Differential Diagnosis for Left Upper Quadrant Pain Radiating to the Left Flank

Single Most Likely Diagnosis

• Constipation: Given the symptoms of not passing much stool, nausea, and anorexia, constipation is a common condition that could cause left upper quadrant (LUQ) pain radiating to the left flank due to the proximity of the colon to these areas. The pain could be referred from the colon.

Other Likely Diagnoses

• Gastroesophageal Reflux Disease (GERD): Although more commonly associated with heartburn, severe GERD can cause upper abdominal pain that might radiate to the flank, especially if there's an association with nausea and anorexia.
• Peptic Ulcer Disease: Peptic ulcers can cause severe abdominal pain that may radiate to the back or flank, accompanied by nausea and anorexia, especially if the ulcer is located in the duodenum or stomach near the spleen.
• Diverticulitis: Inflammation of a diverticulum in the colon, particularly if it's located on the left side, can cause pain in the LUQ that radiates to the left flank, along with changes in bowel habits and nausea.

Do Not Miss Diagnoses

• Splenic Infarct or Rupture: Although less common, a splenic infarct or rupture can cause severe LUQ pain radiating to the left flank. This condition is critical and requires immediate medical attention.
• Pancreatitis: Pancreatic inflammation can cause severe abdominal pain that radiates to the back, nausea, vomiting, and anorexia. The pain can be in the upper abdomen and radiate to the flank.
• Kidney Stone: A stone in the left ureter can cause severe flank pain (renal colic) that may radiate to the groin and is often accompanied by nausea and vomiting.

Rare Diagnoses

• Splenic Artery Aneurysm: A rare condition where an aneurysm of the splenic artery can cause LUQ pain radiating to the left flank, especially if it ruptures.
• Intestinal Obstruction: Although more commonly presenting with severe abdominal pain and vomiting, an obstruction in the intestines can lead to LUQ pain and changes in bowel habits.
• Left-Sided Pyelonephritis: An infection of the left kidney can cause flank pain, nausea, and changes in urinary habits, which might be accompanied by LUQ pain if the infection involves the upper pole of the kidney.