The Bowel Obstruction Table
BOWEL OBSTRUCTIONS
The flow must go on
A bowel obstruction refers to the cessation of digested food through the intestines, similar to a traffic jam. Food and air build up behind the lesion, resulting in abdominal pain, tenderness and distension. The blockage prevents food or air from traveling downstream, resulting in a complete inability to poop or fart (obstipation). Bowel obstructions are easily spotted on abdominal x-rays because the loops of bowel are dramatically dilated. If they stretch too much, they can pop resulting in fatal peritonitis and internal bleeding. 75% occur in the small bowel, 25% in the large bowel. Even though there are many different types of bowel obstructions, most of them have the same symptoms and physical exam.
Small Bowel Obstructions (SBO) are the most common type. They are usually caused by adhesions, which are bands of fibrous scar tissue that pop up after an abdominal surgery. Adhesions can strangulate the bowel. Although you can surgically remove adhesions, they’ll just grow back. Prior abdominal surgery is the biggest risk factor for an SBO. Other mechanical forces like cancers and hernias can squish the bowel too. Bowel sounds are initially high-pitched, because the bowel works extra hard in an attempt to squeeze material past the lesion. But as the proximal bowel begins to dilate, the delicate bowel circulation is compressed, and ischemia sets in. Once the bowel starts to die, the bowel sounds quiet. There will be dilated loops of bowel on imaging, with an abrupt cutoff point and no air in the colon. There are often air fluid levels (flat lines, see image on right). The management of an SBO is a little bit complicated. All patients are kept NPO, and vomiting patients even have their stomach decompressed with an NG tube. Some simple SBOs are simply observed, but more complicated ones require surgery.
Partial SBOs refer to a lesion that only partially obstructs the bowel lumen. Unlike with a complete SBO, air and liquid can bypass the lesion. That enables them to pass gas and diarrhea. These are usually managed conservatively with bowel rest and observation.
VOLVULUS
Balloon animal bowel
A volvulus refers to a bowel that’s twisted itself into a knot. This blocks the gut lumen and the fragile mesenteric circulation. The bowel will slowly strangle and infarct unless surgically corrected. When the large bowel is tied into a pretzel, the trapped bacterial flora continue to produce gasses like methane, resulting in a big painful air-filled cavity. There are three common types.
A sigmoid volvulus refers to twisting of the sigmoid colon. It’s usually seen in older adults with a long history of constipation. With constipation, the sigmoid colon is stretched by big build ups of poop, resulting in extra redundant tissue. On an abdominal x-ray, the bubble typically looks like a large coffee bean. If the patient has stable vital signs and no peritoneal signs, you should attempt to untwist the knot by advancing a flexible sigmoidoscopy scope up their rear end (90% success rate). But if they are unstable, you have to do surgery to remove the affected piece of bowel.
A cecal volvulus refers to twisting of the cecum. It’s a little less common than the sigmoid volvulus. The dilated knot is more likely to start in the RLQ and point up to the left. Will require surgery. I don’t have a lot more to add.
A midgut volvulus refers to twisting of the small intestine. It’s only seen in children whose gut didn’t properly rotate in utero. Symptoms usually appear in the first two weeks of life. Their vomiting will be bilious, since the knot is located downstream from the duodenum. Surgery is required.
Coffee bean sign (sigmoid)
The unhealthy gray sac on top is a volvulus. The pink tube below is healthy.
GUT PARALYSIS
Goodnight moon, goodnight jejunum
An ileus refers to paralysis of the entire intestine. It usually occurs after surgery. General anesthesia not only sedates the brain, but the enteric nervous system too. Sometimes these enteric nerves take a few days to “wake up” after surgery. It should make sense why bowel sounds are always quiet with an ileus. Most surgeons will keep you admitted in the hospital until you start to fart! Most ileuses are treated with patience and supportive measures. On abdominal x-ray, both small bowel and large bowel will be uniformly dilated. There won’t be any air-fluid levels.
Ileus
Ogilvie’s Syndrome is an idiopathic dilatation of the colon without an anatomical lesion. It’s also called a pseudo-obstruction since there isn’t an apparent cause. It’s seen in the very old who undergo surgery or become very ill. It’s probably not due to a single problem, but rather a confluence of multiple factors affecting the enteric nervous system. Things like electrolyte abnormalities, autonomic dysregulation, inflammatory cytokines, chronic constipation, opioids, anticholinergics, prior surgeries, natural senescence and a sedentary lifestyle are likely contributory. Typically, the ascending colon dilates. The management is pretty conservative because these patients are typically so fragile already. They are kept NPO, decompressed with NG and rectal tubes, and Neostigmine (cholinergic) is sometimes given to wake the bowel up.
Ogilvie’s
TOXIC MEGACOLON
Febrile large bowel obstruction
A toxic megacolon refers to a necrotic dilated large intestine causing systemic signs like fever. When the large intestine walls undergo a lot of damage, sometimes the ganglionic neurons responsible for bowel constriction are destroyed. This causes the colon to maximally dilate. Autonomic instability ensues from the massive inflammatory insult, which results in a fever and possibly hypotension. Toxic megacolon only occurs in diseases where the colon is heavily inflamed, like ulcerative colitis or C. difficile colitis. If the cause is UC then they’ll benefit from steroids. If the cause is C. diff then they may improve with antibiotics. But many cases only resolve with a colectomy.
Toxic megacolon seen in a UC patient, notice the lead pipe descending colon
PEDIATRIC BOWEL OBSTRUCTIONS
Bwockages
Intussusception refers to telescoping of bowel. It almost exclusively occurs in kids aged 6 months to 2 years old. Bowel only telescopes if it “catches” on something. A peristaltic wave powers the invagination of the bowel into itself. We use the term lead point to refer to any object that catches the bowel. Usually the ileum is dragged into the cecum. Examples of a lead point include Meckel’s diverticula, swollen Peyer’s patches (lymphoid hyperplasia) and tumors. Peyer’s patches often swell up during a viral gastroenteritis. The inner segment’s lumen and vasculature are crushed, causing obstruction and ischemia. The telescope begins to bleed, producing a currant jelly stool. You can sometimes palpate the intussuscepted bowel as a RLQ mass, but the diagnosis is confirmed with imaging with a CT or ultrasound (target sign). An air enema can sometimes unfold the lesion, but if this doesn’t work they require surgery. Some intussusceptions spontaneously unfold and refold, resulting in episodic abdominal pain and fussiness in a child.
Intussusception
Target sign
A meconium ileus refers to a newborn that doesn’t pass its first poop in the first 24 - 48 hours of life. There are two major causes.
Cystic Fibrosis causes a microcolon and extra-thick poop. Treat with a water soluble enema. See the respiratory section for more information.
Hirschsprung Disease refers to aganglionic megacolon. In other words, a baby’s rectosigmoid colon lacks inhibitory neurons. What happens is that neural crest cells somehow fail to migrate to the sigmoid. Without inhibition, the sigmoid maximally constricts and blocks the colon. Pressure builds up behind the blockage, resulting in a megacolon and a dilated belly. You should do a digital rectal exam. This child will have an increased rectal tone, and poop will squirt out around your finger (a positive squirt sign). Some cases take several months to present. It’s seen in Down syndrome. Treat by cutting out the sigmoid.