48 Unilateral Atlantal Facetal Hypertrophy
Several bony and soft tissue anomalies have been associated with anomalies in the craniovertebral region. In this chapter, we present a report of an unusual pathology of the atlas vertebra that involved unilateral facetal hyper-trophy. We had reported a series of four such cases that presented with progressive symptoms of cord compression and torticollis1 and recently treated an additional fifth case.2 Additionally, we recently identified another case of atlantal facetal hypertrophy that appeared to be secondary to osseous changes related to acromegaly.3 Because the pathology is rare, the exact treatment protocol is not clear.
Hypertrophy of the facets of the lumbar and the dorsal spine has been reported frequently.4–7 Less commonly, hypertrophy of the facets of the subaxial cervical spine has been identified. Facetal hypertrophy is generally associated with spondylotic changes. Such hypertrophy usually results in spinal canal stenosis and related symptoms. Although isolated hypertrophy of a single facet has been reported,6,7 the hypertrophy is usually generalized or involves multiple spinal segments.
Unilateral hypertrophy of the facet of the atlas vertebra is extremely rare. The exact cause of the anomaly remains unclear. In none of our five cases was there a defined syndrome complex suggestive of a hereditary or genetic disorder. All of our patients had presented with long-standing torticollis and progressive symptoms of cord compression. The clinical progression of the symptoms is suggestive of either a congenital abnormality or a slow-growing pathology. The remarkable similarity of the symptoms and of the pathology in all our cases suggests a unique congenital abnormality. The presence of associated fusion of the C2–C3 vertebrae in one case also points toward a congenital anomaly complex. Investigations revealed hypertrophic abnormality of no other bone or its component. The maximum transverse dimension of the facet of the atlas ranged from 2.8 to 4.9 cm in size. In two cases, there was associated syringomyelia, suggesting chronicity of the problem. The bone appeared normal in its architecture and moderately brittle in consistency in two of our cases where drilling of the part impinging into the canal was done. Histological examination of the bone in this case did not reveal the presence of any bony tumor, such as fibrous dysplasia. At follow-up, there was no growth in the size of the lesion that could suggest a tumorlike pathology.
Treatment
Several treatment options for spinal canal stenosis in the presence of facetal hypertrophy have been reported. A decompressive procedure that involves resection of the posterior arch of the atlas and adjoining parts of the foramen magnum and lamina of the axis was done in our first three cases ( Figs. 48.1 and 48.2 ). In the fourth and fifth cases, direct decompression of the part of the bone compressing the cord was performed. Our familiarity with the surgical anatomy of the region of the facets of the atlas and axis and our techniques involving manipulation of the lateral masses of the atlas and axis for fixation of the region8,9 probably influenced our surgical strategy in the latter case. Atlantoaxial fixation was done in the fourth case ( Fig. 48.3 ), as the articular surface was manipulated during surgery, although the joint appeared intact and normal. In the fifth case, no atlantoaxial fixation was done ( Fig. 48.4 ).
The technical ease of a posterior decompressive surgical procedure over direct manipulation and fixation of the region favors the former. However, it appears to us that direct decompression of the indenting part of the abnormal bone could be a more rational way of treatment. The more remarkable clinical recovery and improvement in torticollis in the patient undergoing the latter form of treatment are also suggestive of the superiority of the treatment modality. The need and effectiveness of unilateral fixation can be questioned. However, to define the best treatment protocol for this most unusual and uncommon anomaly, more experience appears to be mandatory.
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