What is Polypoid Low-Grade Dysplasia similar to Tubular Adenoma?

Polypoid Low-Grade Dysplasia Similar to Tubular Adenoma

Polypoid low-grade dysplasia similar to tubular adenoma refers to a raised dysplastic lesion in inflammatory bowel disease (IBD) that histologically resembles a sporadic tubular adenoma but arises in the context of chronic inflammation. These lesions are also known as adenoma-like dysplasia-associated lesions or masses (adenoma-like DALMs) 1.

Histopathological Features

Polypoid low-grade dysplasia in IBD shares several morphological features with sporadic tubular adenomas:

• Glandular architecture resembling tubular adenomas 1
• Neoplastic crypt cells that are elongated and crowded
• Hyperchromatic nuclei that maintain polarity with respect to the basement membrane
• Low-grade dysplastic changes with preserved architecture 1

However, several distinguishing features may help differentiate IBD-related polypoid dysplasia from sporadic adenomas:

• IBD-related features 1:
  • Occurs in younger patients (typically <50 years)
  • Associated with longer disease duration (>10 years)
  • More prominent villous architecture
  • Mixture of normal and dysplastic epithelium at the surface
  • Increased inflammation within the polyp
  • Presence of dysplasia in the stalk (if pedunculated)
  • Higher frequency of p53 mutations and lower frequency of KRAS mutations
  • May have associated flat dysplasia in surrounding mucosa

Clinical Significance and Management

The distinction between polypoid low-grade dysplasia similar to tubular adenoma (adenoma-like DALM) and non-adenoma-like DALM is crucial for patient management:

1. Adenoma-like DALMs 1:

   • Can be managed with complete polypectomy and continued surveillance
   • Lower risk of progression to cancer compared to non-adenoma-like DALMs
   • Requires careful examination of surrounding flat mucosa to rule out flat dysplasia

2. Non-adenoma-like DALMs 1:

   • Strong association with synchronous and metachronous carcinoma (38-83%)
   • Require colectomy due to high risk of cancer
   • Present as velvety patches, plaques, irregular bumps, nodules, or broad-based masses

Important Diagnostic Considerations

• Expert pathologist review is essential: Inter-observer agreement is poor for low-grade dysplasia, making confirmation by an expert GI pathologist recommended 1

• Sampling of surrounding mucosa: Critical to obtain samples of the surrounding non-elevated mucosa to determine if flat dysplasia is present, which would suggest IBD-related dysplasia rather than a sporadic adenoma 1

• Molecular markers: Co-expression of p53 and AMACR may indicate higher risk of progression to advanced neoplasia (86% vs. 27% without co-expression) 1

Surveillance and Follow-up

For patients with polypoid low-grade dysplasia similar to tubular adenoma:

• Complete excision is necessary, as incomplete removal of raised adenoma-like dysplasia is associated with a high rate of progression to cancer 1

• More intensive surveillance is recommended for distal lesions, as distal low-grade dysplasia progresses more rapidly to cancer than proximal low-grade dysplasia 1

• Even subtle villous changes (1-20%) may indicate increased malignant potential, as these lesions show molecular features characteristic of more advanced tubulovillous adenomas 2

Pitfalls to Avoid

1. Misclassification: Tubular adenomas are often misclassified as tubulovillous or villous adenomas (35% of readings), which can affect surveillance recommendations 3

2. Missing high-grade dysplasia: High-grade dysplasia is correctly identified in only 47% of cases, missed in 31%, and overcalled as invasive cancer in 22% 3

3. Incomplete excision: Ensure complete removal of the lesion, as incomplete excision significantly increases cancer risk 1

4. Neglecting surrounding mucosa: Always sample and examine the surrounding flat mucosa for dysplasia 1