Diverticulitis

1. THE 2-MINUTE PHYSIOLOGY (Rapid Pathophysiology)

• The Core Mechanism: Diverticular disease is driven by a mechanical and structural failure of the colon wall. Weakness in the noncircumferential muscular layers (often at the insertion points of the vasa recta) combined with high intraluminal pressure forces the mucosa and submucosa to herniate, forming diverticula.
• The Pressure Drivers: High intraluminal pressure is heavily driven by increased collagen crosslinking with age (leading to a more distensible but highly contractile bowel), colonic stasis, chronic constipation, and low dietary fiber intake.
• Cellular/Mechanical Breakdown: Diverticulitis occurs when these outpouchings become obstructed or undergo micro-/macro-perforation. This leads to localized ischemia, inflammation of the surrounding pericolic fat (fat stranding), and can progress to frank abscess formation or free rupture spilling bowel contents into the peritoneum.
• The Fistulous Tracts: Severe, chronic localized inflammation can erode directly into adjacent pelvic organs, causing fistulas—most notably colovesical (colon to bladder) or colovaginal (colon to vagina).

2. THE BEDSIDE ACTION PLAN (Rapid ER Management)

• Uncomplicated / Low-Risk Patients:
• Resuscitation: Keep the patient NPO initially until a surgical abdomen is ruled out. Once stable, initiate a trial of oral fluids.
• Medications: Administer oral analgesics and antiemetics. Current guidelines support outpatient management +/- antibiotics. (Outside information: If antibiotics are utilized, standard ED oral regimens include Ciprofloxacin 500 mg PO BID + Metronidazole 500 mg PO TID, or Amoxicillin-Clavulanate 875/125 mg PO BID for 7-10 days).
• Complicated / High-Risk Patients:
• Resuscitation: Establish IV access. Initiate fluid resuscitation for any signs of sepsis or peritonitis resulting from gross perforation. Keep the patient strictly NPO for bowel rest.
• Medications: Initiate broad-spectrum IV antibiotics immediately. (Outside information: Standard regimens include Piperacillin-Tazobactam 3.375g IV or Ceftriaxone 1g IV + Metronidazole 500mg IV).
• Consultation: Obtain early General Surgery consultation for gross perforation with peritonitis, and consider Interventional Radiology (IR) for percutaneous drainage of localized abscesses.

3. THE DIAGNOSTIC GRID (Differential Diagnosis & Workup)

• "Can't-Miss" Mimics:
• Acute Appendicitis (can present with left-sided or pelvic pain).
• Ischemic Bowel / Mesenteric Ischemia.
• Ectopic Pregnancy or Ovarian Torsion (in females of childbearing age).
• Pyelonephritis / Complicated UTI.
• Prioritized Diagnostic Workup:
• Urinalysis: Mandatory to rule out a primary UTI and to screen for a colovesical fistula (which can present with dysuria or pneumaturia).
• Complete Blood Count (CBC): Assess for severe leukocytosis, which is a criterion for hospital admission.
• Gold-Standard Imaging: Computed Tomography (CT) of the abdomen and pelvis with contrast is the definitive modality if the diagnosis is unclear or if complications (abscess, perforation) are suspected.

4. THE VISUAL BOARD (ECG / POCUS / Imaging)

• CT Abdomen/Pelvis (The Classic Findings):
• Diverticula: Look for multiple small, air-filled structures lining the edge of the colon, most commonly in the descending/sigmoid colon.
• Fat Stranding: Scrutinize the pericolic fat for a "hazy outer border" or haziness surrounding the bowel segment, which is the hallmark of acute inflammation.
• Complications: Look explicitly for free air (gross perforation), fluid collections adjacent to the sigmoid colon (abscess formation), or proximally dilated loops of bowel (obstruction).

5. THE SCORING MATRIX (Risk Stratification & Guidelines)

• Safe Outpatient Discharge Criteria: Patients may be discharged if they meet ALL of the following criteria: Uncomplicated diverticulitis, normal vital signs, mild to moderate symptoms with mild tenderness, no abdominal distention, able to tolerate PO fluids, pain controlled with oral medications, and good home support with reliable 2-3 day follow-up.
• Mandatory Admission Criteria: Patients MUST be admitted if they exhibit: Intractable vomiting, significant comorbidities, high leukocytosis, high fevers, persistent pain, complicated diverticulitis (abscess, fistula, perforation), or failed outpatient management.
• High-Risk Demographics: The elderly and the immunocompromised (including those on chronic steroids) mandate admission for IV antibiotics and bowel rest.

6. THE DANGER ZONE (Pitfalls & Critical Actions)

• Cognitive Trap (The Subtle Presentation): Relying on a classic presentation with severe pain and high fever in high-risk groups. Correction: The elderly and immunocompromised patients often present with very subtle signs and symptoms despite having severe disease. These groups have a much higher rate of perforation and high mortality.
• Cognitive Trap (Misdiagnosing the Fistula): Treating a patient for a simple UTI or gastroenteritis without connecting the symptoms to the colon. Correction: Dysuria can be the primary symptom of a colovesical fistula, and vomiting with distension may indicate a proximal bowel obstruction secondary to diverticular stricture.
• Critical Action (The Disposition): You must not discharge patients who cannot tolerate oral fluids or those with poor home support. Ensure clear discharge instructions to return immediately for worsening pain, high fever, or intractable vomiting.

7. MCQ MASTERCLASS (Written Exam Tips)

• Epidemiology Buzzwords: The prevalence of diverticulosis increases dramatically with age: 5% in patients <40 years, 30% by age 60, and >70% by age 85.
• Radiology Buzzword: "Hazy outer border of the bowel segment" or "Pericolic fat stranding" on CT scan is the classic descriptor for uncomplicated diverticulitis.
• Diagnostic Distractor: A patient presents with acute lower GI bleeding. While diverticulitis causes pain, painless lower GI bleeding is classically caused by diverticulosis. Chronic NSAID or aspirin use is highly predictive of diverticular hemorrhage.
• Complication Clue: A patient with known diverticular disease presenting with "feculent vaginal discharge" has a colovaginal fistula, while one presenting with "air in the urine (pneumaturia)" has a colovesical fistula.

8. THE BOARDROOM SCRIPT (OSCE & Oral Board Tips)

• The Initial Hook: "This is an elderly patient presenting with left lower quadrant abdominal pain. Given their age, they are at high risk for a subtle presentation of a catastrophic disease. I will immediately assess their ABCs, establish IV access, and keep them NPO. My differential includes complicated diverticulitis, mesenteric ischemia, and a ruptured abdominal aortic aneurysm."
• The Physical Exam: "I will carefully palpate the abdomen for a localized mass that would suggest an abscess, and check for guarding or rebound tenderness which would indicate gross perforation and peritonitis."
• The Workup & Disposition: "I am ordering a CBC, chemistry panel, urinalysis to check for fistulization, and a CT of the abdomen and pelvis with contrast. The CT shows uncomplicated diverticulitis with fat stranding but no abscess or free air. Because the patient is elderly and has comorbidities, I will admit them for IV antibiotics, bowel rest, and serial abdominal examinations."