Diagnosis of ED: Second Level

Second level diagnostic evaluation uses specialistic instrumental exams that can be helpful for accurate aetiological diagnosis of ED.

Penile dynamic colour-duplex Doppler ultrasonography allows direct visualization of penile vessels and evaluation of possible strictures and dysfunctions. Using Doppler methodology urologists are able to study both arterial and venous flow velocity, assessing erectile haemodynamics as a whole. This exam is performed after injection of alprostadil (PGE 1 ) 10 or 20 mg in order to induce erection and reduce false positive; some authors reported that oral administration of sildenafil seems to be as effective than PGE1 in inducing erection, but less invasive and more capable of reducing false positive venous leakage diagnosis. If full rigidity is not obtained after a period of privacy and self-stimulation, a second injection (alprostadil 10 mg plus phentolamine 1-2 mg) should be performed in order to achieve the best erection and get over anxiety-induced failures.

Ultrasonoghrapy is performed 5-10 minutes after injection, using high-frequency linear transducers (7.5-13 MHz). When it's possible, Power Doppler technique should be used because of better definition of vascular details and less dependence on transducer position.

During exam, parameters which could be mainly considered are the Peak Systolic Velocity (PSV), the End Diastolic Velocity (EDV) and the Resistance Index (RI= (PSV-EDV)/PSV); the last one can predict venous leak probability in patients suffering ED.

Dynamic ultrasonography also allows to value anatomical aspects of penile circulation (for example strictures, high-speed jets, duplication of the cavernosal artery, cross-communications between the two cavernosal arteries, etc.) and corpora cavernosa, especially after vasoactive drugs injection.

Men with normal erectile function present a PSV value > 30 cm/s and an EDV value < 5 cm/s and the RI always > 0.85. As the PSV decreases with ageing, the PSV cut-off value should be calculated as following in order to increase test predictivity: PSV = 6.73 + (0.7 * age).

Patients showing normal PSV value and complete erectile response can be considered as normal subjects; patients showing low PSV value but normal erection probably suffer arterial insufficiency, offset by effective veno-occlusive system (RI > 0.85).

In patients showing normal PSV value associated with incomplete erectile response and RI value under 0.85, a probable veno-occlusive mechanism alteration should be considered as cause of erectile dysfunction. Nevertheless, penile dynamic colour-duplex Doppler ultrasonography is not sufficient to make diagnosis of venous leak because of its low specificity due to incomplete rigidity of corpora cavernosa and persistence of diastolic flow. In order to formulate a correct diagnosis of venous leak gold standard remain the cavernosometry/cavernosography.

Role of penile Doppler ultrasonography has been discussed because it provides operator dependent information and, considering currently available therapy for ED (especially PDE5-inhibitors), rarely alters following patient management.