A 42-year-old woman undergoes emergency appendicectomy for perforated appendicitis. On postoperative day 3, she develops fever and abdominal distension. Clinical examination reveals localized right lower quadrant tenderness and a palpable mass. Which investigation is most appropriate to confirm the diagnosis of postoperative intra-abdominal abscess?

Explanation

## Investigation of Choice for Postoperative Intra-Abdominal Abscess ### Clinical Presentation The patient presents with fever, abdominal distension, and a palpable mass on postoperative day 3 following emergency appendicectomy—classic features of intra-abdominal abscess formation. Imaging confirmation is essential before intervention. ### Why Contrast-Enhanced CT Abdomen & Pelvis is Correct **Key Point:** Contrast-enhanced CT is the gold standard for diagnosis and characterization of postoperative intra-abdominal abscess because it: - Provides high sensitivity (95–100%) and specificity for fluid collections - Localizes the abscess precisely (critical for percutaneous drainage planning) - Characterizes fluid density (simple vs. complex, presence of gas) - Assesses surrounding structures and complications (fistula, perforation) - Guides percutaneous catheter placement (image-guided drainage) **High-Yield:** Timing of abscess formation: - Early (POD 1–3): Often related to anastomotic leak, bowel perforation - Late (POD 5–7+): Localized infection, inadequate source control ### Advantages of CT over Alternatives | Investigation | Sensitivity | Specificity | Limitation | Use Case | |---|---|---|---|---| | **CT (contrast-enhanced)** | 95–100% | 95–100% | Radiation, contrast allergy | Gold standard; guides drainage | | **Ultrasound** | 70–85% | 80–90% | Operator-dependent, limited by bowel gas, body habitus | Bedside screening in stable patients | | **Diagnostic laparoscopy** | High | High | Invasive, risk of perforation, therapeutic limited | Therapeutic when drainage/washout needed | | **Abdominal X-ray** | 30–40% | 60–70% | Poor soft tissue detail, misses small collections | Screening for free air only | **Clinical Pearl:** Once CT confirms abscess, percutaneous catheter drainage under CT or ultrasound guidance is the first-line intervention (avoids re-exploration in most cases). Surgery is reserved for failed drainage or diffuse peritonitis. ### Mnemonic: **CTAT** - **C**ontrast-enhanced CT - **T**opography (precise localization) - **A**bscess characterization - **T**herapy planning (drainage vs. surgery) **Warning:** Do not delay imaging with clinical suspicion of abscess. Early diagnosis and drainage reduce morbidity and mortality.