Chapter 28: Scrotal and Penile Sonography

Scrotum Anatomy

Suspended from male pelvis between perineum and penis; contains: testis, testicular appendages, epididymis, proximal portion of vas deferens, and spermatic cord; sac of cutaneous tissue that supports testicles is divided internally and externally:

Externally - into lateral portions by median ridge called the median raphe

Internally - scrotum is divided into sacs by a septum called the dartos or tunica dartos (dartos contains superficial fascia and contractile tissue)

Cremaster Muscle

Surrounds each testicle and extends into abdomen over spermatic cord; covered by cremaster fascia; contraction of cremaster muscle performs the important function of regulating temperature of testicles

Tunica Vaginalis

Peritoneal sac composed of three layers; covers and surrounds testis and epididymis; outer parietal layer is closely attached to internal spermatic fascia; cavum vaginale is potential space between visceral and parietal layer; inner visceral layer that is closely attached to testicle

Testis Anatomy

Covered by dense, white fibrous tissue called tunica albuginea

Tunica albuginea extends into posterior wall of testicle; forms mediastinum testis and interlobar septa; septa of mediastinum radiate into testicle and separates into 200-300 lobules; each lobule contains one to three convoluted seminiferous tubules; seminiferous tubules are connected to straight tubules, which lead to the rete testis; rete testis is located within mediastinum testis; exits mediastinum as coiled efferent ducts

Normal Measurements (adult): 3-5cm length, 2-3cm width, 2-3cm height)

Sonographic Appearance of Testes

Homogeneous; medium-level echoes; hyperechoic linear structure is the mediastinum testis; low-resistance arterial blood flow; mediastinum testis – hyperechoic band running in cephalocaudad orientation in longitudinal plane and ovoid structure in transverse

Epididymis Anatomy

Posterolateral to testis; composed mostly of single convoluted tube, ductus epididymis; encapsulated by serosal layer; divided into the:

• Head (globus major) – large superior portion, superolateral to testis (most common portion viewed on ultrasound)

• Body – adjacent to posterolateral margin of testis

• Tail (globus minor) – inferolateral to testis

Efferent ducts of the head empty into ductus deferens

Normal Measurements (adult): Head is 10-12mm AP and 5-12mm length, body is 2-4mm AP, and tail is 2-5mm AP

Sonographic Appearance of Epididymis

Iso/hypoechoic compared with normal testicle; coarse in appearance compared to normal testicle; head is superior and posterior to testicle, body courses posterior, and tail lies at inferior aspect

Spermatic Cord

Bilateral; extend from inguinal canal and internal inguinal ring into pelvis; each contains:

• ductus deferens

• testicular arteries (on image)

• venous pampiniform plexus (on image)

• lymphatics

• autonomic nerves

• fibers of cremaster muscle

Ductus/Vas Deferens

thicker, less convoluted continuation of the ductus epididymis; three smooth muscle layers contribute to this duct’s increased thickness; runs in the spermatic cord through scrotum and inguinal canal; unites with seminal vesicle posterior to bladder to form ejaculatory duct; at terminal portion near seminal vesicles, the ductus deferens dilates; divided into four segments:

• Scrotal – inferior

• Suprascrotal – spermatic cord

• Prepubic – inguinal region

• Pelvic – posterior urinary bladder

Normal Measurements: 45cm length

Penis Anatomy

Composed of 3 cylindrical masses of tussue:

• Two corpora cavernosa situated dorsolaterally

• Single corpus spongiosum in midventral region, which contains the spongy urethra

Bound and separated by tunica albuginea

Buck’s fascia: superficial to tunica albuginea and is a thick, fibrous, loosely applied covering of skin that envelops penis

Sonographic Appearance of Penis

Corpus Spongiosum: lies anterior to the paired corpus cavernosa; homogeneous texture composed of medium-level echoes

Tunica Albuginea: highly echogenic covering of the corpus cavernosa

Septum Penis: echogenic plane dividing the two corpora cavernosa; extension of the tunica albuginea

Paired Corpora Cavernosa: Lie posterior to the corpus spongiosum and appear symmetrical, round or oval, with a medium-level homogeneous echo texture

Testis Vasculature

Arterial

Testicular arteries provide primary blood supply; arise from anterior AO; in spermatic cord, testicular artery accompanied by deferential artery and cremasteric artery

• Deferential – supplies epididymis and vas deferens

• Cremasteric – supplies peritesticular tissue

Superior epididymal artery supplies epididymis

Venous

Via pampiniform plexus; begins in scrotum with veins arising from mediastinum testis; plexus reduces to single vein – testicular vein as it ascends through inguinal canal; RIGHT testicular vein drains into IVC and LEFT testicular veins drains into LRV

Physiology

Testicles are classified as both endocrine and exocrine glands; testes produce testosterone at puberty which causes growth of male sex organs and secondary male sex characteristics; testes also produce spermatozoa which are transported through ducts (exocrine) that store and transport them; production of sperm one of most important functions

Testis Variants

Cryptorchidism is failure of testicles to descend into scrotum; common locations of undescended testes include: Inguinal canal, External inguinal ring, and Abdomen

Sonographic Application

Scrotum exams indicated for testicular size, inflammatory processes (epididymitis, orchitis), presence and composition of masses, detection of peritesticular fluid collections (hydrocele), evaluation of scrotal trauma, doppler evaluation to rule out testictesticular torsion, evaluation of scrotal pain, or location of undescended testicles

Penis exams indicated for detection of fibrosis (Peyronie’s disease) or scar tissue and plaques, evaluation of tumors or periurethral disease, penile hematoma, or doppler evaluation of vasculogenic impotence

Associated Tests

MRI, CT, or nuclear medicine