Priapism.

Priapism is a prolonged, painful, penile erection that fails to subside despite orgasm. An erection lasting longer than 4-6 h is considered to be priapic; nevertheless, pain does not usually ensue until 6-8 h have elapsed. Priapism is considered a failure of the detumescence mechanism, which may be due to excess release of contractile neurotransmitters, obstruction of draining venules, malfunction of the intrinsic detumescence mechanism, or prolonged relaxation of intracavernosal smooth muscle. There are essentially two main types of priapism: high flow (non-ischemic) and low flow (ischemic). Low flow priapism is the more common form, and it is associated with a decrease in venous outflow and vascular stasis that, in turn, cause tissue hypoxia and acidosis. This form of priapism is usually quite painful because of tissue ischemia. Penile blood aspirated from cavernous spaces appears dark in color. Immediate treatment is necessary or penile fibrosis will ensue. High flow priapism is usually due to trauma, although, on rare occasions it has been idiopathic or due to sickle cell disease. The hallmark of this type of priapism is an increase in arterial inflow in the setting of normal venous outflow. Aspirated penile blood is noted to be bright red and has a high pO(2). This form of priapism is not usually painful because it is non-ischemic. Treatment is dependent on the wishes of the patient but is not mandatory. International Journal of Impotence Research (2000) 12, Suppl 4, S133-S139.