A flank injury with blood in the underwear most strongly suggests injury to which organ?

• A. Kidney.
• B. Liver.
• C. Spleen.
• D. Bladder.

Answer: (A)

Blunt trauma to the flank points most directly to kidney injury because the kidneys sit in the flank region of the retroperitoneal space. When a kidney is damaged, bleeding often involves the urinary tract, so blood can appear in the underwear as part of the urine or from regional bleeding. The liver and spleen are located higher in the abdomen (right and left upper quadrants, respectively) and their injuries typically present with signs of intra-abdominal bleeding and upper quadrant tenderness, not a flank bruise with blood on clothing. The bladder is in the pelvis; its injuries usually produce urinary symptoms and blood in the urine rather than flank-area bleeding.