This transcript details a pathological examination revealing an angioinvasive fungal infection, primarily characterized by fungal hyphae growing directly from and through the walls of dilated, thrombosed blood vessels. The speaker describes this as "metastatic fungus," capable of causing widespread ischemic necrosis, particularly in immunocompromised patients, and provides a clinical example of a fatal Aspergillus case. A critical diagnostic principle emphasized is the unreliability of definitively identifying specific fungal species (e.g., Aspergillus) based solely on tissue morphology due to potential inaccuracies and altered appearance from treatment. Pathologists are advised to report "angioinvasive fungus with septate and acute angle branching" and rely on cultures or PCR for precise identification. The specific case presented was later confirmed to be Aspergillus versicolor and other Aspergillus species.
Angioinvasive Fungal Infection: Pathology and Diagnostic Principles
0:00 Low-Power Observation: Initial low-power view of tissue shows dilated vessels filled with blood or fibrin/thrombus, with minimal inflammation, suggesting a significant vascular compromise.
0:13 High-Power Confirmation of Fungal Angioinvasion: Closer examination reveals distinct fungal hyphae growing directly from and through the vessel walls, definitively identifying an angioinvasive fungal infection, likened to "metastatic fungus."
0:30 Clinical Implications & Case Example: The speaker recounts a past autopsy of an immunocompromised transplant patient who died from widespread Aspergillus infection, spreading from the lung to the GI tract via vessels, highlighting the aggressive and fatal potential of angioinvasive fungi.
0:58 Clinical Presentation in Skin & Diagnostic Approach: Such infections often present as purple/black ischemic necrosis in the skin, evolving into eschars. Biopsies of these lesions necessitate careful examination of vessels for thrombi and fungal invasion, as this is an urgent, acute emergency, alongside other vascular causes of ischemia.
1:27 Microscopic Features in Immunocompromised Patients: While hyphae may be visible on routine H&E stain, special fungal stains are beneficial. In immunocompromised patients, a lack of inflammatory response often results in a "pink, wiped-out" microscopic appearance due to hemorrhage and fibrin without immune cell infiltration.
1:49 Crucial Diagnostic Caveat: Species Identification: Pathologists are cautioned against definitively identifying specific fungal species (e.g., Aspergillus or Mucor) based solely on tissue morphology. A cited AJCP 2010 paper supports this unreliability, particularly given that antifungal treatments can alter fungal morphology. The appropriate diagnosis from tissue is "angioinvasive fungus with septate and acute angle branching."
2:20 Definitive Identification via Culture/PCR: For accurate species identification, culture or PCR testing is essential.
2:26 Case-Specific Outcome: In the particular case discussed, later cultures confirmed the presence of Aspergillus versicolor and other Aspergillus species.