Cerebral Angiography

🧠 Introduction

• 🩸 Angiography visualises the lumen of blood vessels — the “pipes” of the circulation. It helps identify narrowing, occlusion, beading, dissection, aneurysm, or vascular spasm in stroke and other cerebrovascular diseases.
• 🧬 It can detect vascular malformations and track contrast movement temporally (through arterial, capillary, and venous phases) and spatially (in 3D reconstruction).
• 🧲 Modalities include X-ray–based (DSA/CTA) and MRI–based (MRA) techniques. The gold standard remains digital subtraction angiography (DSA), although CTA and MRA have greatly reduced the number of diagnostic catheter angiograms.

🎥 Cerebral Digital Subtraction Angiography (DSA)

• 🏅 Gold standard for vessel imaging — provides the highest spatial and temporal resolution.
• ⚙️ Technique: Catheter introduced (usually via femoral artery; radial increasingly common) → contrast injected (≈5 mL per artery) → dynamic X-ray sequence. Computer subtraction removes bone for a clear vascular image.
• 🕒 Procedure time: 20–30 min under local anaesthetic. Risks: ≈1% stroke, 0.1% mortality, vascular injury, or contrast reaction.
• 📈 Indications: used when findings will alter management — e.g. aneurysm, AVM, vasculitis, pre-operative embolisation. CTA can sometimes outperform DSA for aneurysm detection.

🩻 CT Angiography (CTA)

• 💡 Provides rapid 3D vascular imaging using iodinated contrast and CT reconstruction.
• ⚡ Excellent for detecting large vessel occlusion (LVO) in acute stroke → guides thrombectomy.
• 📈 Almost as accurate as DSA for extracranial stenosis and highly accurate for intracranial stenosis and dissection.
• 🚫 Avoid or use cautiously in contrast allergy or renal impairment — check eGFR.
• ⚠️ Carries radiation exposure; uses iodine-based contrast that can cause nephrotoxicity.

🧲 MR Angiography (MRA)

• 🧠 Non-invasive imaging of cerebral vasculature using blood flow signal differences. Can be done without contrast (TOF or phase-contrast) or with gadolinium contrast.
• Time-of-Flight (TOF): Flow-dependent, uses inflow enhancement of unsaturated blood — good for arteries, may overestimate stenosis.
• Phase-Contrast (PC): Uses velocity phase shifts — good for both arteries and veins, often used for cardiac/aortic studies.
• Contrast-Enhanced MRA (CE-MRA): Gadolinium shortens T1 relaxation, producing high intravascular signal and excellent vessel definition.
• ⚠️ Risks: Gadolinium reactions, nephrogenic systemic fibrosis (rare, CKD), and slight overestimation of stenosis.
• ✅ Accuracy similar to DSA for many cerebral indications; faster and safer for routine use.

🩸 CT Venography (CTV)

CTV assesses venous anatomy and patency and can be combined with CTA for dual arterial-venous imaging. Particularly useful in suspected Cerebral Venous Thrombosis (CVT) — shows sinus filling defects and collateral drainage.

🧲 MR Venography (MRV)

Investigation of choice in suspected CVT. Demonstrates absence of flow or intraluminal thrombus in dural venous sinuses. Can be performed non-contrast TOF or contrast-enhanced for better delineation.

🔎 Angiographic Findings

🧬 Causes of “Beading” Appearance

💡 Teaching tip: - DSA remains gold standard for intervention planning. - CTA excels for acute stroke triage and dissections. - MRA/MRV preferred when radiation or iodine contrast contraindicated. - Beading = think vasculitis, RCVS, or sympathomimetic drugs.