Normal topography of the conus elasticus. Anatomical bases for the spread of laryngeal cancer.

The topographic relations of the conus elasticus were studied with special regard to the local spread of laryngeal cancer. Sections of twelve plastinated adult human larynges were investigated. Lateral from the median cricothyroid ligament, the conus elasticus reveals two broad gaps containing adipose tissue and blood vessels. Along these routes, tumors of the larynx may easily extend into the ventral extralaryngeal tissues by continuous growth. Fibres of the conus elasticus cover the entire cranial surface of the vocalis muscle near the muscle's insertion at the thyroid cartilage. This part of the conus elasticus has been termed "thyroglottic ligament" in the fetus [22]. In the adult, this ligament prevents early cancer of the anterior vocal cords from invading adjacent structures. Other collagenous fibres continuous with the conus elasticus provide only an incomplete layer separating the lateral cricoarytenoid and the thyroarytenoid muscle. These fibres do not constitute an effective barrier against cancer growth.