Vascular intrusion is a mimic of true vascular invasion in large bowel adenomatous polyps.

Aims: 'Vascular intrusion' is a proposed but poorly recognised phenomenon of colorectal adenomas whereby dysplastic epithelium is forced into blood vessels. This study aimed to validate its existence and to characterise histological features that distinguish it from true vascular invasion.

Methods and results: Three gastrointestinal pathologists independently assessed 38 colorectal polyps showing possible vascular intrusion as two cohorts. After the cohort A (15 cases) assessment, the pathologists met to decide upon diagnostic criteria and consensus diagnoses. They met again after the cohort B (23 cases) assessment to establish final consensus diagnoses. Histological features found to favour vascular intrusion were: absence of adenocarcinoma; presence of adjacent epithelial misplacement; low-grade cytology; crush artefact; and presence of lamina propria among the intravascular glands. The proportion of cases where all three pathologists independently agreed upon diagnoses of vascular intrusion versus vascular invasion increased from 53% for cohort A to 74% for cohort B. However, while there were final consensus diagnoses of vascular intrusion and vascular invasion for 21 and seven cases, respectively, the assessors were unable to agree upon either diagnosis for 10 cases. Follow-up of 17 patients who had undergone polyp resection > 3 years previously (including eight with consensus diagnoses of vascular intrusion) did not demonstrate recurrent or metastatic colorectal carcinoma.

Conclusions: Vascular intrusion may be caused by forcing of adenoma into vessels as part of epithelial misplacement or during resection or laboratory processing of the polyp. Histological features of the intravascular glands and surrounding adenoma help to distinguish this benign/artefactual phenomenon from true vascular invasion.