Answer:
In creating a differential diagnosis for right lower quadrant (RLQ) pain, the very first step would be to divide the causes into the following categories:
1) ABDOMINAL i.e. pain arising from structures in the region of the abdomen, and
2) EXTRA-ABDOMINAL i.e. “referred pain” arising from structures outside the abdominal area but perceived in the RLQ.
Explanation:
Abdominal causes
A useful way to think of abdominal pain to establish its etiology is to subclassify it as arising from either one or a combination of the following layers from exterior towards the interior:
Abdominal wall
Peritoneum and peritoneal cavity
Viscera – intraperitoneal and retroperitoneal
Vasculature/lymphatics
a)Abdominal wall
Skin & subcutaneous tissues – cellulitis, herpes zoster (shingles), tumor.
Muscle – hematoma, rupture, strain.
Inguinal canal – inguinal hernias (specific to the lower abdominal quadrants).
b)Peritoneum and peritoneal cavity
Peritonitis – localized to the RLQ e.g. as in acute appendicitis or cecal perforation.
Intraperitoneal abscess/hemorrhage e.g. diverticular abscess or ruptured abdominal aortic aneurysm (AAA).
c)Viscera: (Intraperitoneal and retroperitoneal)
In considering the etiologies under this heading, the key concept would be to think of the RLQ in anatomic terms. This area primarily overlies the Ileocecal junction and appendix and disease states affecting these organs are a common cause of RLQ pain.
Other relevant intra-abdominal viscera in this location include the proximal half of the ascending colon, lower pole of right kidney, right ureter and in females – the right ovary and fallopian tube and certain conditions affecting these organs should be considered in the differential.
Most common etiologies include:
Appendix – acute appendicitis.
Ileocecal junction – terminal ileitis (infectious, Crohn’s disease), irritable bowel syndrome.
Cecum – cecal volvulus and intestinal obstruction, cecal perforation.
