What are the potential causes and management options for left flank pain with abdominal distension?

Left Flank Pain with Abdominal Distension

CT abdomen and pelvis with IV contrast is the diagnostic test of choice and should be obtained urgently to identify the underlying cause, with sigmoid volvulus, bowel obstruction, and diverticulitis being the most likely diagnoses requiring immediate intervention. 1

Immediate Clinical Assessment

Critical History and Physical Examination Elements

• Assess for peritonitis immediately: Check for diffuse tenderness, guarding, rebound tenderness, or absent bowel sounds, which indicate possible perforation requiring emergent surgery 2
• Evaluate vital signs: Tachycardia, hypotension, or altered mental status suggest bowel ischemia, perforation, or septic shock requiring immediate surgical consultation 1
• Examine for asymmetric gaseous distention: Asymmetric abdominal distention with emptiness of the left iliac fossa is pathognomonic for sigmoid volvulus 1, 3
• Perform digital rectal examination: An empty rectum is commonly found in sigmoid volvulus 1, 3
• Assess bowel sounds: Diminished or absent bowel sounds suggest advanced obstruction or peritonitis 1, 3

Key Historical Features

• Duration and progression of symptoms: Sigmoid volvulus typically presents 3-4 days after symptom onset in Western countries, with abdominal pain, constipation, and vomiting 1
• Previous episodes: 30-41% of sigmoid volvulus patients report prior episodes of abdominal distention 1
• Surgical history: Prior abdominal surgery strongly suggests adhesive bowel obstruction (85% sensitivity) 1
• Chronic constipation or diverticulitis history: Suggests sigmoid volvulus or diverticular stenosis 1
• Neuropsychiatric conditions: Elderly, institutionalized patients on psychotropic medications are at high risk for sigmoid volvulus 1

Laboratory Evaluation

Obtain blood gas and lactate levels immediately, as these are crucial for detecting bowel ischemia, though normal values do not exclude it. 1, 3

• Complete blood count: Marked leukocytosis suggests bowel ischemia or perforation 1, 3
• Electrolytes and renal function: Assess for dehydration and pre-renal acute renal failure from vomiting 1
• Blood gas analysis: Low serum bicarbonate, low arterial pH, and elevated lactate indicate intestinal ischemia 1

Diagnostic Imaging Strategy

Plain abdominal radiographs should be obtained first, looking for the classic "coffee bean sign" projecting toward the upper abdomen, which is diagnostic of sigmoid volvulus. 1, 3

• CT abdomen/pelvis with IV contrast is the definitive test when diagnosis is uncertain or complications are suspected, with 89% positive diagnostic yield for sigmoid volvulus 1
• IV contrast enhances detection of bowel wall ischemia, pericolic abnormalities, vascular pathology, and fluid collections 1
• CT identifies free air indicating perforation, which has surgical implications and higher mortality with larger volumes 1
• Chest radiograph can detect free air in cases of perforation 1

Differential Diagnosis by Pathology

Sigmoid Volvulus (Most Likely with Classic Presentation)

• Classic triad: Abdominal pain, constipation, and vomiting (late sign) with abdominal distention 1
• Imaging findings: Coffee bean sign on plain radiograph; "whirl sign" on CT 1
• Risk factors: Elderly, institutionalized, chronic constipation, psychotropic medications 1

Large Bowel Obstruction

• Causes: Colorectal cancer (60%), volvulus (15-20%), diverticular disease (10%) 1
• Presentation: Progressive abdominal distension, constipation, colicky pain 1
• Imaging: CT shows transition point and identifies underlying cause 1

Acute Diverticulitis

• Presentation: Left lower quadrant pain and tenderness, fever, elevated inflammatory markers 1
• Imaging: CT shows bowel wall thickening, pericolic fat stranding, possible abscess 1
• Complications: Abscess formation, perforation, fistula 1

Bowel Ischemia

• Key feature: Pain out of proportion to examination findings 2
• Laboratory: Elevated lactate, metabolic acidosis, though these may be absent early 1
• Mortality: 30-90% if not recognized early 2

Management Algorithm

If Peritonitis, Free Air, or Hemodynamic Instability Present

Immediate surgical consultation is mandatory for signs of peritonitis, free air on imaging, hemodynamic instability, or clinical deterioration despite medical management. 1, 2

• NPO status and IV fluid resuscitation with isotonic crystalloids 1
• Nasogastric tube placement for decompression 3
• Broad-spectrum antibiotics if perforation or sepsis suspected 1, 2

If Sigmoid Volvulus Confirmed Without Peritonitis

Endoscopic decompression is the initial treatment of choice for sigmoid volvulus without signs of ischemia or perforation. 1, 3

• Surgical intervention is required if endoscopic decompression fails or for recurrent episodes 1, 3
• Elective sigmoid resection should be considered after successful decompression to prevent recurrence 1

If Uncomplicated Diverticulitis

• Antibiotics may be avoided in CT-confirmed uncomplicated diverticulitis without significant comorbidities or sepsis, with clinical monitoring 1
• If antibiotics used: 4-7 days depending on severity and immune status 1, 3
• Percutaneous drainage for abscesses >3-4 cm diameter 1, 3

If Bowel Obstruction from Other Causes

• Conservative management initially: NPO, IV fluids, nasogastric decompression 1, 3
• Surgical intervention indicated for complete obstruction, signs of ischemia, or failure to improve within 24-48 hours 1, 3

Antibiotic Regimens if Infection/Perforation Suspected

For community-acquired intra-abdominal infection: Ertapenem 1g q24h or Eravacycline 1mg/kg q12h 2

For septic shock: Meropenem 1g q6h by extended infusion, Doripenem 500mg q8h by extended infusion, or Imipenem/cilastatin 500mg q6h by extended infusion 2

Duration: 4 days post-source control for uncomplicated infections in immunocompetent patients; extend to 7 days for immunocompromised or critically ill patients 2

Critical Pitfalls to Avoid

• Do not rely on absence of peritonitis to exclude bowel ischemia: Ischemia may be present without peritoneal signs 1
• Do not delay imaging in elderly or neuropsychiatric patients: History may be unreliable, making physical examination and imaging crucial 1, 3
• Do not assume normal lactate excludes ischemia: Bowel ischemia may be present with normal lactate levels 1
• Do not discharge patients with unexplained left flank pain and distension without definitive imaging: Misdiagnosis rates are 34-68% without imaging 2
• Do not delay surgical consultation if clinical deterioration occurs: Mortality increases significantly with delayed intervention in bowel ischemia or perforation 1, 2