Chapter 23: Scrotum

Chapter 23: Scrotum

Anatomy of the Scrotum

Testes

  • Definition: Symmetric, oval-shaped glands residing in the scrotum.

  • Measurements: Adult testis measures between 3-5 cm in length, 2-4 cm in width, and 3 cm in height.

Characteristics

  • Each testis is divided into 250 to 400 conical lobules.

  • Each lobule contains seminiferous tubules that converge at the apex of each lobule.

  • The seminiferous tubules anastomose to form rete testis situated in the mediastinum.

  • Draining Mechanism: Rete testis drains into the head of the epididymis through efferent ductules.

  • Sonographic Appearance: Smooth, medium gray structures with fine echo texture.

Epididymis

  • Structure: A tubular structure measuring 6 to 7 cm that begins superiorly and courses posterolaterally to the testis.

  • Division: Divided into head, body, and tail.

    • Head: Largest part measuring 6 to 15 mm in width, located superior to the upper pole of the testis.

    • Body: Smaller than the head, follows the posterolateral aspect of the testis from the upper to the lower pole.

    • Tail: Slightly larger and positioned posterior to the lower pole of the testis.

    • Appendix: Small protuberance from the head of the epididymis.

Characteristics

  • Duct Structure: Includes 10 to 15 efferent ductules from the rete testis that converge into a single duct called the ductus epididymis, which continues as the vas deferens.

  • Sonographic Appearance: Isoechoic or hypoechoic compared with the testis; echo texture is coarser.

Mediastinum Testis

  • Definition: Covered by dense fibrous tissue termed as tunica albuginea.

  • Structure: Posterior aspect of the tunica albuginea reflects into the testis to form a vertical septum known as the mediastinum testis.

  • Septa Formation: Multiple septa (septa testis) formed from the tunica albuginea at the mediastinum separate the testis into lobules. Supports vessels and ducts within the testis.

  • Sonographic Appearance: Often seen as a bright hyperechoic line on sonography coursing cranio-caudally within the testis.

Tunica Vaginalis

  • Definition: Lines the inner walls of the scrotum and covers each testis and epididymis. Consists of two layers:

    • Parietal Layer: Inner lining of the scrotal wall.

    • Visceral Layer: Surrounds the testis and epididymis.

  • Characteristics: There is a small bare area posteriorly where the testicle is against the scrotal wall, preventing torsion. Blood vessels, lymphatics, nerves, and spermatic ducts travel through this area.

  • Hydrocele Formation: Hydroceles can form in the space between the layers of the tunica vaginalis.

Vas Deferens

  • Definition: Continuation of the ductus epididymis that is thicker and less convoluted.

  • Dilating: It dilates at the terminal portion near the seminal vesicles, forming the ampulla of the deferens.

  • Function: Joins with the duct of the seminal vesicles to create the ejaculatory duct, which empties into the urethra.

Junction of Ejaculatory Ducts and Urethra

  • Known as verumontanum. The urethra runs from the bladder to the end of the penis, transporting both urine and semen outside the body.

Spermatic Cord

  • Composition: Contains vas deferens, testicular arteries, venous pampiniform plexus, lymphatics, autonomic nerves, and fibers of the cremaster muscle.

  • Function: Suspends the testis in the scrotum, extending from the scrotum through the inguinal canal and internal inguinal rings to the pelvis.

Vascular Supply

Testicular Arteries

  • Origin: Right and left testicular arteries arise from the abdominal aorta, below the level of the renal arteries.

  • Capsular Arteries: These arteries give rise to centripetal arteries, which course from the testicular surface toward the mediastinum along the septa.

  • Recurrent Rami: Before reaching the mediastinum, they curve backward to form recurrent rami (centrifugal arteries) and branch further into arterioles and capillaries.

Venous Drainage

  • Mechanism: Venous drainage occurs through the pampiniform plexus, which exits from the mediastinum testis and courses in the spermatic cord.

  • Convergence: Pampiniform plexus converges into three sets of anastomotic veins:

    1. Testicular

    2. Deferential

    3. Cremasteric

  • Drainage Points: The right testicular vein drains into the inferior vena cava while the left testicular vein joins 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.

Clinical Considerations

Clinical Questions for Patients

  • Inquire if the patient was referred due to palpable mass, scrotal pain, swollen scrotum, or other reasons.

  • Symptoms to discuss include:

    • History, location, and duration of pain

    • Ability to feel a mass

    • Any trauma experienced, including timeline and description of events

    • History of vasectomy procedure.

Patient Positioning and Scanning Protocol

  1. Positioning: Patient should be in the supine position with the penis positioned on the abdomen and covered with a towel. The patient should place legs together for support, and a rolled towel can be placed between the thighs to support the scrotum.

  2. Gel Application: Generous amount of warmed gel should be applied to the scrotum.

  3. Probe Frequency: Utilize high-frequency probes ranging from 10 to 14 MHz.

  4. Exam Protocol: Conduct bilateral exams, using the asymptomatic side as a comparison for the symptomatic side. Each testis should be scanned from superior to inferior.

Scanning Evaluation

  • Evaluate the size, echogenicity, and structure of each testis to ensure uniformity between sides.

  • Assess whether the parenchyma is homogeneous or heterogeneous, noting any masses that may be cystic or solid and identifying their location as either intratesticular or extratesticular.

  • Determine if one testis appears much larger or smaller than the other, and assess the condition of the epididymis and skin thickness. Check blood flow using color Doppler and assess for hyperemia or lack of flow in the testis.

Technical Considerations

Selection of Transducer and Doppler Settings

  • Relevant Factors: Color Doppler and power Doppler settings should be adjusted appropriately, including:

    • Gain

    • Pulsed Repetition Frequency (PRF)

    • Wall filter

    • Line density

    • Threshold

    • Packet size.

Scrotal Pathology

Acute Scrotum Overview

  • Trauma Presentation: Scrotal trauma often presents as painful and swollen; trauma can arise from various sources such as motor vehicle accidents (MVA), athletic injuries, direct blows, or straddle injuries.

  • Rupture Possibility: Assess for any presence of rupture; if surgery occurs within 72 hours post-injury, up to 90% of testes can be saved; only 45% salvageable after 72 hours.

Complications of Trauma

  • Hydrocele and Hematocele: Both may arise as complications of trauma. Hematoceles contain blood and frequently occur in advanced cases of epididymitis or orchitis.

Sonographic Findings for Rupture

  • Indicators:

    • Focal alteration of testicular parenchyma

    • Interruption of tunica albuginea

    • Irregular testicular contour

    • Thickened scrotal wall

    • Presence of hematocele.

Hematoceles

  • Appearance: Acute hematoceles appear echogenic with numerous, visible echoes that may be seen to float/move. As time progresses, hematoceles develop low-level echoes and may form fluid-fluid levels or septations. Presence of hematocele does not confirm rupture.

Hematomas

  • Characteristics: Associated with trauma, hematomas may be large, causing displacement of the testis and appear as heterogeneous areas in the scrotum, becoming more complex over time, possibly developing cystic components.

  • Involvement Potential: Hematomas can involve testis or epididymis, or be contained within the scrotal wall.

Blood Flow Disruption

  • Indicator of Rupture: Disruption in blood flow across the testis surface is indicative of rupture. Epididymitis may also stem from trauma; increased vascularity can be identified through color Doppler imaging. Torsion may also accompany trauma; absence of flow indicates torsion.

Epididymo-orchitis

  • Definition: Infection of the epididymis and testis, often stemming from urinary tract infections via the spermatic cord, and is the most common cause of acute scrotal pain in adults, typically secondary to epididymitis.

Sonographic Findings

  • Enlargement: Epididymitis presents as an enlarged, hypoechoic gland, possibly exhibiting focal hyperechoic areas in cases of hemorrhage.

  • Color Doppler: Hyperemic flow confirmed with color Doppler, showing increased vascular signal on the affected side compared to the asymptomatic side.

Hydrocele, Pyocele, and Hematocele

Ruptured Infections or Trauma

  • Hydrocele: Collection of serous fluid, most common cause of painless scrotal swelling; often idiopathic or associated with epididymo-orchitis or torsion.

  • Pyocele: Collection of pus that occurs with untreated infections or following abscess rupture.

  • Hematocele: Collection of blood associated with trauma, surgery, neoplasms, or torsion.