Penile Duplex Ultrasound: Technique, Waveforms, and Erectile Dysfunction Evaluation

Penile duplex ultrasound with pharmacostimulation is the primary vascular imaging study for erectile dysfunction (ED). It directly assesses cavernosal artery blood flow before and after intracavernosal injection of a vasoactive agent, allowing classification of ED as arteriogenic, venogenic, or mixed. This is a specialized study typically performed by experienced vascular sonographers.

Anatomy

Two corpora cavernosa: The paired erectile bodies running the length of the penile shaft, separated by the midline septum.

Corpus spongiosum: Ventral, surrounds the urethra.

Cavernosal arteries: One within each corpus cavernosum, running centrally. These are the vessels interrogated in penile duplex.

Helicine arteries: Branch off cavernosal arteries → dilate during erection to fill the lacunar spaces.

Venous drainage: Via emissary veins → dorsal vein → pudendal veins. During erection, venous outflow is restricted by tunica albuginea compression against the sinusoids (veno-occlusive mechanism).

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Why Penile Duplex?

Differentiates two types of vasculogenic ED:

1. Arteriogenic: Insufficient arterial inflow — peak systolic velocity (PSV) < 25 cm/s
2. Venogenic (veno-occlusive dysfunction): Normal arterial inflow but failure of venous restriction — normal PSV with persistent end-diastolic velocity (EDV) > 5 cm/s

Knowing which mechanism is involved guides treatment: PDE5 inhibitors, penile revascularization (rare), penile prosthesis implantation.

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Pharmacostimulation

The study cannot be done without inducing a pharmacologic erection. Cavernosal arteries are in a high-resistance, low-flow state at baseline. After intracavernosal injection, they dilate and peak systolic flow increases dramatically.

Agent: Alprostadil (prostaglandin E1) — most common. Dose varies (5–20 mcg). Some labs use a trimix (papaverine + phentolamine + alprostadil).

Who injects: A physician or trained provider (urologist, radiologist, or delegated per institutional protocol). You may take post-injection Doppler measurements. Know your institution's protocol.

Timing: Measurements are taken at specific intervals post-injection:

• 5 minutes: Tumescence beginning
• 10 minutes: Peak response expected
• 20–25 minutes: Final assessment

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Technique

Probe

High-frequency linear transducer: 9–15 MHz.

Patient Position

Supine, penis stretched and placed on the lower abdomen against the ventral surface, tip pointing toward the umbilicus. This standardizes the scanning approach.

Baseline (Pre-Injection)

1. Transverse survey of both corpora cavernosa — identify both cavernosal arteries (small, round pulsatile structures centrally within each corpus)
2. Long-axis view of each cavernosal artery
3. Color Doppler to confirm vessel identification
4. Spectral Doppler baseline (usually low-amplitude, high-resistance waveform)

Post-Injection Measurements

After injection and at each interval:

Spectral Doppler of each cavernosal artery:

• Angle of insonation: ≤ 60°, preferably 45°–60° for cavernosal arteries
• Measure: PSV, EDV, RI = (PSV − EDV) / PSV

Also measure: Cavernosal artery diameter before and after injection — normal dilation is > 75% or > 0.7 mm increase.

Both sides: Always measure both cavernosal arteries. Asymmetric PSV (< 70% of contralateral) suggests unilateral disease.

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Normal and Abnormal Values

Peak Systolic Velocity (PSV)

PSV	Interpretation
≥ 25 cm/s	Normal arteriogenic response
20–25 cm/s	Borderline — may be adequate; correlate clinically
< 20 cm/s	Arteriogenic ED — insufficient inflow
< 25 cm/s with poor erection	Arteriogenic component likely

Some references use ≥ 30 cm/s as the robust normal threshold.

End-Diastolic Velocity (EDV) and RI

The EDV reflects venous outflow. As erection develops and the veno-occlusive mechanism engages, EDV should fall toward zero (or reverse slightly) with good erection.

EDV	Interpretation
≤ 0–5 cm/s at full tumescence	Normal veno-occlusion
> 5 cm/s at full tumescence	Venogenic ED — persistent outflow; veno-occlusion fails

Resistive index at full erection: Should approach 1.0 (near-zero EDV, high resistance as the veno-occlusive mechanism maximally restricts outflow).

Summary of Patterns

PSV	EDV	Interpretation
≥ 25 cm/s	< 5 cm/s	Normal vascular function
≥ 25 cm/s	> 5 cm/s	Venogenic ED
< 25 cm/s	Any	Arteriogenic ED
< 25 cm/s	> 5 cm/s	Mixed arteriogenic + venogenic

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Cavernosal Artery Diameter

Measure in transverse before and after injection:

• Normal baseline: ~0.3–0.5 mm
• Post-injection: should dilate ≥ 75% or ≥ 0.7 mm increase
• Poor dilation: suggests smooth muscle dysfunction or fibrosis (Peyronie's)

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Peyronie's Disease

Peyronie's disease is fibrosis of the tunica albuginea causing penile curvature and painful erections. Often evaluated concurrently.

Sonographic findings:

• Echogenic plaques within or on the tunica albuginea — focal thickening
• Calcification within plaques (posterior shadowing)
• Located at the site of maximal curvature
• Document: number, size, location (dorsal, ventral, lateral)

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Priapism (Urgent Indication)

Priapism (prolonged erection ≥ 4 hours) may require urgent evaluation.

Ischemic (low-flow) priapism:

• Most common (90%)
• Medical emergency — compartment syndrome of the penis
• Doppler: absent or very low cavernosal artery flow — the engorged, ischemic corpora prevent arterial entry
• Requires aspiration ± irrigation ± sympathomimetic injection; surgical shunt if refractory

Non-ischemic (high-flow) priapism:

• Post-traumatic arteriovenous fistula (perineal or penile trauma)
• Doppler: turbulent, high-velocity arterial flow within the corpora (fistula feeding the priapism)
• Color Doppler: chaotic, disorganized color signal at the fistula site

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Key Images

1. Transverse bilateral corpora cavernosa — baseline
2. Long-axis cavernosal artery × 2 sides — baseline spectral
3. Post-injection at 5, 10, 20 minutes: spectral Doppler both sides with measurements
4. Cavernosal artery diameter pre and post injection
5. Peyronie's plaques if present — location, size, calcification
6. Color Doppler of any fistula (if priapism evaluation)

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Reporting Language

Normal: "Following intracavernosal alprostadil injection, bilateral cavernosal arteries demonstrate adequate response. Peak systolic velocity: right 38 cm/s, left 34 cm/s (both ≥ 25 cm/s). At maximal tumescence, end-diastolic velocity is ≤ 3 cm/s bilaterally, indicating intact veno-occlusive mechanism. No plaques or calcification. Normal penile vascular response — arteriogenic and venogenic ED excluded."

Arteriogenic ED: "Peak systolic velocity: right 14 cm/s, left 18 cm/s (both < 25 cm/s despite pharmacostimulation). Limited cavernosal artery dilation. End-diastolic velocity appropriate. Findings are consistent with arteriogenic erectile dysfunction. Venogenic dysfunction cannot be assessed in the setting of inadequate arterial response."

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SonoBuddy's vascular protocols include penile duplex, renal artery stenosis, and peripheral arterial studies.