Introduction
Background
Priapism is defined as an abnormal persistent erection of the penis. It is an involuntary prolonged erection unrelated to sexual stimulation and unrelieved by ejaculation. As with many medical emergencies, the saying "time is tissue" holds true for priapism. This condition is a true urologic emergency, and early intervention allows the best chance for functional recovery.
Pathophysiology
The penis is composed of 3 corporeal bodies: 2 corpora cavernosa and 1 corpus spongiosum. Erection is the result of smooth-muscle relaxation and increased arterial flow into the corpora cavernosa, causing engorgement and rigidity (see Image 1).
Engorgement of the corpora cavernosa compresses the venous outflow tracts (ie, subtunical venules), trapping blood within the corpora cavernosa. The major neurotransmitter that controls erection is nitric oxide, which is secreted by the endothelium that lines the corpora cavernosa (see Image 2). These events occur in both normal and pathologic erections. The pathophysiology of priapism involves failure of detumescence and is the result of the underregulation of arterial inflow (ie, high flow) or, more commonly, the failure of venous outflow (ie, low flow). Priapism typically involves engorgement of corpora cavernosa. The corpus spongiosum is typically not engorged.
Priapism must be defined as either a low-flow (ischemic) or a high-flow (nonischemic) type because the causes and treatments for these 2 types are different. Low-flow priapism, which is by far the most common type, is a failure of the detumescence mechanism due to (1) an excessive release of neurotransmitters, (2) blockage of draining venules (eg, mechanical interference in sickle cell crisis, leukemia, or excessive use of intravenous parenteral lipids), (3) paralysis of the intrinsic detumescence mechanism, or (4) prolonged relaxation of the intracavernous smooth muscles (most often caused by the use of exogenous smooth-muscle relaxants such as injectable intracavernosal prostaglandin E1).
Prolonged low-flow priapism leads to a painful ischemic state, which can cause fibrosis of the corporeal smooth muscle and cavernosal artery thrombosis. The degree of ischemia is a function of the number of emissary veins and the duration of occlusion. Light-microscopy studies conducted early on demonstrated that corporeal tissue becomes thickened, edematous, and fibrotic after days of priapism. Further studies with electron microscopy have demonstrated trabecular interstitial edema after 12 hours of priapism and destruction of sinusoidal endothelium, exposure of the basement membrane, and thrombocyte adherence after 24 hours of priapism. At 48 hours, thrombi in the sinusoidal spaces and smooth-muscle cell histopathologic findings varied from necrosis to fibroblastlike cell transformation. Priapism for longer than 24 hours is associated with the likelihood of permanent impotence.
High-flow priapism, in contrast, is the result of uncontrolled arterial inflow from a fistula between the cavernosal artery and the corpus cavernosum. This is generally secondary to blunt or penetrating injury to the penis or perineum. Differentiation between these 2 types of priapism is accomplished by taking a thorough history, performing a careful physical examination, and measuring the oxygen content of blood within the corpora cavernosa by penile blood gas (PBG) analysis (see Workup). The presence of bright red blood during aspiration is a helpful but not pathognomonic finding of high-flow priapism.
Frequency
United States
The frequency of priapism depends on the population being considered. The combination of intracavernosal agents and other drugs is the cause of approximately 21-80% of all adult priapism. Agents used to treat erectile dysfunction are common causes of adult priapism in the Western world. The overall rate of priapism in persons using these agents ranges from 0.05-6%. This group tends to be better educated about the risk of priapism; therefore, they seek treatment earlier. At other centers, sickle cell disease (SCD) and sickle cell trait predominate as the cause of adult priapism. The rate of priapism in adults with SCD is as high as 89%. Approximately two thirds of all pediatric patients who have priapism also have SCD. The rate of priapism among children with SCD is as high as 27%.
Mortality/Morbidity
- Priapism is painful at onset. Corporeal fibrosis due to persistent priapism can result in deep-tissue infections of the penis.
- The major chronic morbidity associated with all types of priapism is persistent erectile dysfunction and impotence.
- The duration of symptoms is the most important factor affecting outcome. A recent Scandinavian study reported that 92% of patients with priapism for less than 24 hours remained potent, while only 22% of patients with priapism that lasted longer than 7 days remained potent.1
Race
- Priapism is common in African Americans with SCD.
Sex
- Priapism occurs exclusively in males.
Age
- Priapism can occur in males of any age group, with peaks at age 5-10 years and 20-50 years.
- Among patients with SCD, the prevalence is higher in men aged 19-21 years.
Clinical
History
Patients with priapism report a persistent erection. The symptoms depend on the type of priapism and the duration of engorgement.
- Low-flow, ischemic-type priapism is generally painful, although the pain may disappear with prolonged priapism.
- High-flow, nonischemic priapism is generally not painful. This type of priapism is associated with blunt or penetrating injury to the perineum. It may manifest in an episodic manner.
- Aspects of history are as follows:
- Erection: Duration of longer than 4 hours is consistent with priapism.
- Duration of pain
- Similar prior episodes
- Genitourinary (GU) trauma
- Medical history (eg, sickle cell disease [SCD]): Onset occurs during sleep, when relative oxygenation decreases.
- Medication and/or recreational drug use, especially the antidepressant trazodone, intracavernosal injections of prostaglandin E1 used to treat impotence, and illicit cocaine injection into the penis
- History of malignancy (prostate cancer)
- Penile prosthesis: The permanent erection that occurs with some penile prostheses may mimic priapism.
- Recent urologic surgery
- Aspects of history in high-flow priapism are as follows:
- Not painful
- May be sexually active
- Straddle injury usually the initiating event
- Chronic recurrent presentation
- Generally not caused by medication
- Aspects of history of low-flow priapism are as follows:
- Painful
- Inactive sexually and without desire
- No history of trauma
- Usually presents to emergency department (ED) within hours
- Associated with substance abuse or vasoactive penile injections
- Rarely caused by leukemia, fat embolism, acute spinal cord injury, or (extremely rare) cancer metastases to the corporeal bodies
Physical
Obvious erection is the key physical finding in any case of priapism. Penile priapism generally involves only the paired corpora cavernosa, with the glans and corpora spongiosum remaining flaccid or softly distended without rigidity. Careful physical examination may reveal specific causal factors. Remember that no single pathology excludes all others; therefore, a thorough history and physical examination should address the patient as a whole.
- Aspects of the physical examination are as follows:
- Penile color, rigidity, and sensation (soft glans vs firm glans)
- Penile discharge, lesions, or both
- Evidence of local trauma
- Presence of prosthetic devices: Hardware malfunction may cause pseudopriapism.
- Regional lymphadenopathy (ie, metastatic disease)
- Rectal tone: High spinal cord lesions or stenosis may cause priapism.
- Aspects of the physical examination consistent with high-flow priapism are as follows:
- Adequate arterial flow
- Well-oxygenated corpora
- Evidence of trauma
- Aspects of the physical examination consistent with low-flow priapism are as follows:
- Rigid erection
- Ischemic corpora as indicated by dark blood upon corporeal aspiration
- No evidence of trauma
Causes
Priapism can result from idiopathic or secondary causes. In the United States, the most common cause of priapism in the adult population involves agents used to treat erectile dysfunction. The most common cause of priapism in the pediatric population is SCD. Internationally, the most common cause is idiopathic.
- Uncommonly, both low- and high-flow priapism are idiopathic in nature.
- Secondary causes of low-flow priapism are as follows:
- Thromboembolic/hypercoagulable states
- Sickle cell anemia - Polycythemia
- Thalassemia
- Total parenteral nutrition
- Fabry disease
- Dialysis
- Vasculitis
- Fat embolism (after multiple long-bone fractures or after iatrogenic intravenous lipids as part of total parenteral nutrition)
- Neurogenic disease
- Spinal cord stenosis (ie, trauma to the medulla)
- Autonomic neuropathy and cauda equina compression
- Neoplastic disease (metastatic to the penis or obstructive to venous outflow)
- Prostate cancer and GU (highest risk) bladder cancer
- Hematological (leukemia)
- Renal carcinoma
- Melanoma
- Pharmacologic causes
- Intracavernosal agents - Papaverine, phentolamine, prostaglandin E1
- Intraurethral pellets (ie, medicated urethral system for erection with intracavernosal prostaglandin E1)
- Antihypertensives - Ganglion-blocking agents (eg, guanethidine), arterial vasodilators (eg, hydralazine), alpha-antagonists (eg, prazosin), calcium channel blockers
- Psychotropics - Phenothiazine, butyrophenones, hypnotics (eg, mesoridazine, perphenazine), trazodone, selective serotonin reuptake inhibitors (eg, fluoxetine, sertraline)2
- Anticoagulants - Heparin, warfarin
- Recreational drugs - Cocaine, marijuana, ethanol
- Hormones - Gonadotropin-releasing hormone (GnRH), tamoxifen, testosterone
- Herbal medicine - Ginkgo biloba with concurrent use of antipsychotic agents3
- Miscellaneous medications - Metoclopramide, omeprazole, penile injection of cocaine, epidural infusion of morphine and bupivacaine4
- Secondary causes of high-flow priapism are as follows:
- GU trauma
- Straddle injury
- Intracavernous injections with direct cavernosal artery injury
- Drugs - Cocaine
- Other causes of priapism (rare) are as follows:
- Amyloidosis (massive amyloid infiltration)
- Gout (one case report)
- Carbon monoxide poisoning
- Malaria
- Black widow spider venom
- Asplenia
More on Priapism |
 Overview: Priapism |
| Differential Diagnoses & Workup: Priapism |
| Treatment & Medication: Priapism |
| Follow-up: Priapism |
| Multimedia: Priapism |
| References |
| Further Reading |
| Next Page » |
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Keywords
priapism, cavernosal shunts, Ebbehoj procedure, El-Ghorab procedure, erectile dysfunction, ED, erection, Grayhack shunt, prolonged erection, Quackel shunt, Quackel's shunt, sexual dysfunction, sickle cell disease, SCD, Winter procedure, low-flow priapism, ischemic priapism, high-flow priapism, nonischemic priapism, pathologic erection, permanent impotence, impotence, penile injury, penile trauma, penis trauma, penis injury, persistent erection, pseudopriapism
