Testicular Ultrasound: Normal Values, Protocol, and Common Findings

Scrotal ultrasound is one of the most time-sensitive studies a sonographer performs. A patient presenting with acute scrotal pain needs a rapid, accurate assessment — testicular torsion is a surgical emergency with a narrow window for salvage. At the same time, the study is used for a wide range of non-urgent indications: palpable masses, infertility workup, post-trauma evaluation, and follow-up of known pathology. Knowing the protocol cold and recognizing the key patterns under pressure is what separates a good scrotal study from a great one.

Normal Testicular Measurements

Both testes should be measured and compared. Size discrepancy between sides is often as clinically meaningful as absolute size.

Adult Male

Measurement	Normal Range
Length (craniocaudal)	3.0–5.0 cm
Width	2.0–3.0 cm
Height (AP)	2.0–3.0 cm
Volume	12–20 mL (typical)

Volume formula (prolate ellipsoid):

Volume = Length × Width × Height × 0.523

A volume difference of >2 mL between sides is considered asymmetric and worth noting. Significant atrophy (volume <6 mL in an adult) should be documented and correlated clinically.

Epididymis

Structure	Normal Size
Epididymal head (globus major)	5–12 mm
Epididymal body	2–4 mm
Epididymal tail (globus minor)	2–5 mm

The epididymal head sits at the superior pole of the testis. It should appear isoechoic or slightly hyperechoic relative to the testis. Any enlargement, hypoechogenicity, or increased vascularity of the epididymis is abnormal.

Probe Selection and Patient Setup

Use a high-frequency linear probe (10–18 MHz). The scrotum is superficial — you want maximum resolution, not depth penetration. Most modern probes in this range provide excellent detail of testicular parenchyma, epididymis, and scrotal wall.

Patient position: Supine with the scrotum supported on a towel placed between the thighs. The penis should be draped superiorly onto the abdomen. This stabilizes the testes and keeps them in the focal zone.

Gel: Use generous gel — liberal coverage reduces artifact and improves contact without the patient discomfort of firm probe pressure.

Protocol: What to Document

Grayscale (B-mode)

For each testis, obtain and document:

1. Long axis — craniocaudal length, anterior-posterior height
2. Transverse — width at the widest point
3. Volume — calculated from the three dimensions
4. Echotexture — homogeneous medium echogenicity is normal; any focal hypo/hyperechoic area is abnormal
5. Mediastinum testis — the echogenic linear band running along the posterior aspect; normal finding, but a mass at the mediastinum warrants attention
6. Epididymis — head, body, tail; size and echogenicity
7. Hydrocele — small physiologic fluid collections (2–3 mm anterior to the testis) are normal; larger collections should be measured
8. Scrotal wall — thickening suggests inflammation or dependent edema

Color and Spectral Doppler

Doppler is not optional in scrotal ultrasound — it is required for every study. Vascular asymmetry between sides is the key finding in torsion.

Color Doppler:

• Apply to each testis and compare side to side using identical settings
• Normal: symmetric intratesticular flow bilaterally
• Abnormal: absent or markedly decreased flow on one side (torsion) or markedly increased flow (orchitis, torsion-detorsion)

Spectral Doppler (waveform):

• Sample intratesticular arteries and the main testicular artery
• Document peak systolic velocity (PSV) and resistive index (RI)
• Normal RI: 0.48–0.75
• Markedly elevated RI (>0.75) or absent diastolic flow can indicate early torsion even when color flow appears present
• Always compare RI between sides

Critical point: Do not rely on color Doppler alone. In early or partial torsion, some color flow may persist. Spectral waveform showing absent or reversed diastolic flow is more sensitive.

Testicular Torsion — What to Look For

Torsion is the diagnosis you cannot miss. The testis undergoes ischemia within hours; salvage rates drop significantly after 6 hours and approach zero after 24 hours.

Sonographic Findings

Early torsion (within 6 hours):

• Testis may appear normal on grayscale
• Absent or markedly decreased intratesticular flow on color Doppler
• Spectral waveform shows high-resistance pattern or no diastolic flow
• Epididymis may appear enlarged

Late torsion (>6–12 hours):

• Testis becomes heterogeneous — mixed echogenicity as infarction progresses
• Hyperechoic areas represent hemorrhagic infarct
• Complete absence of flow
• Reactive hydrocele and scrotal wall thickening

"Whirlpool sign":

• Twisting of the spermatic cord at the external inguinal ring or within the scrotum
• Seen on grayscale as a round echogenic structure with concentric rings
• Color Doppler shows the twisted cord with the "whirlpool" of vessels
• Pathognomonic of torsion — if you see it, call it immediately

What to Do If You Suspect Torsion

Do not delay to get more images. If you see absent flow unilaterally and the patient has acute onset pain, communicate the finding to the ordering provider immediately — this is a surgical emergency. Document what you have and send the patient.

Epididymo-Orchitis

The most common cause of acute scrotal pain in adult men. Infection typically ascends from the lower urinary tract.

Sonographic findings:

• Enlarged, hypoechoic epididymis (head most often affected first)
• Markedly increased epididymal vascularity on color Doppler
• Orchitis: diffuse or focal hypoechogenicity of the testis with increased flow
• Reactive hydrocele common
• Scrotal wall thickening

Key distinction from torsion: Flow is increased, not absent. In torsion, flow is absent or markedly decreased. The clinical picture also differs — epididymo-orchitis typically has a more gradual onset, fever, and dysuria.

Testicular Masses

Any solid intratesticular mass should be treated as malignant until proven otherwise. Testicular cancer predominantly affects men aged 15–35 and is highly curable with early detection.

Malignant Features

• Solid, hypoechoic intratesticular mass
• Internal vascularity on Doppler
• Irregular margins
• Involvement of the mediastinum testis
• Microlithiasis (scattered punctate calcifications throughout) is associated with increased risk but is not malignant itself

Benign Intratesticular Findings

• Cysts (tunica albuginea cysts, epididymal cysts, spermatoceles): anechoic, thin-walled, no internal flow — almost universally benign
• Varicocele: dilated tortuous veins in the pampiniform plexus (>3 mm), increases with Valsalva, located posterolateral to the testis; left side far more common
• Microlithiasis: five or more punctate hyperechoic foci without shadowing per image; document and note; protocol varies by institution

Reporting Tips

A complete scrotal report documents:

1. Size and volume of each testis (both sides)
2. Echotexture — homogeneous or any focal abnormality
3. Epididymis — size and echogenicity bilaterally
4. Doppler — symmetric or asymmetric flow; RI if measured
5. Hydrocele — size and bilateral comparison
6. Any extratesticular findings (hernia, varicocele, scrotal wall)

Never report a scrotal study without commenting on vascularity. An unlabeled scrotal image without Doppler documentation is an incomplete study.

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Reference: ACR–AIUM–SRU Practice Parameter for the Performance of Scrotal Ultrasound; European Association of Urology guidelines. Clinical decisions should involve the interpreting physician.