Ultrasound is close to the ideal modality for evaluating the scrotum; it is inexpensive, readily and rapidly available, and is performed without ionizing radiation. This article reviews scrotal ultrasound and addresses eight areas: technique, anatomy, torsion, infection, masses, varicocele, trauma, and testicular microlithiasis.
Dr. Winter is a Professor of Radiology and Director of
Ultrasound at the University of Wisconsin Medical Center,
Ultrasound is close to the ideal modality for evaluating the
scrotum; it is inexpensive, readily and rapidly available, and is
performed without ionizing radiation. Ultrasound is nearly 100%
sensitive at detecting intrascrotal masses
and delineates between testicular and extratesticular pathology
with 95% to 100% accuracy.
Recent improvements in technology, both in hardware and in
software, permit phenomenal high-resolution gray-scale and color
Doppler examination of intrascrotal pathology. This article will
briefly review scrotal ultrasound and will cover eight areas:
technique, anatomy, torsion, infection (epididymo-orchitis),
masses, varicocele, trauma, and testicular microlithiasis.
Support the scrotum with a towel placed over the thighs. Avoid a
cold room for the sake of patient comfort and also because lowered
room temperatures may cause skin thickening and testicular
retraction. Acquire hardware that is capable of demonstrating flow
in every normal testicle (which includes almost any reputable
machine currently), so that the absence of flow truly implies
infarction, rather than a technical problem. Use a transducer with
the highest possible frequency (current broad bandwidth technology
for small-parts imaging ranges between 5 and 14 MHz). Optimize your
color software for the low-volume, low-velocity flow present within
the normal testicle by choosing the correct preset package offered
by your ultrasound machine manufacturer.
Begin with gray-scale findings. Decide whether any lesion is
inside or outside the testicle and then assess the testicle for
size, echogenicity, and architecture. Assess the epididymis for
cysts, enlargement, and mass lesions. Evaluate for any hydro-,
pyo-, or hematoceles. Look at the surrounding tissues of the
scrotum for thickening or abscess, and the suprascrotal region for
obvious hernias. Assess vascularity using color or power Doppler
(color sensitivity on high-end machines is very close to
equivalent, with perhaps a slight edge in flow sensitivity for
power Doppler in older or mid-range machines
). Is it increased, decreased, or disordered, and where are the
abnormal vessels? Are they within the testicle, the epididymis, or
elsewhere? Obtain and document at least one pulsed Doppler spectral
tracing from each testicle. Finally, always remember to compare the
symptomatic testicle to the asymptomatic side.
In general, decreased testicular flow implies torsion/infarction
and increased flow implies epididymo-orchitis (some uncommon
exceptions are discussed below). Disorganized flow raises the
specter of intratesticular tumor, while increased venous flow in
the pampiniform plexus implies varicocele.
There are three arteries in the supratesticular region: 1) the
testicular artery that arises from the aorta, which is the major
blood supply to the testis; 2) the deferential artery that arises
from the vesicular artery, which supplies the epididymis and vas
deferens; and 3) the cremasteric artery that arises from the
inferior epigastric artery, which supplies the peritesticular
tissues. There are anastomoses between all three of these arteries,
but with occlusion of the testicular artery the collateral flow
from the other two vessels is not sufficient to keep the testicle
from infarcting. Therefore, the presence of arterial flow in the
supratesticular region on Doppler does not exclude torsion. The
intratesticular arterial anatomy is more important in ruling out
torsion. The testicular artery runs posteriorly and pierces the
tunica albuginea and forms the capsular artery in the tunica
vasculosa. Within the testicle, centripetal branches radiate from
the capsular artery toward the mediastinum, which then branch into
recurrent rami that course away from the mediastinum. The recurrent
rami may be difficult to see routinely with color Doppler, but the
capsular and centripetal arteries should always be visible. In
approximately 50% of cases, a transmediastinal artery will course
through the mediastinum toward the periphery. Venous
intratesticular flow may be seen with newer technology. Capsular
and intratesticular arteries should have resistive indices in the
range of 60% to 65%, with reversed end diastolic flow being a
potential indicator of torsion.
An exception is prepubertal males, in whom absence of end diastolic
flow is often a normal finding.
Symmetry is expected from side to side.
When a patient presents with a nontraumatic acute scrotum,
clinical diagnosis centers upon differentiating between torsion and
acute epididymitis. This differentiation is crucial since
epididymitis is treated medically and torsion is a surgical
emergency. If one can surgically detorse a twisted testicle within
6 hours, the majority of the testicles will probably be saved;
whereas after 12 hours the salvage rate drops precipitously.
Gray-scale findings overlap significantly, so color Doppler is
crucial in distinguishing the two. With the advent of modern
ultrasound technology, nuclear medicine imaging rarely has a role
in this diagnosis. Absent testicular blood flow almost always
implies torsion in the acute setting (although infarction can occur
after vasculitis, infection, or trauma). Because torsion is such a
surgical emergency, several authors have described using color
Doppler to assist in manually untwisting the testicle to reperfuse
the gland while the operating room is being prepared.
(This practice is far from widely accepted, however, since the
potential exists to worsen the ischemia if the testicle is twisted
the wrong way). Testicular torsion is possible at any age, but is
most common between the ages of 12 and 18 years, after which the
incidence slowly decreases.
Patients typically present with sudden onset of pain. Torsion
occurs because an abnormally narrow mesenteric attachment from the
cord onto the testis and epididymis allows the testis to rotate
like a clapper in a bell. This deformity is usually bilateral,
hence if torsion is confirmed on the symptomatic side, the
contralateral uninvolved testis is also fixed to the scrotum
Gray-scale findings range from normal to a swollen, hypoechoic
testicle with or without epididymis, with heterogeneous
architecture. A normal gray-scale appearance (but abnormal color
Doppler) is a good finding as it is more likely to be associated
with a salvageable testicle than is a gland with an abnormal
On color Doppler, the sonographic findings are simple. There is
generally no intratesticular blood flow, whereas you see normal
blood flow on the asymptomatic side (figure 1). Although recent
improvements in technology may allow a tiny amount of flow to be
seen in a torsed testicle, this is generally not a diagnostic
dilemma; as the marked asymmetry in flow from side to side and the
clinical presentation make correct diagnosis clear (figure 2). In
the future, ultrasound contrast agents may prove useful in
evaluating torsion, particularly in infants.
In general, increased testicular and epididymal blood flow
implies epididymitis and orchitis. Ultrasound is highly accurate in
making the diagnosis.
Clinically, these patients are slightly older than the torsion
patients, with two-thirds presenting between 20 and 30 years of
age. A common etiology is a retrograde ascent of urethral pathogens
via the ejaculatory duct into the vas deferens. The patient
presents with scrotal pain and swelling developing over hours. In
approximately 9% of cases, the disease is bilateral. Although the
epididymis alone is involved initially, by the time most patients
with clinical evidence of epididymitis present to the emergency
room, they have concomitant orchitis. The gray-scale findings of
orchitis overlap significantly with those of torsion--specifically,
the testicle may be normal or may be enlarged and hypo-echoic. Skin
thickening or reactive hydrocele may be present. Blood flow in the
normal epididymis is detected routinely with modern equipment.
However, symmetry is the rule in the scrotum, so asymmetric
hyperemia of an epididymis in the appropriate setting should
suggest infection. Because of the common concomitant orchitis,
color Doppler evidence of ipsilateral testicular hyperemia is often
present (figure 3). Complications of epididymitis are not uncommon
and some may be diagnosed by ultrasound. These complications
(figure 4) include testicular infarctions, scrotal abscess, chronic
draining scrotal sinus, chronic epididymitis, and infertility.
Distinguishing torsion from epididymo-orchitis may be quite
difficult clinically, but is usually easy with ultrasound. However,
there is a differential diagnosis for the sonographically
identified hyperemic epididymis and testicle. First, spontaneous
detorsion--torsion that spontaneously (nonsurgically) untwists--may
present as a high-flow testicle immediately after detorsion as the
reactive hyperemia is imaged (figure 5). Diagnosis is often made on
a clinical basis (no evidence for infection and the fact that 19%
to 68% of men with torsion had a history of similar pain that
resolved spontaneously--eg, prior episodes of spontaneous
detorsion). Spontaneous detorsion hyperemia is not a surgical
emergency, but these patients are at increased risk for future
torsion (including the opposite side since the bell-clapper
deformity is usually bilateral) and will benefit from orchiopexy
(surgically anchoring both testicles so that they cannot twist in
the future). Second, torsion of the testicular and/or epididymal
appendages may present with a hyperemic epididymis or testicle. In
5% of adults, and a much higher percentage of children, appendage
torsion is the etiology for an acute scrotum; but this is not a
surgical problem and resolves with supportive therapy. Third,
leukemic or lymphomatous infiltration may present with an enlarged,
hypoechoic, hyperemic testicle, potentially mimicking orchitis.
The testicles are a sanctuary site for these malignancies during
chemotherapy. Clinical history (which is usually readily available
during an ultrasound exam since one can talk to the patient!) helps
in making the correct diagnosis.
Intratesticular masses should be considered malignant until
proven otherwise, while extratesticular intrascrotal masses are
generally benign. Testicular cancer is the most common neoplasm in
males in the 20- to 34-year-old age group.
Testicular cancer is often one of the most curable. There have been
several high-profile athletes recently diagnosed with testicular
cancer who were treated successfully, raising public awareness of
this curable disease. For example, Lance Armstrong had brain
metastases and went on to win the Tour de France.
It has been suggested that males should perform scrotal
self-examinations every month.
The majority of affected patients present with a painless
unilateral testicular mass. Other clinical presentations include
diffuse testicular enlargement or evidence of metastatic disease
(approximately 10% of patients
Approximately 90% to 95% of primary tumors are of germ cell
origin. A great deal has been written about the sonographic
appearance of various testicular tumors. Although of intellectual
interest, diagnosing and distinguishing among the various malignant
cell-types is rarely of practical import to the general
radiologist, since the finding of any potentially malignant mass
within the testicle generally prompts surgical consultation. For
superb radiologic reviews of the various testicular tumors, see the
articles by Geraghty et al
or Dambro et al.
Color Doppler cannot distinguish benign from malignant
intratesticular lesions reliably, although, in general, large
avascular lesions and small hypervascular lesions are less likely
to be malignant. Tumors tend to have unorganized blood flow. Color
may have a role in detecting tumors in children, in whom tumors
have more of a tendency to be isoechoic.
The most common testicular tumors are seminoma and mixed
germ-cell tumors (MGCT) (eg, mixtures of embryonal, teratomatous,
and choriocarcinoma cells). Seminomas occur in a slightly older age
group than do other testicular neoplasms. Seminomas are typically
quite homogeneous, hypo-echoic nodules that range from a small
sharply demarcated mass (figure 6) to a large mass causing diffuse
testicular enlargement (figure 7).
As a group, MGCT are much more heterogenous in sonographic
appearance than seminomas (figure 8). Margins are more ill-defined,
tunica invasion is more common, and cystic regions, echogenic areas
(including calcifications), and mixed echogenic regions (necrosis
or hemorrhage) are much more common than with the typical
hypoechoic and homogeneous pure seminoma tumors. Other more unusual
primary testicular tumors do occur, as do metastases to the
Although it is important to remember that testicular solid
masses are tumor until proven otherwise, radiologists should also
be aware that benign processes may manifest as an intratesticular
mass at sonography.
Besides tumor, the differential for a mass includes infection,
hematoma, infarct/ vasculitis,
Consider recommending an inguinal biopsy, rather than a radical
orchiectomy if the lesion is atypical. In conjunction with clinical
history, suggestive (but nondiagnostic) sonographic features of a
benign tumor include hyperechoic lesion, pure simple cyst, or
avascular, solid, nonpalpable lesion >1 cm.
Two common entities should never be mistaken for malignancy: 1)
cysts of the tunica albuginea, and 2) tubular ectasia of the rete
testis. Cysts of the tunica albuginea are small (2 to 5 mm),
located in the tunica (generally on the anterior or lateral aspects
of the testicle), solitary or multiple, asymptomatic, often
palpable, and discovered in older (40- to 50-year-old) patients.
Tubular ectasia of the rete testis (figure 9) can generally be
diagnosed confidently as the benign lesion that it is, sparing the
patient anxiety and potential surgery.
A typical appearance of this lesion is multiple small spherical or
tubular anechoic structures in the region of the mediastinum
testis, often associated with epididymal cysts/spermatoceles and
occurring in an elderly patient with no palpable mass.
The subtly heterogeneous testicle without obvious discrete mass
presents a diagnostic challenge. The newest high-frequency probes
now show us exquisite detail and hence more heterogeneity, so make
sure that one does not overdiagnose. The machine should be
optimized (eg, no focal bump in the time gain curve), and the image
of the symptomatic testicle should be compared with that of the
opposite testicle. Heterogeneous testes in an elderly population
may occur in 14% of cases and typically represent seminiferous
tubule atrophy and sclerosis.
Harris and colleagues concluded that "older patients with a mottled
or heterogeneous testis, normal color Doppler flow, and no palpable
abnormality probably do not need sonographic follow-up."
However, patients with a history of testicular cancer and
heterogeneous changes on sonography require strict attention, since
a heterogeneous appearance to the contralateral testicle following
orchiectomy for cancer has been reported to have an approximately
25% risk of being cancer.
Rigorous follow-up is recommended in this group.
A varicocele is an abnormal degree of venous dilatation in the
pampiniform plexus that generally occurs on the left side,
presenting as a soft mass or swelling above the testicle; the mass
or swelling is most prominent with upright position or straining.
Gray-scale findings include two or three venous channels dilated to
2 or 3 mm that demonstrate an increase in size with Valsalva's
maneuver or standing. Color Doppler has been shown in multiple
studies to be more sensitive than physical examination. Classic
Color Doppler criteria include spontaneous venous flow and
increased venous flow with Valsalva's maneuver or standing. The
distinction between a small varicocele and a normal variant is not
completely straightforward given the incredible low-flow
sensitivity of the new ultrasound machines, since spontaneous
venous flow and augmentation with Valsalva's maneuver may be seen
now in normal patients, and diagnosis is a question of degree.
Varicocele size, situs, acuity of onset, change with position, and
correlation with clinical history help in deciding when to make the
diagnosis (see below).
There are two important clinical points that should be
remembered when encountering a varicocele. First, patients with
sudden onset of a varicocele, a right-sided varicocele, or a
varicocele that does not reduce in size in the supine position
should be suspected of having a retroperitoneal neoplasm (eg, renal
cell carcinoma, sarcoma, adenopathy) blocking the testicular vein
where it enters either the renal vein on the left or the inferior
vena cava on the right. These patients should undergo further
evaluation to rule out malignancy before receiving treatment for
the varicocele (figure 10).
Although the examination is low yield, we briefly scan the
ipsilateral renal hilum in every patient with a varicocele, with
particularly high suspicion for right-sided varicoceles. Second,
although the data is contradictory, most experts agree that
varicoceles can at least potentially cause infertility.
Approximately 40% of men who present to an infertility clinic have
a varicocele, and in more than half of these men, correction of the
varicocele improves the semen parameters.
Color Doppler can be used to follow treatment.
Only 50 kg of pressure will rupture the tunica albuginea.
Surgical exploration is performed with a very low threshold if
there is any question of testicular rupture because early
aggressive surgery reduces morbidity and leads to a 90% testicular
salvage rate. Early surgery may also decrease the incidence of
secondary autoimmune male infertility. Because of these two
factors, ultrasound is not commonly performed in the setting of
significant trauma as these patients often go straight to the
However, sonography plays a role in assessing the testicles in
patients with minor injury. It is crucial to remember that
associated neoplasms may be predisposed to rupture after minor
injury, with about 15% of patients with testicular tumors
presenting following trauma (figure 11). Be very wary about focal
hypoechoic intratesticular lesions after trauma, since although
these may simply represent intratesticular hematomas, the
possibility of a primary testicular tumor predisposed to rupture
should be considered. In the rare situation in which the patient is
not explored surgically, it is mandatory to sonographically follow
the intratesticular lesion to document the rapid interval change of
a true hematoma so that a malignancy is not missed.
Sonographic signs of testicular trauma include loss of the
bright margin of the tunica albuginea and intratesticular hematoma.
Although uncommonly seen, testicular enlargement without focal
lesion may represent trauma, and most urologists will explore if
gonadal enlargement is greater than a factor of three. A hematocele
(blood within layers of the tunica vaginalis) is a sensitive but
nonspecific sign of scrotal injury.
Testicular microlithiasis (TM) refers to the presence of
multiple small (1 to 3 mm), typically bilateral, nonshadowing,
hyperechoic foci representing calcified concretions within the
lumina of the seminiferous tubules. This entity occurs in
approximately 6:1000 sonograms and should be diagnosed only with 5
or more microliths in one sonographic image (figure 12). TM is
associated with germ cell neoplasm,
but the strength of this association with malignancy is quite
controversial. Two reports have estimated the relative risk for
cancer in association with TM as anywhere between 2
but difficulties in performing these studies make any numeric
estimate of risk problematic.
So what should be done for the patient with TM? The presence of
a focal testicular mass with TM is treated the same way a focal
testicular mass without TM is, eg, considered as malignant until
proven otherwise. What about TM and the absence of a focal mass?
The literature varies widely here, from stating "sonographic
surveillance of testicular microlithiasis cases for tumor is
to "question the need for routine U/S in this population."
Until further good scientific data becomes available, I recommend
6- to 12-month follow-up ultrasound examination
and patient education on self-examination.