Is the atlas size associated with the pathophysiology of symptomatic spinal canal stenosis at the C1 level?

•The characteristics of patients with C1 stenosis (CIS) were compared with subaxial stenosis (SAS).•Patients with CIS were significantly older and their height and weight were significantly lower than SAS patients.•The atlas size of CIS group was significantly smaller than patients with SAS.•The atlas size of CIS group was also statistically smaller than asymptomatic controls.•Small atlas size can be associated with symptomatic spinal canal stenosis at the C1 level. Narrow cervical spinal canal is an important risk factor for the development of cervical myelopathy. Patients with this disease often present with congenital narrowness of the cervical spinal canal. While there are studies on patients with subaxial spinal canal stenosis (SAS), few examined the coexistence of congenital narrow spinal canal in patients with cervical myelopathy at the C1 level. We investigated the characteristics of patients with C1 stenosis (C1S) with special reference to the size of the atlas. Thirteen patients (8 men, 5 women, mean age 76 years) with C1S were retrospectively analyzed and their clinical characteristics and radiological findings were compared with 27 SAS patients and with 26 age-, sex-, and body habitus-matched asymptomatic individuals. Of the 13 C1S patients, 6 presented with a retro-odontoid pseudotumor, 5 with atlantoaxial subluxation, and 2 with ossification or calcification of the transverse ligament; they were significantly older and shorter, and their body weight was significantly lower than in SAS patients (p