Eagle syndrome, which is also known as stylohyoid syndrome, is caused by compression of various structures of the neck, including the internal carotid artery, the internal jugular vein, branches of the glossopharyngeal nerve, and their surrounding anatomic structures. Eagle syndrome is caused by an abnormally elongated styloid process or a calcified stylohyoid ligament (Figs. 15.1 and 15.2). Named after Watt Weems Eagle, an American otolaryngologist who described the syndrome in 1937, Eagle syndrome is characterized by a constellation of symptoms, which include a sharp stabbing pain that occurs with turning of the neck or mandible. The pain starts below the angle of the mandible and radiates into the tonsillar fossa, temporomandibular joint, and the base of the tongue. A trigger point may be present in the tonsillar fossa in a manner analogous to glossopharyngeal neuralgia. Patients suffering from Eagle syndrome may also complain of otalgia, dysphagia, and tinnitus. Eagle syndrome is a syndrome of the third to fifth decade although the syndrome can occur at any age. Eagle syndrome is slightly more common in females. The ultrasound-guided injection technique for Eagle syndrome serves as both a diagnostic and therapeutic maneuver. Ultimately, surgical resection of the elongated styloid process and/or calcified stylohyoid ligament may be required to cure the syndrome.

The word styloid is derived from the Greek word for pillar, stylos. The temporal styloid process extends from the temporal bone in a caudad and ventral direction and serves as the cephalad attachment of the stylohyoid ligament (see Figs. 15.1 and 15.2). The ligament attaches caudally to the hyoid bone. Patients suffering from Eagle syndrome have either an abnormally elongated styloid process or a calcified stylohyoid ligament, which in certain positions of the head and neck has the potential to compress the internal carotid artery, the internal jugular vein, branches of the glossopharyngeal nerve, and surrounding structures (Figs. 15.3 and 15.4). The glossopharyngeal nerve exits from the jugular foramen in proximity to the vagus and accessory nerve and the internal jugular vein and passes just inferior to the styloid process (see Fig. 15.1). All three nerves lie in the groove between the internal jugular vein and internal carotid artery. When treating Eagle syndrome with the ultrasoundguided injection technique described below, the key anatomic landmark is the styloid process of the temporal bone.

To perform ultrasound-guided injection technique for Eagle syndrome, place the patient in supine position with the head turned away from the side to be blocked. An imaginary line is drawn from the mastoid process to the angle of the mandible (see Fig. 15.1). In most patients, the styloid process lies just above the midpoint of this line. After preliminary identification of the approximate location of the styloid process, the skin is prepped with antiseptic solution, and 5 mL of local anesthetic is drawn up in a 10-mL sterile syringe, with 40 to 80 mg of depot steroid added if the condition being treated is thought to have an inflammatory component. A linear ultrasound transducer is then placed over the previously identified approximate location of the styloid process in the transverse plane (Fig. 15.5).