous molds or brown/black molds, such as Exserohilum rostratum, Ochroconis gallopava, Curvularia spp, and Alternaria spp. [9][10][11] Subtle histologic features among the acute angle branching septate molds may narrow the differential diagnosis. For example, the presence of terminal annelloconidia (dark conidia extruding from a narrow-tipped cell) in hyaline hyphae ...