subcostal

Subcostal is an anatomical term used to describe structures located beneath a rib or along the inferior margin of the thoracic cage. It is applied to muscles, nerves, vessels, spaces, and surgical approaches in relation to the ribs.

Subcostal muscles are a small group of thin slips on the inner surface of the lower thoracic wall. They originate from the internal surface of a rib near its angle and insert on the internal surface of a rib two or more above, spanning two to four intercostal spaces. They function to depress the ribs during expiration and are considered part of the thoracic wall musculature, with variable presence and size.

The subcostal nerve refers to the ventral ramus of the twelfth thoracic spinal nerve (T12). It runs along the inferior border of the 12th rib and travels through the subcostal space, giving motor innervation to the anterolateral abdominal wall muscles and providing sensory innervation to the overlying skin. Clinically, it can be involved in nerve entrapment or targeted in regional anesthesia, such as subcostal nerve blocks.

Subcostal space or region denotes the area below a costal margin, particularly below the 12th rib. Subcostal incisions are surgical approaches placed along the subcostal margin to access the upper abdomen, gallbladder, liver, or other structures, and may be tailored to the side and extent of exposure required.

Etymology: from Latin subcostalis, “below the rib.” See also intercostal, costal, thorax.