Ultrasound image of the posterior approach for an intermediate cervical plexus block at C4-5 level in a 3-year-old torticollis patient undergoing unipolar sternocleidomastoid (SCM) release with myectomy. Hydrodissection of the posterior cervical space between the SCM muscle and prevertebral fascia by local anesthetic is seen, and local anesthetic spreads to the area near the carotid sheath. CA: carotid artery, IJV: internal jugular vein, LA: local anesthetic. White arrow points: prevertebral fascia.