Dr. Winter is a Professor of Radiology and Director of Ultrasound at the University of Wisconsin Medical Center, Madison, WI.

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 ¹ and delineates between testicular and extratesticular pathology with 95% to 100% accuracy. ^2,3 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.

Technique

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 ⁴ ). 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.

Anatomy

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. ⁵ An exception is prepubertal males, in whom absence of end diastolic flow is often a normal finding. ⁶ Symmetry is expected from side to side.

Torsion

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. ^7,8 (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. ⁹ 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 surgically.

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 gray-scale appearance. ¹⁰ 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.

Epididymo-orchitis

In general, increased testicular and epididymal blood flow implies epididymitis and orchitis. Ultrasound is highly accurate in making the diagnosis. ¹¹ 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. ¹² 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. ¹³ 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.

Testicular masses

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. ¹⁴ 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. ¹⁵ It has been suggested that males should perform scrotal self-examinations every month. ^9,14 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 ⁹ ).

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 ¹⁶ or Dambro et al. ¹⁷

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. ¹⁸

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 testicle.

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. ¹⁹ Besides tumor, the differential for a mass includes infection, hematoma, infarct/ vasculitis, ²⁰ and post-biopsy. ²¹ 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. ²² 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. ^17,23-25 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. ^26-32 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. ³³ 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." ³³ 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. ³⁴ Rigorous follow-up is recommended in this group.

Varicocele

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). ⁹ 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. ⁹ Color Doppler can be used to follow treatment.

Scrotal trauma

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 operating room.

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

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, ³⁵ 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 ³⁶ and 20, ³⁷ 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 mandatory" ³⁷ to "question the need for routine U/S in this population." ³⁸ Until further good scientific data becomes available, I recommend 6- to 12-month follow-up ultrasound examination ^38,39 and patient education on self-examination. AR