Scrotal Ultrasound

Scrotal ultrasound uses a high frequency linear probe (10 to 15 MHz) to image the testes, epididymides, spermatic cords, scrotal wall and scrotal contents, with colour and power Doppler to show testicular blood flow. The patient lies supine with the scrotum supported by a towel, the penis laid on the abdomen, and both testes are examined in two planes and compared with each other.

Normal testes measure 4 to 5 cm in length, 2.5 to 3 cm in width and 3 cm in depth (volume 12 to 20 mL, by the ellipsoid formula length x width x depth x 0.71). The examination takes 10 to 20 minutes, with no radiation. Scanning with Valsalva manoeuvre and in the standing position shows varicocele. Elastography and contrast enhanced ultrasound are used selectively for tumours.

Acute scrotal pain and swelling are urgent presentations, mostly from epididymo orchitis, testicular torsion (1 in 4000 males under 25 years each year) and torsion of the testicular appendage. Torsion is a surgical emergency with a salvage rate of about 90 to 100% within 6 hours, 50% at 12 hours and under 10% after 24 hours, so clinical suspicion should not wait for ultrasound.

Testicular cancer is the commonest cancer in men aged 15 to 40 (incidence about 5 in 100 000), and is curable in over 95% of localised cases; any solid intratesticular mass is considered malignant until proven otherwise. Ultrasound has a sensitivity and specificity of 95 to 100% for intratesticular masses and 90 to 100% for torsion with colour Doppler in expert hands.

Indications. Acute scrotal pain or swelling (torsion, epididymo orchitis, torsion of appendage, trauma, hernia, abscess, haematoma). Palpable testicular mass or hard lump, or an intrascrotal mass of uncertain origin. Painless scrotal swelling (hydrocele, varicocele, spermatocele, hernia). Trauma (rupture of the tunica albuginea, haematocele, haematoma).

Infertility (varicocele, testicular size and texture, obstructive causes), abnormal semen analysis. Undescended or impalpable testis. Follow up of testicular microlithiasis in high risk men, previous tumour, or contralateral testis. Metastatic cancer of unknown primary in a young man (burnt out testicular tumour). Gynaecomastia with suspected testicular tumour (hormone secreting).

Chronic scrotal pain. Not for routine screening of asymptomatic men.

Contraindications and precautions. None absolute. Examination can be painful and requires gentle technique and warm gel. Doppler gain is set low to show slow flow, and pulse repetition frequency is adjusted. In suspected torsion, ultrasound must not delay surgery; if the clinical picture strongly suggests torsion, the patient goes directly to surgery. A chaperone is offered. Children and adolescents need privacy and parental consent.

Preparation and technique. No fasting or bladder preparation is needed. Grey scale images of each testis in long and transverse axis with the epididymal head, body and tail, and the spermatic cord are taken. Both testes are compared in the same image (side-by-side views) for symmetry of size, echotexture and Doppler flow.

Colour and power Doppler with low flow settings, and spectral Doppler of the intratesticular arteries (resistive index 0.5 to 0.7) and veins, are recorded. Valsalva manoeuvre and standing position show varicocele (veins over 2 to 3 mm in diameter with reflux). The inguinal canal is examined for hernia and undescended testis.

Normal appearances. Testis: oval, homogeneous medium level echoes (fine granular), smooth surface, with a thin echogenic tunica albuginea, a central echogenic line of the mediastinum testis, and volume 12 to 20 mL (smaller in puberty, atrophic in disease). Epididymis: head 10 to 12 mm, body and tail 2 to 5 mm, iso- to slightly hyperechoic to testis, coarse echotexture.

Spermatic cord: pampiniform plexus veins under 2 mm. Scrotal wall under 5 mm. Small amount of fluid between the layers of the tunica vaginalis is normal. Appendix testis and appendix epididymis (3 to 5 mm) may be seen as small ovoid structures.

Doppler: low resistance arterial flow with a continuous diastolic component, and venous flow, equal on both sides, with visible intratesticular colour flow.

Interpretation.

• Testicular torsion: enlarged, heterogeneous, hypoechoic testis (later, with haemorrhagic areas), absent or reduced intratesticular colour flow compared with the other side (the key sign), high resistance flow or reversed diastolic flow, twisted spermatic cord (the "whirlpool" sign), enlarged epididymis, reactive hydrocele, and scrotal wall thickening. Partial torsion and intermittent torsion may preserve some flow, so normal Doppler does not exclude torsion when clinical suspicion is high. After detorsion, hyperaemia is seen. Late torsion (over 24 hours) shows a small, heterogeneous testis with infarction and a hyperaemic rim.
• Epididymo orchitis: enlarged, hypoechoic or heterogeneous epididymis (head and tail), increased colour flow, thickened scrotal wall, reactive hydrocele with debris, and an enlarged hypoechoic and hyperaemic testis when orchitis coexists; complications are abscess (complex collection, loss of normal structure), infarction (focal avascular area) and pyocele. Mumps orchitis, tuberculous epididymitis (nodular, with sinus tracts and calcification) and brucellosis occur.
• Torsion of the appendage: a small round echogenic or hypoechoic nodule near the upper pole with hyperaemic surrounding tissue and a normal testis with normal flow ("blue dot" sign on the skin).
• Testicular tumour: intratesticular solid mass, usually hypoechoic and well defined (seminoma: homogeneous and lobulated; non-seminomatous germ cell tumour: heterogeneous with cysts, calcification and haemorrhage), vascular on Doppler, and may enlarge the testis; Leydig cell tumours are small hypoechoic and hypervascular; lymphoma (older men, bilateral, diffuse infiltration with hypoechoic texture and preserved vessels), and leukaemic infiltration. Extratesticular tumours are rare and usually benign (adenomatoid tumour, lipoma).
• Benign intratesticular lesions: epidermoid cyst (onion skin ring pattern, avascular), simple cyst (anechoic, near the mediastinum), tubular ectasia of the rete testis (dilated tubular structures at the mediastinum), segmental infarct (wedge shaped avascular area), focal orchitis, haematoma after trauma, testicular microlithiasis (5 or more echogenic foci of 1 to 3 mm in a section, "starry sky"), and adrenal rests in congenital adrenal hyperplasia (bilateral hypoechoic nodules).
• Hydrocele: anechoic fluid around the testis (simple), or with septa and debris (infected, haemorrhagic, post-operative, chronic); haematocele after trauma shows echogenic fluid with clots.
• Varicocele: dilated veins of the pampiniform plexus (over 2 to 3 mm) with reflux on Valsalva, more often left sided (90%); a right sided or sudden varicocele raises suspicion of retroperitoneal mass; grading is from subclinical to grade 3.
• Spermatocele and epididymal cysts: anechoic or low level echo cyst in the epididymal head; epididymal cysts are common.
• Hernia: bowel loops (with peristalsis) or omentum in the scrotum, continuous with the inguinal canal.
• Trauma: rupture of the testis (loss of tunica albuginea outline, heterogeneous parenchyma, extruded tissue, absent flow, haematocele), haematoma, scrotal wall haematoma, and dislocation.
• Undescended testis: oval hypoechoic structure in the inguinal canal (80%), smaller than normal, higher risk of malignancy; intra-abdominal testes are not seen on ultrasound.
• Infertility: small volume (under 12 mL) or heterogeneous testes, microlithiasis, varicocele, dilated epididymis or absent vas deferens.
• Fournier gangrene: gas in the scrotal wall, thickened wall, and fluid, a surgical emergency.

Critical values and findings needing immediate action.

• Testicular torsion (absent or reduced flow, twisted cord): immediate surgical exploration, with manual detorsion as a temporary measure; do not wait for the scan if clinically suspected.
• Intratesticular solid mass: urgent urology referral, tumour markers (alpha fetoprotein, beta human chorionic gonadotrophin, lactate dehydrogenase) before orchidectomy, and staging CT; no scrotal biopsy.
• Testicular rupture after trauma: urgent surgical exploration within 72 hours (salvage over 80%).
• Fournier gangrene (gas in the scrotal wall): emergency debridement and antibiotics.
• Epididymo orchitis with abscess or pyocele: antibiotics and drainage or orchidectomy.
• Strangulated inguinal hernia in the scrotum: emergency surgery.
• Suspected torsion in a newborn (perinatal torsion): urgent surgical review.
• Right sided varicocele or sudden onset of left varicocele that does not empty when supine: CT of the abdomen for renal or retroperitoneal tumour.

Limitations and artefacts.

• Doppler can be falsely normal or falsely negative: intermittent or partial torsion (less than 360 degrees) may keep some flow, early torsion has preserved flow, and inflammation causes hyperaemia that can hide reduced flow; flow in the testis of a prepubertal boy or neonate is low and hard to detect (use high sensitivity settings); a hyperaemic epididymis or scrotal wall flow can be mistaken for testicular flow.
• Absent flow can result from technical settings (gain too low, wrong pulse repetition frequency), deep oedema or a large hydrocele; always compare with the other side.
• The ultrasound appearance of a tumour cannot determine its type; the impalpable lesion under 5 mm can be benign (small hypoechoic lesions are benign in about 80%) but needs follow up or surgery.
• Distinguishing intratesticular from extratesticular lesions is key (extratesticular masses are usually benign).
• Normal variants mimic disease: mediastinum testis (echogenic band), tubular ectasia, appendices, epididymal heterogeneity, and the normal asymmetric size.
• Microlithiasis alone does not require follow up in the absence of other risk factors (maldescent, previous tumour, infertility), and screening has no proven benefit.
• Ultrasound is operator dependent, and a poor view in a painful, tense scrotum can be repeated.
• Delay in diagnosis of torsion from waiting for imaging is the most important error.

Special groups.

• Newborns and infants: perinatal torsion, hydrocele, hernia and undescended testis; the testis is small and flow is low.
• Adolescents (peak age 12 to 18): torsion is the commonest cause of acute scrotal pain; the appendage torsion is common in boys aged 7 to 14; any acute pain is torsion until proven otherwise.
• Young men: testicular tumours, epididymo orchitis due to sexually transmitted infection, varicocele and infertility.
• Older men: epididymo orchitis from urinary tract infection or prostate disease, hydrocele, hernia, and lymphoma.
• Patients with undescended testis: higher cancer risk, orchidopexy before 12 to 18 months of age.
• Men with infertility: ultrasound of the testes, varicocele and genital tract.
• Regions: filarial hydrocele, tuberculous epididymitis, schistosomal and brucella epididymo orchitis, delayed presentation of torsion with infarction, and testicular tumours with late stage are seen; ultrasound with Doppler is the main imaging, and clinical diagnosis with prompt exploration is critical when scanning is delayed.

Follow up tests. Urgent surgical exploration for suspected torsion, serum tumour markers (alpha fetoprotein, beta human chorionic gonadotrophin, lactate dehydrogenase) and CT of the chest, abdomen and pelvis for staging of tumour, urine microscopy and culture, urethral swab or urine polymerase chain reaction for chlamydia and gonorrhoea, tuberculosis tests, semen analysis,

hormone tests for infertility (follicle stimulating hormone, luteinising hormone, testosterone), ultrasound follow up of small indeterminate testicular lesions and microlithiasis in high risk men, CT or MR for retroperitoneal masses causing varicocele, karyotype and genetic tests for azoospermia, and referral to urology, andrology or oncology.