Scrotal dermoid extending to the posterior urethra through a corpus cavernosum in a child

A 3-year-old boy presented with an asymptomatic intertesticular mass increasing in size. Plasma tumor markers (α-fetoprotein and β-human chorionic gonadotrophin) were negative. The mass had a pattern similar to testicular parenchyma but no discernable blood flow on scrotal Doppler ultrasound. Magnetic resonance imaging scan showed that it reached the posterior urethra after passing through the right corpus cavernosum with a progressive tapering extending into the pelvis. The mass was excised surgically and histologically found to be consistent with a dermoid cyst. Such rare benign lesions should be considered in the differential diagnosis of painless scrotal masses in children. Its anatomy was accurately defined by magnetic resonance imaging and was essential to minimize the risk to adjacent structures.