Thursday, June 2, 2011

What Is Eagle Syndrome?

Eagle syndrome (ES) is a clinical condition in which there is abnormal ossification of the stylohyoid apparatus, consisting of the styloid process, the attached stylohyoid ligament, and the lesser cornu of the hyoid bone. Anatomically, the styloid process arises from the temporal bone and passes downwards, forwards, and medially. Embryologically, it is derived from the Reichert's cartilaginous component of the second branchial arch. Ossification of the styloid process and the stylohyoid ligament leads to an increase in the thickness and length of the styloid process, which then presses on the adjacent structures like the internal jugular vein, carotid artery, facial nerve, vagal nerve, glossopharyngeal nerve, and hypoglossal nerve, resulting in various pressure symptoms. The styloid process normally measures 2.5-3 cm in length; when the length exceeds 3 cm, it is said to be elongated.

The cause of this elongation of the styloid process is not well understood. It can be idiopathic, congenital (due to the persistence of cartilaginous elements of precursors of the styloid process), or acquired (due to the proliferation of osseous tissue at the insertion of the stylohyoid ligament). 

The symptoms that patients complain of have varied pathophysiological explanations; for example, symptoms may be due to: 1) fracture of the styloid process leading to granulation tissue proliferation, which results in pressure on surrounding structures; 2) compression of adjacent nerves, eg, the glossopharyngeal, the lower branch of the trigeminal, or the chorda tympani; 3) degenerative and inflammatory changes at the tendinous portion of the stylohyoidinsertion, which is known as insertion tendonitis; 4) irritation of the pharyngeal mucosa due to direct compression, or post-tonsillectomy scarring involving the cranial nerves V, VII, IX, and X; and 5) impingement of the carotid vessels with irritation of the sympathetic nerves in the arterial sheath.

There are two types of ES as described originally by Eagle: first is the classic styloid process syndrome due to fibrous tissue causing distortion of the cranial nerve endings in the tonsillar bed after tonsil removal; and a second type due to compression of the sympathetic chain in the carotid sheath. 

ES can be diagnosed radiologically and by physical examination. The elongated styloid process can be felt in the tonsillar fossa, and palpation can lead to an increase in symptoms. This elongation can be confirmed radiologically using conventional radiographs or CT scan. 3DCT helps in surgical planning and allows the physician to better explain the lesion and the surgical details to patient. It also helps to obtain measurements in three dimensions, along the plane of the styloid process being measured; in contrast there is underestimation of the length of the styloid process with two-dimensional cross-sectional imaging, where even in the coronal plane, the images are usually not parallel to the styloid process.

ES can be treated by surgical and nonsurgical means. Nonsurgical treatments involve reassurance to the patient, analgesics, and steroid injections. Surgical treatment can be performed using one of two approaches: transpharyngeal or extraoral. The latter is thought to be superior because it is less likely to cause deep space infection of the neck.

Figure Bilateral hypertrophied styloid processes as shown with three-dimensional CT scan

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