Partial Aplasia of the Posterior Arch of the Atlas with an Isolated Posterior Arch Remnant: Findings in Three Cases
Aseem Sharmaa,
Shailesh B. Gaikwad
,a,
Parminder S. Deola,
Nalin K. Mishraa and
Shashank S. Kalea
a From the Departments of Neuroradiology (A.S., S.B.G., P.S.D., N.K.M.) and Neurosurgery (S.S.K.), Neurosciences Centre, All India Institute of Medical Sciences, New Delhi, India.
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FIG 1. 32-year-old woman with intermittent weakness and numbness of all four limbs.
A and B, Lateral radiographs of cervical spine taken in flexion (A) and extension (B) reveal partial aplasia of the posterior arch of the atlas with an isolated posterior bony fragment. Note the anterior displacement of the bony fragment during extension (B).
C, Midsagittal T1-weighted MR image through the cervical spine shows no compression of the cord by the posterior bony fragment (arrow).
D, Corresponding T2-weighted image shows a small, localized region of hyperintensity within the cord (arrow). Note that the signal alteration is seen slightly inferior to the anteroinferior margin of the isolated posterior arch remnant. A superimposed canal stenosis was noted from C2 through C5.
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FIG 2. 35-year-old woman with neck pain and paresthesias in both upper limbs.
A and B, In varying degrees of extension, plain radiographs show partial aplasia of the posterior arch of the atlas, with an isolated posterior tubercle. No obvious anterior displacement of the posterior tubercle is observed during extension.
C, Midsagittal T1-weighted MR image reveals no cord compression.
D, Corresponding T2-weighted image shows small, focal intramedullary hyperintensity (arrow) located just below the level of the posterior tubercle. In addition, there is focal canal stenosis at the C2–C3 disk level.
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FIG 3. 30-year-old man with neck pain and occasional upper limb paresthesias.
A and B, Flexion (A) and extension (B) plain radiographs of the cervical spine show partial aplasia of the posterior arch of the atlas with an isolated posterior arch remnant. The isolated posterior fragment moves anteriorly into the spinal canal during extension (B).
C and D, Midsagittal T1-weighted (C) and T2-weighted (D) MR images reveal no compression or signal alteration of the spinal cord. Significant canal stenosis from C3 to C7 is present along with a superimposed disk bulge/protrusion at C5–C6.
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