Ultrasound (US) offers timely and accurate differentiation of many causes of scrotal pain. Advances in high-resolution gray-scale and color Doppler US have expanded the clinical applications of scrotal US and have made it the ideal imaging modality for evaluation of the acute scrotum in both children and adults. The authors review proper US techniques and findings of a variety pathologies of the scrotum.
is an Associate Professor of Radiology and
is a Professor and the Chair of the Department of Diagnostic and
Interventional Imaging, University of Texas Medical School at
Houston, Houston, TX.
While acute scrotal pain is a common clinical problem in both
children and adults, symptoms are often vague and clinical findings
are nonspecific. Ultrasound (US) allows for expedient and accurate
differentiation of many causes of scrotal pain, including prompt
diagnosis of testicular torsion that helps maximize testicular
viability. Advances in high-resolution gray-scale and color Doppler
US have expanded the clinical applications of scrotal US and have
made it the ideal imaging modality for evaluation of the acute
scrotum in both children and adults.
Scrotal US is best performed with a linear 7.5- to 12-MHz
transducer. A lower-frequency transducer may be helpful with marked
scrotal swelling. Direct scanning with copious acoustic gel is
performed most frequently, but a standoff pad may be useful for
superficial abnormalities. A towel or the examiner's hand may be
used to elevate and support the scrotal sac. In addition to imaging
in the longitudinal and transverse planes, it is helpful to obtain
simultaneous images of both testes for comparison. Color Doppler is
used to evaluate for abnormalities of flow and to differentiate
vascular from nonvascular lesions but may be hampered in the
younger child by motion artifacts. Attention to appropriate color
Doppler settings to optimize detection of slow flow is critical.
Power Doppler is a useful adjunct to color Doppler in low-flow
states, but it is more sensitive to motion artifacts. The Valsalva
maneuver or scanning in the upright position should be performed
when evaluating for varicoceles.
The testicles and associated structures are located within the
scrotum, formed by fusion of three fascial layers and divided by a
The septum is contiguous with the dartos muscle underneath the
scrotal skin. The tunica vaginalis is a potential space formed from
the processus vaginalis, an outpouching of the fetal peritoneum
that descends into the scrotum along with the testis. An inner
visceral layer covers the testis and epididymis, and an outer
parietal layer lines the scrotum. The layers join at the
posterolateral aspect of the testis where it attaches to the
scrotal wall. The tunica albuginea forms a dense capsule around the
testis, and a reflection of this capsule along the posterior border
(the mediastinum testis) runs along the superior inferior axis of
the testis. The mediastinum divides the testis into lobules and
serves as a conduit through which the blood vessels, lymphatics,
and spermatic tubules enter and leave the testis. The epididymal
head is located superior to the testis, while the body and tail run
posterior to the testis. The efferent ducts converge and, from the
epididymal tail, become a single vas deferens, which continues in
the spermatic cord. The spermatic cord also contains the
testicular, cremasteric, and deferential arteries, pampiniform
plexus, nerves, and lymphatics.
Four testicular appendages, remnants of embryonic ducts, include
the appendix testis, appendix epididymis, vas aberrans, and the
paradidymis; 92% of males have an appendix testis, and 34% have an
The main blood flow to the testicle is via the testicular
artery, with branches off the deferential and cremasteric arteries.
These arteries course through the spermatic cord, along with their
corresponding veins and nerves. The testicular artery pierces the
tunica albuginea, forming capsular arteries that, in turn, form
recurrent rami that course centrifugally toward the mediastinum. In
10% to 50% of normal testes, a single transmediastinal artery can
be seen unilaterally running directly within the mediastinum and
coursing in an opposite direction from the recurrent rami.
On US, the pediatric testes are ovoid, measuring approximately 1
with uniform low-to-medium echogenicity (Figure 1). The size and
echogenicity increases from age 8 to puberty, at which time the
testes are about 4 cm
. In the adult, the normal testis is roughly 20 cm
, with an approximate diameter of 3 to 5 cm, which decreases with
The mediastinum testis can be seen as a linear echogenic band. The
trans-mediastinal artery, if present, appears as a prominent
intratesticular hypoechoic band with opposite direction of flow
from the recurrent rami (Figure 2). The epididymis has an
echogenicity similar to or slightly hyperechoic to the testis. The
epididymal head may be round or triangular, measures 5 to 12 mm in
length, and lies atop the superior pole of the testis (see Figure
1), while the body and tail run posterior to the testis. The narrow
body (2 to 4 mm) and tail (2 to 5 mm) are often indistinguishable
from surrounding tissues but may occasionally be seen in normal
patients with high-resolution US.
A small amount of fluid between the leaves of the tunica vaginalis
is seen in most normal patients. The appendix testis is attached to
the upper pole of the testis in the groove between the testis and
the epididymis, while the appendix epididymis is attached to the
head of the epididymis. These structures are seen only when torsed
or when a hydrocele is present
(Figure 3). The normal scrotal skin measures 2 to 8 mm in
Torsion occurs most frequently in adolescent boys with an
incidence of 1 in 160 by age 25. Two thirds of cases occur between
12 and 18 years of age.
Up to 70% of young boys with acute scrotal symptoms have conditions
other than torsion-most commonly epididymitis. Ultrasound is
helpful to differentiate testicular torsion from other causes of
acute scrotal pain and to identify testicular torsion promptly,
ensuring the highest salvage rate. The severity of torsion of the
testis can range from 180˚to 720˚, but complete occlusion of blood
flow does not occur until 450˚of tor-sion.
Transient or intermittent torsion with spontaneous resolution
sometimes occurs. Venous congestion progresses to arterial
occlusion, testicular ischemia, and infarction. The collateral
blood flow is typically not adequate to provide viability to the
testicle if the testicular artery is occlud-ed.
Testicular torsion can be classified as extravaginal or
intravaginal. Extravaginal torsion occurs in utero or perinatally
before the testis is fixed, so the torsion occurs proximal to
attachment of the tunica vaginalis, in the inguinal canal or just
This form of torsion is found exclusively in newborn infants.
Intravaginal torsion is more common and is due to a
bell-and-clapper deformity in which the tunica vaginalis has an
abnormally high insertion on the spermatic cord and completely
encircles the testis, leaving the testis free to rotate within the
The deformity is bilateral in most cases.
Intravaginal torsion may also occur in testes that are retractile
or are not fully descended. Blunt trauma, sudden forceful rotation
of the body, or sudden exertion also predispose to testicular
The sonographic appearance of testicular torsion depends on the
duration of the torsion. Within 6 hours, the affected testis may be
slightly enlarged, with normal or decreased echogenicity (Figure
4A). After 24 hours (late or missed torsion), echogenicity of the
testis becomes heterogeneous, a sign of loss of viability.
The epididymal head may be enlarged because of involvement of the
deferential artery. Hydroceles are common.
Spiral twisting of the spermatic cord may be seen with color
Doppler imaging. Normal testicular echogenicity and lack of scrotal
wall thickening or hydrocele are strong predictors of testicular
Color Doppler imaging provides both structural and physiologic
information about the vascular integrity of the testis. Doppler
flow may be difficult to demonstrate in young children, even within
the normal testis.
Unilateral diminished or absent flow is the most accurate sign of
testicular torsion (Figure 4B), but the presence of blood flow does
not exclude torsion.
False-negative studies may occur when torsion is intermittent or
low grade. The torsion may result in hyperemia, mimicking
epididymo-orchitis. Late torsion may be accompanied by peripheral
blood flow, but central testicular blood flow will be absent.
Intravenous microbubble contrast material may improve US
sensitivity but is not routinely available. There are a few
advocates of manual detorsion of the twisted testis under narcotic
analgesia, but it is yet unclear whether this maneuver increases
the salvage rate in torsion.
Torsion of the testicular appendages occurs less frequently than
does testicular torsion (6:1) but can be as painful. Sonography is
important for distinguishing this condition, which is self-limiting
and does not threaten testicular viability. Clinically, the
cremasteric reflex is preserved and a palpable nodule with bluish
discoloration (blue dot) is often detected. Approximately 91% to
95% of cases involve the appendix testis in boys 7 to 14 years of
age.Ultrasound shows a hyperechoic mass with central hypoechoic
area adjacent to the testis or epididymis. Other associated
findings include scrotal wall edema and epididymal enlargement.
Blood flow in the peritesticular structures may be increased.
Ultrasound is helpful to exclude testicular torsion, because blood
flow within the testis is normal in torsion of the appendix testis.
Torsed appendages may atrophy and calcify.
Occasionally, in infants, calcified meconium from an in utero
intestinal perforation can descend into the scrotum, mimicking the
hard mass of an infarcted testis. Segmental testicular infarction
can occur in the absence of torsion, resulting from trauma,
vasculitis (Figure 5), or tumor.
Inflammatory causes of scrotal pain predominate in all age
groups. Epididymitis usually results from descending infection,
frequently associated with urinary tract infection. Genitourinary
anomalies (such as ectopic ureter, ectopic vas deferens, or
urethral stricture) may predispose a child to epididymitis. In
pubertal boys and young adults, epididymitis most commonly results
from sexually transmitted diseases. Less commonly, epididymitis may
result from hematogenous infection, trauma, idiopathic
granulomatous disease, and vasculitides, such as Henoch-Schönlein
purpura and Kawasaki disease. Chemical epididymitis from amiodarone
hydrochloride, an antiarrhythmic agent, has been described.
With infectious epididymitis, the process begins in the tail and
proceeds cephalad. On US, the epididymis is enlarged and hypoechoic
or heterogeneous in echotexture
(Figure 6). Often there is a reactive hydrocele and scrotal wall
thickening. Associated orchitis is seen in 20% of cases and may be
diffuse or focal, characteristically seen as a crescentic
hypoechoic lesion within the testicle, located at the periphery
near the inflamed epididymis.
Isolated orchitis is rare, and is usually a result of postviral or
posttraumatic inflammation (Figure 7). On color Doppler,
epididymitis is seen as diffuse or focal areas of increased color
signal (Figure 6B). Hyperemia is the only US finding in 20% of
patients with epididymitis and 40% of patients with orchitis.
Focal hyperemic areas may mimic testicular mass, hypervascular
epididymal tumors, or spontaneous detorsion of testis with
Testicular ischemia may occur secondary to venous outflow
Fournier's gangrene is a polymicrobial necrotizing fasciitis of the
scrotum that can extend to the lower abdominal wall.
The diagnosis of Fournier's gangrene is made when soft tissue air
is seen as echogenic foci with shadowing within the scrotal
tissues. Such air can be differentiated from bowel within an
inguinal hernia by demonstration of peristalsis of intestinal
loops. The scrotal skin is usually thickened and hyperemic in
scrotal fasciitis. Other complications of epididymitis include
infarction, abscess, and pyocele formation.
Idiopathic scrotal edema can occur in boys 4 to 7 years of age. The
scrotal skin is edematous, but the testis and epididymis are
In most normal patients, a small amount of fluid (1 to 2 mL) can
be seen within the leaves of the tunica vaginalis.
Hydrocele is present when an excessive amount of fluid is present.
Hydrocele is the most common cause of painless scrotal swelling and
may develop secondary to trauma, infection, testicular torsion, or
tumor. Idiopathic hydroceles also occur. Congenital hydrocele
results from a patent processus vaginalis that allows ascites to
enter the scrotal sac. When the fluid contains high protein or
cholesterol content, the hydrocele may appear complex or septated.
Hematoceles and pyoceles are rare and are usually caused by trauma,
surgery, or neoplasm. Pyocele from untreated infection or rupture
of abscess typically shows internal septations and loculations on
US (Figure 8). Skin thickening and calcifications may also be
Inguinal hernias occur because of protrusion of peritoneal
contents, usually omentum or bowel, through a patent processus
vaginalis. Hernias are classified as direct or indirect by their
relationship to the inferior epigastric artery (IEA). Direct
hernias are located medial to the IEA, while indirect hernias are
lateral to the IEA.
Fluid or air-filled loops of bowel with peristalsis in the scrotal
sac are diagnostic of an inguinal hernia (Figure 9). Hyperechoic
areas are likely to represent omentum. Incarceration of a hernia is
most common before 6 months of age and in adulthood and is more
common in indirect hernias. The presence of an akinetic dilated
loop of bowel within the scrotum has a 90% sensitivity and
specificity for strangulation. Be wary of contraction of the dartos
muscle, which can cause movement that may mimic bowel peristalsis.
The bowel wall can be thickened and hyperemic with incarcerated
hernias. A Richter hernia consists of herniation of only the
antimesenteric border of the bowel and may not result in intestinal
obstruction. The diagnosis of Richter hernia is difficult to make
Varicocele represents abnormal dilatation and tortuosity of the
veins of the pampiniform plexus within the spermatic cord, caused
by incompetent valves in the internal spermatic vein. The condition
is more common on the left and is idiopathic in 15% of males
between 15 and 25 years of age.
About one third of men with varicocele will be infertile. The size
of the varicocele does not affect the incidence of infertility.
On US, varicoceles appear as multiple hypoechoic serpiginous and
tubular structures of varying sizes, predominantly >2 mm in
diameter and located superior and lateral to the testis.
Echoes from slow blood flow may be seen within the dilated veins
(Figure 10). Noncompressibility of a varicocele may indicate
retroperitoneal malignancy or other causes of increased pressure on
the spermatic vein. Ultrasound with color Doppler is highly
sensitive for the diagnosis but requires scanning in both the
supine and upright positions and during the Valsalva maneuver.
Primary varicoceles may decompress when the patient is supine, but
the flow within the veins increases when the patient is in an
upright position and with the Valsalva maneuver.
The scrotum and its contents are commonly injured during motor
vehicle accidents and athletic injuries. Direct blow or straddle
injuries result in contusion, hematoma, fracture, or rupture. More
than 50% of testicular ruptures occur from a direct blow to the
groin during sporting activity.
Testicular injuries are surgical emergencies with good prognosis if
treated within 72 hours. Ultrasound shows heterogeneous
echogenicity within the testis due to areas of hemorrhage or
infarction. Other findings include irregular, poorly defined
borders, scrotal wall thickening, and hematocele (Figure 11). The
tunica is disrupted with testicular rupture, and there may be
diminished blood flow in the disrupted capsule. A large hematocele
may displace and obscure the underlying testis, leading to a
false-positive diagnosis of testicular rupture.
In testicular fracture without rupture, the capsule is intact but a
discrete fracture plane is visible in only 17% of cases
(Figure 12). It is important to remember that 10% to 15% of tumors
first manifest after trauma and can mimic an injury; therefore,
sonographic abnormalities should be followed to resolution if
surgery is not performed.
Testicular and paratesticular tumors can occur in all age groups
but are an uncommon cause of acute scrotal pain (10%).
Testicular tumors are more likely malignant, while extratesticular
tumors are more likely benign. In general, palpable masses are more
likely to be malignant than are nonpalpable masses.
The role of US is to distinguish intratesticular from
extratesticular lesions. Approximately 90% to 95% of testicular
tumors are germ cell tumors, most commonly seminomas.
Nonseminomatous germ cell tumors are usually of mixed cell types.
Other testicular tumors include gonadal stromal tumors, lymphoma,
leukemia, and metastases.
The differential diagnosis of focal testicular mass includes
hematoma, abscess, focal orchitis, infarction, and granulomatous
disease. Color Doppler imaging can help to differentiate such
abnormalities from tumor, but distinction may be difficult when
tumor presents as generalized testicular enlargement without focal
mass. In up to 15% of patients, signs and symptoms caused by
metastatic disease are the first indication of testicular tumor.
Occasionally, the primary tumor may have undergone spontaneous
regression and appear as an irregular scar or calcification without
a definite mass.
The adenomatoid tumor of the epididymis is the most common
extratesticular tumor in adults. Adenomatoid tumor is a benign
hamartoma that favors the epididymal tail.
Other extratesticular tumors include lipomas, leiomyomas,
lymphangiomas, sarcomas, and metastases. Malignant lesions to the
scrotal wall are usually of epididymal origin. The most common
malignant paratesticular tumor in infants and children is
rhabdomyosarcoma, which is associated with a better prognosis than
rhabdomyosarcoma found elsewhere in the genitourinary tract.
Testicular microlithiasis (TM) is defined as multiple (>5)
echogenic nonshadowing 2- to 3-mm foci randomly scattered
throughout the testicular parenchyma (Figure 13). The number,
distribution, and laterality of the foci varies. Diagnosis requires
high-frequency US transducers.
Testicular microlithiasis is associated with cryptorchidism,
infertility, pulmonary alveolar microlithiasis, and intratubular
germ cell neoplasia. Eighteen percent to 75% of patients are at
risk for testicular cancer, primarily nonseminomas.
The relation of the number of calcifications to cancer risk has not
been well established, but in the absence of a focal mass, annual
follow-up is recommended in all patients with TM.
Fibrous septae in normal testes can mimic the foci of TM, but
normal septae disappear when scanned at a 90° angle.
Miscellaneous scrotal abnormalities
Epididymal cysts and spermatoceles are common at all ages. Both
types of lesions can be multiple, and about 30% of cases are
Both types of cysts are thought to result from dilatation of the
epididymal tubules. Epididymal cysts contain clear serous fluid,
and spermatoceles generally contain spermatozoa and cellular
debris. The sonographic appearance of these cysts is similar;
however, epididymal cysts can occur anywhere, while spermatoceles
occur only in the epididymal head.
Tubular ectasia of the rete testis can present as multiple cystic
lesions, but its characteristic location near the mediastinum
testis should prompt the diagnosis. Benign testicular cysts include
tunical albuginea cysts, testicular cysts, and epidermoids
An undescended testis is one of the most common genitourinary
anomalies in male infants. Cryptorchidism is found in 3.5% of term
male infants at birth. Cryptorchidism is usually unilateral, but up
to 30% of cases are bilateral. Associated urologic anomalies can be
seen in up to 20% of patients with an undescended testis. The
undescended testis is most commonly located at or just below the
inguinal canal (Figure 14). Patients with an undescended testis are
at higher risk for malignancy, torsion, infertility, and
incarcerated inguinal hernia.
The risk of death from testicular malignancy in men with an
undescended testis is nearly 10 times the risk in normal men, and
the risk is increased in both the undescended testis after
orchiopexy and within the normally descended testis.
Macroscopic calcifications within the scrotum can be
intratesticular or extratesticular. Intratesticular
macrocalcifications may be associated with large cell calcifying
Sertoli cell tumor, burned-out germ cell tumor,
or dystrophic calcifications from prior trauma.
In the epididymis, macrocalcifications may be the result of
inflammation or trauma. Scrotoliths (scrotal pearls)-calcified
bodies within the scrotum with no clinical importance-may represent
loose bodies caused by torsion of the appendix testis or epididymis
High-resolution US is the imaging modality of choice in the
evaluation of the acute scrotum. Knowledge of the normal appearance
of the testis and scrotal contents and familiarity with the many
pathologic conditions that may affect the scrotum are essential for
expedient and accurate diagnosis of scrotal pathology. Proper US
technique is critical, especially in the evaluation of torsion and
testicular rupture. Some conditions have overlapping sonographic
features, and follow-up to resolution is required to exclude