Confusable diagnoses · PANCE / PANRE

Diverticulitis and Diverticulosis vs Acute Appendicitis

Written & clinically reviewed by Ryan Busch, PA-C · Updated August 2026 · Report an error

Diverticulitis and Diverticulosis and Acute Appendicitis are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.

Diverticulitis and Diverticulosis vs Acute Appendicitis at a glance

  • Diverticulitis and Diverticulosis: Acquired colonic outpouchings; inflammation produces left lower quadrant pain and fever.
  • Acute Appendicitis: Obstruction-driven inflammation of the appendix; classic periumbilical-to-RLQ pain with peritoneal signs.

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Question 1GastrointestinalMedium
A 67-year-old man has left lower quadrant pain and fever. CT shows inflamed sigmoid diverticula. Which of the following best explains the pathophysiology?
  • AMucosal ischemia at a colonic watershed zone
  • BSigmoid volvulus with closed-loop obstruction
  • CGranulomatous inflammation with skip lesions
  • DMicroperforation of a colonic diverticulum
Reveal answer & full explanation
Correct answer: D — Microperforation of a colonic diverticulum
  • AMucosal ischemia at a colonic watershed zone
  • BSigmoid volvulus with closed-loop obstruction
  • CGranulomatous inflammation with skip lesions
  • DMicroperforation of a colonic diverticulum✓

Why Microperforation of a colonic diverticulum is correct

  • Diverticulitis develops when a diverticulum obstructs, becomes inflamed, and undergoes microperforation of its thin wall.
  • The resulting localized peritoneal inflammation produces LLQ pain and fever, matching sigmoid involvement on CT.
  • Complications include abscess, frank perforation, fistula, and obstruction.

Why the others are wrong

  • Mucosal ischemia at a colonic watershed zone — Ischemic colitis causes LLQ pain with bloody diarrhea at watershed segments, but CT shows inflamed diverticula, not ischemic mucosa; this is the LLQ-pain look-alike trap.
  • Granulomatous inflammation with skip lesions — That describes Crohn disease, a chronic transmural IBD whose discontinuous ulceration is absent on this CT, not focal microperforation of a diverticulum; this is the chronic-colitis trap.
  • Sigmoid volvulus with closed-loop obstruction — Volvulus causes obstruction with marked distention and a coffee-bean sign, not inflamed diverticula; this is the sigmoid-pathology trap.
Question 2GastrointestinalMedium
A 19-year-old man has periumbilical pain that migrates to the right lower quadrant with anorexia and low-grade fever. Which of the following best explains the initial event?
  • AObstruction of the appendiceal lumen
  • BTerminal ileitis from Crohn disease
  • CInflammation of a Meckel diverticulum
  • DMesenteric lymphadenitis from a virus
Reveal answer & full explanation
Correct answer: A — Obstruction of the appendiceal lumen
  • AObstruction of the appendiceal lumen✓
  • BTerminal ileitis from Crohn disease
  • CInflammation of a Meckel diverticulum
  • DMesenteric lymphadenitis from a virus

Why Obstruction of the appendiceal lumen is correct

  • Acute appendicitis begins with luminal obstruction by lymphoid hyperplasia or a fecalith.
  • Obstruction causes distention, bacterial overgrowth, venous congestion, and ischemia.
  • The visceral periumbilical pain migrates to the RLQ once the inflamed serosa irritates the parietal peritoneum, exactly as described.

Why the others are wrong

  • Mesenteric lymphadenitis from a virus — This RLQ mimic causes pain without the orderly periumbilical-to-RLQ migration and is preceded by a viral prodrome; this is the appendicitis-mimic trap.
  • Inflammation of a Meckel diverticulum — Meckel diverticulitis can imitate appendicitis but is far less common and is not the textbook cause of this migrating-pain syndrome; this is the zebra trap.
  • Terminal ileitis from Crohn disease — Crohn ileitis produces weeks to months of RLQ pain with diarrhea and weight loss rather than an acute periumbilical-to-RLQ migration over hours, so it does not explain the initiating event here.
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Side-by-side comparison

FeatureDiverticulitis and DiverticulosisAcute Appendicitis
At a glanceAcquired colonic outpouchings; inflammation produces left lower quadrant pain and fever.Obstruction-driven inflammation of the appendix; classic periumbilical-to-RLQ pain with peritoneal signs.
Classic presentationOlder adult with LLQ pain, fever, and leukocytosis — 'left-sided appendicitis.'; Diverticulosis: usually asymptomatic; incidental on colonoscopy or imaging; Diverticular bleed: painless, brisk hematochezia (most common cause of LGIB); Diverticulitis: left lower quadrant pain (sigmoid), constant, often worsening over 1-3 days; Fever,…Periumbilical pain → migration to RLQ + anorexia + nausea + low-grade fever + RLQ tenderness with peritoneal signs.; Periumbilical pain migrating to RLQ over 12-24 h (visceral → somatic); Anorexia (highly sensitive); Nausea and vomiting (after onset of pain — unlike gastroenteritis where vomiting precedes pain); Low-grade fever;…
Workup / key labsCT-confirmed pericolonic inflammation with diverticula. Modified Hinchey classification: Ia (pericolic phlegmon), Ib (pericolic abscess), II (pelvic/intra-abdominal abscess), III (purulent peritonitis), IV (feculent peritonitis).; CBC (leukocytosis with left shift); BMP, lactate (if severe); CRP — predicts severity; Urinalysis (exclude…Clinical diagnosis supported by imaging. Histopathology confirms post-operatively.; CBC — mild to moderate leukocytosis (10-18,000) with left shift; very high WBC suggests perforation; BMP, CRP; Urinalysis — exclude UTI; mild pyuria/hematuria possible from inflamed appendix adjacent to ureter; Pregnancy test in women of childbearing age…
ImagingCT abdomen/pelvis with IV contrast — MODALITY OF CHOICE; identifies pericolic inflammation, bowel wall thickening, abscess, fistula, free air; classifies by Hinchey stage; AVOID colonoscopy during acute diverticulitis (perforation risk); perform 6-8 weeks AFTER resolution to exclude malignancy when first episode or alarm features;…CT abdomen/pelvis with contrast — modality of choice in adults; sensitivity and specificity >95%; findings: dilated appendix >6 mm, wall thickening, periappendiceal fat stranding, fluid, abscess, fecalith; Ultrasound — first-line in children and pregnant women to avoid radiation; operator-dependent; MRI — alternative in pregnancy if…
First-line treatmentUncomplicated diverticulitis (Hinchey 0/Ia: no abscess, perforation, fistula, or obstruction): often managed as outpatient; bowel rest as tolerated; antibiotics selective rather than universal per AGA 2015 (consider in elderly, immunocompromised, comorbidities, severe symptoms); Outpatient antibiotic regimens: amoxicillin-clavulanate,…NPO, IV fluids, analgesia, antiemetics; IV antibiotics covering Gram-negative and anaerobic flora — piperacillin-tazobactam, ceftriaxone + metronidazole, or ertapenem; administer pre-operatively; Laparoscopic appendectomy — standard of care; lower wound infection rate and faster recovery vs open; Open appendectomy — alternative when…

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Full outlines

Diverticulitis and Diverticulosis Acute Appendicitis All 514 diagnoses

Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.