Duplex Ultrasound Evaluation of the Male Genitalia

Anatomy and normal sonographic features

The anatomy of the scrotum, testicles, and epididymis is illustrated in Figs. 30.1 and 30.2 . As seen with ultrasound, each testicle is homogeneous and medium in echogenicity ( Fig. 30.3 ), with a smooth outer border encapsulated by the thin layer of tunica albuginea. In adults, each testicle measures 3 to 5 cm in long axis and 2 to 3 cm in short axis. The testicles are relatively hypoechoic before the age of puberty and achieve adult echogenicity thereafter. The mediastinum testis is visible as an echogenic band running along one side of the testicle. The epididymis is similar to or slightly less echogenic than the testicle. Its echotexture may be heterogeneous.

The arterial and venous anatomy of the testicles is illustrated in Figs. 30.4 and 30.5 . In postpubertal boys and adults, blood vessels are normally visible within and at the periphery of the testicle with color Doppler ( Fig. 30.6 ). The capsular arteries, which course around the periphery, give rise to the centripetal arteries, which penetrate the parenchyma. Thus blood flow in the centripetal arteries is from the capsule inward. Testicular veins follow the same pattern as the arteries and are generally readily visualized and can be differentiated from the arteries with spectral Doppler. In some normal individuals, one or more large artery/vein pair(s) may traverse the testicle obliquely from the mediastinum. These transmediastinal vessels may be visible on gray-scale imaging and should not be mistaken for pathology.

Arterial flow to the testicle and epididymis characteristically exhibits a low-resistance pattern on spectral Doppler, including continuous flow during diastole ( Fig. 30.7 ). In contrast, a high-resistance blood flow pattern is seen in extragonadal arteries, which are part of the cremasteric system. These arteries are occasionally visualized along the course of the spermatic cord. It is important not to mistake extragonadal Doppler flow signals for testicular flow. Peak systolic velocity in testicular arteries ranges from 4 to 19 cm/s (mean 9.7 cm/s), and end-diastolic velocity ranges from 1.6 to 6.9 cm/s (mean 3.6 cm/s). These values permit quantitative assessment of arterial flow when a sufficiently long arterial segment is visualized with color Doppler imaging, allowing for angle correction of the Doppler signal. When angle correction is not possible, spectral Doppler features are evaluated qualitatively.

Sonographic technique

A linear-array transducer with a frequency output of 10 MHz or higher is generally used for examining the testicles. A lower frequency setting may be needed if the scrotum is severely swollen. A towel is draped over the penis for the sake of modesty. The penis is then placed over the lower abdomen to keep it out of the examination field. For best results, another towel is placed between the patient's legs to prop up and support the scrotum.

The first step in scanning the scrotal contents is to get oriented. Long- and short-axis images of each testicle and epididymis are taken. The testicles are measured in their long and short axes. A composite transverse view showing both testicles simultaneously is obtained so that testicular echogenicity can be compared. If both testicles cannot be viewed simultaneously on a transverse view, separate images should be recorded side by side, using identical ultrasound settings. Any pathologic finding should be imaged in whatever plane best documents the abnormality, but additional long- and short-axis views should also be obtained to aid orientation.

Blood flow signals can be evaluated with either color Doppler or power Doppler imaging. In either case, the pulse repetition frequency (color velocity scale) must be set to a low setting to detect very low velocity blood flow signals and the wall filter must also be at a low setting. A relatively high color Doppler gain setting is typically needed, as the testicular vessels are quite small and produce weak Doppler signals. One method to improve the visualization of blood flow signals is to increase the color Doppler gain until artifacts appear in the image and then decrease the gain slightly. It is important to maximize the size of the Doppler waveform display by using an appropriate spectral display scale because this facilitates the assessment of arterial pulsatility patterns, the measurement of blood flow velocities and velocity ratios, and the comparison of testicular blood flow from one side to the other.

Scrotal masses

Masses and mass-like lesions within the scrotum include cysts, tumors, hematomas, inflammation, infection, abscesses, contusions, and focal infarction. The location of the pathology, the gray-scale appearance, and the Doppler blood flow features will, in many cases, help narrow down the diagnostic possibilities.

Testicular cysts

Testicular cysts are idiopathic and benign. They are fairly common, seen with increasing frequency with increasing age and are present in approximately 8% of adults at sonography. Most intratesticular cysts are located near the mediastinum testicle and are not palpable. They are typically small, measuring less than 1 cm in diameter, and are thought to arise from the rete testis, the convergence of intratesticular tubules at the mediastinum. These cysts may be single or multiple. Sometimes, in the presence or absence of discrete cysts, a region of dilated tubules is seen in the vicinity of the mediastinum, representing a dilated rete testis. Cysts located on the testicular surface are almost always tunical cysts, arising in the tunica albuginea, the fibrous layer that encapsulates the testicle. Tunical cysts may be palpable, prompting ultrasound investigation.

The most important point about testicular cysts and a dilated rete testis is distinguishing these benign lesions from other pathologies, including tumors and abscesses. Testicular cysts ( Fig. 30.8 ) have the following sonographic features: (1) anechoic contents, (2) sharply defined borders and an invisible wall, (3) enhanced through-transmission of ultrasound, and (4) no blood flow within or surrounding the cyst (other than normal testicular vessels). Cysts meeting these criteria are benign and inconsequential and require no follow-up. A dilated rete testis appears as small serpiginous tubular structures clustered in the mediastinum ( Fig. 30.9 ).

Testicular neoplasms

Testicular neoplasms are most often primary testicular tumors of germ cell origin ( Table 30.1 ). These neoplasms occur most frequently between the ages of 25 and 35 years and are almost always malignant. The prognosis is generally excellent with an overall 5-year survival of 95%, assuming timely treatment with surgery, radiation therapy, and/or chemotherapy. Less common testicular neoplasms arise from the stromal parenchyma and are either Sertoli or Leydig cell tumors. Rarely, nontesticular malignancies involve the testicle, including leukemia, lymphoma, and metastatic disease. Testicular tumors usually present in one of two ways: as an asymptomatic palpable mass or with sudden onset of pain and swelling caused by hemorrhage. It is not uncommon for the latter presentation to follow minor trauma. Tumors may also present with symptoms of epididymitis. A small number of patients can present with signs and symptoms caused by metastatic testicular cancer, for example back pain from retroperitoneal disease.

TABLE 30.1

Classification of Testicular Malignant Neoplasms.

Testicular Malignancies of Germ Cell Origin (95%)

Seminoma Embryonal cell carcinoma Teratocarcinoma Choriocarcinoma Mixed germ cell carcinoma

Other Primary Testicular Malignancies

Sertoli cell carcinoma Leydig cell carcinoma

Metastases

Leukemia Lymphoma Genitourinary primaries Other primaries (e.g., lung)

Ultrasound can distinguish intratesticular from extratesticular pathology with extremely high accuracy. Nevertheless, ultrasound generally cannot differentiate between different histologic types of testicular tumors, nor can it generally differentiate between malignant (common) and benign (uncommon) neoplasms. Most testicular tumors are well-defined hypoechoic intratesticular masses, but some may be poorly marginated or grossly infiltrating. ^a

a References .

They may exhibit some degree of internal heterogeneity because of hemorrhage and/or necrosis, and calcifications are occasionally present. Vascularity is evident within testicular neoplasms on the color Doppler flow examination, helping to distinguish tumors from cysts, hematomas, and abscesses, which do not have internal vascularity. Testicular tumor vascularity ( Fig. 30.10 ) is variable; however, most malignant tumors are hypervascular compared with the surrounding normal testicular parenchyma. ^b

b References .

The distribution of tumor blood vessels is variable, with some lesions showing an orderly distribution of blood vessels and others, a chaotic distribution. Large avascular areas may be present in a testicular tumor when necrosis or hemorrhage is present. Spectral Doppler generally shows low-resistance blood flow within tumor vessels, a typical finding seen in malignant neoplasms regardless of location. Blood flow velocities may be substantially elevated in markedly hypervascular tumors. In general, the larger the testicular tumor, the more hypervascular it will be.

Testicular microlithiasis, scattered small calcifications in the testicular parenchyma as shown in Fig. 30.10A , is associated with an eightfold increased risk of testicular cancer, but the level of risk and follow-up requirements remain controversial. Recent publications recommend urologic referral in patients with concomitant risk factors for testicular cancer. In patients without other risk factors for cancer, monthly self-examination for masses is suggested.