Predicting survival after acute civilian penetrating brain injuries: The SPIN score

Abstract

Objective: To identify predictors associated with survival in civilian penetrating traumatic brain injury (pTBI) utilizing a contemporary, large, diverse 2-center cohort, and to develop a parsimonious survival prediction score for pTBI.

Methods: Our cohort comprised 413 pTBI patients retrospectively identified from the local trauma registries at 2 US level 1 trauma centers, of which one was predominantly urban and the other predominantly rural. Predictors of in-hospital and 6-month survival identified in univariate and multivariable logistic regression were used to develop the simple Surviving Penetrating Injury to the Brain (SPIN) score.

Results: The mean age was 33 ± 16 years and patients were predominantly male (87%). Survival at hospital discharge as well as 6 months post pTBI was 42.4%. Higher motor Glasgow Coma Scale subscore, pupillary reactivity, lack of self-inflicted injury, transfer from other hospital, female sex, lower Injury Severity Score, and lower international normalized ratio were independently associated with survival (all p < 0.001; model area under the curve 0.962). Important radiologic factors associated with survival were also identified but their addition to the full multivariable would have resulted in model overfitting without much gain in the area under the curve.

Conclusions: The SPIN score, a logistic regression-based clinical risk stratification scale estimating survival after pTBI, was developed in this large, diverse 2-center cohort. While this preliminary clinical survival prediction tool does not include radiologic factors, it may support clinical decision-making after civilian pTBI if external validation confirms the probability estimates.

Figure 1. Head CT (hCT) examples of the radiologic grading for trajectory and anatomy

(A–C) hCTs for 3 different patients, all with penetrating trajectories without perforation but involving different lobes (anatomy): (A) single lobe involvement; (B) unilateral involvement of multiple lobes (temporal, parietal, and occipital); (C) bilateral involvement of multiple lobes (bitemporal, parietal). (D, E) hCT of one patient with tangential trajectory: (D) bone window captures the bullet tangentially penetrating the dura; (E) brain window of same patient reveals an associated small subdural hematoma (arrow). (F) Perforating trajectory with through-and-through injury involving bilateral hemispheres and the ventricles.

Figure 2. Receiver operating characteristic (ROC) curves for the multivariable models

Base model: motor Glasgow Coma Scale (mGCS) and pupillary reactivity on admission. Model 1 (base + injury variables): base + Injury Severity Score (ISS) + self-inflicted + transfer + sex. Model 2 (base + radiologic variables): base + trajectory + intraventricular hemorrhage (IVH) + cisterns + multiple brain wounds. Model 3 (base + laboratory variables): base + international normalized ratio (INR). Model 4 (base + injury + laboratory variables): base + ISS + self-inflicted + transfer + sex + INR. The corresponding area under the curve values (C statistic) are shown in parentheses under each ROC.

Figure 3. Surviving Penetrating Injury to the Brain (SPIN) score

(A) Components of the SPIN score and assigned score points. (B) Estimated survival probability (y-axis) plotted against the total survival (SPIN score). (C) Comparison of the observed (red bars) to predicted (blue bars) proportion of survivors by SPIN score categories. Y-axis: percent of patients who survive at hospital discharge and 6 months after penetrating traumatic brain injury. X-axis: SPIN score categories. Data table: percent of predicted and observed patients in the entire cohort per SPIN score category. GCS = Glasgow Coma Scale; INR = international normalized ratio.