During the years 1930s, Amelita Galli-Curci was probably the most famous soprano in the world. Unfortunately, a fairly large goiter was diagnosed, and she underwent a thyroidectomy under local anesthesia, with careful identification and preservation of both recurrent laryngeal nerves. However, her voice became permanently hoarse due to damage to the superior laryngeal nerve, and she could sing no more. Since that time, the external branch of the superior laryngeal nerve (EBSLN) has been known as “the nerve of Amelita Galli-Curci.”

The EBSLN is the only motor supply to the cricothyroid muscle (CTM). This muscle causes an elevation of the cricoid cartilage, shortening the distance with the thyroid cartilage, thus increasing the length and tension of the vocal fold. This increased tension is crucial for the emission of high-frequency sounds, especially among females and professional voice users.

The injury of the EBSLN causes a complete paralysis of the CTM, evidenced by a so-called electrical silence at electromyography (EMG). Functionally, the fundamental frequency of the voice is lowered and voice performance is markedly worsened, especially when producing high-frequency sounds. The impact of this paralysis can be devastating.

The EBSLN may be injured during a thyroidectomy, due to its close anatomic relationship with the superior pole and thyroid vessels. Generally, the nerve crosses the superior thyroid artery and vein well superior to the superior border of the superior pole. However, sometimes it is dangerously close to the superior pole or, in some instances, is even caudal to it.

In 1992, I proposed the following surgical anatomical classification of the EBSLN, based on the relationships between the nerve, the superior thyroid vessels, and the superior border of the superior pole of the thyroid (Fig. 20.1):

Clearly, type 2b has the highest risk of damage during thyroidectomy. Using cadaver dissection studies, I found that 20% of the EBSLN were of this type. In the clinical setting, I have observed 14% type 2b nerves in a series of normally sized or slightly enlarged thyroid glands. Conversely, type 1 nerves were the most common anatomic presentation (60% in cadaver anatomical series and 68% in our clinical series).

The anatomic classification proposed by me in several recent papers has been widely accepted. Some authors have reported similar proportions of the high-risk type 2b EBSLN as in my original results.

Some individual biometric features can be related to an increased incidence of type 2b EBSLN. Furlan et al. conducted an anatomic study on 36 fresh cadavers. Type 2b nerves were statistically more prevalent among individuals with shorter stature (P = 0.0006) and with increased volume of the gland (P = 0.0007).