Mild Subarachnoid Hemorrhage (SAH) With Low Hounsfield Unit Value (HUV) or Hijdra Scores Still Carries Outcome Risk: A Subgroup Analysis

The prognostic value of the initial Hounsfield unit value (IT-HUV) in aneurysmal subarachnoid hemorrhage (SAH) has been demonstrated in previous work, but it remains uncertain whether patients with mild clinical presentation and low clot burden can truly be considered low risk. To address this question, we analyzed two subgroups of WFNS 1-2 patients: (1) limited hemorrhage volume (Hijdra 0-19; n = 46) and (2) low hemorrhage density (IT-HUV <46; n = 51). Despite their favorable initial appearance, both subgroups exhibited substantial rates of poor outcome, occurring in 13/46 (28.3%) and 15/51 (29.4%), respectively, while delayed cerebral ischemia (DCI) and symptomatic vasospasm (SVS) also occurred with nonnegligible frequency. Within these restricted cohorts, IT-HUV no longer demonstrated meaningful discriminatory ability, whereas age consistently remained the strongest predictor of outcome. Intraventricular hemorrhage contributed modest but clinically relevant additional risk information. These findings indicate that mild SAH accompanied by low-volume or low-density hemorrhage does not reliably correspond to a benign course. Elderly patients, particularly those with intraventricular extension, may still be vulnerable to complications and therefore warrant careful clinical monitoring rather than exclusion from vasospasm prophylaxis based solely on initial mild features.