4- Small_large bowel (2)

Fistulas and Complications in Crohn's Disease

Fistulas can develop between loops of bowel and may also involve other structures such as the urinary bladder, vagina, and perianal skin. Common complications of Crohn's Disease (CD) include perforations and peritoneal abscesses. Fibrosing strictures are particularly common in the terminal ileum and often require surgical resection to mitigate associated risks. Additionally, patients with long-standing colonic Crohn's disease have an increased risk of developing colonic adenocarcinoma. Furthermore, several extra-intestinal manifestations can arise, such as uveitis, arthritis, sacroiliitis, ankylosing spondylitis, erythema nodosum, and clubbing of the fingertips, which may occur even before gastrointestinal symptoms are diagnosed.

Ulcerative Colitis Overview

Ulcerative Colitis (UC) is a condition restricted to the colon and rectum. Like CD, UC can present with similar extra-intestinal manifestations—such as arthritis, sacroiliitis, ankylosing spondylitis, uveitis, skin lesions, and primary sclerosing cholangitis. Notably, UC involves the rectum invariably and extends in a continuous proximal manner, affecting part or all of the colon, termed pancolitis. In contrast to CD, UC does not exhibit skip lesions. Specific types of involvement include ulcerative proctitis, which is disease of the rectum only, or ulcerative proctosigmoiditis, which involves the rectosigmoid region. In severe cases of pancolitis, mild mucosal inflammation of the distal ileum, identified as backwash ileitis, can sometimes be present despite the small intestine primarily remaining unaffected.

Histological and Gross Features of Ulcerative Colitis

Upon gross examination, the mucosa in UC appears red and granular or may exhibit extensive ulcers. There is often a stark transition between diseased and unaffected areas of the colon, with ulcers oriented along the bowel's axis, differing from the serpentine ulcers typically seen in CD. Regenerating mucosa may form isolated bulging islands, known as pseudopolyps. Contrary to CD, UC does not present with mural thickening; the serosal surface is generally normal, and strictures do not occur. However, inflammation and inflammatory mediators can impair the muscularis propria, leading to conditions like colonic dilation and toxic megacolon, which is associated with a high risk of perforation. Histologically, similarities to CD exist with inflammatory infiltrates, crypt abscesses, crypt distortion, and Paneth cell metaplasia; however, skip lesions are absent, and inflammation is typically confined to the mucosa and superficial submucosa, with rare involvement of the muscularis propria and no granulomas present.

Non-Neoplastic Polyps

Colonic polyps are prevalent in various parts of the gastrointestinal tract, particularly the colon. They can be categorized based on morphology into sessile (without stalks) and pedunculated (with stalks). Non-neoplastic polyp types include:

  1. Inflammatory Polyps: Commonly related to solitary rectal ulcer syndrome, presenting with rectal bleeding, mucus discharge, and an inflammatory lesion on the anterior rectal wall.

  2. Hamartomatous Polyps: These may be sporadic or familial, consisting of tumor-like growths of disorganized mature cell types. The most common variant is juvenile polyps, typically found in children under 5 years of age, which present with rectal bleeding. Sporadic juvenile polyps tend to be solitary, whereas juvenile polyposis syndrome features between 3 to 100 polyps, increasing the risk of colonic adenocarcinoma. Juvenile polyps are usually pedunculated, reddish, less than 3 cm in diameter, and display characteristic cystic spaces microscopically.

Peutz-Jeghers Polyps and Hyperplastic Polyps

Peutz-Jeghers polyps are another type of hamartomatous polyp associated with Peutz-Jeghers syndrome, a rare autosomal dominant condition marked by multiple gastrointestinal hamartomatous polyps and mucocutaneous hyperpigmentation, along with an increased risk of various extra-intestinal malignancies. Grossly, these polyps are large, pedunculated, and lobulated. 3. Hyperplastic Polyps: Common in the colon, they result from decreased epithelial cell turnover and delayed shedding of surface epithelial cells, leading to a build-up of goblet cells. These polyps have no malignant potential and are typically found in the left colon, measuring less than 5 mm and appearing as smooth, nodular mucosal protrusions.

Neoplastic Polyps

Typical adenomas range from 0.3 to 10 cm and may be either pedunculated or sessile. Histologically, they feature epithelial dysplasia characterized by nuclear hyperchromasia and stratification, with classifications into tubular, tubulovillous, or villous types. Tubular adenomas are generally small and pedunculated, while villous adenomas are larger, sessile and covered with slender villi. Tubulovillous adenomas display a mixture of both tubular and villous components. Although the majority of colorectal adenomas are benign, a small percentage may contain invasive cancer at detection, with size being a critical characteristic that correlates with malignancy risk.

Familial Syndromes and Colorectal Cancer

Certain familial syndromes, including Familial Adenomatous Polyposis (FAP) and Adenomatous Polyposis Coli (APC), are linked to increased colon cancer risk. FAP is an autosomal dominant disorder characterized by the appearance of numerous polyps during teenage years due to APC gene mutations. Classic FAP requires a diagnosis of at least 100 polyps, with some individuals potentially harboring thousands. These adenomas appear morphologically indistinguishable from sporadic adenomas, but colorectal adenocarcinoma is virtually certain in untreated FAP patients, necessitating prophylactic colectomy for those with known APC mutations.

Colon Cancer Morphology

Colorectal tumors manifest differently based on their location. Proximal colon tumors often grow as polypoidal exophytic masses along one side of the bowel wall, rarely obstructing the lumen. In contrast, distal colon tumors typically present as annular lesions that can narrow the lumen significantly, potentially leading to obstruction. Histologically, these tumors consist of infiltrating malignant glands formed of tall columnar cells akin to dysplastic epithelium present in adenomas. Poorly differentiated tumors may feature scant gland formation, with some tumors producing abundant mucin, leading to poor prognosis outcomes. Tumors may also comprise signet ring cells, further resembling gastric cancer characteristically.

Acute Appendicitis Findings

In cases of early acute appendicitis, there is an observable congestion of vessels coupled with modest neutrophilic infiltration across all layers of the appendiceal wall. In severe presentations, focal abscesses can form, leading to acute suppurative appendicitis, which may progress to acute gangrenous appendicitis resulting in rupture and peritonitis. Clinically, acute appendicitis is characterized by periumbilical pain that migrates to the right lower quadrant, along with nausea, vomiting, low-grade fever, and slight elevation in white blood cell count. A prominent physical sign is McBurney's sign, which indicates deep tenderness located two-thirds of the way from the umbilicus to the right anterior superior iliac spine.