Eagle Syndrome Secondary to Osteoradionecrosis of the Styloid Process

INTRODUCTION

Eagle syndrome, also called stylohyoid syndrome or stylocarotid artery syndrome, is believed to result from the elongation of the styloid process or ossification of the stylohyoid ligament, resulting in irritation of cranial nerves V, VII, IX, and X.1 Symptomatology varies widely and may include dysphagia, odynophagia, otalgia, foreign body sensation, facial pain, trismus, headache, tinnitus, increased salivation, and/or voice changes.1,2 We present a novel case in which Eagle syndrome apparently resulted from radiation-associated osteonecrosis of the styloid process and also review the literature on Eagle syndrome including the history of the disease entity, symptomatology, epidemiology, etiology, diagnosis, and treatment.

CASE REPORT

A 58-year-old male with a medical history significant for pT2N1M0 squamous cell carcinoma of the right tonsil underwent transoral robotic surgery consisting of a right lateral oropharyngectomy with palatal flap and posterior pharyngeal wall–flap reconstruction and a right modified radical neck dissection of level I to level IV lymph nodes in November 2013. He subsequently received intensity-modulated radiation therapy (66 Gy) that was completed in March 2014 after surgical ablation and reconstruction. Fields of radiation covered the tonsillar fossa to the clavicle on the right side, with the styloid process receiving at least 100% of the desired radiation dose. On the left side, the area of the submandibular gland to the clavicle was radiated with care to spare the parotid gland to minimize the risk of subsequent xerostomia.

Five months after completing radiation therapy, the patient presented with right-sided jaw pain, trismus, intermittent right-sided otalgia, dysphagia, and feelings of warmth and redness over his right parotid region. His clinical examination revealed a desiccated area of the lateral pharyngeal wall with what appeared to be exposed bone. Soft tissue neck computed tomography (CT) with contrast revealed a right styloid process that was fragmented distally and abutting against the posterior right oropharynx (Figure). The patient agreed to an intraoral resection of the styloid process. Intraoperatively, a necrotic right styloid process was visualized extruding into the right oropharynx, and a 2-cm segment was resected. Final pathologic diagnosis revealed acute osteomyelitis with no evidence of metastatic disease. During the follow-up 1 month later, the patient denied any further pain, dysphagia, otalgia, or odynophagia.

• Download figure
• Open in new tab
• Download powerpoint

Figure.

Axial computed tomography of the neck with contrast demonstrates the fragmented right styloid process projecting into the oropharynx (arrow).

DISCUSSION

Eagle syndrome was first described by Watt Eagle in 1937 when he reported 2 cases involving elongation of the styloid process resulting in a constellation of symptoms that were distinct from primary glossopharyngeal neuralgia.3 The styloid process—a columnar-shaped, bony projection from the petrous portion of the temporal bone—is situated anterior to the stylomastoid foramen, lateral to the pharyngeal wall, and between the internal and external carotid arteries.4 It derives from the Reichert cartilage, part of the second brachial arch. The stylohyoid ligament connects the styloid process to the lesser cornu of the hyoid bone. Eagle syndrome is anatomically characterized by elongation of the styloid process or calcification of the stylohyoid ligament, resulting in a wide range of clinical symptoms.

In a subsequent publication in 1949, Eagle defined 2 syndromes related to the styloid process: the classic syndrome and the styloid process-carotid artery syndrome.5 The classic syndrome is more common and often associated with a tonsillectomy. The predominant symptoms are pain/soreness in the throat, a foreign-body sensation, and otalgia that can be attributed to the postoperative healing process that indirectly encompasses cranial nerves V, VII, IX, and X.5 The styloid process-carotid artery syndrome results from an elongated, angulated, or displaced styloid process impinging on the internal or external carotid artery.5,6 This impingement can decrease blood flow and/or cause carotidynia, resulting in symptoms of headache and facial pain, depending on where the impingement occurs. If the impingement occurs on the internal carotid artery, parietal headaches throughout the distribution of the ophthalmic artery are likely. Alternatively, if the impingement is on the external carotid artery, facial pain below the level of the eye is common.5

Eagle syndrome is thought to be an uncommon occurrence; however, the reported incidence of an elongated styloid process varies. Eagle reported a clinical incidence of 4%, while Kaufman found an incidence of 28% radiographically.5,7 While the incidence of an elongated styloid process in the general population is controversial, only 4%-10% of patients with this anatomic variation report symptoms.5,6,8 Additionally, Eagle syndrome has been diagnosed in patients with a normal-length styloid process. In this situation, the pathology is attributed to inflammatory and degenerative changes in the area, specifically insertion tendonitis.9

A normal styloid process is 2.5-3.0 cm and never palpable.1,5,10 When the styloid process becomes longer than 3 cm, it is considered elongated and is at increased risk for causing symptoms.1,6 Typically, the styloid processes are elongated bilaterally, but patients tend to experience unilateral symptoms.11 Eagle syndrome is more common in patients >30 years and has a female preponderance.2,5,12

While length of the styloid process is paramount in the discussion of Eagle syndrome, discussing the orientation of this structure in space is also important.1 The styloid process is in an important region of the neck, as it is surrounded by the external carotid artery, the internal carotid artery containing the sympathetic chain, the occipital artery, the internal jugular vein, the accessory nerve, the hypoglossal nerve, the vagus nerve, and the glossopharyngeal nerve.2 Any deviation of the styloid process can interfere with this important anatomy and cause symptoms of Eagle syndrome. In a retrospective controlled study in which all subjects had an elongated styloid process (>30 mm), Okur et al found a significant difference in medial angulation measurement on 3-dimensional (3D) CT of the styloid process in symptomatic vs asymptomatic patients.6 Furthermore, Yavuz et al reported a significant difference in anterior angulation measurement on plain radiographs in a retrospective controlled study.4

The proposed etiologies of Eagle syndrome are diverse. One explanation is regressive ontogenic development in which mesenchymal elements in Reichert cartilage provoke ossification of the stylohyoid complex. A related theory involves reactive metaplasia causing ossification, presumably after trauma. Additionally, variations of the stylohyoid complex are suggested to result from developmental anomalies of aging, congenital dysmorphism, reactive hyperplasia following surgery or chronic irritation, rheumatologic-related processes, and genetic makeup of an autosomal recessive trait with low penetrance and expressivity.10 Last, the dysendocrine theory proposes that ossification results from hormone disruption in postmenopausal women.1,10 This theory is interesting because Eagle syndrome has a female preponderance.

Based on our review of the English language literature, we believe that our case is the first reported case of Eagle syndrome apparently resulting from osteoradionecrosis of the styloid process. Osteoradionecrosis, one of the severe complications of radiotherapy, results from hypovascular-hypoxic-hypocellular conditions that cause breakdown of tissue that leads to bone exposure. Additionally, any inflammation or trauma to the area further increases the energy/oxygen needs of the local tissues, compounding the risk of osteoradionecrosis.13 The possibility of osteoradionecrosis development is dose-dependent and highest at a dose of >60 Gy.14 While intensity-modulated radiation therapy has many benefits compared to traditional radiation therapy, how this treatment affects the chance of developing osteoradionecrosis is not clear.14 Therefore, it seems reasonably important to consider the development of osteoradionecrosis of the styloid process causing Eagle syndrome following radiation treatments of the head and neck.

Huang et al propose 3 important components for diagnosing skull base osteoradionecrosis.13 First, considering symptoms in relation to the location of the necrotic bone is important. This point is especially relevant to the presented case, as the osteoradionecrosis of the styloid process appears to have caused Eagle syndrome. Second, radiologic evaluation with CT or magnetic resonance imaging is valuable. Third, endoscopic visualization (if possible) is helpful in determining the diagnosis. Huang et al concluded that surgical resection is the best treatment for osteoradionecrosis at the skull base, and thus, the diagnosis can be definitively confirmed by pathologic evaluation.13

Eagle syndrome is typically diagnosed in a standard fashion including symptom evaluation, palpation of the styloid process in the tonsillar fossa, radiologic interpretation, and possibly, a lidocaine infiltration test.12 Palpation of the styloid process in the tonsillar fossa may reproduce or intensify symptoms for the patient.1 Ability to palpate the styloid process depends on the height of the patient, the length and thickness of the patient's neck, the position of the styloid process in terms of angulation, and the provider's experience in palpating the tonsillar fossa.2 The protrusion of the styloid process into the tonsillar fossa can be classified into 3 grades: grade I in the upper pole, grade II in the middle pole, and grade III in the lower pole of the tonsillar fossa. Grades II and III are the most common classifications for location of the styloid process within the tonsillar fossa.12

In addition to a thorough history and physical examination, radiologic evaluation is valuable in the diagnosis of Eagle syndrome. Traditionally, plain radiographs have been used to view the styloid process, particularly using an orthopantomogram. However, these films are limited by the appearance of superimposed structures and magnification.1 In fact, Monsour et al reported a magnification of 1.37× inherent in orthopantomography.15 Thus, 3D-CT is the gold standard for diagnosis of Eagle syndrome because it is more accurate in determining the length and angulation of the styloid process.16 In a 2014 article, Kamal et al further support 3D-CT as the best imaging modality to diagnose Eagle syndrome.17 They state that the images allow visualization of the detailed anatomy of the area that can help the clinician deduce the exact etiology and plan a surgical approach.

While quantifying the length and angulation of the styloid process is important, Kent et al suggest that the proximity of the styloid process to the tonsillar fossa is a more appropriate diagnostic component.8 In their 2015 study, they used 3D-CT imaging to measure the distance from the tip of the styloid process to the mucosal-air interface of the ipsilateral palatine tonsil and showed that the styloid process was significantly closer to the tonsillar fossa in the symptomatic group compared to the control group. This finding supports a hypothesis of glossopharyngeal nerve irritation causing the symptoms of Eagle syndrome, as the nerve runs deep in the tonsillar fossa.

A lidocaine infiltration test can establish the diagnosis of Eagle syndrome. This test involves injection of 1 mL of 2% lidocaine into the tonsillar fossa in an awake patient. If the patient's symptoms diminish or disappear within 5 minutes of injection, the test is considered positive and supports the diagnosis of Eagle syndrome.12

Most cases of Eagle syndrome can be successfully treated with surgical resection of the styloid process. However, conservative management should be attempted first, as surgery puts the valuable structures surrounding the styloid process at risk. Pharmacologic treatment options include antiinflammatories, anticonvulsants, and antidepressants. Additionally, repeated corticosteroid/anesthetic injections can be performed in the office setting.18,19

When conservative options fail, surgery is the treatment of choice. Two approaches are typically considered for resection of the styloid process: the intraoral approach and the extraoral approach. The intraoral approach is simpler, has a shorter operative time, and does not leave a visible scar; however, the surgical exposure is wider, putting critical nerves and blood vessels at risk. The intraoral method also has the potential to lead to a deep neck space infection.1,19 To prevent infection, prophylactic antibiotics are recommended whenever the pharynx is incised.2 Alternatively, the extraoral approach involving a cervical incision provides good visualization and a reduced risk of infection; however, more surgical time is required, recovery is longer, and scarring may be a cosmetic concern.1,19 In 2015, Kiralj et al proposed that the length of the styloid process or the calcified ligament should determine the surgical approach.19 In the presence of ossification of the stylohyoid complex or a styloid process extending to the hyoid bone, the extraoral approach is safer. However, if the styloid process is shorter or not ossified, the intraoral approach should suffice.

CONCLUSION

Eagle syndrome is a rare entity with vague symptomatology and ambiguous incidence and etiology, yet the approach to diagnosis and treatment is well defined. To our knowledge, our case is the first reported case of Eagle syndrome apparently resulting from osteoradionecrosis of the styloid process; however, we believe it is probably not the only case following head and neck radiation therapy. Although the incidence of Eagle syndrome is low, this disorder is an important consideration for patients presenting with vague complaints following radiation to the head and neck, and if the condition is diagnosed, it can be treated successfully.