Penile Metastases

Metastasis to the penis are rare, with genitourinary and gastrointestinal tumors comprising 80%: mainly bladder, prostate, rectum, kidney, and testis (in that order).51,52 Other reported sites of origin are lung, nasopharynx, pancreas, liver, and melanoma, as well as lymphoma.52 The route of spread is debated: seeding from instrumentation in prostate and bladder tumors is possible, but arterial, venous, and even extension along nerves has been postulated, and in around three quarters there is spread to other organs, resulting in a poor prognosis.52 The commonest site of involvement is the corpora cavernosa, with tumor in corpus spongiosum and glans less common, and a common presentation is of difficulty in voiding.28 Here we might mention the use of cavernosometry to delineate intracavernosal filling defects53 - an invasive and sometimes painful technique that has been almost entirely superseded in this context by the use of MR or ultrasound, especially with intracavernosal agents.

The imaging appearances of metastases vary from discrete nodules to extensive, often peripheral infiltration3,28 (Fig. 4.13). Both ultrasound and MRI can be used to delineate tumor and in spite of one case report describing a false-positive infiltration of the tunica albuginea on ultrasound but not MRI,54 there are little data to suggest which modality is most sensitive or specific in this context.

Penile metastases may result in priapism, and this was the presenting symptom in 27% of a case review of 51 patients with penile metsatasis.52 The mechanism is likely to be interruption to venous drainage leading to stasis and thrombosis,52 although at least in some cases there may be malignant irritation of the nerves55 or intracavernosal shunting, with the last two likely to show increased, rather than reduced, flow on Doppler ultra-sound.56 MRI and ultrasound may have complimentary roles in this context, and may be used to distinguish true priapism from extensive infiltration. MRI likely provides the best anatomical detail - including the distinction of thrombus from tumor if contrast is used,8 with ultrasound providing additional information on the flow in the cavernosal arteries.

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