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%). In most cases only the corpora cavernosa are affected.
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, after or not related to sexual stimulation, lasting >4 hours.
Clinically, priapism can be differentiated 3 types based on symptoms, blood gases and treatment 6:
- Ischemic, veno-occlusive or low-flow priapism is by far the most common form and primarily due to failure of detumescence. Clinically the penis is rigid and painful. Cavernosal blood gases are hypoxic, hypercarbic, and acidotic. There is little or no cavernous blood flow. It is an emergency.
- Nonischemic or high-flow priapism is associated with penile or perineal trauma. It is due to unregulated cavernous arterial inflow. Clinically the penis is not fully rigid nor painful. Cavernosal blood gases are not hypoxic or acidotic. It is not an emergency.
- Stuttering or episodic priapism is defined by the American Urological Assocition as "recurrent form of ischemic priapism in which unwanted painful erections occur repeatedly with intervening periods of detumescence" 6.
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. Surgical shunting is considered after failure of intracavernosal sympathomimetics and can be performed proximally or distally:
- Proximal shunting involves either an incision of the tunica of the corpora in the base of the penis (corporospongisal) or placement of graft bypass shunting corporal blood to a nearby vein (corpora-saphaneous).
- Distal shunting (cavernoglanular) involves removal or incision of the tunica of the distal tips of the corposa cavernosa with either a biopsy needle or scalpel respectively, to allow drainage into the glans.
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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