Fluid inside the scrotum is both normal and, in many cases, a sign of a specific medical condition. A small amount of lubricating fluid naturally sits between the layers of tissue surrounding each testicle. When that fluid accumulates beyond the usual trace amount, the result is typically a hydrocele, the most common cause of painless scrotal swelling in adults and children alike. But hydroceles are not the only possibility. Blood, pus, and fluid from entirely different body systems can also end up in the scrotum, each pointing to a different cause and requiring a different response.
The Normal Fluid and What Happens When There Is Too Much
Each testicle sits inside a double-layered sac called the tunica vaginalis. A thin film of fluid between those layers lets the testicle move freely and reduces friction. You never notice this fluid because the body produces and reabsorbs it in balance. A hydrocele develops when that balance tips: either too much fluid is produced, or not enough is reabsorbed. The swelling is usually painless, feels smooth, and can range from barely noticeable to the size of a grapefruit or larger. Hydroceles are classified by their underlying cause, including primary (no identifiable trigger), secondary to infection or inflammation, trauma-induced, tumor-related, and congenital types that trace back to fetal development.1Current Urology. Classifying Hydroceles of the Pelvis and Groin: An Overview of Etiology, Secondary Complications, Evaluation, and Management
Hydroceles are not the only fluid collections that occur in the scrotum, though. Ultrasound studies have identified a range of fluid-filled structures in this area, including epididymal cysts (small, benign sacs on the tube that carries sperm), spermatoceles (cysts containing dead sperm cells), and hematoceles (collections of blood). Each has a distinct appearance on imaging, and telling them apart matters because the treatment path differs.2Europe PMC. Common and Uncommon Presentation of Fluid within the Scrotal Spaces
Why Fluid Builds Up in Adults
In adults, the most common hydroceles are idiopathic, meaning no clear trigger is found. These tend to develop gradually in men over 40 and are thought to result from a slow imbalance between fluid secretion and absorption in the tunica vaginalis. They are almost always painless and grow slowly enough that some men live with them for years before seeking treatment.
Infection is one of the better-understood secondary causes. Epididymitis and orchitis, inflammations of the sperm-carrying tube and the testicle respectively, often produce a reactive hydrocele as part of the body’s inflammatory response. When the infection clears, the fluid sometimes resolves on its own, but not always. In tropical and subtropical regions, parasitic infections caused by filarial worms remain a significant cause of hydrocele, damaging the lymphatic drainage of the scrotum and leading to chronic, sometimes massive fluid buildup.3Europe PMC. Filarial Affections of the Male Genital Tracts
Trauma to the groin can cause both hydroceles and hematoceles. A hematocele is a collection of blood rather than clear serous fluid, and it is usually painful, unlike a typical hydrocele. Most hematoceles follow a direct blow to the scrotum and are associated with a clear history of injury, though on rare occasions they appear without an obvious cause.4PubMed Central. The strange case of a hematocele mistaken for a neoplastic scrotal mass This distinction matters clinically because a painless mass that looks like a hematocele but has no trauma history can sometimes mimic a tumor on exam.
Scrotal Fluid in Babies and Children
Hydroceles in newborns and infants work differently from adult hydroceles. During fetal development, a small channel called the processus vaginalis allows the testicle to descend from the abdomen into the scrotum. This channel normally closes off shortly after birth. When it stays open, abdominal fluid can trickle down into the scrotum, creating what’s called a communicating hydrocele. The swelling often changes in size throughout the day, getting bigger when the baby is upright and crying, and shrinking when the baby lies down and relaxes.5PubMed Central. Persistence of the processus vaginalis and its related disorders
The good news for parents is that many infant hydroceles resolve without surgery. One study tracking 110 boys found that about 63% had complete resolution without an operation, at an average age of roughly 12 months. The remaining 37% went on to surgery, usually because the swelling persisted or a hernia developed during observation. Importantly, none of the boys who developed a hernia during the waiting period had a dangerous incarceration (where bowel gets trapped).6PubMed. Infant communicating hydroceles–do they need immediate repair or might some clinically resolve? A separate study found a similar pattern, with about 60% of infant communicating hydroceles resolving spontaneously within 18 months of follow-up.7Egyptian Pediatric Association Gazette. Watchful waiting for communicating hydrocoele in infants
The general approach pediatric surgeons take is watchful waiting, typically holding off on surgery for at least 12 to 18 months unless there are signs of a hernia. This applies to standard communicating hydroceles. A rarer variant called an abdominoscrotal hydrocele, where the fluid extends up into the abdomen, is more complex. Even with this type, research suggests that roughly a quarter of cases in infants resolve on their own, though the rest require earlier intervention.8PubMed. Early Surgery Versus Watchful Waiting Strategy for Infantile Abdominoscrotal Hydrocele
When the Problem Is Not Local
Sometimes scrotal swelling has nothing to do with the scrotum itself. The scrotum sits low on the body and has loose, distensible tissue, making it a collecting point for fluid that is really coming from a whole-body problem. Heart failure is one of the more common systemic culprits. In advanced heart failure, the body retains fluid and it pools in dependent areas, including the legs, abdomen, and scrotum. This widespread fluid overload, called anasarca, can produce severe scrotal edema that causes significant pain and difficulty with basic activities like walking or sitting.9PubMed Central. Relieving the burden: palliative centesis of an oedematous scrotal wall due to anasarca in end-stage heart failure
Liver failure and conditions that cause low blood protein levels produce the same downstream effect. When the liver can’t make enough albumin, fluid leaks out of blood vessels throughout the body. Right-sided heart failure from any cause, including conditions like severe obstructive sleep apnea combined with obesity, can also drive massive peripheral edema that manifests prominently in the scrotum.10PubMed Central. Massive scrotal edema: an unusual manifestation of obstructive sleep apnea and obesity-hypoventilation syndrome Ultrasound in these patients shows a characteristic thickened scrotal wall with a layered “onion-like” appearance, while the testicles themselves look normal underneath all that swelling.11PubMed. The ultrasound appearances of scrotal oedema
The treatment in these systemic cases is not scrotal surgery. It’s managing the underlying condition: diuretics for heart failure, treating the liver disease, or addressing the sleep apnea. Draining the scrotal fluid directly only provides temporary relief unless the root cause improves.
How Doctors Tell What’s Going On
The first step when someone notices scrotal swelling is usually a physical examination. A classic bedside test involves holding a light against the scrotum in a dark room. Clear fluid, like you’d find in a hydrocele, lets light pass through and the scrotum glows (transillumination is positive). Solid masses or blood collections block the light. This test is simple and useful but not definitive on its own.
Scrotal ultrasound is the workhorse of diagnosis. It’s painless, doesn’t involve radiation, and gives a detailed look at the testicle, the epididymis, and the surrounding fluid. An ultrasound can distinguish between a simple hydrocele (clear fluid, smooth walls), a complex hydrocele (fluid with debris or internal dividers), a hematocele (blood), and cystic structures like epididymal cysts, which appear as well-defined fluid pockets within the epididymis with no blood flow on Doppler imaging.12Cureus. Decoding Acute Scrotum: Diagnostic Accuracy of Ultrasound in Urgent Clinical Settings Importantly, ultrasound also checks whether the testicle itself looks healthy, ruling out tumors or torsion that might be hiding behind the fluid.
When Scrotal Fluid Is an Emergency
Most fluid collections in the scrotum are not urgent. A slowly growing, painless hydrocele can be evaluated at a scheduled appointment. But there are exceptions that demand fast attention.
A scrotal pyocele, where the fluid between the tunica vaginalis layers becomes infected and fills with pus, is a rare but dangerous condition. It typically develops from an untreated or inadequately treated infection of the epididymis or testicle, from trauma, or from medical instrumentation. The risk is that a pyocele can progress to Fournier’s gangrene, a rapidly spreading and life-threatening soft tissue infection. Treatment requires surgical drainage and strong antibiotics, and delay worsens outcomes significantly.13Europe PMC. Scrotal pyocele: Uncommon urologic emergency
Another situation worth watching for is when a hydrocele masks a tumor. Most hydroceles are benign, but occasionally a hydrocele forms as a secondary response to a testicular or paratesticular tumor. Case reports have documented rare tumors like mesothelioma of the tunica vaginalis presenting initially as nothing more than a hydrocele.14PubMed Central. Malignant mesothelioma of tunica vaginalis: an extremely rare case presenting without risk factors This is why ultrasound is so valuable. It lets the doctor see through the fluid to check the testicle itself. A hydrocele that appeared suddenly, is associated with pain, or developed after a recent illness deserves prompt imaging.
Surgical Repair for Hydrocele
When a hydrocele in an adult doesn’t resolve on its own (and most adult hydroceles won’t), the standard treatment is surgery. Three main techniques are used, and the evidence on which is best has some nuance.
Jaboulay’s eversion involves opening the sac, draining the fluid, and folding the sac wall behind the testicle so fluid can no longer accumulate in a closed space. Lord’s plication gathers the sac wall into folds using stitches, without cutting it away. Hydrocelectomy excises the sac entirely. A study of 276 hydrocele surgeries found that about 6% of patients needed a repeat operation for recurrence regardless of which technique was used, with no statistical difference between the three approaches. Overall complications occurred in about 12% of cases and included bruising, pain, and infection. Lord’s repair had the lowest complication rate in that analysis.15PubMed. Comparison of Recurrence and Postoperative Complications Between 3 Different Techniques for Surgical Repair of Idiopathic Hydrocele
A separate comparative study found somewhat different results, reporting that Jaboulay’s eversion had fewer postoperative complications (17%) compared to Lord’s plication (72%), along with shorter hospital stays and earlier recovery. Neither group had any recurrence at six months. The authors recommended Jaboulay’s eversion particularly for large or thick-walled hydroceles.16International Surgery Journal. Comparative analysis of Lord’s plication and Jaboulay’s eversion in the surgical management of primary vaginal hydrocele The disagreement between studies likely reflects differences in patient populations, surgical skill, and how complications were defined. In practice, the surgeon’s experience and the size and characteristics of the specific hydrocele tend to drive the choice of technique.
Sclerotherapy as a Less Invasive Alternative
For men who are poor surgical candidates or who prefer to avoid an operation, aspiration and sclerotherapy offer a middle path. The procedure involves draining the fluid with a needle and then injecting a chemical agent that irritates the sac lining, causing it to scar shut and (ideally) stop producing fluid. Several sclerosant agents have been used, including polidocanol, phenol, and tetracycline-class antibiotics. Of these, phenol has shown the highest clinical success rate, reported at about 97%, while tetracycline-based agents have achieved cure rates around 93%.17PubMed. Sclerotherapy in the Treatment of Hydroceles: A Comprehensive Review of the Efficacy, Types of Sclerosants, and Comparative Outcomes Against Hydrocelectomy
The trade-off is recurrence. A systematic review and meta-analysis comparing sclerotherapy with surgery found that sclerotherapy had a substantially higher recurrence rate. While there was no statistically significant difference in initial clinical cure, the recurrence risk after sclerotherapy was roughly nine times higher than after surgery.18PubMed. Aspiration and sclerotherapy versus hydrocelectomy for treating hydroceles: a systematic review and meta-analyses On the flip side, sclerotherapy carries fewer complications than surgery and can be done as an office procedure. For elderly patients or those with significant surgical risk factors, the higher recurrence rate may be an acceptable trade-off for a simpler recovery.
Simple aspiration alone, without sclerotherapy, is the least durable option. The fluid almost always returns within weeks to months, so aspiration by itself is mainly used for temporary relief or diagnostic purposes, not as a definitive treatment.
Scrotal Fluid You Can Feel Versus Fluid You Cannot
Not all fluid in the scrotum produces an obvious lump. Small hydroceles, tiny epididymal cysts, and early spermatoceles are frequently discovered incidentally on ultrasound performed for some other reason, like evaluating fertility or investigating pain. These findings almost never need treatment. Many men walk around with a small cyst on the epididymis their entire lives without knowing it. Unless a fluid collection is growing, causing pain, or large enough to be bothersome, the default approach is to leave it alone and monitor periodically.
On the other end of the spectrum, chronic conditions like lymphedema of the scrotum, though technically involving fluid buildup in the tissue rather than in a defined sac, can become severe. Massive localized lymphedema of the scrotum, sometimes seen in the setting of extreme obesity, can involve tissue weighing 20 kilograms or more. Surgical reconstruction in these cases is complex but can dramatically improve quality of life, with patients reporting overall quality-of-life scores jumping from poor to good after treatment.19Urology. Reconstruction of Massive Localized Lymphedema of the Scrotum: Results, Complications, and Quality of Life Improvements
Common Misconceptions About Scrotal Swelling
One persistent myth is that a hydrocele means something is wrong with the testicle. In the vast majority of cases, the testicle inside a hydrocele is completely healthy. The fluid is between the surrounding layers, not inside the testicle itself. The testicle just happens to be sitting in a bag that has overfilled.
Another misconception is that scrotal swelling in a baby always needs surgery. As the pediatric data shows, most infant communicating hydroceles close on their own within the first one to two years. Rushing to the operating room for a newborn hydrocele is not only unnecessary in most cases, it means subjecting the child to general anesthesia for a problem that will likely fix itself. Pediatric surgeons generally recommend waiting unless a hernia is also present or the swelling clearly isn’t improving.
A third misunderstanding is that draining the fluid once solves the problem. For adult hydroceles, simple aspiration is almost never a permanent fix. The sac is still intact and still producing fluid, so the hydrocele refills. Definitive treatment requires either surgery to alter or remove the sac, or sclerotherapy to scar it closed. Aspiration has its place as a temporizing measure, particularly in patients who can’t tolerate other treatments, but expecting it to be the last word in treatment usually leads to disappointment.
Epididymal Cysts and Spermatoceles
These deserve a brief mention because they are among the most common incidental fluid-filled findings in the scrotum and often cause unnecessary worry. An epididymal cyst is a small fluid-filled pocket that sits on the epididymis and contains clear fluid. A spermatocele is essentially the same thing but contains fluid mixed with dead sperm cells, giving it a slightly cloudier appearance on ultrasound. Both are benign and usually painless. On ultrasound, they show up as well-defined, round, and without any blood flow, which is one of the ways they are reliably distinguished from more concerning findings.12Cureus. Decoding Acute Scrotum: Diagnostic Accuracy of Ultrasound in Urgent Clinical Settings
Surgery for epididymal cysts and spermatoceles is only considered when they become large enough to cause discomfort or the patient finds them distressing. Even then, the procedures are straightforward and complication rates are low. For the overwhelming majority of men who are told they have one of these on an ultrasound, the correct next step is simply knowing it’s there and not worrying about it.