Figure 1a. CT scans in a 21-year-old man with acute onset right lower quadrant abdominal pain. (a) Nonenhanced transverse CT scan shows the appendix as a nonspecific soft-tissue mass (black arrow) located anterior to the lumbosacral junction. The borders of the appendix are difficult to discern because of minimal retroperitoneal fat and the proximity of the adjacent right external and internal iliac vessels (white arrow). (b) Contrast-enhanced transverse CT scan shows the inflamed appendix (black arrow), located medial to the enhanced iliac vessels (white arrow). The appendix is readily identifiable by its abnormally thickened and enhanced wall. No periappendiceal inflammatory change is present.