Bacillary Angiomatosis: Dermatopathology Pearls

• 0:30 Clinical Presentation: Often presents as a red or purple nodule, particularly on the leg of an older adult.
• 0:41 Key Differential Diagnoses: Kaposi sarcoma, infectious granuloma, epithelioid sarcoma, tuberculosis.
• 1:55 Cellular Characteristics: Cells resemble histiocytes, with blood vessel lumens present.
• 2:49 Diagnostic Field: Highlighted field showing the characteristic features of bacillary angiomatosis.
• 2:52 Diagnosis: Bacillary angiomatosis, a rare condition caused by Bartonella henselae (the same bacteria responsible for cat-scratch disease).
• 3:28 Fibrin and Fibrinoid: The central pink homogeneous material is identified as fibrin and fibrinoid, not necrosis.
• 4:22 Identifying the Organism: Key diagnostic feature is the presence of hazy, fluffy purple colonies of Bartonella organisms, too small to see individually with a light microscope.
• 5:01 Staining Considerations: Warthin-Starry stain for highlighting the organism is often unreliable and not routinely used. PCR for Bartonella can be considered for confirmation.
• 5:30 Patient Characteristics: Though commonly associated with AIDS patients, this case was found in an older adult with potential immunosuppression from age or medication.
• 5:54 Diagnostic Pearls:
  • The colonies have a distinct hazy look.
  • Lesions can mimic pyogenic granuloma (lobular capillary hemangioma). If inflammation is unusual for pyogenic granuloma, consider bacillary angiomatosis.
  • Vessels in bacillary angiomatosis can become atypical, potentially leading to misdiagnosis as angiosarcoma.
• 7:00 Importance of Learning from Past Mistakes: The video emphasizes the value of learning from misdiagnoses made by experienced pathologists in the past, highlighting that even experts can encounter challenges. This type of storytelling is crucial for education and improving patient care.