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Otolaryngology/head and neck surgery is a surgical subspecialty that focuses on the management of a wide range of disorders of the head and neck, from hearing loss or nasal hemorrhage (epistaxis) to endocrine surgery and expert management of acute airway emergencies. This chapter presents an overview of selected disease processes in otolaryngology that are of importance to the general surgeon in training.

Anatomy & Physiology

The external ear consists of two parts, the auricle (projecting from the lateral aspect of the head) and the external auditory canal (EAC) projecting medially to the tympanic membrane. Functioning as resonant amplifiers of sound energy, the concha of the auricle (Figure 15–1) has a resonance frequency of approximately 5 KHz, and the EAC has a resonance frequency of approximately 3.5 KHz. Combined, the external ear amplifies sound by approximately 10–15 dB in the 2–5 KHz range.

The tympanic membrane is positioned in an oblique plane, separating the external auditory canal from the middle ear. It functions in transforming acoustic energy from sound waves to mechanical energy, which is transmitted via the ossicles, malleus, incus, and stapes to the oval window of the cochlea. The mechanics of the middle ear further amplify sound energy using two methods. First, the tympanic membrane is approximately 17 times larger than the footplate of the stapes; second, the ossicles act as a lever, providing a mechanical advantage of 1:1.3 from the tympanic membrane to the oval window. Combined, the result in a 25 to 30 dB gain in amplification.

The temporal bone houses the bony portion of the external auditory canal, the middle, and the inner ear. The otic capsule of the inner ear is the hardest bone in the human body. Other important structures passing through or adjacent to the temporal bone include the carotid artery, the jugular vein, and the facial nerve (seventh cranial nerve). All of these structures are at risk for injury from temporal bone trauma.

The inner ear consists of the cochlea, which is both the auditory and vestibular sense organ. The vestibular system senses both linear acceleration (gravity) and angular acceleration (rotation). The hearing portion of the cochlea is a coiled tube that resembles a snail. The cochlea has separate chambers: The scala vestibule and the scala tympani are filled with perilymph (similar in composition to extracellular fluid), and the scala media is filled with endolymph (similar in composition to intracellular fluid). The endolymph composition is maintained by Na+/K+ ATPase pumps within the stria vascularis found on the lateral walls of the scala media. These different chambers thus have different electrolyte composition, creating an electrical potential between the compartments. The sound energy, once transferred through the ossicles to the oval window of the cochlea, is coupled directly to the perilymph of ...

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