Priapism - Definition Prolonged and often painful erection in the absence of a sexual stimulus, lasting >4 - 6h, which predominantly affects the corpus cavernosa.
Epidemiology Peaks in incidence at ages 5 - 10 and 20 - 50.
Classification - Low-flow (ischaemic) priapism Due to veno-occlusion (intracavernosal pressures of 80 - 120mmHg). More common than high-flow priapism. Manifests as a painful, rigid erection, with absent or low cavernosal blood flow. Ischaemic priapism beyond 4h requires emergency intervention. Blood gas analysis shows hypoxia and acidosis. - High-flow (non-ischaemic) priapism Due to unregulated arterial blood flow, presenting with a semi-rigid, painless erection. Blood gas analysis shows similar results to arterial blood.
Aetiology - Causes are primary (idiopathic) or secondary (see boxes) including: - Intracavernosal injection therapy PGE1; papaverine - Drugs alfa-blockers; antidepressants; antipsychotics; psychotrophics; tranquilizers; anxiolytics; anticoagulants; recreational drugs; alcohol excess; total parenteral nutrition - Thromboembolic sickle cell disease (may cause stuttering/recurrent priapism); leukaemia; thalassaemia; fat emboli - Malignant infiltration of the corpora cavernosa (e.g. advanced bladder cancer) - Neurogenic spinal cord lesion; autonomic neuropathy; anaesthesia - Trauma penile or perineal injury resulting in cavernosal artery laceration or arterio-venous fistula formation - Infection malaria; rabies; scorpion sting
Pathophysiology Priapism lasting for 12h causes trabecular interstitial oedema, followed by destruction of sinusoidal endothelium and exposure of the basement membrane at 24h, and sinusoidal thrombi, smooth muscle cell necrosis and fibrosis at 48h.
Evaluation - Serum testing to exclude sickle cell and leukaemia. - Cavernous blood samples to determine type of priapism. - Colour Doppler ultrasound scan of cavernosal artery and corpora cavernosa. Reduced blood flow in ischaemic priapism; ruptured artery with pooling of blood around injured area in non-ischaemic priapism.
Management Low-flow priapism Aspiration of blood from corpora (50ml portions using a 18 - 20 gauge butterfly needle) intracavernosal injection of alfa-adrenergic agonist (phenylephrine 10mg in 19ml saline, injected in 0.5 - 1ml aliquots every 5 min until detumescence occurs). Monitor BP and pulse during drug administration. Oral terbutaline may be effective for intracavernosal injection-related cases. Sickle cell disease requires, in addition, aggressive rehydration, oxygenation, analgesia, and haematological input (consider exchange transfusion).
High-flow priapism Early stages may respond to a cool bath or icepack (causing vasospasm arterial thrombosis). Delayed presentations require arteriography and embolization of the internal pudendal artery.
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