H.31 Reducing Risk of Nontarget Embolization and Improving Therapeutic Delivery During Prostate Artery Embolization (PAE)

Title: Reducing Risk of Nontarget Embolization and Improving Therapeutic Delivery During Prostate Artery Embolization (PAE)

Project Statement:

Prostate artery embolization (PAE) is a procedure increasing exponentially in demand. Lower urinary tract symptoms (LUTS) in the setting of benign prostatic hyperplasia (BPH) are very common; up to 80% of men aged 80 years or older will experience LUTS secondary to BPH in their lifetimes. Given the high demand for therapies, innovations have improved upon traditional treatments. Transurethral resection of the prostate (TURP) represents the “gold standard” for prostate treatment, however, rates of retrograde ejaculation (which can occur in roughly half of patients in some studies) and sexual health impairment remain high. TURP also is effective in prostates up to 80-100 ml. Interestingly, one barrier to understanding its limitation is that measurement of prostate volume is highly inaccurate. From our experience, we find that digital rectal exam or ultrasound (frequently performed in office) underestimates the size of the prostate gland in comparison with prostate magnetic resonance imaging (MRI). Nevertheless, MRI is not part of the routine workup of BPH in the office setting.

Other technologies for BPH tend to be limited by prostate volume. Very few of the latest innovations work in large or very large prostate glands (over 100 ml). The two therapies at this size that remain effective are: PAE and holmium laser enucleation of the prostate (HoLEP). In addition, many men seek treatments that do require a transurethral catheter. At present and to our knowledge, PAE represents the only mainstream therapy for BPH that does not require a transurethral approach and can be performed in an outpatient setting. We typically use a transradial (left wrist) approach and patients go home the same day after procedure with a small bandage on the single access site. In early studies, PAE either had no impact or showed slight trend towards improvement in sexual health; this is a striking finding in comparison with just about every other therapy for BPH.

As a result, demand for PAE has increased significantly. While minimally invasive and performed in an outpatient setting, the procedure remains technically complex (and thus limited to highly skilled centers, like our practice). Challenges include tortuous and highly variable anatomy. The prostate arteries typically are 1-2 mm in diameter and need to be found among several vessels in the pelvis with high variability in anatomy (even from side to side). In our practice, we tend to use advanced imaging technology for navigation and guidance. 

In addition to this level of complexity (e.g., location, origin, and number of prostate arteries on each side), an additional challenge remains: collateralization with other vessels in the pelvis is very high. Complications arise from “nontarget embolization” – we try to deliver millions of small particles (usually 100-300 micromillimeters or 300-500 micromillimeters) to the small vessels in the prostate to “plug up” and stop blood flow. If these small particles travel through collaterals to other organs in high enough numbers, complications can occur. The literature describes events where patients required bladder or rectal surgery, however, fortunately, these remain rare.

The more statistically probable collateral in the prostate bed is collateralization with the pudendal artery. Should small particles travel through these vessels, ulcers on the scrotum or near the tip of the penis can occur. Fortunately, these ulcers often resolve with topical medications but can be extremely uncomfortable for patients while they await resolution of symptoms and, ultimately, improvement in quality of life with their prostate symptoms.

Some have proposed using medications or balloon-occlusion microcatheters to alter flow characteristics, although with mixed success. Few studies actually look at flow dynamic models and actually test an ideal solution’s impact on diversion of that flow. An ideal solution would ensure delivery of embolics (microparticles) to the prostate and prevent flow through collaterals to nontarget areas. 

We believe an ideal solution that consistently and reliably mitigates collateral flow in fluid models would be a game-changer in this space.