What is the most likely diagnosis for a 75-year-old man with sudden lower abdominal pain, progressive abdominal distension, nausea, vomiting, absolute constipation, and a massively distended bowel loop on X-ray?

Sigmoid Volvulus

The most likely diagnosis is sigmoid volvulus (Option A), given the classic presentation of a 75-year-old patient with sudden onset lower abdominal pain, progressive distension, absolute constipation, and the pathognomonic X-ray finding of a massively distended bowel loop pointing to the right upper quadrant. 1

Clinical Presentation Supporting Sigmoid Volvulus

The patient's presentation is textbook for sigmoid volvulus:

• Age and demographics: 75-year-old male fits the typical profile, as sigmoid volvulus predominantly affects elderly patients 1
• Sudden onset: The 12-hour acute presentation with sudden lower abdominal pain is characteristic of volvulus rather than the more gradual presentation of malignancy 1
• Absolute constipation: Complete absence of bowel movement and flatus (90% sensitive for large bowel obstruction) strongly suggests mechanical obstruction 1
• Progressive distension: Grossly distended abdomen indicates acute colonic obstruction 1
• Normal bowel sounds: Early in the course, bowel sounds may remain present before progressing to absent sounds with ischemia 1

Radiographic Findings Clinching the Diagnosis

The X-ray description of a "massively distended bowel loop pointing to the right upper quadrant" is the classic "coffee bean sign" or "bent inner tube sign" pathognomonic for sigmoid volvulus 1. This represents the twisted sigmoid colon with its apex pointing toward the right upper quadrant, creating the characteristic appearance that distinguishes it from other causes of large bowel obstruction.

Why Not the Other Options

Rectosigmoid cancer (Option B) typically presents with:

• Gradual onset of symptoms over weeks to months, not sudden 12-hour presentation 1
• History of bloody stools or change in bowel habits preceding acute obstruction 1
• Would not produce the characteristic massively distended single loop pointing to RUQ 1

Closed loop obstruction (Option C) refers to:

• Primarily a small bowel phenomenon where a segment is obstructed at two contiguous points 2, 3
• CT findings show U or C-shaped loops with radial distribution of mesenteric vessels 3, 4
• The clinical description and X-ray findings point to large bowel pathology, not small bowel 1

Acute sigmoid diverticulitis (Option D) presents with:

• Localized left lower quadrant pain and tenderness 1
• Fever and signs of inflammation/infection 1
• Does not typically cause complete obstruction with absolute constipation and massive distension 1
• Would not produce the characteristic X-ray finding described 1

Critical Next Steps

Immediate management priorities include:

• CT scan with IV contrast to confirm diagnosis, assess for ischemia/perforation, and guide intervention (sensitivity >90% for large bowel obstruction) 1
• Fluid resuscitation and correction of electrolyte abnormalities (particularly potassium) 1, 5
• Nil per os and nasogastric decompression 1, 5
• Urgent surgical consultation as sigmoid volvulus requires definitive intervention 1

Treatment Approach

• Endoscopic decompression is first-line if no signs of peritonitis or ischemia, with success rates of 70-80% 1
• Emergency surgery is mandatory if signs of perforation, peritonitis, or failed endoscopic decompression 1
• Elective sigmoid resection should follow successful decompression to prevent recurrence (high recurrence rate without definitive surgery) 1

Common Pitfalls to Avoid

• Delaying CT imaging: Plain X-rays alone have limited sensitivity and specificity; CT is essential for confirming diagnosis and detecting ischemia 1
• Missing signs of strangulation: Fever, tachycardia, peritoneal signs, elevated lactate, or leukocytosis indicate ischemia requiring immediate surgery rather than endoscopic decompression 1, 5
• Assuming cancer without imaging: The acute presentation and characteristic X-ray findings make volvulus far more likely than malignancy in this scenario 1