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What is Priapism and explain in detail?
Priapism is a condition in which a penis remains erect for hours in the absence of stimulation or after stimulation has ended. There are three types: ischemic (low-flow), nonischemic (high-flow), and recurrent ischemic (intermittent). Most cases are ischemic. Ischemic priapism is generally painful while nonischemic priapism is not. In ischemic priapism, most of the penis is hard; however, the glans penis is not. In nonischemic priapism, the entire penis is only somewhat hard. Very rarely, clitoral priapism occurs in women.Sickle cell disease is the most common cause of ischemic priapism. Other causes include medications such as antipsychotics, SSRIs, blood thinners and prostaglandin E1, as well as drugs such as cocaine. Ischemic priapism occurs when blood does not adequately drain from the penis. Nonischemic priapism is typically due to a connection forming between an artery and the corpus cavernosum or disruption of the parasympathetic nervous system resulting in increased arterial flow. Nonischemic priapism may occur following trauma to the penis or a spinal cord injury. Diagnosis may be supported by blood gas analysis of blood aspirated from the penis or an ultrasound.Treatment depends on the type. Ischemic priapism is typically treated with a nerve block of the penis followed by aspiration of blood from the corpora cavernosa. If this is not sufficient, the corpus cavernosum may be irrigated with cold, normal saline or injected with phenylephrine. Nonischemic priapism is often treated with cold packs and compression. Surgery may be done if usual measures are not effective. In ischemic priapism, the risk of permanent scarring of the penis begins to increase after four hours and definitely occurs after 48 hours. Priapism occurs in about 1 in 20,000 to 1 in 100,000 males per year.

Classification
Priapism is classified into three groups: ischemic (low-flow), nonischemic (high-flow), and recurrent ischemic. The majority of cases (19 out of 20) are ischemic in nature.Some sources give a duration of four hours as a definition of priapism, but others give six.  "The duration of a normal erection before it is classifiable as priapism is still controversial. Ongoing penile erections for more than 6 hours can be classified as priapism."Priapism in females (continued, painful erection of the clitoris) is significantly rarer than priapism in men and is known as clitoral priapism or clitorism. It is associated with persistent genital arousal disorder (PGAD). Only a few case reports of women experiencing clitoral priapism exist.

Signs and symptoms
Complications
Because ischemic priapism causes the blood to remain in the penis for unusually long periods of time, the blood becomes deprived of oxygen, which can cause damage to the penile tissue. Such damage can result in erectile dysfunction or disfigurement of the penis. In extreme cases, if the penis develops severe vascular disease, the priapism can result in penile gangrene.

Low-flow priapism
Causes of low-flow priapism include sickle cell anemia (most common in children), leukemia, and other blood dyscrasias such as thalassemia and multiple myeloma, and the use of various drugs, as well as cancers. A genome-wide association study on Brazilian patients with sickle cell disease identified four single nucleotide polymorphisms in LINC02537 and NAALADL2 significantly associated with priapism.Other conditions such as Fabrys disease, as well as neurologic disorders such as spinal cord lesions and spinal cord trauma (priapism has been reported in people who have been hanged; see death erection).
Priapism can also be caused by reactions to medications. The most common medications that cause priapism are intra-cavernous injections for the treatment of erectile dysfunction (papaverine, alprostadil). Other medication groups reported are antihypertensives, antipsychotics (e.g., chlorpromazine, clozapine), antidepressants (most notably trazodone), anti-convulsant and mood stabilizer drugs such as sodium valproate. Anticoagulants, cantharides (Spanish Fly) and recreational drugs (alcohol, heroin and cocaine) have been associated. Priapism is also known to occur from bites of the Brazilian wandering spider.

High-flow priapism
Causes of high-flow priapism include:

blunt trauma to the perineum or penis, with laceration of the cavernous artery, which can generate an arterial-lacunar fistula.
Anticoagulants (heparin and warfarin).
Antihypertensives (i.e., hydralazine, guanethidine and propranolol).
Hormones (i.e., gonadotropin releasing hormone and testosterone).

Diagnosis
The diagnosis is often based on the history of the condition as well as a physical exam.Blood gas testing the blood from the cavernosa of the penis can help in the diagnosis. If the low-flow type of priapism is present, the blood typically has a low pH, while if the high-flow type is present, the pH is typically normal. Color Doppler ultrasound may also help differentiate the two. Testing a person to make sure they do not have a hemoglobinopathy may also be reasonable.

Ultrasonography
Penile ultrasonography with Doppler is the imaging method of choice, because it is noninvasive, widely available, and highly sensitive. By means of this method, it is possible to diagnose priapism and differentiate between its low- and high-flow forms.In low-flow (ischemic) priapism the flow in the cavernous arteries is reduced or absent. As the condition progresses, there is an increase in echogenicity of the corpora cavernosa, attributed to tissue edema. Eventually, changes in the echotexture of the corpora cavernosa can be observed due to the fibrotic transformation generated by tissue anoxia.In high-flow priapism normal or increased, turbulent blood flow in the cavernous arteries is seen. The area surrounding the fistula presents a hypoechoic, irregular lesion in the cavernous tissue.

Treatment
Medical evaluation is recommended for erections that last for longer than four hours. Pain can often be reduced with a dorsal penile nerve block or penile ring block. For those with nonischemic priapism, cold packs and pressure to the area may be sufficient.

Pseudoephedrine
Orally administered pseudoephedrine is a first-line treatment for priapism. Erection is largely a parasympathetic response, so the sympathetic action of pseudoephedrine may serve to relieve this condition. Pseudoephedrine is an alpha-agonist agent that exerts a constriction effect on smooth muscle of corpora cavernosum, which in turn facilitates venous outflow. Pseudoephedrine is no longer available in some countries.

Aspiration
For those with ischemic priapism, the initial treatment is typically aspiration of blood from the corpus cavernosum. This is done on either side. If this is not sufficiently effective, then cold normal saline may be injected and removed.

Medications
If aspiration is not sufficient, a small dose of phenylephrine may be injected into the corpus cavernosum