Small Bowel Obstruction, Ileus & Hernias

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Pathophysiology

Summary

Small bowel obstruction (SBO) and related pathologies present a variety of challenges in diagnosis and treatment. Small bowel obstruction is most commonly caused by abdominal adhesions, often a consequence of prior abdominal surgery. Symptoms include nausea, vomiting, colicky abdominal pain, and obstipation. X-ray may reveal distended bowel loops, air-fluid levels, and a transition point at the location of obstruction.

Differential diagnosis includes ileus, which mimics the symptoms of small bowel obstruction but arises from hypomotility of the bowel. Ileus is associated with surgery, medications, or systemic conditions like diabetes and sepsis. Unlike small bowel obstruction, ileus is characterized by uniformly dilated bowel including the colon and rectum, as well as diminished or absent bowel sounds.

Superior mesenteric artery (SMA) syndrome involves compression of the third portion of the duodenum between the aorta and the SMA, usually induced by rapid weight loss, and often manifests as recurrent postprandial pain. Intussusception involves telescoping of one segment of bowel into another, commonly at the ileocecal junction. It may be triggered by lead points like hyperplastic lymphoid tissue or Meckel's diverticulum, presenting with ‘currant jelly’ stools and a palpable ‘sausage-shaped’ mass.

Various types of hernias also contribute to small bowel pathology. Hernias occur due to weakening of the fibromuscular tissues, and are categorized based on their anatomical location. Direct inguinal hernias pass through Hesselbach's triangle, while indirect inguinal hernias move through the inguinal canal. Femoral hernias pass through the femoral canal and are more common in women. Strenuous exercise, chronically elevated intra-abdominal pressure, and old age are common risk factors. Complications include incarcerated hernias and bowel strangulation, which can cause necrosis and perforation.

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FAQs

What is the primary cause of small bowel obstruction?

Adhesions are the most common cause of small bowel obstruction, which are most commonly associated with prior abdominal surgery. These are most commonly formed following abdominal surgery. They cause mechanical constriction of the bowel, leading to obstruction. Other causes can include tumors in the small bowel.

What clinical features are associated with small bowel obstruction?

Patients with small bowel obstruction typically present with nausea and vomiting, along with colicky abdominal pain. Obstruction can also cause obstipation, which is an inability to pass flatus or stool. Abdominal distension and a tympanitic abdomen may also be present due to a backup of gas in the intestines, and a high-pitched “tinkling” sound is often heard on abdominal auscultation, as a result of abnormal peristalsis. X-ray displays a “transition point” at the location of obstruction where dilated proximal bowel meets normal distal bowel.

What is ileus and how does it present clinically?

Ileus is a condition characterized by hypomotility of the bowel. This can cause similar symptoms to small bowel obstruction. However, in ileus, the entire bowel, including the colon and rectum, is uniformly dilated. Patients with ileus may present with diminished or absent bowel sounds due to decreased peristalsis. Common causes of ileus can include recent surgery, certain drugs, sepsis, and diabetes.

What is an intussusception and how is it typically diagnosed?

Intussusception occurs when a segment of proximal bowel telescopes beneath more distal bowel. This can cause bowel ischemia and necrosis due to impaired venous return. It commonly presents with ‘currant jelly’ stools, which are bloody and contain mucus. A palpable ‘sausage-shaped' mass in the RUQ may be found on examination. It can usually be diagnosed via abdominal ultrasound, which will reveal a ‘target’ or ‘bull's eye’ appearance due to the telescoped bowel.

What is a hernia and what conditions are associated with an increased risk in their development?

Hernias occur when intra-abdominal contents protrude through a defect as a result of weakening of fibromuscular tissues. Conditions that increase intra-abdominal pressure, such as strenuous exercise, heavy lifting, chronic cough, constipation, and pregnancy, can put an individual at a higher risk of developing a hernia. They are commonly seen in older age due to decreased tissue strength and are seen more frequently in men.