Anatomy of the penis
Let's start by reviewing the anatomy of the penis.
Urine and semen travel through the urethra which is surrounded by the corpus spongiosum. There are two nerves on the dorsal side that innervate the penis, and multiple layers of connective tissue surrounding the corpora cavernosa including the outer Buck’s fascia and the inner tunica albuginea.
It is important that you do not inject anything into the urethra during the priapism treatment. As well, you need to know the location of the two penile nerves to perform a dorsal nerve penile block.
Erection of the penis is achieved by increased arterial flow and decreased venous outflow in the corpora cavernosa causing engorgement. The two regions of corpora cavernosa are connected to each other, which is why you don’t have to inject both sides of the penis during the treatment.
What is priapism?
Priapism is a prolonged and painful erection lasting over four hours in the absence of sexual stimulation.
There are two types of priapism. The most common (~ 95%) is ischemic priapism, which is caused by painful venous engorgement of the corpora cavernosa. The second—and rarer—type is non-ischemic priapism, which is caused by increased arterial inflow to the penis by trauma causing an arteriocavernosal fistula.
Ischemic priapism is a urologic emergency that can lead to permanent erectile dysfunction. This happens as the pressure in the penis approaches the arterial pressure and venous return is diminished. At this point, there is no new blood flow to the penis and the blood in the penis becomes hypoxic and acidotic. Sometimes, the stagnant blood can even clot.
Confirmation of ischemic priapism
If there's a question about ischemic versus non-ischemic priapism, a blood sample from the corpora cavernosum will confirm ischemic priapism. The priapism is ischemic if the sample has high lactate, low pH and low PaO2. However, these tests are rarely needed. If the patient presents with priapism in the absence of trauma, you are dealing with ischemic priapism.
Causes of ischemic priapism
There are three common causes of ischemic priapism:
- Impotence medications
- Vasoactive medications
- Sickle cell disease
The most common cause for ischemic priapism is impotence medications, mostly the kind that patients inject directly into the penis to achieve an erection right before sex.
Psychiatric medications, certain blood pressure medicines, hormones, and illicit drugs, such as cocaine, can lead to priapism. All these vasoactive medications promote blood flow to the penis, but decrease venous outflow.
Sickle cell disease
The other important category of patients that can develop priapism are men with sickle cell disease. The prevalence or priapism in this group is up to 40%, and of those affected, 30% will develop erectile dysfunction.
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