- US accurately diagnoses a range of scrotal pathology from acute conditions requiring emergent surgery, such as torsion and testicular rupture, to more chronic conditions, including benign and malignant palpable lesions. Furthermore, due to its widespread availability, high resolution, lack of ionizing radiation, and Doppler capabilities, US is the 1st-line imaging modality for scrotal symptoms.
Ultrasound Technique for Scrotal Evaluation
- Proper US technique is crucial for a good-quality study. The patient should be positioned supine with a towel between their legs such that the scrotum is elevated upon the towel and does not fall between the legs. The penis is positioned along the abdominal wall and covered with a towel so that it is out of the way and only the scrotum is exposed. High-frequency linear transducers should always be used to achieve maximal resolution. The testes are imaged in grayscale with multiple images obtained in longitudinal and transverse (to the testis) planes. The epididymes are imaged documenting the head, body, and tail.
- Pampiniform plexus and other paratesticular structures should be included as necessary. Depending on symptoms, the spermatic cord should be evaluated fully to the internal inguinal ring, for presence of a hernia. Hernia evaluation should always include Valsalva and standing views, as this maximizes sensitivity.
- Color Doppler should always be used with multiple images of the testis, epididymis, and any focal abnormality or palpable complaint. Spectral Doppler may be used in the setting of acute pain and concern for torsion, though color Doppler is the mainstay of evaluation.
- Grayscale and color Doppler of the testis should be compared to the contralateral side. While this can be done in split-screen mode, it is best done in the transverse plane showing both testes at the same time in 1 image. This is called the "buddy shot" and ensures that the same settings are used such that an accurate comparison can be made.
- Occasionally the scrotum is enlarged due to scrotal edema, large hydrocele, hernias, or other pathology, and linear transducers do not suffice. In these cases, a curved transducer should be used to maximize penetration and visualization.
- Any palpable complaint should be documented by asking the patient to show exactly where the abnormality is and imaging carefully in that area. This allows for confident reporting and reassurance for the patient as these abnormalities are often benign.
- Contrast-enhanced US (CEUS) has recently become available in the USA and is being used more frequently across many pathologies. CEUS can be helpful in equivocal cases of torsion or mass, as it is very sensitive to tissue perfusion.
Imaging of Acute Scrotum
- Several conditions can present with acute pain, and accurate diagnosis is critical because treatment widely varies based on pathology. Testicular torsion, if not promptly diagnosed, can lead to testicular loss. Absent color Doppler flow is the best diagnostic clue, as generally within the first 6 hours the grayscale appearance will be normal. Asymmetrically decreased flow on the side of pain should also raise concern for torsion, and identification of a "torsion knot" or corroboration with absent venous flow on pulse wave Doppler can help increase diagnostic confidence.
- Epididymitis is a common diagnosis in the setting of acute pain. Generally the epididymis is enlarged, hyperechoic, and highly vascular on color Doppler. Orchitis may also be seen with increased vascularity of the testis on the side of pain. Complications may coexist, including complex hydrocele/pyocele, testicular or epididymal abscess, and segmental infarction of testis. It is important to remember that epididymitis is an ascending infection from the urinary tract and begins in the epididymal tail. Therefore, a focal, vascular, heterogeneous, mass-like area in the epididymal tail is most often epididymitis.
- US may be the 1st-line imaging performed for Fournier gangrene, and, therefore, it is important to obtain thorough views of extratesticular structures, including the skin and areas of pain or erythema. While US is sensitive for the detection of soft tissue gas, accurate interpretation requires a high degree of suspicion.
- In the setting of scrotal trauma, US is highly accurate in diagnosing testicular injury. Testis fracture and rupture are seen as areas of disruption of the tunica and extrusion of tubules. This is a surgical emergency, as testicular function is at risk. Hematoceles without testis injury may undergo conservative or surgical management. Rarely, trauma can induce testicular torsion.
Imaging of Palpable and Nonacute Complaints
- One of the most common indications for scrotal US is evaluation of a palpable lesion or vague complaints. The majority of palpable abnormalities are benign lesions. These commonly include epididymal cyst, spermatocele, varicocele, hydrocele, hernia, scrotal pearl, tunica cyst, sperm granuloma, and other benign extratesticular masses. Many of these abnormalities are also seen commonly and incidentally in asymptomatic men. Therefore, it is important to document what the palpable abnormality corresponds to on the images and in the report, as this serves to reassure men who are anxious about having testicular cancer.
- Fortunately, the minority of palpable complaints are due to testicular cancer. US readily diagnoses germ cell tumors, which account for 95% of all testicular masses. Most masses are hypoechoic and show vascular flow, and, as such, any mass encountered in the testis should be considered to be highly suspicious for malignancy. Doppler helps distinguish solid malignant lesions from benign intratesticular lesions, such as an epidermoid cyst or abscess. While the majority of cases are clear, some equivocal cases can benefit from additional imaging with CEUS or scrotal MR. Exploratory surgery with intraoperative biopsy/frozen section is also utilized when imaging findings are equivocal.
- While there are many subtypes of germ cell tumors with various imaging descriptions, characterizing a mass is not necessary. Since most masses are malignant, the work-up includes tumor markers and proceeding straight to radical orchiectomy. Biopsy is rarely indicated. The exception to this rule is lymphoma, which typically presents in the 6th decade or later and may be multifocal or bilateral.
- Remember to always recommend scrotal US in a young to middle-aged man presenting with a retroperitoneal mass. Since these masses are often germ cell metastases to "landing zone" paraortic lymph nodes, the testicular mass can be readily identified and the patient can be placed on the correct treatment path without unnecessary work-up or delay.
- Sharbidre KG et al: Imaging of scrotal masses. Abdom Radiol (NY). 45(7):2087-108, 2020
- Rebik K et al: Scrotal ultrasound. Radiol Clin North Am. 57(3):635-48, 2019
- Sweet DE et al: Imaging of the acute scrotum: keys to a rapid diagnosis of acute scrotal disorders. Abdom Radiol (NY). 45(7):2063-81, 2020
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