Priapism is an abnormal sustained erection, classified as either low flow
or high flow priapism. In patients with low flow priapism, there is obstruction
to venous outflow. In the genesis of the low flow state, continued arterial
inflow in the absence of venous outflow results in intracavernosal pressures
in the erection chamber that prevent further blood from entering. Thus
low flow priapism is a compartment syndrome associated with the patient
having a sustained erection without arterial inflow. This irony is very
confusing to most healthcare professionals as well as the lay public who
often joke about erectile capability.
An erection that is sustained without the patient’s permission up
to 4 hours is considered a prolonged erection. The diagnosis of low flow
priapism is established by the history of an erection persistent beyond
4 hours. Since arterial inflow is usually absent, the tissue lacks oxygen
and the penis becomes painful. This is a medical emergency that must be
treated promptly to avoid permanent erection tissue damage and erectile
dysfunction. In low flow priapism, the chamber that surrounds the urinary
passageway (corpus spongiosum) is not erect, so the physical examination
reveals a hard erection shaft and soft glans penis.
Mandatory laboratory tests assess for the presence or absence of arterial
flow in the erection chamber. A needle can be placed in the side of the
shaft of the penis, blood can be withdrawn, and the sample sent for oxygen
content. In addition, an ultrasound study can localize the erection artery
and verify if there is flow within. Other laboratory tests that can help
establish the cause of the artery blockage include hemoglobin, hematocrit
and testing to see if the patient has sickle cell disease. Certain drugs
such as trazedone, heparin and some anti-psychotic drugs are associated
The most common reason for priapism is intracavenosal self-injection. Prior
to initiating home self-treatment, careful in office training programs
are mandatory in order to minimize the chance of priapism. Patients on
self-injection therapy need to be cognizant of priapism.
It is important to give patients with low flow priapism the opportunity
to carefully weigh the risks and benefits of all treatment options, despite
the emergent situation.
In contrast, high flow priapism is an abnormal erection associated with
unregulated persistent blood flow into the erection chamber. This is commonly
a result of blunt trauma to the perineum in which the abrupt force lacerates
the erection artery. Distinct from low flow priapism, high flow priapaism
is not associated with lack of oxygen, as proven by blood tests and Doppler
ultrasound, and therefore is not a medical emergency.
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