Radiation colitis

Colorectal cancer is an adenocarcinoma that arises through the adenoma-carcinoma sequence and presents differently by location, with right-sided tumors causing occult bleeding and iron-deficiency anemia and left-sided tumors causing obstruction and hematochezia. Colonoscopy with biopsy confirms the diagnosis, TNM staging on CT chest/abdomen/pelvis with CEA guides treatment, and management ranges from surgical resection alone for localized disease to adjuvant FOLFOX for node-positive colon cancer, neoadjuvant chemoradiation for rectal cancer, and molecularly targeted systemic therapy for metastatic disease.

Ischemic colitis is the most common form of gastrointestinal ischemia, caused by a nonocclusive low-flow state in colonic microvessels that classically injures the watershed splenic flexure and rectosigmoid junction. Most cases are mild and self-limited with supportive care, but segmental CT thickening with peritoneal signs, pneumatosis, or gangrene demands emergent surgery rather than antibiotics alone.

Acute mesenteric ischemia is an abrupt drop in small-bowel blood flow, most often superior mesenteric artery embolism, presenting as severe abdominal pain out of proportion to an unimpressive early examination. CT angiography confirms the diagnosis, and survival depends on immediate resuscitation, antibiotics, and anticoagulation followed by urgent revascularization or resection before infarction and peritonitis develop.

Chronic mesenteric ischemia, or intestinal angina, is atherosclerotic stenosis of at least two of the three splanchnic vessels producing postprandial epigastric pain, food fear, and weight loss. Diagnosis rests on CT or magnetic resonance angiography showing severe stenosis after alternative causes are excluded, and treatment is revascularization, preferably endovascular stenting, with aggressive atherosclerotic risk-factor control.

Clostridioides difficile infection is toxin-mediated colitis that follows disruption of normal colonic flora, most often by antibiotics, and ranges from watery diarrhea to fulminant colitis with shock, ileus, or megacolon. Diagnosis rests on unformed stool testing (NAAT and/or toxin EIA) in a patient with three or more unformed stools in 24 hours, and treatment is chosen by IDSA/SHEA severity grade, oral vancomycin or fidaxomicin for 10 days, escalating to high-dose vancomycin plus IV metronidazole for fulminant disease.

Ulcerative colitis is a chronic immune-mediated disease of continuous mucosal inflammation that begins in the rectum and extends proximally through the colon, presenting with bloody diarrhea and tenesmus and confirmed by colonoscopy with biopsy. Treatment is stepped by extent and severity from 5-aminosalicylates through corticosteroids, immunomodulators, and biologics, with acute severe disease requiring IV corticosteroids and medical or surgical rescue, and colectomy remains curative.

Microscopic colitis is a cause of chronic watery, non-bloody diarrhea in older women with a grossly normal colonoscopy, diagnosed only by random colon biopsy showing lymphocytic or collagenous histology. Management starts with stopping culprit drugs and antidiarrheals, then oral budesonide for induction and, if needed, maintenance.

Diverticular bleeding is painless arterial hematochezia from rupture of a vasa recta at the neck or dome of a colonic diverticulum, the most common cause of severe acute lower gastrointestinal bleeding, and it stops spontaneously in about 75% of episodes. Diagnosis rests on hemodynamic triage followed by urgent colonoscopy or CT angiography to localize the source, and management combines resuscitation with a restrictive transfusion threshold, endoscopic hemostasis, and angiographic embolization or surgery for refractory bleeding.

Hemorrhoids are symptomatic engorgement and prolapse of the normal anal vascular cushions, internal above the dentate line causing painless bright-red bleeding and prolapse and external below the dentate line causing pain, especially with thrombosis. Diagnosis is clinical by inspection and anoscopy, and treatment escalates from fiber and topical measures through office procedures such as rubber band ligation to hemorrhoidectomy for advanced or refractory disease.

Anal fissure is a longitudinal tear of the anoderm distal to the dentate line that causes severe pain during and after defecation with bright-red bleeding, most often from hard stool passage and high internal sphincter tone. Diagnosis is clinical on gentle inspection, a posterior midline location is typical, and treatment steps from fiber and topical vasodilators to botulinum toxin and lateral internal sphincterotomy for disease refractory to medical therapy.

Prostate cancer is the most commonly diagnosed cancer in men, usually found through an elevated PSA in an asymptomatic patient, with risk stratified by PSA, Grade Group (Gleason score), and TNM stage. Localized low-risk disease is often managed with active surveillance, while higher-risk and metastatic disease require radiation, surgery, or androgen deprivation therapy escalated through castrate-sensitive and castrate-resistant phases.

Invasive cervical carcinoma is a human papillomavirus-driven squamous or glandular cancer staged by FIGO criteria, treated with fertility-sparing or radical surgery for early disease and cisplatin-based chemoradiation for locally advanced disease.

Acute lower gastrointestinal bleeding is hematochezia from a source distal to the ligament of Treitz, most often diverticular, that requires simultaneous resuscitation and localization because a brisk upper source can masquerade as the same presentation. Colonoscopy after rapid bowel preparation is the first-line diagnostic and therapeutic study in stable patients, while CT angiography localizes active bleeding in unstable or rapidly bleeding patients before catheter embolization or surgery.

Short bowel syndrome is malabsorption from insufficient functional small intestine, usually after massive resection for Crohn disease, mesenteric ischemia, or tumor. Diagnosis rests on residual bowel length and colon continuity; first-line treatment sequences diet, high-dose loperamide, and antisecretory therapy, escalating to parenteral nutrition and teduglutide.