PMC5386156_01
Lateral cervical spine radiograph showing radiodense bony mass (asterisk) located at the posterior part of C1.
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F1
 Lateral cervical spine radiograph showed radiodense bony mass at the posterior part of the atlas (Fig. 1).
Preoperative three-dimensional cervical computed tomography scan showing bony lesion (arrowheads) on the right side of the C1 (A) and the bony lesion (arrowhead) protruded into the spinal canal (B).
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F2
C1 level was 18 mm within the normal range. Computed tomography (CT) scan showed a bony lesion on the right side of the C1 lamina which moderately protruded into the spinal canal (Fig. 2A, B).
Preoperative axial (A) and sagittal (B) T2-weighted magnetic resonance image showing cord compression and intramedullary signal change at the level of the C1.
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F3
T2-weighted magnetic resonance imaging (MRI) was observed (Fig. 3A, B). The intramedullary signal change occurred at a site distant from the bony lesion. 
Axial dynamic myelo-computed tomography scan showing an ovoid, radiodense, sharply-marginated bony lesion (asterisk) located at the right dorsal side with neutral position (A), moving to the dorsal side and compressing the spinal cord with right rotation of the neck (B). No compression of the spinal cord with left rotation of the neck (C).
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F4
Myelo-CT scan revealed that the ovoid bony lesion located at the right dorsal side of the spinal cord in the neutral position (Fig. 4A), which moved to the dorsal side caused compression of the spinal cord from behind when the neck was rotated to the right (Fig. 4B). Compression of the spinal cord decreased when the neck was rotated to the left (Fig. 4C).
Photomicrographs of hematoxylin and eosin staining showing surgical specimen composed of mature, uniform dense, compact, cortical-like, lamellar bone. Original magnification x40.
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F5
The histopathological study revealed the lesion was composed of mature, dense, compact, cortical-like, lamellar bone, and a diagnosis of osteoma was made (Fig. 5).
Postoperative three-dimensional cervical computed tomography scan revealing removal of the bony lesion (A) and no bony lesion protruded into the spinal canal (B).
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F6
Postoperative CT scan (Fig. 6A, B) and MRI (Fig. 7A, B) documented total removal of the bony lesion.