A 28-year-old woman presents with acute right lower abdominal pain. On examination, she has rebound tenderness at McBurney's point and a positive Rovsing's sign. Her WBC is 12,500/μL with left shift. Imaging confirms acute appendicitis. Which clinical feature best distinguishes acute appendicitis from acute mesenteric adenitis?

Explanation

## Distinguishing Acute Appendicitis from Acute Mesenteric Adenitis ### Clinical Comparison | Feature | Acute Appendicitis | Acute Mesenteric Adenitis | |---------|-------------------|-------------------------| | **Localization of pain** | McBurney's point (RLQ), well-localized | Periumbilical, diffuse, may shift | | **Peritoneal signs** | Marked (rebound, guarding, Rovsing's) | Minimal or absent | | **Fever** | Present in 50–70% | Often present | | **WBC elevation** | Common (>11,000) | Common (>11,000) | | **Preceding URI** | Rare | Frequent (viral prodrome) — **KEY DISCRIMINATOR** | | **Imaging (ultrasound/CT)** | Thickened, non-compressible appendix | Enlarged mesenteric nodes, normal appendix | ### Key Point: **The single best clinical feature that *distinguishes* acute appendicitis from acute mesenteric adenitis is a recent upper respiratory tract infection (URI) preceding the abdominal pain.** A viral prodrome (URI, pharyngitis, gastroenteritis) is the hallmark of mesenteric adenitis, reflecting reactive lymph node enlargement in response to viral infection. This history is characteristically *absent* in acute appendicitis. **High-Yield:** Mesenteric adenitis is most common in children and young adults and almost always follows a viral illness. The abdominal pain is diffuse or periumbilical with *minimal peritoneal signs*. In contrast, appendicitis produces *focal* RLQ tenderness at McBurney's point with *marked* peritoneal irritation — but these signs (Rovsing's, guarding, rebound) can also occur in severe mesenteric adenitis, making them less specific as discriminators. **Clinical Pearl (Bailey & Love / Schwartz's Principles of Surgery):** The history of a preceding URI or pharyngitis in the 1–2 weeks before onset of abdominal pain strongly favors mesenteric adenitis over appendicitis. Fever and elevated WBC are present in *both* conditions and do not discriminate. Rovsing's sign and guarding reflect peritoneal irritation, which can occur in both, though more pronounced in appendicitis. **Why Option D is Correct:** - Option A (fever + elevated WBC): Present in both — NOT a discriminator. - Option B (Rovsing's sign + guarding): These are signs of peritoneal irritation seen predominantly in appendicitis, but they describe features *of* appendicitis rather than a feature that *distinguishes* it from mesenteric adenitis in a clinically ambiguous scenario. Mesenteric adenitis can occasionally produce peritoneal signs. - Option C (localization to McBurney's point with *minimal* peritoneal signs): This is internally contradictory — appendicitis characteristically produces *marked*, not minimal, peritoneal signs. This option does not correctly describe appendicitis. - **Option D (recent URI preceding abdominal pain):** This is the classic distinguishing feature. Its presence strongly favors mesenteric adenitis; its absence (as in this patient) supports appendicitis. This is the best clinical discriminator between the two conditions. **Reference:** Schwartz's Principles of Surgery, 11th ed.; Bailey & Love's Short Practice of Surgery, 27th ed.