Prostatic Artery Embolization: Indications, Preparation, Techniques, Imaging Evaluation, Reporting, and Complications.

Abstract

Benign prostatic hyperplasia (BPH) is a non-cancerous growth of the transitional zone, which surrounds the prostatic urethra. Consequently, it can cause lower urinary tract symptoms (LUTS) and bladder outlet obstruction symptoms, which may significantly reduce patient’s quality of life. There are several treatments of BPH, including medications, such as alpha-blocker and 5α-reductase inhibitors, and surgical options including transurethral resection of the prostate and prostatectomy. Recently, prostatic artery embolization (PAE) has emerged as a minimally invasive treatment option for selected men with BPH and moderate to severe LUTS. An adequate pre- and post-procedure evaluation with clinical exams and questionnaires, laboratory tests, urodynamic and imaging exams, particularly ultrasound, magnetic resonance imaging and computed tomography, are of key importance to achieve a successful treatment. Considering that the use of PAE has been increasing in several tertiary hospital facilities, radiologists and interventional radiologists should be aware of the main technical concepts of PAE and key features to be addressed on imaging reports in both pre- and post-procedure settings.

SUMMARY STATEMENT

The aims of this article are: (a) to review the pathophysiology of benign prostatic hyperplasia, its clinical and anatomical implications, and available treatments; (b) to provide a didactic and illustrative step-by-step explanation of the prostatic artery embolization (PAE) technique, including the importance of knowing prostate vascular anatomy before and during the procedure, and key technical concepts, including the use of Cone-Beam CT and dose reduction strategies; (c) to demonstrate the importance of imaging modalities and their applications in the pre- and post-procedure evaluation; (d) to provide a standardized imaging report before and after PAE; and (e) to show the spectrum of post-procedure complications particularly related to non-target embolization beyond the prostate gland.

Introduction

Benign prostatic hyperplasia (BPH) is a non-cancerous growth of the transitional zone, which surrounds the prostatic urethra (Figure 1). Consequently, it can cause lower urinary tract symptoms (LUTS) and bladder outlet obstruction symptoms, which may significantly reduce patient’s quality of life (1–3). LUTS can be divided into storage (irritative) and voiding (obstructive) symptoms (4).

Figure 1.

Illustration showing the benign prostatic hyperplasia, characterized by a non-neoplastic growth of the transitional zone and its main morphological consequences in the bladder and urethra.

The treatment options of LUTS are divided into drug therapy and surgery. Alpha-blocker therapy is the first-line drug therapy (2–5); and the most common surgical options are transurethral resection of the prostate (TURP) and prostatectomy. Currently, TURP is still considered the gold standard surgical treatment (1, 2); however, several complications can occur, including transurethral resection syndrome, bleeding and irritative urinary symptoms on early postoperative period, and long-term ejaculatory dysfunction (6–8).

Several minimally invasive techniques are now available, such as prostatic artery embolization (PAE), transurethral microwave thermotherapy, interstitial laser thermoablation, transurethral needle ablation and water-induced thermotherapy (9–11). Recently, PAE has emerged as a promising minimally invasive treatment option for selected men with BPH and moderate to severe LUTS. PAE is a safe procedure, that reduces prostate volume, improves clinical symptoms and quality of life of patients with low rates of complications (9, 12, 13).

Multidisciplinary approach with urologists and interventional radiologists is essential to evaluate clinical outcomes, guide medical or surgical therapies, in order to optimize treatment results and to avoid complications (14). The indications of PAE include BPH with refractory LUTS or intolerance to medical treatment, long waiting time for TURP or open surgery, contraindications for surgery or patients who refuse surgery, patients with urinary retention and indwelling Foley catheters, and patients with hematuria originating from prostate gland (3, 15–16). In 2019, the Society of Interventional Radiology published a Multisociety Consensus Position Statement on PAE for Treatment of LUTS Attributed to BPH (17) (Table 1).

Table 1:

Recommendations regarding PAE based on the Society of Interventional Radiology (SIR)

Recommendations Regarding PAE based on the SIR	Level of evidence	Strength of recommendation
1. Acceptable minimally invasive treatment option for appropriately selected men with BPH and moderate to severe LUTS.	B	strong
2. Treatment option in patients with BPH and moderate to severe LUTS who have very large prostate glands (> 80 cm3), without an upper limit of prostate size.	C	moderate
3. Treatment option in patients with BPH and acute or chronic urinary retention in the setting of preserved bladder function as a method of achieving catheter independence.	C	moderate
4. Treatment option in patients with BPH and moderate to severe LUTS who wish to preserve erectile and/or ejaculatory function.	C	weak
5. Treatment option in patients with hematuria of prostatic origin as a method of achieving cessation of bleeding.	D	strong
6. Treatment option in patients with BPH and moderate to severe LUTS who are deemed not to be surgical candidates for any of the following reasons: advanced age, multiple comorbidities, coagulopathy, or inability to stop anticoagulation or antiplatelet therapy.	E	moderate
7. PAE should be included in the individualized patient-centered discussion regarding treatment options for BPH with LUTS.	E	strong
8. Interventional radiologists, given their knowledge of arterial anatomy, advanced microcatheter techniques, and expertise in embolization procedures, are the specialists best suited for the performance of PAE.	E	strong

PAE = Prostate Artery Embolization, SIR = Society of Interventional Radiology, BPH = Benign Prostatic Hyperplasia, LUTS = Lower Urinary Tract Symptoms. Source — Reference 22.

Anatomy Concepts

Prostate gland is the largest accessory sex gland, with weight of 20g in normal adults. It is divided into four histological zones. The transitional zone, which encircles the prostatic urethra, and where BPH develops [1] (1, 18) (Figure 2).

Figure 2.

Illustration showing the prostate gland and its four histological zones.

The prostate has extraperitoneal location and is lined by a thin and firm capsule, which binds to pubic symphysis through puboprostatic ligament. It has several anatomical relationships that are important in the planning of PAE to avoid the possible complications. The prostatic artery may have common origins and anastomoses with feeding arteries of important structures and organs of the male pelvis, making the risk of nontarget embolization a potential issue (NTE) (19) (Figure 3).

Figure 3.

Illustrations showing the anatomical relationships of the prostate and the main structures with risks of nontarget embolization. (A) Bladder. (B) Seminal vesicle. (C) Rectum. (D) Pubic symphysis. (E) Penis.

The evaluation of vascular prostate anatomy is of key importance in the planning of PAE and is critical for PAE success (3, 20–22). Table 2 summarizes the anatomical classification of the origin of the inferior vesical artery [2] (21) (Table 2) (Figure 4).

Table 2:

Angiographic anatomical classification of the origin of the inferior vesical artery (prostatic artery)

Classification	Anatomical Description	Incidence
Type I	IVA originating from anterior division of IIA, in a common trunk with SVA	28.7%
Type II	IVA originating from anterior division of IIA, inferiorly to SVA	14.7%
Type III	IVA originating from obturator artery	18.9%
Type IV	IVA originating from IPA	31.1%
Type V (others)	Less common origins	5.6%

IVA = inferior vesical artery (prostatic artery), IIA = internal iliac artery, SVA - superior vesical artery, IPA - internal pudendal artery. Source — Reference 28.

Figure 4.

Illustrations showing common anatomical variations of inferior vesical artery (IVA) origin (prostatic artery). (A) Type I: IVA originating from anterior division of IIA, in a common trunk with SVA. (B) Type II: IVA originating from anterior division of IIA, inferiorly to SVA. (C) Type III: IVA originating from obturator artery. (D)Type IV: IVA originating from IPA.

Pre-PAE evaluation

The pre-procedure evaluation should exclude conditions that cause bladder outflow obstruction and/or LUTS other than BPH, such as overactive bladder, detrusor and urethral dysfunction, neurologic abnormalities, prostate cancer, prostatitis, bladder cancer, urethral stenosis and urinary tract infection. Additionally, it is important to evaluate the prostate gland and local vascular anatomy.

Physical exam, specific questionnaires, laboratory and urodynamic and imaging exams should all be performed (4, 12, 15). Figure 5 summarizes the pre-PAE evaluation. Imaging options include prostate ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI).

Figure 5.

Flowchart summarizing pre-PAE evaluation.

Prostate ultrasound (US) and US elastography (US-E)

US provides Important information about prostate, kidneys and bladder, such as size, volume, morphology, and post void residual volume (PVR). US can be performed transabdominal or transrectal, the latter being the most accurate form of assessment. When evaluating morphology, the peripheral zone is homogeneous and hyperechoic compared to the transitional zone. Central zone and transitional zone may not be easily distinguished from each other and are described together as the central gland. In older patients, the transitional zone may become more heterogeneous. Prostatic capsule is a thin line between the parenchyma and adjacent fat. The prostate volume when performed suprapubically is more accurate when the volume is greater than 50 mL (23). The use of PVR assesses degree of bladder outlet obstruction (BOO), however it has interobserver variation, so other parameters are used to improve accuracy, such as the residual fraction, calculated as (PVR x 100) / prevoid volume (24).

US-E is a new tool in the pre- and post-PAE evaluation, which provides important anatomical and functional information of BPH. Prostatic elasticity is performed by shear wave velocity (SWV) measurements, with strong correlation between transitional zone elastic modulus (EM) and severity of BOO (25). Mean SWV values of the whole transitional zone, at the middle third of the prostate are obtained. Sample SWV values are obtained using a 0.5 cm² region of interest (ROI) at the right periurethral transitional zone and at the adjacent peripheral zone, and the ratio between them is calculated. Elastography endpoints include SWV (in m/s) and EM, in Kilopascal (kPa) (25) (Figure 6A).

Figure 6.

Pre-PAE (A) and 1-month follow-up (B) transrectal ultrasound elastography demonstrating volumetric reduction of the gland and reduction of prostatic elastic modulus.

Computed Tomography (CT) and CT angiography (CTA)

MRI and US are the most common imaging modalities to evaluate prior to PAE, while CT is sometimes used. CTA may allow for better procedure planning by characterizing the origin of the prostatic artery prior to the procedure. It is also useful in the evaluation of small prostate arteries and may help identify troublesome anastomoses and may detect atherosclerosis, prior to the procedure (Figure 7). Maclean et al. (26) analyzed 110 pre-procedure CTA exams of patients who underwent PAE and identified prostatic arterial supply in 214/220 pelvic sides, with an accuracy of 97.3%. This study also showed a sensitivity of 59.0% and specificity of 94.2% for anastomoses detection. However, there are disadvantages for CTA including limited of prostate parenchymal evaluation, need of intravenous contrast, and radiation exposure. Pre-PAE cone-beam CT (CBCT) is an option that allows for PA identification with less radiation dose compared to conventional CTA (and improved signal-to-noise ratio and contrast-to-noise ratio) (27).

Figure 7.

(A) 3D cinematic rendering CTA image from a left lateral oblique view shows the left prostatic artery (white arrow), which arises from the anterior division of the left internal iliac artery. Also note the enlarged prostate due to BPH (arrowhead). (B) Origin of the left prostatic artery using MIP reconstruction (white arrow).

Magnetic resonance imaging (MRI) and MRI Angiography (MRA)

MRI provides an excellent anatomical assessment of the prostate gland due to its better soft tissue characterization. Pre-procedure measurements such as central gland volume (CG), whole gland volume (WG), prostate zonal volumetry index (ZVi = CG volume / WP volume) [3] and intravesical protrusion of the prostate (IPP) are better evaluated on MRI (28).

Baseline CG and WP volumes as well as ZVi have a strong correlation with clinical outcomes in patients undergoing PAE. Assis et al. (28) compared baseline volumes to clinical outcomes and showed that higher pre-PAE WP and CG volumes had a positive correlation to the degree of clinical improvement after PAE. ZVi also correlated to degree of clinical improvement. The baseline ZVi cut-off calculated for better clinical outcomes was > 0.45, with 85% sensitivity and 75% specificity. Therefore, these measurements are recommended to be included in pre-treatment evaluation in all imaging modalities (Figure 8).

Figure 8.

Axial (A,C) and sagittal (B, D) T2WI demonstrate the whole prostate volume (WP) calculation and the central gland volume (CG) (central zone + transitional zone) calculation on MRI. Prostate dimensions: 6.7 X 4.7 X 5.6 cm. Whole prostate volume (WP): 92 cm³. Central gland volume (CG) (central zone + transitional zone): 45 cm³. ZVi - zonal volumetry index (CG/WP): 0.49

IPP is a parameter obtained by measuring the prostate, from the tip to the base of the gland, on the circumference of the bladder in the sagittal plane (Figure 9). IPP may correlate to the outcomes of several BPH treatment alternatives. Studies have shown that men with bladder outflow obstruction and higher IPP are poorer responders to medical treatment (29–31). In relation to PAE, current studies are still scarce, but some point out that the increased IPP is not a harmful factor for post-PAE results (32, 33). A recent study (34) showed that IPP does not influence the efficacy of PAE.

Figure 9.

Sagittal T2WI demonstrate the intravesical protrusion of the prostate (IPP) index calculation on MRI. IPP - Intravesical protrusion of the prostate: 2.2 mm.

MRI can also identify other causes of patients’ symptoms, particularly prostate cancer.

The use of magnetic resonance angiography (MRA) pre-PAE by combining anatomical and DCE angiographic sequences allows post processing MIP and volume rendering reconstructions. The best sequences for fusion are the volumetric 3D-T2WI with large FOV (anatomical sequence): study aorto-iliac branches (“flow-void”) in the coronal view and high temporal and spatial resolution DCE (angiographic sequence) also in the coronal view with the same field of view (FOV) and angulation of T2WI (Figure 10; Movie 1). This “roadmap” protocol allows to accurately identify prostatic artery origins prior to embolization, potentially reducing the number of DSA acquisitions, and thus the time and radiation dose (35). Table 3 summarizes the MRI parameters used in pre-PAE evaluation. Table 4 contains a proposal MRI report template summarizing key imaging features to be addressed for PAE. Larger versions of the images in the table are shown in Figure 4.

Figure 10.

(A) Volume rendering post processing reconstruction image demonstrating a type IV right prostatic artery (red arrow). (B) DSA as “gold standard” vascular evaluation in the same patient: a type IV right prostatic artery. Left: proximal DSA view of a type IV right prostatic artery (red arrow). Right: distal DSA of the same artery, showing intraprostatic branches (red arrow).

Movie 1.

Download video file ^{(2.4MB, avi)}

Fusion of volumetric T2 and DCE angiographic sequence (with the same FOV and acquisition plane), using MIP reconstructions, allows to identify prostatic artery and its branches.

Table 3:

Pre-PAE MRI parameters used in our institution

Imaging Parameters	Axial T2WI	Sagittal T2WI	Coronal T2WI	AX DWI	Axial LAVA-Flex	LAVA- Flex tardio	DCE
Sequence/ETL	FRFSE/XL	FRFSE/XL	CUBE T2-3D	DWI-EPI	Lava-flex-3D	Lava-flex-3D	Lava-flex-3D
FOV	160	180	320	220	350	350	320
Slice thickness	3	3	2.6	3	4	4	2.6
Matrix	256×256	256×192	288×288	130×80	320×224	320×224	192×160
TR / TE	2500–11000/160	2500–11000/150	2000/Min (100–140)	2000–17000/Min 40–80	Min/Min. Full	Min/Min Full	Min/Min. Full

Note: DCE: dynamic contrast enhanced; Field of view and section thickness are measured in millimetres. ETL = echo train length; FOV = field of view; FRFSE = fast relaxation FSE; TE = echo time; TR = repetition time; TR/TE is measured in milliseconds.

^*Institutional protocol GE 3.0T equipment

Table 4:

MRI report template summarizing the key imaging features to be addressed on pre-PAE scenario

The PErFecTED PAE Technique in 10 Steps

The PErFecTED Technique (Proximal Embolization First, Then Embolize Distal) produces greater prostate ischemia and infarction than previously described methods, as well as better clinical improvement of lower urinary symptoms and lower recurrence rates (3, 36).

For a better understanding of the technique, we divided the procedure into 10 steps and these in two main groups: proximal embolization (Step 1 to 7) (Figures 11, 12, 13, 14) and distal embolization (Step 8 to 10) (Figures 15, 16, 17).

Figure 11.

Step 1: identifying iliac vessels and its branches (anterior trunk of the internal iliac artery). Internal Iliac Artery (IIA).

Figure 12.

Step 2: Selective CBCT of the internal iliac artery anterior trunk and its branches named by PROVISO acronym (iP = internal Pudendal, mR = middle Rectal, Ob = Obturator, VI = Inferior Vesical, S = Superior vesical artery, under Oblique perspective). Branches from the internal iliac artery posterior trunk: il = iliolumbar, ls = lateral sacral, sg = superior gluteal, ig - inferior gluteal. IIA: Internal Iliac Artery.

Figure 13.

PAE steps 3 and 4 IVA = Inferior vesical artery.

Figure 14.

PAE steps 5 and 6.

Figure 15.

PAE steps 8 and 9. Distal intraprostatic embolization to achieve more embolic material delivery and greater tissue ischemia (urethral intraprostatic group of arteries).

Figure 16.

PAE steps 8 and 9. Distal intraprostatic embolization to achieve more embolic material delivered and greater tissue ischemia (capsular intraprostatic group of arteries).

Figure 17.

PAE step 10: true flow stasis must bee seen.

Step 1 –

An initial pelvic angiography can be performed to evaluate the iliac vessels and its branches (anterior trunk of the internal iliac artery) (Figure 11); this step may be skipped based on pre-procedure CT or MRI vascular findings.

Step 2 –

Proximal CBCT: with a catheter placed at the anterior division of the internal iliac artery a CBCT is performed to study its branches (PROVISO acronym), assess the blood supply to the prostate and to catheterize the prostatic artery (PA) under optimal angulation indicated by CBCT-fluoroscopic overlay, which is typically a 40 – 55° ipsilateral oblique view. 45° ipsilateral oblique Digital Subtracted Angiography (DSA) is standardly used in this step instead of, or in additional to CBCT; it was however shown to bring less clinical information than CBCT (37), which we thus recommend as a standard imaging to support PAE planning and navigation into the PA. It is extremely important to identify (to embolize in the next steps) all the PA branches to avoid symptoms recurrence (Figure 12).

Step 3 –

After entering the IVA, vasodilator (nitroglycerine or isosorbide mononitrate) is injected through a microcatheter to prevent vasospasm and to increase artery size to facilitate microcatheter navigation and distal positioning (Figure 13).

Step 4 –

The microcatheter should cross any collateral branch to the bladder, rectum, corpus cavernosum, gonad, or penis and be placed distally in the IVA, before its division in the central gland branch (anteromedial) and peripheral zone branch (posterolateral) (Figure 13). CBCT can also be used at this time to confirm prostate parenchyma perfusion and identify non-target embolization. Alternatively, protective embolization of non-target arteries or a high-flow anastomoses, usually using coils or gelatin sponge, can be performed to redirect blood flow to the prostatic artery and avoid complications.

Step 5 –

At this point, an additional dose of vasodilator is injected to increase the diameter of the intraprostatic arteries so they can receive a greater volume of microspheres (Figure 14).

Step 6 (embolic injection) –

High dilution and very slow injection with 1 mL injection syringe are essential to avoid early occlusion and to obtain diffuse gland parenchymal ischemia. Embolize slowly and reduce fluoroscopy exposure as much as possible [5] (Figure 14).

Step 7 –

When reaching near stasis, a manual injection of contrast is performed with a 3 mL syringe before proceeding to the second moment to observe any collateral shunts. Attention to avoid reflux of embolic agent.

Step 8 –

The microcatheter should be advanced distally into the prostatic parenchyma branches for intraprostatic embolization. The anteromedial branch should be embolized first because BPH occurs mainly in this region (anteromedial and posterolateral branches should be embolized separately) [6]. After moving forward into the intraprostatic branches, a very slow manual injection DSA may demonstrate microvessels, and more embolic material can be delivered (Figures 15 and 16).

Step 9 (embolic injection) –

Embolize slowly and reduce fluoroscopy exposure as much as possible. Collimation of the target area is also very important to reduce staff and patient radiation exposure. The physician must be cautious during injection because extravasation may occur when the microcatheter is wedged into the gland. Using this technique 30–100% additional embolic material can be delivered into the prostate gland (36) (Figures 15 and 16).

Step 10 –

In this final step, true flow stasis must be seen. Then, the microcatheter should be slowly retracted while additional embolic agent is injected to “pack-back” the entire PA until its origin, and a manual contrast injection run DSA in performed for final control as well as to search for additional prostatic branches (Figure 17). This paking-back step is performed with the aim of avoiding earlier recanalization of the main prostatic artery.

All steps must be done in each pelvic side.

Cone-beam CT mentioned above is useful for many reasons. First, it can help to identify the IVA origin, investigate accessory prostatic branches and collateral circulation to avoid non-target embolization; also, it can show the percentage of the prostate that is filled by a specific prostatic artery. Consequently, cone-beam CT improves the procedure safety and efficacy (27, 38) (Figure 18; Movies 2–7).

Figure 18.

MIP (A) and volume rendering (B) Cone-beam CT reconstructions showing the presence of a rectal branch (red arrows), originating from prostatic posterolateral branch (white arrow) confirmed in DSA (C).

Movie 2.

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Intraprocedure Cone-Beam CT angiographic volume rendering reconstruction: can help to identify the origin of the prostatic artery, investigate accessory prostatic branches and collateral circulation to avoid non-target embolization.

Movie 7.

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Post-PAE DSA imaging control shows true flow stasis.

The size of the microspheres is important. It is known that smaller particles have greater distal penetration leading to greater ischemia of the gland, however they have greater risk of non-target embolization (39). One study showed that the combination of different sizes of embolic agents (trisacryl gelatin microspheres, 100–300 um and 300–500 um) could achieve better outcomes when compared with 300–500-um microspheres alone (40). Others compared different particle sizes, however showed that there is no significant difference (41, 42).

Conventional embolization technique as an alternative to PErFecTED technique consists of arterial access of the internal iliac artery, to identify the anterior and posterior branches. The microcatheter is positioned in the PA and angiography is performed to localize the vasculature of prostate and its collateral branches. Embolic material is injected slowly until complete stasis, which is followed with another angiography to identify other feeders which also are embolized (3, 9, 43).

PAE can be performed using either femoral or radial artery access. The safety profile and technical results are similar in both approaches. However, access through the radial artery entails a shorter procedure, thus involving less radiation, lower contrast volume, and a shorter recovery time (44, 45).

Reduction of Radiation Dose

PAE technical complexity can result in long procedure times and high radiation doses for both patients and staff, especially with early experience. Dose reduction measures are currently being investigated. While Schott et al. demonstrated that DSA was responsible for 43.3%, CBCT for 30.3%, and fluoroscopy for 26.4% of Dose Area Product (DAP) during PAE (38), Andrade et al. reported that DSA was responsible for 71.5% of their total DAP [7] (46), and that imaging settings optimization could allow them to reduce staff radiation exposure by up to 83% (47).

While imaging settings and staff’s experience (48) with strict application of ALARA principles are decisive in reducing radiation exposure, imaging workflow optimization and standardization with advanced guidance can also help in reducing contrast load and patients and staff radiation exposure, while making PAE more effective. At our institution, imaging workflow optimization (49), along with routine use of CBCT for PAE planning and of CBCT-fluoroscopic overlay for live 3D augmented navigation guidance (Innova 4100 with Vessel ASSIST, GE Healthcare), showed promising radiation dose reduction. Additional features such as digital zoom, and pulsed fluoroscopy are further opportunities to decrease dose levels.

MR angiography “roadmap” protocol prior to embolization can also help decrease radiation exposure time by providing vascular anatomical information before the PAE procedure (35).

Post-PAE evaluation

Post-PAE imaging analysis is based on interpretation of the findings at US / US elastography and MRI.

US Elastography Post-PAE

There are two main components responsible for the pathophysiology of BPH, the static and the dynamic. PAE showed results in both components. Ischemia caused by the occlusion of the microvasculature leads to coagulation necrosis of the nodules and prostate volume reduction, thus a reduction in the static component of BPH. The dynamic component, represented by the increase in stromal smooth muscle tone (responsible for the increase in stiffness), is also affected by the procedure. The prostatic elasticity is significantly changed, with a demonstrated reduction in the EM measured by US elastrography with sheer wave velocity (2, 25, 50).

This dynamic component is related to activation of alpha-receptors inside the prostate gland and in the bladder neck, which leads to increase in the overall stiffness of the gland, creating a functional obstacle in the prostatic urethra. PAE leads to ischemic necrosis of the tissue in the transition zone, reducing the density of local receptors and the overall prostatic alpha activity (25, 50, 51).

US elastography is a tool for pre- and post-PAE evaluation. A prospective pilot study conducted by Assis et al. showed significant reduction of both transitional zone sheer wave velocity and elastic modules after PAE (−19.0%, P < 0.001 and −29.8%, P = 0.02, respectively), and a reduction of the transition/peripheral zone ratio (- 45.35%, P < 0.05) (25) (Figure 6B).

MRI Post-PAE

Follow-up with MRI plays a key role in identifying PAE success. MRI should be used primarily to assess prostate volume post-PAE, changes in signal intensity and ADC values of infarction and assessment of lesions due to non-target embolization (28, 52–54) (Figure 19 and 20).

Figure 19.

(A) Pre-PAE MRI shows heterogeneous intense enhancement of central gland due to different components of BPH. (B) Post-PAE MRI shows the evolution of the infarction areas (arrows), the so called “Black Holes”.

Figure 20.

Pre-PAE: BPH nodule shows heterogeneous sinal intensity on T2-weighted image (A*), isointense in T1 (B*) and hyperintense sinal in DCE image (C*). Axial images obtained 3 months after PAE shows infartion areas in the central gland in different MRI sequences: predominant hypointensity with some hyperintense foci on T2-weighted image (D), infarcts represented by new areas in the central gland with hyperintensity on T1-weighted image (red arrow in E); typical “black Holes” on DWI sequence (red arrow in F). Red circle represents the whole prostate gland.

Ali et al. demonstrated that after 6 months of follow-up 100% of patients showed a decrease in size of median lobe, 93% decrease whole prostate volume, 100% decrease central gland volume, 33% showed imaging features of infarction, 79% had decrease in T2-signal intensity, and 51% with decrease in enhancement, none of them had infection/inflammation, edema or peri-prostatic fat changes (53).

Frenk et al. demonstrated central gland infarcts in 70.6% of cases post-PAE. MRI features of infarcts include: hyperintensity on T1-weighted images and predominant hypointensity on T2-weighted images which became smaller and isointense to the remaining central gland over time) (52). Zhang et al. evaluated MRI at intervals of 10 days, 1, 3, 6, and 12 months post-PAE and showed that ultrahigh b value DWI can show early infarction better than lower b value DWI (54).

The prostate gland should be systematically and comparatively reviewed with comparison to previous exams and, whenever possible, the imaging findings should be correlated with clinical findings. MRI must include DCE sequences and DWI / ADC maps.

Table 5 demonstrates an MRI report template summarizing the key imaging features to be addressed on post-PAE scenario.

Table 5.

MRI report template summarizing the key imaging features to be addressed on post-PAE scenario.

PAE Outcomes

Embolization of at least one half of the prostate varied from 90 to 98% in almost all published papers. However, the goal of PAE should always be to achieve bilateral embolization, as it presents with better clinical results, higher primary treatment success rates, less recurrence of symptoms and less need for re-embolization (55–57). The clinical success and failure criteria after PAE were established by CIRSE (Cardiovascular and Interventional Radiological Society of Europe) in December 2019 (56). The criteria of symptomatic improvement are defined by an International Prostate Symptom Score (IPSS) < 18 with a decrease of at least 25% and a Quality of life (QoL) score ≤ 3 with at least 1-point decrease compared to baseline. On the other hand, clinical failure of the procedure is defined as the persistence of severe symptoms (IPSS decrease ≤ 25%, IPSS score ≥ 18, QoL score decrease ≤1, and a QoL score ≥ 4), or a decrease in the peak urinary flow.

PAE shows success rates of 78% in 6 months and 75% in 12 months (57). PAE also shows an average reduction in PSA levels by 24% and prostate volume by 20%–30%. However, it is worth mentioning that there is no statistical association between reduction in prostate volume and clinical improvement (56).

In patients with indwelling bladder catheter, PAE has been shown to be effective and safe, especially for patients at high surgical risk. Studies show similar results after the procedure, with catheter removal occurring in up to 86.7% (58) of patients. PAE is effective with refractory hematuria, achieving good results, of up to 92% in 18 months (59) of follow-up.

Carnevale et al. (40) showed only 1.9% early clinical failure and symptom recurrence in 23% men at a median 72 months.. Unilateral PAE was associated with higher recurrence. Baseline PSA was inversely related with recurrence. Embolization with combined microspheres sizes (100–300 μm + 300–500 μm) did not significantly reduce LUTS recurrence. None of the patients presented with urinary incontinence or erectile dysfunction.

Pisco et al. (55) also demonstrated the good results of PAE in patients with BPH. The cumulative clinical success rates at medium-term follow (1–3 years) were 81.9% and long-term follow (> 3 – 6.5 years) were 76.3%. In this study it was also shown that no patient had urinary incontinence or erectile dysfunction.

When comparing PAE with conventional treatment (TURP), we can consider five important aspects as follows (8, 13, 56, 60–62):

• Clinical failure rates between TURP and PAE do not differ significantly.

• Hospital stay time is significantly lower after PAE.

• Adverse events are less frequent after PAE.

• Reduction in IPSS in 3 months is similar.

• The changes in peak urinary flow, post void residual volume, prostate volume and desobstructive effectiveness according to pressure flow studies in 3 months are smaller in PAE.

Another important study (UK-ROPE study) demonstrates the importance of PAE in patient care as a therapeutic alternative between drugs and surgery. The results indicate that the PAE is safe and shows significant clinical improvement, as well as early return to activities due to the shorter hospital stay compared to TURP. Regarding IPSS and quality-of-life (QoL) improvement, however, the study failed to prove non-inferiority of PAE when compared to TURP. Nonetheless, the results of PAE in the UK-ROPE were inferior to what is usually seen in most experienced centers. It also emphasizes the importance of highly qualified interventional radiologists and the use of CBCT as an essential tool for better results (63).

PAE is already an important non-invasive option for the treatment of BPH, with increasingly accurate indications that were revised and reestablished in 2019 (Table 1) (17). Also, the United Kingdom institute responsible for indicating improvements in healthcare, National Institute for Health and Care Excellence (NICE), also advises PAE for properly selected patients in services with well-trained professionals (3).

Overall, PAE scientific evidence is rapidly evolving, as described by SIR in the publication of the Multisociety Consensus Position Statement on PAE for Treatment of LUTS Attributed to BPH (17). In this article, it was observed that the number patients studied increased from 400 in 2014 to 2200 in September 2018 and the follow-up time increased from 3 years to 6.5 years.

PAE Complications

Low rates of adverse events have been reported in PAE. We can divide it into two groups: side effect that refers to any expected, but untoward response; or complications, that refers to any unanticipated negative outcome related to treatment (64). Figure 21 summarizes the adverse events post PAE.

Figure 21.

Flowchart summarizing PAE adverse events.

The systematization of post-PAE adverse events aims to facilitate the identification and management of these changes. Clavien–Dindo grading system (I–IV) for classification of surgical complications can be used for this purpose (58, 65, 66). Moreira et al. suggest a modified Clavien classification adapted to PAE (64) (Table 6).

Table 6:

Clavien-Dindo classification of surgical complications adapted to PAE

Grade	Definition
I	Any unexpected deviation from the normal post-embolization course without the need for additional pharmacological, urologic surgical/endoscopic or radiological procedures.
II	The need for pharmacological treatment with drugs other than those allowed for grade I, as therapeutic use of antibiotics due to infection. Indwelling catheters are used in case of early acute urinary retention. Additional noninvasive tests.
III	The need for pharmacological treatment with drugs used in grade II, as well as surgical/endoscopic or radiological procedures, under or without general anesthesia.
IV	Any deviation from the normal post-embolization course with a life-threatening complication requiring ICU-management due to single or multi-organ dysfunction.
V	Death.
Suffix ‘d’	If the patients suffer from a complication at the time of discharge, the suffix ‘‘d’’ (for ‘disability’) is added to the respective grade of complication. This label indicates the need for a follow-up to fully evaluate the complication.

Source — Reference 63.

One of the concerns with the procedure is the risk of infection, so antibiotic prophylaxis is recommended as a form of prevention (67). Adverse events can also be divided into intraoperative and postoperative. Intraoperative events may be listed as follows: drug or contrast reaction, accidents on vascular access, device failure or incompatibility, failure on catheterization and embolization technique, manufacturing defects or inappropriate use of materials (64, 68). Postoperative events include dysuria (9%), urinary infection (7.6%), macroscopic hematuria (5.6%), hemospermia (0.5%), acute urinary retention (2.5%) and rectal bleeding (2.5%). Most post-PAE adverse effects are classified as type I or II (minor), reaffirming PAE as a safe procedure (64). Routine adoption of CBCT may help improve clinical outcomes and reduce postoperative events. Figures 22, 23, 24, 25, 26, 27, 28, 29 demonstrate case examples of adverse events mostly of them were detected on MRI, which is the main imaging modality indicated in the evaluation of post-PAE complications. Then, in order to deepen the discussion on post-PAE complications, this sub-topic was divided into two main groups: prostate involvement and NTE.

Figure 22.

One year post-PAE pelvic MRI demonstrating a small well defined avascular area in the right prostate central zone (A), DWI (B) and fusion T2-DWI (C) show diffusion restriction in the same area consistent with prostate focal abscess. (Reprinted, under order number: 4832670026330, from Springer Nature).

Figure 23.

Sagittal T2 weighted MRI showing ssignificant volume reduction post PAE, but a “ball-valve effect” of the middle lobe protusion causing a persistant infravesical obstruction (arrow).

Figure 24.

Axial T2 weighted MRI of the prostate before (A) and 12 weeks post PAE (B) showing a prostatic cavity (arrow) in the left central gland and tissue detachment within the bladder (arrowhead in C). Spontaneous prostatic tissue elimination (D).

Figure 25.

Axial T2 weighted post-PAE MRI showing a bladder diverticulum (arrow) caused by bladder wall ischemia (A). Retrospectively analyses of DSA showed a small branch of vesical superior artery (arrowheads) that caused a nontarget embolization (B).

Figure 26.

Axial T2-weighted MRI image demonstrates abnormal low-intensity signal of the right seminal vesicle and medial segment of the left seminal vesicle (dotted line), suggestive of infarction. (Reprinted, under order number: 4832670026330, from Springer Nature).

Figure 27.

Transient ischemic proctitis caused by a nontarget embolization for midle rectal artery. Colonoscopy (A) demonstrating small rectal ulcers due to ischemic proctitis (arrows). After 10 days, a new examination (B) found a local healing process. (Reprinted, under order number: 4832670026330, from Springer Nature).

Figure 28.

Hip MRI post-PAE showing a small asymptomatic infarction zone in left pubis (arrows).

Figure 29.

Ischemia of the penis glans that happened due to inadvertent reflux of embolic agents or misembolization during PAE (which occurs because the dorsal penile arteries are terminal vessels) and its evolution / spontaneous resolution after 40 days. Although rare, penile ischemia is a potentially irreversible complication, as penile arteries are terminal feeding vessels.

The ischemia post-PAE leads to an important inflammatory process in the prostate, causing a series of signs and symptoms (pelvic pain and discomfort, irritative voiding symptoms, ejaculatory pain, fever, nausea and vomiting, among other less common findings) featuring a post-embolization syndrome, which is not a complication, but are considered expected side effects (16, 64, 69). Some treated areas may undergo superinfection including prostatitis, abscess and urosepsis. The treatment may be clinical with antibiotic therapy, but percutaneous drainage and even surgery may be necessary (64, 70–71).

The prostatic urethra, with its arterial branches, may be affected by embolic agents and leads to ischemia, and pelvic pain however low risk for strictures (64, 72).

Non-target embolization of bladder can result in ischemic areas and even perforation. Small areas are treated with antibiotics and Foley catheter. There are no reports of patients with urinary incontinence in the follow-up of post-PAE patients (40, 55).

The rectum can be uncommonly affected by non-target embolization and results in ischemic proctitis. Patients may complain of low abdominal pain, diarrhea that may include bloody discharge and even fistulas and abscesses. In more severe cases, colonoscopy or proctoscopy may be necessary. So far, there are no reports with serious conditions that required surgical approach (19, 64, 73).

Penile ischemia can occur due to reflux of embolic agents into the dorsal penile arteries. There are no reports of irreversible injuries or post-PAE erectile dysfunction to date in the literature. It is important to note that erythematous areas on the glans may also be superinfected. Color Doppler US and culture are important in diagnosis and proper management, which includes antibiotics (55, 64).

The seminal vesicle can rarely be affected by non-target embolization, but the true incidence is not known. The patient may experience pain in the perineal region, hematospermia, reduced semen volume, pain during ejaculation and irritative or obstructive urinary symptoms (57, 64).

Bone structures, nerves and skin can also be affected, but these are rare events (64).

To prevent NTE, adequate training of the technique and the proper study of vascular anatomy pre-procedure and during the procedure, as well as the use of collateral branch protection techniques, are essential for the safety and effectiveness of procedure (26, 64, 74).

Table 7 contains some important tips to avoid pitfalls in PAE.

Table 7:

Tips to avoid pitfalls.

Check List	How to do it right
I	Multidisciplinary team work and adequate PAE procedure patient selection.
II	Prompt investigation of contraindications and treat pre procedure urinary tract infection if needed.
III	Customized pre-procedure preparation including: symptomatic medications and prophylactic antibiotics.
IV	Take time and resources ( CTA, MRA, CBCT ) to adequate study prostate vascular anatomy: knowing classification type and anatomical variations are mandatory for a safe and effective PAE.
V	Technical skills and IR training: know all PAE steps and technique.
VI	Avoid NTE. Use protective embolization techniques or anti reflux microcatheters devices, mainly to protect high-flow anastomoses or reflux to non-target vessels. We strongly recommend using CBTC either to differentiate prostatic from non-target branches, as to confirm that the whole prostatic lobe has been broadly embolized.
VII	Search for alternatives to reduce radiation exposure: specific pre-PAE imaging protocols, wise use of DSA, collimation, pulsed fluoroscopy, road map software, CBCT.
VIII	Urinary retention during immediate PAE follow-up must be actively managed by Foley urinary catheter placement. Patients should be discharged 3 to 6 hours after PAE. Hemostatic devices can be used to reduce hospital stay.
IX	Be prepared for post procedure care: clinical and imaging follow-up for an active search for complications in prostate gland or NTE.
X	Management of post-embolization syndrome is paramount for the well-being and patient care. During the first one to two weeks, patients will also receive proton-pump inhibitors, anti-emetics, nonopioid analgesics and nonsteroidal anti-inflammatories, opioids and steroidal anti-inflammatory drugs may also be used whenever necessary. Prophylactic antibiotics are mandatory for at least 7 days.

Follow-up

The follow-up proposal is based on clinical and imaging aspects. The clinical follow-up appointments include the application of the following questionnaires: IPSS, International Index of Erectile Function (IIEF) and quality of life Questionnaire. We suggest clinical and imaging assessment using ultrasound and MRI at 3 and 12 months after PAE, and yearly thereafter [10] (14, 54, 75).

Conclusion

BPH is a major health problem worldwide that has a major impact on men’s quality of life. PAE has emerged as a minimally invasive and highly effective treatment option for selected men with BPH and moderate to severe symptoms. An adequate pre- and post-procedure evaluation, as well as PAE technique standardization, is of key importance to achieve a successful treatment. With the use of PAE increasing in many tertiary hospital facilities, radiologists and interventional radiologists should be aware of the main technical concepts of PAE to comprehend the key features to be addressed on imaging reports.

In the near future, an increase in the availability of the procedure in more intervention centers and countries is expected. It is also expected to define better selection criteria for PAE candidates, new randomized trials comparing PAE and other procedures, validation of outcome biomarkers for prediction of success or treatment failure and, consequently, greater acceptability by the urological community.

Movie 3.

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DSA video shows a rectal branch originating from the IVA.

Movie 4.

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CBCT video shows a rectal branch originating from the IVA, with lower rectum contrast enhancement.

Movie 5.

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Catheterization of the undisered branch with coil inserction, to avoid NTE.

Movie 6.

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DSA imaging control after coil inserction.