Penile ultrasound examination technique request considerable experience and skill and a complete examination usually takes about 30 minutes. The penis is placed across the pubic region and the transducer is applied to the ventral aspect of the shaft of penis. The cavernous arteries are visualized in transverse and sagittal planes, and the inner diameters of these arteries are measured. Other penile structures including the tunica albuginea, cavernoma sinusoidal tissue, corpus spongiosum, and dorsal penile arteries are evaluated for any pathological findings like Pyronines’ disease plaque, secondary deposits, vascular malformation, etc. These abnormalities can be better visualized on ultra- sound examination during the state of full erection.
Pharmacologically induced erection is then produced by intracavernosal injection of post injection continuous evaluation of cavernosal arteries is undertaken up to 20 minutes. The percentage increase in inner diameter is calculated and recorded. Returning to the sagittal plane the cavernosal and dorsal arteries are identified and pulse picked up by placing a cursor over the artery. Colour flow mapping is very helpful in identifying these small vessels. Angle correction if necessary is made. The peak systolic velocity (PSV) and end diastolic velocities (EDV) are recorded at different phases of erection and resistivity index (RI) can be calculated.
Conclusions that could be drawn from this examination are shown in the following list:
Criteria of normal penile vascular status :
Maximum PSV ≥ 30 cm/sec
Minimum EDC ≤ 3 cm/sec
RI ≥ 0.91
Maximum increase if inner diameter of caver – nosal arteries should be at least 75 percent
Maximum PSV 30 cm/sec should be achieved within 10 minutes failing which the diagnosis of borderline arteriopathy is made.
- Reversal of flow in diastole suggests high intracavernosal pressure and suggest good penile rigidity.
- PSV decrease normally with increasing penile rigidity as inteacavernous pressures are close to systemic systolic pressure, thus, compressing the arteries and diminishing the flow.
- If dorsal penile and cavernous arterial velocities are both diminished then we should suspect disease of internal pudendal artery or more proximal vessels. If the dorsal penile arterial velocities are exceeding the cavernous arterial velocities by more than 50 cm/sec, then isolated cavernous arterial disease should be suspected. This could be confirmed with internal pudendal arteriography. A dorsal – to – cavernous arterial bypass could be beneficial here.
- Occasionally we may indentify cavernous arteries with adequate internal diameters (>0.7mm) which does not dilate with blockade.
- Cavernous arteries that dilate adequately with blockade (1- 2mm in diameter) may not always reveal adequate blood flow.
- Corporal survey could reveal Peyronie’s disease plaque, clacification and secondary deposits and these could be accurately measured.
- Very anxious and apprehensive patients tend to have high catecholamine levels in blood producing vaso constriction of cavernosal arteries and, hence, a false diagnosis of arteriopathy could be made in such cases. We routinely use anti – anxiety medication for such patients before subjecting them to this examination.
- Arteriopathy: Severity of arteriopathy is labeled according to normal and abnormal values:
PSV in cm/sec Increase in diameter %
Normal ≥ 30 > 75
Mild arteriopathy 25-30 50-75
Moderate arteriopathy 20-25 25-50
Severe arteriopathy <20 <25
- Veno – occlusive disorder: Persistent high EDV, i.e., > 3cm/sec and low RI < 0.91and poor axial penile rigidity, i.e., 400gm, bucking pressure, and suggestive of veno-occlusive disorder. High flow in subtunical veins and / or site of venous leak into dorsal penile vein may be identified in some cases.
- Mixed arteriogenic and veno – occlusive disorder: This reveals subnormal PSV and persistent abnormally high EDV with low RI and poor penile rigidity. These cases may require dynamic infusion cavernosography and cavernosometry to confirm the diagnosis of veno – occlusive disorder. Intracavernosal injection (papaverine test) with or without visual sexual stimulation appears to be a good screening test but has subjective predominance. It does not give objective evidence and is dependent on several factors. Penile colour Doppler duplex ultrasound scanning forms an objective first line investigation. It gives functional assessment of penile vasculature and differentiates vasculogenic from non vasculogenic causes and also sub – classifies it. In brief, it forms an invaluable adjunct in management of erectile dysfunction.