Basilar Invagination

Описание: Dr Himanshu Tyagi, Senior consultant spine surgeon.
Phone : 9654095717
MCh Orthopaedics (U.K), FNB Spine surgery, DNB Orthopaedics.


Basilar invagination is an abnormality at the craniovertebral junction, either congenital or degenerative, resulting in the odontoid prolapsing into the already limited space of the foramen magnum. While frequently seen in rheumatoid arthritis, it more commonly presents in a myriad of congenital conditions (i.e., Chiari malformation, syringomyelia, Klippel-Feil syndrome, and hydrocephalus). Clinical presentations can range from chronic headaches, limited neck motion, and acute neurologic deterioration. This activity outlines the evaluation, management, and reviews upon the latest anatomical basis pertaining to basilar invaginations pathogenesis as well as addresses the paradigm shift pertaining to its surgical management.


As the posterior edge of the foramen magnum could not always be visualized, McGregor described a modification of the Chamberlain line from the posterior portion of the hard palate to the lowest edge of the midline occipital surface. The odontoid may normally be higher than if the Chamberlain line was used. Lastly, the McRae line delineates the foramen magnum from anterior margin to the posterior border, for which the odontoid tip should not cross.
Radiographs remain an important screening tool in the evaluation of basilar invagination. However, the interpretation of radiographs of the cervical spine is frequently challenging, and the surgeon should readily employ additional modalities such as cineradiography, myelography, dynamic computed tomography scans, magnetic resonance imaging, and arteriography. More specifically, MRI is needed for the assessment of soft tissues, including neural components.
Recently, basilar invagination has been divided into group A wherein the odontoid tip will be above the Chamberlain line, McRae line, and Wackenheim’s clival line. On the contrary, group B variant the tip of the odontoid process, anterior arch of the atlas as well as clivus was above Chamberlain’s line in unison but all below McRae’s and Wackenheim’s lines.


Treatment -

Criteria for the treatment of basilar invagination has not been well described, and treatment preoperative the neurological status of the patient. For patients who present with neurologic deficits, surgical intervention may be required to attempt to alleviate symptoms and to prevent the progression of neurologic disturbances. For the few patients without any neurological disturbances, clinical and radiological a preoperative traction for progression of the disease has been described as a reasonable alternative to operative stabilization.
Surgical stabilization may involve a posterior-only decompression and fusion, or an anterior decompression with posterior stabilization. The determination of approach is usually a result of the reducibility of the basilar invagination. Given the importance of reducibility in surgical approach, preoperative traction is a valuable tool in determining the degree of reducibility and assessment of neurological status In a case series of surgically treated patients with basilar invagination performed by Goel et al., 82 patients without any associated Chiari malformation were placed in cervical traction, and 82% of these patients noted rapid clinical improvement after application of traction.
Ultimately, the approach should be made on a case by case basis after a thorough evaluation of clinical findings, plain cervical radiographs, and MRI findings.
A recent study has validated the role of atlanto-axial facetal distraction with fusion posterior only for group A variant, whereas only suboccipital and foramen magnum decompression without need for duroplasty in group B variant, even in the presence of syringomyelia.

While surgery can improve some neurological symptoms, complete recovery is not always possible. Residual neurological deficits are common and in some cases, may be disabling.


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