Subkostalnerv

Subcostal nerve, or nervus subcostalis, is the ventral ramus of the twelfth thoracic spinal nerve (T12). It is the final thoracic spinal nerve and serves as part of the thoracoabdominal nerve complex that supplies the lower thorax and upper abdomen.

Origin and course: The subcostal nerve emerges from the spinal canal via the intervertebral foramen below the T12 spinal level. It runs forward along the lower border of the 12th rib, typically in the neurovascular plane between the internal oblique and transversus abdominis muscles. In its course, it may give off muscular branches before continuing toward the anterior abdominal wall. The nerve is often accompanied by the subcostal vessels.

Branches and distribution: The subcostal nerve provides motor innervation to the abdominal wall muscles, including the external oblique, internal oblique, and transversus abdominis. It also supplies sensory innervation to the skin of the lower anterior abdominal wall and parts of the hip region, with branches that can be described as lateral and anterior cutaneous components as they approach the abdominal wall.

Clinical relevance: The subcostal nerve is relevant in regional anesthesia; a subcostal nerve block can be used to provide analgesia after upper abdominal surgery or procedures involving the costal margin. Injury or entrapment of the nerve can cause pain, paresthesias, or weakness in the lower abdominal wall. Knowledge of its course is important during flank, kidney, or subcostal approaches in surgery to avoid iatrogenic injury.

Variations: While typically T12, anatomical variations exist in its course or branching patterns. It is distinct from the iliohypogastric and ilioinguinal nerves (L1), which innervate adjacent regions.