Unilateral atlantal lateral mass hypertrophy associated with atlanto-occipital fusion

Abstract

Purpose: Unilateral hypertrophy of the lateral mass of the atlas is an extremely rare condition. The authors present a rare type of unilateral atlantal mass hypertrophy with atlanto-occipital fusion which is associated with an invaginated lateral mass of the atlas and the odontoid process into the foramen magnum.

Methods: A 45-year-old woman presented with a 2-year history of progressive bilateral weakness in the upper and lower extremities and gait disturbance. The left lateral mass of the atlas was hypertrophied and had invaginated into the foramen magnum with the odontoid. The spinal cord was severely compressed at the level of the foramen magnum, surrounded by the lateral mass of the atlas, the odontoid process and the occipital bone.

Results: First, ventral decompression was performed using a transmandibular approach. The anterior arch of the atlas, the medial side of the hypertrophied lateral mass and the odontoid process were resected. Two weeks after primary surgery, posterior occipitocervical fusion was performed. The postoperative course of the patient was uneventful. Three years after the operation, she could walk without assistance and her paresthesia improved.

Conclusions: To our knowledge, such a case of unilateral atlantal mass hypertrophy associated with atlanto-occipital fusion has not been described previously. The authors discuss the pathology of this case and review the literature on unilateral atlantal mass hypertrophy and associated anomalies of the upper cervical spine.

Fig. 1

a This 3D-CT image shows an anterior view of the cervical spine. The atlas was rotated and its left lateral mass had prolapsed into the foramen magnum. b, c Sagittal and coronal 3D-CT images show invagination of the left hypertrophied lateral mass of the atlas (white arrow) and the odontoid process. The left lateral mass of the atlas fuses with the occiput (dotted arrow). d An axial CT myelograph at the level of the foramen magnum. Spinal cord (dotted circle), the lateral mass of the atlas (LM), odontoid process (white arrow)

Fig. 2

This preoperative T2-weighted magnetic resonance imaging scan of the cervical spine shows severe compression of the spinal cord at the CVJ by the hypertrophied lateral mass of the atlas (white arrow)

Fig. 3

a 3D-CT image after anterior decompression surgery. b Sagittal CT image. The anterior arch of the atlas and the medial side of its left hypertrophied lateral mass and the odontoid process were removed

Fig. 4

Plain X-ray after occipitocervical fusion. The divided mandible was fixed with a plate and screws