Appendiceal abscess mimicking a painless abdominal wall mass in an adolescent: a case report.

Background: Acute appendicitis is the most common surgical abdominal emergency in children. Its atypical presentations remain a significant source of diagnostic error. The presentation of an appendiceal abscess as an isolated abdominal wall mass, in the complete absence of abdominal pain, represents a misleading manifestation that directly contradicts the classic teaching that peritoneal signs are essential for diagnosis. Case presentation: A previously healthy 13-year-old boy presented with a 10-day history of a painful right lower abdominal wall swelling, explicitly denying any abdominal pain. Initially misdiagnosed with a soft tissue infection based on a focused abdominal wall ultrasound, he was referred after 10 days of unsuccessful treatment. A non-contrast computed tomography scan revealed a secondary abdominal wall abscess connected via an inflammatory tract to a large periappendiceal abscess. Management followed a staged strategy: intravenous antibiotics led to resolution, followed by an uncomplicated delayed laparoscopic appendectomy 3 months later. The patient recovered fully. Interpretation: This case illustrates a critical diagnostic pitfall where the absence of expected abdominal pain and a prominent local finding led to initial misdiagnosis as soft-tissue infection. This case highlights the diagnostic challenge posed by this presentation and serves to remind clinicians of the importance of considering an intra-abdominal source and obtaining a comprehensive ultrasound evaluation in children with an unexplained abdominal wall mass, even in the absence of abdominal pain. A diagnostic consideration pathway is presented as a teaching schematic to illustrate a systematic approach to evaluation in such ambiguous scenarios. It is crucial to emphasize that this pathway is derived from a single case and is presented for educational purposes, not as a validated clinical tool.