This study demonstrated that ultrasonography quantitatively evaluated reduced laryngeal movement help in the assessment and diagnosis of pharyngeal phase dysphagia in CP children with sensitivity of 96%, and it can be used as an alternative to the FESS as it is a less-invasive and less costly bedside test.
Cerebral palsy is a permanent movement disorder which is attributed to disturbances in the developing fetal or infant brain, and it appears in early childhood .
Dysphagia is closely related to gross motor dysfunction in children with CP , and oropharyngeal dysphagia occurs in about 85% of children with CP .
Over the years, endoscopy has become a standard tool for diagnosing dysphagia  . FEES investigates the pharyngeal phase only .
Real-time ultrasound is a non-ionizing imaging modality and has been used to observe deglutitive movements since the late 1970s [14, 15]. It was used in preliminary investigations of infants to visualize the bolus movement through the pharyngeal area while they are being breastfed .
Larynx elevation is crucial for airway protection and cricopharyngeal muscle relaxation [9, 16, 17]. As the thyroid cartilage approximates to the hyoid bone, the larynx elevates, the epiglottis tilts down and closes to prevent the bolus from entering the trachea, and cricopharyngeal muscle opens subsequently, allowing the bolus to pass through [18, 19]. So incomplete laryngeal elevation is assumed to be one of the major mechanisms in dysphagia and often leads to aspiration . The fiberoptic endoscopic evaluation of deglutition is invasive and does not allow one to quantify swallowing movements .
The relative laryngeal movement is used in this study rather than the approximation distance to exclude the normal interpersonal variation, especially as the study deals with children in different ages.
In this study, the mean relative laryngeal movement in CP children with no pharyngeal abnormalities was 66.19% ± 3.42. Similar results were concluded by Kuhl et all.  who have examined 42 healthy people and 18 dysphagic patients suffering from different neurological diseases, and they found that the mean relative laryngeal movement was 61% ± 3 in normal subjects. Huang et al.  have also examined 15 normal volunteers, 20 patients without dysphagia, and 20 patients with dysphagia, and they found that the mean relative laryngeal movement in normal volunteers was 47.26 ± 4.9% and in stroke non-dysphagic patients 42.66 ± 8.3%.
In our study, the mean relative laryngeal movement in the dysphagic CP children suffering from pharyngeal abnormalities was reduced to less than 40% (20.10 ± 13.73); similar results were also concluded by Huang et al.  and Kuhl et al.  who showed reduced relative laryngeal movement to less than 40% in patient suffering from dysphagia (34.06 ± 10.9% and 42% ± 10 respectively).
In addition to the evaluation of relative laryngeal movement, B mode examination at the level of the thyroid cartilage may increase the sensitivity of US examination in diagnosing the pharyngeal phase of dysphagia, as the spillage of water into the laryngeal airway could be visualized in these children as air bubbles intermixed with water droplets, and it was beneficial in this study as the only false negative case which showed borderline reduced relative laryngeal movement (45%); penetration of water over the vocal cord was identified during B mode examination and the final US diagnosis was pharyngeal dysphagia.
The reduced relative laryngeal movement cut off value in this study was 45%, which was also similar to Huang et al.’s  result who found that the relative laryngeal movement of less than 40% may imply dysphagia, with acceptable sensitivity and specificity.
The limitation of this study is that we compare the result of reduced relative laryngeal movement with the clinical result of FEES, rather than the videofluoroscopic examination which is the gold standard examination for the evaluation of swallowing where the laryngeal movement can be readily measured and compared, yet we use the FEES to avoid exposing the children to X-rays, and despite the limitation of this study, the advantage of US of being a noninvasive, radiation-free, and less-expensive bedside procedure in addition to its quantitative value makes it an emergent and promising examination which can be used in the screening and serial monitoring for treatment response of dysphagia in children; another advantage of US examination is that it can be repeated many times without influencing the children or their parent any psychological disturbance.