The development of the cricoid cartilage and its implications for the use of endotracheal tubes in the pediatric population.

BACKGROUND: The rigid cricoid cartilage is functionally the narrowest portion of the larynx. There is some controversy over the shape of the pediatric cricoid cartilage in the transverse plane. It is important to understand the development of the cricoid cartilage so that endo-traceheal tubes can be used more safely. AIM: To determine changes in the internal diameter and shape of the cricoid cartilage during development and explore the implications of those changes for the selection of ETT type and size for children. METHODS: The cervical computed tomography scans were reviewed in patients aged 1-20 years. After performing the multiplanar reconstruction and correcting the slant, the transverse and anteroposterior internal diameters of the inlet and outlet of the cricoid cartilage were measured, respectively. The angle between the arch and the lamina of the cricoid cartilage in the middle sagittal plane was measured. The ratios of transverse to anteroposterior diameter for the inlet and outlet of the cricoid cartilage were calculated, respectively. RESULTS: In females, the internal diameters of the cricoid cartilage increased linearly with age. In males, the internal diameters of the cricoid cartilage exhibited a growth spurt during adolescence. The transverse diameter of the inlet was the smallest diameter of the cricoid cartilage, and the predicting formula of the transverse diameter of the inlet for children aged 1-12 was 0.4 × age (year) + 5.1, R2  = .758. The angle between the arch and lamina of the cricoid cartilage and the ratios of transverse to anteroposterior diameter correlated weakly with age. CONCLUSION: The transverse inner diameter of the inlet is the smallest diameter of the cricoid cartilage. The "funnel shape" of the cricoid cartilage remains unchanged during development. The outer diameter should be considered when selecting an endotracheal tube.

The anatomy of the pediatric airway: Has our knowledge changed in 120 years? A review of historic and recent investigations of the anatomy of the pediatric larynx.

BACKGROUND: There is disagreement regarding the anatomy of the pediatric airway, particularly regarding the shape of the cricoid cartilage and the location of the narrowest portion of the larynx. AIMS: The aim of this review is to clarify the origin and the science behind these differing views. METHODS: We undertook a review of published literature, University Libraries, and authoritative textbooks with key search words and phrases. RESULTS: In vivo observations suggest that the narrowest portion of the airway is more proximal than the cricoid cartilage. However, in vitro studies of autopsy specimens measured with rods or calipers, confirm that the nondistensible and circular or near circular cricoid outlet is the narrowest level. These anatomic studies confirmed the classic "funnel" shape of the pediatric larynx. In vivo studies are potentially misleading as the aryepiglottic, vestibular, and true vocal folds are in constant motion with respiration. These studies also do not consider the effects of normal sleep, inhalation agents, and comorbidities such as adenoid or tonsil hypertrophy that cause some degree of pharyngeal collapse and alter the normal movement of the laryngeal tissues. Thus, the radiologic studies suggesting that the narrowest portion of the airway is not the cricoid cartilage may be the result of an artifact depending upon which phase of respiration was imaged. CONCLUSION: In vivo studies do not take into account the motion of the highly pliable laryngeal upper airway structures (aryepiglottic, vestibular, and vocal folds). Maximal abduction of these structures with tracheal tubes or bronchoscopes always demonstrates a larger opening of the glottis compared to the outlet of the cricoid ring. Injury to the larynx depends upon ease of tracheal tube or endoscope passage past the cricoid cartilage and not passage through the readily distensible more proximal structures. The infant larynx is funnel shaped with the narrowest portion the circular or near circular cricoid cartilage confirmed by multiple in vitro autopsy specimens carried out over the past century.

Pediatric upper airway dimensions using three-dimensional computed tomography imaging.

INTRODUCTION: Computed tomography- (CT) and magnetic resonance imaging (MRI)-based measurements have recently suggested that the narrowest dimension of the pediatric airway is the subglottic region. These data are contrary to the previously held tenets of a funnel- or conical-shaped airway. The current study evaluates airway volumes and shapes using three-dimensional CT images of the air way column in spontaneously breathing children. METHODS: The study included CT-based radiological images of the neck in children who required imaging unrelated to airway symptomatology. The children were evaluated during spontaneous ventilation during natural sleep or with sedation without airway devices in place. The three-dimensional images of the airway column were evaluated, volumes calculated, and comparisons made between the subglottic, cricoid, and tracheal volumes and shapes. RESULTS: The study cohort included 54 children, ranging in age from 2 months to 8 years. An increase in the airway volumes was observed from the subglottic (0.17 ± 0.06 mm3 ) to the cricoid (0.19 ± 0.06 mm3 ) to the tracheal regions (0.22 ± 0.07 mm3 ). The volumes of the subglottic, cricoid, and tracheal regions demonstrated a linear relationship with age. CONCLUSION: This study confirms recent studies demonstrating that the subglottic region not the cricoid is the narrowest part of the airway.

Age-dependent structural and radiological changes in the larynx.

AIM: To define radiological physiological changes in the larynx by establishing an age-related scale. MATERIALS AND METHODS: The present retrospective study used radiological records of patients that had undergone lateral cervical imaging. Three hundred patients were included. Thyroid cartilage was divided into anatomical regions. The hyoid bone was evaluated as the body and greater horns. Cases were compared by grouping by age and gender. RESULTS: Thyroid tissue and cricoid cartilage only became visible after the second decade. Ossification in the thyroid cartilage began in the posterior inferior horn and progressed to the superior horn and central lamina. It also began in the posterior part of the cricoid cartilage and moved forward with age. In the first decade, the body and greater horn parts of the hyoid bone could be seen more distinctly, and after the third decade the hyoid bone appeared as a single bone. The hyoid bone was the only structure ossified in the laryngeal region below the age of 20 and formed an image on direct imaging. CONCLUSIONS: Age-related changes to the laryngeal tissues are evident on radiographs. Clinicians should bear this in mind when evaluating neck radiographs.

Structural and functional development in airways throughout childhood: Children are not small adults.

Children are not small adults and this fact is particularly true when we consider the respiratory tract. The anatomic peculiarities of the upper airway make infants preferential nasal breathers between 2 and 6 months of life. The pediatric larynx has a more complex shape than previously believed, with the narrowest point located anatomically at the subglottic level and functionally at the cricoid cartilage. Alveolarization of the distal airways starts conventionally at 36-37 weeks of gestation, but occurs mainly after birth, continuing until adolescence. The pediatric chest wall has unique features that are particularly pronounced in infants. Neonates, infants, and toddlers have a higher metabolic rate, and consequently, their oxygen consumption at rest is more than double that of adults. The main anatomical and functional differences between pediatric and adult airways contribute to the understanding of various respiratory symptoms and disease conditions in childhood. Knowing the peculiarities of pediatric airways is helpful in the prevention, management, and treatment of acute and chronic diseases of the respiratory tract. Developmental modifications in the structure of the respiratory tract, in addition to immunological and neurological maturation, should be taken into consideration during childhood.

Alignment of cricoid cartilage and esophagus and its potential influence on the effectiveness of Sellick maneuver in children.

OBJECTIVE: The effectiveness of cricoid pressure in preventing aspiration of gastric contents during rapid sequence intubation may be limited if the esophagus is laterally displaced from the trachea at the level of the cricoid cartilage. Esophageal lateral displacement has been reported to occur in 50% to 90% of adults. Children 8 years and older assume the anatomic airway characteristics of adults, and therefore, we hypothesized that esophageal displacement would be significantly more common in older versus younger children. The purposes of this study were to determine the alignment of the trachea to the esophagus at the level of the cricoid cartilage on cervical spine or neck computed tomographic (CT) scans and to compare the frequency and quantity of esophageal displacement between children younger than 8 years and children 8 years and older. METHODS: This is a retrospective cross-sectional study of children (aged 0-17 years) who had cervical spine/neck CT scans performed at a 110-bed urban children's hospital. Two pediatric radiologists blinded to the patients' clinical symptoms and signs and final diagnosis independently determined the alignment of the airway at the level of the cricoid cartilage with the esophagus from cervical spine/neck CT scans. Lateral displacement of the esophagus from the airway was determined by measuring the distance from the ipsilateral outer wall edges of the esophagus and trachea. RESULTS: There were 172 cervical spine/neck CT scans reviewed. Of 87 children younger than 8 years, 27 were excluded, and of 85 children 8 to 17 years, 25 were excluded. The remaining 120 patients were eligible for the study, 60 patients were younger than 8 years and 60 patients were aged 8 to 17 years. For children younger than 8 years, their mean age was 3.58 years. There were 34 (57%) males. The most common indication for CT scan of the cervical spine/neck was motor vehicle crash 26 (46%). For children aged 8 to 17 years, their mean age was 13.3 years. There were 30 (50%) males. The most common indication for CT scan of the cervical spine/neck was motor vehicle crash 34 (57%). Alignment of the airway with the esophagus showed esophageal displacement in 36 (30%) of the patients with displacement in 27 (45%) of the younger children compared with 9 (15%) of the older children. The rate of displacement was significantly greater in the younger children (difference in rates was 30% and 95% confidence interval was 14%-46%). All displacements were to the left. The mean distance of esophageal displacement was significantly greater in the older children (2.42 vs 1.81 mm). The difference in the means was 0.61 mm, and the 95% confidence interval was 1.2 to 0.02 mm. CONCLUSIONS: This is the first pediatric study on the rate and degree of esophageal displacement from the airway at the level of the cricoid cartilage. Lateral displacement of the esophagus occurred at a significantly greater rate in the younger (45%) compared with the older (15%) children, which was directly opposite of our hypothesis. Of the 36 children (30%) with esophageal displacement, all had displacement to the left of the cricoid cartilage.

Pediatric laryngeal dimensions: an age-based analysis.

BACKGROUND: In children, the cricoid is considered the narrowest portion of the "funnel-shaped" airway. Growth and development lead to a transition to the more cylindrical adult airway. A number of airway decisions in pediatric airway practice are based on this transition from the pediatric to the adult airway. Our primary aim in this study was to measure airway dimensions in children of various ages. The measures of the glottis and cricoid regions were used to determine whether a transition from the funnel-shaped pediatric airway to the cylindrical adult airway could be identified based on images obtained from video bronchoscopy. METHODS: One hundred thirty-five children (ASA physical status 1 or 2) aged 6 mo to 13 yr were enrolled for measurement of laryngeal dimensions, including cross-sectional area (G-CSA), anteroposterior and transverse diameters at the level of the glottis and the cricoid (C-CSA), using the video bronchoscopic technique under general anesthesia. RESULTS: Of the 135 children enrolled in the study, seven patients were excluded from the analysis mainly because of poor image quality. Of the 128 children studied (79 boys and 49 girls), mean values (+/-standard deviation) for the demographic data were age 5.9 (+/-3.3) yr, height 113.5 (+/-22.2) cm and weight 23.5 (+/-13) kg. Overall, the mean C-CSA was larger than the G-CSA (48.9 +/- 15.5 mm(2) vs 30 +/- 16.5 mm(2), respectively). This relationship was maintained throughout the study population starting from 6 mo of age (P < 0.001, r = 0.45, power = 1). The mean ratio for C-CSA: G-CSA was 2.1 +/- 1.2. There was a positive correlation between G- and the C-CSA versus age (r = 0.36, P < 0.001; r = 0.27, P = 0.001, respectively), height (r = 0.34, P < 0.001; r = 0.29, P < 0.001, respectively), and weight (r = 0.35, P < 0.001; r = 0.25, P = 0.003, respectively). No significant gender differences in the mean values of the studied variables were observed. CONCLUSION: In this study of infants and children, the glottis rather than cricoid was the narrowest portion of the pediatric airway. Similar to adults, the pediatric airway is more cylindrical than funnel shaped based on these video bronchoscopic images. Further studies are needed to determine whether these static airway measurements in anesthetized and paralyzed children reflect the dynamic characteristics of the glottis and cricoid in children.

Pediatric transtracheal and cricothyrotomy airway devices for emergency use: which are appropriate for infants and children?

Cricothyrotomy or insertion of a transtracheal device is a life-saving maneuver that may be performed on an emergent or semi-elective basis as a means of bypassing an obstructed upper airway. A surgeon is trained to perform this life-saving procedure whereas most anesthesiologists are not facile with the scalpel. It is for this reason that many percutaneous devices have been developed for use by surgeons and nonsurgeons alike. Unfortunately, the majority of such devices are designed for use in adults and/or teenagers but are not appropriate for neonates and infants. The unique anatomy of the infant larynx, the small size of the cricothyroid membrane, and the technical difficulty of locating the correct anatomical structures make the use of most of these devices impractical if not outright dangerous in neonates and infants. This paper will review many (but not all) of the available devices, associated literature, pitfalls and dangers. It is emphasized that each clinician should become familiar with the advantages and disadvantages of these devices and obtain training with simulators or animal models. A strategy for management of the 'cannot ventilate, cannot oxygenate, cannot intubate' situation should be developed with age and size appropriate equipment.

Transforming growth factor beta3 increases chondrocyte proliferation and decreases apoptosis in murine cricoid cartilage in vitro.

OBJECTIVE: To determine if the luminal epithelium and/or exogenous transforming growth factor beta (TGFbeta) affects growth of the cricoid. DESIGN: Subglottises from 20 neonatal mice were subdivided into four groups: A, five subglottises with luminal epithelium grown in basic medium; B, five epithelium-free subglottises in basic medium; C, five epithelium-free subglottises in basic medium with supplemental TGFbeta1, and D, five epithelium-free subglottises in basic medium with supplemental TGFbeta3. RESULTS: Groups A and D demonstrated the greatest luminal area expansion. Group A rings demonstrated statistically higher chondrocyte proliferation than Groups B and C and lesser amounts of luminal apoptosis. Groups B and C rings demonstrated the least amount of cell proliferation, and greater luminal apoptosis relative to Group A. Groups A and D rings had similar apoptotic and proliferative results. CONCLUSIONS: Luminal epithelium exerts influence over the cricoid by increasing chondrocyte proliferation and decreasing the relative proportion of luminal chondrocytes that undergo apoptosis. Exogenous TGFbeta3, not TGFbeta1, also increases chondrocyte proliferation within the cricoid and appears to influence apoptosis as well.

Morphometric study on the anatomy of the fetal cricoid cartilage and comparison between its inner diameter and endotracheal tube sizes.

OBJECTIVES: The high incidence of respiratory disorders is one of the main problems in perinatal medical care. With the increased use of intubation, the incidence of laryngeal injury causing stenosis has also increased. The principal constriction point in the infant's larynx is the midcricoid area. We sought to provide detailed morphometric data on the anatomy of the cricoid cartilage and its relationship with growth and body characteristics of fetuses at 5 to 9 months of gestational age. METHODS: Nineteen larynges obtained from 17 stillborn infants and 2 newborn infants ranging in gestational age from 5 to 9 months were studied. Measurements of the cricoid cartilage were made with a millimeter-graded caliper. RESULTS: Weight was the variable most correlated with cricoid measurements. The cricoid lumen configuration showed an almost elliptic shape and did not change with gestational age. The mean inner subglottic cricoid area was 19.27 +/- 9.62 mm2 and was related to weight and body surface area. Cricoid growth was more pronounced at the outer portion of the cartilage. CONCLUSIONS: The cricoid lumen configuration was elliptic, and its mean area was smaller than that of available endotracheal tubes. This lumen area was most influenced by weight and height.

Local control of murine subglottis development.

OBJECTIVE: To determine if subglottic development is at least partially under local control and to determine which tissue layer(s) is predominantly responsible. DESIGN: The suglottises of 12 day-3 CD1 mice were grown in whole organ culture. The 12 subglottises were divided into 3 individual groups: +++, -++, and ---. Group+++ had all tissue layers of the subglottis intact: luminal epithelium, cricoid cartilage, inner and outer perichondrium. Group-++ had all layers intact with the exception of luminal epithelium. Group--- had all layers removed (luminal epithelium, inner and outer perichondrium) resulting in cricoid cartilage-only rings. All rings were grown in basic medium without the use of growth factors or serum for 15 days. Measurements of the rings were taken before and after organ culture growth. RESULTS: Group+++ was the only group that experienced growth. Only luminal growth was statistically significant although all rings experienced growth in both the luminal and external diameter. Group-++ did not experience any growth. Group--- lost structural integrity with collapse of the ring and did not experience growth of any dimension of the cartilage. CONCLUSIONS: Growth of the subglottis is under local control but may have additional influences from the outside that were not investigated here. Removal of just the epithelium stunts growth of the entire ring, but preferentially the lumen more so than the external diameter. Removal of all tissue layers around the cricoid cartilage results in a structural collapse of the ring, suggesting that the cartilage in this age group is dependent on surrounding tissues for structural integrity.

Airway growth following cricotracheal resection in puppies.

A canine animal model was developed to study the effects of cricoid resection on cricoid cartilage growth and subglottic lumen size. Twenty-four healthy, postweanling mongrel puppies, aged 5 to 7 weeks, were randomly divided into two groups. The first group, consisting of 13 puppies, underwent cricotracheal resection with primary anastomosis. A second group, consisting of 11 puppies, served as controls and did not have surgery. Animals from both groups were killed at age 13 weeks. Most of the animals, however, were allowed to mature to adulthood and were killed between age 26 to 28 weeks. Comparative histologic examinations of the laryngotracheal complexes of operated-on and control dogs showed uninterrupted cartilage growth at the anastomosis site after cricotracheal resection. There was no significant difference in the mean area of the cricoid lumen between the two groups when luminal area was adjusted for body weight. The results demonstrate that cricotracheal resection in this animal model does not interrupt cricoid luminal area or cricoid cartilage growth, and provides rationale for further investigation of cricoid resection with primary anastomosis in humans. Cricotracheal resection in growing puppies appears to be an excellent model for further studies in the surgical treatment of acquired subglottic stenosis in infants and children.

Novel cell proliferation marker for identification of a growth center in the developing human cricoid.

BACKGROUND: Developmental histomorphology of the human cricoid cartilage has never been well described. Regional growth centers in the cricoid have been hypothesized, but have never been demonstrated in histological sections. OBJECTIVES: To apply Mib-1 immunostaining, a monoclonal antibody directed at a nuclear proliferation marker, in human cricoids to identify a growth center and to study the changing histomorphology of the developing cricoid. DESIGN: Immunohistochemical Mib-1 studies were performed on postmortem cricoid sections of 2 fetuses (gestational age, 18.5 and 33 weeks), 1 newborn (full term, 41 weeks), and 3 children (aged 1, 4, and 13 years, respectively). Cell counts, surface areas, and organizational patterns of the chondrocytes were studied and described in hemotoxylin-eosin-stained sections. RESULTS: Differential Mib-1 staining was found. The 18.5-week fetus showed diffuse cell proliferation throughout the cricoid. The cricoid sections of the 33-week fetus and 1-year-old child revealed a distinct ring of proliferation in the outer third of the cricoid ring. The 4- and 13-year-old exhibited no cell proliferation. Histomorphologically, with increasing age came chondrocyte hypertrophy, decreasing cell count per standard square, and increasing organization from a scattered to radial columnar pattern. CONCLUSIONS: Growth of the cricoid involves a diffuse pattern of cell proliferation throughout the cricoid in fetal tissue. At term and until age 1 year, the region of proliferation is more restricted to the outer subperichondrial surface. By age 4 years, cell proliferation has stopped. Histomorphologic changes in the developing cricoid include decreasing cell counts per standard unit area, but increasing surface area with age. The aging chondrocytes develop an increasingly organized layout to form a radially arranged columnar pattern similar to that in the growth plate of the developing limb bud.

Lateral division of the rabbit cricoid cartilage: its effect on cartilage growth.

Laryngotracheoplasty often includes bilateral lateral division of the cricoid cartilage, despite the theoretical risk that cartilage growth centers might be located in the lateral cricoid. To investigate the effect of lateral cricoid cartilage division on subsequent cartilage growth, 60 five-week-old New Zealand white rabbits were divided into four groups of 15 animals each. Group I was comprised of unoperated controls. The remaining animals underwent anterior (group II), anterior and posterior (group III), and anterior, posterior, and bilateral lateral (group IV) division of the cricoid cartilage. Animals were killed 20 weeks after surgery, and the cross-sectional area of each animal's cricoid cartilage and of each animal's airway was determined. There was no statistically significant difference in mean cartilage cross-sectional area between any of the four groups; the group IV mean was larger than that of any other group, though the difference was not significant. There was no significant difference in airway cross-sectional area between any of the groups operated on. From these results, lateral cricoid division in the growing animal does not appear to interfere with subsequent normal growth of the larynx.

Growth and development of the human cricoid cartilage: an immunohistochemical analysis of the maturation sequence of the chondrocytes and surrounding cartilage matrix.

OBJECTIVES: The goal was to determine maturational changes in the human cricoid cartilage. STUDY DESIGN: The study involved immunohistochemical staining of collagen II (a marker of proliferating chondrocytes), matrilin-1 (a marker of post-proliferative chondrocytes), and collagen X (a marker of hypertrophic chondrocytes). Specimens included uninjured human cricoid cartilages at 18 and 41 weeks' gestation and 1, 4, and 13 years postpartum. RESULTS: This study demonstrated that type II collagen peaks in concentration at approximately 41 weeks' gestation. Matrilin-1 is present in progressively lower concentration in the central core of the cricoid ring, but the peripheries of the ring contain the protein in relatively high concentration. Type X collagen is not expressed in the age groups tested. CONCLUSIONS: These biochemical markers lend further support to a chondrocyte proliferative phase that slows between 1 and 4 years of age. Chondrocytes then enter a phase histologically similar to the hypertrophic phase but are biochemically different than hypertrophic chondrocytes destined for endochondral ossification.

Apoptosis in the developing human cricoid cartilage: a pilot study.

Apoptosis is widely recognized as a major phenomenon in normal development. Deficiencies in this process may lead to developmental abnormalities such as congenital subglottic stenosis. We studied apoptosis using in situ end labeling of the 3'-OH ends of fragmented DNA in 5 progressively older, normal, human cricoid cartilage specimens. Results show that apoptosis is a very active process in fetal and neonatal tissue. The process gradually slows with advancing age. In the 4- and 13-year-old specimens, minimal to no apoptosis was seen. We conclude that apoptosis plays a critical role in the intraluminal and extraluminal expansion of the cricoid cartilage.

Gross and histologic changes in the developing rabbit subglottis in response to a controlled depth of injury.

OBJECTIVE: Our goal was to determine the effects of both perichondrial and intracartilaginous injury in the developing rabbit subglottis versus normal development. DESIGN: We conducted a descriptive, pilot study of changes in the shape and histology of the subglottis after a controlled depth of injury in 27 New Zealand White rabbits, ages 4 weeks, 8 weeks, and 1(1/2) years. INTERVENTION: Within each age group, 3 animals underwent no surgery, 3 underwent perichondrial injury, and 3 underwent intracartilaginous injury. RESULTS: Perichondrially injured animals in the 4-week age group developed a marked abnormality in the shape of the cricoid cartilage in the injured region. Cartilage of the perichondriallly injured animals in the 8-week and 1(1/2)-year groups became histologically consistent with fibrous tissue. The cartilage of all animals that underwent intracartilaginous injury was replaced with fibrous tissue. CONCLUSION: In this observational study, we identified 3 relevant findings. First, the responses of the cartilage to a perichondrial injury suggest that the luminal soft tissues may exert some morphologic control in developmentally young animals. Second, only the 4-week-old group's cartilage was tolerant of a perichondrial injury with continued growth of the ring. Third, no animal's cartilage could withstand an intracartilaginous injury regardless of age.

Tracheal growth after resection and anastomosis in puppies.

Tracheal morphology, morphometric changes, and growth and histologic changes were studied in puppies submitted to tracheal resection and anastomosis. Fifteen mongrel puppies about 12 weeks old and weighing on an average 5.5 kg were operated under general anesthesia using fluothane. A median cervicotomy incision was made in ten puppies (experimental group, EG) and the proximal 14 tracheal rings were resected (average length 5.08 cm or about 35% to 38% of total tracheal length). One layer anastomosis was done using vicryl 4.0 maintaining the average tension of 1,450 g. Five puppies (control group, CG) were submitted to tracheal transection and anastomosis and the following parameters were studied. Tracheal morphology the trachea of the EG was a rounded triangle whereas in the CG it was oval in shape, there was increase in the intercartilageneous spaces in the EG, no granulation tissue was present, two mucous webs were seen in the EG and one in the CG. Morphometric changes average tracheal length EG 13 cm, CG 17.7 cm, intercartilagenous space EG 3.08 mm, CG 1.3 mm, intercricothyroid space EG 1.2 cm, CG 0.53 cm, sagittal and transverse tracheal thickness at the anastomosis EG 2.6 and 3.3 mm, CG 2 and 1.5 mm, sagittal and transverse diameter reduced on an average 2 mm in EG. Histology Moderate fibrosis was found at the level of anastomosis with no modification of chondrocytes at the cartilagenous rings in the EG. Even with high anastomotic tension, the dogs had normal tracheal growth without stenosis; the sagittal and transverse growth at the anastomosis in the EG was 90% and 85%, respectively, when compared with the CG.

Androgen stimulation and laryngeal development.

Androgen-induced changes in laryngeal growth patterns were studied using a sheep animal model. Forty-eight lambs were divided into eight treatment groups. Lambs in seven of the groups were castrated at birth, while lambs in the eighth group served as an intact (noncastrated) control. Six groups were then treated with varying doses of testosterone and dihydrotestosterone, while the seventh served as a castrated, nontreated control. All animals were killed and gross dissections of the larynges were performed. Thirty-four linear and angular measurements were obtained from each larynx. The mean superior thyroid horn separation showed the most dramatic androgen-induced effect (p = 0.023). Laryngeal anterior-posterior diameter, superior thyroid horn height, posterior thyroid cartilage width, thyroid cartilage angle, and vocal process to arytenoid base distances all demonstrated positive dose-response relationships. Hypoandrogenic levels appeared to have an inhibitory effect upon laryngeal growth when compared to castrated controls.