Despite newer imaging techniques, acute appendicitis can be very difficult to diagnose.
Acute appendicitis is thought to begin with obstruction of the lumen
Obstruction can result from food matter, adhesions, or lymphoid hyperplasia
Mucosal secretions continue to increase intraluminal pressure
Eventually the pressure exceeds capillary perfusion pressure and venous and lymphatic drainage are obstructed.
With vascular compromise, epithelial mucosa breaks down and bacterial invasion by bowel flora occurs.
Increased pressure also leads to arterial stasis and tissue infarction
End result is perforation and spillage of infected appendiceal contents into the peritoneum
Initial luminal distention triggers visceral afferent pain fibers, which enter at the 10th thoracic vertebral level.
This pain is generally vague and poorly localized.
Pain is typically felt in the periumbilical or epigastric area.
As inflammation continues, the serosa and adjacent structures become inflamed
This triggers somatic pain fibers, innervating the peritoneal structures.
Typically causing pain in the RLQ
The change in stimulation form visceral to somatic pain fibers explains the classic migration of pain in the periumbilical area to the RLQ seen with acute appendicitis.
In some males, retroileal appendicitis can irritate the ureter and cause testicular pain.
Pelvic appendix may irritate the bladder or rectum causing suprapubic pain, pain with urination, or feeling the need to defecate
Multiple anatomic variations explain the difficulty in diagnosing appendicitis.