The Human Ear – Auricle/Pinna

The human ear is an important defining feature of the human face.  It has subtle structures that convey signs of age and sex that are unmistakable, yet not easily defined.

The anatomy of the external ear, also known as the auricle or pinna, is complex and remarkably inaccurately described by most authors.  Although ear anatomy use is approached differently by various disciplines (surgeons, dysmorphologists, anatomists, artists, forensics personnel, hearing aid dispensers, etc.), it is incumbent that identification features and terminology be consistent when describing the ear.

This is a first in a series of presentations on the auricle, and describes the basic anatomy of the auricle.  Future posts will describe its dimensional anatomy.

The anatomy of the auricle in this post follows the standardization of terms provided by the work of an international group of clinicians working in the field of dysmorphology, of which their work on the ear is part of a series of six papers defining the morphology of regions of the human body1.  Their goal is to standardize the terms, but even more so, to reach consensus regarding their definitions.  Descriptions in this post follow their suggestions.


Surface Structures of the Auricle/Pinna

 

The major landmarks of the auricle/pinna are depicted in Figure 1.  The auricle consists of skin (with adnexa), cartilage, and extrinsic and intrinsic muscles.  The auricle is the visible, funnel-like, flap-like part of the hearing mechanism that is fastened to the side of the head at an angle of about 30 degrees.  Its surface is uneven and filled with pits, grooves, and depressions.  It is commonly called, the ear.

Figure 1 – Surface anatomical features of the human auricle. (Adapted from Sullivan, 19962).


Detailed Identification of the Surface Structures of the Auricle

 

Helix

Figure 2. Normal anatomy of the helix: ascending, superior, and descending parts. The helix root area, where the helix arises from the scalp, is shown by the yellow oval.

The helix is the outer rim-like periphery of the ear that extends from the superior insertion of the ear on the scalp (root) to the termination of the cartilage at the earlobe (Figure 2).  The helix can be divided into three approximate parts:  1) the ascending helix, which extends vertically from the root, 2) the superior helix, which begins at the top of the ascending portion and extends horizontally and curves posteriorly to the site of Darwin’s tubercle, and 3) the descending helix (sometimes called posterior), which begins inferior to Darwin’s tubercle and extends to the superior border of the earlobe.  The lower portion of the posterior part is often non-cartilaginous.  The border of the helix usually forms a rolled rim but the helix is highly variable in shape. 


Helix root
– Superior insertion of the auricle to the scalp.

Antihelix

Figure 3. Normal anatomy of the antihelix, shown in the red dotted lines.

The antihelix is a Y-shaped curved cartilaginous ridge arising from the antitragus and separating the concha, triangular fossa, and scapha/scaphoid fossa (Figure 3).  The antihelix represents a folding of the conchal cartilage and it usually has similar prominence to a well-developed helix.  The stem (the part below the bifurcation) of the normal antihelix is gently curved and branches about two thirds of the way along its course to form the broad fold of the superior (posterior) antihelical crus, and the more sharply folded inferior (anterior) crus.  The inferior and superior crura of the antihelix can vary both in volume and degree of folding.

Antihelix, inferior crus

This is the lower cartilaginous ridge arising at the bifurcation of the antihelix that ends beneath the fold of the ascending helix, and separates the concha from the triangular fossa (Figure 3).  The inferior antihelical crus runs in an anterior and slightly superior direction, is usually sharply defined, and appears less variable than its superior counterpart.  A synonym is anterior crus of the antihelix.

Antihelix, superior crus

This is the upper cartilaginous ridge arising at the bifurcation of the antihelix that separates the scapha from the triangular fossa (Figure 3).  The superior crus runs in a superior and slightly anterior direction and is usually less sharply folded than the lower portion and inferior crus.  A synonym is the posterior crus of the antihelix.


Scapha (Scaphoid fossa)

The scaphoid fossa is the groove between the helix and the antihelix.

Triangular Fossa

This is a concavity bounded by the superior and inferior crura of the antihelix and the ascending portion of the helix.

Helix, Crus

The crus of the helix is a continuation of the anteroinferior ascending helix, which extends in a posteroinferior direction into the cavity of the concha above the external auditory meatus (Figures 4 and 8).  The average helix crus extends about one half to two thirds the distance across the concha.  It partially separates the upper portion of the concha (concha cymba) from the lower portion of the concha (concha cavum), as shown in Figure 8. 

Tragus

The tragus is a slightly inferior protrusion of skin-covered cartilage, anterior to the auditory meatus (Figure 5).  The inferoposterior portion of the tragus forms the anterior wall of the intertragal notch.   

Antitragus

The antitragus is a cartilaginous protrusion, smaller and opposite to the tragus.  It lies between the intertragal notch and the origin of the antihelix (Figure 6).  It forms the inferior boundary of the concha and the posterior wall of the intertragal notch.

Figure 4.  Normal anatomy of the helix crus.  The crus of the helix extends about one half to two thirds the distance of the concha.

Figure 5.  The tragus is a cartilaginous flap that partially occludes the opening into the external auditory meatus.

Figure 6.  Normal anatomical position of the antitragus.


Intertragal Notch

The intertragal notch is the space between the tragus and antitragus.  It is the most inferior portion of the concha (Figure 7).

Concha

The concha is a fossa (shallow depression or hollow) bounded by the tragus, intertragal notch, antitragus, antihelix, inferior crus of the antihelix, and root of the helix, into which opens the external auditory meatus.  It is partially bisected by the crus of the helix into the cymba superiorly and cavum inferiorly (Figure 8).

Lobe (Lobule)

The lobule is the inferior extremity of the auricle.  It is soft and fleshy, with no underlying cartilaginous framework.  It is bounded on its posterosuperior border by the end of the descending helix, on the anterosuperior border by the inferior border of the antitragus and anteriorly by the intertragal notch (Figure 9).  The earlobe is highly variable in size and in the degree of attachment to the anteroinferior portion to the face.

Figure 7.  The intertragal notch (Incisure) is formed anteriorly by the tragus and posteriorly by the antitragus.

Figure 8.  The concha is the deepest depression or hollow of the auricle.  It is partially divided into a superior portion (cymba) and an inferior portion (cavum) by the crus of the helix.

Figure 9.  The lobule is the inferior extremity and contains no cartilage.

 

Following posts will describe dimensional characteristics of the auricle.


References

  1. Hunter A, Frias J, Gillessen-Kaesbach G, Hughes H, Jones K, Wilson L.   Elements of morphology: Standard terminology for the ear.  Am J Med Genet Part A 149A:40-60.
  2. Sullivan, RF. Forum: Sullivan and Sullivan, Inc., Garden City, NY. http://www.rcsullivan.com/www/ears.htm – 13.0, 1996.

Personnel who dispense hearing aids often listen to them using some kind of listening device to checke if an aid is functioning, how it sounds, to check for different programmed environmental settings, or for any number of other reasons.  A representative sample of commonly-used devices to listen to hearing aids is shown in Figure 1.  A number of hearing aid listening devices look and operate in a similar manner.

Figure 1. Sample systems used for listening to hearing aids by hearing professionals. (A), (B), and (C) are yokes with arms that go to each ear. The hearing aid is connected to a flexible tube attached to the yoke where the two arms meet. Listening system (D) consists of a hearing aid connected by a tubing length to a personal earmold to the ear of the listener. This generally goes to a single ear.

Differences exist between the systems relative to yoke arm inside diameters (ID) and the diameter of tubing connecting the yoke to the hearing aid as shown in Table I.  The length of the tube connecting the hearing aid to the listening device also varies.  For this study, two lengths were used: 1) 3” (76.2 mm) and 2) 10” (254 mm).  It should be noted that the yoke listening systems have, in fact, a much longer listening tube system because of the added length of the yoke arms.  Tubing IDs were measured using the tubing guide in Figure 2, except for those larger than 2.39 mm, where a caliper was used.

Figure 2. Hearing aid tubing guide. The holes at the top are used to determine the outside diameter (OD) of the tubing based on the size hole the tubing fits. The tips at the bottom are used to determine the inside diameter (ID) of the tubing based on the tip size the tubing fits over without extending the tubing ID.

 

                                      

What Are They Thinking?

Anyone skilled in the art would know that what they hear through such attachments to the hearing aid does not represent the performance of the hearing aid.  It has been known for years that tubing length, internal diameter, wall thickness, and connections affect the hearing aid response.  Still, such listening devices continue to be used daily, by perhaps several thousand hearing professionals.  The question is, what do they think they are listening to?


What Are They Hearing?

To determine what is being delivered through such listening devices, this author decided to conduct a short test.  Three different listening yoke brands and one earmold were connected to a hearing aid (as shown in Figure 1) with different lengths of tubing connecting the yoke or earmold to the hearing aid.  Tubing lengths of 3 and 10 inches were attached to the yokes and earmold using a snap-in B adapter. 

Figure 3. Flat and hi-frequency responses programmed into the same hearing aid on two different settings, as measured in a 2cc coupler.

The hearing aid used was a RIC (receiver-in-canal) programmed to two responses: 1) a relatively flat frequency response, and 2) a high-frequency response (Figure 3).  The hearing aids were attached to the tubing by inserting the speaker outlet tube into the tubing provided by the different devices.  Two yoke devices used grey tubing with an inside diameter (ID) of 2.5 mm, and one used #13 tubing (ID=1.93 mm), as did the earmold connection. 

Connections to the hearing aid by the two units using #13 tubing allowed for a good friction fit with the RIC speaker (without tip) to eliminate sound leakage (Figure 4a).  The larger diameter tube devices required a reduction and sealing process (Figure 4b).  The earmold was sealed into the 2cc coupler with putty (Figure 4c).

Figure 4. Hearing aid speaker connection to listening systems. In (a), the speaker tip friction fits into the #13 tubing without sound leakage. This arrangement was used for the earmold connection and for the listening yoke (C). The larger grey tube used with the other two yoked listening systems (A) and (B) required reduction to match the speaker sound bore nub to the larger diameter listening tube as shown in (b). The earmold was puttied to the 2cc coupler as in (c).


Measurement

Figure 5. Setup in a hearing aid analyzer test box for measurement of listening tube performance. One of the ear tips was sealed to the 2cc coupler, while the other was plugged. The length of the tube connecting the hearing aid to the listening yoke or to an earmold was adjusted to meet the measurement length required for the comparison.

Measurement was made using a Frye Electronics 8000 Hearing Aid Analyzer, with one of the listening yoke’s ear tubes putty-sealed to a 2cc coupler.  The other ear tube was sealed (Figure 5).  For the earmold connection, the earmold was putty-sealed to the 2cc coupler.  (Figure 4c).


Results

Comparisons of measured response results for the 3” and 10” tubing for the flat and high-frequency responses are shown in Figure 6.  The graphs are self-explanatory, and as a result, there is no need to explain each of the graphs separately.  Suffice it to say that none of the measured results as measured through the listening devices evaluated here is close to the 2cc coupler measurements.  This was expected.

Figure 6. Measured responses for a sampling of the different devices commonly used to listen to hearing aids by hearing professionals. Response comparisons for 3” and 10” of tubing for the flat programmed response are shown in blue. Response comparisons for 3” and 10” for the high-frequency programmed response are shown in red. The measured response is in the light gray color.  Yoke and earmold designations are indicated in Figure 1.

Comments

Because none of the listening devices approximates that of the 2cc coupler response, it is unclear how a hearing professional can determine if the hearing aid is functioning properly, aside from it functioning as a dead hearing aid, as  a wildly distorted product, or if it is providing some amplification, regardless of how good.

Based on acoustics, a hearing professional should know that tubing resonances, based on length and diameter of the plumbing, lead to the multiple peaks and valleys recorded.  Harmonics are easily seen.  Realize also that these were smoothed responses shown in Figure 7.  It is too embarrassing to show the unsmoothed (actual) responses.

There is no excuse for a hearing professional to make any judgments about the actual performance of a hearing aid when listening to it through any of the systems shown.  Other similar devices would suffer the same non-usable information.


Recommendations

  1. Measure the hearing aid’s performance using an appropriate hearing aid testing system.
  2. Listen to the hearing aids as does the client. Put them on and listen to them!  It has to be assumed that all dispensers have disinfectant means, and with most of today’s hearing aids, one could also easily replace the tips with a new one or one of their own of similar design.
  3. Do not make judgments about a hearing aid performance by listening to it through listening devices as described in this brief comparison.