Describing and measuring areas of the squamous epithelium lining the subglottic space in the larynx.

What is it about?

Using an alcian blue/phloxine dye technique to display the lining cells of the larynx in normal healthy specimens (non-smokers) with particular reference to the subglottic space. This dye technique facilitated measuring of areas of squamous cells by compressing the specimens between perspex sheets and tracing areas of squamous cells using Indian ink and cellophane. The tracing was then placed over graph paper and measurements calculated. The purpose of this endeavor was to record the incidence and extent of any areas of squamous epithelium in the subglottis in a non-smoking, non-bronchitic population, and to assess any possible correlation between the incidence and extent of this type of lining cell and factors such as age and gender.

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Why is it important?

Earlier descriptions (1838 and 1885) of the epithelial lining of the larynx were inaccurate because of the difficulty examining the mucosa of this cartilaginous organ. Also, the subglottic space was not considered part of the larynx until the end of the 19th century. Around 1890, islands of squamous epithelium were reported in this space and were believed to be either of embryonic origin or representative of metaplasia. All these investigations were done by embedding tissue and producing microscope slides for histological examination - a method fraught with error in terms of mapping the lining epithelium of the cartilaginous larynx. Around the middle of the twentieth century, researchers found islands of squamous epithelium in the subglottic space and they were thought to be rare. More recently, scanning electron microscopy confirms that the subglottic space is, in fact, almost exclusively lined by ciliated respiratory epithelium. However, the results of our work showed the presence of areas squamous epithelium to be common in the subglottic space in both sexes (54% in males, 44% in females). Since no squamous epithelium has been found in the subglottis of neonates, the presence of this type of cell would indicate metaplasia. Detecting the presence of squamous cells in the subglottis, being able to measure areas and compare specimens from a healthy population, has benefits not only in defining the normal distribution of the lining cells, but to examine and determine factors that may contribute to squamous metaplasia and its link to the early signs of disease.

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