Cervical myelopathy accompanied with hypoplasia of the posterior arch of the atlas: case report.
METHODS
Case reports of 2 patients having cervical myelopathy accompanied with idiopathic hypoplasia of the posterior arch of the atlas.


OBJECTIVE
A standard for the sagittal inside diameter (SID) of the vertebral foramen of the atlas was determined for use in the diagnosis of hypoplasia. From the point of view of short SID, the etiologies of myelopathy in patients with this disease were analyzed.


BACKGROUND
There is no established definition of hypoplasia of the atlantal vertebral foramen. The mechanism underlying the occurrence of this myelopathy in adulthood is unknown.


METHODS
Lateral x-ray views of the cervical vertebrae of 150 Japanese men and 150 Japanese women were investigated, and the standard values of the SID were obtained. The features of myelopathy associated with this disease were analyzed in 2 cases managed at our facility and in the literature.


RESULTS
The mean standard value was 34.4 mm in women and 37.1 mm in men, showing a significant sex difference (P<0.0001). When a case with a value -2 SD below the standard was regarded as having hypoplasia, case 1 (female) showed 25 mm, that is, -3.9 SD, and case 2 (male) showed 30 mm, that is, -2.7 SD. The space available for the spinal cord of the atlas was 8.0 mm in case 1 and 9.5 mm in case 2. Both patients showed atlantoaxial subluxation on images, but atlantodental interval on flexion in cases 1 and 2 was 3.8 and 4.5 mm, respectively, showing the degree to be mild.


CONCLUSIONS
In the presence of congenital hypoplasia of the posterior arch of the atlas, the spinal cord is highly susceptible to injury because congenital spinal canal stenosis is present. Therefore, the presence of even a mild mechanical compressive lesion leads to myelopathy. Acquired mild atlantoaxial subluxation was associated with this hypoplasia, and the association was considered to be the mechanism underlying the occurrence of myelopathy in adulthood.
Musha
Yoshiro
Y
Department of Orthopaedic Surgery, Toho University School of Medicine, Meguro-ku, Tokyo, Japan. yoshiro2006musha@yahoo.co.jp
Mizutani
Kazuhiro
K
D000368:Aged; D000886:Anthropometry; D001268:Atlanto-Axial Joint / Q000002:abnormalities / Q000000981:diagnostic imaging / Q000473:pathology; D001368:Axis, Cervical Vertebra / Q000000981:diagnostic imaging / Q000473:pathology; D001270:Cervical Atlas / Q000002:abnormalities* / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D007564:Japan; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology; D012727:Sex Characteristics; D013115:Spinal Canal / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000473:pathology; D013117:Spinal Cord Compression / Q000000981:diagnostic imaging / Q000209:etiology* / Q000473:pathology*; D013130:Spinal Stenosis / Q000151:congenital / Q000209:etiology* / Q000473:pathology*; D014057:Tomography, X-Ray Computed; D021801:Zygapophyseal Joint / Q000002:abnormalities / Q000473:pathology / Q000503:physiopathology