Noticing that one side of your child's scrotum is larger than the other is a common reason for a paediatric surgery consultation, and, most of the time, the explanation is a simple one. It's called a hydrocele: a collection of fluid around the testicle. It can appear on one side or on both.
What worries parents most isn't the name, but what happens next. This article covers the essentials: how to recognise it, what distinguishes the different types, when a physical examination is enough, when watchful waiting is the right approach, and when treatment is needed.
What a hydrocele actually is
During pregnancy, the testicles descend from the abdomen into the scrotum through a channel called the processus vaginalis. Normally this channel closes before birth or shortly afterwards.
When it doesn't close, or when fluid stays trapped along the way, a hydrocele forms. The result is a set of situations that look identical from the outside but are not managed or treated in the same way.
When the channel stays open, it can allow more than fluid to pass through from the abdomen. This is exactly why a communicating hydrocele and an inguinal hernia are so easily confused.
The two look the same from the outside, which is why the examination focuses on how the swelling behaves, not only on its size.
Three different situations, not two
This is where precision matters, because the distinction shapes everything that follows.
Communicating hydrocele
Varies through the dayThe channel has stayed open. Fluid from the abdomen travels down and surrounds the testicle, which means the swelling changes size through the day: it is usually smaller first thing in the morning and larger when the child has been standing, crying, running or straining.
That variation is the most characteristic sign, and the one that deserves the most attention, because the same open channel can allow more than fluid to pass through.
Congenital non-communicating hydrocele
StableThe channel has closed, but fluid remains trapped around the testicle. This is very common in newborns and infants.
Here the swelling is stable: it doesn't grow by the end of the day or with exertion. The body gradually reabsorbs the fluid, and most of these cases resolve on their own during the first or second year of life.
Secondary or acquired hydrocele
Appears laterThis appears later, in a child who previously had no swelling, as a response to injury, inflammation or infection. Less commonly, it can be linked to a testicular lesion or tumour.
In this case the order is reversed: the cause is identified and treated first, and only then is the hydrocele itself considered.
When an examination is enough, and when an ultrasound is needed
A clinical examination assesses the size, the consistency, whether the swelling varies through the day and, above all, the testicle itself. One classic sign is transillumination: a light held against the scrotum passes through the fluid, which does not happen with other causes of swelling.
A physical examination is usually sufficient when
- ✓The swelling is smooth, painless and not growing quickly
- ✓The testicle can be felt and examined
- ✓There is no doubt about the diagnosis
- ✓The testicle cannot be felt
- ✓There is pain, firmness or rapid growth
- ✓The swelling appears in an older child
- ✓There has been an injury, or a secondary cause is suspected
The useful rule is this: appearance alone does not confirm the cause. If there is any doubt between a hydrocele and an inguinal hernia, assessment should not be delayed.
Watch, investigate, or treat?
The decision depends far more on age, on how the swelling is changing and on the underlying cause than on size alone.
In an infant with a non-communicating hydrocele, watchful waiting is the usual and safe approach. Most resolve on their own by 12 to 24 months without any intervention.
Surgery is considered if
- ✓The hydrocele persists beyond the expected period
- ✓It grows or causes discomfort
- ✓There is any suspicion of an associated hernia or a problem with the testicle
- ✓The size clearly varies through the day, suggesting an open channel
In a secondary hydrocele, the cause is investigated and treated. The hydrocele may shrink as the underlying problem improves, may be monitored for a few months where it is safe to do so, or may be operated on if it persists, grows or causes symptoms.
A simple, painless hydrocele does not usually harm the testicle.
Any urgency comes from diagnostic uncertainty, not from the fluid itself.
If surgery is needed
The technique depends on whether there is a communication with the abdomen.
In the communicating form, surgery is performed under general anaesthetic through a small incision in the groin. The communication is closed and the fluid is drained. This is the same approach used for an inguinal hernia.
In a secondary hydrocele, the cause is treated first. If the hydrocele itself needs treating, the approach is usually through the scrotum and tailored to the individual case.
Unlike in adults, draining the fluid with a needle is not an option in children.
The fluid simply builds up again while the channel remains open, and the procedure carries unnecessary risk.
Approximate timings for a simple one-sided repair
These are guide figures. The total time at the clinic is longer than the operation itself, and some swelling or bruising in the first few days is expected. Always follow the guidance of the team caring for your child.
Signs that need urgent assessment
A simple hydrocele is usually painless. Sudden pain or a rapid change is not consistent with a simple hydrocele and needs urgent medical assessment to rule out other causes, in particular testicular torsion, an emergency with a short window for treatment.
Seek urgent assessment if there is
- !Sudden, severe pain in the scrotum or groin
- !Pain with nausea or vomiting
- !Swelling that is rapid, hard, red or very tender
- !Fever, feeling unwell, or significant swelling after an injury
- !A lump in the groin that will not go down, with vomiting or irritability (this may indicate a trapped hernia)
Contact the team if there is fever, increasing pain, spreading redness, warmth, pus, persistent bleeding or difficulty passing urine.
Confirming the type is what matters
If you notice persistent swelling in your child's scrotum, arrange an assessment. In the vast majority of cases this is a benign condition that either resolves on its own or is corrected with a straightforward operation and a quick recovery.
What matters is confirming which type it is, and that cannot be done by eye alone.
Book an appointment
Paediatric surgery consultations assess the swelling, the testicle and the need for any further investigation, and define the most appropriate approach for your child.
This article is for information only and does not replace individual medical assessment.
- European Association of Urology — Paediatric Urology Guidelines, Hydrocele chapter: uroweb.org/guidelines/paediatric-urology/chapter/hydrocele
- European Association of Urology — Paediatric Urology Guidelines, Acute Scrotum chapter: uroweb.org/guidelines/paediatric-urology/chapter/acute-scrotum
- Cambridge University Hospitals NHS — Hydrocele in boys: cuh.nhs.uk/patient-information/hydrocele_in_boys
- Great Ormond Street Hospital NHS — Inguinal hernias and hydroceles: gosh.nhs.uk/conditions-and-treatments/conditions-we-treat/inguinal-hernias-and-hydroceles
