Fig. 3

a Receiver operating characteristic (ROC) curve of V3 diameter measured by TCS to detect hydrocephalus diagnosed on CT. The ROC curve represents the specificity and sensitivity of TCS to diagnose hydrocephalus. AUC was 0.91% [95% CI 0.85–0.98%], the estimated best threshold was at 6.25 mm, with a specificity of 0.79 and a sensibility of 0.88. Positive predictive value (PPV) and negative predictive value (NPV) are provided for thresholds on either side of the grey zone (see Fig. 3b). b Two-curve sensitivity/specificity representation of grey zone for V3 diameter measured by TCS, associated with a hydrocephalus diagnosed on CT. We defined a grey zone for cut-offs with a sensitivity lower than 90% and a specificity lower than 90% (diagnosis tolerance of 10%). On either side of these cut-offs, patients were assigned to a low-risk or a high-risk. The diagnosis of hydrocephalus was thus excluded in 35 (40%) patients with a V3 diameter < 5.2 mm and confirmed in 25 (29%) patients with a V3 diameter > 7.7 mm. TCS was inconclusive in 27/87 (31%) patients. The V3 measurement from the right side was included for these analyses because right side was the most frequently assessable side. The left side was included when V3 was not assessable from right side