A previously healthy 4-year-old girl with a history of prematurity (31 weeks' gestational age) presented as a transfer from an outside facility with abdominal pain. She had presented to an outside emergency department 2 days prior with lower abdominal pain that subsequently localized to the right lower quadrant. Her pain was accompanied by anorexia and nonbloody, nonbilious emesis. She denied fevers or chills. She was noted to have voluntary guarding and focal right lower quadrant tenderness to palpation. Laboratory analyses demonstrated a mild leukocytosis (white blood cell count = 14 × 10 3 /μL [to convert to ×10 9 /L, multiply by 0.001]) and normal urinalysis results. Abdominal ultrasonography images were obtained that failed to show her appendix and demonstrated no secondary signs of inflammation. Because of her notable tenderness, she was admitted for observation at the referring facility. No antibiotics were initiated, and her activity improved with intravenous hydration. However, her right lower abdominal pain persisted, prompting further evaluation. Computed tomography images of the abdomen and pelvis were obtained, and the representative images are shown in Figure 1. She was transferred to our facility for surgical evaluation. In our emergency department, pelvic ultrasonography images were obtained that failed to show both the appendix and right adnexal structures. Axial section A Coronal section B Figure 1. Computed tomographic images. Axial (A) and (B) coronal sections demonstrate an inflamed retrocecal mass. WHAT IS YOUR DIAGNOSIS? A. Perforated appendicitis B. Meckel diverticulitis C. Crohn disease D. Ectopic ovarian torsion Clinical Review & Education