Styloid Process Injection for Eagle Syndrome

Indications and Clinical Considerations

Eagle syndrome (also known as stylohyoid syndrome ) is caused by pressure on the internal carotid artery and surrounding structures, including branches of the glossopharyngeal nerve, by an abnormally elongated styloid process or a calcified stylohyoid ligament ( Fig. 11.1 ). The pain of Eagle syndrome is sharp and stabbing and occurs with movement of the mandible or with turning of the neck. The pain starts below the angle of the mandible and radiates into the tonsillar fossa, the temporomandibular joint, and the base of the tongue ( Fig. 11.2 ). A trigger point may be present in the tonsillar fossa. Injection of the attachment of the stylohyoid ligament to the styloid process with local anesthetic and corticosteroid serves as both a diagnostic and a therapeutic maneuver. Rarely, the elongated styloid process or calcified stylohyoid ligament may actually cause vascular occlusion ( Fig. 11.3 ).

Clinically Relevant Anatomy

The styloid process extends in a caudal and ventral direction from the temporal bone from its origin just below the auditory meatus. The stylohyoid ligament’s cephalad attachment is to the styloid process; its caudal attachment is to the hyoid bone. In Eagle syndrome, the styloid process is abnormally elongated, either alone or in combination with calcification of the stylohyoid ligament. The elongated process or calcified ligament impinges on the internal carotid artery and branches of the glossopharyngeal nerve ( Fig. 11.4 ). The glossopharyngeal nerve exits from the jugular foramen in proximity to the vagus and accessory nerves and the internal jugular vein and passes just inferior to the styloid process ( Fig. 11.4 ). All 3 nerves lie in the groove between the internal jugular vein and the internal carotid artery.

The key landmark for injection when treating Eagle syndrome is the styloid process of the temporal bone. This osseous process represents the calcification of the cephalad end of the stylohyoid ligament. Although the styloid process is usually easy to identify, if ossification is limited, it may be difficult to locate with the exploring needle.