Doppler sonography of the penile vessels

The penis consists of two corpora cavernosa and a corpus spongiosum that surround the urethra and form the bulb proximally and the glans distally. The smooth muscle of the corpora cavernosa forms endothelial-lined cavities (sinusoids) that communicate with the arterial vascular system of the penis. Both corpora cavernosa are lined by a taut fascial layer called the tunica albuginea (protein coat).

The penis is supplied with blood from two arteries of the same name, which are terminal branches of the internal genital arteries. Behind the root of the bulb of the penis, the artery of the penis divides on each side into the artery of the urethra, the superficial dorsal artery, and the deep artery of the corpus cavernosum. Inside, the deep artery divides into many spiral arteries that open into the cavernous sinusoids. The cavernous bodies are drained by the subthecal venules, which open into the deep dorsal vein of the penis.

Physiology of erection

At rest, the smooth muscles of the corpora cavernosa of the penis are in a state of complete contraction. Peripheral resistance is high, and as a result, moderate arterial blood flow is observed. At the beginning of an erection, the smooth muscles of the corpora cavernosa relax due to a neurotransmitter response, the resistance of the corpora cavernosa decreases, and the feeding arteries dilate. This leads to an increase in arterial blood flow and an increase in the volume of the penis (swelling phase). Since the dense protein coat is slightly elastic, the increase in blood volume compresses the venules between the filled sinusoids and the coat. Venous outflow ceases, and the penis becomes hard.

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Research methodology and normal ultrasound anatomy of the vessels of the penis

The examination is performed with the patient lying on his back using a high-frequency linear transducer. The deep penile arteries are examined in longitudinal and transverse sections from the ventral side of the base of the penis with recording of their Doppler spectra. Measurements are standardized for the basal part of the penis, since as the caliber changes to the distal side, a decrease in peak systolic velocity is noted.

Examination of the vessels of the penis in the pre-injection phase (before intracavernous administration of drugs that cause erection) is not necessary, since the same picture of arterial blood flow is observed both in healthy individuals and in patients with erectile dysfunction.

Peak systolic velocity in the penile arteries at rest is only 5-20 cm/s, combined with high resistance. No antegrade diastolic flow is detected (end diastolic velocity = 0 cm/s). Resistance index = 1. A minimum pulse repetition rate and a wall filter are required to obtain high-quality color images and an adequate spectrum.

An elastic tourniquet is applied to the base of the penis, then a vasoactive drug is injected, causing relaxation of smooth muscles to dilate the sinusoids and arteries. The needle is inserted from the dorsal side of the penis, the drug is injected into the cavernous body on one side, since the presence of anastomoses will allow it to spread in all directions. Prostaglandin E1 (10-20 mg) is preferable to papaverine or a mixture of papaverine and phentolamine, since it reduces the risk of prolonged erection. After the drug is injected and the tourniquet is removed, both deep arteries of the penis are scanned to determine the peak systolic velocity (PSV), end diastolic velocity (EDV) and resistance index (RJ). Post-injection dilation of the arteries and sinusoids leads to an increase in peak systolic velocity to 40 cm/s. Due to a sharp decrease in peripheral resistance, the diastolic blood flow velocity increases to more than 10 cm/s, while the resistance index decreases to 0.7.

As the sinusoids fill, the resistance to blood flow in the penis increases again. As a result, the peak systolic velocity decreases, and the blood flow level still remains significantly higher than in the relaxed state. The diastolic wave approaches the isoline and finally drops below it during diastole, as a symptom of bidirectional blood flow in the deep arteries of the penis. The resistance index increases to 1.0. Peak systolic velocity, end diastolic velocity and resistance index should be re-measured. The study time is about 30 minutes, since the dynamics of blood flow changes can vary significantly in different individuals.

The dorsal arteries of the penis are less important in maintaining erectile function, so scanning them is not necessary. After recording all spectra, ultrasound Dopplerography of the penis is performed to detect anomalies of the arterial vascular bed. At the end of the examination, the patient should be informed that in the case of a pharmacologically induced prolonged erection for 4 hours, a urologist should be consulted to avoid irreversible loss of erectile function.

Arterial erectile dysfunction

Since congenital anomalies of the penile vascular bed can be accurately diagnosed using color mode imaging, the diagnosis of erectile dysfunction is often based on the results of spectral Doppler analysis of the deep penile arteries. In patients with pelvic arterial stenosis, scanning after prostaglandin administration reveals a peak systolic velocity in the swelling phase that is below normal. A peak systolic velocity of less than 25 cm/s in the deep penile arteries is considered peak. Values of 25-35 cm/s are considered borderline. The systolic rise is significantly flattened, and a broadened spectral wave appears. In contrast to the peak systolic velocity, the degree of arterial dilation after pharmacological stimulation is an unsuitable parameter for the assessment of erectile dysfunction and is not part of the standard ultrasound examination.

Due to subjective unpleasant sensations of post-injection examination, subtotal pharmacological erection is often encountered. Before diagnosing erectile dysfunction, the patient is advised to perform self-stimulation for 2-3 minutes while the doctor leaves the office. After which a repeated scanning of the penis vessels and an assessment of the Doppler spectra are performed.

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Venous erectile dysfunction

Signs of venous erectile dysfunction are indirectly revealed by analyzing Doppler spectra recorded from the deep arteries of the penis. Normal compression of the draining veins with an increase in blood volume is manifested by a decrease in direct diastolic blood flow or reverse blood flow in the deep artery of the penis. The resistance index reaches a level above 1.0.

In the presence of venous insufficiency, the increase in intracavernous pressure is significantly reduced and resistance decreases due to constant venous outflow from the cavernous bodies. Persistence of antegrade diastolic blood flow occurs, and the resistance index does not increase more than 1.0.

The detection of venous blood flow in the penis does not always indicate venous insufficiency, since some venous outflow is present even with full erection. It is difficult to determine normal values for end-diastolic velocity and resistance index, since both parameters vary depending on individual characteristics. Recent studies have shown that even the preservation of antegrade end-diastolic velocity in the deep arteries of the penis can be combined with normal venous function. Despite this, the limitation of ultrasound Dopplerography provides important information about venous insufficiency, after which cavernosography and cavernosometry are performed.