What is the treatment approach for subarachnoid hemorrhage with a negative intracranial Computed Tomography Angiography (CTA)?

Treatment of Subarachnoid Hemorrhage with Negative Intracranial CTA

For patients with subarachnoid hemorrhage (SAH) and negative initial CTA, digital subtraction angiography (DSA) is strongly recommended as the next diagnostic step, particularly for diffuse SAH patterns, as it can identify vascular pathology in approximately 13% of cases that CTA fails to detect. 1

Diagnostic Approach Based on Hemorrhage Pattern

Initial Evaluation

• When CTA is negative in a patient with confirmed SAH, the pattern of hemorrhage should guide further diagnostic workup 2
• Hemorrhage patterns include diffuse, perimesencephalic, sulcal, isolated intraventricular hemorrhage (IVH), or xanthochromia 1

Follow-up Imaging Based on SAH Pattern

• Diffuse SAH pattern:

  • Requires DSA as this pattern has the highest yield (approximately 10-17%) for detecting aneurysms missed by CTA 2, 1
  • 3D rotational angiography should be included as it is more sensitive than 2D angiography 2

• Perimesencephalic SAH pattern:

  • While some authors suggest a negative CTA may be sufficient, this remains controversial 2
  • DSA is still recommended as aneurysms are found in approximately 3% of these cases despite negative CTA 1

• Sulcal SAH pattern:

  • Highest association with vasculitis/vasculopathy (32%) 1
  • CTA should be carefully scrutinized for vasculitis, and DSA is recommended for confirmation 2
  • Also associated with arteriovenous malformations (3%) and dural arteriovenous fistulas (3%) 1

Timing of Follow-up Imaging

• If initial DSA is negative, a repeat delayed DSA is recommended, which can detect small aneurysms in up to 14% of cases with initially negative findings 2
• Additional aneurysms/pseudoaneurysms (approximately 4%) can be identified on follow-up DSA 1

Medical Management

Nimodipine Administration

• All patients with SAH should receive nimodipine 60 mg (two 30 mg capsules) orally every 4 hours for 21 consecutive days 3
• Treatment should commence as soon as possible within 96 hours of SAH onset 3
• Nimodipine is indicated to improve neurological outcomes by reducing ischemic deficits regardless of post-ictus neurological condition (Hunt and Hess Grades I-V) 3
• For unconscious patients or those who cannot swallow, the capsule contents can be extracted and administered via nasogastric tube 3

Blood Pressure Management

• Careful monitoring of blood pressure is essential, particularly in patients with liver dysfunction who may experience increased bioavailability of nimodipine 3
• Systolic blood pressure >160 mm Hg may be associated with increased risk of rebleeding 2

Special Considerations

Technical Limitations of CTA

• CTA has limited sensitivity for aneurysms <3 mm in size 2
• Overlying bone can be problematic with CTA, especially at the skull base 2
• Vessel tortuosity can decrease the specificity of CTA, leading to misinterpretation 2
• The quality of CTA interpretation depends on radiologist experience 2

Potential Causes of CTA-Negative SAH

• Aneurysmal thrombosis is the most common reason for a lesion not being detected on initial angiography 4
• Small aneurysms (<3 mm) may be missed by CTA 2
• Vasculitis/vasculopathy accounts for approximately 7% of causes in CTA-negative SAH 1

Additional Diagnostic Modalities

• MRI with fluid-attenuated inversion recovery, proton density, diffusion-weighted imaging, and gradient echo sequences may be helpful when CT scan is negative 2
• MRI of the brain and cervical spine may detect rare causes such as spinal lesions 4

Follow-up Recommendations

• For patients with persistent clinical suspicion despite negative initial imaging, the complete diagnostic algorithm should include:
  1. Initial CTA (already negative in this scenario)
  2. DSA with 3D rotational angiography 2
  3. Repeat delayed DSA if initial DSA is negative 2
  4. Consider MRI brain and cervical spine if both CTA and DSA are negative 4