Elongated styloid process: A study.

The styloid process (SP) on the temporal bone is a highly variable formation. The normal length of the SP ranges from 20 to 30 mm. In spite of its being normally distributed in the population, SPs could be divided into two groups - short SPs with >20 mm and long SPs with <20 mm in length. The SP is often denoted as elongated when it is longer than 30 mm or 33 mm. These dimensions, based on early reports, do not respect the natural variation of the SP. The aim of this study is to investigate the natural variation of the length of the SP.

Styloid process (SP) is derived from the Greek word stylos, meaning a pillar. This structure is a long, cylindrical, cartilaginous bone located on the inferior aspect of temporal bone, posterior to the mastoid apex, anteromedial to the stylomastoid foramen, and lateral to the jugular foramen and carotid canal. Medial to the SP is the internal jugular vein along with cranial nerves VII, IX, X, XI, and XII. The tip of the SP is close to the external carotid artery laterally while medially, it is in close proximity to the internal carotid artery and accompanying sympathetic chain. It forms with the stylohyoid apparatus along with stylohyoid ligament and a small horn of the hyoid bone. Three muscles originate from the SP: The styloglossus, stylohyoid, and stylopharyngeus. The styloid and the stylomandibular ligaments are also attached to the SP.[12]

Background and theory

Eagle's syndrome occurs due to elongation of the SP or calcification of the stylohyoid ligament, which may produce a pain sensation due to the pressure exerted on various structures in the vicinity.

The SP is a cylindrical bony projection arising from the lower surface of the petrous portion of the temporal bone. It lies in front of the stylomastoid foramen and its tip projects anteriorly and inferiorly between internal and external carotid arteries and also laterally to the pharyngeal wall and tonsillar fossa. The SP provides the origin attachments for several muscles such as the styloglossus, stylohyoid and stylopharyngeus muscles and for ligaments such as the stylohyoid and stylomandibular ligaments.[3] Important structures surrounding the SP include facial and hypoglossal nerves, the occipital artery and the posterior belly of the digastric muscle laterally and the lingual, facial, superficial temporal, maxillary, and internal carotid arteries, internal jugular vein and the stylomandibular ligament medially.

The purpose of this study was to evaluate the length of SP in the dry skulls present in the department.

The elongated SP and the ossified stylohyoid ligament can compress the structure in close vicinity, leading to symptoms like sore throat, dysphasia, otalgia, the sensation of a foreign body in the throat, facial pain radiating to the ear or along the mandible, and head and neck mimicking neuralgic pain.[456] A SP is considered to be elongated when it is longer than 30 mm.[78] This anomaly appears in adults with varying frequency, ranging from 2% to 30%.[7]

Materials and Methods

The study has been conducted in 45 dry skulls at the Department of Anatomy, Sree Balaji Dental College and Hospital. All skulls were regular in shape, without obvious evidences of deformities. It was observed in 4 skulls belonging to that, SP was elongated in 1, bilaterally, and 3, unilaterally. These skulls were studied and scrutinized for any other variation. The length of the SP is measured and recorded. And the skulls with the elongated processes were photographed.

Observations

Among the skulls, SP was elongated unilaterally in 3 skulls and bilaterally in 1 skull. It is seen in photographs 1 and 2.

Photograph 1

Unilateral enlargement measurements - 3.1 cm, 3 cm, 2.7 cm respectively.

Photograph 2

Bilateral enlargement measurements - 3.2 cm on left side and 3 cm on right side

Discussion

The SP can be elongated bilaterally or unilaterally, however unilateral elongation of the SP is more frequent.[9] Ossification of the stylohyoid ligament occurs with differing frequency and may be as low as 2–4% or as high as 84.4% but may be asymptomatic.[1011] In the Eagle's syndrome, the elongated SP or ossified stylohyoid ligament is a source of pain.[4512]

“Elongated SP” is a term used since the publication by Eagle[13] in reports concerning findings in both dentomaxillofacial and ear–nose–throat patients.[78141516] This term denotes a SP exceeding its normal length. Eagle's[13] definition was: “The normal SP measures between 2.5 cm and 3 cm.” His method of measurement was not described, but his examples showed lateral radiographs of the skull.

Eagle described the syndrome and stated that the normal SP is approximately 2.75 cm and any SP beyond that may be considered elongated. Eagle divided the syndrome into two categories. He described the classic syndrome as persistent pain in the pharynx, aggravated by swallowing with the pain frequently referred to the ear on the side of the elongated SP. He also noticed increased salivation, hesitancy and difficulty in swallowing, gagging and a foreign body sensation.[13]

In the first group, symptoms are characterized by pain located in the areas of distribution of the fifth, seventh, eighth, ninth and tenth cranial nerves. It is associated in most cases with tonsillectomy that may have been performed many years earlier.[17] Pain following tonsillectomy is presumably created by stretching or compressing the nerve or nerve endings of cranial nerves in the tonsillar fossa either during healing or due to scar formation.[18] The elongated SP can be palpated by inserting a finger orally along the occlusal plane posterior to the region of the tonsillar fossa. Pain is reproduced by palpation of the SP. Confirmation is made with radiographs showing an elongated SP or mineralization of the stylohyoid complex.[19]

The second type, the carotid artery syndrome, usually is not associated with tonsillectomy. The carotid artery syndrome is caused by mechanical irritation of the sympathetic nerve tissue in the walls of the internal and/or external carotid artery by the tip of the SP or the ossified ligament. This irritation produces referred pain in the respective area of vascularization.[815]

Eagle syndrome is most commonly seen after the age of 30 years. There is no significant sex predilection in occurrence of mineralization of the SP; however, symptoms are more common in females.[8] Eagle's syndrome is not frequently suspected in clinical practice. The symptoms in Eagle's syndrome range from mild discomfort to acute neurologic and referred pain. These may include: Pain in the throat, sensation of a foreign body in the pharynx, difficulty in swallowing, otalgia, headache, pain along the distribution of the external and internal carotid arteries, dysphasia, pain on cervical rotation, facial pain, vertigo, and syncope.[1218]

Conclusion

The SP may develop inflammatory changes or impinge on the adjacent arteries, on sensory nerve endings leading to the symptoms. Diagnosis can usually be made on physical examination: By digital palpation of the SP in the tonsillar fossa, which exacerbates the pain. Relief of symptoms with injection of local anesthetic into tonsillar fossa relieving the pain can be used as a diagnostic tool.[19] Over the years, authors have given much pathogenic relevance to the length of SP, as well as to the shape and position in suggesting the etiology of painful syndromes.[11] However, not all elongated SPs are symptomatic, since some SPs of normal length can also lead to the syndrome.[4] Clinicians must be aware of the anatomy of the SP, which may aid them in establishing a clinical diagnosis.