Penoscrotal extravascular papillary endothelial hyperplasia (Masson's tumour): Contrast-enhanced ultrasound features with magnetic resonance imaging and histopathology correlation.

Papillary endothelial hyperplasia, or Masson's tumour, is a benign, reactive endothelial proliferation classified as intravascular, mixed or extravascular, with the extravascular subtype arising as a reactive process at a site of vascular injury. Genitourinary presentations are rare and predominantly intravascular; extravascular disease at the penoscrotal junction is exceptionally rare and can mimic soft-tissue sarcoma due to its hypervascular, avidly enhancing appearance. We report a case of penoscrotal extravascular papillary endothelial hyperplasia and describe, to our knowledge, the first documented contrast-enhanced ultrasound features of this entity. A man in his sixties presented with a 4-week history of a small, non-tender lump at the left penoscrotal junction, with no reported history of local trauma. Grey-scale ultrasound demonstrated a well-defined, hypoechoic lesion abutting the tunica albuginea, with internal vascularity on colour Doppler. Contrast-enhanced ultrasound showed marked hypervascularity with rapid, avid, and persisting enhancement during the arterial and late venous phases, together with a large, serpiginous vein in close proximity to the lesion and appearing mildly compressed by the mass - a distinctive vascular morphology not previously described in papillary endothelial hyperplasia at any site. Magnetic resonance imaging confirmed a well-defined, uniformly enhancing nodule, with an adjacent peripheral vessel of indeterminate arterial or venous nature. Given residual diagnostic uncertainty, staging computed tomography excluded metastatic disease before surgical excision. Histopathology confirmed extravascular papillary endothelial hyperplasia, most likely reactive, possibly arising at a site of previously unrecognised local trauma. This case highlights a novel contrast-enhanced ultrasound appearance in extravascular papillary endothelial hyperplasia that may aid diagnostic confidence and support multimodality triage of indeterminate penoscrotal masses.