Pyocele

A pyocele is a purulent fluid collection within the potential space between the visceral and parietal layers of the tunica vaginalis surrounding the testicle — in effect, an infected hydrocele. It most often complicates acute epididymo-orchitis, but can also arise from scrotal trauma, an infected simple hydrocele, or intra-abdominal infection tracking down a patent processus vaginalis (e.g., perforated appendicitis). On ultrasound, a pyocele appears as a complex, heterogeneous scrotal fluid collection with septations, loculations, and occasionally fluid-fluid or air-fluid levels, distinguishing it from a simple hydrocele’s anechoic fluid. Prompt recognition matters because untreated pyocele can progress to testicular infarction, abscess, or Fournier’s gangrene.

Quick Reference

• Definition: purulent collection between the visceral and parietal tunica vaginalis (infected hydrocele)
• Most common cause: acute epididymo-orchitis with secondary infection of an existing hydrocele
• Other causes: scrotal trauma with secondary infection, patent processus vaginalis allowing intra-abdominal pus to track into the scrotum (e.g., perforated appendicitis, peritonitis), hematogenous or urinary tract spread (neonates), idiopathic (infants)
• Key US findings: complex/heterogeneous fluid, internal septations, loculations, debris, fluid-fluid or air-fluid levels, thickened and hyperemic scrotal wall
• Associated testicular findings: heterogeneous echotexture and increased color Doppler flow when orchitis coexists
• Key pitfall: in infants, a septated pyocele with diminished intratesticular flow can mimic missed/late testicular torsion on Doppler US
• Simple hydrocele vs. pyocele: simple hydrocele = anechoic, no septations; pyocele = complex, septated, often with wall thickening/hyperemia
• Management: broad-spectrum antibiotics plus drainage — surgical exploration/drainage in most cases; ultrasound-guided percutaneous aspiration is a described alternative in select pediatric cases
• Why it matters: delayed treatment risks testicular loss, abscess, or Fournier’s gangrene — this is a urologic emergency, not a routine hydrocele

Background

Pyocele of the scrotum is an uncommon but important urologic emergency: a purulent collection forming in the potential space of the tunica vaginalis, most often as a complication of acute epididymo-orchitis (Bruner et al., 2012). It has also been described following blunt scrotal trauma with subsequent rupture and purulent contamination of the collection (Sood et al., 2023), secondary to Staphylococcus lugdunensis epididymo-orchitis (Asif et al., 2021), and — notably in neonates and infants — from intra-abdominal or urinary tract sources tracking through a patent processus vaginalis, including cases secondary to perforated appendicitis (Al Bazroon et al., 2024) and neonatal urinary tract infection (Jamali et al., 2024). In infants, a substantial proportion of cases remain idiopathic, with no identifiable source despite thorough workup (Terentiev et al., 2015).

Imaging Anatomy

The tunica vaginalis is a closed, mesothelium-lined sac derived from the processus vaginalis, consisting of a visceral layer applied directly to the testis and epididymis and a parietal layer lining the inner scrotal wall. Normally this potential space contains only a thin film of serous fluid. A pyocele occupies this same potential space but with purulent, proteinaceous, and often necrotic debris rather than simple transudate — the anatomic compartment is identical to that of a simple hydrocele, which is why the sonographic distinction rests entirely on the character of the fluid and the surrounding soft tissues rather than its location.

In neonates and infants, an incompletely obliterated processus vaginalis creates a direct anatomic conduit between the peritoneal cavity and the tunica vaginalis, explaining how intra-abdominal infection (appendiceal perforation, peritonitis) can present as a scrotal collection with minimal or absent abdominal signs (Al Bazroon et al., 2024).

Imaging Findings

Ultrasound (modality of choice)

Grayscale ultrasound is the first-line and generally sufficient modality for suspected pyocele. Characteristic findings include:

• A heterogeneous, complex fluid collection surrounding the testicle, in contrast to the anechoic fluid of a simple hydrocele
• Internal septations and loculations, sometimes numerous, occasionally extending from the testicular surface to the scrotal wall
• Debris, low-level internal echoes, or a dependent fluid-fluid level from settling purulent material
• Air-fluid levels in select cases, particularly with gas-forming organisms or following instrumentation
• Thickened, hyperemic parietal tunica/scrotal wall on grayscale and color Doppler imaging
• Concomitant epididymo-orchitis in many cases: enlarged, heterogeneous testis and/or epididymis with increased color Doppler flow

A point-of-care ultrasound case series and multiple published reports describe this pattern consistently: a complex, septated collection with wall thickening and hyperemia, often with an inflamed testis/epididymis adjacent to it, rather than the simple anechoic fluid expected of an uncomplicated hydrocele.

The torsion mimic pitfall

A well-documented pitfall in infants is that a septated pyocele can closely mimic missed or late testicular torsion on Doppler sonography. In one reported case, a complex fluid collection with septations and a fluid-fluid level surrounded a hypoechoic, poorly defined testis with thickened scrotal wall and hypervascularity of the wall but no detectable intratesticular flow — a pattern indistinguishable from infarcted, torsed testis on imaging alone; surgery was required to make the diagnosis (Lim et al., 2003). Radiologists evaluating an infant with a complex scrotal collection and absent intratesticular flow should include pyocele in the differential alongside torsion, since the sonographic appearance can overlap substantially and clinical correlation (fever, gradual rather than acute onset, absence of the torsion “whirlpool” cord sign) may be the only distinguishing feature.

CT

CT is not the primary tool for scrotal evaluation but is frequently obtained when the presentation raises suspicion for an intra-abdominal source, such as perforated appendicitis. In that setting, CT may show fat stranding or fluid tracking along the inguinal canal toward the scrotum, indicating a patent processus vaginalis as the conduit — a finding that directs both diagnosis and surgical planning (Al Bazroon et al., 2024).

Differential Diagnosis and Pitfalls

• Simple hydrocele: anechoic, no septations, no wall thickening or hyperemia — the key discriminator from pyocele
• Hematocele: complex fluid can look similar to pyocele; history of trauma, absence of infectious signs, and sometimes a fluid-debris level of blood products help distinguish, though the two can coexist or be difficult to separate on imaging alone, particularly after traumatic rupture (Sood et al., 2023)
• Testicular torsion (missed/subacute): especially in infants, absent intratesticular flow with a complex extratesticular collection can mimic torsion; septated pyocele has been reported to closely reproduce this appearance (Lim et al., 2003)
• Testicular/epididymal abscess: a discrete intratesticular or intraepididymal fluid collection may coexist with or be mistaken for pyocele; careful evaluation of whether the collection is intra- or extratesticular clarifies this
• Tumor with reactive hydrocele: a solid intratesticular mass with reactive simple fluid should not be confused with the septated, purulent-appearing fluid of pyocele; if the testis itself is difficult to assess due to surrounding complex fluid, this should be flagged for follow-up once the acute infection resolves

Clinical Impact and Management

Recognizing pyocele on imaging changes management directly: this is a surgical urologic emergency, not an entity managed with hydrocelectomy alone. Standard treatment is broad-spectrum antibiotics combined with drainage, historically via surgical exploration and washout, with orchiectomy reserved for cases where the testis is unsalvageable (Bruner et al., 2012). In selected pediatric cases without frank testicular necrosis, ultrasound-guided percutaneous aspiration under local anesthesia has been reported as an effective, less invasive alternative to open surgical drainage, avoiding general anesthesia and its associated risks (Oberlin & Cheng, 2015). Delayed diagnosis or treatment carries risk of testicular infarction, abscess formation, and Fournier’s gangrene, underscoring why the radiologist’s report should clearly flag a complex, septated collection as concerning for pyocele rather than describing it simply as a “hydrocele.”

When an intra-abdominal source is suspected — particularly in a child or adult with a right-sided collection and gastrointestinal symptoms — the report should prompt evaluation for a patent processus vaginalis and an intra-abdominal source such as appendicitis, since management in that scenario also requires addressing the abdominal pathology, not just the scrotal collection (Al Bazroon et al., 2024). In neonates, an unexplained pyocele should prompt urinalysis and urine culture in addition to the traditional workup for hematogenous or intraperitoneal sources, since urinary tract infection has been documented as a cause (Jamali et al., 2024).

Frequently Asked Questions

What is a pyocele of the scrotum?

A pyocele is a collection of purulent (infected) fluid within the potential space of the tunica vaginalis surrounding the testicle — essentially an infected hydrocele. It most commonly develops as a complication of acute epididymo-orchitis, though trauma and intra-abdominal or urinary sources are also recognized causes.

How is pyocele different from a simple hydrocele on ultrasound?

A simple hydrocele appears as anechoic (simple) fluid without septations or wall thickening. A pyocele appears as complex, heterogeneous fluid with internal septations, loculations, debris, and often a thickened, hyperemic scrotal wall — these features indicate infection rather than a benign fluid collection.

Can pyocele mimic testicular torsion on imaging?

Yes. In infants especially, a septated pyocele with a hypervascular scrotal wall but absent intratesticular Doppler flow can closely resemble missed or late testicular torsion. Surgical exploration may be needed to distinguish the two when the sonographic picture is ambiguous.

What causes a scrotal pyocele?

The most common cause is secondary infection complicating acute epididymo-orchitis. Other recognized causes include scrotal trauma with secondary infection, a patent processus vaginalis allowing intra-abdominal infection (such as perforated appendicitis) to track into the scrotum, hematogenous or urinary tract spread in neonates, and idiopathic cases, particularly in infants.

How is pyocele treated?

Treatment is broad-spectrum antibiotics combined with drainage. Surgical exploration and drainage is standard, with orchiectomy reserved for a non-viable testis. Ultrasound-guided percutaneous aspiration has been described as an effective, less invasive alternative in select pediatric cases.

Is pyocele a surgical emergency?

Yes. Because delayed treatment can lead to testicular infarction, abscess formation, or Fournier’s gangrene, pyocele is managed as a urologic emergency requiring prompt antibiotics and drainage, not observation or hydrocelectomy alone.

References

1. Bruner DI, Ventura EL, Devlin JJ. Scrotal pyocele: uncommon urologic emergency. J Emerg Trauma Shock. 2012;5(2):206. PMID: 22787360
2. Oberlin DT, Cheng EY. Management of pediatric pyocele using percutaneous imaging-guided aspiration. J Pediatr Urol. 2015. PMID: 26453938
3. Al Bazroon AA, Alabandi AM, Alnemer MM, Abu Alsaud S. Scrotal pyocele secondary to perforated appendicitis in middle-aged man: a case report and review of literature. Cureus. 2024;16(1):e51476. PMID: 38298279
4. Sood A, Mishra GV, Khandelwal S, Saboo K, Suryadevara M. Post-traumatic ruptured scrotal collection: pyocele or hematocele? Cureus. 2023;15(9):e45198. PMID: 37842434
5. Jamali Z, Shafie’ei M, Soltani Nejad N. Neonatal pyocele originating from a urinary tract infection: a case report. J Med Case Rep. 2024. PMID: 38414046
6. Lim GY, et al. Infantile scrotal pyocele simulating missed testicular torsion on sonography. J Clin Ultrasound. 2003;31(2):116-118. PMID: 12539255
7. Terentiev V, Dickman E, Zerzan J, Arroyo A. Idiopathic infant pyocele: a case report and review of the literature. J Emerg Med. 2015;48(4):e93-96. PMID: 25278135
8. Asif AA, Shah N, McBee Orzulak FJ. Staphylococcus lugdunensis causing epididymo-orchitis with scrotal pyocele. IDCases. 2021;24:e01133. PMID: 33996467