The coexistence of crowned dens sign and calcification of ligamentum flavum in the cervical spine: mere coincidence or meaningful association?

We present a case series of cervical radiculomyelopathy caused by calcification of the ligamentum flavum (CLF), with or without concomitant periodontoid calcification. A brief literature review is presented, highlighting a potential relationship between these 2 conditions. In this retrospective study, we reviewed medical records of 33 patients diagnosed with cervical CLF. And we propose the term "crowned dens sign" (CDSign) to describe the characteristic radiographic finding of circumferential calcification around the odontoid process of the axis. Among the 33 patients, 28 (84.8%) were female and 5 (15.2%) were male, with a mean age of 70.6 years. Based on the cervical computed tomography images, a total of 81 cervical segments of CLF were recorded. The most commonly involved levels were C4-5 and C5-6, demonstrating the characteristic pattern of mid-cervical predominance. The CDsign was identified in 26 cases (79%), demonstrating a high prevalence in this cohort. The patient cohort comprised the following treatment groups: 2 patients received conservative management, twenty-three underwent posterior surgical procedures, and 8 were treated with anterior cervical surgery. The coexistence of CDSign and CLF represents an exceptionally rare clinical occurrence. The correlation between these 2 conditions extends beyond mere coincidence. The coexistence of CLF and CDSign may represent a rare but distinct cervical manifestation of calcium pyrophosphate dihydrate deposition disease.