Ischaemic priapism, between the subtypes, represents the most common form and must be managed as an emergency considering that there is an absent or poor cavernous arterial inflow and thus dramatic histological changes related to hypoxia, hypercarbia and acidosis. The first changes observed after 12 h are oedema and endothelium damages, while after 48 h, the coagulation cascade stimulated by thrombocyte adherence to the basement membrane has already caused a significant thrombosis of the corpora. At this moment necrosis is generally evident, and fibrosis is developing (Spycher and Hauri 1986). In the aetiology of this particular condition, haematological diseases and iatrogenic factors play the principal role. Between blood dyscrasias sickle-cell disease (SCD) represents a common cause due to erythrocyte entrapment in the corpora cavernosa with resulting obstructed venous outflow after an erection (Lue 2002). It is reckoned that one third of ischaemic priapism are related to this condition, and for this reason a careful screening for SCD as first investigation is reasonable in these patients (Broderick et al. 2010).

Other common causes for low-flow priapism are treatment for erectile dysfunction (ED)–related complications. Particularly intracorporal injections (ICI) rather than oral drugs can be followed by prolonged erections and priapism. In literature different incidence rates of priapism are reported after ICI of vasoactive substances, and generally the range is between 0 and 35 %: combined therapy based on papaverine or phentolamine has higher rates, while in investigations conducted only with PGE1 (alprostadil), this percentage drops to 5 % for prolonged erection and only 1 % for priapism (Broderick and Lue 2002; Porst 1996). The involvement of PDE5 inhibitor in the aetiology of ischaemic priapism is debatable considering that a possible link is showed only by case reports in which, additionally, patients suffered from co-morbidities possibly related to the priapism onset themselves (Wilt and Fink 2004; Sur and Kane 2000). The above-mentioned factors are undoubtedly the commonest causes of ischaemic priapism, but malignancies such as pelvic and haematological tumours, recreational drugs and antipsychotic treatments have been related even if with lower rates (Broderick et al. 2010).

The aetiology of stuttering priapism is essentially linked to SCD, and the main difference with the previous subtype lies in the intermittence of its episodes which last several hours before resolution; generally stuttering priapism leads up to the onset of ischaemic priapism (Broderick et al. 2010).

The third kind of priapism, the non-ischaemic, is characterized by a persistent erection, not always painful, caused by unregulated cavernous arterial inflow. Considering its pathophysiology non-ischaemic priapism does not represent an emergency because there isn’t any outflow obstruction or intrasinusoidal coagulation risk resulting in tissue necrosis. For this reason this condition can be managed with a conservative approach (Broderick et al. 2010). Generally non-ischaemic priapism is caused by a penile trauma, blunt or sharp, resulting in the formation of an arteriolar-sinusoidal fistula which supports the prolonged erection. Iatrogenic causes are represented by urological procedure including Nesbit or mini-invasive diagnostic investigations that could cause an arterial injury through a needle insertion (Liguori 2005).

Anamnesis can certainly help to understand the subtype of priapism considering that ischaemic and non-ischaemic show different factors as mentioned above. An accurate inspection of the patient has the aim to value the degree of tumescence considering that a partial erection not associated to pain is a common feature of non-ischaemic priapism, while the evidence of a full tumescence is more often related to the ischaemic and stuttering priapism. The presence of traumas in the external genitalia and the suspicion of malignancies in the abdomen and perineal area with deep palpation can be further elements for a correct diagnosis. Past medical history and physical examination represent the first step in the diagnosis. The successive step is represented by investigations: a penile doppler ultrasound is indicated in case of high flow priapism in order to confirm high flow, the site of the trauma and the fistula if present (Broderick et al. 2010; Broderick and Lue 2002). A blood gas represents the instrumental investigation which determines if there are signs of ischaemia in the corpora: a PO₂ lower than 30 mmHg and a PCO₂ higher than 60 mmHg with a pH lower than 7.25 are typical signs of an ischaemic priapism (Montague et al. 2003). In selected cases in which a malignancy is supposed, a CT scan or an MRI of the abdomen/pelvis is recommended. It is important to determine the real nature of the priapism before any treatment considering that in case of ischaemia, the patient should be treated as soon as possible in order to avoid necrosis and fibrosis of the corpora, while in case of non-ischaemic priapism, a conservative approach can be adopted.

The immediate treatment of ischaemic priapism is mandatory to prevent erectile dysfunction (ED) which is evident after 24 h of ischaemic priapism in 90 % of patients (Pryor and Hehir 1982). The first treatment is the decompression of the corpora with local aspiration and ICI of sympathomimetic agents (Montague et al. 2003). Sympathomimetic drugs such as etilefrine and phenylephrine acting on smooth muscle contraction determine the contraction of the erectile tissue with resulting detumescence in a high percentage of patients. The rate of priapism resolution after this approach has been demonstrated to reach 81 %, while in case of aspiration alone with the irrigation of the corpora, the success rate is only 36 % (Montague et al. 2003). When this treatment is used, a careful monitoring of blood pressure and pulse is recommended considering that arrhythmia, hypertension, reflex bradycardia and tachycardia are reported side effects of ICI of sympathomimetics. If these preliminary approaches do not show any satisfactory results, the use of alpha-adrenergic agonists is contraindicated or has determined important side effects, and surgical therapy represents the only feasible strategy to re-oxygenate the cavernosal tissue. In order to achieve this aim, it is necessary to create a shunt between the corpora and the nearby structures including the glans, corpus spongiosum or saphenous vein. These techniques allow an outflow of the stagnant blood in the cavernosal tissue with the resulting re-establishment of arterial flow. The procedures can be divided in four groups: percutaneous and open distal shunts, open proximal and saphenous vein shunts (Broderick et al. 2010). Generally the first procedure adopted is an open distal shunt eventually followed by more proximal and aggressive approaches in case detumescence is not achieved and nil arterial flow within the corpora is detectable. Between the percutaneous procedure an outflow through the glans can be performed with biopsy needle (Winter 1976), n°11 blade (Ebbehoj 1974) or with a T-shape incision in the distal tip of the corpora (Brant et al. 2009). If priapism persists a more aggressive approach is recommended such as the open shunting between corporas and glans. With this technique the removal of a conic segment of tunica albuginea at the corporal tip is recommended and the dilatation of the corpora with Hegar dilators can be helpful to improve drainage (Burnett and Pierorazio 2009). Proximal shunt including cavernosum-spongiosum and saphenous shunt are the most aggressive techniques which have between their potential side effects the risk of pulmonary embolism, and for this reason their use is generally limited (Quackles 1964; Kandel et al. 1968).

In case of long-term ischaemic priapism in which necrosis of the corpora is evident, ED is unavoidable. In these cases a delayed insertion of a penile prosthesis can be extremely difficult and with higher complication rates. For this reason some authors recommend an immediate implantation to avoid penile shortening and increased peri-operative and post-operative complications such as infections (Ralph et al. 2009; Rees et al. 2002). A different management is necessary for stuttering priapism considering that in this case, medical treatments are employed more than surgical approaches. The main target of systemic therapy is represented by the suppression of the androgenic effects on erection: this aim can be achieved using GnRh agonists and anti-androgens thanks to their inhibiting action, respectively, on the pituitary gland and peripheral androgen receptors or prescribing diethylstilbestrol (DES) and ketoconazole which have a negative feedback respectively on pituitary and adrenal glans (Broderick et al. 2010).

Regarding high-flow priapism a different treatment is advocated because this subtype does not represent an emergency considering the absence of cavernosal necrosis and thus of any negative impact on erectile function. An observational approach is generally suggested for this disease thanks to its spontaneous resolution; for this reason all patients should be counselled regarding the potential negative effects of the therapy more than non-ischaemic priapism itself. If the patient requires treatment due to remarkable discomfort, the options available are the selective embolization or the open ligation of the fistula responsible for the high flow. The first treatment is preceded by an arteriographic study in order to demonstrate the fistula, while in case of long-term arterial priapism, an intraoperative Doppler ultrasonography can be useful. Embolization has a high rate of success, but its principal side effect regardless of the kind of agent used is represented by ED which can occur in up to 39 % of patients treated (Savoca et al. 2004; Mwamukonda et al. 2010). Other adverse events are related to the possible occlusion of major arterial branches of the gluteal area and the penile shaft resulting in local ischaemia (Tønseth et al. 2006).