The Interscalene Triangle: A Cadaveric Dissection of a Critical Neurovascular Corridor at the Root of the Neck.

The interscalene triangle is a key cervicothoracic gateway bounded by the anterior and middle scalene muscles and the first rib. It transmits the roots and trunks of the brachial plexus (C5-T1) and the subclavian artery (SA), while the subclavian vein (SV) courses anterior to the anterior scalene muscle and the phrenic nerve (PN) descends along its anterior surface. Cadaveric dissection highlights these critical topographic relationships, providing an anatomical basis for understanding thoracic outlet syndrome, optimizing ultrasound-guided regional anesthesia, and minimizing the risk of iatrogenic nerve injury during cervicothoracic surgery.