Keratinizing squamous dysplasia of the larynx

What is keratinizing squamous dysplasia of the larynx?

Keratinizing squamous dysplasia in the larynx is a pre-cancerous disease. It develops from the squamous cells in the epithelium on the inner surface of the larynx. Keratinizing squamous dysplasia can start in any part of the larynx although the most common location is the vocal cord.

Keratinizing squamous dysplasia is considered a pre-cancerous disease because it can over time turn into a type of laryngeal cancer called squamous cell carcinoma. The risk associated with keratinizing squamous dysplasia turning into cancer depends on how abnormal the squamous cells look under the microscope. The risk of cancer is highest when your pathologist describes the changes as severe (see Grade below).

The larynx

When we breathe, air travels from our mouth and nose to our lungs. On its way to the lungs, air passes through a part of the throat called the larynx. You cannot see your larynx because it starts at the very back of the tongue.

Most of the larynx is a hollow tube filled with air. The larynx helps us breathe and create sound when we talk. For this reason, diseases involving the larynx often make it difficult to breathe or talk normally. The inside surface of the larynx is lined by specialized cells called squamous cells. These cells form a barrier called the epithelium. The tissue below the epithelium is called the stroma.

normal squamous mucosa larynx

The larynx is divided into three sections from top to bottom and each section is made up of smaller parts. Most pathology reports will describe the sections or parts of the larynx examined.

Supraglottis

The supraglottis is the first section of the larynx. The supraglottic larynx is made up of several smaller parts including:

  • Epiglottis.
  • Aryepiglottic folds.
  • Arytenoids.
  • False vocal cords.
  • Ventricle.
Glottis

The glottis is the second section and it is in the middle of the larynx. The glottis is made up of several smaller parts including:

  • True vocal cords.
  • Posterior commissure.
  • Anterior commissure.
Subglottis

The subglottis is the third and last section of the larynx. Unlike the other sections of the larynx, the subglottis is not made up of many smaller parts. The subglottic larynx connects with the trachea (windpipe).

What causes keratinizing squamous dysplasia in the larynx?

The most common cause of squamous dysplasia in the larynx is smoking. Other causes include excessive alcohol consumption, immune suppression, and prior radiation to the neck.

How do pathologists make this diagnosis?

The diagnosis of keratinizing squamous dysplasia is usually made after a small sample of tissue is removed in a procedure called a biopsy. The biopsy is usually performed because your doctor saw an abnormal-looking area of tissue during an examination of your larynx. Your pathology report will probably say what part of the larynx was sampled in the biopsy.

Compared to normal, healthy squamous cells, the abnormal cells in an area of keratinizing squamous dysplasia are larger, darker, and disorganized. Pathologists use the word hyperchromatic to describe cells that look darker than normal cells. Large clumps of genetic material called nucleoli may also be seen in the nucleus of the abnormal cells.

The word keratinizing means that the squamous cells are producing a specialized protein called keratin. This causes the cells to look bright pink when examined under the microscope. Keratinization is abnormal in the larynx.

keratinizing squamous dysplasia

The abnormal cells in squamous dysplasia are only seen in the epithelium. This is different from squamous cell carcinoma where the abnormal cells are also seen in the stroma below the epithelium. The movement of abnormal cells from the epithelium into the stroma is called invasion. Your pathologist will carefully examine your tissue sample to make sure there is no evidence of invasion before making the diagnosis of squamous dysplasia.

Grade

Pathologists use the term grade to describe the difference between the abnormal cells in an area of keratinizing squamous dysplasia and the normal squamous cells that are usually found in the larynx. Pathologists use the size, colour, and shape of the cell to determine the grade. Using these features, dysplasia in the larynx is usually divided into three levels:

  • Mild dysplasia – The abnormal squamous look very similar to normal squamous cells.
  • Moderate dysplasia – The abnormal squamous cells are darker and larger than normal squamous cells and the normal organization of the epithelium may be disrupted.
  • Severe dysplasia – The abnormal squamous cells look similar to cancer cells but they are still only seen in the epithelium. Another name for severe dysplasia is squamous carcinoma in situ.

Some pathology reports will group moderate and severe dysplasia together and call them both high-grade dysplasia. Mild dysplasia is called low-grade dysplasia.

The grade is very important because it is related to the risk of developing invasive cancer in the future. Mild (low grade) dysplasia has a very low risk of turning into cancer and is often left untreated. Moderate and severe (high grade) dysplasia is associated with a much higher risk of becoming cancer and patients with this condition are usually offered treatment to remove the diseased tissue.

Margins

A margin is any healthy tissue that was cut by the surgeon in order to remove the abnormal area of tissue from your body. Whenever possible, surgeons will try to cut healthy tissue well outside of the abnormal area to reduce the risk that any abnormal cells will be left behind after the tissue is removed.

Your pathologist will carefully examine all the margins in your tissue sample to see how close the abnormal cells are to the edge of the cut tissue. Margins will only be described in your report after the entire abnormal area of tissue has been removed. Margins are not described in a report after a biopsy has been performed.

A negative margin means that squamous dysplasia was not seen at the very edge of the cut tissue. If all the margins are negative, most pathology reports will say how far the closest abnormal cells were to the cut edge of the tissue. The distance is usually described in millimeters.

A margin is considered positive when squamous dysplasia is seen at the very edge of the cut tissue. A positive margin is associated with a higher risk that the disease will come back (recur) in the same site after treatment.

by Jason Wasserman, MD PhD FRCPC (updated July 28, 2021)
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