POCUS for Priapism: Point to the PDS
Written by: Kevin Hon, DO Edited by: Jeff Greco, MD
If you’re experiencing an erection lasting longer than 4 hours, seek emergency care. If you’re the physician caring for this patient, seek a needle, syringe, and an ultrasound.
Case
A 28 year old man comes into the emergency department with a chief complaint of painful erection that has not detumesced for the last 4 hours. Prior chart review shows that he has a history of Sickle Cell Anemia with prior emergency visits for pain crises. This visit, however, is for a different sort of pain crisis. Upon further questioning, the patient has not taken any performance enhancing drugs for the bedroom, nor has he had prior episodes of priapism. He fortunately denies any recent trauma to the genital region or surgeries to enhance his function.
Vitals: HR:90 RR:16 BP:126/94
Physical exam is significant for an erect, tender penis. Rigid corpora cavernosa. No deformity, lesions, or cyanosis (yet).
You prepare yourself and the patient for the following procedure as it will be more emotionally traumatizing than physically. In the meantime, you grab your ultrasound machine to assess what’s happening behind the closed doors.
Overview
Priapism is a pathological erection lasting 4 or more hours1 It is classically defined as either an erection due to a high flow (non-ischemic) state or a low-flow (ischemic) state. While high-flow priapism may be managed conservatively, the low-flow ischemic state is a medical emergency requiring prompt detumescence with injected phenylephrine into the corpora cavernosa and possibly with needle decompression of the corpora cavernosa. Both types of priapism will have a tense, blood filled corpora cavernosa but a flaccid corpus spongiosum and glans as they are not immediately affected by the cavernosal arteries. This phenomenon can be extremely painful in the setting of ischemic priapism and it is important to determine what type of priapism is being presented as time equals tissue. Prolonged ischemic priapism may result in erectile dysfunction if not emergently treated.
Ultrasound can be a handy tool to use in performing a penile Doppler study (PDS). A cavernosal blood gas is the most definitive diagnostic test for priapism, with dark, crankcase oil-like blood with a high CO2 content, low O2 content, and low pH indicating ischemic priapism.
Penile imaging with the Ultrasound (Dick pics)
A quick overview of the penile anatomy. In a normal erection, increased blood flow through the cavernous, bulbo-cavernous, and dorsal artery causes filling of the corpus cavernosa, corpus spongiosum, and glans penis, respectively. Often in the case of ischemic priapism, venous congestion can prevent proper outflow through the appropriate veins, hence, the low-flow state.
When the time is right, firmly grasp your linear probe and turn it onto the vascular setting. The Penile Doppler Study, as appropriately named, will target the cavernous arteries. This can either be achieved with in line stabilization or by cross-sectional view of the artery and can be performed with the probe dorsal or ventral to the object of interest. However in the interest of preserving signal fallout, sitting the probe on the dorsal surface would allow for better visualization of the arteries using Color Doppler or Pulse Wave Doppler.
Pulse Wave Doppler can then be used to assess for the velocity of the blood within the arteries.
After obtaining a proper arterial waveform, you can calculate the Resistive Index (RI) by comparing the peaks of the Systolic velocity versus the Diastolic velocity. Higher RI is more likely in the ischemic, low-flow state. Note, if there is an absence of arterial flow, this may represent very poor flow and thus, serious hypoxia risk to the penile tissue. Peak systolic velocity less than 25cm/s is also more indicative of a low flow state.
References
Chiou RK, Aggarwal H, Chiou CR, Broughton F, Liu S. Colour Doppler ultrasound hemodynamic characteristics of patients with priapism before and after therapeutic interventions. Can Urol Assoc J. 2009;3(4):304-311. doi:10.5489/cuaj.1125
Bertolotto M., Mucelli F.P., Liguori G., Sanabor D. (2008) Imaging Priapism: The Diagnostic Role of Color Doppler US. In: Bertolotto M. (eds) Color Doppler US of the Penis. Medical Radiology (Diagnostic Imaging). Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-36677-5_10
https://radiopaedia.org/articles/priapism?lang=us