Bowel Obstruction (small and large), Differential Diagnosis

Proximal GI obstruction:
Esophageal disorders/achalasia
Pyloric stenosis

Small bowel obstruction:
Mechanical obstruction of the small intestine or proximal colon due to:
-Adhesions,
-Volvulus,
-Intussusception
-Strangulated hernia
-Crohn’s disease
-Malignancy
Acute paralytic ileus due to:
-GI or abdominal surgery
-Peritoneal irritation, eg, pancreatitis, peritonitis, ruptured viscus
-Severe medical illness, eg, sepsis, electrolyte abnormality
-Drugs, eg, opioids, anticholinergics
Myxedema (hypothyroidism)
Chronic intestinal pseudo-obstruction

Large Bowel Obstruction
Mechanical obstruction of the colon from:
-Malignancy: Colorectal cancer; Extracolonic tumors (peritoneal carcinomatosis, local invasion, lymphadenopathy)
-Colonic Diverticulitis (causing strictures)
-Fecal impaction,
-Volvulus (Cecal volvulus, Sigmoid volvulus)
-Adhesions
-Ischemic stricture
-Intussusception
-Endometriosis
-Inflammatory bowel disease (causing stricture)
-Enterolith
-Hernias
Chronic intestinal pseudo-obstruction
Toxic megacolon: From C. difficile colitis or inflammatory bowel disease.
Megacolon due to:
-Chagas’ disease,
-Aganglionic megacolon (Hirschsprung’s disease),
-multiple sclerosis, sacral nerve damage,
-myxedema (hypothyroidism)
Colonic pseudo-obstruction (Ogilvie’s syndrome) associated with:
-MI or CHF
-Pancreatitis
-Intestinal ischemia
-Cancer
-Respiratory failure
-Stroke or subarachnoid hemorrhage
-Trauma, burns, or postoperative
-Drugs, eg, opioids, anticholinergics
Adynamic ileus

Further Reading
J Clin Imaging Sci. 2017; 7: 15. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5404618/