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basilar_invagination_diagnosis

Basilar invagination diagnosis

Basilar invagination is diagnosed by various imaging modalities such as plain x rays, CT scans, and MRI.

Measurements used in BI

1. McRae’s line:

Drawn across foramen magnum (tip of clivus (basion) to opisthion) 1). The mean position of the odontoid tip below the line is 5 mm (± 1.8 mm SD) on CT and 4.6 mm (± 2.6 mm SD) on MRI 2).

No part of odontoid should be above this line (the most accurate measure for BI)

2. Chamberlain’s line 3):

Less than 3 mm or half of dens should be above this line, with 6 mm being definitely pathologic. Seldom used because the opisthion is often hard to see on plain film and may also be invaginated. On CT 4) and MRI 5) the normal odontoid tip is 1.4 mm (± 2.4) below the line

3. McGregor’s line:

http://www.ebmconsult.com/content/images/Xrays/McGregor_Line.png

It refers to a line connecting posterior edge of the hard palate to the most caudal point of the occipital curve. If the tip of the dens lies more than 4.5 mm above this line it is indicative of basilar invagination.

4. Wackenheims line

Normally the tip of the dens is ventral and tangential to this line. In basilar invagination odontoid process transects this line.

5. Fischgold’s digastric line

joins the digastric notches.The normal distance from this line to the middle of the atlanto-occipital joint is 10 mm (decreased in BI) 6).

6. Fischgold’s bimastoid line

joins tips of mastoid processes. The odontoid tip averages 2 mm above this line (range: 3 mm below to 10 mm above) and this line should cross the atlanto-occipital joint.

Basilar impression diagnosis in rheumatoid arthritis

Erosion of the tip of the odontoid, commonly seen in rheumatoid arthritis (RA), obviates use of any measurement that is based on the location of the tip of the odontoid 7). For this reason, other measures have been developed, including the Clark station, 8).

Redlund-Johnell criteria, 9) and Ranawat criteria 10). Since even these methods will miss up to 6% of cases of BI in RA, 11), it is recommended that suspicious cases be investigated further (e.g.with CT and/or MRI).

MRI: optimal for demonstrating brainstem impingement, poor for showing bone.

Cervicomedullary angle: the angle between a line drawn through the long axis of the medulla on a sagittal MRI and a line drawn through the cervical spinal cord. The normal CMA is 135 – 170 ° . A CMA < 135 ° correlates with signs of cervicomedullary compression, myelopathy or C2 radiculopathy 12).

CT: primarily done to assess bony anatomy (erosion, fractures…).

CTA should be performed when surgery is contemplated, to show detail of VA anatomy.

Myelography (water soluble) with CT: also good for delineating bony pathology.

References

1)
McRae DL. The Significance of Abnormalities of the Cervical Spine. AJR. 1960; 70:23–46
2) , 5)
Cronin CG, Lohan DG, Mhuircheartigh JN, Meehan CP, Murphy JM, Roche C. MRI evaluation and meas- urement of the normal odontoid peg position. Clin Radiol. 2007; 62:897–903
3)
Chamberlain WE. Basilar Impression (Platybasia); Bizarre Developmental Anomaly of Occipital Bone and Upper Cervical Spine with Striking and Mis- leading Neurologic Manifestations. Yale J Biol Med. 1939; 11:487–496
4)
Cronin CG, Lohan DG, Mhuircheartigh JN, Meehan CP, Murphy J, Roche C. CT evaluation of Chamber- lain's, McGregor's, and McRae's skull-base lines. Clin Radiol. 2009; 64:64–69
6)
Hinck VC, Hopkins CE, Savara BS. Diagnostic Criteria of Basilar Impression. Radiology. 1961; 76
7) , 11)
Riew KD, Hilibrand AS, Palumbo MA, Sethi N, Bohlman HH. Diagnosing basilar invagination in the rheumatoid patient. The reliability of radiographic criteria.J Bone Joint Surg.2001; 83-A:194–200
8)
Clark CR, Goetz DD, Menezes AH. Arthrodesis of the Cervical Spine in Rheumatoid Arthritis. J Bone Joint Surg. 1989; 71A:381–392
9)
Redlund-Johnell I, Pettersson H. Radiographic measurements of the cranio-vertebral region. Designed for evaluation of abnormalities in rheumatoid arthritis. Acta Radiol Diagn (Stockh). 1984; 25:23–28
10)
Ranawat CS, O'Leary P, Pellicci P, et al. Cervical Spine Fusion in Rheumatoid Arthritis. J Bone Joint Surg. 1979; 61A:1003–1010
12)
Bundschuh C, Modic MT, Kearney F, Morris R, Deal C. Rheumatoid arthritis of the cervical spine: sur- face-coil MR imaging. AJR Am J Roentgenol. 1988; 151:181–187
basilar_invagination_diagnosis.txt · Last modified: 2019/01/20 11:46 by administrador