Scrotum Anatomy and Pathology — Quick Reference

Testes anatomy

The testes are symmetric, oval-shaped glands residing in the scrotum. In adults, each testis measures $3-5\ \text{cm} \times 2-4\ \text{cm} \times 3\ \text{cm}$ and is divided into more than 250 to 400 conical lobules containing the seminiferous tubules. Tubules converge at the apex of each lobule and anastomose to form the rete testis in the mediastinum; the rete testis drains into the head of the epididymis through efferent ductules.

Epididymis anatomy

The epididymis is a 6- to 7-cm tubular structure beginning superiorly and coursing posterolaterally to the testis. It is divided into head, body, and tail, with the head being the largest part (6 to 15 mm in width) and located superior to the upper pole of the testis. It contains 10 to 15 efferent ductules from the rete testis, which converge to form a single duct in the body and tail (the ductus epididymis), and it becomes the vas deferens as it continues in the spermatic cord.

Mediastinum and tunica albuginea

The testis is covered by dense, fibrous tunica albuginea. The posterior aspect of the tunica albuginea reflects into the testis to form the vertical septum known as the mediastinum testis. Multiple septa (septa testis) formed from the tunica albuginea extend through the testis to partition it into lobules. The mediastinum supports vessels and ducts coursing within the testis and is often visible on sonography as a bright hyperechoic line within the testis.

Tunica vaginalis and scrotal wall

The tunica vaginalis lines the inner walls of the scrotum and covers each testis and epididymis. It consists of two layers: the parietal layer (inner lining of the scrotal wall) and the visceral layer (surrounding the testis and epididymis). The scrotal wall comprises skin, dartos fascia and muscle, external and internal spermatic fascia, cremaster muscle and fascia, and tunica vaginalis (parietal and visceral layers).

Testicular and epididymal vessels and cords

The vas deferens continues as the ductus epididymis and forms part of the spermatic cord. Along with the testicular artery and pampiniform venous plexus, these structures, plus lymphatics, autonomic nerves, and cremaster fibers, constitute the spermatic cord, which extends from the scrotum through the inguinal canal to the pelvis.

Vascular supply

The right and left testicular arteries arise from the abdominal aorta below the level of the renal arteries. Capsular arteries give rise to centripetal arteries that course from the testicular surface toward the mediastinum along the septa. Before reaching the mediastinum, they curve backward forming recurrent rami (centrifugal arteries), which branch further into arterioles and capillaries. The cremasteric and deferential arteries accompany the testicular artery within the cord and may provide some flow to the testis.

Venous drainage and pampiniform plexus

Venous drainage occurs via the pampiniform plexus, which exits from the mediastinum testis and runs in the spermatic cord. The pampiniform plexus converges into three sets of anastomotic veins: the testicular, deferential, and cremasteric veins. The right testicular vein drains into the inferior vena cava, while the left testicular vein drains into the left renal vein. The deferential vein drains into pelvic veins, and the cremasteric vein drains into tributaries of the epigastric and deep pudendal veins. Varicocele is an abnormal dilation of the pampiniform plexus veins, typically > $2\ \text{mm}$ in diameter and enlarging with Valsalva maneuver.

Scrotal scanning protocol and technique

Clinical scanning uses a supine patient, with the penis positioned on the abdomen and legs together for scrotal support. A rolled towel between the thighs helps. Apply warmed gel and use high-frequency probes (typically 10$-$14\ \text{MHz}). Perform bilateral exams, comparing the symptomatic side with the asymptomatic side. Examine each testis from superior to inferior, assessing size, echogenicity, and parenchymal structure; parenchyma should be uniform with equal echogenicity between sides. Turn on color Doppler to assess vascular flow and compare flow between sides. Evaluate the epididymis on both sides.

Acute scrotum and trauma

Acute scrotum from trauma presents a diagnostic challenge due to pain and swelling. Rupture may occur; timely surgical intervention matters: surgery within $5 \text{ to } 6\ \text{hours}$ yields about $80\%\text{ to }100\%$ testis salvage, between $6 \text{ to } 12\ \text{hours}$ about $70\%$, and after $>12\ \text{hours}$ about $20\%$. Hydroceles and hematoceles are common trauma-related complications.

Epididymo-orchitis

Epididymo-orchitis is infection of the epididymis and testis, usually arising from spread of lower urinary tract infection via the spermatic cord; it is the most common cause of acute scrotal pain in adults. Sonographically, the epididymis is enlarged and hypoechoic, with hyperemic flow on color Doppler; if secondary hemorrhage occurs, focal hyperechoic areas may be present. Associated findings include scrotal wall thickening and hydrocele; pyocele may occur in severe cases.

Torsion

Testicular torsion results from abnormal testicular mobility (Bell clapper deformity can allow free rotation). Twisting of the testis and epididymis within the scrotum cuts off vascular supply and is a surgical emergency. Salvage rates depend on time to surgery: about $80\%\text{ to }100\%$ within 5\ to \6\ \text{hours}, around $70\%$ between 6\ to \12\ \text{hours}, and about $20\%$ after $12\ \text{hours}$. Peak incidence is around age $14$. Presenting symptoms include sudden, severe unilateral scrotal pain with swelling and sometimes nausea/vomiting.

Extratesticular masses

Extratesticular cysts include epididymal cysts, spermatoceles, and tunica albuginea cysts. Spermatoceles are cystic dilatations of efferent ductules in the epididymal head, containing proteinaceous fluid and spermatozoa, and are more common after vasectomy. Epididymal cysts are small serous cysts within the epididymis, generally asymptomatic. Tunica albuginea cysts are benign cystic lesions arising from the tunica albuginea.

Hydrocele, pyocele, and hematoceles

The space between visceral and parietal layers of the tunica vaginalis can accumulate fluid (hydrocele), pus (pyocele), or blood (hematoceles). Hydroceles are the most common painless scrotal swelling and may be idiopathic or associated with epididymo-orchitis or torsion. Pyoceles and hematoceles are less common but can occur with infection, trauma, or neoplasm.

Sperm granuloma

Sperm granulomas are chronic inflammatory reactions to extravasation of spermatozoa, most often after vasectomy. They may be located anywhere within the epididymis or vas deferens.

Benign testicular masses

Benign masses include tubular ectasia of the rete testis (dilated tubules near the hilum associated with epididymal or testicular cysts or obstruction on the same side), epididymal cysts, spermatoceles, and tunica albuginea cysts. These lesions are usually asymptomatic. Cysts are more common in men over age $40$.

Malignant testicular masses

Germ cell tumors account for about $95\%$ of testicular tumors and are most common in men between 15\ to \35\ (relatively younger), with peak incidence in that range. Undescended testes are $2.5\text{ to }8$ times more likely to develop cancer. Germ cell tumors often present as a painless lump; intratesticular masses are more likely malignant than extratesticular masses. Common germ cell tumors include seminoma (most common), embryonal carcinoma, and choriocarcinoma. Serum markers such as hCG and AFP may be elevated in germ cell tumors.

Sonographic appearance by type

Germ cell tumors: most appear as focal, hypoechoic masses. Seminomas are usually homogeneous and hypoechoic with smooth borders and rarely contain calcifications or cystic components. Embryonal cell carcinoma is heterogeneous and less well circumscribed, sometimes with calcifications or hemorrhage. Choriocarcinoma shows variable appearance due to mixed cell types but often irregular borders. Metastasis to the testis is rare but tends to be bilateral with multiple lesions. Lymphoma and leukemia can involve the testis and may be bilateral or unilateral, often in older patients.

Congenital anomalies

Cryptorchidism (undescended testicle) occurs when the testis fails to descend into the scrotum; location can be abdomen or inguinal canal, often in the inguinal canal and sometimes bilateral in $10\%\text{ to }25\%$ cases. Ultrasound findings include a smaller, less echogenic testis; the mediastinum is rarely seen. Testicular ectopia is very rare and refers to ectopic testis resting outside the normal descent path (most commonly in superficial inguinal pouch); other ectopic sites include perineum, femoral canal, suprapubic area, penis, and other scrotal compartments. Anorchia is uncommon (unilateral) and may result from in utero torsion or poor vascular supply; polyorchidism (testicular duplication) is very rare, more often left-sided, and can be bilateral in about $5\%$; duplicated testes are typically small and may lack an efferent ductal system, with increased risk of malignancy, cryptorchidism, and torsion.

Scrotal hernia

Scrotal hernias involve protrusion of bowel, omentum, or other structures into the scrotum. Clinically diagnosed in many cases; ultrasound helps when findings are equivocal.