Dinesh K. Chhetri

Measurement of Young's modulus of vocal folds by indentation.

OBJECTIVES To assess the accuracy of the indentation method for stiffness measurements and to estimate the Youngs modulus of the vocal fold using this technique. STUDY DESIGN Basic science. METHODS Indentation tests were performed using a range of indenter diameters and indentation depths on single- and double-layer silicone rubber models with various cover-layer thicknesses with known geometry and Youngs moduli. Measurements were repeated on intact vocal folds and isolated muscle and cover-layer samples from three cadaveric human larynges. RESULTS Indentation on single-layer rubber models yielded Youngs moduli with acceptable accuracy when the indentation depth was equal to or smaller than the indenter diameter, and both were smaller than the physical dimensions of the material sample. On two-layer models, the stiffness estimation was similarly influenced by indenter diameter and indentation depth, and acceptable accuracy was reached when indentation depth was much smaller than the height of the top cover layer. Measurements on midmembranous vocal fold tissue revealed location-dependent Youngs moduli (in kPa) as follows: intact hemilarynx, 8.6 (range=5.3-13.1); isolated inferior medial surface cover, 7.5 (range=7-7.9); isolated medial surface cover, 4.8 (range=3.9-5.7); isolated superior surface cover, 2.9 (range=2.7-3.2); and isolated thyroarytenoid muscle, 2.0 (range=1.3-2.7). CONCLUSIONS Indenter diameter, indentation depth, and material thickness are important parameters in the measurement of vocal fold stiffness using the indentation technique. Measurements on human larynges showed location-dependent differences in stiffness. The stiffness of the vocal folds was also found to be higher when the vocal fold structure was still attached to the laryngeal framework compared with that when the vocal fold was separated from the framework.

Lamina Propria Replacement Therapy with Cultured Autologous Fibroblasts for Vocal Fold Scars

OBJECTIVES: To develop a canine model of vocal fold scar and to evaluate its treatment with lamina propria replacement therapy using autologous cultured fibroblasts. MATERIALS AND METHODS: Full thickness of the lamina propria layer in canine vocal folds was injured with a laser. Fibroblasts were cultured and expanded in the laboratory from a buccal mucosal biopsy. The scarred vocal folds were treated with 3 weekly injections of fourth, fifth, and sixth passage autologous fibroblasts. Mucosal waves and acoustic parameters were measured at baseline, after scarification, and several months after injection therapy. Histologic evaluation of the vocal folds for fibroblasts, collagen, elastin, reticulin, and hyaluronic acid was performed. RESULTS: Nine beagle dogs were used, and 1 animal served as control. Vocal fold scarring resulted in absent or severely limited mucosal waves and significantly worse acoustic parameters. Significant improvements in mucosal waves and acoustic parameters were obtained after lamina propria replacement therapy. After therapy, mucosal waves became normal in 4 animals and near normal in the other 4. No statistical difference was found in mucosal waves between baseline and post-therapy. All animals tolerated therapy without complications. The treated vocal folds demonstrated an increased density of fibroblasts, collagen, and reticulin, a decreased density of elastin, and no change in hyaluronic acid. CONCLUSIONS AND SIGNIFICANCE: Therapeutic options for vocal fold scars are limited. Lamina propria replacement therapy in the form of autologous cultured fibroblasts improves mucosal pliability and returns normal or near normal mucosal waves in experimentally scarred vocal folds. This novel therapeutic modality may hold new promise for treating vocal fold scars.

Epithelial differentiation of adipose‐derived stem cells for laryngeal tissue engineering

One potential treatment option for severe vocal fold scarring is to replace the vocal fold cover layer with a tissue‐engineered structure containing autologous cells. As a first step toward that goal, we sought to develop a three‐dimensional cell‐populated matrix resembling the vocal fold layers of lamina propria and epithelium.

Ansa Cervicalis Nerve: Review of the Topographic Anatomy and Morphology

In recent years, there has been a proliferation of techniques utilizing the ansa cervicalis nerve to reinnervate the paralyzed larynx. The anatomic course and morphology of the ansa cervicalis are complicated by the variable course and location along the great vessels of the neck, as well as the significant differences observed in the arrangement of its contributing roots and regional branching patterns. Herein, we review the surgical anatomic course of ansa cervicalis and its innervation of the muscles of the neck, and develop specific recommendations with respect to the use of this nerve in laryngeal reinnervation.

Injection Laryngoplasty with Calcium Hydroxylapatite Gel Implant in an in Vivo Canine Model

The ideal injectable agent for vocal fold medialization is biocompatible, durable, sized to prevent phagocytosis and migration, and formulated for easy injection and does not adversely affect the viscoelastic properties of the vocal fold. We tested a cohesive implant of calcium hydroxylapatite (CaHA) particles in a gel carrier in an in vivo canine model of phonation. Six dogs underwent unilateral recurrent laryngeal nerve section and injection laryngoplasty of the paralyzed vocal fold with a CaHA implant. The six follow-up examinations were performed at 1,2, 3, 6, 9, and 12 months, and the larynx and bilateral neck lymphatic system were harvested for histologic analysis. The CaHA implant adequately medialized the vocal fold to regain glottal closure. The mucosal waves remained unaltered from baseline. The implant remained soft in the larynx and did not migrate to the neck lymphatic system. A localized foreign body giant cell reaction was present on histologic evaluation, but not acute or other chronic inflammation. A size analysis revealed no resorption of the CaHA particles. A decrease in medialization was noted at all follow-up intervals related to resorption of the aqueous-based gel carrier. The CaHA implant appears to be relatively safe and suitable for injection laryngoplasty.

Carcinoma of the buccal mucosa

OBJECTIVE: The goal was to analyze the outcome of surgical therapy for buccal carcinoma. STUDY DESIGN: A retrospective chart review was done. SETTING: The study took place in a major tertiary-care hospital. RESULTS: Twenty-seven patients received first-time surgical therapy for buccal carcinoma. Treatment was surgery alone in 15 and surgery followed by radiation therapy in 6 patients. Six additional patients received surgical salvage for radiation therapy failure. Composite resection of the tumor was performed in 16 patients (59%). Five-year observed actuarial survival rates were 100%, 45%, 67%, and 78%, and locoregional recurrence rates were 0%, 27%, 44%, and 0% for stages I to IV, respectively. The 5-year actuarial survival rates were 80% after surgery and 82% after surgery and postoperative radiation therapy. Patients who underwent surgical salvage after radiation therapy failure had a 1-year survival rate of 0%. CONCLUSION: Aggressive surgical treatment of buccal carcinoma may result in better survival rates. SIGNIFICANCE: The article analyzes buccal carcinoma in regards to the patterns of presentation, treatments rendered, and patterns of failure.

Heterogeneity in the clinical presentation of Eagle's syndrome.

OBJECTIVE: Eagles syndrome (ES) or symptomatic elongated styloid process is an uncommon but important cause of chronic head and neck pain. This study reports our experience in the diagnosis and treatment of a series of patients with ES. STUDY DESIGN: Patient histories, radiographic tests, and operative reports of 3 patients over a 3-month period were prospectively collected. SETTING: Tertiary referral otolaryngology service. RESULTS: All patients had resolution of symptoms relating to their elongated styloid processes after surgical resection. CONCLUSION: Although sometimes clouded by coexisting symptoms, ES can be easily diagnosed based on good history taking and physical examination. If diagnosed appropriately, surgical treatment can be administered promptly. SIGNIFICANCE: Patients with ES commonly have a long history of chronic pain treated by multiple physicians. Appropriate diagnosis can lead to prompt treatment of this condition. EBM rating: C-4

Long-term follow-up results of selective laryngeal adductor denervation-reinnervation surgery for adductor spasmodic dysphonia.

Selective laryngeal adductor denervation‐reinnervation surgery for the treatment of adductor spasmodic dysphonia was reported in 1999 in 21 patients with encouraging results. Here, we report long‐term results of this procedure. Surgical outcome was evaluated using patient surveys and perceptual voice assessment. Measured outcomes included Voice Handicap Index (VHI)‐10 scores, patient questionnaire, and perceptual evaluation for voice breaks and breathiness. Patient survey was obtained from 83 patients, and perceptual voice evaluation was performed in voice samples from 46 patients. Average follow‐up interval was 49 months. Mean VHI‐10 scores improved from a mean of 35.6 to 12.7. Eighty‐three percent showed significantly improved VHI‐10 scores, representing improved physical, social, and emotional well‐being. There was a high degree of patient satisfaction, with 91% agreeing that their voice is more fluent after the surgery. Perceptual evaluation of postoperative voice samples revealed voice breaks in 26% (15% mild, 4% moderate, 7% severe) and breathiness in 30% (11% mild, 13% moderate, 6% severe). A majority of patients had stable, long‐lasting resolution of spasmodic voice breaks.

Combined Arytenoid Adduction and Laryngeal Reinnervation in the Treatment of Vocal Fold Paralysis

Objective/Hypothesis: Glottal closure and symmetrical thyroarytenoid stiffness are two important functional characteristics of normal phonatory posture. In the treatment of unilateral vocal cord paralysis, vocal fold medialization improves closure, facilitating entrainment of both vocal folds for improved phonation, and reinnervation is purported to maintain vocal fold bulk and stiffness. A combination of medialization and reinnervation would be expected to further improve vocal quality over medialization alone.

Neuromuscular control of fundamental frequency and glottal posture at phonation onset

The laryngeal neuromuscular mechanisms for modulating glottal posture and fundamental frequency are of interest in understanding normal laryngeal physiology and treating vocal pathology. The intrinsic laryngeal muscles in an in vivo canine model were electrically activated in a graded fashion to investigate their effects on onset frequency, phonation onset pressure, vocal fold strain, and glottal distance at the vocal processes. Muscle activation plots for these laryngeal parameters were evaluated for the interaction of following pairs of muscle activation conditions: (1) cricothyroid (CT) versus all laryngeal adductors (TA/LCA/IA), (2) CT versus LCA/IA, (3) CT versus thyroarytenoid (TA) and, (4) TA versus LCA/IA (LCA: lateral cricoarytenoid muscle, IA: interarytenoid). Increases in onset frequency and strain were primarily affected by CT activation. Onset pressure correlated with activation of all adductors in activation condition 1, but primarily with CT activation in conditions 2 and 3. TA and CT were antagonistic for strain. LCA/IA activation primarily closed the cartilaginous glottis while TA activation closed the mid-membranous glottis.