23.3 Scrotum & Testes

Technique and Normal Anatomy

Scrotal sonography is performed with a high-frequency linear-array transducer (7.5–15 MHz or higher). The penis is retracted onto the abdomen, and a towel supports and elevates the scrotum. Because many pathologies are unilateral, side-by-side split-screen comparison views of both testes in grayscale and color Doppler are essential. Doppler settings are optimized for slow flow (low pulse repetition frequency, low wall filter, high gain), and the Valsalva maneuver is added when evaluating for varicocele.

The normal testis measures roughly 3–5 × 2–3 × 2–3 cm with homogeneous, medium-level echogenicity. Normal variants and landmarks include:

• Tunica albuginea — the echogenic fibrous capsule surrounding the parenchyma
• Mediastinum testis — a linear echogenic band along the posterior testis where vessels and ducts enter; a landmark, not a mass
• Rete testis — tubular network in the mediastinum; cystic dilation (tubular ectasia) is benign
• Epididymis — posterolateral; the head caps the superior pole, with body and tail running behind the testis; normally isoechoic to the testis with similar flow

Color Doppler of the normal testis shows symmetric low-velocity arterial and venous flow.

The Acute Scrotum: Torsion versus Epididymo-Orchitis

Distinguishing testicular torsion from epididymo-orchitis is the central task of scrotal Doppler, and the two show opposite flow patterns.

Testicular torsion is twisting of the spermatic cord that cuts off arterial inflow. It is a urologic emergency — testicular salvage drops sharply after about 6 hours and is unlikely beyond 24 hours. Risk is highest in adolescents with the bell-clapper deformity, in which the tunica vaginalis completely surrounds the testis so it hangs freely and can rotate. The testis may look normal in the first hours, then becomes enlarged and hypoechoic from edema (heterogeneity and hemorrhage suggest non-viability). The decisive finding is on Doppler: absent or markedly decreased intratesticular flow compared with the normal side. The twisted spermatic cord may show the "whirlpool sign."

Epididymo-orchitis is infection/inflammation, the most common cause of acute scrotal pain in adults. Ultrasound shows an enlarged, hyperemic epididymis (the head usually first), often extending to the testis as orchitis, with increased color Doppler flow — the opposite of torsion. A reactive hydrocele and scrotal wall thickening are common.

Fluid Collections and Varicocele

A varicocele is abnormal dilation of the pampiniform plexus, diagnosed when the serpiginous veins measure greater than about 2–3 mm, with flow that increases or reverses during Valsalva. It is described as a "bag of worms." Roughly 85% occur on the left because the left testicular vein drains at a right angle into the left renal vein (creating higher pressure), whereas the right drains directly into the inferior vena cava. A new right-sided or non-decompressing varicocele in an older man warrants retroperitoneal evaluation for an obstructing mass. Varicoceles elevate scrotal temperature and impair spermatogenesis, making them the most common correctable cause of male infertility.

Testicular Microlithiasis

Testicular microlithiasis appears as multiple tiny (1–2 mm) non-shadowing echogenic foci scattered through the parenchyma — calcium deposits within the seminiferous tubules. Classic microlithiasis is defined as five or more foci in a single transducer field. It is usually incidental and benign, but a reported association with germ cell tumors prompts self-examination counseling and sometimes follow-up imaging when other risk factors are present.

Testicular Tumors

The cardinal rule: any solid intratesticular mass is considered malignant until proven otherwise. About 95% of testicular malignancies are germ cell tumors, and they are the most common solid cancer of young men (ages roughly 15–35). Risk factors include cryptorchidism (even after orchiopexy), a prior contralateral tumor, and family history. Testicular cancer most often presents as a painless mass and typically spreads first to the retroperitoneal (para-aortic) lymph nodes.

• Seminoma — the most common germ cell tumor. Sonographically it is a well-defined, homogeneous, hypoechoic solid mass, usually confined by the tunica, sometimes lobulated.
• Nonseminomatous tumors — embryonal carcinoma, yolk sac tumor (the typical pediatric germ cell tumor, with elevated alpha-fetoprotein), choriocarcinoma (elevated human chorionic gonadotropin, early hematogenous spread), teratoma, and mixed types. These tend to be heterogeneous, with cystic areas, coarse calcifications, and irregular margins.
• Stromal tumors — Leydig and Sertoli cell tumors, usually small and benign.
• Lymphoma — the most common testicular malignancy in men over 60; often bilateral and diffusely infiltrating.

Extratesticular masses, in contrast, are usually benign — spermatoceles, epididymal cysts, adenomatoid tumors (the most common epididymal tumor), and lipomas of the spermatic cord. Distinguishing intratesticular from extratesticular location is therefore critical.

Cryptorchidism is failure of testicular descent; ultrasound localizes the undescended testis, usually in the inguinal canal as a small, hypoechoic oval. Beyond infertility, it confers a markedly increased (roughly 5–10×) malignancy risk in the affected testis that persists even after orchiopexy.

Trauma

In scrotal trauma, ultrasound assesses integrity of the tunica albuginea. Testicular rupture shows a disrupted capsule with heterogeneous parenchyma extruding and loss of normal contour — a surgical emergency requiring prompt repair to salvage the testis. A testicular fracture is a linear hypoechoic band across the parenchyma with the capsule intact. An intratesticular hematoma appears as an avascular complex area, and Doppler confirms whether the injured testis remains perfused.