Intestinal Pathologies

Ischemic, Structural, Misc. Blood flow to the intestines is interrupted. This can cause tissue damage and necrosis, and can lead to death. Recall that, under healthy conditions, the intestines receive 20-25% of cardiac output. Knowing this general arterial pattern can help us identify which vessels and segments of the intestine are involved in ischemia. We draw the aorta, then the stomach, small intestines, and large intestine. The celiac trunk supplies the stomach (and other organs). The superior mesenteric artery supplies the small intestine and proximal large intestine. The inferior mesenteric artery supplies the distal large intestine. Most often due to arterial emboli that become lodged in the superior mesenteric artery. The emboli often originate in the heart, so patients with arrhythmias or heart disease are at increased risk. Be aware that drugs, including cocaine, can cause vasopressin and cause intestinal ischemia. Patients experience sudden, severe abdominal pain, with possible nausea and vomiting. Most often due to atherosclerosis. Patients experience severe stomach pain approximately 20 minutes after eating; this can lead to food avoidance and weight loss. Most common form of intestinal ischemia. Patients have non-specific symptoms of lower abdominal pain and bloody stools. Most cases are nonocclusive and transient. On imaging we'll see "thumbprinting" – a wave-like pattern that looks like someone has pressed their thumb in the wall of the intestine. Thumbprinting reflects the thickening of the bowel wall due to inflammation and edema; it is not specific to colonic ischemia. Colonic ischemia tends to occur at "watershed areas" - the splenic flexure and rectosigmoid junction. These areas receive the most distal branches of the SMA and IMA, and are therefore vulnerable to hypoperfusion. This is a common vascular abnormality in GI tract, characterized by tortuous, dilated, and fragile blood vessels that are visible upon gross inspection as bright red areas. We typically see them in older patients in the right-side colon. Patients may be asymptomatic or experience pain, GI bleeding, and anemia. The etiology of angiodysplasia is unclear, but it is associated with aortic stenosis, von Willebrand disease, end-stage renal disease. Structural abnormalities can lead to bowel obstruction and ischemia. Generally, these pathologies are associated with abdominal pain, cramping, nausea, and vomiting. Occurs when part of the intestine slides (aka, telescopes) into an adjacent section. This usually occurs at the ileocecal junction, when the ileum slides into the large intestine. The mesentery also gets dragged into the bowel, which can cause ischemia and lead to perforation, peritonitis, shock, and death. Intussusception most commonly occurs in children, and is idiopathic. In adults, it is usually due to tumors or other pathologies. The tumor acts as the "lead point," the abnormality that gets trapped and dragged into the adjacent intestinal section. Patients experience episodes of abdominal cramping, with vomiting, bloating, and bloody stool; upon physical examination we might find a "sausage-shaped" mass in the abdomen. Treatment: In stable, non-emergency patients, treatment consists of enema reduction with hydrostatic or pneumatic pressure. Unstable patients, those with perforation, and in cases where enema reduction isn't successful will need surgery. Occurs when a loop of intestine and mesentery twists around itself and causes obstruction and potential ischemia (latin "volvere" = to roll or twist). This is a rare but serious phenomenon. Patients have distended and tympanic abdomens with tenderness and pain, vomiting, constipation, and bloody stool; symptoms are usually progressive, and can lead to perforation, peritonitis, and shock. In adults, the sigmoid colon and cecum are most commonly involved; in children, the small intestine and stomach are commonly involved. Be aware that there are different types of volvulus: gastric (associated with anatomic abnormalities), midgut (more common in infants/children), sigmoid (coffee-been sign on x-ray, most common in elderly men). Risk factors include intestinal malrotation, enlarged colon, pregnancy, abdominal adhesions. Treatment: in patients without perforation or peritonitis, we can attempt to untwist the segment with flexible sigmoidoscopy. If perforation has occurred, then we need to resection the bowel. Recall that during development the intestines protrude from the abdominal cavity, then returns with a counterclockwise rotation. Review Congenital abnormalities of the GI tract. Most congenital malrotations are the result of incomplete rotation and can produce bowel obstruction from volvulus or from retroperitoneal Ladd bands stretching across the duodenum. Most cases present within the first 5 years, with abdominal pain and vomiting of bile. Surgery to correct the volvulus or release the Ladd bands can be done to prevent ischemia. Be aware that diverticula are common structural abnormalities of the GI tract, but we discuss these elsewhere in our GI path series. Aka, paralytic ileus, functional ileus. Characterized by intestinal hypomobility. Up to 30% of abdominal surgery patients experience ileus within a few days after surgery; other causes of ileus include sepsis, hypokalemia, and drugs (opiates, anticholinergics). The exact pathophysiology is unclear, but it seems that paralysis is due to neuroimmune interactions – for example, abdominal surgery induces inflammatory changes that inhibit gut motility. Patients have distended and tympanic abdomens with bloating and constipation and reduced flatus; on exam, we'll notice reduced or absent bowel sounds. On imaging, look for uniform distribution of gas in the intestine (as we'll learn, this is different from the unequal distribution seen in small bowel obstruction). Patients should receive supportive therapy, including bowel rest and possible nasogastric suction, and treatment for the underlying causes. Ileus usually resolves without surgery. Occurs in infants, especially premature infants who are formula-fed. In these infants, the digestive system microbiome is imbalanced, leading to inflammation and necrosis. Breastmilk seems to protect against this process. There is an inverse relationship between gestational age and timing of symptom onset. Signs and symptoms include sudden onset of feeding intolerance with other nonspecific symptoms: abdominal distention and pain, diarrhea (possibly bloody), and bilious vomiting. Abdominal distention can impair breathing, so look for apnea. In advanced stages, blood pressure falls, and the intestines can perforate from necrosis. On imaging, look for gas within the walls of the intestines (called pneumatosis intestinalis), pneumoperitoneum (caused by perforation), and portal venous gas. We show pneumatosis intestinalis in histologic illustration – note the necrotic villi and gas bubbles in the submucosa. Mechanical blockage that leads to gas and fluid accumulation with intestinal dilation. Most often the result of intraperitoneal adhesions, hernias, tumors. Though rare, small bowel obstructions in newborns is caused by a meconium plug (meconium ileus). Patients have sudden onset of abdominal pain & distention, nausea, and bilious vomiting. Watch for dehydration & electrolyte imbalances due to reflex vomiting, reduced absorption, and increased intestinal secretion proximal to obstruction. Hypovolemia can lead to hypotension, irregular heart beat, altered mental status, oliguria. Blood flow may be compromised, leading to ischemia, necrosis, and perforation. On upright x-ray, we see dilated sections of small bowel with visible air/fluid levels and visible valvulae connivents (plicae circulares). We may also see "gasless abdomen" or "strings of pearls sign" (gas bubbles appear as small bubbles instead of large air/fluid level) (not shown in our diagram). Treatment can include GI decompression with nasogastric tube and bowel rest. If necessary, surgery to get rid of adhesions. For references, see full tutorial.