A 28-year-old man presents with a 3-day history of right-sided flank pain radiating to the back, with positive psoas sign on examination. Imaging reveals inflammation of the appendix in the position marked **C** in the diagram. Which of the following best explains why this anatomical variant commonly leads to delayed diagnosis and atypical clinical presentation?

Explanation

## Why the retrocecal position leads to atypical presentation The retrocecal appendix (marked **C**, the most common position at ~65%) lies posterior to the cecum, partially or completely covered by peritoneum and shielded from the anterior parietal peritoneum. This anatomical relationship explains the characteristic atypical features: (1) **Reduced peritoneal signs** — guarding and rebound tenderness are less prominent because the inflamed viscus does not directly irritate the anterior parietal peritoneum; (2) **Lateral or posterior pain** — pain is felt in the flank or loin rather than the classic right iliac fossa, reflecting the retroperitoneal location; (3) **Positive psoas sign** — the overlying psoas muscle becomes irritated by the inflamed appendix, causing pain on hip extension; (4) **Late presentation** — the atypical pain location and reduced peritoneal signs delay recognition and diagnosis. This contrasts sharply with the pelvic position (marked **D**), which causes bladder/rectal irritation, and the classic presentation at McBurney's point (marked **B**), which occurs when the appendix is in a more typical anterior or medial location. Bailey & Love emphasizes that anatomical position is the primary determinant of clinical presentation in appendicitis. ## Why each distractor is wrong - **Pelvic position (option 1 describes this, but it's the wrong answer)**: While the pelvic position does cause atypical symptoms (dysuria, tenesmus, obturator sign), it is NOT the most common variant — it accounts for only ~30% of cases. The question specifically asks about position **C**, which is retrocecal. - **Subcecal position (option 2)**: The subcecal position is rare and does not cause the psoas sign or lateral flank pain described in the clinical vignette. It is not the most common variant. - **Preileal position (option 3)**: The preileal position is very rare and would cause prominent peritoneal signs and early diagnosis, not delayed diagnosis. It does not explain the atypical presentation or positive psoas sign. **High-Yield:** Retrocecal appendix (65%) → atypical pain (flank/posterior), positive psoas sign, reduced peritoneal signs, late diagnosis. Pelvic appendix (30%) → dysuria, tenesmus, obturator sign. [cite: Bailey & Love 28e; Gray's Anatomy 42e Ch 65]