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30 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 50
This photograph shows the sinus tympani as
it lies medial to the facial nerve, separated from
the round window niche by the subiculum.
Medially lies the ampullated end of the posterior canal. The carotid canal is located close to
the basal turn of the cochlea (male, age 69yr).
Figure 51
The protympanum is that portion of the middle
ear space anterior to a coronal plane passing
through the anterior margin of the tympanic
annulus. It leads into the eustachian tube. Note
the hook end of the cochlear duct and the utricular opening into the ampulla of the posterior
canal (female, age 68yr).
THE PINNA
Chapter 2
The Pinna and External Auditory Canal
In vernacular parlance, the term “ear” evokes an image of that bilaterally
symmetric, cartilage-framed, cranial appendage known as the pinna or
auricle. This structure acts to focus and localize sound; otoplasty (surgical
correction of lop ears), if not properly done, can increase the error in the latter function from 4° to 20° (1). The pinna normally rests at an angle of 30° to
the sagittal plane of the head, while the concha lies at an angle of 90° (⫾15°)
to the bony cortex of the mastoid (2). The pinna’s growth parallels overall
body growth until approximately nine years of age; in general, the left ear is
smaller than the right (2). This text is not concerned with auricular congenital deformities and diseases. Suffice it to say that, due to the multi-component
nature of its embryologic development, the pinna manifests a wide variety of
configurations. Despite this variability, there are certain relatively constant
features that can be recognized in the human ear.
The topography of the visualized pinna is determined almost solely by
the contour of its underlying cartilaginous frame. The flange-like pinna has
a convex medial surface which attaches to the head at its medial one-third;
the lateral surface is concave. The major concavity of the lateral aspect of the
pinna is the concha (Fig. 1). Anteriorly, the tragus delimits the concha as it
extends over the orifice of the external auditory canal. Superiorly and posteriorly the concha is bounded by the anthelix and its anterior crus. The inferior extent of the concha is determined by the antitragus, which is separated
from the anthelix posteriorly by the posterior auricular sulcus, and from the
tragus anteriorly by the intertragic incisura. The concha is partitioned at the
crus of the helix into a superior cymba concha and an inferior cavum concha;
the latter depression points to the meatus of the external auditory canal.
Anteroinferiorly, the crus of the helix is separated from the tragus by the
anterior incisure. The helix, with its furled edge, sweeps superiorly and posteriorly from the crus of the helix to end at the lobule; a projection, the
Darwinian or auricular tubercle, occasionally exists at its posterosuperior
aspect. There are two additional depressions of note. As it curves anterosuperiorly, the anthelix bifurcates into two crura, between which lies a
depression known as the triangular fossa. The scaphoid fossa is a trench-like
groove separating the helix from the anthelix. Lop ears lack an anthelix, with
the consequence that the helix assumes an outstanding position; therefore in
a surgical correction an anthelix must be created.
The medial aspect of the pinna is a negative relief model of the lateral
aspect. The scaphoid, conchal, and triangular eminences correspond to the
respective fossae on the lateral surface. Similarly, depressions of the medial
aspect (i.e., the transverse sulcus of the anthelix, the sulcus of the crus of the
31
32 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 1
The right auricle (pinna) of the co-author
(AJG) showing the principal anatomic
features of its lateral surface.
helix, and the fossa of the anthelix) correspond to elevations of the lateral
surface of the pinna and are hidden by the cranial attachment of the pinna.
The framework of the pinna consists of elastic cartilage, the contours of
which determine its topography; the cartilage measures 0.5 to 2mm in thickness (3). It consists of two furled plates of cartilage separated by the terminal incisure. The larger plate supports the major bulk of the pinna; the lesser
underlies the tragus and is connected to the larger by a narrow isthmus.
While the cartilage features much the same topography as the surface of the
pinna, there are additional elements which are obscured by its mantle of skin
and subcutaneous tissue. Anteriorly, from that portion of the helix just superior to the crus, arises the spine of the helix. Inferiorly, the antitragohelicine
fissure separates the tail of the helix (cauda helicis), the posteroinferior terminus of the helix, from the antitragus.
CHAPTER 2: THE PINNA AND EXTERNAL AUDITORY CANAL ■ 33
The pinna is attached to the cranium by its skin, cartilage, and a complex of muscles and ligaments. There are three extrinsic ligaments and three
extrinsic muscles, both sets referred to as superior, anterior, and posterior.
The superior ligament links the superior aspect of the bony external auditory
canal to the spine of the cartilaginous helix, the anterior ligament connects
the zygoma to the helix and the tragus, and the posterior ligament attaches
the eminence of the concha to the mastoid process.
The three extrinsic muscles originate from the galea aponeurotica of
the scalp. The superior auricular muscle inserts upon the eminence of the triangular fossa, the anterior auricular muscle inserts upon the spine of the
helix, and the posterior auricular muscle inserts upon the eminence of the
cavum concha.
The six intrinsic auricular muscles show great individual variability in
their extent of development and are poorly represented in man; four are
found on the lateral surface and two on the medial surface. On the lateral
surface, the helicis major extends from the spine of the helix to attach tangentially to the anterosuperior curve of the helix. The helicis minor hugs the crus
of the helix. The tragicus overlies the tragus, and the antitragicus spans the
antitragohelicine fissure between the tail of the helix and the inferior aspect
of the antitragus. On the medial surface, the transverse auricular muscle
links the eminence of the scaphoid fossa and the cavum concha. The oblique
auricular muscle connects the eminence of the triangular fossa and the cymba
concha.
The skin and subcutaneous tissue reproduce the irregular contours of
the cartilaginous frame; the skin of the medial aspect is only loosely attached,
while on the lateral surface it is snugly secured by subcutaneous areolar tissue. The usual skin adnexal structures are present, including sebaceous and
sudoriferous (sweat) glands, and hair. The sebaceous glands are distributed
both medially and laterally, especially in the regions of the concha and triangular fossa (4). Sudoriferous glands are sparse. A rudimentary type of hair is
in abundance over the entirety of the pinna; in elderly male persons, the hairs
may be long and large, especially over the tragus and antitragus.
The lobule, the inferior appendage of the pinna, is essentially a fibrofatty nodule. While the lobule has no known physiologic function, its adipose tissue serves as a reservoir for autogenous tissue grafts and its convenient anatomical site serves admirably as a tethering base for ornamentation.
THE EXTERNAL AUDITORY CANAL
Normal Anatomy
The external auditory canal is approximately 2.5cm in length and serves as a
channel for sound transmission to the middle ear. It also functions to protect
the middle and inner ears from foreign bodies and fluctuations in environmental temperature (1). Its lateral one-third is bolstered by elastic cartilage
oriented in an upward and backward fashion; its anterior aspect is pierced by
two or three variably present vertical fissures known as the fissures of
Santorini (Fig. 6); these fissures are a potential route for spread of infections
or neoplasms between the external auditory canal and the parotid gland.
The medial two-thirds of the external auditory canal is osseous and is
oriented in a downward and forward direction. Because of the different
angulations of the fibrocartilaginous and bony canal walls, the adult auricle
34 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
must be pulled upward and posteriorly to achieve alignment during
otoscopic examination.
The narrowest portion of the external auditory canal or isthmus is
located just medial to the junction of the bony and fibrocartilaginous canals.
The inferior tympanic recess is a depression in the inferior aspect of the
osseous canal. Because of the angulation of the tympanic membrane, the canal
is approximately 6mm longer anteroinferiorly than posterosuperiorly, thus
creating an acute angle between the tympanic membrane and anteroinferior
Figure 2
This horizontal section demonstrates
the anatomy of the normal osseous
external auditory canal (EAC). The anterior wall of the canal forms an acute
angle with the tympanic membrane.
An excessive convexity of the anterior
wall can impair otoscopic visualization
of the anterior part of the tympanic
membrane. Surgically created dehiscences of the anterior canal wall can
result in herniation of the contents of the
mandibular fossa into the EAC (female,
age 32 yr).
Figure 3
In our collection of temporal bones
there are several examples of pneumatization of the tympanic bone (male, age
70 yr).
CHAPTER 2: THE PINNA AND EXTERNAL AUDITORY CANAL ■ 35
bony canal wall (Fig. 2). Although the condition is unusual, our collection contains several examples of pneumatization of the anterior wall of the external
auditory canal (Fig. 3).
The skin of the osseous canal is much thinner than that of the fibrocartilaginous portion (Fig. 4), measuring about 0.2mm in thickness (3), and is
continuous with the skin of the tympanic membrane. The subcutaneous layer
has no glands or hair follicles. The bony posterior wall of the external auditory
canal, which overlies the mastoid air cells, may be extremely thin (Fig. 4).
The thinness of the skin of the bony external auditory canal has the following clinical implications: (1) it is easily traumatized during manipulations such as removing cerumen, (2) it is easily torn in the course of surgical
procedures such as tympanotomy, and (3) it permits thermal irritation of the
periosteum and consequently the formation of exostoses caused by swimming in cold water.
The skin of the fibrocartilaginous part of the canal averages 0.5 to 1mm
in thickness (3), with an epidermis of four layers (basal, squamous, granular,
and cornified) blanketing a true subcutaneous layer. The lateral one-third of
the fibrocartilaginous canal is replete with hair follicles, but they are less
numerous in the medial part. Both sebaceous and modified apocrine (ceruminous) glands (Figs. 5–7) develop from the outer root sheath of hair follicles; hence their numerical distribution follows a pattern similar to that of
the hair follicles. In addition, the modified apocrine glands are found mainly
on the superior and inferior walls of the canal. Arrector pili muscles are not
found in association with the hair follicles in any portion of the external
auditory canal.
The apocrine glands are the ceruminous glands of the ear canal (Fig. 7).
They are located in the dermis deep to the sebaceous glands and have three
major components (3): (1) a coiled secretory portion, (2) a secretory duct
within the dermis, and (3) a terminal funnel. A myoepithelial cell layer is
associated with the coiled secretory portion.
Main and Lim (5) detected both apocrine and eccrine modes of secretion in these glands. Moreover, they found that these modified apocrine
Figure 4
Surgical enlargement of the external
auditory canal (EAC) (canalplasty) is
necessarily limited by the thinness of
its bony walls, both anteriorly and
posteriorly (female, age 67 yr).
36 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
glands secreted a heterogeneous population of granules as well as secretory
vesicles. The exact nature of their secreted product is unclear. They are
easily differentiated from the parotid glands which consist principally of
serous cells (Fig. 8). The sebaceous glands (Fig. 9) expel the combined products of several acini into the hair follicles via short excretory ducts. These
sebaceous glands manifest the holocrine mode of secretion; they contain
only one type of secretory granule, presumed to consist of squalene and saturated fatty acids (5).
Acute circumscribed external otitis is a bacterial infection of a sebaceous or apocrine gland. It is an extremely painful disorder requiring aggressive antibiotic and pain therapy. Acommon cause is swimming in bacterially
contaminated water.
Figure 5
This schematic drawing illustrates the
adnexae and secretory system of the
skin of the external auditory canal.
Source: Courtesy of Main and Lim (5).
CHAPTER 2: THE PINNA AND EXTERNAL AUDITORY CANAL ■ 37
Chronic external otitis is a low-grade inflammatory disorder of the skin
of the external auditory canal, characterized symptomatically by itching and
weeping and also by being exceptionally recalcitrant to treatment. Fibrous
tissue proliferation in the subepidermal tissue may lead to stenosis requiring
surgical correction.
The ear wax (cerumen) of humans, to a large extent, is the combined
product of the sebaceous (lipid-producing) and apocrine (ceruminous)
Figure 6
This photomicrograph shows the
anterior wall of the fibrocartilaginous
part of the external auditory canal (EAC)
of a 3-mo-old infant. The sebaceous
(lipid-producing) and apocrine (ceruminous) glands are histologically distinct
from the glandular tissue of the adjacent
parotid gland. The fissures of Santorini
in the anterior fibrocartilaginous wall
facilitate the spread of bacterial and neoplastic diseases between the EAC and
the parotid gland. Outlined areas A and
B are shown in higher magnification in
Figures 7 and 8, respectively.
Figure 7
A higher magnification of the outlined
area A in Figure 6 showing the crosssectioned, coiled, secretory portion of
apocrine (ceruminous) glands. These
are modified sweat glands.
38 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 8
A higher magnification of outlined area
B in Figure 6 shows the serous cells of
the parotid gland.
Figure 9
This photomicrograph of the skin of the
fibrocartilaginous part of the external
auditory canal (EAC) demonstrates the
sebaceous glands. These glands, as well
as hair follicles, are most numerous at
the meatus of the canal.
CHAPTER 2: THE PINNA AND EXTERNAL AUDITORY CANAL ■ 39
glands; there is also a variable component of desquamated epithelial cells.
Impacted cerumen is a common cause of conductive hearing loss.
There are genetically and racially determined differences in the physical characteristics of ear wax; Caucasians and blacks tend to secrete a wet,
brown wax, and Orientals a dry, gray wax (6). These differences in appearance and consistency seem to be associated with differences in immunoglobulin and lysozyme content (7). The implications of these differences in
relation to the role of the external auditory canal in immunocompetence are
unknown and possibly irrelevant.
Exostoses
Exostoses are benign bony excrescences of the external auditory canal usually
caused by refrigeration periostitis from swimming in cold water (Fig. 10).
Histologically, they demonstrate a laminated structure (Figs. 11 and 12)
consistent with a periodic growth pattern.
Exostoses remain clinically silent until they become large enough to
impair the egress of epithelial debris and water from the canal, in which case
there may be an associated external otitis and fluctuating hearing loss. They
may also cause a hearing loss by impinging upon the tympanic membrane
and/or manubrium. Symptomatic relief is attained by surgical removal
and skin grafting of the epithelially denuded areas of the bony walls of the
external auditory canal.
Figure 10
This view shows occult (asymptomatic) exostoses of the anterior and
posterior walls of the external auditory
canal (male, age 75 yr).
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