Adenotonsillectomy is the most commonly performed operation in children within the field of otorhinolaryngology [1]. Postoperative complications include bleeding, pain, and vocal changes, etc. Among them, changes to the voice after surgery often occur.

Fant [2] presented the source-filter theory in the acoustic theory of speech production. According to this theory, the human voice is produced through the larynx and vocal tract. The human vocal tract includes the oral, nasal, pharyngeal, and laryngeal cavities, which are important resonant cavities. Among them, the space within the oral and laryngeal cavities can be changed freely; thus, these cavities can create various resonance changes. Therefore, changes to the resonance properties after removal of the tonsils and adenoids located in the oral and nasal cavities may affect the voice. In children, in particular, the tonsils and adenoids occupy a relatively large area of the oral and nasal cavities and therefore have a large influence on the voice, because the vocal organs are in the process of growth and have yet to undergo voice mutation. Therefore, tonsillectomy or adenoidectomy, which changes the resonance energy in children, is important for childhood voice. Previous studies have produced conflicting results. Some have reported that the postoperative voice will be improved and others have reported that tonsillectomy has little effect on the voice, while others have reported that it can lead to velopharyngeal insufficiency [1,3-6]. These conflicting results may have resulted from the inclusion of different languages or a variety of methods for evaluating the voice. Therefore, our study explored vocal changes in a homogeneous population: Korean children who underwent adenotonsillectomy.

Resonance cavities include the oral cavity, nasal cavity, pharynx, and larynx. Among them, the space within the oral cavity and larynx can be freely transformed, leading to various vocal changes. Removal of the tonsils located on either side of the oral cavity and the adenoids located in the middle portion between the pharynx and nasal cavity causes a change in the resonance cavity after adenotonsillectomy and thus has a huge influence on the voice. This has been of great concern not only to occupational voice users but also to children who are still growing and to the general public.

Several studies have investigated vocal changes associated with tonsillectomy and adenoidectomy. Analysis of formant frequency is a helpful method that can predict changes in the upper airways that act as resonance organs. Previous research has found that variations in F1 reflect airway changes in apneic snorers, whereas variations in F2 reflect changes in the morphology of the tongue and variations in F3 reflect lip movements [11-13]. Some recent studies have used objective analysis of formants as well as subjective analyses. Some have reported that F0, F1, and F2 formant frequencies do not change significantly after tonsillectomy with or without adenoidectomy [14-17]. In contrast, Lin, et al. [18] observed an increase in F0 after surgery, and Kara, et al. [19] reported significant changes in F3 and F4 in 36 children at 3 months after adenotonsillectomy.

Our study revealed changes in acoustic characteristics of the voice after adenotonsillectomy. We observed a significant change in formant frequency was only for vowel /i/, which decreased significantly in F2, CD, and GA values. We believe that /i/ is most affected by postoperative tongue position changes because it is a front-high vowel. F2 is mainly dependent on the height of the tongue, CD is the parameter that reflects the height of the tongue, and GA is the parameter that determines the fore and aft position of the tongue. The oropharyngeal space after surgery becomes widened and causes the tongue to pronounce in the posteroinferior position. /u/ is a back-low vowel with no significant change in the movement of the tongue. /a/ is a back-high vowel with little fore and aft motion of the tongue. Therefore, these vowels appear not to change after surgery. The change in dB for the vowel /u/ was statistically significant, where the mean preoperative dB was 70.57±3.81 and the mean postoperative dB was 67.49±4.93 (p=0.025). However, a 3-dB change may not be large enough to be of clinical significance because sound is perceived to be twice as loud for every increase of 10 dB.

Our results differ slightly from those of previous studies, due to the nature of research measuring vocal parameters. The measurement of vocal parameters is highly sensitive, so statistical values vary depending on the selection of subjects and the postoperative follow-up duration.

The degree of tonsillar hypertrophy varies from grade I to grade IV, depending on size. Saida and Hirose [14] reported that vocal changes occur when grade III or higher tonsils are removed. Ilk, et al. [17] reported that the greater the grade of tonsil, the more severe the change of postoperative voice. Therefore, we included patients with grade III or IV tonsillar hypertrophy. We also limited the age range of subjects, because children under the age of 5 years may not be able to phonate as requested, and children aged 10 years and older may have already experienced voice mutation.

In vocal analysis, perceptual analysis of subjective vocal changes is important. Previous perceptual analyses performed by language pathologists or otolaryngologists have yielded variable results. Chuma, et al. [15] reported that the majority of perceptual categories did not change significantly postoperatively, except for a significant decrease in hyponasality. Lunderborg, et al. [20] reported that their study population had more hyponasality, compressed/throaty voice, and lower pitch, and that these were significantly improved and normalized after surgery. In our study, we found that most patients had postoperative changes, indicating the possibility of vocal change after surgery. Although the κ value was low, the OA was 0.75, which was highly consistent among raters. However, a particular limitation of our study is that we did not investigate detailed perceptual parameters such as hoarseness, breathiness, nasality, pitch, roughness, etc., and we did not aim to reach a consensus about the definition of ‘voice change.’

We used the PVHI to conduct a subjective analysis according to the parents’ response. The PVHI is a validated questionnaire for assessing the psychosocial aspects of voice disorders. Naraghi, et al. [21] recruited 86 children aged 3-13 years and reported an improved PVHI score after tonsillectomy with or without adenoidectomy (mean preoperative score: 14.39, mean postoperative score: 2.93). A study that compared the PVHI scores of normal and dysphonic groups of Korean children aged 3-11 years reported a score of 2.33 for the control group (mean age: 7.73±1.43 years, n=15) and 23.13 for a dysphonia group (mean age: 7.33±2.87 years, n=15) diagnosed with vocal cord nodules [22]. In our study, the mean preoperative score was 2.70±3.37 and the mean postoperative score was 1.65±2.21 (p=0.011). Although the difference before and after surgery was statistically significant, the preoperative PVHI scores of our patients were very similar to those of normal Korean children, and the postoperative PVHI scores were within the normal range. This could not explained may be a placebo effect related to the parents’ expectations of a positive change postoperatively. Therefore, this result indicates that, at the least, the parents did not perceive a negative change in their child’s voice after surgery.

In conclusion, tonsillectomy with or without adenoidectomy may affect the voice acoustically and perceptually in Korean children. Voice research is highly sensitive, so our study of postoperative vocal changes in Korean children is valuable. When performing adenotonsillectomy, consideration should be given to the possibility that Korean children’s voices may be altered after surgery. In the future, it will be necessary to study more diverse subject groups, use various research methods, and allow a longer follow-up duration for Korean children who undergo adenotonsillectomy.