Diverticulitis: This is a common cause of lower left quadrant abdominal pain, especially in older adults. The pain is usually constant and accompanied by tenderness, fever, and changes in bowel habits. Diverticulitis occurs when diverticula (small pouches) in the wall of the colon become inflamed.

Constipation: Can cause lower left quadrant pain due to the accumulation of feces in the sigmoid colon, which is located in the lower left abdomen.
Irritable Bowel Syndrome (IBS): Characterized by recurring abdominal pain associated with a change in bowel habits, such as diarrhea or constipation. The pain can be localized to the lower left quadrant.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic inflammation of the gastrointestinal tract, leading to abdominal pain, including in the lower left quadrant.
Ovarian Cysts or Torsion: In females, ovarian cysts or torsion can cause severe lower abdominal pain that may be localized to the left side.

Appendicitis (if the appendix is located in the lower left quadrant, which is less common): Although appendicitis typically presents with right lower quadrant pain, an ectopic appendix can cause pain in other areas, including the lower left quadrant. Missing this diagnosis can lead to perforation and severe complications.
Ectopic Pregnancy: A life-threatening condition where the embryo implants outside the uterus, often causing severe abdominal pain, which can be localized to one side.
Intestinal Obstruction: A blockage of the intestine that can cause severe abdominal pain, vomiting, and constipation. The pain can be localized to the lower left quadrant depending on the site of obstruction.
Inferior Mesenteric Artery Embolism: A rare but potentially fatal condition where an embolus blocks the inferior mesenteric artery, causing ischemia to the colon and severe abdominal pain.

Colonic Volvulus: A condition where the colon twists around itself and its mesentery, cutting off the blood supply. It can cause severe abdominal pain, nausea, and vomiting.
Sigmoid Colon Cancer: Although more common in older adults, cancer of the sigmoid colon can cause abdominal pain, changes in bowel habits, and weight loss.
Endometriosis: A condition where tissue similar to the lining inside the uterus grows outside of it, causing pain, especially during menstruation. The pain can be localized to the lower abdomen, including the left quadrant.
Intra-abdominal Testicular Torsion (in males with an undescended testicle): A rare condition where the testicle twists, cutting off its blood supply, and can cause severe abdominal pain if the testicle is located intra-abdominally.