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?

Question

Accepted Answer

B. Contrast-enhanced CT abdomen and pelvis. ## 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.

Answer

A. Abdominal X-ray

Answer

C. Diagnostic laparoscopy

Answer

D. Abdominal ultrasound

Explanation

Investigation of Choice for Postoperative Intra-Abdominal Abscess

Clinical Presentation

Why Contrast-Enhanced CT Abdomen & Pelvis is Correct

Advantages of CT over Alternatives

Mnemonic: CTAT

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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