Final answer:
The disease characterized by a megacolon is Hirschsprung's disease, which is treated with surgery and is different from Crohn's disease and ulcerative colitis, both forms of inflammatory bowel disease.
Step-by-step explanation:
The disease characterized by a megacolon is d. Hirschsprung's disease. Hirschsprung's disease is a condition that affects the large intestine (colon) and causes problems with passing stool. It is present when a baby is born (congenital) and results from missing nerve cells in the muscles of part or all of the baby's colon. A newborn who has Hirschsprung's disease is usually unable to have a bowel movement in the days after birth. In mild cases, the condition might not be detected until later in childhood. Hirschsprung's disease is treated with surgery to bypass or remove the diseased part of the colon.
It is different from Crohn's disease and ulcerative colitis, which are both forms of inflammatory bowel disease that can involve various parts of the gastrointestinal tract but do not cause megacolon as a defining characteristic. Crohn's disease may affect any part of the GI tract and presents with symptoms such as abdominal pain and diarrhea. Ulcerative colitis, on the other hand, is limited to the colon and rectum, causing lower abdominal pain and bloody diarrhea.