Scintigraphic Characteristics of the Occipitoatlantoaxial Region in Clinically Sound Horses

The equine occipitoatlantoaxial (OAA) region is biomechanically complex, yet normative scintigraphic reference data for this area are lacking. This retrospective study characterized the physiological radiopharmaceutical uptake pattern in the OAA region of 60 clinically sound horses, assigned equally into four age groups: under 6 years (Group A), 6-10 years (Group B), 11-15 years (Group C), and over 15 years (Group D). A standardized, semiquantitative analysis of lateral bone-phase scintigrams was performed using region of interest (ROI) ratios to determine uptake patterns. A highly consistent pattern was observed across all groups, with the atlantoaxial region (cranial C2) demonstrating the highest uptake, approximately 5.8 times greater (SD 1.93; 95% CI: [5.6-6.6]) than the lowest uptake in the atlanto-occipital region. While age had no significant overall effect on the pattern, Group C (11-15 years) showed slightly higher uptake in the ventral atlas (ROI vC1) and cranial axis (ROI C2) compared to other groups. This study provides the first detailed baseline of normal OAA scintigraphic appearance across a representative age range, establishing essential reference data to improve diagnostic accuracy for cervical pathology in clinical practice.