Erectile dysfunction is a common condition. Doppler ultrasound is a highly accurate means of assessing patients with erectile dysfunction.
Psychological factors (mental impulse) cause transmission of parasympathetic impulses to the penis. This causes relaxation of arterioles and corpora cavernosa sinusoids. As the sinusoidal spaces start filling, the corporal veno-occlusive mechanism activates, and the fibrous tunica albuginea compresses the emissary veins of the corpora, and rigid erection is achieved.
Penile erection is a result of a complex interaction between the nervous, arterial, venous and sinusoidal systems. Any defect in one of these components can lead to erectile dysfunction.
- psychogenic (~10%)
- endocrine disorders
- arteriogenic impotence (~30%)
- venogenic impotence (~15%)
- penile venous insufficiency
- combined arteriogenic and venogenic (~10%)
- morphological penile abnormalities
- ACE inhibitors
- excessive alcohol and smoking
Penile Doppler procedure
The procedure should be explained in detail prior to the examination. It is advisable to stop smoking three days prior to the examination. Medication history and cardiac status should be enquired.
A high-frequency transducer (7.5-9.0 MHz) is used for penile Doppler examination. The patient is placed in a supine position and the penis is positioned in its anatomical position along the anterior abdominal wall. Doppler angle is set at 30-60 degrees.
60 mg of papaverine (2 mL ampoule of 30 mg/mL) is injected intracavernosally. 10-15 micrograms of prostaglandin E1 (PGE1), also known as alprostadil, can also be injected. A combination of papaverine and phentolamine may also be used.
Corpora cavernosa are localized as two well-defined oval compartments with central cavernosal artery on both sides of the corpus spongiosum (urethra is in center of corpus spongiosum). Insulin syringe is used for injection under sonographic guidance.
Post-injection measurements (at 5, 10, 15, 20 minutes): inner diameter of cavernosal artery (normal value is 0.6-1.0 mm), peak systolic velocity, end-diastolic velocity, visual tumescence and erection.
Assessment of erection following papaverine injection
- phase 1: sudden increase in both systolic and diastolic flow velocity in cavernosal artery with minimal tumescence
- phase 2: with further increase in intracavernosal pressure, there is a decrease in diastolic flow with a classical 'dicrotic' notch
- phase 3: as the intracavernosal pressure increases, diastolic flow reaches zero with further increase in tumescence
- phase 4: diastolic flow reversal occurs with maximum systolic velocity; this is associated with penile rigidity
- phase 5: decrease in the systolic flow velocity occurs; this is usually 15 minutes post-injection which is associated with a reduction in tumescence and rigidity
In the flaccid state, monophasic flow is seen with absent/minimal diastolic flow. With onset of erection, systolic and diastolic flow both increases. With further increase in pressure, 'dicrotic notch' appears with dip in diastolic flow. End-diastolic flow may go down to zero or reversal may be seen. Then monophasic flow is seen with sharp systolic peak, corresponding with visual full erection.
Peak systolic velocity is the best Doppler indicator of arteriogenic impotence. Its value <30 cm/sec during the examination indicates arterial dysfunction. Some people consider <25 cm/sec as definite arterial dysfunction and 25-30 cm/sec as borderline case. Less than 60% increase in cavernosal diameter after papaverine injection is also an indicator of arterial impotence.
End-diastolic velocity is the best Doppler indicator of venogenic impotence. Its value >5 cm/sec indicates venous dysfunction. A good diastolic reversal virtually rules out venous insufficiency.
Angiography with selective internal iliac angiography is the gold standard for arteriogenic impotence. However, it is invasive and not recommended for screening or primary diagnosis.
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