76 Papilloma of the Larynx
Squamous cell papilloma is by far the commonest benign tumour of the larynx. Adenomas, chondromas, fibromas, haemangiomas and other neurogenic and mesodermal benign tumours are all rare and will not be considered further.
76.1 Aetiology and Pathogenesis
The aetiology of laryngeal papillomas is now known to be infection of the epithelial cells with human papillomavirus (HPV), a DNA virus with over 170 subtypes. HPV subtypes 6 and 11 are responsible for over 90% of laryngeal papillomas. HPV 11 is associated with more aggressive and extensive disease. Laryngeal papillomatosis shows a bimodal distribution, affecting young children (typically ages 2–5) and young adults (typically in the third and fourth decades). It is thought that the disease is transmitted from infected secretions in the birth canal during delivery, although in a small proportion the virus is transmitted via the placenta prior to birth. In adults, HPV is spread through sexual contact. Electron microscopy and immunofluorescent techniques have shown that HPV DNA is incorporated into the host’s cellular DNA. Polymerase chain reaction (PCR) and in situ hybridisation (ISH) are the most sensitive techniques available to show evidence of HPV infection. Apparently, normal mucosal cells adjacent to the papillomas also contain viral DNA, which may become activated to form a recurrent lesion. This partly explains the difficulty in curing the disease.
Squamous papillomas may grow anywhere in the respiratory tract from the lips to the lungs, but the vocal cords, anterior commissure and vestibular folds are the commonest sites of involvement. The lesions have a predilection for points of airway constriction, where there is increased airflow, drying, crusting and irritation. These areas of microtrauma allow HPV to infect the basal layer of the epithelium. Laryngeal mucus is thought to behave as a protective blanket in some sites, for example, the interarytenoid area. The growths may present as scattered single lesions or clusters or as a huge exuberant mass. They can be sessile or pedunculated and are characteristically non-keratinising with a connective tissue core.