Peritruncal Blood Volume Predicts Shunt Dependency and Functional Recovery in aSAH

Refining Prognostic Accuracy in Aneurysmal Subarachnoid Hemorrhage

When managing aneurysmal subarachnoid hemorrhage, clinicians frequently rely on radiological grading systems to predict patient trajectories and the risk of secondary complications. The Fisher scale and its modified version have long served as the standard for assessing blood distribution and predicting delayed cerebral ischemia, a condition where reduced cerebral blood flow leads to new neurological deficits or infarction [1]. However, these established tools focus predominantly on supratentorial blood, often leaving the clinical impact of infratentorial blood distribution poorly defined [1]. This gap in assessment is significant because blood localized in the cisterns surrounding the brainstem may influence the development of chronic hydrocephalus or impact overall functional recovery [1]. A recent retrospective study demonstrates that quantifying blood in these frequently neglected peritruncal compartments can significantly refine clinical risk stratification, offering a more accurate prediction of long-term disability.

Quantifying Infratentorial Blood Distribution

To address the limitations of current radiological grading, researchers conducted a retrospective single-center analysis of 675 patients diagnosed with aneurysmal subarachnoid hemorrhage who underwent baseline CT imaging between 2012 and 2022. Established severity scores, such as the modified Fisher scale, primarily evaluate supratentorial blood components located above the tentorium cerebelli. While peritruncal blood (hemorrhage surrounding the brainstem) is frequently present in these patients, it remains underrepresented in standard grading systems. This omission is clinically relevant because the brainstem houses critical autonomic pathways, and blood pooling in these basal areas can severely disrupt cerebrospinal fluid flow. To capture a comprehensive picture of this deep blood load, the researchers utilized manual segmentation, a precise technique where a clinician traces the boundaries of a hematoma on each CT slice to calculate its exact volume. The team quantified hematoma volumes in predefined peritruncal cisterns, specifically the interpeduncular, prepontine, premedullary, and magna cisterns, as well as within the third and fourth ventricles. By assessing both individual and cumulative peritruncal blood volumes, the investigators sought to determine if these specific anatomical measurements provided better prognostic value than traditional scales that prioritize cortical and sylvian fissure blood.

Predicting Shunt Dependency and Functional Disability

The investigators evaluated several primary complications following aneurysmal subarachnoid hemorrhage, including macrovasospasm, delayed cerebral ischemia, and ventriculoperitoneal shunt dependency (the requirement for permanent surgical diversion of cerebrospinal fluid due to chronic hydrocephalus). The analysis demonstrated that peritruncal cisternal and ventricular blood volumes were significantly associated with ventriculoperitoneal shunt dependency. For practicing neurointensivists and neurosurgeons, this suggests that blood accumulation in infratentorial compartments plays a more critical role in obstructing cerebrospinal fluid pathways than supratentorial grading systems account for. Functional outcomes were measured using the modified Rankin Scale, a standard 6-point metric used to quantify disability, at hospital discharge and at a 6-month follow-up. The study found that peritruncal cisternal and ventricular blood volumes were significantly associated with functional outcome at both discharge and 6 months. While peritruncal blood proved to be a robust predictor of shunt needs and long-term disability, it showed weaker associations with delayed cerebral ischemia compared to other clinical outcomes. Crucially, peritruncal blood volume was independently associated with outcome, and these associations persisted even in patients with low Fisher scale grades (≤ 2). This finding is highly relevant for daily practice because it identifies a subset of patients who might be categorized as low-risk by standard scales but actually remain at high risk for poor functional recovery. Furthermore, the predictive value of peritruncal blood remained significant in patients with anterior circulation aneurysms, indicating that infratentorial blood distribution provides critical prognostic information regardless of the primary site of vascular rupture.

Comparison With Established Fisher Scales

When evaluating the predictive accuracy of these radiological markers, cumulative peritruncal hematoma volume demonstrated a stronger association with functional outcome at discharge and 6 months than traditional Fisher-based scales. The researchers compared these metrics using pseudo-R2 values, a statistical measure that quantifies how well a given model explains the variability of the clinical data. For cumulative peritruncal volume, the absolute model fit was pseudo-R2 0.141 at discharge and 0.139 at 6 months. These figures represent a notable increase in predictive power compared to the standard Fisher scale, which demonstrated an absolute model fit of pseudo-R2 0.078 at discharge and 0.067 at 6 months. Similarly, the modified Fisher scale showed less predictive strength than the peritruncal model, yielding pseudo-R2 values of 0.098 at discharge and 0.090 at 6 months. Although the absolute model fit for peritruncal volume remains modest overall, its superior performance relative to established scales indicates that current grading systems overlook critical prognostic information contained within the infratentorial space. To translate these findings into actionable clinical tools, the researchers are currently developing an extended Fisher approach that integrates infratentorial compartments into the existing framework. If validated in prospective multicenter trials, this refined grading system could provide clinicians with a more comprehensive method for predicting long-term disability and the need for permanent cerebrospinal fluid diversion.

References

1. Neyazi M, Fischer I, Weiss D, et al. Peritruncal hematoma volume: is it a neglected prognostic marker in aneurysmal subarachnoid hemorrhage?. Journal of neurosurgery. 2026. doi:10.3171/2025.12.JNS252313