A 35-year-old man presents with 36 hours of right lower quadrant pain, fever (38.5°C), and guarding on examination. Clinical suspicion for acute appendicitis is high. However, the patient is hemodynamically stable and has no signs of peritonitis. Before proceeding to surgery, which investigation is most appropriate to exclude perforation and assess for localized abscess formation?

## Investigation of Choice for Complicated Appendicitis **Key Point:** Contrast-enhanced CT (CECT) abdomen and pelvis is the investigation of choice to assess for complications of acute appendicitis, including perforation and localized abscess formation, in a hemodynamically stable patient. ### Role of CT in Complicated Appendicitis **High-Yield:** CECT can identify: - Appendiceal perforation (loss of appendiceal wall integrity, free fluid) - Periappendiceal abscess (loculated fluid collection with rim enhancement) - Generalized peritonitis vs. localized inflammation - Extent of contamination and need for percutaneous drainage - Presence of fecalith (risk factor for perforation) ### Imaging Findings in Complicated Appendicitis | Finding | Significance | Management Implication | |---|---|---| | **Appendiceal wall discontinuity** | Perforation | Urgent surgery; risk of sepsis | | **Free fluid + fat stranding** | Localized peritonitis | Surgery vs. percutaneous drainage | | **Loculated fluid collection** | Abscess | May allow interval appendectomy after drainage | | **Free air** | Perforation | Urgent surgery | | **Fecalith** | Risk factor for complications | Higher perforation risk | **Clinical Pearl:** In this patient with 36 hours of symptoms (longer duration increases perforation risk), CT is essential to: 1. Confirm appendicitis diagnosis 2. Assess for perforation and abscess 3. Guide treatment strategy (immediate surgery vs. percutaneous drainage + interval appendectomy) ### Management Algorithm Based on CT Findings ```mermaid flowchart TD A[Suspected acute appendicitis]:::outcome --> B[CECT abdomen/pelvis]:::action B --> C{Perforation or abscess?}:::decision C -->|No perforation| D[Acute uncomplicated appendicitis]:::outcome D --> E[Urgent appendectomy]:::action C -->|Perforation + localized abscess| F[Hemodynamically stable?]:::decision F -->|Yes| G[Percutaneous drainage + antibiotics]:::action F -->|No| H[Urgent surgery]:::action G --> I[Interval appendectomy in 6-8 weeks]:::action C -->|Perforation + generalized peritonitis| J[Urgent appendectomy]:::action ``` **Mnemonic for CT signs of perforation — "FLAW":** - **F**ree air (pneumoperitoneum) - **L**oculated fluid (abscess) - **A**ppendix wall discontinuity - **W**idespread fat stranding (peritonitis) ### Why CT Over Other Modalities **Warning:** Diagnostic laparoscopy (option 2) is invasive and not indicated for diagnosis when imaging can provide the same information non-invasively. It is reserved for cases where imaging is inconclusive or when therapeutic intervention (appendectomy) is planned. **Ultrasound (option 3)** cannot reliably detect perforation or assess the extent of abscess formation; it is operator-dependent and limited by bowel gas. **Technetium-99m WBC scan (option 4)** is a functional imaging modality with low specificity and poor spatial resolution; it is not used for acute appendicitis diagnosis or complication assessment in modern practice.