Background: Vascular malformations are characterized by anomalous vascular channels with fragile walls and a propensity to bleed. Arteriovenous malformations (AVMs) in particular have disorganized vascular spaces with intervening fibrosis. Characterization of the structural abnormalities of these vessels has not been comprehensively evaluated. We hypothesize that AVMs are likely to demonstrate altered elastic and collagen fiber organization and distribution, reflecting their fragility, vascular instability, and abnormal development.
Methods: Fifteen AVMs were histologically evaluated by H&E, elastin and trichrome staining. To identify potential differences between extracranial and intracranial AVMs, 5 AVMs were harvested from the brain (n=5) and 10 from extracranial sites involving the skin and deep soft tissue (n=10).
Results: The elastin staining demonstrated reduplication, fragmentation and disruption of internal elastic lamina as well as irregular thickness, and inconsistent vascular density of all AVM specimens. Trichrome staining revealed thickening of the intimal layers of AVM arteries and demonstrated an irregular thickness of venous walls within the malformation and some areas of medial degeneration. Intracranial AVMs are characterized by more intramural inflammation with predominant neutrophil and lymphocyte infiltration. In contrast, extracranial AVMs display more extravascular inflammation with mast cell and neutrophil infiltration. Microvascular proliferations intervening between larger blood vessels were also noted in both types of AVMs, but more obvious in extracranial AVMs.
Conclusion: These observed histologic anomalies of AVMs demonstrate disorganized deposition of elastin and collagen that point to the clinically observed vascular instability and fragility of these lesions.