Acute Appendicitis
Understand Acute Appendicitis in Right Lower Quadrant Computed Tomography imaging, what it means, and next steps.
30-Second Overview
Dilated appendix (>6 mm) with wall thickening and peri-appendiceal fat stranding.
Common surgical emergency; untreated rupture can cause peritonitis.
benignRate
followUp
Imaging Appearance
Computed Tomography FindingDilated appendix (>6 mm) with wall thickening and peri-appendiceal fat stranding.
Clinical Significance
Common surgical emergency; untreated rupture can cause peritonitis.
Understanding Acute Appendicitis
Acute appendicitis is inflammation of the appendix, a small finger-shaped pouch attached to the beginning of the large intestine. Before we look at how this condition appears on imaging, let's understand why prompt diagnosis and treatment are essential.
Dilated appendix ＞6 mm with wall thickening and enhancement; peri-appendiceal fat stranding; possible appendicolith
Here's how accurate CT is at diagnosing acute appendicitis:
Excellent accuracy; negative appendectomy rate ＜5%
Correctly rules out healthy patients
Annual new cases
Think of the appendix like a small dead-end street—when it becomes blocked or infected, there's nowhere for the pressure and inflammation to go. This can lead to increased pressure, compromised blood flow, and eventually rupture if not treated promptly.
What Is Acute Appendicitis?
Acute appendicitis is sudden inflammation of the vermiform appendix, typically caused by obstruction of the appendiceal lumen. The obstruction leads to increased pressure, bacterial overgrowth, ischemia, and potentially perforation.
What causes appendicitis:
| Cause | Frequency | Description | |-------|-----------|-------------| | Appendicolith (fecalith) | 30-40% | Hardened stool blocking the opening | | Lymphoid hyperplasia | 20-30% | Enlarged lymph tissue from infection | | Tumor | ＜5% | Carcinoid, adenocarcinoma (rare, usually older) | | Parasites | ＜5% | Enterobius vermicularis (pinworm) | | Idiopathic | 20-30% | No specific cause identified |
Why CT is preferred:
- Highest diagnostic accuracy among imaging modalities
- Visualizes the entire appendix in most cases
- Detects complications (perforation, abscess)
- Identifies alternative diagnoses when appendix is normal
- Essential for atypical presentations
How Appendicitis Appears on CT
CT scan with intravenous contrast is the gold standard for diagnosing acute appendicitis in adults, especially when the diagnosis is uncertain.
What Normal Appendix Looks Like
Normal appendix appears as a thin tubular structure ＜6 mm in diameter, filled with air or fluid. Wall is thin and normally enhancing. Peri-appendiceal fat appears clean without stranding. No surrounding fluid collections. The appendix may be variably positioned (retrocecal, pelvic, or paracolic).
What Appendicitis Looks Like
Dilated appendix ＞6-7 mm in diameter with wall thickening and enhancement. Peri-appendiceal fat stranding (inflammatory changes). Possible appendicolith (calcified fecalith). Adjacent bowel loop thickening. Free fluid or abscess suggests perforation. Enlarged mesenteric lymph nodes may be present.
Key Findings Pattern
When evaluating for acute appendicitis on CT, radiologists look for specific signs:
Key Imaging Findings
Appendiceal dilation ＞6 mm
Outer diameter of appendix exceeding 6 mm measured on axial images
Peri-appendiceal fat stranding
Inflammatory changes (increased attenuation) in fat surrounding appendix
Appendicolith
Calcified or high-attenuation structure within appendiceal lumen
Abscess or phlegmon
Fluid collection with or without air; inflammatory mass in right lower quadrant
Enhancement pattern
Intense homogeneous wall enhancement of thickened appendix
When Your Doctor Orders This Test
Here's a typical scenario where CT is ordered for suspected appendicitis:
Clinical Scenario
Common presenting symptoms:
- Pain: migrates from periumbilical to right lower quadrant (McBurney's point)
- Anorexia: present in 70-80% of cases
- Nausea and vomiting: more common after pain onset
- Fever: typically low-grade (99-101°F)
- Rebound tenderness and guarding
Atypical presentations (higher diagnostic uncertainty):
- Elderly patients (often have delayed presentation)
- Young children (cannot communicate symptoms well)
- Pregnant women (appendix displaced by uterus)
- Immunocompromised patients (may have minimal symptoms)
Differential Diagnosis
Several conditions can mimic acute appendicitis on CT scan:
What Else Could It Be?
Dilated appendix ＞6 mm with fat stranding. No abscess or free air. Prompt appendectomy recommended. Laparoscopic approach preferred. Outpatient recovery typically 1-2 weeks.
Abscess, free fluid, or extraluminal air in right lower quadrant. Perforation rate 15-30%. May require antibiotics and drainage first, with interval appendectomy 4-8 weeks later.
Enlarged mesenteric lymph nodes with normal-appearing appendix. Often preceded by upper respiratory infection. Treatment is supportive; surgery not required.
Wall thickening of terminal ileum and cecum with skip lesions. Mesenteric fat wrapping and fibrofatty proliferation. Treated with medical therapy; surgery only for complications.
Adnexal mass, lack of free fluid, normal appendix. PID may have tubo-ovarian abscess and bilateral findings. Gynecology consultation recommended.
How Accurate Is CT for Appendicitis?
CT is highly accurate for diagnosing acute appendicitis in adults:
CT with IV contrast is the most accurate imaging test for acute appendicitis in adults. It correctly identifies ＞95% of true cases and correctly rules out appendicitis in ＞90% of cases. This accuracy has reduced the negative appendectomy rate from 15-20% to ＜5%.
Perforation risk increases with delayed presentation. Children ＜5 years and adults ＞60 years have higher perforation rates due to atypical presentations and delayed diagnosis. CT findings of perforation include abscess, extraluminal air, and marked fat stranding.
Recent studies show that uncomplicated appendicitis can often be treated successfully with antibiotics alone, avoiding surgery. However, 25-30% eventually require appendectomy for recurrence. CT helps identify which patients are candidates for this approach.
What Happens Next?
Management depends on whether appendicitis is complicated (perforated) or uncomplicated:
What Happens Next?
Confirm diagnosis and assess complications
CT findings determine if appendicitis is present and whether perforation has occurred. Blood tests (CBC, CRP) support diagnosis. Surgical consultation obtained.
Uncomplicated appendicitis: urgent appendectomy
Laparoscopic appendectomy is standard of care. Same-day discharge common if uncomplicated. Antibiotics given preoperatively and continued postoperatively (typically 5 days). Return to normal activities in 1-2 weeks.
Perforated appendicitis with abscess: conservative management
IV antibiotics and percutaneous abscess drainage if indicated. Interval appendectomy performed 4-8 weeks later after inflammation resolves. This approach reduces complication rates compared to emergency surgery.
Alternative: antibiotics-first approach
Some patients with uncomplicated appendicitis opt for antibiotic treatment alone. 70-75% recover without surgery. 25-30% have recurrence and need delayed appendectomy. Shared decision-making with surgeon is essential.
Post-treatment follow-up
Surgical follow-up if appendectomy performed. Pathology results reviewed. For antibiotics-first approach, prompt evaluation if symptoms recur. Long-term prognosis is excellent for both approaches.
When to Seek Immediate Care
Return to the emergency department immediately if you experience:
- Severe, worsening abdominal pain despite treatment
- High fever ＞102°F (38.9°C) with shaking chills
- Inability to pass gas or have a bowel movement
- Severe vomiting or dehydration
- Redness, swelling, or drainage from surgical incision
- Shortness of breath or chest pain (possible pulmonary embolism)
Frequently Asked Questions
Can appendicitis resolve without surgery?
Rarely. Some cases of uncomplicated appendicitis may improve with antibiotics alone, but recurrence rates are 25-30%. Surgery remains the definitive treatment and prevents recurrence. The decision between surgery and antibiotics should be made with your surgeon after discussing risks and benefits.
Is CT safe with all that radiation?
CT uses more radiation than X-ray, but the diagnostic benefit in suspected appendicitis outweighs the small radiation risk. Modern CT scanners use lower radiation doses while maintaining image quality. For pregnant women and children, ultrasound is often preferred first, with CT reserved for inconclusive cases.
Why can't the doctor just diagnose without imaging?
Clinical diagnosis alone has a negative appendectomy rate of 15-20%, meaning unnecessary surgery in up to 1 in 5 patients. CT reduces this to ＜5% while also identifying alternative diagnoses. In atypical presentations, imaging prevents unnecessary surgery and delays in treatment.
What happens if my appendix bursts?
Ruptured appendicitis typically causes an abscess (collection of pus) in the abdomen. Treatment usually involves antibiotics and drainage first, with surgery 4-8 weeks later after inflammation subsides. This approach is safer than emergency surgery in the setting of severe inflammation and infection.
Can I get appendicitis again after surgery?
No, once your appendix is removed, you cannot get appendicitis again. The appendix serves no essential function, and its removal doesn't affect your digestive system or overall health. People live normal, healthy lives without an appendix.
References
Medical References
This content is referenced from authoritative medical organizations:
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Medical Disclaimer: This information is for educational purposes. Acute appendicitis requires prompt surgical evaluation. Always seek immediate medical attention for symptoms of appendicitis.
Correlate with Lab Results
When Acute Appendicitis appears on imaging, doctors often check these lab tests:
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