Overview
Embosphere Microspheres (Merit Medical) are biocompatible, hydrophilic, calibrated microspheres composed of tris-acryl gelatin. They are one of the most widely used particulate embolic agents in interventional radiology and are considered the gold standard for uterine artery embolisation (UAE) in the UK.
Indications
Uterine fibroid embolisation (UFE/UAE)
Hypervascular tumour embolisation (renal, hepatic, meningioma)
Pre-operative tumour devascularisation
Haemorrhage control (post-partum haemorrhage, pelvic trauma)
Prostatic artery embolisation (PAE)
Available Sizes
| Size Range (µm) | Colour Code | Common Use |
|---|---|---|
| 100–300 | Purple | PAE, hypervascular tumours |
| 300–500 | Blue | Renal tumours, pre-op devascularisation |
| 500–700 | Red | UAE (most common for fibroids) |
| 700–900 | Yellow | UAE (larger fibroids), haemorrhage |
| 900–1200 | White | Large vessel occlusion |
Key Features
Calibrated and compressible — spheres are precisely sized and can compress to pass through smaller catheters, then re-expand to their calibrated size at the target site
Non-resorbable — provides permanent occlusion, unlike gelatin sponge
Hydrophilic surface — minimises catheter clogging and aggregation
Predictable penetration depth — calibrated sizing ensures consistent distal occlusion level
Technique Tips
Mix with contrast (typically 50:50 with non-ionic contrast) to create a visible slurry. Avoid mixing with saline alone as this reduces fluoroscopic visibility.
Inject slowly under continuous fluoroscopic observation. Stasis or reflux indicates endpoint — stop immediately.
For UAE, the 500–700 µm size is the workhorse. Start here unless there is a specific reason to up-size or down-size.
Use a 2.4–2.8 Fr microcatheter for selective embolisation. The microspheres compress through the catheter lumen.
Agitate the syringe regularly during injection to prevent sedimentation.
Contraindications
Presence of significant arteriovenous shunting (risk of non-target embolisation to the lungs)
Vasospasm or inability to achieve selective catheter position
Known allergy to gelatin-based products