Priapism is a term for a penile erection that occurs longer than desired. It may occur for multiple reasons, and the role of imaging in priapism is to distinguish between ischemic low-flow priapism (95%) and non-ischemic high-flow priapism (5%).
Ultrasound is a useful imaging modality for initial evaluation and distinguishing between the two entities. MRI may be used for problem-solving on occasion.
Priapism is a prolonged erection, not related to sexual stimulation, typically lasting >4 hours.
Clinically, priapism can be differentiated into ischemic, nonischemic, and episodic/"stuttering". Ischemic or "veno-occlusive" priapism is typically associated with a low-flow priapism. Non-ischemic, "high-flow" priapism is associated with penile or perineal trauma.
Pain is more typically associated with the increased pressure and possible tissue ischemia of ischemic low-flow priapism, than with non-ischemic high-flow priapism
Sickle cell disease and thrombophilias are associated with low-flow priapism due to the risk of thrombosis. Ischemic low-flow priapism is also associated with intracavernosal injection of medication (both prescribed and recreational).
Colour and spectral Doppler ultrasound can help distinguish between etiologies that may cause a high-flow priapism from a low-flow priapism:
- low-flow priapism (typically ischemic)
- thrombosis of the corpora cavernosa or corpus spongiosum
- decreased/absent colour flow or spectral Doppler in the cavernosa
- there may be flow in the superficial penile vein
- increased RI of the penile artery
- high-flow priapism (typically non-ischemic)
- an arteriovenous fistula may be visualised
- penile artery Doppler velocities are typically normal or elevated
A high-frequency transducer (>7 MHz) should be used.
MRI is not indicated for emergent evaluation of low-flow priapism due to the time it takes for the scan. It may be used in the non-emergent setting for problem-solving.
- T1: abnormally increased signal in the penile corpora may indicate thrombus
- T2: flow voids in the cavernosa may be present in high-flow priapism
T1 C+ (Gd):
- post contrast evaluation may be useful for pre-treatment planning of high-flow priapism
- asymmetric cavernosal enhancement may occur with either type of priapism
MRI may be more likely to see associated conditions that may lead to priapism (e.g. malignancy).
Treatment and prognosis
If untreated, priapism can lead to permanent damage with potential erectile dysfunction, and ischemic priapism is a surgical emergency.
Treatments include irrigation with sympathomimetics and surgical shunts. Penile prosthesis implantation is a last resort.
History and etymology
The term "priapism" derives from a rural Greek fertility god called "Priapus," who sported a permanent erection.
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