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
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.
Normal external ear anatomy.
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
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 ...