Chapter 6
Laryngoscopy
Andrew J. Kinshuck and Gurpreet S. Sandhu
National Centre for Airway Reconstruction, Dept of Ear, Nose and Throat Surgery, Imperial College Healthcare NHS Trust, Charing Cross Hospital, London, UK.
Correspondence: Andrew Kinshuck, Dept of Ear, Nose and Throat Surgery, Imperial College Healthcare NHS Trust, Charing Cross Hospital, Fulham Palace Road, London, W6 8RF, UK. E-mail: akinshuck@gmail.com
Laryngoscopy has become a routine part of the examination of patients presenting to the ENT specialist. The development of flexible fibreoptic endoscopes has enabled laryngoscopy to be performed in the clinic in patients of all ages. It provides a visual assessment and allows dynamic evaluation of the larynx and upper airway. Laryngoscopy continues to gain popularity and is now regularly used by other specialists, including respiratory specialists, speech therapists and anaesthetists. There has been a continued growth in office-based procedures on the larynx using a variety of laryngoscopy and anaesthetic techniques. Suspension laryngoscopy allows the surgeon to perform endoscopy and surgical procedures on the entire airway, from the supraglottis to the bronchi, under general anaesthesia. Suspension laryngoscopy enables the surgeon to use both rigid and flexible endoscopes, surgical instruments, fibre lasers, cryoprobes, and insert stents. Adding the operative microscope allows binocular vision, magnification, improved illumination and use of the carbon dioxide laser through a “line-of-sight” technique.
Cite as: Kinshuck AJ, Sandhu GS. Laryngoscopy. In: Herth FJF, Shah PL, Gompelmann D, eds. Interventional Pulmonology (ERS Monograph). Sheffield, European Respiratory Society, 2017; pp. 78–88 [https://doi.org/10.1183/2312508X.10002817].
The larynx is a complex structure in the neck consisting of a framework of cartilages connected by ligaments, membranes and muscles. The primary functions of the larynx include protection of the airway, phonation, Valsalva and control of respiration. Examination of the larynx (laryngoscopy) is routinely performed by specialists to evaluate laryngeal structure and function. Laryngoscopy also allows procedures on the larynx and upper airway to be performed. Laryngoscopy has progressed since it was first described, and continues to develop and evolve along with advances in technology.
History of laryngoscopy
There remains debate regarding the invention of laryngoscopy. From as far back as 1743, Leveret reported visualisation of the nasopharynx with a metal spatula and removal of a laryngeal polyp [1]. However, it was not until the 19th century that further advances in laryngoscopy were made. During this pre-antibiotic era, the common airway and laryngeal pathologies were the result of infective causes, including syphilis, diphtheria and tuberculosis. Previously, these could only be treated with a tracheostomy and diagnoses only made post mortem.
Philip Bozzini, in 1807, invented a primitive endoscope known as the “lichtleiter” or light conductor. This enabled examination of anatomical orifices, including the mouth and larynx [2]. In 1855, Manuel Garcia presented his findings on laryngoscopy to the Royal Society of London [3]. The technique of visualising the larynx relied on an angled mirror in the mouth with light provided by a head-mounted mirror. This method of indirect laryngoscopy was further developed by Johann Czermak, in Budapest, who was able to make adjustments to focus the light. In 1858, Czermak presented his work to the Vienna Imperial Society of Medicine and this helped indirect laryngoscopy become popular among laryngologists [4]. In 1865, Sir Morrell Mackenzie published a book on “The Use of the Laryngoscope in Diseases of the Throat” and indirect laryngoscopy (using laryngeal mirrors) continued to be widely used around the world until the development of the endoscope [5].
Direct laryngoscopy was first described by Horace Green, in 1855, in the USA [1]. A blade-like instrument was used; however, it was not well tolerated by patients prior to the development of anaesthesia. In 1864, Albert Tobold in Germany was able to directly visualise laryngeal papillomatosis [1]. Further work in Germany by Alfred Kirstein, in 1895, using an electric light and a tubed oesophagoscope, which he termed an “autoscope”, developed direct laryngoscopy [1].
In 1909, suspension laryngoscopy was developed by Gustav Killian to allow both hands to be free to operate on the larynx [6]. In the USA, in 1904, Chevalier Jackson continued to make further advances in laryngoscopy, bronchoscopy and oesophagoscopy with improved light and suction [7].
At this period at the turn of the 20th century advances in anaesthesia had allowed intubation and enabled anaesthesiologists to make further developments to laryngoscopy. In 1913, in the USA, Henry Janeway developed a laryngoscope with an internal light source which was battery powered for tracheal intubation [8].
Fibreoptic endoscopy was developed in 1957 by Basil Hirschowitz and Larry Curtiss [9]. This was first used in examining the gastrointestinal tract. However, there were limits to the image quality. Harold Hopkins solved this problem in the 1950s by inventing the rod lens telescope with improved light and optics. He used rods of glass between the lenses in the rigid endoscope, thus preventing any loss of image quality [10]. The Hopkins rod lens system is still used today, but with the addition of a detachable digital chip camera head to provide a high-definition view with recording capabilities. These rigid endoscopes are used under general anaesthesia and suspension laryngoscopy to provide a detailed view of the airway. The Hopkins rods are available in various lengths and diameters, which allows them to be used with rigid bronchoscopy sets in the paediatric airway. The endoscopes are made with different angulations at the tip, ranging from 0° to 120°. A 70° endoscope enables a view of the anterior commissure and ventricle (the area between the true and false vocal cords), which is important when assessing vocal fold tumours.
The first fibreoptic bronchoscope was developed in the 1960s in Japan by Shigeto Ikeda [11]. The fibreoptic flexible endoscope continued to develop over the 20th century with the addition of working channels and suction. Further advances in flexible endoscopes, including distal chip or “chip-on-tip” systems, have virtually confined indirect laryngoscopy to the history books. Recent advances in technology have greatly improved the quality of modern flexible endoscopes. The “chip-on-tip” endoscopes provide high-definition image quality not seen previously with flexible endoscopes [12]. Digital recording allows laryngoscopy to be documented, analysed and demonstrated to patients.
Flexible nasoendoscopy
Flexible nasoendoscopy is now the main method for performing diagnostic laryngoscopy. In the ENT clinic it is used to assess the nasal cavity, pharynx and larynx. It is also used by speech and language therapists (SLTs) to perform swallow assessments. This is known as a fibreoptic endoscopic evaluation of swallowing. Unlike flexible bronchoscopes, standard nasoendoscopes have no suction or port for instrumentation. This makes them cheaper, easier to clean, portable and readily available.
The flexible nasoendoscope is passed along the floor of the nose and directed at the post-nasal space to assess the larynx. There are numerous sizes of nasoendoscopes and an ultra-thin (2.2 mm diameter) flexible nasoendoscope is available to assess the neonatal airway [13]. Nasoendoscopy is well tolerated by patients. Topical anaesthesia, decongestant or lubricant can be used, although there is no clear evidence in the literature if these provide any benefit [14].
Flexible nasoendoscopy is a safe procedure with most patients only experiencing mild discomfort. The endoscopist must be careful not to cause trauma to the nasal mucosa, which can cause epistaxis (although normally only mild). In patients with a strong gag reflex, retching and vomiting can occur, and the scope should be withdrawn to prevent further discomfort. In patients with acute airway oedema, nasoendoscopy may cause further airway compromise and should only be performed by a specialist in a safe environment.
Training in flexible nasoendoscopy is performed routinely by ENT, anaesthesiology and SLT trainees. In the authors’ department the trainees first perform nasoendoscopy on a plastic model to help them become familiar with the equipment and demonstrate the anatomy. This is followed by practice on other trainees before supervised use on patients. The use of a camera and a video display helps to demonstrate the anatomy and to teach useful tips and manoeuvres to visualise anatomical structures. ENT trainees in the UK, as part of their syllabus, have to complete a work-based assessment in direct observation nasoendoscopy procedures. The Royal College of Speech and Language Therapists produced a position paper in 2008 on nasoendoscopy, which includes recommendations on achieving adequate competencies and training [15].
For detailed assessment of vocal fold movement and vibration, rigid endoscopes have traditionally been used due to the improved image. Rigid 70° or 90° rigid endoscopes are passed through the mouth and positioned just beyond the tongue base. This provides an excellent image of the vocal folds and, together with the use of stroboscopy, demonstrates the mucosal waveform of the vocal folds. Laryngeal stroboscopy creates an apparent slow-motion video by sampling successive phases of the vocal fold cycle.
Office-based procedures in laryngology
Office-based procedures in laryngology have been performed since the first descriptions of visualising the larynx. In 1865, MACKENZIE [5] described how to apply remedies to the larynx with the aid of the laryngoscope. This required a great deal of skill and cooperation from the patient to use a laryngeal mirror and curved forceps on the larynx. The development of safe general anaesthesia and the operative microscope enabled the majority of laryngeal procedures to be performed under general anaesthesia. More recently there has been a drive towards redeveloping office-based procedures in laryngology using topically applied anaesthesia. The various laryngeal procedures include injection of botulinum toxin, vocal fold medialisation, biopsies of laryngeal lesions, and laser treatment for laryngeal papillomatosis and laryngeal dysplasia [16]. Some of these procedures require a flexible endoscope with a channel to pass instruments or a laser fibre. The KTP (potassium titanyl phosphate) laser can be passed via the endoscope through a small channel. The KTP laser has a wavelength of 532 nm, corresponding to a greater absorption for oxyhaemoglobin. Thus, the light is well absorbed by haemoglobin and pigmented tissue. The KTP laser has been used for treating both laryngeal papillomatosis and laryngeal dysplasia in the clinic [17]. The arrival of the carbon dioxide (CO2) laser “fibre” system has also allowed its use in the clinic setting.
In specialist voice clinics the laryngologist works closely with SLTs. The development of digital cameras attached to the endoscope allows joint assessment of laryngeal function. Patients with vocal fold immobility due to malignancy often present with a weak, breathy voice. If they are not medically fit for general anaesthesia then vocal fold augmentation or medialisation can be performed in the clinic with the assistance of the SLT (figure 1). Optimising the amount of material injected into the vocal fold will enable good vocal fold contact and ultimately improved phonation and swallowing safety [18].
