CTA-based risk assessment of the carotid variant of Eagle syndrome: development and internal validation of a nomogram

Eagle syndrome (ES) is uncommon; its carotid variant [ES-CA, sometimes termed vascular Eagle syndrome (VES)] can produce internal carotid artery (ICA) dissection or stenosis and ischemic stroke, yet is frequently underrecognized. This study leveraged large-sample computed tomography angiography (CTA) to quantify structural determinants of styloid-ICA contact and to develop and internally validate a nomogram for early risk stratification.

We retrospectively included 414 consecutive head-neck CTA examinations (January 2023-March 2025). Volume rendering (VR) and maximum intensity projection (MIP) were used to delineate styloid-vessel relationships and to measure styloid process length (SPL), anterior tilt angle (FTA), and medial inclination angle (IA). Univariable/multivariable logistic regression identified correlates of ICA contact; receiver operating characteristic (ROC) analyses compared alternative SPL metrics (ipsilateral, bilateral mean, bilateral maximum) to select the optimal predictor. A nomogram incorporating significant predictors underwent 1,000-bootstrap internal validation with assessment of discrimination, calibration, and decision-curve analysis (DCA).

ICA contact was present in 110/414 (26.6%). Men had longer styloids and larger FTAs than women (both p < 0.001), but smaller IAs (left: 19.00° vs. 21.00°, p < 0.001; right: 22.00° vs. 23.00°, p = 0.010). Female sex independently predicted ICA contact (OR = 3.838, p < 0.001), and SPL on both sides was an independent risk factor (left OR = 1.063; right OR = 1.085; both p < 0.05). Sex-stratified models revealed laterality: in men, right-sided SPL (OR = 1.101, p = 0.006) was decisive; in women, left-sided SPL (OR = 1.092, p = 0.050) was decisive. Among SPL metrics, the bilateral maximum (SPL-max) performed best for predicting contact (overall AUC = 0.731; men = 0.787; women = 0.733) with sex-specific cut-offs of 30.20 mm (men) and 26.75 mm (women). The nomogram combining SPL-max, sex, and age showed good performance (AUC = 0.779; calibration slope = 0.96) and yielded positive net benefit on DCA across 1-65% threshold probabilities.

Risk of ES-CA-related ICA contact was unrelated to age or angular parameters. Styloid length and sex were the principal structural risk factors, with right-sided predominance in men and left-sided predominance in women, suggesting sex-side interaction. SPL-max was the optimal predictor, with a 3.45-mm lower cut-off in women, and the internally validated nomogram demonstrated clinical utility for early, imaging-based screening.