The Scrotum and Penis

Wayne C. Leonhardt

Aaron M. Chandler

OBJECTIVES

Illustrate the normal gross and sectional anatomy of the scrotum and penis, including the vascular anatomy.
Describe the sonographic appearance of the normal scrotal and penile anatomy.
Explain the technique and protocol for sonographic evaluation of the scrotum and penis.
State the indications for a sonographic examination of the scrotum and penis.
Identify the common pathologic conditions that can result in an acute painful scrotum and penis.
Differentiate common extratesticular abnormalities from intratesticular abnormalities.
Describe the sonographic characteristics and laboratory values associated with scrotal masses.
Describe the sonographic characteristics associated with penile abnormalities.

GLOSSARY

AFP
alpha-fetoprotein levels are measured during pregnancy to detect certain fetal anomalies; blood levels may also be elevated with hepatocellular carcinoma and certain testicular cancers

beta-hCG
human chorionic gonadotropin is produced during pregnancy and is also secreted by some malignant tumors, including certain testicular cancers

corpora cavernosa
two cylindrical columns of spongy tissue running parallel dorsally that serve as the main erectile structures in the penis

corpus spongiosum
single column of spongy tissue that contains the urethra and expands distally to form the glans penis; this tissue expands slightly during an erection but not to the extent of the cavernosa

cryptorchidism
undescended testicle—occurs when one or more of the testis fails to descend into the scrotum before birth

hydrocelectomy
surgical procedure to remove a hydrocele

hyperemia
an increase in blood flow to the tissue

infarction
tissue death that occurs owing to a lack of blood flow

inguinal canal
passage in the anterior abdominal wall in both females and males that transmits structures from the pelvis to the perineum

orchiopexy
a surgical procedure done to fasten an undescended testicle into the scrotum or to repair an acute testicular torsion

pampiniform plexus
a network of veins that drain the epididymis and testis; it is located in the spermatic cord and empties into the right and left testicular veins

Peyronie disease (penile fibromatosis)
characterized by fibrotic thickening of the tunica albuginea, resulting in the formation of fibrous plaques, which can lead to severe curvature of the penis and difficulty in achieving an erection

priapism
defined as a painful and prolonged penile erection, with or without stimulation

resistive index
a sonographic indicator of an organ to perfusion; it is calculated from the peak systolic velocity and the end diastolic velocity of blood flow

scrotal pearl
scrotoliths or scrotal pearls are benign extra testicular macrocalcifications located within the scrotum, between the layers of the tunica vaginalis

spermatogenesis
process in which spermatozoa are produced

tunica albuginea
dense fibrous sheath that encapsulates and provides structure and support to the testicles and corpora of the penis

Valsalva maneuver
consists of forced expiration against a closed glottis after a full inspiration; the Valsalva maneuver increases the intra-abdominal pressure and is helpful in diagnosing a varicocele and scrotal hernia

vasectomy
surgical procedure in which the vas deferens is cut, tied, cauterized, or otherwise interrupted; the semen no longer contains sperm, preventing conception

yolk sac
a membranous sac attached to an embryo formed by cells adjacent to the embryonic disk

High-frequency grayscale sonography with spectral, color, and power Doppler is the imaging modality of choice and the gold standard for evaluating patients with acute scrotal pain, a scrotal mass, or to assess testicular perfusion when testicular torsion is suspected.¹, ² and ³ Compared with other imaging modalities, sonography provides expedient and accurate differentiation of many causes of scrotal pain.³, ⁴ and ⁵ The diagnosis of scrotal disease is based on many factors, including a thorough clinical history, physical examination, and sonographic findings.³^,⁶^,⁷ When patients present with scrotal pain or abnormality, clinical evaluation alone is difficult, and the cause of the patient’s symptoms frequently remains unanswered. Sonography is used to determine whether a palpable mass is cystic or solid and differentiate between intratesticular and extratesticular abnormalities.¹^,³^,⁷ The distinction between an intratesticular lesion and an extratesticular lesion is an important one considering most intratesticular solid masses are considered malignant until proven otherwise.⁸^,⁹ Conversely, extratesticular masses tend to be benign regardless of their cystic or solid nature.¹^,⁸^,¹⁰ High-resolution grayscale sonography has been shown to be nearly 100% accurate in its ability to characterize the intrascrotal anatomy and distinguish intratesticular and extratesticular abnormalities.³^,⁷^,¹⁴

Sonography is also useful in the follow-up examination of infection and trauma. Incidentally, 10% to 15% of testicular tumors are identified after an episode of scrotal trauma.¹¹^,¹² Owing to its speed and efficacy, color Doppler sonography is the most useful imaging technique to establish the diagnosis of testicular torsion in addition to differentiating torsion from epididymo-orchitis.⁹^,¹³^,¹⁵ With an accuracy approaching 100%, sonography is considered the primary imaging modality to assess intratesticular arterial perfusion.¹³, ¹⁴, ¹⁵ and ¹⁶ Nuclear medicine and sonography are comparable in the detection of reduced or absent intratesticular flow.¹⁵

When a patient presents with an undescended testis, the evaluation begins with sonography to explore the inguinal canal. In 80% of cases, the undescended testis is located in the inguinal canal.¹⁴^,¹⁵ Magnetic resonance imaging (MRI) is recommended to locate intra-abdominal testes when sonography fails to locate an undescended testis within the inguinal canal. MRI is 90% to 95% sensitive for identifying intra-abdominal testes.¹⁵

SONOGRAPHIC IMAGING TECHNIQUE

Optimal imaging of the scrotum is achieved using a high-frequency, 12 to 18 MHz, transducer with spectral, color, and power Doppler capabilities.³ In patients with severe scrotal swelling, a high-frequency curved linear-array transducer increases the field of view (FOV) and is useful for evaluating large segments of intrascrotal anatomy¹¹ (Fig. 19-1). Extended FOV imaging is extremely helpful
when evaluating large anatomic segments with inflammatory processes and fluid collections because a wider FOV provides a greater understanding of anatomical relationships¹⁰ (Fig. 19-2).

FIGURE 19-1 Convex transducer. Transverse image of enlarged scrotum best seen with a convex probe. Note the large echogenic hydrocele compressing and displacing the testis (T).

FIGURE 19-2 Extended field of view (FOV). Longitudinal extended FOV image of the scrotum, including the testis and the epididymal head (H), body (B), and tail (T).

Using high-resolution grayscale imaging with a transducer frequency greater than 10 MHz simplifies correlating a palpable mass with real-time imaging.¹¹ High-frequency transducers have excellent spatial resolution and can resolve anatomic structures as small as 0.5 mm.⁷^,¹⁰ Imaging techniques such as harmonics, compound imaging, and multifocal zones are essential to optimizing image quality.⁶ Adjusting color Doppler parameters by utilizing a low pulse repetition frequency (PRF), with a low wall filter, and a relatively high color gain output can improve the display of the intratesticular arteries.⁶^,¹⁰^,¹⁷

Technical Considerations

When evaluating patients for acute scrotal pain (torsion, inflammatory processes) immediately, perform a transverse image of both testes comparing echogenicity and arterial perfusion. Optimize the color and power Doppler settings.³

Obtain power, color, and spectral Doppler tracings to confirm the presence or absence of intratesticular arterial and venous flow.
Grayscale images are often nonspecific for evaluating testicular torsion and often appear normal when torsion is acute.¹⁶
Spectral Doppler findings suggestive of partial torsion include asymmetry in resistive indices with decreased diastolic flow or diastolic flow reversal.¹⁶
In the clinical setting of epididymo-orchitis, when focal hypoechoic areas are detected within the testis, ultrasound follow-up is recommended after antibiotic treatment is completed to confirm the diagnosis and observe resolution, so that tumor and or infarction can be ruled out.⁷
Large hydroceles, hematomas, marked scrotal edema, and epididymo-orchitis are scrotal conditions that decrease intratesticular perfusion, mimicking testicular torsion.
In patients presenting with acute epididymo-orchitis, spectral Doppler demonstrates decreased vascular resistance (resistive index [RI] < 0.5) compared with the normal contralateral testis and epididymis.¹¹
Reversal of the spectral diastolic component of the intratesticular arterial flow in patients with acute epididymo-orchitis suggests venous infarction.¹⁸
Use color and power Doppler to differentiate epididymitis from an enlarged, noninflammatory epididymis status postvasectomy.
Because primary varicoceles may decompress when the patient is supine, perform the Valsalva maneuver or scan the patient in the upright position to increase venous blood flow.
Large varicoceles can extend posteriorly, lateral, and inferiorly to the testis, mimicking epididymitis.
The inguinal canal and abdomen are imaged when hernia, secondary varicocele, undescended testis, and or postsurgical complications are suspected.
Evaluate the spermatic cord to detect abnormalities such as solid masses, hematomas, abscess, torsion, hernias, and hydroceles.
Use a gel standoff pad to evaluate anterior and/or superficial lesions, such as those in the tunica vaginalis.

Protocol for Real-Time Sonography

Before scanning the scrotum, review previous studies and obtain a thorough clinical history, including the patient’s chief complaint, useful laboratory data, and any pertinent surgical history such as vasectomy, hernia repair, orchiopexy, and hydrocelectomy. Have the patient locate the area of pain, swelling, or palpable mass, and ask if the patient is currently being treated with antibiotics.⁶^,¹⁰ Once the history is obtained and documented on the anatomy worksheet, explain the procedure to the patient. The scrotal exam is performed with the patient in the supine position. The scrotum is supported on a rolled towel placed between the thighs to isolate and immobilize the anatomy for scanning.⁶^,¹¹^,¹⁶ The penis is positioned over the suprapubic region and covered with a second towel.¹¹ Generous amounts of warm gel should be applied to the scrotal skin as a coupling.⁷

Procedure for Real-Time Sonography Overview

Sonographic evaluation of the scrotum begins with a side-by-side, large-FOV image including both testes using grayscale and color Doppler imaging, comparing their echogenicity and arterial perfusion³^,¹⁰^,¹⁴^,¹⁹ (Fig. 19-3A, B). This is paramount in the setting of acute scrotal pain with suspected testicular torsion. Longitudinal images of each testis (lateral to medial, include cine-clips) are obtained. Oblique scanning planes are useful for demonstrating the intrastesticular arteries.²⁰ In mid testes, document the intratesticular arterial and venous waveforms with color and color with spectral Doppler. Obtain transverse images (superior, mid, inferior, include cine-clips). Document a color Doppler image mid-testis. The relevant extratesticular structures (e.g., spermatic cord, epididymis) and skin thickness are evaluated in both longitudinal and transverse image planes⁷^,¹⁰ (Figs. 19-4 and 19-5). Include the body and tail of the epididymis when scanning the middle and lower portions of the testis, in the longitudinal plane.⁷^,¹¹^,²¹

Documented Longitudinal Images

Longitudinal midline testis grayscale: Measure the length, and anteroposterior (AP) diameter. Midline testis: assess arterial and venous flow with color and/or power Doppler and color with spectral Doppler. Obtain an RI measurement of arterial flow.

FIGURE 19-3 Comparison. A: Transverse image of normal bilateral right (RT) and left (LT) testes (T) demonstrating similar homogeneous echogenicity. B: Transverse image of normal bilateral right (RT) and left (LT) testes (T) demonstrating normal flow bilaterally.

FIGURE 19-4 Schematic illustration of longitudinal scrotal anatomy and relevant adjacent structures. 1, spermatic cord; 2, head of epididymis; 3, testis superior; 4, testis—mid; 5, testis—inferior; 6, tail of epididymis. Note that the body of the epididymis is seen in sections 3, 4, and 5.

FIGURE 19-5 Schematic illustration of transverse scrotal anatomy and relevant adjacent structures. 1, spermatic cord; 2, head of epididymis; 3, testis—superior; 4, testis—mid; 5, testis—inferior; 6, tail of epididymis. The body of the epididymis is seen in sections 3, 4, and 5.

Measure the AP diameter of the scrotal wall. Subsequent images should include the lateral and medial portions of the testis.
Longitudinal “cine-clip” of testis lateral to medial.
Longitudinal epididymal head grayscale: Measure the AP diameter and length.
Longitudinal epididymal head with color and/or power Doppler to assess vascular perfusion.
Longitudinal epididymal body: The normal narrow body of the epididymis lies adjacent to the posterolateral margin of the testis. Measure the AP diameter. Perform color and/or power Doppler imaging to assess vascular perfusion.
Longitudinal inferior testis and epididymal tail: Measure the superior to inferior diameter of the epididymal tail. Use color and/or power Doppler to assess vascular perfusion.
Longitudinal spermatic cord grayscale at rest and with the Valsalva maneuver and with color and/or power Doppler, to assess venous reflux and increased flow: Measure the AP diameter of the largest vein(s) on the grayscale image.

Documented Transverse Images

Transverse superior testis with epididymal head in grayscale and color to assess vascularity of epididymis compared with the testis.
Transverse mid-testis: Obtain transverse measurement in grayscale, and document with color Doppler. Subsequent images should include inferior testis and inferior testis with epididymal tail. Obtain grayscale and color Doppler to assess the vascularity of the epididymis compared with the testis.
Measure the AP diameter of the scrotal wall.
Transverse “cine-clip” testis superior to inferior.
Transverse spermatic cord grayscale at rest and with the Valsalva maneuver, and with color and/or power Doppler: Measure the AP diameter of the largest vein on the grayscale image.

NORMAL ANATOMY AND SONOGRAPHIC APPEARANCE

A clear understanding of normal scrotal anatomy and vascular perfusion is paramount. Without a clear concept of normal anatomy, pathologic processes may be missed or a normal variant may be mistaken for disease.

Three major structures are contained in the scrotum: the spermatic cord; the epididymis (head, body, and tail); and the testes. The scrotum is a fibromuscular sac composed of several layers of fascia and muscle, which includes the tunica dartos, external spermatic fascia, middle spermatic fascia, cremasteric muscle, internal spermatic fascia, and tunica vaginalis.²^,³^,⁸^,¹⁴^,¹⁹ The normal scrotal wall thickness is approximately 2 to 8 mm, depending on the state of contraction of the cremasteric muscle.²^,⁸^,¹⁴^,²¹ The normal sonographic appearance of the scrotal wall is homogeneous, and slightly echogenic, compared with the testis⁷ (Fig. 19-6). The scrotum is divided into two compartments by a midline septum, the median raphe, a fibrous band of tissue that runs ventral to the undersurface of the penis and dorsal along the middle of the perineum to the anus.²^,⁸^,¹⁰^,²¹

Spermatic Cord and Ductus (Vas) Deferens

The spermatic cords are paired and pass from the abdominal cavity through the inguinal canal down into the scrotum.¹⁹ Each spermatic cord lies above and parallel to the inguinal ligament and suspends the testis in the scrotum. The spermatic cord is composed of arteries (the testicular, cremasteric, and deferential), veins of the pampiniform plexus, nerves, lymphatics, vas deferens, and connective tissue.²^,⁷^,⁸^,¹⁵^,²²

FIGURE 19-6 Scrotal wall. Longitudinal image of normal scrotal wall thickness (calipers).

The ductus (vas) deferens are thick paired muscular ducts about 45 cm in length. Each duct runs in the spermatic cord, through the scrotum, inguinal canal, and into the abdomen. It is a major component of the male reproduction system. The ductus (vas) deferens is a continuation of the epididymis, (tail) and transports spermatozoa from the epididymis to the ejaculatory ducts. It is divided into three segments: (1) scrotal, inferior; (2) suprascrotal, mid; and (3) prepubic, superior.²

The sonographic appearance of a normal spermatic cord in the longitudinal scan is comprised of numerous hypoechoic, slightly tortuous, linear structures measuring up to 2 mm in diameter⁷^,¹⁵^,¹⁹ (Fig. 19-7A). In the transverse plane, the sonographic appearance of the normal spermatic cord comprises of numerous hypoechoic ovoid structures with echogenic borders representing vascular walls and connective tissue²^,⁷^,¹⁵ (Fig. 19-7B).

Normal veins of the pampiniform plexus measure less than 2 mm in diameter.¹⁵^,²¹ With color Doppler, the normal spermatic cord shows minimal flow within the arteries and veins of the pampiniform plexus at rest (Fig. 19-7C, D). In a normal patient, performing the Valsalva maneuver slightly increases the venous flow⁷ (Fig. 19-7E, F).

The sonographic appearance of the normal ductus (vas) deferens is a linear hypoechoic structure superior to the epididymis. The cross section view shows an ovoid structure, representing a “target” or “doughnut.” The ductus (vas) deferens is noncompressible and avascular. The normal thickness (AP) of the duct measures between 1.5 and 2.7 mm. The ductus (vas) deferens in the transverse dimension measures less than 0.5 mm² (Fig. 19-8 A, B). The scrotal, inferior portion of the ductus (vas) deferens close to the tail of the epididymis demonstrates a convoluted tortuous appearance that is hypoechoic (Fig. 19-8C).

Epididymis

The epididymides store small quantities of sperm prior to ejaculation. Additionally, they act as a conduit for sperm originating in the testis and expressed via the seminal vesicles and secrete a small portion of the seminal fluid.⁷^,²³ The epididymis is divided anatomically into the head, body, and tail.⁷ The head of the epididymis, the globus major, is located superolaterally to the testis and measures 10 to 12 mm in AP diameter, and 5 to 12 mm in length.²^,⁹^,¹⁹ The body of the epididymis, the corpus, lies adjacent to the posterolateral margin of the testis and measures 2 to 4 mm in AP diameter.²^,¹⁴^,²⁴^,²⁵ The tail of the epididymis, or globus minor, lies on the inferolateral surface of the testis and measures 2 to 5 mm in superior to inferior diameter.²^,⁴^,¹⁴^,²¹^,²⁴^,²⁵ The latter continues on to become the vas deferens²^,⁷ (Fig. 19-9).

The normal sonographic appearance of the epididymal head is homogeneous and largely isoechoic to or slightly more echogenic than the testis.²^,⁹^,¹¹^,¹⁶^,²¹^,²⁴^,²⁵ The epididymal head is best evaluated in the longitudinal scan plane appearing as a triangle-, crescent-, or teardrop-shaped structure superior to the testis²^,⁷, ⁸ and ⁹^,¹⁵^,²¹ (Fig. 19-10A). The echogenicity of the normal body and tail is isoechoic to hypoechoic compared

with the testis.²^,⁹^,²⁴^,²⁵ The narrow body and curved tail are smaller, more variable in position, usually posterior and inferior to the testis, and best evaluated in the longitudinal scan plane²^,⁴^,¹⁵^,²¹^,²⁴^,²⁵ (Fig. 19-10B, C). Color flow imaging of the normal epididymis demonstrates speckled intraepididymal arterial flow⁷ (Fig. 19-10D).

FIGURE 19-7 Spermatic cord. A: Longitudinal image of the normal spermatic cord (arrows). B: Transverse image of the normal spermatic cord (arrows) with sonolucent ducts and vessels. C: Longitudinal and transverse (D) images of the normal spermatic cord (arrows) with color flow at rest. Longitudinal (E) and transverse (F) images of the normal spermatic cord (arrows) with slightly increased venous flow during the Valsalva maneuver.

FIGURE 19-8 Ductus (vas) deferens. A: Longitudinal color Doppler image of the normal suprascrotal segment of the ductus (vas) deferens. Calipers measure the total AP thickness. Arrow represents the inner lumen of the duct. B: Transverse color Doppler image of the normal suprascrotal segment of the ductus (vas) deferens within the spermatic cord. Note the duct is avascular. Calipers measure the AP and transverse diameter. Arrow designating the “target” appearance. C: Longitudinal grayscale image of the normal ductus (vas) deferens, scrotal segment. Calipers measure the convoluted shaped duct arising from the tail of the epididymis, inferior to the testis (T).

FIGURE 19-9 Schematic illustration of the sagittal anatomic section of normal scrotum.

Postvasectomy Changes in the Epididymis

When obtaining a patient history, it is important to know whether the patient has had a vasectomy. Patients with an undiscovered history of vasectomy could be misdiagnosed owing to a potential altered sonographic appearance of the epididymis. Epididymal changes occur in 40% of vasectomy patients and include enlargement of the epididymis, inhomogeneity, spermatoceles, dilatation of the rete testis, and sperm granulomas⁷^,⁸^,²⁴^,²⁵ (Fig. 19-11A-G).

Patients presenting with scrotal pain several years after vasectomy may be suspected for “postvasectomy pain syndrome,” resulting from the obstruction of the efferent epididymal duct system with concomitant ductal dilatation, interstitial fibrosis, and chronic perineural inflammation.⁸

The sonographic appearance of the postvasectomy epididymis may mimic epididymitis. Clinical history and the use of color Doppler imaging differentiates between the two entities.⁷

Testis

The primary function of the testes is the production of sperm and testosterone. Spermatogenesis takes place within the seminiferous tubules.²^,²³ Testosterone, secreted by the cells of Leydig, stimulates the production of sperm and is the primary sex hormone responsible for the development of male reproductive tissues and maintenance of male secondary sex characteristics.⁷

Embryologically, the testes develop between the posterior abdominal wall and the peritoneum. The testes begin to pass through the inguinal ring during the seventh month of gestation and lie in the scrotum by the eighth month. During testicular descent, in the inguinal region, the caudal genital ligament is continuous with a band of mesenchyme that connects the fetal testis to the developing scrotum.⁷^,²⁶^,²⁷ This mesenchyme band is known as the gubernaculum testis. The gubernaculum is present only during the development of the urinary and reproductive organs and attaches to the caudal end of the testis.⁷ This anchors the fetal testis to the inguinal region to prevent upward movement.⁷ In the adult, this gubernaculum testis atrophies and its remnant, the scrotal ligament, extends from the inferior pole of the testis and tail of the epididymis to the skin of the scrotal wall.⁷ It secures the testis, tethering it in place and limiting the degree to which the testis can move within the
scrotum.⁷ The scrotal ligament can be seen in the presence of a hydrocele. The sonographic appearance of the scrotal ligament is an echogenic band extending from the caudal end of the testis to the scrotal wall⁷ (Fig. 19-12).

FIGURE 19-10 Epididymis. A: Longitudinal image of normal testis (T) and epididymal head (E). B: Longitudinal image of normal testis (T) with the body of epididymis (B). C: Longitudinal image of normal testis (T) and tail of epididymis (E). D: Longitudinal color image of testis (T) with normal flow in the epididymis (E).

As the testes descend into the scrotum, a peritoneal lining, the processus vaginalis, fuses around the testis to form the tunica vaginalis, whose communication with the peritoneal cavity obliterates after birth.⁷^,²¹ The tunica vaginalis is a peritoneal sac, composed of two layers, the visceral and parietal layers, that cover and surround the testis and epididymis except for a small posterior area.⁷^,¹⁵^,²¹ The visceral layer is a serous membrane that produces secretions and covers the testis and epididymis.⁶^,⁷^,¹⁵ The parietal layer is the inner lining of the scrotal wall⁶^,⁷^,¹⁴^,¹⁵^,²¹ (see Fig. 19-9). The parietal layer contains lymphatics for fluid absorption.²⁶ Both visceral and parietal layers are separated by a potential space that normally contains a few milliliters of fluid.⁶^,¹⁰^,¹⁵^,²¹ Bowel (scrotal hernia) and large amounts of serous fluid (hydrocele) or blood (hematocele) can accumulate in the potential space.⁷^,¹⁹ In the normal scrotum, visualizing a small amount of fluid adjacent to the head of the epididymis is common.⁷^,¹²^,²¹ This normal amount of fluid should not be misinterpreted as a hydrocele.¹⁴^,²¹

The tunica albuginea is a fibrous sheath that covers the testis and is seen as a thin echogenic line¹²^,¹⁶^,¹⁹ (Fig. 19-13). It invaginates the posterior aspect of the testis at the hilum to become the mediastinum testis.⁷^,⁹^,¹²^,¹⁶ Sonographically, the mediastinum testis is seen as an echogenic band running in a cephalocaudal orientation within the testis in the longitudinal plane⁵^,¹⁰^,¹⁵ (Fig. 19-14A). In the transverse plane, it is seen as an ovoid echogenic structure in the 3- or 9-o’clock position¹³ (Fig. 19-14B). The mediastinum testis functions as a supporting system for arteries, veins, lymphatics, and seminiferous tubules.⁹ Numerous fibrous septa extend radially from the mediastinum into the testis, dividing it into 250 to 400 pyramid-shaped compartments called lobuli testis.⁷^,¹⁰^,¹⁴^,¹⁶ Each lobule contains one to three seminiferous tubules. At the apex of each lobule, the tubules join the tubuli recti, which connect the seminiferous tubules to the rete testis.¹⁰^,¹¹^,¹⁴ The rete testis is a network of epithelial-lined channels embedded within the fibrous stroma of the mediastinum testis. They drain into the epididymis through 10 to 15 efferent ductules¹⁰^,¹⁴^,¹⁶ (see Fig. 19-9).

High-frequency sonography can identify the normal rete testis in approximately 18% of patients. Sonographically, the normal rete testis can be seen as a hypoechoic area with striations, located adjacent to or within the mediastinum testis¹⁰^,¹⁴^,¹⁵ (Fig. 19-15). Dilatation of the seminiferous tubules is referred to as tubular ectasia of the rete testis. This is often seen bilaterally and is associated with epididymal cysts and spermatoceles.²⁶

The appendix testis and appendix epididymis are embryologic remnants (Fig. 19-16A). They are not routinely visualized by sonography unless a hydrocele is present. The appendix testis is an ovoid or elongated protuberance about 5 mm in length and is attached to the upper pole of the testis, in the groove between the testis and the epididymis⁷^,¹⁰^,¹¹ (Fig. 19-16B, C). The appendix testis has been identified in 92% of testes unilaterally and 69% bilaterally in postmortem studies. The appendix epididymis

has been identified unilaterally in 34% and bilaterally in 12% in postmortem studies.¹⁰^,¹⁴ The appendix epididymis is approximately the same size as the appendix testis.¹⁰^,¹¹ The shape of the appendix epididymis is more of a stalk-like structure.¹⁰^,¹¹ Appendages of the testis and epididymis are visualized sonographically as isoechoic to echogenic protuberances superior to the testis and epididymis.⁷^,¹⁰^,¹¹^,¹⁴ Occasionally, the appendix epididymis may swell or distend, forming a cyst-like structure, not to be confused with an epididymal cyst¹⁰ (Fig. 19-16D).

FIGURE 19-11 Postvasectomy changes. A: Longitudinal color Doppler image of enlarged avascular heterogeneous epididymal body (EB) (arrows) in a postvasectomy patient. Normal testis (T). B: Longitudinal image of scrotum demonstrating multiple large spermatoceles (S) of the head and body of epididymis. C: Longitudinal image of testis showing cystic changes of dilated rete testis (RT). D: Longitudinal image of diffusely enlarged hypoechoic epididymis with sperm granulomas (SG). Normal testis (T). E: Transverse power Doppler image of a sperm granuloma (arrows) with intravascular flow, within the tail of the epididymis (ET) postvasectomy. F: Longitudinal image of an enlarged “painful” ductus (vas) deferens (arrows) suprascrotal segment, with an echogenic “Clip Artifact” (large arrow) postvasectomy. G: Longitudinal image of a sperm granuloma (SG), adjacent to the “Clip Artifact” (long arrow) within the suprascrotal segment of the ductus (vas) deferens postvasectomy.

FIGURE 19-12 Scrotal ligaments. Longitudinal image of scrotal ligaments (SL, arrow) best seen in the presence of a hydrocele. Normal testis (T).

FIGURE 19-13 Tunica albuginea. Longitudinal image of testis demonstrating normal tunica albuginea (arrows).

FIGURE 19-14 Mediastinum testis. A: Longitudinal image of mediastinum testis (MT) seen as a bright, echogenic band of fibrofatty tissue across testis. B: Transverse image through mediastinum testis (MT) seen as a bright, echogenic area in testis at the 9-o’clock position.

FIGURE 19-15 Rete testis. Longitudinal image of normal testis showing echogenic stroma (arrow) with tubules of rete testis (RT).

The testes are bilateral, symmetrical, ovoid glands located within the scrotum. They attain their maximum size around puberty. The normal adult testis measures 3 to 5 cm in length and 2 to 3 cm in the transverse and anteroposterior diameters²^,⁷^,¹⁴, ¹⁵ and ¹⁶ (Fig. 19-17A, B). The size of both the testis and epididymis decreases with increasing age.⁷^,⁹ Sonographically, a normal adult testis appears homogeneous with medium-level echoes similar to the thyroid gland, with a smooth contour.²^,⁷^,⁹^,¹¹^,¹⁵

In infants and children, the echogenicity of the testis is hypoechoic compared with that of an adult. At birth, the testes measure 1.5 cm in length and 1.0 cm in transverse diameter. Testicular size increases to 2.0 cm in length and 1.2 cm in transverse diameter by the time the infant is 3 months old.⁷^,¹⁵^,²⁶ During puberty, between 9 and 16 years of age, there is a significant increase in testicular echogenicity owing to the growth of seminiferous tubules.⁷^,²⁶

Arterial and Venous Anatomy of the Scrotum

Scrotal blood flow is supplied by the bilateral testicular, cremasteric, and deferential arteries.²^,⁶^,⁷^,⁹ Testicular arteries provide the major blood supply to the testis. They arise from the anterior aspect of the aorta just below the level of the renal arteries and enter the spermatic cord at the internal inguinal ring with the other cord structures.²^,⁷^,⁹^,¹⁰^,²⁸ In the spermatic cord, the testicular artery is joined by the deferential artery (a branch of the vesicular artery) and

the cremasteric artery (a branch of the inferior epigastric artery).²^,⁶^,⁹^,²⁸ The deferential artery supplies the epididymis and vas deferens.²^,⁶^,⁷^,⁹^,¹¹^,²⁸ Major blood supply to the epididymis, however, is via the superior epididymal artery, a branch of the testicular artery.⁶^,¹¹ The cremasteric artery supplies the peritesticular tissues (Fig. 19-18A, B). Both the deferential and cremasteric arteries also contribute a variable amount of blood to the testis via anastomoses with the testicular artery.²^,⁷^,⁹^,²⁸

FIGURE 19-16 Appendix testis and appendix epididymis. A: Schematic illustration of appendix testis and appendix epididymis. B: Longitudinal image of testis (T) shows hydrocele and appendix testis (small arrows). Scrotal pearl is also seen (large arrows). C: Longitudinal image of normal testis (T) with appendix testis (arrow). Normal color flow is seen in the appendix. A small hydrocele is present. D: Longitudinal image of testis (T) with a cyst-like appendix epididymis (arrow) arising from the head of the epididymis (E).

FIGURE 19-17 Testis. A: On the longitudinal of the normal testis, the calipers were used to measure length (1) and the width (2). B: Transverse image of normal testis.

The venous drainage from the scrotum—inclusive of the mediastinum, epididymis, and scrotal wall—is via the pampiniform plexus, which empties into the testicular veins. The right testicular vein drains into the inferior vena cava whereas the left testicular vein drains into the left renal vein²^,⁷^,⁹^,²⁸ (Fig. 19-18C).

FIGURE 19-18 Vascular anatomy. Schematic illustration of normal arterial supply to the scrotum (A), intrascrotal arterial supply (B), and venous drainage form the scrotum (C).

The anatomy of intratesticular arteries is illustrated in Figure 19-18B. At the posterior superior aspect of the testis, the testicular artery pierces the tunica albuginea to form capsular arteries that run along the periphery of the testis in a layer known as the tunica vasculosa. Capsular arteries have centripetal branches that enter the testicular parenchyma and run toward the mediastinum testis. At the mediastinum, centripetal arteries arborize into recurrent rami arteries that course away from the mediastinum testis.
In approximately 50% of normal testes, a transmediastinal arterial branch of the testicular artery enters the mediastinum and courses through the testicular parenchyma in a direction opposite to that of the centripetal arteries to supply the capsular artery. A transmediastinal vein usually accompanies the artery.⁵^,⁷^,⁹, ¹⁰ and ¹¹^,²⁸^,²⁹ The grayscale sonographic appearance of the transmediastinal artery is a prominent hypoechoic band traversing the testis⁵^,⁹ (Fig. 19-19A). With color Doppler, the transmediastinal artery is seen as a prominent arterial branch traversing the mediastinum, demonstrating flow toward the periphery of the testis to supply the capsular arteries⁵^,⁷^,¹⁰^,³⁸ (Fig. 19-19B). Flow in the transmediastinal artery courses in the opposite direction relative to the centripetal arteries⁵^,⁶^,²⁸

Spectral and Color Doppler Sonography of the Intrascrotal Arteries

The testis has low vascular resistance similar to that found in the brain and kidney.⁷ The spectral waveform of the testicular artery, and its intratesticular branches, characteristically has a low-resistance, high-flow pattern, with a mean RI of 0.62 (range: 0.48 to 0.075)¹⁰^,¹¹^,¹⁷^,²⁸ (Fig. 19-20A). The normal spectral waveform of the epididymal artery is similar to that of the testicular artery, which is a low-resistance, high-flow waveform, with an RI ranging from 0.46 to 0.68⁸^,¹⁰^,¹¹^,¹⁵^,¹⁷ (Fig. 19-20B). Cremasteric and deferential arteries have a high-resistance, low-flow pattern with a mean RI greater than 0.75.¹⁷^,²⁸ Supratesticular arteries (testicular, cremasteric, and deferential) within the spermatic cord demonstrate either low- or high-resistance flow patterns, depending on which artery is insonated⁷^,²⁸ (Fig. 19-20C). With color Doppler, intratesticular arterial blood flow corresponds well with the described anatomic morphology.

Intratesticular arteries are oriented in vascular planes that intersect the mediastinum.

Longitudinal oblique views of the testis best demonstrate capsular and intratesticular arteries⁷^,²⁸ (Fig. 19-20D).

SONOGRAPHY OF SCROTAL DISEASE

Sonography is used to evaluate the scrotum when patients present with common symptoms such as acute painful scrotum, scrotal mass, and scrotal enlargement. Scrotal pathologies by anatomic region are shown in Table 19-1.

Decrease in Size of the Testis

Decrease in the size of a testis may be a cause of infertility or an indication of a pituitary or hypothalamus gland abnormality, such as hypogonadotropic hypogonadism. Hypogonadotropic hypogonadism results from the absence of gonadal-stimulating pituitary hormones, causing underdeveloped testicles.⁷^,²⁶ Other causes of testicular atrophy include cryptorchidism, “missed torsion” (ischemic damage owing to compromised blood flow), postsurgical procedures (i.e., inguinal hernioplasty, varicocelectomy), epididymo-orchitis owing to severe inflammation of the spermatic cord, and trauma.¹⁵ The sonographic appearance of testicular atrophy is a small or shrunken heterogeneous testis displaying increased echogenicity owing to fibrosis. A uniform hypoechoic testis may be seen with associated concurrent ischemia.⁷^,¹⁵

Undescended Testis

The testicles of the fetus lie in the peritoneal cavity near the inguinal canal. Most boys’ testes are descended at birth but occasionally they descend later. The unilateral absence of a testis in the scrotum is an important finding because the incidence of malignant degeneration in the undescended testis is 48 to 50 times more likely than in the normally descended testis.⁷^,⁹^,¹⁴ The incidence of seminoma is 2.5 to 8 times higher in patients with undescended testis than in the general population.¹⁰^,¹⁴^,¹⁷ The contralateral intrascrotal testis has up to a 20% increased risk of malignancy.²⁶ An undescended testis is also associated with infertility because sperm are exposed to abnormally high temperatures within the abdomen and/or inguinal canal.⁸^,²¹^,²⁶ When the undescended testis is relocated and orchiopexy is performed before the age of 2, fertility is preserved.¹⁵ Undescended testes are at increased risk for torsion and commonly associated with malignant degeneration.²⁶ Torsion becomes more frequent after puberty because the testis is larger than its mesentery. Sixty-four percent of patients with torsion of an intra-abdominal testis are reported to have associated testicular cancer.²⁶ Congenital inguinal hernia is also associated with undescended testis.²⁸ Failure to close the processus vaginalis, which forms the scrotal sac, increases the chance of bowel herniating into the scrotum. Approximately, 90% of patients with undescended testes have herniated sacs.²⁶

FIGURE 19-19 Intrascrotal arteries. A: Transverse image of the testis showing the transmediastinal artery (TMA, arrow), entering the mediastinum testis (MT), traversing the testis to supply the capsular artery. B: Transverse color image of transmediastinal artery (TMA) entering the mediastinum testis (MT), supplying capsular artery (CA); (arrow) the transmediastinal vein (TMV) accompanies the artery, with color flow seen in the opposite direction (arrow).

FIGURE 19-20 Spectral and color Doppler images of intrascrotal arteries. A: Normal spectral waveform of an intratesticular artery demonstrating low-resistance flow. B: Normal spectral waveform of the epididymal artery with low-resistance flow. C: Normal spectral waveform of the spermatic cord with high-resistance flow from either the cremasteric or deferential arteries. D: Longitudinal oblique images demonstrating normal intratesticular arteries. Color Doppler shows blood flow away from the Mediastinum Testis (MT). The RR are the Recurrent Rami intratesticular arteries which are demonstrated with the arrows. The Mediastinum Testis is a network of fibrous connective tissue that supports the ducts and vessels as they pass into and out of the testicular parenchyma.

TABLE 19-1 Sonographic Appearance of Common Scrotal Lesion

Structure	Lesion		Sonographic Appearance
Spermatic cord	Varicocele		Dilated serpiginous veins of the pampiniform plexus (superior, lateral, and posterior) measuring >2 mm with the patient supine (Valsalva maneuver) or when the veins measure >2.5 mm with the patient standing. Color Doppler enhances dilatation and reflux.
	Hematoma/hematocele		Thickening of spermatic cord. Variable echogenicity, depending on duration. Initially hyperechoic; with age, the hematoma appears hypoechoic or complex.
	Sperm granuloma		Focal hypoechoic-to-heterogeneous solid mass. Intravascular flow present with acute inflammation.
	Hydrocele		Loculated anechoic fluid collection anterior or posterior to the spermatic cord.
	Abscess		Spermatic cord thickening with areas of increased or decreased echogenicity representing pus and microabscess. Associated spermatic cord hyperemia. Color void centrally with peripheral flow associated with focal abscess.
	Torsion		Enlarged cord with variable echogenicity, hypoechoic to hyperechoic with a “knot” or “whirlpool” mass appearance, representing venous congestion, hemorrhage, and arterial occlusion. Color Doppler reveals no flow or partial flow depending on the duration and degree of torsion.
	Hernia		Complex mass with echogenic and anechoic areas representing omentum, air- and fluid-filled segments of bowel. Characteristic haustral appearance and peristalsis (classic appearance). Color Doppler shows blood flow within viable bowel.
	Benign neoplasms
		Lipoma	Solid avascular echogenic mass (typical) to uniformly hypoechoic. Variable echogenicity may likely reflect the number of interstices.
		Adenomatoid tumor	Solid mass, variable echogenicity, equal to or greater than the testis. Minimal flow by color Doppler within and in the periphery of the tumor.
		Hemangioma, cholesteatoma, leiomyoma	Solid mass, variable echogenicity, hyperechoic to hypoechoic. Minimal flow by color Doppler within the tumor (specifically leiomyoma).
	Malignant neoplasms from the mesenchyme Fibrosarcoma, liposarcoma, rhabdomyosarcoma		Solid ill-defined, inhomogeneous echo texture with echogenic areas and focal anechoic areas representing necrosis.
Epididymis	Epididymitis		Enlargement of the epididymis with variable echogenicity depending on the stage of the disease. The testis is normal. A reactive hydrocele/pyocele is often seen with scrotal wall thickening.
		Acute bacterial	Enlarged hypoechoic epididymis owing to edema, with areas of hyperechogenicity, secondary to hemorrhage and infection with hypervascularity.
		Chronic	Epididymis enlarged, focal, or diffuse heterogeneity; tunica is thickened; shadowing from calcifications may be seen.
		Traumatic	Enlarged heterogeneous epididymis, hypervascularity, small hematomas, hematocele.
	Spermatocele		Cystic avascular mass with well-defined walls and few internal echoes secondary to spermatozoa and/or debris in the region of the epididymis, most often located in the head of the epididymis; may be unilocular or multilocular and displaces the epididymal head anteriorly.
	Epididymal cyst		Anechoic avascular mass with well-defined walls occurring anywhere along the epididymis.
	TB		Enlarged heterogeneous and nodular epididymis with scanty vascularity seen within or in the periphery of the nodules.
	Sarcoidosis		Enlarged heterogeneous epididymis with hypoechoic nodules.
	Sperm granuloma		Solid avascular hypoechoic or heterogeneous well-circumscribed mass, located throughout the epididymis.
	Abscess		Hypoechoic mass with irregular walls, low-level internal echoes, and peripheral hyperemia.
	Torsion		Enlarged heterogeneous epididymal body with only few vascular signals and a highly vascular epididymal head. The testis is normal on grayscale and color Doppler images.
	Adenomatoid/leiomyoma tumors		Solid well-circumscribed mass, variable echogenicity, equal to or greater than the testis. Minimal flow by color Doppler imaging within and on the periphery of the tumor.
Tunica vaginalis	Acute hydrocele		Anechoic fluid collection anterolateral to the testis, with strong sound transmission.
	Chronic hydrocele		Low-level fluid collection anterolateral to the testis with mobile echoes—that is, cholesterol crystals, fibrin bodies, inflammatory debris, septations secondary to infection and/or trauma, scrotal calcifications, and diffuse scrotal wall thickening. Power Doppler demonstrates the movement of internal debris.
	Scrotal calcifications/pearls		Highly echogenic spherical focus or foci with associated acoustic shadowing moving freely within the hydrocele.
	Acute hematocele		Complex echogenic fluid collection between the parietal and visceral layers of the tunica vaginalis.
	Chronic hematocele		Complex echogenic fluid collection with thick internal septa, scrotal wall thickening, calcifications, indistinguishable from chronic hydrocele or pyocele.
	Pyocele		Thick hemiscrotal wall; echogenic fluid collection with septations and occasionally focal mural calcifications; similar to chronic hydroceles and hematoceles.
	Hematoma		Appearance of hematoma varies with age; acutely, the scrotal wall is thickened; after 2-3 days, hypoechoic areas are seen (liquefaction); extratesticular hematomas can be solid or septated cystic masses.
	Abscess		Complex intrascrotal mass with focal hypoechoic low-level echoes or mixed areas, with irregular and hypervascular borders.
	Tunica albuginea cyst		Defined anechoic area(s) with posterior enhancement. Meets criteria for a simple cyst.
Testicular focal-benign	Hematoma/trauma		Appearance of hematoma varies with age; focal hyperechoic avascular areas are seen in the acute stage and hypoechoic to complex focal areas develop as the hemorrhage ages.
	Abscess		Focal complex mass with low-level areas, irregular and hypervascular borders.
	Focal orchitis		Ill-defined hypoechoic mass with increased blood flow.
	Liquefactive necrosis (seen in subacute torsion)		Focal anechoic areas; avascular
	Focal ischemic infarction (following infection and torsion)		Focal hypoechoic avascular mass.
	Adenomatoid tumor		Solid well-circumscribed mass, variable echogenicity, equal to or greater than the testis. Minimal flow by color Doppler imaging within and on the periphery of the tumor.
	Sarcoidosis		Solid, focal hyperechoic mass.
	Sperm granuloma		Hypoechoic-to-heterogeneous solid mass. Intravascular flow present with acute inflammation.
	Benign gonadal stromal tumors (Leydig, Sertoli)		Focal, variable echogenicity, usually hypoechoic with prominent peripheral flow by color Doppler imaging.
	Epidermoid cysts		Well-circumscribed avascular mass with variable echogenicity (hypoechoic to hyperechoic) with an echogenic or anechoic rim. Alternatively, it can contain alternating hypoechoic and hyperechoic concentric rings demonstrating an “onion appearance.”
	Dermoid cyst		May simulate simple cyst or may have echogenic areas along the periphery; occasionally, the cyst itself is echogenic.
	Cystadenoma		Multiseptate cystic mass.
Testicular diffuse-benign	Orchitis		Enlarged, diffusely hypoechoic testis with hypervascularity.
	Infarcts (after trauma, infection, and torsion)		Acutely (within 24 hours), enlarged with normal or decreased echogenicity. After 24 hours, heterogeneous with hypoechoic areas representing necrosis, hemorrhage, and infarction. Absent intratesticular flow by color Doppler imaging.
	Granulomatous disease		Enlarged, irregular, heterogeneous testis; may have calcifications.
	Sarcoidosis		Enlarged heterogeneous testis with hypoechoic nodules.
	Microlithiasis		Multiple small 1-3 mm echogenic foci disseminated throughout the testis without posterior shadowing. The pattern of microliths can vary with cluster calcifications centrally and in the periphery. Bilateral involvement is common.
	Acquired atrophy		Small, hypoechoic testis.
Testicular focal-malignant	Seminoma		Uniformly hypoechoic mass; well defined (without tunica albuginea invasion), may have scattered hyperechoic areas. Color/power Doppler imaging demonstrates hypervascularity in tumors >1.6 cm.
	Embryonal cell		Predominantly hypoechoic mass, poorly marginated, texture is heterogeneous with areas of hemorrhagic necrosis or cystic change. The tumor often invades the tunica albuginea.
	Choriocarcinoma		Heterogeneous mass with extensive hemorrhagic necrosis in the central portion, with a mixed cystic and solid appearance.
	Teratoma		Large complex mass with multiple cystic areas representing bone, cartilage, smooth muscle, and other tissues.
	Yolk sac tumor		Nonspecific and inhomogeneous and may contain echogenic foci secondary to hemorrhage or hypoechoic areas owing to necrosis.
	Lymphoma		Enlarged testis, hypoechoic lesions of various sizes with increased vascularity.
	Leukemia		Enlarged testis, hypoechoic mass with increased vascularity.
	Metastases		Multiple hypoechoic (less often echogenic) masses; rarely, both are seen together.
Testicular diffuse-malignant	Leukemia		Enlarged, hypoechoic testis with hypervascularity similar to orchitis.
	Lymphoma		Enlarged, hypoechoic testis with hypervascularity similar to leukemia.
	Diffuse embryonal cell		Enlarged, hypoechoic testis with heterogeneous echotexture, irregular margins, and focal echogenic areas owing to hemorrhage or necrosis. Tunica albuginea invasion.
	Diffuse seminoma		Enlarged, hypoechoic testis with heterogeneous echotexture, lobular or multinodular with hypervascularity similar to diffuse orchitis. The tumor is confined within the tunica albuginea.
TB, tuberculosis.

Undescended testes are bilateral in about 10% of cases.¹⁵ Approximately 80% of undescended testes are located within the inguinal canal, and the remaining 20% are intra-abdominal (from the renal hilum to the inguinal canal).⁷^,¹⁷^,²¹^,²³ The incidence of undescended testis has been reported in 0.28% of adult men and its incidence at birth has been reported to be 30.3% for premature infants and 3.4% for full-term infants.⁷^,²⁷

The sonographic appearance of an undescended testis is an oval or elongated well-circumscribed hypoechoic homogeneous soft tissue structure, smaller than the normal descended intrascrotal testis (Fig. 19-21). Identification of the mediastinum testis helps confirm the presence of the undescended testicle.⁷^,⁹^,¹⁰^,¹⁵^,¹⁷^,²¹ Because sonography is relatively inexpensive, delivers no ionizing radiation, and does not require sedation, it should be the initial imaging method for undescended testis, with adjunctive computed tomography or MRI when sonography cannot definitively localize the testis.²⁶

Acute Painful Scrotum

Acute scrotal pain is a common clinical problem in both children and adults, and it often presents a diagnostic challenge for referring clinicians. Epididymitis and epididymo-orchitis are the most common causes of acute scrotal pain.¹^,⁷^,⁹^,¹¹^,¹⁴^,²⁴^,²⁸ Differentiating patients with epididymitis from those with suspected torsion is critical. Grayscale sonography combined with color, power, and spectral Doppler increases the diagnostic efficacy in distinguishing inflammatory from ischemic processes.⁶^,¹²^,¹⁸^,³² With prompt diagnosis, conditions such as ischemic necrosis and abscess can be surgically corrected to preserve testicular viability and function.⁹^,²⁰^,²³^,³⁰

FIGURE 19-21 Undescended testis. Longitudinal image of a small, undescended testis (arrows) located in the inguinal canal. MT, mediastinum testis.

The major causes of acute scrotal pain include epididymitis, epididymo-orchitis, focal orchitis, testicular torsion, abscess, trauma, torsion of the testicular appendices, scrotal wall inflammation, and incarcerated inguinal hernia.⁷ With complete testicular torsion, arterial flow is occluded and only surgical restoration of blood flow can prevent loss of the testicle.¹⁹ Abscess is also a surgical emergency because drainage of an abscess can prevent loss of the testicle. Epididymitis is painful, but antibiotic treatment usually resolves the symptoms fairly rapidly.⁷ Left untreated, epididymitis may progress to abscess formation, testicular infarction, and necrotizing fasciitis (Fournier gangrene).⁷^,⁸^,¹⁰^,³¹

Testicular Torsion

Testicular (spermatic cord) torsion represents 20% of scrotal disease in postpubertal males.⁷ Torsion occurs most commonly during adolescence, between 12 and 18 years of age, with a peak incidence occurring at 14 years.⁷^,¹⁶^,²⁶ Torsion is caused by a developmental weakness of the mesenteric attachment of the spermatic cord to the testis and epididymis. This faulty development allows the testis to fall forward within the scrotum and rotate freely within the tunica vaginalis, much like a clapper inside a bell.⁷^,⁹^,¹⁶^,²⁶ The severity of testicular torsion ranges from 180 to 720 degrees or greater.⁵^,⁹^,¹¹^,¹⁴^,¹⁶^,³² Twisting of the spermatic cord results in venous congestion. Initially, this prevents venous drainage and progresses to arterial occlusion, scrotal edema, hemorrhage, and infarction.⁵^,¹²^,¹³^,¹⁶ Sonographic detection of a spermatic cord “torsion knot” has been described as a whirlpool pattern, manifested by concentric layers with increased and decreased echogenicity at the external inguinal canal above the testis and epididymis. Visualization of the torsion knot is the most specific and sensitive sign of either complete or incomplete testicular torsion⁷^,¹¹^,¹⁶^,³⁰ (Fig. 19-22). Pulsed Doppler should always be used in conjunction with
color or power Doppler to confirm the presence of arterial and venous flow within the testis because color Doppler can be subject to motion artifacts.¹³

FIGURE 19-22 Testicular torsion. Longitudinal image of spermatic cord demonstrating “the knot” or “whirlpool” pattern (arrows) seen in testicular torsion. (Image courtesy of Dr. Vijayaraghavan S. Boopathy.)

Early diagnosis of testicular torsion is important because it requires orchiopexy, a surgical procedure, to preserve viability and function.⁷^,⁹^,¹¹^,¹⁶^,²⁶ When surgery is performed within 6 hours after the onset of pain, the salvage rate is between 80% and 100%, as opposed to 70% and 76% when performed within 6 to 12 hours.⁵^,¹⁴^,¹⁵ After 12 hours, the salvageability drops to 20%.⁶^,⁷^,¹⁴^,¹⁵^,²⁶ Surgery performed after 24 hours almost never results in successful salvage of the testis and is considered a missed torsion.⁵^,⁶^,¹¹^,²⁶

There are two types of testicular torsion: intravaginal and extravaginal⁷^,⁹^,¹²^,¹⁵^,¹⁶^,³⁰ (Fig. 19-23A, B). In the intravaginal type, the testis rotates freely within the tunica vaginalis by a long stalk of mesorchium. Intravaginal torsion is the most frequent type of testicular torsion and is seen in 80% of cases.⁹^,¹¹^,¹⁶ Extravaginal testicular torsion occurs exclusively in newborns.⁷^,⁹^,¹¹^,¹⁵^,¹⁶^,²⁶ This type of torsion occurs outside the tunica vaginalis when the testes and gubernacula are not fixed and are able to freely rotate.¹¹^,¹⁴^,¹⁶

Clinical signs of testicular torsion include a sudden onset of pain, followed by nausea, vomiting, and a low-grade fever.³² In 50% of cases, the symptoms mimic epididymitis.²⁶ The cremasteric reflex is usually absent, and pain cannot be relieved by elevating the scrotum.³² When the spermatic cord twists, the affected testis maintains a higher and horizontal position in the scrotum.¹⁶ After 24 to 48 hours, the pain usually disappears, generally indicating that the testicle is dead. In newborns, testicular torsion may present with only painless swelling and redness.²⁶

FIGURE 19-23 Types of testicular torsion. A: Schematic illustration of intravaginal testicular torsion. B: Schematic illustration of extravaginal testicular torsion.

Torsion can be divided into three phases: (1) acute (within 24 hours), (2) subacute (1 to 10 days), and (3) chronic (more than 10 days).¹³^,²³ Sonographic findings in testicular torsion depend on the duration and degree of spermatic cord rotation.⁷^,¹¹^,¹⁵^,¹⁶

Grayscale sonographic findings alone of testicular torsion are nonspecific. Differentiation between inflammation and ischemia requires color, power, and spectral Doppler.⁹^,¹¹^,¹⁵^,¹³^,²³^,³³ Within 1 to 6 hours, the affected testis maybe slightly enlarged, with normal or decreased echogenicity⁷^,⁹^,¹¹^,¹⁶^,²³^,²⁶ (Fig. 19-24A). Epididymal enlargement (Fig. 19-24B) is common and is frequently accompanied by the “torsion knot” or “whirlpool” pattern seen in the spermatic cord (see Fig. 19-22), scrotal skin thickening, and a reactive hydrocele (Fig. 19-23C).⁹^,¹¹^,¹⁵^,¹⁶^,²⁶ Because grayscale sonography findings are often normal in the early or acute phase of torsion, the absence of intratesticular arterial flow by color and power Doppler is diagnostic for ischemia⁴ (Fig. 19-24A).

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