Discovering a swelling in a baby boy's scrotum can be alarming for parents, but a hydrocele — the most common cause of scrotal swelling in newborns — is a benign condition that resolves spontaneously in the great majority of cases. Understanding what a hydrocele is, how it develops, what the normal course is, and which features require medical attention helps parents approach this common finding with appropriate calm.
Healthbooq supports parents with evidence-based guidance on common newborn health findings, including those that are benign and self-resolving as well as those that require monitoring or intervention.
What a Hydrocele Is
A hydrocele is a collection of fluid within the tunica vaginalis, the two-layered covering that surrounds the testicle in the scrotum. It presents as a smooth, soft, non-tender scrotal swelling. The key diagnostic feature that distinguishes a hydrocele from other scrotal pathology (such as an inguinal hernia or testicular torsion) is transillumination — when a light is shone through the scrotal swelling in a darkened room, the scrotal sac lights up brightly because it is filled with clear fluid rather than bowel or solid tissue.
Hydroceles are painless and do not cause discomfort to the baby. The baby feeds, sleeps, and behaves normally.
How Hydroceles Develop
During fetal development, the testicles form in the abdomen and descend through the inguinal canal into the scrotum, accompanied by a fold of peritoneum (the lining of the abdominal cavity) called the processus vaginalis. Normally, this connection between the abdominal cavity and the scrotal sac closes before or shortly after birth. If it remains open, peritoneal fluid can track down into the scrotal sac — this is a communicating hydrocele.
In a communicating hydrocele, the scrotal swelling may fluctuate in size — appearing larger when the baby is upright or crying (when abdominal pressure is higher) and smaller when the baby is lying flat and at rest. This fluctuation is characteristic of the communicating type and helps distinguish it from a non-communicating hydrocele.
A non-communicating (simple) hydrocele forms when fluid accumulates around the testicle but has no connection to the abdominal cavity. These are typically stable in size and do not fluctuate.
Natural History and Resolution
Most communicating hydroceles in newborns resolve spontaneously within the first twelve to twenty-four months as the processus vaginalis closes. The majority close by twelve months. The family is advised to monitor the swelling and report if it changes significantly in character (becomes hard, painful, or associated with redness) or if new symptoms develop.
A hydrocele that has not resolved by eighteen to twenty-four months, is unusually large, or is associated with other symptoms should be reviewed by a GP and may be referred to a paediatric surgeon for consideration of elective surgery. Surgical correction (hydrocelectomy) is a straightforward day-case procedure if intervention is indicated.
Distinguishing from Inguinal Hernia
The most important distinction to make for a scrotal swelling in a baby boy is between a hydrocele and an inguinal hernia. An inguinal hernia occurs when abdominal contents (most commonly bowel) protrude through the inguinal canal into the scrotal sac. Unlike a hydrocele, an inguinal hernia does not transilluminate, may contain a bowel sound on auscultation, may be reducible (the contents can be pushed back into the abdomen), and may be associated with discomfort.
An inguinal hernia in an infant requires prompt surgical referral because of the risk of incarceration — the hernia becoming stuck and the bowel being strangled, which is a surgical emergency. If a scrotal swelling is hard, not transilluminable, associated with distress, or if there is concern that contents cannot be reduced, urgent medical assessment is needed.
When to Seek Prompt Medical Attention
Although hydroceles are benign, any scrotal swelling in a baby associated with the following features warrants urgent assessment: acute onset scrotal swelling with pain or distress (may indicate testicular torsion — a surgical emergency requiring treatment within hours); redness and warmth of the scrotal skin (may indicate infection or torsion); hard or non-transilluminable swelling; or sudden increase in size of an established hydrocele.
Key Takeaways
A hydrocele — a collection of fluid in the scrotal sac surrounding the testicle — is one of the most common findings in newborn boys, affecting approximately one to two per cent of term males. The vast majority of communicating hydroceles (where a small connection to the abdominal cavity persists) resolve spontaneously within the first twelve to twenty-four months as the connection closes. Hydroceles that are non-communicating, large, or persist beyond two years, or that are associated with an inguinal hernia, may require surgical referral. Hydroceles are painless, benign, and do not affect the health or fertility of the testicle.
