Priapism

Dr Craig Hacking and Dr Matt A. Morgan et al.

Priapism is a prolonged erection, after or not related to sexual stimulation, lasting >4 hours. The role of imaging in priapism is to distinguish between ischemic low-flow priapism (95%) and non-ischemic high-flow priapism (5%). 

Ultrasound is useful as a first line modality, complemented by arterial blood gasses. Angiography and MRI may be used for problem-solving on occasion.

Clinically, priapism can be differentiated into three types, based on symptoms and arterial blood gases 6:

  1. ischemic, veno-occlusive or low-flow priapism
    • an emergency and by far the most common form and primarily due to failure of detumescence
    • associated with sickle cell disease and thrombophilias due to the risk of thrombosis, and also associated with intracavernosal injection of medication (both prescribed and recreational)
    • clinically the penis is rigid and painful
    • cavernosal blood gases are hypoxic, hypercarbic, and acidotic
    • there is low or no cavernous arterial blood flow
  2. nonischaemic or high-flow priapism
    • associated with penile or perineal trauma and is due to unregulated cavernous arterial inflow such as that due to an arteriocavernous fistula
    • clinically the penis may be either rigid or not fully rigid
    • typically not painful
    • cavernosal blood gases are not hypoxic or acidotic
  3. stuttering or episodic priapism
    • defined by the American Urological Assocition as a "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

A high-frequency transducer (>7 MHz) should be used.

Color and spectral Doppler ultrasound is usually most helpful in distinguishing a high-flow priapism from a low-flow priapism:

  • low-flow priapism (typically ischemic)
    • thrombosis of the corpora cavernosa or corpus spongiosum
    • decreased/absent color flow or spectral Doppler in the cavernosal artery/arteries
      • cavernosal artery velocity <25 cm/s would be considered low velocity, but low velocity flow is technically nonspecific
        • patients with low but present cavernosal arterial flow tend to require arterial blood gas evaluation
      • increased resistive index of the cavernosal artery
        • this can also be seen with a normal erection
    • there may be flow in the superficial penile vein
  • high-flow priapism (typically non-ischemic)
    • an arteriovenous fistula may be visualized
    • penile artery Doppler velocities are typically normal (>25 cm/s) or elevated

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).

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 corpora cavernosa with either a biopsy needle or scalpel respectively, to allow drainage into the glans

Penile prosthesis implantation is a last resort.

The term "priapism" derives from a rural Greek fertility god called "Priapus," who sported a permanent erection.

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Cases and figures

  • Color Doppler ima...
    Case 1: low-flow priaprism
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  • Case 2: high-flow priaprism
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