Background and Indications for Examination
Bedside testicular sonography may assist with the diagnosis and treatment of any patient presenting with acute testicular pain. It can be performed within minutes of arrival and may save time in the diagnosis and treatment of testicular emergencies. It is noninvasive and emergency physicians have been shown to accurately diagnose patients with acute testicular pain using ultrasound.
Testicular torsion and rupture are true surgical emergencies and ultrasound is the diagnostic test of choice for both conditions. Ultrasound may also reveal less acute causes of testicular pain, such as torsion of a testicular appendage, epididymitis, orchitis, hydrocele, and varicocele. These conditions represent the vast majority of cases of nontraumatic testicular pain presenting to the acute care setting.
Probe Selection and Technical Considerations
The testes are superficial structures; therefore, probes with higher frequencies that provide better resolution are preferred.
Color-flow Doppler helps to detect the presence and direction of blood flow within the testes. By convention, the color is blue when blood is traveling away from the probe and red when it is flowing toward the probe. The color does not necessarily indicate arterial or venous flow, which must be determined by the character of the flow. The Doppler gain can be increased as needed in order to improve the sensitivity and to detect lower flow states. The pulse repetition frequency (PRF) or “scale” can also be lowered to increase Doppler sensitivity. The sonographer must keep in mind that decreasing the PRF or increasing the gain too much may create unwanted artifact that will erroneously appear as color flow across the testes and can result in a false-negative scan. In contrast, increasing the PRF or decreasing the gain too much (both of which lower sensitivity for flow) may miss blood flow that is actually present, resulting in a false-positive interpretation.
Power Doppler detects the presence of blood flow only without regard to direction. It appears as shades of red depending on the volume of flow. It is more sensitive and less angle-dependent than color-flow Doppler at picking up low-flow states, and therefore is useful for structures such as the testes. But, due to its increased sensitivity, it is also more prone to motion artifact. The sonographer must be careful not to interpret this color artifact as a false-negative study.
Pulse wave is a form of spectral Doppler that calculates flow velocity over time and produces a graphic waveform. Blood flow velocities are important to calculate for a particular sample volume. This graphic waveform typically shows a systolic and a diastolic peak (Fig. 13-1). With increasing resistance (due to torsion), the diastolic flow will decrease, ultimately reversing if the resistance is very high. The resistive index (RI) is defined by the following formula:
A transverse image demonstrating normal testicular blood flow. The top of the image shows the left testicle picking up normal color flow. Pulse-wave Doppler is being used to interrogate flow in the area bounded by the small double dashed lines within the box (the “gate”). The spectral image in the lower part of the screen shows velocity (on the y-axis) vs time (on the x-axis). PSV: peak systolic velocity, EDV: end diastolic velocity. The PSV and EDV in this image are approximately 5 and 2, respectively (corresponding to the numbers on the right side of the graph). This makes the calculated resistive index (RI) in this patient at about 0.6, which is considered normal.
A normal testicular RI is between 0.5 and 0.7. The RI will be lower in inflammatory conditions such as epididymitis or orchitis. The RI will be elevated in high-resistance states such as torsion. When there is no diastolic flow, the RI will be equal to 1, and may actually be greater than 1 if diastolic flow reverses.
Normal Ultrasound Anatomy
The adult testicles are ovoid shaped; approximately 5 × 3 × 2 cm and lie in a vertical position with a slight anterior tilt (Fig. 13-2). They have a homogenous, granular echogenic texture on ultrasound, similar to that of the liver. Immediately surrounding the testes is the thin, fibrous, hyperechoic tunica albuginea. The mediastinum testis is a band formed by the invagination of the tunica albuginea and can be seen on ultrasound as a longitudinal echogenic stripe within the testicle. In some patients, an embryologic remnant called the appendix testis can be visualized as a small extra-testicular nodule (2–7 mm) between the upper pole of the testicle and the head of the epididymis.
The tunica vaginalis is a remnant of the peritoneum that accompanies the testicles on their descent into the scrotum. It contains both visceral and parietal layers that envelop the entire testicle, except posteriorly, at the attachment of the epididymis. The “bell-clapper” deformity occurs when the tunica vaginalis completely surrounds the posterior testicle and epididymis, preventing its normal fixation and allowing for increased mobility within the scrotum. This is the main cause of torsion beyond the neonatal period.
The epididymis is 6–7 cm long and curves in a half-loop. Its head sits atop the superior-lateral aspect of the testicle and can be seen as a distinct structure of similar echogenicity. The body is 2–5 mm thick and runs caudally along the posterior testicle before coursing cranially to ultimately become the vas deferens. The epididymis may also contain an appendage, the appendix epididymis, and is seen attached to the head when visualized on ultrasound.
The spermatic cord contains the vas deferens, three arteries (testicular, cremasteric, and deferential), the pampiniform plexus of veins, nerves, and lymphatics. It is difficult to visualize on ultrasound, but an experienced sonographer may visualize the spermatic cord exiting the inguinal canal. The testicular artery supplies both testicles. The artery and all its branches have a low-resistance flow pattern with persistent diastolic flow.