Unilateral atlantal lateral mass hypertrophy. Report of four cases.

The authors report the cases of four patients in whom they diagnosed an extremely rare and hitherto unreported clinical condition-unilateral hypertrophy of the C-1 lateral mass causing symptomatic cord compression. All patients presented with long-standing torticollis and progressive myelopathy. Three patients underwent posterior decompressive surgery and one underwent resection of the part of the lateral mass invading into the spinal canal and subsequent atlantoaxial plate and screw fixation. Clinical improvement of varying degrees occurred in all cases following surgery. The clinical recovery, however, was most remarkable in the patient who underwent resection of the bone portion indenting the cord. The follow-up periods ranged from 2 to 14 years. The remarkable similarity in the presenting clinical and radiological/neuroimaging features in all four patients suggests that unilateral hypertrophy of the lateral mass of atlas may be a defined clinical entity. The treatment strategy needs to be evaluated; however, resection of the compression-causing portion of the hypertrophic bone appears to be the best treatment option.