How does Crohn's disease affect the intestines?

During the initial stages of the disease, small, shallow and scattered ulcerations (also known as erosions which are crater-like), will form on the bowel’s inner surface. These ulcerations are known as aphthous ulcers and in time they will grow to be larger and deeper as they ultimately form true ulcers, which are basically deeper than regular erosions. These ulcers then cause the bowel to stiffen and scar. As Crohn's disease progresses, the intestine (bowel) will increasingly become narrowed and eventually, it will become obstructed. The deep ulcers can result in perforations, which are like punctures in the bowel wall. From here, bacteria found in the bowel can spread and infect the surrounding organs, as well as the abdominal cavity.

When Crohn's disease results in the small intestine being obstructed and the flow of contents through it cease, the obstruction is sometimes the result of poorly digested vegetables or fruit that create a plug in the segment that has already been narrowed. When this obstruction occurs, the process of digestion is impacted as food and gas cannot pass from the stomach and small intestine through to the colon. This results in the severe abdominal pain and cramps, as well as nausea and vomiting. The small intestine is narrower than the colon, thus, obstruction is more likely to occur.

Ulcers that developed may form deeply within the tissue lining, creating a tunnel (puncture hole) between the adjacent organs and the intestine. If one of these tunnels reaches through the empty space of an adjacent organ (within the abdominal cavity), then an abscess known as an abdominal abscess will form (this is a collection of pus that is infected). If an individual has an abdominal abscess, then they may develop high fevers, abdominal pain and tenderness of the abdominal masses.

The types of fistulas:

• A fistula (tunnel or channel) is the result of the deep ulcer forming a puncture hole in a surrounding organ.
• When a fistula forms between the intestine and the bladder, known as an enteric-vesicular fistula, this can result in the patient suffering from UTIs (urinary tract infections) on a frequent basis, as well as faeces and gas passing during urination.
• If an enteric-cutaneous fistula develops (this is a fistula between the intestine and the skin), this will cause mucous and pus to emerge from a tiny and painful opening in the abdomen’s skin.
• If a colonic-vaginal fistula forms (this is a fistula between the colon and the vagina), this can cause faeces and gas to emerge from the vagina.
• If an anal fistula forms (this is a fistula between the intestine and the anus), this will lead to the discharge of pus and mucous from the opening of the fistula around the area of the anus.