Diagnostic Accuracy of Scintigraphy for Detecting Morphological Variation of the Sixth Cervical Vertebral Ventral Lamina in Horses: A Retrospective Study.

Morphological variations or transposition of the ventral lamina of the sixth cervical vertebra (C6) are well documented in horses. Radiography remains the primary modality for identifying these osseous variations, whereas scintigraphy provides a functional assessment of bone activity; however, its diagnostic accuracy for this condition has not been established. This retrospective single-center study evaluated the diagnostic performance of scintigraphy compared with radiography for detecting C6/C7 ventral laminar anomalies and determined an optimal C6:C7 uptake ratio cutoff. Thirty-four horses underwent both radiographic and scintigraphic examination. Radiography served as the reference standard, classifying horses as normal (n = 22) or abnormal (n = 12; unilateral n = 5, bilateral n = 7). Semiquantitative scintigraphic analysis was performed using a C6:C7 uptake ratio derived from background-corrected counts per pixel. The visual scintigraphic assessment demonstrated 75.0% sensitivity (95% CI: 42.8%-94.5%) and 72.7% specificity (95% CI: 50.9%-88.7%). Semiquantitative receiver-operating characteristic (ROC) analysis yielded an optimal C6:C7 ratio cutoff of 0.81 (area under the curve [AUC] = 0.762), providing 66.7% sensitivity and 81.8% specificity. The C6:C7 ratio was significantly higher in abnormal horses compared with normal horses for both the left (0.860 ± 0.149; p = 0.006) and right (0.812 ± 0.148; p = 0.035) sides. No significant differences within-subject side-to-side (left-right) C6:C7 ratio were detected. Scintigraphy demonstrated moderate diagnostic accuracy for detecting C6:C7 ventral laminar anomalies. A C6:C7 ratio threshold of 0.81 may serve as a practical adjunct screening parameter, though validation in larger populations is warranted.