Mechanical Small Bowel Obstruction: This is the most common cause of bowel obstruction, often due to adhesions from previous surgeries, hernias, or tumors. The likelihood of this diagnosis is high due to its frequency and the typical presentation of abdominal pain, vomiting, and obstipation.

Mechanical Large Bowel Obstruction: Similar to small bowel obstruction but involves the large intestine, often caused by colorectal cancer, volvulus, or diverticulitis. Symptoms can include abdominal pain, constipation, and vomiting.
Adynamic Ileus: A condition where there is a temporary cessation of the normal contractions of the bowel muscles, often following surgery, illness, or medication use. It presents with similar symptoms to mechanical obstruction but without a physical blockage.
Pseudo-obstruction: A condition that mimics the symptoms of bowel obstruction without any physical blockage, often seen in patients with chronic illnesses or those taking certain medications.

Volvulus: A condition where a portion of the intestine twists around its base, cutting off blood supply. It's less common but can lead to ischemia and necrosis if not promptly treated.
Intussusception: A condition where a part of the intestine slides into an adjacent part, potentially cutting off blood supply. It's more common in children but can occur in adults, often associated with a lead point like a tumor.
Ischemic Bowel: Reduced blood flow to the bowel can cause symptoms similar to obstruction and can lead to necrosis if not addressed promptly.
Incarcerated or Strangulated Hernia: A hernia that becomes trapped and cuts off blood supply to the intestine, which is a surgical emergency.

Internal Hernia: A rare condition where intestine herniates through a defect within the peritoneal cavity, which can cause obstruction.
Gallstone Ileus: A rare condition where a gallstone enters the intestine through a fistula and causes a mechanical obstruction.
Foreign Body Obstruction: Though more common in children, adults can also experience obstruction due to ingestion of foreign bodies.
Inflammatory Bowel Disease: Conditions like Crohn's disease can cause strictures that lead to bowel obstruction, though this is less common as a presenting symptom.