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I had to copy and paste the abstract, as this is from Medlink Neurology. You can also type in atlantoaxial dislocation and get this link.

Historical note and nomenclature

Please note the terms ?odontoid process? and ?dens? are synonymous and used interchangeably in this clinical summary.

Clinical manifestations

Antecedent conditions such as trauma, neck or upper airway infection (Grisel syndrome), coughing or weight loss (tuberculosis), congenital syndromes (Morquio, Down, Ehlers-Danlos), or autoimmune and inflammatory diseases (rheumatoid arthritis, systemic lupus erythematosus) should be noted.

Clinical manifestations vary based on the type of atlantoaxial dislocation. The classic findings in rotatory subluxation are neck and suboccipital pain, reduced neck range of motion, and the ?**** robin? head position of torticollis. In the **** robin position, the head is tilted to one side, rotated to the opposite side, and flexed forward (Maile and Slongo 2007). Neurologic signs are rare in rotatory subluxation because the upper cervical spinal canal is capacious and rotation of C1 on C2 does not narrow canal diameter significantly. Many patients with torticollis do not have pathologic C1-C2 rotation or fixation, so the diagnosis of atlantoaxial dislocation cannot be made simply by documenting torticollis (Hicazi et al 2002). Radiologic studies are required. Note that less severe subluxations are more likely to present in a delayed fashion than more severe subluxations (Pang and Li 2005).

Anterior atlantoaxial dislocation due to fracture of the base of the odontoid process or disruption of the transverse ligament also presents with neck pain and reduced range of motion but is more likely to have associated neurologic deficit from spinal cord compression. Bilateral disruption of the C1-C2 articulations allows forward translation of C1 on C2. This can result in spinal cord impingement by the posterior ring of C1. Neurologic deficit may range from mild sensory changes to complete paralysis. These patients may die suddenly as C1 spinal cord injury causes respiratory paralysis. Chronic dislocation and spinal cord compression can present with mechanical neck pain and myelopathic signs (eg, hyperreflexia, proprioceptive loss).

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Basilar impression


Brian H Le

Historical note and nomenclature

Basilar impression, a skeletal malformation involving the relation between the cervical spine and the base of the skull, was first described as a postmortem anatomic entity by anatomists in 1790. The first ante-mortem cases in patients were described in Europe in the early 20th century (Paradis and Sax 1972; Gosain et al 1994). Basilar impression emerged in the American literature in 1939, with the establishment of diagnostic criteria by Chamberlain, who defined a line, to be known as Chamberlain's line, drawn from the dorsal margin of the hard palate to the dorsal tip of the foramen magnum, caudal to which all parts of the atlas and axis should lie (Chamberlain 1939). In 1948, McGregor proposed a modification of Chamberlain's line by defining a line drawn from the upper surface of the posterior edge of the hard palate to the most caudal point of the occipital curve, to be known as McGregor's line (McGregor 1948). Subsequently, McRae in 1953 proposed another landmark below which the odontoid tip should lie. Known as McRaie's line, this is the line drawn from the anterior border to the posterior border of the foramen magnum (McRae 1953). In 1955, Bull and colleagues performed a comparative study of 120 patients, measuring the distance of the odontoid tip above Chamberlain's line and McGregor's line. In addition, the investigators proposed a new parameter to diagnose basilar impression. Referred to as Bull's angle, this is the angle between the plane of the hard palate and the line formed by joining the midpoints of the anterior and posterior arches of the atlas in a lateral radiograph of the skull and cervical spine (Bull et al 1955). This study established general means for these measurements, postulating that exceeding 3 standard deviations in any 1 of these criteria is sufficient to diagnose basilar impression.

Basilar impression can be classified as either primary, in which there is no discernible underlying intrinsic abnormalities of bone, or as secondary due to the effects of bone softening caused by an underlying disease, although there are inherent nuances to such a classification scheme. As the literature on basilar impression evolves, the term ?basilar invagination? has been used and deemed as synonymous in describing this entity. Although the term ?platybasia? has also been used synonymously, it is not currently recognized as such. Rather, platybasia refers to a skull base with an abnormally obtuse angle between the plane of the clivus and the plane of the anterior fossa. It is a finding that carries no particular clinical significance, although it can occur in basilar impression (Bhangoo and Crockard 1999; Pearce 2007). Furthermore, recently accepted diagnostic criteria for basilar impression includes progressive deformity of the occipital bone in a setting of odontoid compression of the neuraxis; as such, odontoid compression of the neuraxis in the region of the foramen magnum without associated occipital bone deformity should be referred to as ?odontoid invagination? (Kyoshima et al 2005).

Clinical manifestations

Basilar impression demonstrates a wide range and spectrum of clinical manifestations. Depending on the degree of impression, or specifically, invagination, clinical manifestation may range from asymptomatic with a normal physical exam to severe symptomatology requiring surgical intervention (Dirheimer and Babin 1971). In familial cases of primary basilar impression, this skeletal anomaly may manifest as a shortened neck accompanied by progressive stiffness and weakness of the extremities (Paradis and Sax 1972). As the contents of the brainstem invaginates into the foramen magnum, patients may show strabismus and nystagmus. Respiratory depression, caused by compression of the brainstem, has also been described (Frank et al 1982; Wang et al 1994). In an 8-patient case series of basilar impression with associated occipitalization of the atlas, major symptoms at onset were nuchal pain (100%), vertigo (85%), hyposthenia (62%), paresthesia (37%), unsteady gait (25%), dysphagia (25%), dysarthria (25%), and diplopia (12%) (Bassi et al 1992). In this series, main neurologic signs included spastic tetraparesis (100%), hypesthesia (75%), sphincteral troubles (50%), and symptoms localized to dysfunction of cranial nerves X (25%), V (12%), and XII (12%). Furthermore, 75% of the patients studied had symptoms that were progressive, whereas 25% had symptoms that were intermittently progressive and remitting (Bassi et al 1992). Disturbances in sexual potency have also been described, and a case series reports a severity spectrum ranging from decrease potency to complete impotence in all patients studied (Caetano de Barros et al 1975).

Multiple structural abnormalities and syndrome constellations have been associated with basilar impression. Bares, in 1975, classified this entity and its associated congenital anomalies into 4 clinicopathologic groups: (1) parenchymal abnormalities with pathogenetic significance, (2) skeletal abnormalities with pathogenetic significance, (3) skeletal abnormalities with dubious pathogenetic significance, and (4) distant anomalies (Bares 1975). As the literature continues to expand, some of these anomaly clusters as well as others have been described. They include syringobulbia/syringomyelia (Hertel et al 1974; Goel and Sharma 2005), cervical arachnoidal cyst (Fiaschi et al 1992), hypoplasia of the paravertebral cervical musculature, the Klippel-Feil syndrome (Paradis and Sax 1972), Chiari malformation (da Silva 1992; Goel and Sharma 2005), tricho-rhino-phalangeal syndrome type I (Fernandez et al 1993), achondroplastic dwarfism (Luyendijk et al 1978), Goldenhar syndrome (Gosain et al 1994), and the SUNCT syndrome (Ter Berg and Goadsby 2001). A case report of basilar impression postulated the incidence as secondary to trauma (Kuroiwa et al 1995), and 1 case caused by tuberculosis manifesting as neck pain with cervical myelopathy (Daniel and Rajshekhar 1999) has been described. Additionally, a case of basilar impression with assimilation of the atlas, manifesting as essential hypertension accompanied by other neurologic symptoms, has been characterized (Dickinson et al 1993). Recently, a case of Paget disease leading to secondary basilar impression was described; in this case, the resultant basilar impression caused obstruction of cerebrospinal fluid through the basilar cisterns, resulting in ventricular enlargement associated with a syndrome resembling normal pressure hydrocephalus (gait disturbance, incontinence, and dementia) (Roohi et al 2005).

The remainder of this Clinical Summary is available to subscribers only. Current subscribers, please log in at the MedLink Home page. If you are not a subscriber, please choose one of the following options:

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