Laryngocele arises as herniation of laryngeal mucosa through the following membrane:

Laryngocele is an air-filled cystic swelling which occurs due to dilatation of saccule. Saccule is a diveiculum arising from anterior pa of ventricle/sinus of larynx. External laryngocele is one in which distended saccule herniates through the thyrohyoid membrane and presents as a reducible swelling in the neck, which increases in size on coughing or performing Valsalva.