Priapism is the clinical term for a persistent and prolonged erection that occurs without sexual excitement or continues well after sexual stimulation has ended. This condition is an involuntary and often painful occurrence resulting from a malfunction in the normal blood flow mechanism of the penis. It represents a serious medical situation because a sustained erection can deprive the penile tissue of oxygen, leading to potential permanent damage.
Defining Priapism and Recognizing Urgency
Priapism is formally defined as an erection lasting longer than four hours that is not related to sexual arousal. The persistence of this state signals a disruption in the physiological processes that regulate blood flow into and out of the erectile tissues. The “four-hour rule” is the definitive marker for seeking urgent medical care, and anyone experiencing an erection lasting this long must go to an emergency department immediately. Prolonged priapism can lead to a condition similar to compartment syndrome, where pressure from trapped blood cuts off the oxygen supply to the smooth muscle tissue within the penis. This oxygen deprivation, known as ischemia, can cause extensive tissue death and scarring if not resolved quickly.
Distinguishing Ischemic vs. Non-Ischemic
Priapism is classified into two main types based on the mechanism of blood flow: ischemic (low-flow) and non-ischemic (high-flow). Ischemic priapism accounts for the vast majority of cases, representing over 95% of episodes, and is the true emergency that requires immediate intervention. Ischemic priapism occurs when blood becomes trapped in the corpora cavernosa—the two main erectile chambers—and is unable to drain properly, causing a state of venous occlusion. This trapped blood is deoxygenated, leading to tissue hypoxia, acidosis, and pain that typically worsens as the duration of the erection increases. This lack of oxygen causes the most damage, putting the patient at high risk for corporal fibrosis and subsequent permanent erectile dysfunction.
Non-ischemic priapism, by contrast, is rarer and is caused by an unregulated, high flow of arterial blood entering the penis. This high flow is often the result of trauma to the perineum or penis that creates a fistula, or an abnormal connection, between an artery and the erectile tissue. While this type of priapism can be persistent, the blood flow is still oxygenated, meaning it does not lead to the immediate tissue death seen in the ischemic form. Non-ischemic priapism is usually less painful and the penis may be only partially rigid, differentiating it clinically from the rigid, intensely painful nature of the ischemic type.
Common Underlying Causes and Triggers
Hematological disorders are a major cause, with sickle cell disease being the most common trigger in children and a frequent cause in adults. The abnormally shaped red blood cells in sickle cell disease can mechanically obstruct the small veins responsible for draining blood from the penis, leading directly to low-flow priapism. Medications also play a substantial role, particularly those that affect the smooth muscle relaxation necessary for erection. Specific classes of drugs implicated include certain antidepressants, especially trazodone, and antipsychotic medications. Alpha-adrenergic blockers, which are sometimes used to treat high blood pressure or prostate enlargement, can also lead to priapism.
Another significant trigger is the misuse or complication of injection therapy for erectile dysfunction, where vasoactive agents are administered directly into the penis. Trauma to the perineum—the area between the anus and the scrotum—or direct injury to the penis is the most common cause of the high-flow, non-ischemic type of priapism. This blunt force can damage a cavernosal artery, creating the arterial-lacunar fistula that causes uncontrolled blood inflow. Neurological conditions, such as spinal cord injury, can also disrupt the nerve signals that regulate blood flow.
Medical Intervention and Treatment Strategies
Emergency medical management focuses on resolving the erection to prevent irreversible tissue damage, with the approach tailored to the type of priapism diagnosed. For the urgent low-flow (ischemic) priapism, the initial treatment involves a minimally invasive procedure called aspiration. This procedure involves inserting a needle into the side of the penis to drain the trapped, deoxygenated blood from the corpora cavernosa. If aspiration alone does not resolve the erection, the next step is the intracavernosal injection of a sympathomimetic agent, most commonly phenylephrine. This medication is an alpha-agonist that works by constricting the blood vessels, forcing the blood to drain from the erectile tissue.
Phenylephrine is administered in small, monitored doses, with continuous monitoring of heart rate and blood pressure due to its potential cardiovascular effects. Should these initial, less invasive methods fail, typically after 60 to 90 minutes, surgical intervention is required to create a shunt. A shunt procedure creates a new pathway between the erectile tissue and the veins, allowing the trapped blood to bypass the blockage and drain from the penis. Distal shunts are a common type of procedure used to restore circulation.
High-flow (non-ischemic) priapism, which is less time-sensitive, may initially be managed with observation, as a majority of cases can resolve spontaneously. If intervention is necessary, the primary treatment is selective arterial embolization, a specialized procedure that uses imaging to block the specific damaged artery causing the excessive blood flow.