Inverted "V" sign (pneumoperitoneum)

The inverted "V" sign, also known as the lateral umbilical ligament sign, is a sign of pneumoperitoneum manifested by the visualization of an inverted "V"  shape in the pelvis on supine view of abdominal radiographs. It represent free gas outlining the lateral umbilical ligaments. In infants, the lateral umbilical ligaments contain the umbilical arteries, while in adults, they contain the inferior epigastric vessels.

It should not be confused with the inverted "V" sign of the spinal cord seen in subacute combined degeneration of the spinal cord, or the inverted "V" sign of the cerebellum due to bilateral PICA infarction.