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- Penile (or less common clitoral) erection lasting for >4 hours and unrelated to sexual stimulation or arousal
- Classified into three types: ischemic, nonischemic, and stuttering:
- Ischemic (low-flow, veno-occlusive) priapism is associated with ischaemia of the corpora cavernosa, is prolonged and painful, and requires urgent clinical intervention.
- Nonischemic (high-flow, arterial) priapism is less common and often painless, may be related to prior trauma, and does not require urgent treatment.
- Stuttering priapism (recurrent, ischemic) is episodic, short-lived, and may not require intervention.
- Malignant priapism is a rare condition resulting most commonly from penile metastases related to primary bladder, prostatic, rectosigmoid, and renal tumors.
- System(s) affected: reproductive and vascular
- Functional impairment: neurophysiologic, sexual, psychosocial (quality of life) (1)
- In children, nearly all priapism is related to either sickle cell disease (SCD) (65% of cases). Less commonly related etiologies, occurring more typically in the adolescent years, are leukemia, idiopathic, penile trauma (e.g., post circumcision), or illicit drugs (up to 35% of cases).
- Neonatal priapism is also rare, occurring in the first few days of life (2).
- The incidence and prevalence of priapism is largely unknown because the vast majority of empirical literature and data only include cases in which men sought medical intervention. In a study published by Roghmann and colleagues (2013), the number of priapism cases reported by emergency departments between 2006 and 2009 was 32,462 visits, representing a national incidence of 0.73 per 100,000 men per year (3).
- Age: There has been an age shift since 2008 toward men in their 40s. The incidence doubles in men aged >40 years (2.9 vs. 1.5/100,000 person-years).
- Race: 61.1% black (correlated with incidence of SCD), 30% white, 6.3% Hispanic
- Anatomy and physiology:
- The penis consists of three longitudinally oriented corpora: two dorsolaterally paired corpora cavernosa that are responsible for penile erection and a single ventral corpus spongiosum that surrounds the glans penis and extends distally to form the glans penis.
- In general, the penile artery (a branch of the internal pudendal artery that, in turn, is a branch from the internal iliac artery) supplies the penis. It divides into three branches: dorsal artery, bulbar artery (supplies the corpus spongiosum), and cavernosal artery (the main blood supply to the erectile tissue).
- During an erection, smooth muscle relaxation of the cavernosal arterioles results in high-volume inflow to the sinusoids, resulting in compression of the exiting venules. This leads to significant volume expansion of the corpora cavernosa.
- During the flaccid resting state, the sympathetic nervous system is predominantly in control. Penile tumescence and erection are driven by the parasympathetic nervous system through the generation of nitric oxide.
- Smooth muscle relaxation occurs via usage of the phosphodiesterase type 5A (PDE5A) pathway, which generates cyclic guanosine monophosphate (cGMP) (2).
Etiology and Pathophysiology
- Priapism is a pathologic condition that has been observed since ancient times during the upper Paleolithic prehistoric period. There existed iconographic images and statues of the god, Priapus, depicted with an oversized, permanent erection in the posture, anasurma (exposing oneself), and leaning on a pillar while using a scale to weigh his genitalia.
- Initially attributed to sexually transmitted diseases, priapism was later associated with spinal cord trauma in the 17th century (4).
- In ischemic priapism (accounting for >95% of reported episodes), decreased venous outflow results in increased intracavernosal pressure. This leads to erection, decreased arterial inflow, blood stasis, local hypoxia, and acidosis (a compartment syndrome). Penile tissue necrosis and fibrosis may occur if priapism persists >24 hours. The exact mechanism is unknown and may involve trapping of erythrocytes in the veins, draining the erectile bodies.
- In nonischemic priapism, increased arterial flow without decreased venous outflow results in a sustained, nonpainful, partially rigid erection.
- Aberrations in the PDE5A pathway have been proven in mice to be one mechanism of priapism (1).
- Causes: ischemic priapism (1)
- Idiopathic, estimated to about 50%
- Intracavernosal injections of vasoactive drugs for erectile dysfunction
- Oral agents for erectile dysfunction
- Pelvic vascular thrombosis
- Prolonged sexual activity
- Leukemia and other malignancies that can infiltrate the corpora
- SCD and trait
- Other blood dyscrasias (G6PD deficiency, thalassemia, thrombophilia)
- Pelvic hematoma or neoplasia (penis, urethra, bladder, prostate, kidney, rectal)
- Cerebrospinal tumors
- Fabry disease
- Tertiary syphilis
- Total parenteral nutrition, especially 20% lipid infusion (results in hyperviscosity)
- Bladder calculus
- UTIs, especially prostatitis, urethritis, cystitis
- Several medications or illicit drugs have been reported to cause priapism (i.e., chlorpromazine, prazosin, trazodone, and some corticosteroids; anticoagulants [heparin and warfarin]; phosphodiesterase inhibitors [sildenafil, others]; immunosuppressants [tacrolimus]; antidepressants; methylphenidate; antihypertensives [hydralazine, propranolol, guanethidine]; antipsychotics [quetiapine, risperidone, aripiprazole]; and cocaine [can be directly injected into penis]).
- Intracavernous fat emulsion
- Hyperosmolar IV contrast
- Spinal cord injury
- General or spinal anesthesia
- Heavy alcohol intake
- Causes: nonischemic priapism (1)
- The most common cause is penile or perineal trauma resulting in a fistula between the cavernous artery and the corpus cavernosum.
- Acute spinal cord injury
- Rarely, iatrogenic causes for the management of ischemic priapism can result in nonischemic priapism.
- Certain urologic surgeries have also resulted in nonischemic priapism.
Commonly Associated Conditions
- SCD (42.9%) or sickle cell trait (2.5%)
- Drug abuse (7.9%)
- G6PD deficiency