The erect abdominal x-ray shows a radio opaque density just above the right iliac crest. This is an appendicolith.

The patient underwent a CT scan of the abdomen which revealed appendicitis.

An appendicolith is formed by calcium deposition around a nidus of inspissated fecal material.An appendicolith is seen in approximately 14% of patients with acute appendicitis. There is a positive correlation between appendicolith and acute appendicitis in the right clinical context.

Reference: Fundamentals of Diagnostic Radiology by Brant and Helms.