Examining the larynx
The larynx is positioned low in the neck and requires some special skills and tools for examination.
The simplest form of laryngeal examination is called "indirect laryngoscopy". The examiner can place a small mirror in the back of the throat and angle it down towards the larynx. Light can be reflected downward and the larynx can be seen in the mirror. Indirect laryngoscopy is quick an easy, and gives a nice three dimensional view of the larynx in true color. However, some individuals have a strong gag reflex and cannot tolerate the mirror exam. Also, the patient cannot be examined during normal speech since the mirror must remain in the back of the throat.
Flexible and Rigid Endoscopes
There are two special optical instruments that can assist the physician in examination of the larynx during an office visit. The instrument shown below on the left is a nasopharyngoscope. The curved part of the scope is a flexible fiberoptic cable that can be passed through the nose and through the pharynx until it gives a view of the vocal folds. The flexible scope causes very little gagging and is actually quite comfortable. Using this flexible endoscope, the larynx can be examined during normal speech. However, the resolution through this scope is reduced since the image must travel through a bundle of small optical fibers.
The instrument on the right is called a 90 degree telescope. The scope is placed at the back of the mouth. At the back there is a prism that reflects light 90 degrees. This scope is a little more difficult for the patient, but it gives an extremely clear and magnified image of the vocal cords.
A camera can be attached to each of these scopes and the examination can becorded for documentation. The image on the left shows a picture taken through a 90 degree telescope of normal vocal folds. The folds are partially opened and the opening into the trachea can be seen between them.
During speech, the vocal folds vibrate 100 times per second or more. This is too fast to be seen by our eyes. In order to more carefully examine the vocal folds in action, a special light source called a strobe light is used. The strobe sends off a very bright and very short flash of light. If the strobe flash is repeated at the exact same rate that the vocal folds are vibrating, they will appear "frozen" in time. (This is the same principle as a timing light that is used to tune up a car). If the firing rate is then adjusted so that it is a little faster or a little slower than the vibration rate of the folds, the folds will appear to move in slow motion.
The strobe exam is extremely useful because it allows us to see how the vocal folds are functioning. Some voice disorders are caused by subtle changes in the tissue that makes up the folds. These changes may not be apparent on a regular fiberoptic or mirror exam of the larynx, but can be seen with a careful strobe exam.
To the left is a photo taken from a stroboscopic exam of the normal vocal cords during speech. The movie was taken through a flexible examining scope like the one shown above.
(The file is in .MOV format and is about 1 Mb in size.
Another type of examination is called "direct laryngoscopy", and this involves directly looking at the larynx. Because of the gag reflex, direct laryngoscopy is most often done in the operating room under a general anesthetic. During direct laryngoscopy, biopsies can also be taken of any suspicious lesion in the larynx or other parts of the throat.
The image to the right shows how direct laryngoscopy is done. The examiner holds an instrument called a laryngoscope in his or her hand, and looks through this instrument to examine the larynx. A microscope can also be used to look at the vocal folds and other parts of the larynx under high magnification.