Unilateral occipital condylar dysplasia: 3‐dimensional multidetector computed tomography and magnetic resonance findings

Abstract

Occipital condylar dysplasia is a rare congenital anomaly that is caused by failure to form lateral elements of the 4 occipital sclerotome from the 4 week of gestation (Tubbs et al. 2013). This flattened and underdeveloped condyle occurs as an isolated anomaly or as part of complex Atlanto-occipital abnormality (Shapiro and Robinson 1976). Although its clinical manifestations are headache, stiff neck, torticollis, ataxia, and neurological signs associated with cervicomedullary compression, this congenital anomaly is difficult to be recognized, due to late onset of symptoms that usually occurs no sooner than the second decades (Kruyff 1965; Shapiro and Robinson 1976). Therefore, imaging examination is mandatory for its diagnosis. A 6-year-old girl underwent brain magnetic resonance imaging (MRI) to evaluate a recent episode of lateral deviation of the left eyeball. Contrast-enhanced brain MR images showed displaced medulla oblongata and upper cervical cord by a bony protrusion into the foramen magnum (Fig. 1a,b). Multidetector computed tomography (CT) with three-dimensional reconstruction revealed that the left occipital condyle is asymmetrically small as compared with the right one, so the craniovertebral junction (CVJ) was tilted with the SchmidtFisher angle of 130° which is no more than 125° in normal CVJ. The bony protrusion on MR was the medial part of the left occipital condyle, which was due to the pressure by atlas, leading to displaced medulla, tilting of atlas and axis, and atlanto-axial subluxation (Fig. 1c–e). Due to the tilting atlas, the course of the left vertebral artery and the canal for the left hypoglossal nerve were aberrant and elongated, as compared with the normal contralateral ones (Fig. 1f). Considering the lateral displacement of brainstem and cervical cord, we are planning an operation to decompress the deformity in order to prevent cord compression and attain stability of CVJ. Craniovertebral junction is comprised of occiput, atlas, axis, and supporting ligaments (Smoker 1994). Anatomically, this articulation surrounds the cervicomedullary junction, including medulla oblongata, spinal cord, and lower cranial nerves (Smoker 1994; Tubbs et al. 2013). Functionally, CVJ keeps movement of the head on the neck and the stability of the vertebrae, thus protecting the spinal cord (David et al. 1998). As a part of CVJ, occipital condyles articulate with the superior faces of the atlas to form the atlanto-occipital joints that contribute to the flexion and extension of the head and neck (Tubbs et al. 2013). Thus, occipital condylar hypoplasia can lead to instability of CVJ and compression of the cervicomedullary junction as well as adjacent vascular structures, resulting in various neurological disorders such as ataxia, spastic quadriparesis and lower cranial nerve palsies (Kruyff 1965). However, symptoms usually begin insidiously and generally occur near adolescence when the axial growth is accelerated (Ryken & Menezes, 1993). In our case, the symptom that made the patient visit the hospital was lateral deviation of the left eye. In addition, she had developmental delay, dysarthria, and left leg disturbance for a while without being evaluated. However, we could not identify any relations between these symptoms and the cervicomedullary displacement due to occipital condylar anomaly. Physical examination revealed torticollis that was so subtle that her parents did not even notice it before. We concluded that the left occipital condylar dysplasia in this case was an incidental finding not associated with the seizure, developmental delay, dysarthria, and shuffled leg of the patient. Since Kruyff first introduced plain radiographs of occipital dysplasia in 1965, CT is considered as the best modality to evaluate the articulations of CVJ and to investigate occipital condylar hypoplasia (Kruyff 1965; Ilkko et al. 1998). Currently, with the widespread availability of multidetector CT, we can obtain state-of-the art 3D images of CVJ, as shown in this case. In addition, MR can reveal detailed features of brainstem, spinal cord, lower cranial nerves, and ligaments in multiple orthogonal planes. In conclusion, occipital condylar dysplasia is a rare congenital anomaly that can occur in CVJ as an isolated anomaly or as part of a syndrome. Since its symptoms are diverse with late manifestation, physicians should be aware of imaging features of congenital abnormalities in CVJ. 3D CT and MR features can demonstrate detailed articulation in CVJ. A visualization of neurovascular structures surrounding CVJ is essential for surgical planning.