Pathology Cheat Sheet
Map the Intestinal Pattern
Intestinal inflammation for NEET-PG: ileocaecal TB, Crohn vs ulcerative colitis, crypt abscesses, adenoma-carcinoma sequence, APC, and Lynch syndrome.
MedNext Academy | 3 min read
Map the Intestinal Pattern
Intestinal inflammation for NEET-PG: ileocaecal TB, Crohn vs ulcerative colitis, crypt abscesses, adenoma-carcinoma sequence, APC, and Lynch syndrome.
Intestinal tuberculosis, inflammatory bowel disease, and colorectal carcinoma, distinguished by distribution, depth, and molecular pathway.
High-yield lines
- Intestinal tuberculosis favours the ileocaecal region and shows caseating granulomas with confluent transverse ulcers.
- Crohn disease shows non-caseating granulomas, transmural inflammation, skip lesions, and a cobblestone mucosa.
- Crohn disease can affect any part of the gut from mouth to anus, most often the terminal ileum, with fistulae and strictures.
- Ulcerative colitis is continuous mucosal inflammation beginning in the rectum and extending proximally.
- Ulcerative colitis shows crypt abscesses, pseudopolyps, and a limited depth of injury without granulomas.
- Toxic megacolon and increased colorectal cancer risk are complications of ulcerative colitis.
- Colorectal adenocarcinoma arises through the adenoma-carcinoma sequence driven by APC, KRAS, and TP53 mutations.
- APC mutation is the earliest event in the classic adenoma-carcinoma sequence.
- The serrated pathway is driven by BRAF mutation and CpG island methylation.
- Left-sided colon cancers tend to cause obstruction, while right-sided cancers tend to cause iron deficiency anaemia.
- Familial adenomatous polyposis results from germline APC mutation with numerous colonic adenomas.
- Lynch syndrome results from defective DNA mismatch repair causing microsatellite instability.
Mapped competency codes
- PA24.5
- PA24.6
- PA24.7
Continue into the full chapter
This summary maps to PA24-gastrointestinal-tract.
Frequently Asked Questions
How is Crohn disease distinguished from ulcerative colitis?
Crohn disease has transmural inflammation, skip lesions, and non-caseating granulomas anywhere in the gut, while ulcerative colitis has continuous mucosal inflammation from the rectum with crypt abscesses and no granulomas.
What is the classic molecular sequence of colorectal cancer?
The adenoma-carcinoma sequence, beginning with APC mutation and progressing through KRAS activation to TP53 loss.
How does intestinal tuberculosis differ from Crohn disease histologically?
Intestinal tuberculosis shows caseating granulomas, whereas Crohn disease shows non-caseating granulomas.
How do right-sided and left-sided colon cancers present?
Right-sided cancers tend to cause occult bleeding and iron deficiency anaemia, while left-sided cancers tend to cause obstruction and altered bowel habit.
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