Distinct Inflammatory Profiles in Angiography-Negative Subarachnoid Hemorrhage: A Focused Case Series

This retrospective study reveals that angiography-negative subarachnoid hemorrhage (anSAH) exhibits an early cerebrospinal fluid cytokine profile and inflammatory signature more similar to intracerebral hemorrhage than to aneurysmal subarachnoid hemorrhage, suggesting that anSAH represents a biologically distinct phenotype.

The Gist

The Big Picture: Two Types of Brain Bleeds

Imagine your brain is a bustling city. Sometimes, a pipe bursts inside a building (this is an Intracerebral Hemorrhage, or ICH). Other times, a pipe bursts in the streets or the sewers surrounding the buildings (this is a Subarachnoid Hemorrhage, or SAH).

Doctors have known for a long time that these two types of bleeds are different. But there is a confusing third group: Angiography-Negative SAH (anSAH). These are street-level bleeds where doctors look for a broken pipe (an aneurysm) using high-tech cameras, but they can't find one. It's like a flood in the street, but no one can find the source.

The Big Question: Is this "mystery flood" (anSAH) actually just a street problem (like SAH), or is it secretly a building problem (like ICH)?

The Investigation: Listening to the "Smoke Alarms"

When blood leaks into the brain, it triggers an emergency response. The brain sends out chemical "smoke alarms" called cytokines. These chemicals call in the cleanup crew (immune cells) to fix the damage.

The researchers took a look at the "smoke alarms" (specifically IL-8 and VEGF-A) in the fluid surrounding the brain (CSF) of patients within the first 72 hours after their bleed. They wanted to see if the alarms sounded different depending on where the bleed happened.

The Findings: The "Mystery Flood" Looks Like a Building Collapse

Here is what they discovered, using our city analogy:

1. The Building vs. The Street:

   • ICH (Building Burst): When the bleed happened inside the brain tissue, the smoke alarms were screaming very loudly. The levels of IL-8 and VEGF-A were high.
   • aSAH (Aneurysm Street Burst): When the bleed was caused by a known broken pipe (aneurysm) on the street, the smoke alarms were quieter. The levels of those specific chemicals were lower.
   • anSAH (Mystery Street Burst): This is the surprise! Even though the bleed was on the street, the smoke alarms sounded exactly like the building burst. The levels of IL-8 and VEGF-A were just as high as in the ICH patients.

2. The Conclusion:
   The "mystery flood" (anSAH) isn't acting like a typical street flood (aneurysmal SAH). Biologically, it behaves much more like a bleed inside the brain tissue (ICH). It seems that when blood touches the brain tissue directly, it causes a massive inflammatory reaction, regardless of whether there was a visible broken pipe or not.

3. The Outcome:
   The study also looked at how patients recovered. Unfortunately, patients with the "building burst" (ICH) and the "mystery flood" (anSAH) tended to have worse recoveries compared to the patients with the "known street burst" (aneurysmal SAH).

Why Does This Matter?

Think of it like a fire department.

• If you have a small trash can fire (aneurysmal SAH), you send a small fire truck.
• If you have a skyscraper fire (ICH), you send a massive fleet of trucks, heavy water cannons, and hazmat teams.

For a long time, doctors treated the "mystery flood" (anSAH) like the small trash can fire because they couldn't find the source. But this study suggests that the "mystery flood" is actually a skyscraper fire in disguise. It needs the heavy-duty treatment plan used for ICH, not the lighter plan used for standard SAH.

The Takeaway

This research is like finding a new fingerprint at a crime scene. It tells us that anSAH is a unique biological beast. It shares the same "inflammatory signature" as a bleed inside the brain, not a bleed on the surface.

What's next?
The researchers admit this is just the beginning (a "hypothesis-generating" study). They have a small sample size, like finding five fingerprints at a crime scene. They need to look at more cases to be sure. But if they are right, this could change how doctors treat these patients, potentially saving lives by matching the treatment to the biology of the bleed, not just the location.

In short: If the brain's smoke alarms are screaming like a building fire, treat it like a building fire, even if you can't find the broken pipe.

Technical Summary

1. Problem Statement

Hemorrhagic strokes, specifically Intracerebral Hemorrhage (ICH) and Subarachnoid Hemorrhage (SAH), carry high mortality and morbidity rates. While the inflammatory cascade triggered by blood in the central nervous system (CNS) is known to contribute to secondary injury, the specific inflammatory profiles of different hemorrhage subtypes remain poorly characterized.

• The Gap: Most existing studies analyze ICH and aneurysmal SAH (aSAH) separately. There is a significant lack of data regarding angiography-negative SAH (anSAH), a subgroup where vascular imaging fails to identify an aneurysm or malformation.
• Clinical Uncertainty: Patients with anSAH (approx. 10–30% of SAH cases) are often managed using aSAH protocols. However, it is unclear if their underlying biology and prognosis align more closely with aneurysmal SAH or primary ICH. Understanding the early cytokine signature of anSAH is crucial for determining if it represents a distinct biological phenotype.

2. Methodology

• Study Design: Retrospective, observational cohort study conducted at Yale School of Medicine (2014–2025).
• Cohorts:
  • Cytokine Analysis Cohort: 120 adult patients with spontaneous hemorrhagic stroke (43 ICH, 77 SAH) who had External Ventricular Drains (EVDs) placed. Only the first CSF sample collected within 72 hours of symptom onset was analyzed.
  • Outcome Cohort: A broader cohort of 490 patients (ICH or SAH) to assess functional outcomes.
• Exclusion Criteria: Traumatic hemorrhage, hemorrhagic transformation of ischemic stroke, and non-vascular causes (infection, tumor, venous sinus thrombosis).
• Classification:
  • ICH: Primary (hypertension/CAA) vs. AVM-associated.
  • SAH: Aneurysmal (aSAH) vs. Angiography-negative (anSAH).
• Biomarkers: Multiplex bead-based assay (Cytometric Bead Array) measured five cytokines/chemokines in CSF:
  • Interleukin-6 (IL-6)
  • Interleukin-8 (IL-8)
  • Vascular Endothelial Growth Factor A (VEGF-A)
  • C-C motif chemokine ligand-2 (CCL2)
  • Granulocyte colony-stimulating factor (G-CSF)
• Statistical Analysis: Cytokine concentrations were log-transformed due to non-normal distribution. Linear regression models compared groups (e.g., ICH vs. SAH, anSAH vs. aSAH). Outcomes were assessed using the modified Rankin Scale (mRS) at discharge and 3 months.

3. Key Contributions

• First Direct Comparison: This study provides the first systematic comparison of early CSF cytokine profiles between ICH, aSAH, and the distinct anSAH subgroup.
• Biological Characterization of anSAH: It challenges the assumption that anSAH is biologically identical to aSAH, proposing instead that anSAH shares a distinct inflammatory signature more similar to primary ICH.
• Specific Biomarker Identification: The study identifies IL-8 and VEGF-A as key differentiators in the early inflammatory response, suggesting that the presence of blood in the parenchyma (ICH/anSAH) drives a different immune response than aneurysmal rupture alone (aSAH).

4. Key Results

• ICH vs. SAH (General):
  • ICH patients exhibited significantly higher levels of log[IL-8] ($\beta = 0.42, p=0.004$) and log[VEGF-A] ($\beta = 0.81, p<0.001$) compared to the overall SAH group.
  • ICH was associated with worse functional outcomes at both discharge and 3 months compared to SAH.
• anSAH vs. aSAH (Within SAH):
  • anSAH patients had significantly higher levels of log[IL-8] ($\beta = -0.85, p=0.030$) and log[VEGF-A] ($\beta = -1.18, p=0.003$) compared to aSAH patients.
  • This indicates that the absence of a detected aneurysm correlates with a "more ICH-like" inflammatory profile.
• anSAH vs. Primary ICH:
  • There were no statistically significant differences in any of the measured cytokines between anSAH and primary ICH. This strongly supports the hypothesis that anSAH and primary ICH share a similar early inflammatory mechanism.
• AVM-ICH vs. aSAH:
  • AVM-associated ICH differed from aSAH primarily in VEGF-A levels, suggesting that the presence of a vascular malformation (AVM) does not simply mimic the aSAH profile.
• Outcome Correlations:
  • In the broader cohort, ICH location was a strong predictor of poor functional outcome.
  • Within the SAH group, higher CSF log[G-CSF] was associated with poor functional outcomes (OR = 1.41, $p=0.046$).

5. Significance and Implications

• Reclassification of anSAH: The findings suggest that anSAH is not merely a "diagnostic mystery" of aSAH but a biologically distinct phenotype. Its inflammatory profile (high IL-8 and VEGF-A) aligns with the parenchymal blood exposure seen in ICH rather than the subarachnoid blood exposure of aSAH.
• Mechanistic Insight:
  • IL-8: Elevated levels suggest robust neutrophil recruitment and innate immune activation driven by direct blood contact with brain parenchyma or ventricular surfaces.
  • VEGF-A: Higher levels in ICH and anSAH (vs. aSAH) imply greater endothelial injury and blood-brain barrier (BBB) disruption, potentially driven by hypoxia or direct tissue injury rather than the rupture of a pre-existing vessel.
• Clinical Management: These results argue against a "one-size-fits-all" approach for SAH. Patients with anSAH may require management strategies or immune-targeted therapies more akin to ICH protocols, particularly regarding neuroinflammation and BBB protection.
• Future Directions: The study is hypothesis-generating. It calls for larger, multicenter validation and mechanistic studies to explore how IL-8 and VEGF-A signaling pathways contribute to secondary injury in these specific subtypes, potentially leading to targeted biomarker-guided therapies.

Limitations: The study is limited by a small sample size (specifically the anSAH group, $n=5$), a single-center design, and a short observation window (72 hours). Functional outcomes were limited to discharge and 3 months.