Radiologically defined acute hydrocephalus in aneurysmal subarachnoid haemorrhage

Ventriculomegaly is common in aneurysmal subarachnoid haemorrhage (aSAH). An imaging measure to predict the need for cerebrospinal fluid (CSF) diversion may be useful. The bicaudate index (BCI) has been previously applied to aSAH. Our aim was to derive and test a threshold BCI above which CSF diversion may be required.

Review of prospective registry. The derivation group (2009-2015) included WFNS grade 1-2 aSAH patients who deteriorated clinically, had a repeat CT brain and underwent CSF diversion. BCI was measured on post-deterioration CTs and the lower limit of the 95% confidence interval (95%CI) was the hydrocephalus threshold. In a separate test group (2016), in WFNS ≥ 2 patients, we compared BCI on diagnostic CTs with CSF diversion within 24 hours.

The derivation group (n = 62) received an external ventricular (n = 57, 92%) or lumbar drain (n = 5, 8%). Mean post-deterioration BCI was 0.19 (95%CI 0.17-0.22) for age ≤49 years, 0.22 (95%CI 0.20-0.23) for age 50-64 years and 0.24 (95%CI 0.22-0.27) for age ≥65 years. Hydrocephalus thresholds were therefore 0.17, 0.20 and 0.22, respectively. In the test group (n = 105), there was no significant difference in BCI on the diagnostic CT between good and poor grade patients aged ≤49 years (p = 0.31) and ≥65 years (p = 0.96). 30/66 WFNS ≥ 2 patients underwent CSF diversion, although only 15/30 (50%) exceeded BCI thresholds for hydrocephalus.

A significant proportion of aSAH patients may undergo CSF diversion without objective evidence of hydrocephalus. Our threshold values require further testing but may provide an objective measure to aid clinical decision making in aSAH.