I. Introduction and Indications

Acute scrotal pain accounts for approximately 0.5 % of all complaints presenting to the emergency department. Differential diagnosis of acute scrotal pain includes epididymitis, orchitis, testicular torsion, torsion of the testicular appendage, testicular trauma, and herniation of abdominal contents into the scrotum. The history and physical examination findings of various etiologies of acute scrotal pain have a significant overlap, therefore making it difficult to differentiate these entities clinically. However, distinction between the underlying pathology is critical as prompt intervention is required in cases of testicular torsion, trauma, and incarcerated hernias. Misdiagnosing testicular torsion can lead to organ loss and infertility. Patient distress and the possibility of fertility-threatening disease place significant pressure on the emergency physician to make an accurate diagnosis. Bedside ultrasonography of the acute scrotum is a relatively new application to emergency medicine ultrasound and has high utility for emergency physicians managing patients with acute scrotal complaints.

Indications:

1.Testicular pain

2.Testicular swelling/mass

3.Trauma

II. Anatomy

The scrotum is a saccular structure divided into two compartments by the median raphe. Each compartment contains a testicle, epididymis, vas deferens, and spermatic cord. The testes are surrounded by a fibrous capsule, called the tunica albuginea, which is covered by the tunica vaginalis. The tunica vaginalis has two layers, an outer parietal layer and an inner visceral layer which are separated by a small amount of fluid. The normal adult testis is ovoid in shape and measures approximately 2 to 3 cm in width and 3 to 5 cm in length. The size of the testicle varies with age, increasing in size from birth to puberty and then decreasing later in life. Structurally, the testes are divided into lobules by septa radiating from the tunica albuginea. Within the testicular parenchyma, seminiferous tubules converge at the mediastinum testis, an incomplete septum formed through invagination of the tunica albuginea. It is located in the posterior aspect of the testis.

The epididymis is found along the posterolateral aspect of each testis. The epididymis measures approximately 6 to 7 mm in length and consists of a head, body and tail. The head of the epididymis is located adjacent to the superior pole of the testis, the body runs posteriorly, with the tail at the inferior pole. The largest portion of the epididymis is the head and is usually round or triangular in shape. The tail of the epididymis becomes the vas deferens as it ascends superiorly out of the scrotum. The spermatic cord suspends the testis in the scrotum and consists of arteries, veins, nerves, lymphatics, and the vas deferens. The appendix testis and the appendix epididymis are both embryological remnants that are found toward the superior pole of the testis. Blood supply to the testis primarily originates from the testicular artery, which arises from the aorta. Other sources of blood supply include the deferential artery, which supplies the epididymis and the vas deferens and the cremasteric artery supplies the peritesticular tissues. Venous outflow from the scrotum is via the pampiniform plexus, which empties into the testicular veins. (1,5,6,7)

Illustration 1: Overview of testicular anatomy.

Normal Variants

In 50 % of men the transmediastinal artery, a large branch of the testicular artery, courses through the mediastinum testis to supply the capsular arteries and is usually accompanied by a large vein.

III. Scanning Technique and Normal Findings

Prior to performing a scrotal ultrasound examination adequate analgesia and reassurance should be provided. The patient is placed in a supine position with the legs slightly spread apart. The scrotum is placed in a sling designed from a towel to improve exposure and should be supported and immobilized on a rolled towel placed between the patient’s thighs. The penis is covered with a towel and the towel is taped to the abdominal wall. Alternatively, one can request the patient to support the penis with his hand in a cephalad direction and a drape can be placed on top. Of note, utilizing cold gel may cause the skin on the scrotum to contract and become thick or may cause the testicles to ascend in the scrotal sac making imaging more difficult.

A high frequency broadband linear transducer (7.5-10 MHz) that can perform both power and spectral Doppler ultrasonography is used. The scrotum and its contents are scanned in at least two planes, along the longitudinal and transverse axis. The unaffected hemiscrotum is scanned initially to familiarize the patient with the process, and also to provide a comparison of anatomy and blood flow as well. The scan is performed initially in a long axis to the testicle, with the indicator directed cephalad showing a longitudinal cut through the testis with the epididymis on the left side of the screen (Figure 1).

Figure 1: A properly exposed and draped patient with the scrotum supported in a sling of towels. (Courtesy of Michael Blaivas, M.D.)

The entire testis is scanned from one extreme to another, noting the echotexture and abnormalities. The epididymis is visualized as well. The transducer is moved smoothly and slowly, examining all aspects of the anatomy. The scan is then repeated with the probe turned 90° toward the patient’s right to obtain a transverse image of the testicle. A coronal scan showing both testicles side by side should be performed to identify differences in size and echogenicity, and vascularity.

The visceral and parietal layers of the tunica are visualized as one echogenic stripe. The normal testis has midgray or medium-level echoes and is homogenous in appearance. The echogenicity of the testis is similar to that of the liver or the thyroid gland. The epididymis has similar or slightly increased echogenicity as compared to the normal testis. The mediastinum testis is seen as a linear echogenic band running craniocaudally or parallel to the epididymis. The appendix testis and appendix epididymis are small ovoid hyperechoic protuberances found at the superior pole of the testis, normally hidden by the epididymal head. Unless outlined by fluid from a hydrocele, they are difficult to find on ultrasound. The spermatic cord appears as multiple hypoechoic linear structures in the longitudinal plane and circular hypoechoic structures in the transverse plane. (1,5,6,7)

Power Doppler examination is performed after gray-scale imaging is complete. The unaffected side is scanned initially to obtain accurate Doppler settings. To adequately evaluate blood flow, Doppler parameters should be adjusted to their most sensitive settings without introducing significant artifact. Power Doppler and pulsed Doppler should be optimized to display low-flow velocities to demonstrate blood flow in the testes and adjacent structures. The wall filter, scale and gain may need to be adjusted to pick up maximal blood flow without significant artifact. The wall filter should be set at the lowest selection possible and the PRF (Pulse Repetition Frequency) is minimized as well. The color gain should be adjusted carefully, as the artifactual appearance of flow may be created in a torsed testicle. Intratesticular and epididymal flow should be confirmed using both power Doppler

and spectral Doppler waveform analysis. Power Doppler helps to detect blood flow within the testicle and spectral Doppler allows identification of the flow whether it is venous or arterial. Spectral Doppler waveforms should be obtained in several areas of blood flow detected by power Doppler to document both arterial and venous flow patterns. Typically, power and spectral Doppler scan can be performed on the same ultrasound window.

Figure 2: Image of the normal testicle with the epididymal head on the left and body of testicle on the right. (Courtesy of Michael Blaivas, M.D.)

VI. Pathology

Illustration 2: Schematic overview of testicular pathology.

Hydrocele

A hydrocele is the most common cause of scrotal swelling. The normal scrotum contains small amounts of serous fluid between the layers of the tunica vaginalis. Abnormal collection of fluid in the space between the visceral and parietal layers of the tunica vaginalis results in a hydrocele. The fluid collections are usually confined to the anterolateral portions of the scrotum because of the posterior location of attachments of the tunica to the testis and scrotum. Hydroceles may be unilateral or bilateral and can be seen as an isolated finding or in conjunction with acute or chronic pathology. Many of these fluid collections are congenital. Acquired hydroceles are associated with infection, tumors, trauma, torsion and radiation therapy. Hematoceles and pyoceles are complex hydroceles. Sonographically, a simple hydrocele is seen as an anechoic dark fluid collection surrounding the testicle (Figure 3), whereas a complex hydrocele may contain internal echoes with septations and loculations. A chronic hydrocele may also demonstrate internal echoes from cholesterol crystal formation. (1,2,3,6)

Figure 3: Image of right and left testicles with hydrocele on right. (Courtesy of Michael Blaivas, M.D.)

Varicocele

A varicocele is a collection of tortuous and dilated veins within the pampiniform plexus of the spermatic cord. They are found in approximately 15 % of adult males and can result in infertility secondary to decreased sperm motility and count. They are due to incompetent valves in the testicular vein. The vast majority of varicoceles are located on the left side and only 1 % are bilateral. The left sided predominance of varicoceles is thought to be due to the long course and angle of entry of the left testicular vein as it empties into the left renal vein. The right testicular vein is shorter and empties directly into the inferior vena cava. Varicoceles are much more apparent when the patient performs a Valsalva maneuver or is standing. Hence, ultrasound should be performed in both supine and standing positions. Sonographically, they appear as multiple anechoic serpiginous tubular or curvilinear structures of varying sizes (larger than 2 mm in diameter) in the region of the epididymis (Figure 4). Power Doppler should be used to confirm flow in the varicocele. (5,6,7)

Figure 4: Longitudinal view of testicle with enlarged pampiniform plexus. Also note the thickening of the surrounding connective tissue secondary to scrotal inflammation after a failed penile implant. (Courtesy of Beatrice Hoffmann, M.D.)

Testicular Torsion

Testicular torsion is a urologic emergency. Prompt diagnosis and early treatment is essential as time is critical for testicular salvage. Torsion is more common in children but can occur in post pubertal males. The majority of testicular torsions result from anatomic defects that lead to redundant spermatic cord and anomalous suspension of the testes in the scrotum. An undescended testicle also increases the likelihood of torsion. A redundant spermatic cord is mobile and during torsion it begins to twist upon itself. As the twisting progresses, venous flow is interrupted initially due to easily collapsible vessel walls and the low intravascular pressure. Venous obstruction is followed by a decrease in arterial inflow, which eventually progresses to complete obstruction. Once the spermatic cord is fully torsed and no blood flow is present, infarction and loss of the testicle can occur quickly. Rapid diagnosis of testicular torsion is critical to preserve fertility. The salvage rates are approximately 100 % at 3 hours, 83-90 % at 5 hours, 75 % at 8 hours, and 50-70 % at 10 hours. The salvage rates decrease to 10 to 20 % when the testicle remains torsed for more than 10 hours. After 24 hours, salvage of a testicle is rare unless there has been intermittent detorsion. Sonographic findings can be variable depending on the duration of torsion and extent of vascular compromise. The testicle can appear enlarged and hypoechoic and the parenchyma of the testicle will become less homogenous when compared with the unaffected testicle (Figure 5). Unfortunately ultrasound may not always be helpful, as sonographic findings may be subtle early in the course. Color Doppler or power Doppler may be helpful to identify flow patterns in the acutely tender testicle (Figure 6). When blood flow is absent in the affected testicle, the diagnosis of testicular torsion is clear. Occasionally decreased blood flow seen in early torsion can be erroneously diagnosed as normal. Thus, comparison to the contralateral side is crucial. Color Doppler alone will not assure both venous and arterial flow in the testicle. Spectral Doppler tracings should also be obtained to confirm both arterial and venous flow. The absence of a venous pattern by spectral Doppler on the affected side suggests early torsion. If the diagnosis is in doubt due to torsion-detorsion, repeat color Doppler imaging along with spectral examination in one hour is recommended. (2,3,4)

Figure 5: Transverse scan of both testicles showing normal left testicle and right testicular torsion. Note the hypoechogenicity of the right testicle. (Courtesy of Michael Blaivas, M.D.)

Figure 6: Transverse plane through both testes. The power Doppler image of the scrotum demonstrates right testicular perfusion. The swollen left testicle is not perfused. (Courtesy of Michael Blaivas, M.D.)

Epididymitis

Epididymitis is the most common cause of acute scrotal pain in postpubertal males. Classically, patients present with a painful tender scrotum, dysuria, and fever. Retrograde spread of infection from the bladder or prostate is usually the underlying etiology with the head of the epididymis most commonly involved. Gray-scale findings of acute epididymits include an enlarged epididymis with decreased echogenicity. Often, a reactive hydrocele is noted as well (Figure 7). A chronically inflamed epididymis becomes thickened and has focal echogenicity with areas of calcification. With Doppler sonography increased blood flow secondary to epididymal inflammation is noted. The presence of normal or increased blood flow in the affected testicle when compared to the contralateral side differentiates epididymitis from testicular torsion. (2,3,4)

Figure 7: A slightly oblique view of a testicle with an enlarged hypoechoic epididymis. (Courtesy of Michael Blaivas, M.D.)

Orchitis

Orchitis is an acute infection of the testicle usually following epididymitis. Orchitis often presents with a tender and inflamed testicle. On gray-scale ultrasound, orchitis is seen as an enlarged testicle with heterogeneous echogenicity. This appearance is nonspecific and can be seen in many other conditions such as tumors, metastasis, infarct and torsion. Standard B-mode is not a reliable method to differentiate between orchitis and testicular torsion. For both orchitis and torsion, inflammation and edema can lead to enlargement and heterogeneous echogenicity of the testis. Color Doppler is helpful to differentiate between orchitis and torsion since blood flow in orchitis is increased in comparison with the unaffected side due to inflammation (Figure 8). (2,3,4)

Figure 8: Orchitis. Marked increase in blood flow is seen along with a reactive hydrocele. (Courtesy of Michael Blaivas, M.D.)

Scrotal Trauma

Blunt trauma to the scrotum can lead to damage of the testicle and adjacent structures. Injuries to scrotum include laceration, hemorrhage, or contusion of the testicle. The goal of scrotal ultrasound in patients with acute trauma to the scrotum is to evaluate injury to the testicle. Blood flow to the testicle should also be evaluated since trauma could lead to testicular torsion. Visualization of a normal testicle on ultrasound virtually excludes any significant injury. Any abnormalities visualized within the testis in the setting of scrotal trauma should be considered as testicular rupture (Figure 9). Sonographic findings suggestive of testicular injury include irregular outline and a inhomogeneous echotexture from hemorrhage or infarction. A discrete fracture line is seen by ultrasound in only 17 % of ruptures. A significant hematocele is an indirect finding for possible testicular rupture. Hemorrhage within the testicle changes its appearance depending on the age of the hemorrhage. Acute hemorrhage will appear inhomogeneously echogenic, but later will develop large anechoic regions within it. Color Doppler helps to differentiate hematomas from tumors. Tumors are usually vascular, whereas hematomas will not reveal any blood flow. (2,3,4,6)