The choice of the frequency used is determined by a balance between depth of penetration required and the detail of the image required. As the frequency increases the image resolution (axial resolution) improves and the depth of penetration decreases. Broad bandwidth transducers allow for multiple focal zones, eliminating the need for adjustment during the examination. Multiple frequency transducers allow the transducer to be set to several distinct frequencies. A high frequency (7.5–18 MHz) array transducer is most often used for scrotal scanning. A linear array probe with a “footprint” able to measure the longitudinal length of testis is ideal. A curved array probe can be used with a thickened scrotal wall or in the presence of scrotal edema or for a large testis. The curved array transducer is also useful to compare echogenicity of the testes, however, the frequency is usually lower with a curved array probe, resulting in decreased axial resolution. Color and spectral Doppler are essential elements of scrotal ultrasound because they provide documentation of testicular blood flow and paratesticular findings. The highest possible frequency, normally in the 7.5–18 MHz range, providing the best axial resolution and blood flow detection, should be used [1].

In the longitudinal view, the standard orientation of the image should be with the superior pole of the testis to the left and the inferior pole to the right on the monitor screen (Fig. 5). In the transverse plane, the standard orientation is for the patient’s right testis to be on the right side of the screen. Therefore, for the right testis, the lateral aspect is located on the left side of the screen and the medial aspect to the right. Conversely, for the left testis, the lateral aspect should be to the right and the medial aspect to the left (Fig. 6).

The evaluation of the scrotal contents should begin with a longitudinal survey scan, progressing medial to lateral to get an overall impression of the testis and paratesticular structures . If the testis is larger than the footprint of the transducer, it is important to document views of the superior and inferior portions of the testis including the epididymis in these regions. The transverse view is obtained by rotating the transducer to 90°. A survey scan is performed using the mid-testis as a starting point and proceeding first towards the superior pole then back to the to mid-testis before scanning to the inferior pole.

At least one image should visualize both testes to document the presence of two testes and their relative echogenicity (Fig. 7). Measurements of the testicular width and height are taken and documented at the mid-testis. A measurement should also be made of the long axis at the mid-testis and a testicular volume is calculated (Fig. 8). If the equipment being used has split-screen capabilities, comparative views of echogenicity can easily be made and documented.

All relevant extratesticular structures should be evaluated, including but not limited to the epididymis , spermatic cord, and scrotal skin. Techniques that improve visualization, such as Valsalva maneuver or upright positioning, may be used as needed.

Color and spectral Doppler should be considered an integral part of the scrotal US examination. Many inflammatory, neoplastic, and benign conditions have characteristic flow patterns that can assist in diagnosis. At least one side-by-side image containing both testes with identical Doppler settings should be included to evaluate symmetry of flow. If blood flow cannot be visualized on color Doppler (Fig. 9a), power Doppler may increase the sensitivity to detect blood flow (Fig. 9b) [1].

The written report and archived images are a reflection of the quality of the examination. The old adage “If it’s not documented, it wasn’t done” should guide the sonographer in developing a quality report. The static images obtained during the evolving ultrasound examination should represent the sonographer’s impression of the findings. If electronic storage space is available and the equipment allows, video clips, which demonstrate important findings and survey scans, can and should be obtained. A quality report can aid in diagnosis, and is therefore in the best interest of our patients.

All the measurements and anatomical findings of the examination should be documented. Images should be attached to the report. It is essential to include patient identification information, the examination date, and the indications for performing the examination. The transducer used and its frequency should also be documented. The area of interest should be clearly identified. The orientation and measurements should be labeled along with the pertinent anatomy and any abnormalities. There is no minimum number of images that are required for proper documentation. It is a best practice to provide images that depict the measurements being taken and the pathology being described. The physician who performed the examination should sign the report.

There are many specific indications for scrotal ultrasound (Table 1). Scrotal ultrasound is often performed when the physical examination is inconclusive or difficult to complete (or both) because of patient discomfort or inability of the examiner to precisely identify the scrotal structures on palpation. In these instances the scrotal ultrasound examination is therefore an integral part of the physical examination of the male genitalia. In other situations ultrasound evaluation is essential to diagnosis and treatment and is well supported in the literature. However, the decision on whether or not to obtain an ultrasound study is discretionary and without a clearly defined evidence based approach. “Appropriateness” criteria are necessary and high level evidence base studies are required in order to determine appropriateness. Part of the work of urologic imaging research in the future should look to assess the limitations of the current literature and then create an evidence base that will define the value of the imaging services critical to the practice of urology [2, 3].

The normal scrotal wall thickness varies between 2 and 8 mm. The scrotal wall contains the following structures: rugated skin, superficial fascia, dartos muscle, external spermatic fascia, cremasteric fascia and internal spermatic fascia . The scrotum is separated into right and left hemiscrotal compartments by a septum termed the median raphe. As the testis descends in utereo from the abdomen, it acquires each layer of the scrotal compartment. The external spermatic fascia is derived from the external oblique fascia and is attached to the external inguinal ring. The cremasteric fascia and muscle derive from the internal oblique muscle. Encasing each testis is the tunica vaginalis, derived from the peritoneum, which consists of parietal and visceral layers. These layers are normally separated by 2–3 ml of straw colored fluid often referred to as a physiologic hydrocele. Ultrasound of this fluid is seen as a thin echo free rim around the head of the epididymis [4] (Fig. 10). The parietal and visceral layers join at the posterolateral aspect of the testes where the tunica attaches to the scrotal wall [5] .

The testes descend into the scrotum at approximately the 28th week of gestational age through the inguinal canal along with the processus vaginalis. The processus vaginalis gradually closes through infancy and early childhood. The size and shape of the testis changes with the age, influenced by gonadotropic hormones testicular volume gradually rises from birth to up to 5 months of age due to peak in gonadotropic hormones levels [6, 7]. After 5 months of age, the testicular volume steadily declines and reaches its minimum volume at approximately 9 months of age and remains approximately the same size until puberty [8]. In newborns, the testis is round and gradually becomes ovoid with growth. The echogenicity of the testis increases in puberty due to the development of germ cell elements [9] .

The adult testis is a smooth ovoid gland, approximately 4–5 cm long, 3 cm wide, 2–3 cm in the anterior-posterior (AP) dimension, and typically between 20 and 30 ml in volume. The testis exhibits medium homogenous echogenicity. A dense fibrous capsule the tunica albuginea envelops the testis, which is apparent as a thin echogenic line on ultrasound. Each testis has approximately 200–300 cone shaped lobules each containing at least one seminiferous tubule [10] (Fig. 11). The lobules are separated by the fibrous septa of tunica albuginea that extend from the mediastinum of the testis in to the parenchyma of the testis [11]. Testicular lobules are occasionally identified on ultrasound as lines radiating from the mediastinum testis (Fig. 12). The seminiferous tubules contained within the lobules open into dilated spaces called rete testis within the mediastinum. The seminiferous tubules are long V-shaped tubules, both ends of which usually terminate in the rete testis. The rete testis is connected to the head (caput or globus major) of the epididymis with about 8–12 efferent ductules. The normal rete testis is sonographically evident in 18 % of patients as a hypoechoic area with a striated configuration adjacent to the mediastinum testes [12] . The mediastinum testes appears as a linear avascular echogenic band on ultrasonography [13] (Fig. 13).

The adult epididymis is 6–7 cm long and has three parts, the head (caput) measuring 10–12 mm in diameter, the body (corpus) measuring 2–4 mm in diameter, and the tail (cauda) about 2–5 mm in diameter. In the normal epididymis, the head is routinely identified at posterolateral to the upper pole of the testis. The caput epididymis is triangular in shape, often has the same echogenicity as the testis (Fig. 14). However, it can be heterogenous with areas that are hyper- or hypoechogenic. The smaller corpus epididymis can be seen as a hypoechoic structure containing multiple echogenic linear structures representing the coiled epididymal tubule, and lies posteriorly along the long axis of the testis (Fig. 15).

The testicular appendages are the remnants of the mesonephric and paramesonephric ducts. There are four testicular appendages: the appendix testis, the appendix epididymis, the vas aberrans, and the paradidymis [14] (Fig. 16). The appendix testis and the appendix epididymis are commonly seen on scrotal ultrasound [15]. The appendix testis (hydatid of Morgagni) is a small ovoid structure usually at the upper pole of the testis in the groove between the testis and the epididymis, better seen in the presence of fluid around the testis. The appendix testis is the vestigial remnant of the paramesonephric (Mullerian) duct (Fig. 17). The appendix epididymis originates from the mesonephric (Wolffian) duct and is seen associated with the epididymal head on ultrasound images (Fig. 18) .

The spermatic cord is normally seen superior to the posteromedial aspect of the testis and contains the vas deferens, the testicular and cremasteric and deferential arteries, the pampiniform plexus of veins, genital branch of the genital femoral nerve, testicular plexus of the sympathetic trunk, and lymphatic vessels [11]. The blood supply to the scrotal structures is from three primary arteries: the testicular, deferential, and cremasteric arteries (Fig. 19). The testicular artery testis or gonadal artery, which arises from the aorta and courses through the scrotum with the spermatic cord, is the major supply to the testis. The deferential artery, which arises from the superior vesical artery and supplies the vas deferens and epididymis . The cremasteric artery, a branch of the inferior epigastric artery, which supplies the scrotal skin and coverings of the spermatic cord. As the testicular artery approaches the posterolateral aspect of the testis it divides. The branches pierce through the tunica albuginea to run in a layer called the tunica vasculosa. Capsular arteries run peripherally in the tunica vasculosa, supplying centripetal arteries that course towards the mediastinum and divide further to recurrent rami that flow away from the mediastinum [13]. The veins draining the testis and epididymis converge to form the pampiniform plexus at the mediastinum on the superior pole of the testis. The pampiniform plexus is primarily drained by the testicular and external pudendal veins [16]. The testicular vein on the left drains into the renal vein and the testicular vein on the right directly into the inferior vena cava [17].

Ultrasongraphy with Color-Flow imaging provides visualization of the intratesticular, epididymal, and paratesicular blood flow. Under normal conditions, Color Flow images show equivalent vascularity of the bilateral testis. When vascularity is not well visualized, Power Doppler increases the sensitivity of detection. Spectral Doppler is used to calculate the Resistive Index (RI) of intratesticular arteries. The RI of intratesticular arteries has been found to correlate with testicular function, namely spermatogenesis .