Normal Variant Occipital Pneumatization.

Objective:Evaluate prevalence and pattern of occipital pneumatization (OP).Patients:Individuals with imaging evidence of OP on computed tomography (CT).Intervention(s):High resolution CT scans of the temporal bone.Main Outcome Measure:The prevalence and pattern of OP on 1000 CT scans performed at a large academic healthcare system.Results:OP had a prevalence of 11.8% (n=118) while occipital condyle pneumatization occurred in only 0.3%. Occipital air cells were right-sided in 27.1% (n=32), left-sided in 51.7% (n=61), and bilateral in 21.2% (n=25), and OP was contiguous with the occipitomastoid suture. In cases of unilateral OP, the contralateral jugular foramen demonstrated relative enlargement (p=0.006), but a direct association could not be established.Conclusions:The occipital bone is an accessory site of skull base pneumatization in 11.8% of the population undergoing temporal bone CT, while air cell extension into the occipital condyle occurs more rarely. These occipital air cells have a left-sided predilection and are always in direct proximity to the occipitomastoid suture, suggesting developmental egress from the mastoid. OP is a normal variant and lacks features of craniocervical pneumatization, which is a rare disorder.