External auditory canal

Otic preparations are instilled in the external auditory canal and may be used to relieve pain, treat infection and inflammation, and aid in the removal of earwax. When the patient has an inner ear infection, systemic antibiotic therapy is indicated. 

Right cerebral hemisphere External auditory canal Right cranial nerve V... 

Earwax is a normal secretion. The main component, cerumen, is a protective wax-like substance with antifungal and antibacterial properties that traps particles and so helps keep the ears clean. Earwax is formed when cerumen secreted by the sebaceous and apocrine glands in the external auditory canal combines with sebum, exfoliated skin cells, sweat, hair and retained dust. 

The normal external auditory canal has several mechanisms that protect if from infections. The S-shaped anatomy of the external auditory canal provides protection from foreign bodies under normal circumstances. The tragus provides protection anteriorly, and hair from follicles found just inside the meatus prevent airborne debris from entering. 

The external auditory canal skin is normally acidic, with a pH level between 4 and 5. Keratin, which consists of desquamated epithelial cells, is produced by the epithelial (skin) lining of the external ear canal it has an isoelectric point of pH 5. Any increase above this value causes hydration of the keratin layer, increasing susceptibility to pathogenic organisms. Because as most organisms responsible for otitis... 

A baby was born missing its right ear and external auditory canal. At 20 months an MRI scan of the brain showed focal atrophy and encephalomalacia of the right parieto-occipital lobe. His mother had used topical tretinoin (Retin A 0.025%) on her face and a large surface of the back before conception and during the first 2-3 months of pregnancy. His father had used oral isotretinoin before conception. 

The human hearing apparatus is commonly considered in three sections the outer ear, middle, and inner ear. The outer ear consists of the pinna (generally called the ear) and the external auditory canal, which terminates in the tympanic membrane or eardrum. The outer ear collects sound, amplifying some frequencies and attenuating others. The eardrum... 

Otitis externa is inflammation of the external auditory canal. The acute form is usually caused by bacterial infection, but it may also be fungal or viral. The chronic form is eczematous and may be atopic or a contact dermatitis. Dermatitis may become infected and the two types of otitis externa can exist together. 

Acetic acid has antibacterial activity. A 2% spray solution of acetic acid is licensed for the treatment of superficial infections of the external auditory canal in adults and children over the age of 12 years. Use should be discontinued and medical advice sought if symptoms do not improve within 48 hours of starting treatment. 

External ear Anotia Micropinna Small or absent external auditory canals... 

The human external (outer) ear includes the external auditory canal (ear canal) and the surrounding auricle or pinna (fleshy cartilaginous shell-... 

Pseudomonas aeruginosa Man External auditory canal Gal + Man+NeuAc [159]... 

Other reports also support a role for bacterial lectins in natural infections. Sialylated glycoproteins, administered orally, protected colostrum-deprived, newborn calves against lethal doses of enterotoxigenic E. coli K99[158]. In a clinical trial in humans, patients with otitis externa (a painful swelling with secretion from the external auditory canal) caused by P. aeruginosa were treated at the site of infection with a solution of galactose, mannose and AT-acetylneuraminic acid. The results were fully comparable to those obtained with conventional antibiotic treatment [159]. 

In a review of 36 cases, Thompson and colleagues observed that 25 were found in the middle ear, 4 in the external auditory canal, and 2 in the temporal bone (intraosseous). Five involved multiple sites. 

Treatment of superficial infections involving the external auditory canal... 

The ear consists of three parts the external, middle, and inner ear. The external ear consists of the pinna and the external auditory canal that transmits sound to the middle ear. The middle ear has an air-filled cavity that contains auditory ossicles, which are the malleus, incus, and stapes. The auditory ossicles forward the sound to the inner ear where the eardrum is located. Pressure on both sides of the eardrum is equalized by the eustachian tube that connects to the nasopharynx. The eardrum could rupture if pressure becomes unequal. The inner ear also contains a series of canals called the labyrinths that are made up of the vestibule, cochlea, and semicircular canals. The vestibule maintains equilibrium and balance and the cochlea is the principal hearing organ. 

For spinal images the centre should he within the centre of the area under investigation such for the whole spine, midway between the chin and the symphysis pubis, and for the cervical spine midway between the external auditory canal and the head of the humerus. 

Fig. 2.29a,b. Lateral cervical spine. Centre Midway between the external auditory canal and the head of the humerus. Area imaged Full length of the cervical spine, D thoracic vertebrae and the soft tissue structures of the neck, e.g. trachea... 

An 8-year-old girl presented with bilateral moderate conductive hearing loss, bilateral microtia, left external auditory canal stenosis, and right external auditory canal atresia, after prenatal isotretinoin exposure. Co-morbidities included developmental delay, ventricular septal defects, hypotonia, and retinal maldevelopment. The left EAC was sharply upsloping with a 2-mm-diameter meatus. A CT scan showed normal middle and inner ears bilaterally. Serial CT scans over 6 years showed progressive development of a left canal cholesteatoma. 

Fig. 7.6. CT virtual endoscopy of the middle ear generated from a point of view located in the external auditory canal, shows the incus (/), malleus (M), promontory (P) and oval window (OVy)...

Modern endoscopes are based on Hopkin s optic system with variable diameter (minimum 1 mm in diameter), and length and angle variable on the basis of the region to explore. In the majority of cases the endoscopes are based on a rigid system, but in difficult cases, such as a strong curvature of the external auditory canal, the presence of stenosis or fibrotic tissue, the use of flexible endoscopes is preferred despite the lower spatial resolution and image quality. 

Transtympanic endoscopy can be used as a diagnostic tool or as guidance for otosurgical interventions. In the first case the easy access of the external auditory canal allows the visualization of the tympanic membrane, a barrier between the endoscope and the middle ear only the presence of a pathologic or surgical (miringotomy) perforation permits a limited exploration of the tympanic cavity. 

Creating an endoscopic perspective from the external auditory canal to look toward the middle ear, the tympanic cavity can be divided into four regions on the basis of endoscopic and surgical studies retrotympanum (posterior), epitympanum (superior), protympanum (anterior) and ipotympa-num (inferior). 

VE allows visualizing the entire ossicular chain potentially from any point of view. Positioning the virtual endoscope within the external auditory canal, VE displays the long process of incus, the stapes, and the handle of the malleus. Meanwhile, from a point of view located within the ipotympanum VE can easily display the stapes, the lenticular process of incus... 

This chapter deals with formulatirai and preparation of ear drops for application to the external auditory canal as well as those intended for the middle ear. Creams and ointments for the ear are similar to semisolid preparations for cutaneous use. 

The formulation of ear drops, especially the choice of the vehicle, depends on the site of action the external auditory canal or the middle ear. When ear drops get to the middle ear, they may come into contact with the inner ear and so cause ototoxicity. Because of the ototoxicity of active substances, non-aqueous vehicles and many other excipients, special precautions are needed in formulations that should, or may accidentally, come into contact with the middle ear. Preparations intended for the middle ear are aqueous, sterile and preferably iso-osmotic. When non-aqueous vehicles are used in ear drops for the external auditory canal, it depends on the state of the patient s ear drum whether they will reach the middle ear. 

For the treatment of diseases of the external auditory canal and the auricle non-sterile ear drops or semisolid bases are normally used. In the case of ear drops non-aqueous preparations are preferred, due to the possibility of microbial growth in a moist environment caused by aqueous vehicles. Therefore in external otitis non-aqueous vehicles are the... 

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