Digital Subtraction Angiography (DSA) - ENT Perspective

1. What is DSA? - The Core Concept

2. How Does It Work? - Step by Step

Step 1 - Mask Image (Reference Image)

• Before contrast is injected, a plain fluoroscopic image is captured.
• This image shows bones, soft tissues, and all background structures.
• It is digitized (converted into a grid of numbers) and stored in a computer.

Step 2 - Contrast Injection

• A contrast agent (iodine-based) is injected into a blood vessel via a catheter.
• A second fluoroscopic image is captured when the vessels fill with contrast.

Step 3 - Digital Subtraction

• The computer subtracts the first (mask) image from the second (contrast) image pixel by pixel.
• All background structures that appear in both images cancel out to zero (black).
• Only the contrast-filled vessels remain - shown as bright white.

3. Equipment Used

4. Vascular Access - The Seldinger Technique

1. A needle punctures the common femoral artery (transfemoral route, most common) or occasionally the radial or brachial artery.
2. A flexible guidewire is passed through the needle.
3. The needle is removed; a sheath and catheter are advanced over the guidewire.
4. The catheter is steered under fluoroscopic guidance into the target vessel (e.g., external carotid artery, internal carotid artery).
5. Contrast is injected manually or via a pump injector.

• Both internal carotid arteries (ICA)
• Both external carotid arteries (ECA)
• Both vertebral arteries (if needed)

5. Imaging Parameters

• Frame rate: 2-3 images/second for routine; 4-7/second for fast-flow lesions (AVMs, high-flow tumors)
• 3D DSA: Automatic pump injection of 15-20 mL contrast at 3-5 mL/sec; the C-arm rotates 180-200° during injection, creating a 3D rotational angiogram
• Biplanar units: Allow simultaneous AP and lateral (or two oblique) projections in a single injection, reducing contrast dose and procedure time

6. ENT-Specific Indications

A. Juvenile Nasopharyngeal Angiofibroma (JNA)

• JNA is a highly vascular tumor arising near the sphenopalatine foramen in adolescent males.
• Intranasal biopsy is contraindicated due to risk of life-threatening hemorrhage.
• Selective DSA elegantly maps the feeding vessels and their exact supply territory.
• Pre-operative embolization of feeder vessels is performed at the same sitting.
• Post-embolization surgical resection is then the treatment of choice.
• (Scott-Brown's Otorhinolaryngology, Vol. 2)

B. Glomus Tumors (Paragangliomas)

• Glomus jugulare - arises in the jugular foramen; fed predominantly by the ascending pharyngeal artery and posterior division of the middle meningeal artery; less commonly by the stylomastoid branch of the occipital and posterior auricular arteries.
• Glomus tympanicum - small middle ear tumor; usually no embolization needed.
• Glomus vagale / Carotid body tumor - fed by multiple ECA branches.

Fig. from Cummings Otolaryngology: (A, B) Selective left external carotid artery DSA showing hypervascular area in the nasal region. (C) Post-embolization - occlusion of distal internal maxillary artery with resolution of epistaxis.

C. Intractable Epistaxis

• When conservative measures and packing fail, DSA identifies the offending vessel.
• The culprit vessel (usually the internal maxillary artery or a sphenopalatine branch) is visualized.
• Embolization with polyvinyl alcohol (PVA) particles (e.g., 150-μm) is performed under DSA road map guidance.
• (Cummings Otolaryngology)

D. Meningiomas and Hypervascular Skull Base Tumors

• DSA maps dural blood supply and dangerous ECA-ICA anastomoses.
• Pre-operative embolization reduces intraoperative blood loss.
• If ICA sacrifice is contemplated (tumor encasing the ICA), DSA is used for the Balloon Occlusion Test (BOT) - temporarily inflating a balloon in the ICA to test if the hemisphere can tolerate permanent occlusion.

E. Vascular Malformations

• Arteriovenous malformations (AVMs)
• Arteriovenous fistulas (AVFs) - including carotid-cavernous fistulas
• Venous malformations
• DSA provides definitive mapping of the nidus, feeders, and draining veins.

F. Traumatic Vascular Injuries

• Pseudoaneurysms, carotid laceration, vertebral artery injury
• DSA confirms diagnosis and guides endovascular repair (coils, stents)

7. Embolic Agents Used Under DSA Guidance

8. Dangerous Anastomoses in H&N DSA

9. Advantages of DSA Over Other Methods

10. Contraindications and Risks

• Documented anaphylaxis to iodine contrast (most important; relative if pre-medicated)
• Severe renal failure (relative; haemofiltration can follow the procedure)
• Severe uncorrected coagulopathy (relative in elective settings)

• Cerebral thromboemboli / stroke - from catheter manipulation in the aortic arch and cervical vessels
• Vessel spasm, dissection, or thrombosis - from catheter/guidewire trauma
• Cranial nerve injury - from inadvertent embolization of vasa nervorum (especially cranial nerves IX, X, XI in glomus embolization)
• Reflux of embolic agent into ECA-ICA anastomoses causing blindness or stroke
• Groin hematoma at puncture site
• Contrast nephropathy - minimized by hydration

11. Summary - When to Order DSA in ENT