Extracranial internal carotid artery dissection is a relatively rare disease in Japan. We herein report a case of a 60-year-old woman with spontaneous left internal carotid artery dissection with a dilated and dissected cavity. Following the identification and measurement of the true and false lumens using intravascular ultrasound, a double-layer micromesh stent (Casper stent; Microvention, Terumo, Tustin, CA, USA) was deployed for post-dilation. No perioperative complications were observed, and the patient was discharged on postoperative day 6.