Morphologic Identification of Fungal Infections in Histologic and Cytologic Specimens
Morphologic Identification of Fungal Infections in Histologic and Cytologic Specimens
Despite the advantages of providing an early presumptive diagnosis, fungal classification by histopathology can be difficult and may lead to diagnostic error. To assess the accuracy of histologic diagnosis of fungal infections vs culture (“gold standard”), we performed a 10-year retrospective review at our institution. Of the 47 of 338 positive mold and yeast cultures with concurrent surgical pathology evaluation without known history of a fungal infection, 37 (79%) were correctly identified based on morphologic features in histologic and/or cytologic specimens. The 10 discrepant diagnoses (21%) included misidentification of septateband nonseptate hyphal organisms and yeast forms. Errors resulted from morphologic mimics, use of inappropriate terminology,band incomplete knowledge in mycology. The accuracy did not correlate with preceding antifungal therapy (P = .14) or use of special stains (P = .34) and was not operator-dependent. Among 8 discrepancies with clinical follow-up available, 2 potential adverse clinical consequences resulted. While histopathologic identification of fungi in tissue sections and cytologic preparations is prone to error, implementation of a standardized reporting format should improve diagnostic accuracy and prevent adverse outcomes.
Histopathologic examination remains one of the major diagnostic tools in mycology because it permits rapid, presumptive identification of fungal infections. Histopathologic and/or cytopathologic examination can also provide insight into the diagnostic significance of some culture isolates. Demonstration of tissue invasion or an inflammatory reaction can help to determine whether an organism represents contamination, colonization, or true infection. Furthermore, histopathologic examination remains the only reliable means to identify certain pathogens, including Pneumocystis jiroveci (formerly Pneumocystis carinii), Loboa loboi, and Rhinosporidium seeberi. Several studies have demonstrated improved fungal detection by histopathologic examination in some circumstances, but few have investigated the diagnostic specificity of histopathologic examination vs microbiological culture, while none, to our knowledge, have included a comprehensive formal evaluation of the diagnostic accuracy of surgical pathology for all fungal infections.
Although histopathology and microbiology are thought to be complementary, in recent years, we have encountered a number of cases with discrepant histologic and culture results at the time of frozen section or at final diagnosis. Because some of these discrepancies could lead to unnecessary pharmacologic exposure and/or delayed treatment, we undertook a retrospective 10-year review of all positive mold and yeast cultures that were associated with concurrent surgical pathology specimens at Stanford University Medical Center (SUMC), Stanford, CA. The rate of misclassification was determined, and a root cause analysis was performed on discordant cases to develop an improved fungal identification process for general surgical pathologists.
Abstract and Introduction
Abstract
Despite the advantages of providing an early presumptive diagnosis, fungal classification by histopathology can be difficult and may lead to diagnostic error. To assess the accuracy of histologic diagnosis of fungal infections vs culture (“gold standard”), we performed a 10-year retrospective review at our institution. Of the 47 of 338 positive mold and yeast cultures with concurrent surgical pathology evaluation without known history of a fungal infection, 37 (79%) were correctly identified based on morphologic features in histologic and/or cytologic specimens. The 10 discrepant diagnoses (21%) included misidentification of septateband nonseptate hyphal organisms and yeast forms. Errors resulted from morphologic mimics, use of inappropriate terminology,band incomplete knowledge in mycology. The accuracy did not correlate with preceding antifungal therapy (P = .14) or use of special stains (P = .34) and was not operator-dependent. Among 8 discrepancies with clinical follow-up available, 2 potential adverse clinical consequences resulted. While histopathologic identification of fungi in tissue sections and cytologic preparations is prone to error, implementation of a standardized reporting format should improve diagnostic accuracy and prevent adverse outcomes.
Introduction
Histopathologic examination remains one of the major diagnostic tools in mycology because it permits rapid, presumptive identification of fungal infections. Histopathologic and/or cytopathologic examination can also provide insight into the diagnostic significance of some culture isolates. Demonstration of tissue invasion or an inflammatory reaction can help to determine whether an organism represents contamination, colonization, or true infection. Furthermore, histopathologic examination remains the only reliable means to identify certain pathogens, including Pneumocystis jiroveci (formerly Pneumocystis carinii), Loboa loboi, and Rhinosporidium seeberi. Several studies have demonstrated improved fungal detection by histopathologic examination in some circumstances, but few have investigated the diagnostic specificity of histopathologic examination vs microbiological culture, while none, to our knowledge, have included a comprehensive formal evaluation of the diagnostic accuracy of surgical pathology for all fungal infections.
Although histopathology and microbiology are thought to be complementary, in recent years, we have encountered a number of cases with discrepant histologic and culture results at the time of frozen section or at final diagnosis. Because some of these discrepancies could lead to unnecessary pharmacologic exposure and/or delayed treatment, we undertook a retrospective 10-year review of all positive mold and yeast cultures that were associated with concurrent surgical pathology specimens at Stanford University Medical Center (SUMC), Stanford, CA. The rate of misclassification was determined, and a root cause analysis was performed on discordant cases to develop an improved fungal identification process for general surgical pathologists.
