Differing contributions of the first and second pharyngeal arches to tympanic membrane formation in the mouse and chick.

We have proposed that independent origins of the tympanic membrane (TM), consisting of the external auditory meatus (EAM) and first pharyngeal pouch, are linked with distinctive middle ear structures in terms of dorsal-ventral patterning of the pharyngeal arches during amniote evolution. However, previous studies have suggested that the first pharyngeal arch (PA1) is crucial for TM formation in both mouse and chick. In this study, we compare TM formation along the anterior-posterior axis in these animals using Hoxa2 expression as a marker of the second pharyngeal arch (PA2). In chick, the EAM begins to invaginate at the surface ectoderm of PA2, not at the first pharyngeal cleft, and the entire TM forms in PA2. Chick-quail chimera that have lost PA2 and duplicated PA1 suggest that TM formation is achieved by developmental interaction between a portion of the EAM and the columella auris in PA2, and that PA1 also contributes to formation of the remaining part of the EAM. By contrast, in mouse, TM formation is highly associated with an interdependent relationship between the EAM and tympanic ring in PA1.

Mouse Hoxa2 mutations provide a model for microtia and auricle duplication.

External ear abnormalities are frequent in newborns ranging from microtia to partial auricle duplication. Little is known about the molecular mechanisms orchestrating external ear morphogenesis. In humans, HOXA2 partial loss of function induces a bilateral microtia associated with an abnormal shape of the auricle. In mice, Hoxa2 inactivation at early gestational stages results in external auditory canal (EAC) duplication and absence of the auricle, whereas its late inactivation results in a hypomorphic auricle, mimicking the human HOXA2 mutant condition. By genetic fate mapping we found that the mouse auricle (or pinna) derives from the Hoxa2-expressing neural crest-derived mesenchyme of the second pharyngeal arch, and not from a composite of first and second arch mesenchyme as previously proposed based on morphological observation of human embryos. Moreover, the mouse EAC is entirely lined by Hoxa2-negative first arch mesenchyme and does not develop at the first pharyngeal cleft, as previously assumed. Conditional ectopic Hoxa2 expression in first arch neural crest is sufficient to induce a complete duplication of the pinna and a loss of the EAC, suggesting transformation of the first arch neural crest-derived mesenchyme lining the EAC into an ectopic pinna. Hoxa2 partly controls the morphogenesis of the pinna through the BMP signalling pathway and expression of Eya1, which in humans is involved in branchio-oto-renal syndrome. Thus, Hoxa2 loss- and gain-of-function approaches in mice provide a suitable model to investigate the molecular aetiology of microtia and auricle duplication.

Fetal development and variations in the cartilages surrounding the human external acoustic meatus.

In contrast to the osseus part that develops from the tympanic ring of the squamous part of the temporal bone after birth, there is little information on fetal development of the cartilages surrounding the human external acoustic meatus. Using routine histology and immunohistochemistry, we examine sections of 22 fetuses (CRL 100-270mm) to study the development of these cartilages. Early external ear cartilages are composed of three groups: (1) a ring-like cartilage at the putative tragus on the anterior side of the meatus, (2) two or three bar-like cartilages along the inferior wall of the meatus, and (3) a plate-like cartilage in a skin fold for the putative helix on the posterior side. In contrast to the first and second pharyngeal arch cartilages, all the external ear cartilages express glial fibrillary acidic protein. Notably, the bar-like cartilages along the meatus are connected with a fascia-like structure to the second pharyngeal arch cartilage. Later, with considerable individual variation, new cartilage bars extend from the inferior cartilages to the superior side of the meatus. Thus, via an intermediate stage showing a chain of triangular elastic cartilages, a chain of bar-like cartilages on the inferior side appears to change into a complex of H-shaped cartilages. Numerous ceruminous glands are seen in the thick subcutaneous tissue overlying the cartilaginous part of the meatus. However, they do not insert into the cartilage. The external ear cartilages develop much earlier than, and independently of, the osseus part.

A different type of branchial fistula as part of a branchiootorenal syndrome.

We describe an extremely rare case of a complete fistula, a combination of the first 2 branchial arches as a component of branchiootorenal syndrome. A 13-year-old girl presented with the complaint of intermittent drainage from bilateral preauricular and right lower neck external openings. A contrast fistulogram revealed a complete fistula. Diagnostic features and surgical techniques are discussed in detail.

Temporomandibular joint herniation and the foramen of Huschke: an unusual external auditory canal mass.

OBJECTIVES: We describe a rare case of spontaneous temporomandibular joint herniation into the external auditory canal, and we also review the presentation, aetiology and management of such cases. CASE REPORT: An 87-year-old woman presented with a four-month history of left-sided otorrhoea and otalgia. Examination revealed a soft, polypoid mass in the left ear canal. When the patient opened her mouth the lesion disappeared. Subsequent computed tomographic imaging of the patient's temporal bones confirmed an 8.6 mm defect in the antero-inferior portion of the left ear canal, with herniation of retrodiscal soft tissues. CONCLUSION: The external auditory canal is intimately related to the temporomandibular joint, separated only by its bony anterior wall. Neoplasm, trauma or inflammation in this area can result in displacement of the temporomandibular joint into the ear canal; however, spontaneous herniation is rare. Persistence of the primitive foramen of Huschke can result in dehiscence of the anterior canal wall, allowing articular tissue to prolapse into the ear canal. Surgical closure of these defects is known to be effective in ameliorating symptomatic cases.

Epithelial-mesenchymal transition as a possible mechanism of semicircular canal morphogenesis in chick inner ear.

Semicircular canals are sensory organs for balance, consisting of fluid-filled tubules that are arranged perpendicularly to each other in inner ear. The precise mechanism of the morphogenesis of this unique organ is still under investigation. Semicircular canals arise from the flattened pouch of epithelium. The centers of two apposing wall of the pouch approach each other and form a fusion plate. The clearing of the fusion plate makes a hole and leaves the remaining tissue as semicircular canals. Three mechanisms have been proposed for this clearing: programmed cell death, epithelial-mesenchymal transition, and retraction of the cells in the fusion plate to surrounding semicircular canals. Previous studies have revealed programmed cell death in the fusion plate, although other two hypotheses were not disproved. Here we examined the contribution of epithelial-mesenchymal transition and epithelial retraction to the morphogenesis of semicircular canals. We analyzed immunohistochemically the structural change in the epithelium of the developing fusion plate using molecular markers, basal lamina component laminin, cytoskeletal F-actin, and cellular junctional marker beta-catenin. Our observation revealed that fusion plate epithelium lost its apico-basal polarity and intermingled with facing fusion plate cells, associated with the disruption of basal lamina. Moreover, there were several cells with mesenchymal appearance adjacent to the torn basal lamina. We also found the merging of apposing basal laminae at the border between forming canal and breaking fusion plate. These observations suggest that the epithelial-mesenchymal transition, rather than the epithelial retraction, may be responsible for clearing fusion plate cells.

Does passive smoking affect the outcome of grommet insertion in children?

Bilateral myringotomy with insertion of ventilation tube (grommet) is the most common surgical procedure done on children under general anaesthetic. A prospective study was conducted on children undergoing grommet insertion to ascertain any relationship between exposures of passive smoking to the outcome of grommet insertion. Six hundred and six children (with 1174 ears) who underwent grommet insertion for recurrent secretory otitis media were followed up till the grommets were extruded. Thirty-three children (65 per cent), whose mothers smoked when they were pregnant, had bilateral narrow external ear canals. The median survival rate of grommet was 59 weeks in children who were exposed to passive smoking as compared to 86 weeks for non-exposed children and the extrusion rate of grommet was 36 per cent higher at the end of one year if both parents smoked compared to the non-smoking group. Post-extrusion myringosclerosis was 64 per cent if both parents smoked and less than 20 per cent if neither parents smoked. It is concluded that post-operative infection rate, attic retraction, post-extrusion myringosclerosis and permanent perforations of tympanic membrane were more common in children exposed to passive smoking. The study provides further support to professional and governmental advice that passive smoking is harmful.

First branchial cleft anomalies have relevance in otology and more.

INTRODUCTION: First branchial cleft anomalies account for less than 8% of all branchial abnormalities. Their rarity and diverse presentations have frequently led to misdiagnosis and inappropriate treatment. In a trend towards specialisation/subspecialisation, first branchial cleft duplication anomalies, with their varied clinical manifestations, may possibly present to an Otology, Head and Neck Surgery, Paediatric Otolaryngology, Maxillofacial or even a General Paediatric and General Surgery practice. There is a need to highlight the clinical features which can aid in accurate diagnosis. CLINICAL PICTURE, TREATMENT AND OUTCOME: A case of an adult with Work Type 2 first branchial cleft duplication anomaly presenting as a collaural fistula is described. It first presented as a recurrent upper neck abscess in childhood. The diagnosis had previously been missed although the patient was able to clearly establish a correlation between digging of the ipsilateral ear and precipitation of the abscess. Instead of an epidermal web, a myringeal lesion in the form of a fibrous band-like was present. The lesion was completely excised with no further recurrence. CONCLUSION: This case highlights useful diagnostic features both from the history and physical examination. The specialist/subspecialist must be aware of this condition and be mindful of its possible cross specialty/subspecialty symptoms and signs. Together with a good understanding of the regional embryology and anatomy, the lesion can be diagnosed early at initial presentation with the potential for best treatment outcomes.

Immunohistochemical characterization of the epidermoid formation in the middle ear.

OBJECTIVE: To study the incidence, size, and origin of epidermoid formations after accurately characterizing them by cytokeratin immunohistochemical analysis. STUDY DESIGN: A strategy of screening sections for possible epidermoid formations in the entire eardrum area in paraffin-embedded, serially sectioned developing temporal bones was used. Unstained adjacent sections were subjected to immunohistochemical staining, to provide accurately identified epidermoid formations for a study of their appearance and size in relation to age. METHODS: The immunohistochemical expression patterns for epidermoid cytokeratins of several antibodies at different gestational ages were determined. Then, epithelial structures suspected as epidermoid formations were characterized as epidermoid with age-appropriate antibodies in 36 paraffin-embedded temporal bones from 19 cases with an age range of 6 gestational weeks to 15 months postpartum using a novel method of antigen retrieval by heating sections in a 70 degrees C water bath. RESULTS: Each of 22 temporal bones ranging in age from 16 weeks gestation to 8 months postpartum contained one or more, often numerous, epidermoid formations. Sizes of epidermoid formations increased significantly with increasing age. The formations were found anywhere in the annular lateral wall region of middle ear, but the majority were in the anterosuperior region. A further study of the interface between annular external canal epidermis and middle ear epithelium in a larger group suggested that epidermoid formations arise at approximately 16 gestational weeks from the external canal epidermis. CONCLUSION: The findings indicate that epidermoid tissue in the middle ear normally originates from external canal epidermis at approximately the 16th gestational week and grows before disappearing.

Defects of the external auditory canal: a new reconstruction technique.

This report describes the clinical and radiographic findings together with surgical management of temporomandibular joint contents herniation through the tympanic plate of the external auditory canal. Two patients are reported. A review of the literature is presented, including a brief discussion of the embryological development of the external auditory canal. Excluding infection, trauma or neoplasm, the defect in the tympanic plate of the external auditory canal represents a developmental aberration with failure of the foramen of Huschke to close during development. A pre-auricular approach with insertion and fixation of an onlay polyethylene implant to prevent prolapse of the peri-articular tissues into the ear canal is presented and described.

Programmed cell death in the development of the mouse external auditory canal.

Programmed cell death (PCD) is an essential event for development. The purpose of this work was to ascertain how PCD, in vivo designated apoptosis, is involved in the development of the external auditory canal. We performed a time sequence study of the distribution of apoptosis during the development of external auditory canal (EAC) of the mouse. ICR mice ranging in age from embryonic day 11.5 (E11.5) to 12 days after birth (DAB) were used in the present study. A part of each head including both ears was removed and was processed according to its purpose. Light and electron microscopy for morphological studies and TUNEL method (Gavrieli et al. [1992] J Cell Biol., 119:493-501) for histochemical studies were used. On E11.5, distinct TUNEL-positive staining occurred in the branchial arch. Between E15.5 and 1DAB, TUNEL-positive cells were observed throughout the EAC and the number of these cells decreased with age. On E15.5 and E16.5, numerous TUNEL-positive cells were observed in a cavity remained in the epithelial plate. Transmission electron microscopy revealed that these cells had the features of apoptosis. From 3-12 DAB, no apoptosis was observed in the EAC except for the terminal differentiation of the skin of the EAC. Apoptosis was not observed during recanalization of the EAC, but occurred during the formation of the epithelial plate. The investigation established that PCD is involved in the formation of the epithelial plate, whereas only cornification of the epithelium of the EAC is associated with recanalization.

Recurrent pleomorphic adenoma of the parotid gland involving the osseous external auditory canal. With a note on the foramen of Huschke.

A recurrence of a parotid pleomorphic adenoma presenting as an external ear canal mass is reported. The route of extension was radiographically documented as an incompletely closed foramen of Huschke. The historical and developmental features of this foramen and the mechanisms of tumor extension as they relate to it are discussed.

Development of the human external ear.

External ear development is a lengthy and complex process that extends from early embryonic life until well into the postnatal period. Initial development of the auricle and external auditory canal during the fourth and fifth weeks of gestation is closely associated with anatomical changes involving the pharyngeal arch apparatus of the human embryo. The auricle and external canal are well formed by the time of birth but do not attain their full size and adult configuration until about 9 years of age. Sebaceous and modified apocrine glands, which are responsible for cerumen production, begin their development at about 5 months gestation in association with hair follicles in the outer portion of the external canal. Although they appear anatomically mature before birth, these glands do not reach full functional capacity until puberty.

Desarrollo del oído medio humano entre la 5a y la 17a semana de gestación / Human middle ear development between the 5th and the 17th week of pregnancy

Se realizó un estudio de la embriogénesis del oído medio humano entre la 5a y la 17a semana de gestación, utilizando 50 individuos (9 embriones y 41 fetos), los cuales fueron fijados, realizándose técnicas de tinción corrientes (hematoxilina-eosina), histoquímicas, tricrómicas e inmunohistoquímicas (anticuerpos monoclonales antilaminina, anticolágeno IV, antineurofilamentos). Seis fetos fueron procesados para microscopía electrónica de barrido, intentando obtener la mayor información posible del material humano. El análisis de los resultados reveló que el desarrollo del oído medio humano es mas tardío que el de los animales, distinguimos un crecimiento interesante de la tuba auditiva y como esta recubre a los huesecillos formando sus mesos, describimos la fijación de la platina del estribo a la pared medial de la caja timpánica en un período específico del desarrollo y la posterior formación, por muerte celular programada de la ventana oval y un nuevo pericondrio, hecho llamativo en la embriogénesis. En los embriones y fetos estudiados se describe la formación de nudos epidérmicos en la membrana timpánica (en su capa epitelial), dentro del desarrollo normal de esta estructura. Este hallazgo, no ha sido comunicado en la literatura. Con el conocimiento actual y el avance en la tecnología, se puede utilizar técnicas mas avanzadas de tinciones histológicas, inmunohistoquímicas y el uso de microscopio de barrido, para esclarecer las interrogantes del desarrollo del oído medio humano, agregando nueva información a lo tradicionalmente conocido

Imaging findings of the developing temporal bone in fetal specimens.

PURPOSE: To trace the development of the normal fetal temporal bone by means of plain radiography, MR, and CT. METHODS: Eighteen formalin-fixed fetal specimens, 13.5 to 24.4 weeks' gestational age, were examined with a mammographic plain film technique, CT, and MR imaging at 1.5 T. Temporal bone development and ossification were assessed. RESULTS: The membranous labyrinth grows with amazing rapidity and attains adult size by the middle of the gestation period. The cochlea, vestibule, and semicircular canals are very prominent and easily recognized on MR images. The otic capsule develops from a cartilage model. Ossification of the otic capsule proceeds rapidly between 18 and 24 weeks from multiple ossification centers that replace the cartilaginous framework. The mastoid, internal auditory canal, vestibular aqueduct, and external auditory canal continue to grow after birth. CONCLUSION: The study of fetal developmental anatomy may lead to a better understanding of congenital disorders of the ear. Faster MR scanning techniques may provide a method for in utero evaluation of the fetal temporal bone.

Embryology and anomalies of the external ear.

Malformations of the auricle are not uncommon and occur in 1 out of 12500 births. They can occur alone or can be associated with genetically determined syndromes. Most congenital malformations in the human occur during the third to twelfth weeks of embryonic life. During this period, the external ear is undergoing development and can be affected in many ways. There are three parts to the external ear: the auricle, the cartilaginous external auditory canal, and the bony external canal. The auricle (pinna) and the cartilaginous canal are closely related and probably develop from the same anlage. The bony canal is derived from the tympanic ring which is an incomplete cylinder of membranous bone. It must be clearly understood that, although this article is primarily concerned with the morphogenesis and dysmorphogenesis of the auricle, the rest of the external ear, specifically the external auditory canal, is developing simultaneously. Therefore, maldevelopment of the external canal and the auricle will frequently occur together.

Development of the human external auditory canal.

The embryological and fetal development of the external auditory canal is described and its importance for the migratory properties of the epithelium is discussed.

The embryologic development of the human external auditory meatus. Preliminary report.

During the final period of embryogenesis, a funnel-shaped tube continues medially into the mesenchymal tissue forming a curved path. Although this may sound simple, the development occurring during early fetal life is in fact very complex. At first, ectodermal cells proliferate to fill the lumen of the meatus, forming the meatal plug, and then at 10 weeks the bottom of the plug extends in a disc-like fashion, so that in the horizontal plane the meatus is boot-shaped with a narrow neck and the sole of the meatal plug spreading widely to form the future tympanic membrane medially. At the same time, the plug in the proximal portion of the neck starts to be resorbed. In the 13-week fetus, the disc-like plug begins to show signs of its final destiny; the innermost surface of the plug in contact with the anlage of the malleus is ready to contribute to the formation of the tympanic membrane. In the 15-week fetus, the innermost portion of the disc-like plug splits, leaving a thin ectodermal cell layer of immature tympanic membrane. The neck of the boot forms the border between the primary and secondary meatus, and is the last part to split. In the 16.5-week fetus, the meatus is fully patent throughout its entire length, although the lumen is still narrow and curved. In the 18-week fetus, the meatus is already fully expanded to its complete form.