Developmental Anatomy of the Eustachian Tube: Implications for Balloon Dilation.

OBJECTIVE: To describe the developmental anatomy of the eustachian tube (ET) and its relationship to surrounding structures on computed tomography. STUDY DESIGN: Case series with chart review. SETTING: A tertiary care hospital. METHODS: ET anatomy was assessed with reformatted high-resolution computed tomography scans from 2010 to 2018. Scans (n = 78) were randomly selected from the following age groups: <4, 5 to 7, 8 to 18, and >18 years. The following were measured and compared between groups: ET length, angles, and relationship between its bony cartilaginous junction and the internal carotid artery and between its nasopharyngeal opening and the nasal floor. RESULTS: The distance between the bony cartilaginous junction and internal carotid artery decreased with age between the <4-year-olds (2.4 ± 0.6 mm) and the 5- to 7-year-olds (2.0 ± 0.3 mm, P = .001). The ET length increased among the <4-year-olds (32 mm), 5- to 7-year-olds (36 mm), and 8- to 18-year-olds (41 mm, P < .0001). The cartilaginous ET increased among the <4-year-olds (20 mm), 5- to 7-year-olds (25 mm), and 8- to 18-year-olds (28 mm, P < .0001). The ET horizontal angle increased among the <4-year-olds (17°), 5- to 7-year-olds (21°), and 8- to 18-year-olds (23°, P≤ .003), but the ET sagittal angle did not statistically change after 5 years of age. The height difference between the nasopharyngeal opening of the ET and the nasal floor increased among the <4-year-olds (4 mm), 5- to 7-year-olds (7 mm), and 8- to 18-year-olds (11 mm, P < .0001). CONCLUSION: The ET elongates with age, and its angles and relationship to the nasal floor increase. Although some parameters mature faster, more than half of the ET growth occurs by 8 years of age, and adult morphology is achieved by early adolescence.

Cranial Indicators Identified for Peak Incidence of Otitis Media.

Acute otitis media (AOM) is one of the most common pediatric conditions worldwide. Peak age of occurrence for AOM has been identified within the first postnatal year and it remains frequent until approximately six postnatal years. Morphological differences between adults and infants in the cartilaginous Eustachian tube (CET) and associated structures may be responsible for development of this disease yet few have investigated normal growth trajectories. We tested hypotheses on coincidence of skeletal growth changes and known ages of peak AOM occurrence. Growth was divided into five dental eruption stages ranging from edentulous neonates (Stage 1) to adults with erupted third maxillary molars (Stage 5). A total of 32 three-dimensional landmarks were used and Generalized Procrustes Analysis was performed. Next, we performed principal components analysis and calculated univariate measures. It was found that growth change in Stage 1 was the most rapid and comprised the largest amount of overall growth in upper respiratory tract proportions (where time is represented by the natural logarithmic transformation of centroid size). The analysis of univariate measures showed that Stage 1 humans did indeed possess the relatively shortest and most horizontally oriented CET's with the greatest amount of growth change occurring at the transition to Stage 2 (eruption of deciduous dentition at five postnatal months, commencing peak AOM incidence) and ceasing by Stage 3 (approximately six postnatal years). Skeletal indicators appear related to peak ages of AOM incidence and may contribute to understanding of a nearly ubiquitous human disease. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 300:1721-1740, 2017. © 2017 Wiley Periodicals, Inc.

A defect in early myogenesis causes Otitis media in two mouse models of 22q11.2 Deletion Syndrome.

Otitis media (OM), the inflammation of the middle ear, is the most common disease and cause for surgery in infants worldwide. Chronic Otitis media with effusion (OME) often leads to conductive hearing loss and is a common feature of a number of craniofacial syndromes, such as 22q11.2 Deletion Syndrome (22q11.2DS). OM is more common in children because the more horizontal position of the Eustachian tube (ET) in infants limits or delays clearance of middle ear effusions. Some mouse models with OM have shown alterations in the morphology and angle of the ET. Here, we present a novel mechanism in which OM is caused not by a defect in the ET itself but in the muscles that control its function. Our results show that in two mouse models of 22q11.2DS (Df1/+ and Tbx1(+/-)) presenting with bi- or unilateral OME, the fourth pharyngeal arch-derived levator veli palatini muscles were hypoplastic, which was associated with an earlier altered pattern of MyoD expression. Importantly, in mice with unilateral OME, the side with the inflammation was associated with significantly smaller muscles than the contralateral unaffected ear. Functional tests examining ET patency confirmed a reduced clearing ability in the heterozygous mice. Our findings are also of clinical relevance as targeting hypoplastic muscles might present a novel preventative measure for reducing the high rates of OM in 22q11.2DS patients.

Morphology and ciliary motion of mucosa in the Eustachian tube of neonatal and adult gerbils.

The Eustachian tube is a small canal that connects the tympanic cavity with the nasal part of the pharynx. The epithelial lining of the Eustachian tube contains a ciliated columnar epithelium at the tympanic cavity and a pseudostratified, ciliated columnar epithelium with goblet cells near the pharynx. The tube serves to equalize air pressure across the eardrum and drains mucus away from the middle ear into the nasopharynx. Blockage of the Eustachian tube is the most common cause of all forms of otitis media, which is common in children. In the present study, we examined the epithelial lining of the Eustachian tube in neonatal and adult gerbils, with a focus on the morphological and functional development of ciliated cells in the mucosa. The length of the tube is ∼8.8 mm in adult gerbils. Scanning electron microscopy showed that the mucosal member near the pharyngeal side contains a higher density of ciliated cells and goblet cells than that near the tympanic side. The cilia beat frequency is 11 Hz. During development, the length of the Eustachian tube increased significantly between postnatal day 1 (P1) and P18. Scanning electron microscopy showed that the mucosa contained a high density of ciliated cells with a few goblet cells at P1. The density of ciliated cells decreased while the density of goblet cells increased during development. At P18, the mucosa appeared to be adult-like. Interestingly, the ciliary beat frequency measured from ciliated cells at P1 was not statistically different from that measured from adult animals. Our study suggests that the Eustachian tube undergoes significant anatomical and histological changes between P1 and P18. The tube is morphologically and functionally mature at P18, when the auditory function (sensitivity and frequency selectivity) is mature in this species.

Relação da otite média secretora com o crescimento craniofacial e as características oclusais / Otitis media with effusion and dental occlusion: is there any relationship?

O objetivo deste estudo foi avaliar a morfologia/crescimento craniofacial e a oclusão dentária em pacientes (ambos sexos), entre 4 e 10 anos e aumento adenoamigdaliano com e sem otite média secretora (OMS). Utilizou-se análise cefalométrica e modelos de estudo dentários. Não foram observadas diferenças significativas entre os grupos estudados, em relação às medidas lineares e angulares adotadas, exceto, a medida correspondente ao comprimento do palato ósseo (ENA-ENP), que mostrou relação com a idade e a OMS. Não houve um tipo facial predominante. Observou-se discreta predominância de mordida profunda, mordida cruzada posterior e desvio da linha média em relação à OMS, porém sem significância estatística. A atresia maxilar pode estar associada à OMS, assim como sua redução pode estar relacionada ao crescimento e desenvolvimento craniofacial.

The aim of this study was to evaluate the craniofacial growth/morphology and dental occlusion in 100 patients (male and female) from 4 to 10 years old and tonsils and adenoid enlargement. There were two groups: with and without otitis media with effusion (OME). We used the cephalometric analyses and dental casts. It was not observed significant differences between the two groups, in relationship to the linear and angular measurements adopted, except for the measurement corresponding to the palate bone length, which had shown correlation with age and OME. It was not found a facial pattern predominance. It was observed a discreet predominance of deep bite, posterior cross bite and midline deviation to OME, however without statistical significance. The maxillary narrowing might be associated to OME as well as its reduction may be related to the craniofacial growth and development.

Postnatal development of static volume of the eustachian tube lumen. A computer-aided three-dimensional reconstruction and measurement study.

Eleven human temporal bone-eustachian tube (ET) specimens obtained from 11 individuals (ages, 3 months to 88 years) were studied to investigate the static volume of the ET lumen. The volumes were measured by computer-aided 3-dimensional reconstruction and measurement methods. Four of the 11 individuals were children, and the remaining 7 were adults. The total volume of the ET lumen was significantly larger in the adults than in the children (p < .01). This difference was produced by significant growth of the volume of the cartilaginous and junctional portions (p < .01). The lumen of the bony portion, by contrast, did not change with age. Increased volume of the ET lumen, especially of the cartilaginous and junctional portions, would be expected to increase both ventilation and clearance. Therefore, the small volume of ET lumen of the cartilaginous and junctional portions in children may be a predisposing factor for otitis media.

Postnatal development of the eustachian tube glands.

OBJECTIVE: To delineate a possible difference in the function of the eustachian tube (ET) between infants and adults. STUDY DESIGN: Morphometric and histopathological examination on the human temporal bones. METHODS: The secretory glands in the ET were studied in serial histological sections through the cartilaginous portion of the human ET obtained from 32 individuals whose ages ranged from 1 day to 19 years. Of these, 26 were normal control cases and 6 were cases with otitis media (OM). RESULTS: In both normal and OM groups, the distribution of the glands was predominantly in the medial side of the cartilaginous portion of the ET, and the volume of the ET glands was directly related to both the volume of the ET lumen and the patients' age. In normal cases, the relative proportion of the three types of acinar cells (mucous, serous, and mixed) varied among the different age groups. The cases in patients under 1 month of age had more mucous glands and fewer serous glands. In cases of the 1-month-old to 7-year-old age group, the three ET gland cell types came to be approximately equal. Relative proportion of the serous glands continuously increased with aging, and in cases of patients older than 7 years of age, serous glands were predominant over the other two components. CONCLUSION: It is assumed that the greater proportion of mucous glands and insufficient serous glands by 7 years of age reflects immature development, which may be one of the associated factors contributing to recurrent OM among infants.

Correlação entre a morfologia craniofacial e doença da orelha média em adultos / Correlation between craniofacial morphology and otitis media in adults

A face de cada um de nós apresenta características únicas. Resultado da combinação de tipos variados de mandíbulas, maxilas, órbitas, é o que nos faz reconhecer cada indivíduo. As crianças apresentam proporções faciais distintas dos adultos. O processo de crescimento e desenvolvimento craniofacial é influenciado por diversos fatores: tanto sistêmicos (genéticos, metabólicos, etc.) quanto locais (respiração nasal, dentição, hábitos orais). Sabe-se que a incidência de otites na infância é maior que em adultos e o que se atribui `a posição mais horizontal da tuba auditiva, em relação `a base do crânio nas crianças. A tuba auditiva é parte da orelha média que se estende desde o osso temporal até a nasofaringe, cujo desenvolvimento é influenciado pelo crescimento craniofacial. As doenças da orelha média influenciadas pela função da tuba auditiva, também ocorrem em adultos, ainda que em menor proporção. Uma vez que a menor incidência das doenças em adultos é atribuída ao crescimento da tuba auditiva, e este é dependente do crescimento craniofacial, deve haver relação entre as doenças da orelha média em adultos com as características morfológicas da face. Desse modo, o objetivo deste estudo foi correlacionar as doenças da orelha média, influenciadas pela função da tuba auditiva com a morfologia e tipologia craniofacial e determinar um traçado cefalométrico como fator prognóstico para estas doenças. Foram selecionados 66 pacientes, entre 18 e 40 anos, do Ambulatório da Divisão de Clínica Otorrinolaringológica da FMUSP. Os indivíduos foram divididos em 2 grupos sendo 32 com doença da orelha média e 34 sem, que constituiu o grupo controle. Os indivíduos não apresentavam nenhum dos fatores de exclusão a seguir: história pessoal ou familiar de fissura palatina, cirurgia bucal, maxilar, faríngea, nasal ou facial prévias, tratamento ortodôntico ou processos obstrutivos do óstio da tuba auditiva. Os pacientes foram submetidos a exame...

There are thousand types of faces and each one is unique. Individual faces are the result from the combination of different kinds of maxillas, mandibles, and orbits. The face proportions, in children, are distinct of adult ones. Craniofacial growth and development depends on a diversity of factors, such as: genetic, metabolic, nasal breathing, teeth development, etc. The auditory tube is part of middle ear and extends from temporal bone to nasopharynx. It has a more horizontal position in children than in adults; therefore otitis media is more frequent in this age group. The type of cranial base and the displacement of the maxilla during craniofacial growth influence the growth of the auditory tube. The lower frequency of otitis media in adults relates to the development of auditory tube during craniofacial growth. So, there should be a correlation between caniofacial morphology and otitis media. The aims of this study are to correlate facial types and cephalometric measurement morphology to otitis media and suggest which measurements can be used as a prediction of the evolution of otitis media. Sixty-four patients, 18 to 40 years old, were selected from the Outpatient Center of the Department of Otolaryngology of the University of São Paulo Medical School. They were divided into two groups: 32 with otitis media and 34 controls. We excluded patients with personal or familiar history of cleft palate, previous buccal, maxillar, pharyngeal, facial or nasal surgery, orthodontic treatment or obstructive process of the auditory tube ostia. All subjects underwent to complete ENT physical examination, videotoscopy, fibernasalendoscopy and lateral cephalograms. Statistical analysis of the cephalometric measurements showed significant differences of cranial base; projection of maxilla and facial height, in patients with otitis media when compared to the control group or to the ideal measures of the harmonic face...

Histological and morphometrical studies on the mucosa of the equine guttural pouch (auditory tube diverticulum).

The present study attempted to clarify the characteristics of the guttural pouch mucosa in equines and to evaluate its foreign substance clearance ability. The specimens were collected from nine regions (eight in the guttural pouch mucosa, and one in the nasopharynx mucosa). We first examined the pouch mucosa by light and electron microscopy. We then measured the frequency of goblet cells per 200 epithelial cells, the length of the cilia, the thickness of the epithelial cell layer and lamina propria and statistically analyzed the data. The guttural pouch mucosa consisted of stratified columnar epithelia with brush-like cilia, and there were almost no histological differences between adults and foals. The morphometrical study revealed significant differences in goblet cell frequency (p < 0.001) and the thickness of lamina propria (p < 0.05). By contrast, no statistically significant difference was detected in the length of the cilia or the thickness of the epithelial cell layer. These findings suggest that the guttural pouch mucosa provides foreign substance clearance ability, but that its ability varies among different regions of the epithelium.

Length of the eustachian tube and its postnatal development: computer-aided three-dimensional reconstruction and measurement study.

Eleven normal human temporal bone-eustachian tube (ET) specimens obtained from 11 individuals whose ages were 3 months to 88 years were studied to investigate the path length along the ET lumen and its postnatal development by means of a computer-aided 3-dimensional reconstruction and measurement method. The path length of the ET lumen of the 3-month-old infant was 21.2 mm, and its growth was in correlation with age to attain its adult length (average, 37.00 +/- 4.16 mm). The ratio of the length of the cartilaginous portion together with the junctional portion to the length of the bony portion was 8:1 in an infant at the age of 3 months and 4:1 in adults. That the bony portion of the ET develops relatively more than the cartilaginous and junctional portions may cause this finding. In addition, there is a developmental shift in the orientation of the cartilaginous portion with respect to the bony portion of the ET. In children, the cartilaginous and bony portions are both aligned with the line that connects the pharyngeal orifice and the tympanic orifice. In adults, however, the cartilaginous portion is angled inferiorly and laterally from the bony portion. This change may reflect the relative growth of the face.

Postnatal development of eustachian tube cartilage. A study of normal and cleft palate cases.

Infants with cleft palate (CP) display eustachian tube (ET) dysfunction. This study compared the postnatal development of the volume of ET cartilage in 34 normal cases and 10 CP cases using a personal computer. In cases with age under 1 month old, the total volume of ET cartilage was 61.94+/-20.89 mm(3) (mean+/-S.D.) in 16 normal control cases and 50.07+/-24.69 mm(3) in nine CP cases (t-test, not significantly different from normal). The ratio of lateral lamina (LL) to medial lamina (ML) volume (LL/ML) was reduced significantly (t-test, P<0.001) from 0.23+/-0.07 in 16 normal control cases to 0.09+/-0.05 in nine CP cases under 1 month old. In 34 normal ET cases whose ages were under 20 years, statistically significant positive correlations were found between the total volume of ET cartilage (y1) and age (x), volume of LL (y2) and age, and volume of ML (y3) and age (P<0.01, r=0.731, 0.614, 0.719). The regression lines were y1=20.37x+95.57, y2=2.02x+15.60, and y3=18. 35x+79.97. With the result obtained from this study, it is assumed that immaturity of the ET cartilage in infants, especially that of LL of the ET cartilage in CP infants, may be a significant risk factor for developing otitis media with effusion.

Postnatal development of Eustachian tube: a computer-aided 3-D reconstruction and measurement study.

The postnatal development of the Eustachian tube (ET) and its surrounding structures was investigated by means of computer-aided three-dimensional (3-D) reconstruction methods in 13 normal human temporal bones, obtained from individuals 3 months to 71 years old. The cross-sectional area, width and height of the lumen in most of the cartilaginous portion of the ET were significantly smaller in children than in adults. In particular, there was a marked, age-associated difference in the shape of the lumen in the cartilaginous portion of the ET. In adults, the cross-sectional area of the lumen declined monotonically between a large opening at the pharyngeal orifice and the narrowest portion of the ET (near the border of the cartilaginous and junctional regions). In children, by contrast, the ET lumen was uniformly smaller over the first 80% of its length from the pharyngeal orifice. It is suggested that this immature morphology of the ET lumen may confer increased risk of developing otitis media during childhood.

Clinical-morphological correlation of nasal obstruction with skull base development and otitis media. An experimental study.

Morphological changes of the middle ear were investigated by means of microotoscopy and scanning electron microscopy in 40 developing Albino rats. In 20 one nostril (group B) and in 20 both nostrils (group C) had been experimentally obstructed. 20 rats were used as controls (group A). Microotoscopy and scanning electron microscopy on the middle ear mucosa were performed when the animals were 2 months old, i.e. at 90% of their development. At microotoscopy the tympanic membranes, homolateral to the obstructed nostril, proved to be abnormal in 81% of group B rats and in almost all rats belonging to group C. Scanning electron microscopy, performed after the bullae had been removed, showed the following epithelial surface changes of the middle ear homolaterally to the obstructed nostril: (a) a significant increase of nonciliated elements with a secretory behavior as compared to controls, even of the floor where normally a large number of ciliated cells is present; (b) several ciliated cells were destroyed and their cilia were irregular and untidy; (c) thick mucous secretions covered the floor of the tympanic bulla; and (d) squamous metaplasia of the hypotympanic epithelium. Extrarotation of the eustachian tubes and developmental abnormalities of the skull base in growing rats, caused by nasal obstruction, seem to be able to induce pathological events of the middle ear.

[The ultrastructure of the Eustachian tube].

To observe the ultrastructure of mucous membrane of Eustachian tube in human being, ninteen human's Eustachian tube from various ages, were divided into tympanic segment, isthmus and pharyngeal segment and observed under SEM. The results showed that the epithelium of Eustachian tube consisted of ciliated cells, nonciliated cells and goblet cells. At the isthmus, the bone and cartilage junction, the cells got crowded, and there were more and more goblet cells from tympanic side to pharyngeal side, as well as the cilia of ciliated cell leaned towards the pharyngeal side. The upper one third part of Eustachian tube was covered mostly by nonciliated cells, the floor and lower parts were ciliated cells. It was concluded that the upper parts of Eustachian tube's wall played an important role in maintaining equation of pressure in middle ear, and the floor and lower parts in providing an active mucociliary mechnism. The defence system of the Eustachian tube mucous membrane had developed during the fetal stage and was well established at birth.

Nasal obstruction and skull base development: experimental study in the rat.

The influence of nasal obstruction on the development of the anterior skull base, of the tympanic bulla, and of the Eustachian tube was investigated in three groups of 20 albino Wistar rats in which one (group B) or both nostrils (group C) had been experimentally obstructed by means of synthetic resin mixed with radiopaque material. After two months, a cephalometric investigation demonstrated that the angle formed by the median line passing through the superior interincisive point and the most posterior median point of the occipital bone and by the line connecting the tympanic bulla and the superior interincisive point was significantly increased when the homolateral nostril had been obstructed if compared to controls (group A). On the basis of these preliminary cephalometric observations we suggest that nasal obstruction is able to determine anatomical changes of the superior maxilla, the skull base, and the jaw, with abnormal skeletal growth and consequent possible Eustachian tube dysfunction.

Anatomic relationships between Ostmann's fatty tissue and eustachian tube.

To examine anatomic relationships between Ostmann's fatty tissue (OF) and the eustachian tube (ET), we evaluated serial histologic sections of 32 normal temporal bone-ET specimens and made a quantitative analysis of several measurements (height, width, and volume). We compared results in specimens from individuals in whom the ET was still developing (those 19 years and younger) to results in specimens from individuals with adult ETs (those older than 19). We found that 1) the main body of OF is located at the inferolateral aspect of the ET and 2) postnatally, OF grows in volume, mainly by an increase in height, so that OF maintains the same vertical relationship to the growing ET and does not increase in width. The former finding indicates that OF might exert static pressure on the ET not to open widely. The latter finding indicates that the relatively thicker mass of OF may narrow the ET in those with immature ETs. These results indicate a possible role for OF in ET function, which in turn has been implicated in otitis media with effusion.

Development of secretory elements in murine tubotympanum: lysozyme and lactoferrin immunohistochemistry.

Secretory activity, particularly of antibacterial agents such as lysozyme and lactoferrin, is an important aspect of the mucosal defense mechanism, and the development of these agents may have a direct bearing on the susceptibility of the ear to infection. In this study, the secretory cells of the murine tubal epithelium were first observed at gestational day 17. Although tubal glands began to develop on gestational day 18, their secretory activity was first shown on postnatal day 3. The number of secretory cells of the tubal epithelium increased rapidly immediately after birth, while that of the tubal glands showed a gradual increase from postnatal day 3. The epithelial secretory cells in the tubotympanum matured at birth, but the tubal glands matured gradually after birth. Lysozyme was first recognized in the epithelial secretory cells on postnatal day 1, while lactoferrin was first detected in the tubal glands on postnatal day 3. Both lysozyme and lactoferrin were co-localized in the serous cells of the tubal glands. The secretion of lysozyme and lactoferrin seemed to reflect the maturation of the secretory cells in the murine tubotympanum.

Expression of sialic acids in the developing murine tubotympanum.

Sialoglycoconjugates in the developing murine tubotympanum were characterized using lectin histochemistry with wheat germ agglutinin (WGA), Limax flavus agglutinin (LFA), Sambucus nigra agglutinin (SNA), Maackia amurensis agglutinin (MAA), peanut agglutinin (PNA), and neuraminidase treatment. WGA, LFA, MAA, and neuraminidase-PNA labeled epithelial goblet cells, glandular mucous cells, and cell surfaces of adult and newborn murine tubotympanum. SNA did not label any secretory components. PNA labeled secretory cells and cell surfaces of the fetal tubotympanum without neuraminidase treatment. After birth, these secretory cells and cell surfaces were labeled with PNA only after neuraminidase treatment. These results revealed that: Sialoglycoconjugates are produced from glandular mucous cells and epithelial goblet cells and are present on cell surfaces and within the mucous blanket; their terminal tri-saccharide linkage appears to be the sequence Neu5Ac(alpha 2-3)Gal(beta 1-3)GalNAc; sialic acids appear before birth and gradually increase; terminal galactose residues are masked by sialic acids after birth.

Luminal development of the eustachian tube and middle ear: murine model.

The purpose of this study was to describe the luminal development of the murine eustachian tube and middle ear. Thirty specimens, aging from gestational day 11 to postnatal day 21, were investigated through the light microscopic observations. The present study also used digitizer, computer, and serially sectioned temporal bone specimens for three-dimensional reconstruction to measure the volume of the eustachian tube and middle ear cavity at different gestational and postnatal ages. The first pharyngeal pouch elongated during gestational day 12 to form the tubotympanic recess. Between gestational day 13 and 14 this tubotympanic recess extended to the middle ear area. A rapid increment in the volume of the tubotympanic recess was noted between gestational day 15 and 16. At this age, a definite division of the tubotympanic recess into the eustachian tube and middle ear cavity was observed. During the postnatal period, the maximum change of the middle ear volume was noted on postnatal day 11 when the mesenchymal tissue in the middle ear cavity disappeared completely.

Developmental anatomy of the eustachian tube and middle ear in mice.

PURPOSE: It is generally accepted that the development of the tubotympanum has significant bearing on the susceptibility to ear infection. A detailed study of the differentiation of ciliated cells in secretory elements will be useful in understanding both the normal physiology and the pathology of the tubotympanum. METHOD: Serially sectioned temporal bones of 76 mice ranging from gestational age day 11 to postnatal day 21 were examined microscopically. RESULTS: During the period of gestation, the tubotympanic recess was formed at the 12th day and began to extend to form the middle ear between the 13th and 14th days. A rapid increase in the volume of the tubotympanic recess was observed between the 15th and 16th days when a definitive division of the tubotympanic recess into the eustachian tube and middle ear cavity was observed. Postnatally the tubotympanum attained an adult form around day 9, and the maximum change of middle ear volume was noted on day 11, when the mesenchymal tissue in the middle ear cavity disappeared completely. Development of the ciliated cells was observed concurrently in both the eustachian tube and middle ear on the 16th gestational day, one day earlier than the appearance of the epithelial secretory cells in both the eustachian tube and middle ear. The number of ciliated cells and secretory cells increased rapidly after birth. Tubal glands were well developed with evidence of secretory activity around the time of birth. CONCLUSIONS: Based on these findings, one can conclude that the mucociliary defense system starts to develop during the fetal stage and is well established immediately after birth.