Tiroplastia tipo IV modificada (aproximación cricotiroidea) en un paciente con androfonía / Modified type IV thyroplasty (cricothyroid approximation) in a patient with androphonia

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Reorganization of laryngeal motoneurons after crush injury in the recurrent laryngeal nerve of the rat.

Motoneurons innervating laryngeal muscles are located in the nucleus ambiguus (Amb), but there is no general agreement on the somatotopic representation and even less is known on how an injury in the recurrent laryngeal nerve (RLN) affects this pattern. This study analyzes the normal somatotopy of those motoneurons and describes its changes over time after a crush injury to the RLN. In the control group (control group 1, n = 9 rats), the posterior cricoarytenoid (PCA) and thyroarytenoid (TA) muscles were injected with cholera toxin-B. In the experimental groups the left RLN of each animal was crushed with a fine tip forceps and, after several survival periods (1, 2, 4, 8, 12 weeks; minimum six rats per time), the PCA and TA muscles were injected as described above. After each surgery, the motility of the vocal folds was evaluated. Additional control experiments were performed; the second control experiment (control group 2, n = 6 rats) was performed labeling the TA and PCA immediately prior to the section of the superior laryngeal nerve (SLN), in order to eliminate the possibility of accidental labeling of the cricothyroid (CT) muscle by spread from the injection site. The third control group (control group 3, n = 5 rats) was included to determine if there is some sprouting from the SLN into the territories of the RLN after a crush of this last nerve. One week after the crush injury of the RLN, the PCA and TA muscles were injected immediately before the section of the SLN. The results show that a single population of neurons represents each muscle with the PCA in the most rostral position followed caudalwards by the TA. One week post-RLN injury, both the somatotopy and the number of labeled motoneurons changed, where the labeled neurons were distributed randomly; in addition, an area of topographical overlap of the two populations was observed and vocal fold mobility was lost. In the rest of the survival periods, the overlapping area is larger, but the movement of the vocal folds tends to recover. After 12 weeks of survival, the disorganization within the Amb is the largest, but the number of motoneurons is similar to control, and all animals recovered the movement of the left vocal fold. Our additional controls indicate that no tracer spread to the CT muscle occurred, and that many of the labeled motoneurons from the PCA after 1 week post-RLN injury correspond to motoneurons whose axons travel in the SLN. Therefore, it seems that after RLN injury there is a collateral sprouting and collateral innervation. Although the somatotopic organization of the Amb is lost after a crush injury of the RLN and does not recover in the times studied here, the movement of the vocal folds as well as the number of neurons that supply the TA and the PCA muscles recovered within 8 weeks, indicating that the central nervous system of the rat has a great capacity of plasticity.

Effects of aging on thyroarytenoid muscle regeneration.

OBJECTIVES/HYPOTHESIS: Regenerative properties of age-associated changes in the intrinsic laryngeal muscles following injury are unclear. The purpose of this study was to investigate the regenerative properties of the thyroarytenoid (TA) muscle in an aging rat model. The hypothesis was that following myotoxic injury, old animals would exhibit a decrease in mitotic activities of muscle satellite cells when compared with younger rats, suggesting reduced regenerative potential in the aging rat TA muscle. STUDY DESIGN: Animal group comparison. METHODS: Regeneration responses following injury to the TA muscle were examined in 18 young adult, middle-aged, and old Fischer 344/Brown Norway rats. TA muscle fiber cross-sectional area (CSA), satellite cell mitosis (number/fiber), and regeneration index (CSA injured side/CSA noninjured side) were measured and compared across age groups. RESULTS: Young adult animals had a significantly higher regeneration index than the middle-aged and old groups. Within the lateral region of the TA muscle (LTA), the regeneration index was significantly higher in the young adult animals than in the middle-aged and old animals. The regeneration index of the medial TA was significantly higher than the LTA across all age groups. CONCLUSIONS: The regenerative capacity of the TA muscle is impaired with increasing age.

Airflow efficacy of ballpoint pen tubes: a consideration for use in bystander cricothyrotomy.

OBJECTIVE: To examine the suitability of commonly available ballpoint pens as a substitute emergency tracheostomy tube. METHODS: Commonly available ballpoint pens were examined and compared against two standard cricothyroidotomy sets. The pens were evaluated for dimensions, speed of construction of a temporary tracheostomy tube and airway resistance with differing flow rates. RESULTS: Internal diameters of the pens varied considerably. Time taken to construct a temporary tube ranged from 3 to 170 s, and in the majority of pens the airway resistance increased dramatically as the airflow rate increased. CONCLUSION: Contrary to popular belief, the majority of ballpoint pens appear unsuitable for use as a substitute tracheostomy tube. In this study only two pens fulfilled the criteria for use: the Baron retractable ballpoint and the BIC soft feel Jumbo.

Airway injury complicating excision of thyroglossal duct cysts.

OBJECTIVES: We report on four cases of thyroglossal duct cyst (TGDC) excision using the Sistrunk procedure (resection of the mid-portion of the hyoid bone in continuity with a thyroglossal duct cyst tract) in which the airway was significantly injured. The patterns of injury, their treatment and outcomes as well as preventative measures are detailed. METHODS: Retrospective analysis of four patients referred to a tertiary medical center after sustaining injury to the cricothyroid membrane and/or thyroid cartilages while undergoing a Sistrunk excision of a TGDC. RESULTS: Three patients were repaired after a delay; one patient was immediately repaired. All four patients required application of cartilage grafts, and all ultimately required tracheotomy. Decannulation was achieved in the four patients after an average of 4.5 months, and none suffered from aspiration. Voice outcomes were poor in 3/4. CONCLUSIONS: The Sistrunk procedure has been advocated for TGDC excision, citing a low recurrence rate. However, if the thyroid cartilage is mistaken for the hyoid bone, significant airway injury occurs. Urgent laryngotracheoplasty is indicated, but poor voice outcomes are anticipated. SIGNIFICANCE: Surgeons employing the Sistrunk procedure to excise TGDC must remain oriented to midline cervical anatomy, particularly as the hyoid my override the thyroid notch in young children, placing the larynx at risk for significant injury.

Anatomical and surgical considerations of the external branch of the superior laryngeal nerve: a systematic review.

The anatomical course of the external branch of the superior laryngeal nerve (EBSLN) is variable, and a consistent approach to its preservation during thyroid surgery is needed to reduce risk of post-operative voice impairment. Despite agreement that careful dissection in the region of the superior thyroid pole is required, there is no accepted 'best' approach, nor any universal acknowledgement that location of the EBSLN is actually necessary. The popular cernea classification of EBSLN has limitations, including its decreased reliability with increased thyroid size and its irrelevance in cases of 'buried' variants. * Recent work has identified factors such as ethnicity and stature in the prevalence of EBSLN variants. Consistent approaches to the post-operative detection of EBSLN injury are needed to build an accurate picture of the incidence of surgical nerve injury. Then a standardised approach to EBSLN preservation may emerge.

[Display of different injuries of recurrent laryngeal nerve in laryngeal electromyography].

OBJECTIVE: To study the display of different types injuries of recurrent laryngeal nerve (RLN) in laryngeal electromyography (LEMG). METHODS: LEMGs of one hundred and forty-seven patients (147 sides) with traumatic unilateral vocal cord paralysis (UVCP) were studied. After LEMGs, the RLNs exploration operations were performed. The condition of RLNs injury and laryngeal muscles was observed and recorded during the operation. RESULTS: The severe injuries of RLNs were found during operation. The types of injuries were listed as ligation (58 cases), adhesion (28 cases) and cut (61 cases). The waveform morphology of LEMG was recorded less in the patients with the RLNs cut than that in the patients with the RLN ligation or adhesion, respectively. 75.4% RLNs cut showed spontaneous waveform while 96.4% RLNs adhesion and 94.8% RLNs ligation. When the RLN was cut off, single pattern was showed oftener. When the RLN was adhered or ligated, mixed pattern was showed oftener. 92.9% RLN adhesion showed misdirect-regeneration-potentials while 70.7% RLN ligation and 24.6% RLN cut. There were significant difference between two types, but the compound muscular active potential (CMAP) amplitude wasn't significantly different. Evoked amplitude could be recorded in 91.4% patients with ligation and its amplitude was (23.6 +/- 8.1)%, in 85.7% patients with adhesion and its amplitude (16.3 +/- 5.2)%, in 29.5% patients with cut and its amplitude (2.6 +/- 4.2)%. CONCLUSIONS: The display of different injuries of RLN in LEMG presents significant difference. If RLN was cut off, the CMAP might be recorded in most cases. The clinical injury of RLN often is followed by sub-clinic reinnervation.

Muscle tension dysphonia in patients who use computerized speech recognition systems.

The use of speech recognition systems as a replacement for other types of transcription systems is increasing rapidly, partly because many people are unable to use conventional keyboards as a result of upper-extremity repetitive strain injury (RSI). However, the frequent or continuous use of such systems can cause muscle tension dysphonia in some patients. The scientific literature suggests that there is an association between upper-extremity RSI and muscle tension dysphonia. We present a retrospective case series of five patients with workplace upper-extremity RSI who developed muscle tension dysphonia soon after they began using discrete computerized speech recognition software. The diagnosis of dysphonia was based on laryngovideostroboscopy, acoustic analyses, and voice load testing. All patients had normal voice when using everyday speech, but speaking into the computer resulted in the rapid onset of aperiodicity, strain, and a decrease in fundamental frequency. In three of the five patients, laryngovideostroboscopy showed posterior glottic overapproximation, but no other abnormalities. Treatment was centered on voice therapy and avoidance of long periods of using computerized speech recognition systems. The condition of three of the five patients improved with therapy. We conclude that computer speech recognition programs can lead to the onset of muscle tension dysphonia in some patients. These patients can be successfully treated with voice therapy.

Comparison of concentric needle versus hooked-wire electrodes in the canine larynx.

BACKGROUND: The use of a specific electrode type in laryngeal electromyography has not been standardized. Laryngeal electromyography is usually performed with hooked-wire electrodes or concentric needle electrodes. Hooked-wire electrodes have the advantage of allowing laryngeal movement with ease and comfort, whereas the concentric needle electrodes have benefits from a technical aspect and may be advanced, withdrawn, or redirected during attempts to appropriately place the electrode. OBJECTIVES: This study examines whether hooked-wire electrodes permit more stable recordings than standard concentric needle electrodes at rest and after large-scale movements of the larynx and surrounding structures. A histologic comparison of tissue injury resulting from placement and removal of the two electrode types is also made by evaluation of the vocal folds. METHODS: Electrodes were percutaneously placed into the thyroarytenoid muscles of 10 adult canines. Amplitude of electromyographic activity was measured and compared during vagal stimulation before and after large-scale laryngeal movements. Signal consistency over time was examined. Animals were killed and vocal fold injury was graded and compared histologically. RESULTS: Waveform morphology did not consistently differ between electrode types. The variability of electromyographic amplitude was greater for the hooked-wire electrode (p < 0.05), whereas the mean amplitude measures before and after large-scale laryngeal movements did not differ (p > 0.05). Inflammatory responses and hematoma formation were also similar. CONCLUSIONS: Waveform morphology of electromyographic signals registered from both electrode types show similar complex action potentials. There is no difference between the hooked-wire electrode and the concentric needle electrode in terms of electrode stability or vocal fold injury in the thyroarytenoid muscle after large-scale laryngeal movements.

Intrinsic laryngeal muscle regeneration following endotracheal intubation.

The larynges of 33 premature and term neonates who were intubated for the management of respiratory difficulties were studied. In addition to the changes commonly associated with endotracheal intubation (epithelial erosion, ulceration, squamous metaplasia, edema, inflammation, and perichondritis), the intrinsic laryngeal muscles were damaged in 26 of the 33 cases and, in 4 cases, oriented striated skeletal muscle regeneration was found. The active synthetic nature of the myotube formations in the latter cases was confirmed by the demonstration of concentrated vimentin intermediate-filament immunoreactivity. In view of the frequency of neonatal intubation, the probability of muscle damage, and the generally infrequent critical sequelae of this procedure, regeneration of the intrinsic muscles may help to explain the excellent functional recovery of the neonatal larynx. This phenomenon also occurs in the postintubated adult larynx and is therefore not limited to the neonatal period. In addition, these findings support the fact that skeletal muscle regeneration occurs in nonmyopathic human skeletal muscles following injury, as has been shown in experimental animal models.

A model for neurologic sources of aperiodicity in vocal fold vibration.

The time course of a force twitch in the thyroarytenoid muscle is modeled, and trains of twitches are summed to simulate force tetani. By incorporating means and standard deviations of motoneuron firing rates, and by applying random phase relationships between simulated motor units, a quantitative model of the ripple of vocal fold tension is obtained. From this ripple, perturbations in fundamental frequency are calculated as a function of the number of motor units in the muscle, the mean and standard deviation of the firing rate of dominant motoneurons, and the variability in the size (twitch amplitude) of the motor units. Predicted perturbations range between 0.2% and 1.2%, depending on the choice of parameters. Perturbation decreases with the number of motor units and with increased mean firing rate, but increases with the variability in motor unit size and with variability in the firing rate. Techniques are discussed by which neurologic jitter might be isolated from other sources of irregularity in vocal fold vibration.

A continuous-flow model for phonatory reaction time.

The purpose of this study was to validate a proposed continuous-flow model of phonatory reaction time by investigating the temporal order of selected laryngeal and neurophysiological events involved in a phonatory reaction time task. Ten normal speakers participated in a phonatory reaction time task. Laryngeal positioning movements prior to vocal fold closure (laryngeal shift) and onset of vocal fold vibration (acoustic onset) were recorded with an electroglottograph. P300 brain potentials were collected simultaneously, and they served as an index of a central process underlying reaction time. The obtained temporal ordering of laryngeal shift, P300, and acoustic onset supported a continuous-flow model of phonatory reaction time. Use of this model might yield information that is more accurate in explaining physiological function and more precise in describing temporal patterning than the serial model.

The cricothyroid muscle after cricothyroidotomy. A porcine experimental study.

Cricothyroidotomy in elective use or emergency situations has been discussed by several authors during recent years. The main complication reported has been subglottic stenosis. We have used this method for several years and among our patients there has been no case of stenosis. The major complication in our material has been voice dysfunction. Some of the patients had a change in voice quality consistent with dysfunction in the cricothyroid muscles (diminished voice range and a lowered pitch). The aim of this study was to investigate whether cricothyroidotomy and insertion of a tracheostomy tube caused physiological or morphological changes in the cricothyroid muscle, by direct injury or secondary to a peripheral nerve lesion. In the six animals that were cricothyroidotomized during 7-9 days and examined after 9-15 weeks, we found neither changes in the EMG nor in the muscle morphology indicating injury to the muscle or its peripheral nerve supply.