MR imaging of the penis

Background

While ultrasound (US) remains the 1st line imaging modality for evaluating diseases of the penis, MRI has shown specific advantages, owing to excellent soft tissue contrast and good spatial resolution, ability to evaluate less accessible or complex anatomy and ability to detect subtle disease.

Anatomy of the penis

The penis essentially consists of 3 cylindrical bodies – the paired corpora cavernosa and a midline corpus spongiosum on its underside. The corpora cavernosa are composed of special spaces called sinusoids that engorge with blood to form an erection. The corpus spongiosum on the other hand, surrounds the urethra, the latter responsible for ejaculation and urination. Both the corpora cavernosa and corpus spongiosum are enveloped by a strong fibrous capsule known as the tunica albuginea. Like any other organ, the penis too, has its own vasculature, lymphatics and nerves.

Clinical indications for penile MRI

MRI is increasingly being used both as a problem solving tool in patients who have already undergone US and clinical examination where findings are equivocal or incongruent, and as the 1st choice modality for evaluation of suspected disease.
MRI penis is used to evaluate for:
  • Trauma/ fracture of the penis
  • Inflammation
  • Infection
  • Cancer
  • Penile prosthesis complications

Technique

Appropriate positioning is essential for imaging the penis. The patient is placed lying on his back with feet first into the MRI scanner. The penis is usually taped to the front and midline against the front of the abdominal wall before it is scanned. The scan takes about 45 minutes.

The penis may be imaged in both flaccid and erect states. Imaging an erect penis improves visualisation of penile anatomy.

If imaging in an erect state is desired, injection of a prescribed synethetic hormone called prostaglandin E1 (Caverject) before the scan is performed. It takes approximately 10-20 minutes for the injection to work. There are instances where this injection cannot be given, that is, if the patient has a penile implant, acute penile fracture, painful erection and priapism. Alternative methods are to administer Sildenafil (Viagra) or manual stimulation.

Conclusion

MRI can contribute useful information for many different diseases of the male member but in many cases, not convincingly superior to clinical examination and US to justify its routine use. It is probably most useful in penile cancer staging, evaluation of penile prosthesis complications and imaging complex cases of fibrosis.

References

Lindquist CM et al. MRI of the penis. Abdominal Radiology (NY). 2020 Jul;45 (7):2001-2017. Springer. PubMed PMID: 31701192.

Kirkham A. MRI of the penis. Br J Radiol. 2012 Nov;85 Spec No 1(Spec Iss 1):S86-93. PubMED PMID: 23118102.

Long H. Tu, Spektor M, Ferrante M, Mathur M. MRI of the Penis: Indications, Anatomy, and Pathology. Review. Curr Probl Diagn Radiol. Jan-Feb 2020;49(1):54-63. PubMED PMID: 30704768

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