92 - Anterior Cutaneous Nerve Block

Abstract

Anterior cutaneous nerve block is useful in the evaluation and management of entrapment of the anterior cutaneous nerve. Anterior cutaneous nerve entrapment syndrome consists of a constellation of symptoms, including severe, knifelike pain emanating from the anterior abdominal wall associated with point tenderness over the affected anterior cutaneous nerve. The pain radiates medially to the linea alba but in almost all cases does not cross the midline. Anterior cutaneous nerve entrapment syndrome occurs most commonly in young females. The patient can often localize the source of pain quite accurately by pointing to the spot at which the anterior cutaneous branch of the affected intercostal nerve pierces the fascia of the abdominal wall at the lateral border of the rectus abdominis muscle. It is at this point that the anterior cutaneous branch of the intercostal nerve turns sharply in an anterior direction to provide innervation to the anterior wall. The nerve passes through a firm, fibrous ring as it pierces the fascia, and it is at this point that the nerve is subject to entrapment. The nerve is accompanied through the fascia by an epigastric artery and vein. There is the potential for small amounts of abdominal fat to herniate through this fascial ring and become incarcerated, which results in further entrapment of the nerve. Contraction of the abdominal muscles puts additional pressure on the nerve and may elicit sudden, sharp, lancinating pain in the distribution of the affected anterior cutaneous nerve. The presence of Carnett sign is considered diagnostic for anterior cutaneous nerve entrapment syndrome.