Thanks to the great nineteenth century voice teacher Manuel Garcia (1805–1906) who was the first to perform laryngoscope in vivo. Since then, the basic approach of examining the pharynx and larynx has changed little, although the technology available has improved dramatically [7].
As a technique, indirect mirror examination has some limitations including perceptual difficulties in reliably recording side of lesion, learning curve in acquiring and maintaining skills, and a significant failure rate which prior to the era of readily available flexible endoscopy often mandated direct endoscopy under general anesthesia [8].
Endoscopic assessment, either with a rigid or flexible laryngoscope, has replaced mirrors due to better optical resolution and higher sensitivity. With the advance in technology, video techniques have been involved in most of the endoscopic procedures with a lot of advantages including record ability, magnification power which render better identification of anatomical structures with easy diagnosis of any anomaly or abnormality [8].
Though no significant discussion of complications of flexible nasoendoscopy, the most commonly used diagnostic tool in laryngeal lesions exists in the literature, but these possible complications may include discomfort of variable degrees, occasional epistaxis during difficult insertion, fiberoptic laryngoscopy also lacks the ability to show other important causes of laryngeal lesions such as thyroid diseases or lymph nodes enlargement. Also, fiberoptic laryngoscopy lacks any ability to show hidden laryngeal spaces as pre-epiglottic and para-glottic spaces [9].
CT and MRI are known to play an important role in the diagnosis of head and neck diseases. We know that CT and MRI features of suggesting the paralysis of the recurrent laryngeal nerve as atrophy of thyroarytenoid muscle, an enlarged ventricle ipsilateral enlargement of the pyriform sinus, paramedian position, decreased size, and/or fatty infiltration of the true vocal cord [2].
Unfortunately, CT and MRI cannot reveal the mobility of the vocal folds in real time. In addition to artifact caused by respiration and motion with decreased image quality, especially the need for sedation in children is also considered drawback. CT has the potential to deliver significantly greater radiation doses to children than to adults and in view of their greater susceptibility to radiation effects, care should be taken to avoid unnecessary CT examinations [10].
The disadvantages of MRI include the long acquisition time of the scans with consequent degradation of the images due to motion artifact from breathing, swallowing, and vascular pulsations. Claustrophobia and the contraindications due to the use of a strong magnetic field including the presence of cochlear implants, cardiac pacemakers, aneurysm clips, and any metal within the eye are also a problem [10].
In 1984, Shawker and others used real-time ultrasound during swallowing in ten normal subjects and found that the motions of the tongue, hyoid bone, and larynx can be monitored and timed [11].
The ultrasound appearance of the laryngeal region is always a clinical challenge, so the deep knowledge of the complex of the head and neck was essential. A good knowledge of the normal radiological anatomy of the head and neck renders easy identification of any abnormality.
Recently, US imaging has become a very powerful diagnostic tool, especially in scanning head and neck regions. With the advance in technology of ultrasound, it renders higher image quality with tissue differentiation putting in mind that it is noninvasive, nonionizing radiation dependent, non-time consuming, repeatable, bedside technique in addition to the great advantage of dynamic evaluation of the vocal cords [12].
Also, laryngeal US has numerous advantages in the diagnosis of vocal cords palsy in pediatric age group as it is well tolerated by infants with no need for anesthesia, safe, reliable, and noninvasive bed side [12].
The aim is to evaluate the laryngeal ultrasound as a diagnostic tool to evaluate different laryngeal structure as regarded laryngeal dynamics (range and abnormality), and anatomical structures.
We managed to achieve these goals by measurements of distances and cross sectional areas, calculating the range of cross-sectional areas in patients with vocal fold palsy and partial laryngectomy, assessment of gender variations in normal controls, and identification of all anatomical structures of larynx.
On analysis of the results, it was found that both glottic area and inter-arytenoid distance varies significantly between the phonation and inspiration phases being wider in respiratory phase more than during phonation with a mean percent of change in inter-arytenoid length of 41.99 +/22.66% and a percent of change in glottic area of 40.82 +/25.85%.
We also found that the inter-arytenoid distances during phonation to be highest in partially laryngectomized patients 0.81 ± 0.37 cm with statistically significant difference than control group. This finding is due to the fact that one vocal fold is missing, so the distance will be greater than the control group. However, the percent of change in length and area were much less in group 3 (partially laryngectomized) than group 1 or 2. This could be explained by the fact that laryngeal reconstruction after partial laryngectomies may have decreased the pliability of the larynx causing this significant decrease in the area change than the normal.
On studying the relation between the age and vocal folds movements, it was found that there was inverse relation in males with statistically significance as regard change in area r = 0.713 and length r = 0.687, where the older the age, the less the change in the area between both phases phonation and respiration. This may be due to many possible contributing factors including gradual decline of lung capacity, reduced muscle bulk, decreased type I slow contracting muscle fibers, decreased hyaluronic acid in the lamina propria, arthritic changes, and ossification of the laryngeal skeleton.
A rather interesting finding after data analysis is that we found that change of area during respiration and during phonation was higher among females 53.07 ± 29.25 cm2 than among males 32.25 ± 20.47 cm2. The explanation of this is that vocal folds in females have less tensile stress than males for fixed percent elongation (from 2 to 5 times less) likely due to the approximately 59% of the collagen found in adult male vocal folds. Thus, female vocal folds are significantly less stiff than male vocal folds during equal elongation or strain.
A rather striking correlation was found between area minimum and length minimum which states that: to calculate area min., we can substitute in the following equation: A min = L min + 0.917. We also found that area max. (glottic areas during respiration) are related significantly to length max. (inter-arytenoid length during respiration) with another important statistically valid correlation. This strong correlation was found between area maximum and length maximum which states that: to calculate area max., we can substitute in the following equation: A max = L max + 1.111. These two equations are very important to determine glottic area by measuring inter-arytenoid distance.
We acknowledge the limitations to this study. The linear transducers and convex curved transducers are not conforming to neck anatomy and thus contributing to limiting views. These technical issues may be resolved by development of high-frequency concave curve transducer for preserving skin surface and probe contact; this is essential to assess the airway and airway-related anatomical structures as standard of care. Additional limitation is that the air-mucosa interface has linear hyperechoic appearance which is sometimes difficult to discriminate.
We experienced other technical limitation during our work where we found difficulty in stabilization of the probe over thyroid cartilage. We instructed all patients not to hold their breath as vocal cord movement can be fairly observed during quiet respiration. Some cases with dense laryngeal cartilage calcification can cause image distortion and poor image quality.