• Nodular to dome-shaped/polypoid, dermal-based vascular proliferation
• May have overlying epidermal ulceration and collarette (similar to pyogenic granuloma)
• Vessels are arranged in loose lobular configuration
• Endothelial cells show mild enlargement and oval to epithelioid shape
• No significant cytologic atypia or atypical mitotic activity
• Background stroma shows fibrosis, edema, and mixed inflammatory infiltrate with many neutrophils
• Infiltrate is composed of numerous neutrophils with nuclear dust, macrophages, lymphocytes, and focal collections of basophilic granular material (bacterial collections)
Top Differential Diagnoses
• Pyogenic granuloma
Ulceration and peripheral epidermal collarette are typically present but lack organisms of BA
• Kaposi sarcoma
Dermal tumor composed of slit-like vessels lined by atypical spindle cells
Bacillary Angiomatosis Low-power examination of bacillary angiomatosis (BA) demonstrates a superficial dermal proliferation of blood vessels in a lobular configuration associated with edema and inflammation.
High Magnification of Bacillary Angiomatosis High magnification of BA demonstrates a proliferation of small blood vessels with swollen endothelial cells surrounded by edema and inflammation .
Warthin-Starry Stain in Bacillary Angiomatosis Warthin-Starry silver stain preparation shows numerous clusters of bacterial organisms around blood vessels.
Warthin-Starry Stain at High Magnification Warthin-Starry stain demonstrates positive staining of numerous clusters and single bacterial organisms.
TERMINOLOGY
Abbreviations
• Bacillary angiomatosis (BA)
Synonyms
• Epithelioid angiomatosis
Definitions
• Reactive vascular proliferation associated with Bartonella species bacterial infection
ETIOLOGY/PATHOGENESIS
Infectious Agents
• Caused by infection with Bartonella (gram-negative coccobacilli) species, usually Bartonella henselae or Bartonella quintana
Most patients have history of cat exposure (and may have preceding scratch or bite)
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associated with edema and inflammation.
surrounded by edema and inflammation 
.
around blood vessels.
and single bacterial organisms.
