Diagnostic Imaging Asia Pacific
March 2001

Ultrasound

Color Doppler enables scrotal diagnoses

By Malai Muttarak, M.D.

High-resolution ultrasound is widely used to evaluate patients with suspected scrotal abnormalities. Diagnostic accuracy is enhanced when color Doppler scans are performed. For patients presenting with the most common symptoms, scrotal mass and pain,1-3 ultrasound can determine whether the mass is intratesticular (often malignant) or extratesticular (usually benign).4

Testicular tumors represent the most common solid neoplasm in young men. Patients usually present with gradual, painless scrotal enlargement, but there may be sudden onset of pain due to hemorrhage or necrosis, mimicking testicular torsion or epididymo-orchitis.

Tumors are classified as primary germ cell, primary non-germ cell, or metastatic. About 95% of all primary tumors are malignant and arise from germ cells; seminomas are the most common germinal tumors. Nonseminomatous germ cell tumors (NSGCT) include embryonal cell carcinoma, teratoma, choriocarcinoma, and yolk sac tumor. NSGCT usually have a variety of histology cell types and are referred to as mixed. Seminoma, which is less aggressive, is radiosensitive, whereas nonseminomatous tumors are not.

Seminomas are usually seen on ultrasound as a homogeneous hypoechoic mass (Figure 1), while NSGCT tend to be more complex (Figure 2A).1,4-8 There is great overlap in their appearance, however, making it difficult to differentiate the histologic types of tumors by ultrasound alone.

The two most common non-germ cell tumors, which are frequently benign, are Leydig cell and Sertoli cell tumors.4,5

In color Doppler evaluation of testicular neoplasm, most lesions larger than 1.6 cm in diameter tend to be hypervascular (Figure 2B). Smaller lesions are more often hypovascular in comparison with normal testicular parenchyma. The role of color Doppler in evaluating testicular neoplasm is limited, however. The combination of clinical history, physical examination, and gray-scale ultrasound is needed to make a correct diagnosis.9

Metastases in the testis often originate with renal and prostatic carcinomas. Cancers of the lung, thyroid, and pancreas and melanoma may also metastasize to the testis, but this is rare.4,5 Metastatic deposits are usually seen as focal hypoechoic masses, indistinguishable from the primary testicular tumor. The testis can be involved in lymphoma and leukemia, as well. Malignant lymphoma represents the most common testicular malignancy in men over 60, whereas leukemia of the testis is most often seen in childhood.10-12 Because a blood-gonadal barrier makes chemotherapy ineffective, the testis acts as a sanctuary for leukemia and lymphoma. Consequently, tumors can be present in patients undergoing clinical remission.

Precise detection of lymphoma and leukemia is essential for local radiotherapy to achieve gonadal remission. These tumors can be unilateral or bilateral, appearing as circumscribed hypoechoic masses or areas of diffuse hypoechogenicity on ultrasound. Color Doppler shows increased perfusion within all areas of leukemia or lymphomatous involvement compared to the normal testicular parenchyma.11

Scrotal ultrasound can identify occult testicular tumors in patients who present with metastatic testicular neoplasms but show no symptoms on scrotal examination.13,14 Patients presenting with extragonadal germ cell tumors can also benefit from imaging. Ultrasound cannot, however, differentiate focal intratesticular masses from hematoma, orchitis, abscess, and infarction. Diffuse infiltrative tumors are difficult to differentiate from diffuse orchitis or infarction, as well. The presence of epididymal enlargement and scrotal skin thickening, suggestive of non-neoplastic lesions, may assist in the diagnosis.4,15

Ultrasound plays an important role in diagnosing extratesticular masses. Hydrocele refers to a congenital or acquired fluid collection between the parietal and visceral layers of the tunica vaginalis lining the scrotum. Acquired hydrocele is often idiopathic but can form secondary to intrascrotal inflammation, trauma, and, on rare occasions, tumor. Hydrocele may be unilateral or bilateral and can vary in size. It appears as an anechoic collection surrounding the testis on ultrasound; scattered echoes due to cholesterol crystals or floating calculi may also be seen (Figure 3). Septations and loculations are sometimes found in cases associated with inflammation.16

Epididymal cysts are frequently found in the epididymis, most often in the head. Ultrasound reveals characteristic well-defined anechoic lesions with smooth walls and acoustic enhancement (Figure 4). Spermatoceles are cysts containing spermatic elements that commonly occur in the epididymal head.16 Hyperechoic foci of spermatozoa or debris may be seen in spermatoceles.

Inguinal hernia may occasionally present as a scrotal mass, owing to patent processus vaginalis. Ultrasound can help identify the intestine or omentum within the inguinal canal and extension into the scrotum.16,17

Diagnostic Challenges

Acute scrotal pain remains a difficult diagnostic challenge. While epididymo-orchitis and testicular torsion are by far the most common causes, trauma, tumor, and incarcerated hernia can also result in acutely painful scrotum. The clinical symptoms and physical characteristics of these conditions are frequently indistinguishable. Gray-scale and color Doppler ultrasound provide an accurate, rapid, noninvasive method of diagnosis, leading to proper management.1-5

The most common cause of acute scrotal pain in adults is inflammatory disease. Inflammation may occur in the epididymis alone (most commonly), the testis, the skin of the tunica albuginea, or a combination of the three.1 The disease is usually caused by retrograde spread of infection from the bladder or prostate via the urethra to the vas deferens.5 Orchitis without involvement of the epididymis is rare but may occur as a complication of mumps.3

Epididymitis and epididymo-orchitis are identified on ultrasound by an enlarged, hypoechoic epididymis and/ or testis. Variable degrees of hydrocele and scrotal wall thickening can also be observed. With severe hemorrhagic congestion, there may be foci of hyperechogenicity. Advanced or untreated cases of inflammation can lead to epididymal or testicular abscess formation, which appears as a focal area of complex echogenicity or as an echo-poor mass.3-5 Focal orchitis or testicular abscess can mimic tumors. Associated scrotal wall thickening and epididymal involvement are suggestive of a benign inflammatory process.15

Gray-scale ultrasound findings of epididymo-orchitis overlap with those of testicular torsion. Color Doppler can assist in providing a differential diagnosis. While the normal epididymis and testis have low blood flow, both the size and number of vessels detected increase in epididymo-orchitis (Figure 5). Flow from the epididymis and testis should be compared with that on the contralateral side. Testicular ischemia may occur secondary to compression of testicular vessels by marked epididymal and spermatic cord swelling.18 Color Doppler ultrasound can help detect this severe complication and indicate whether surgical intervention is necessary.

Testicular torsion, also known as spermatic cord torsion, results from an abnormal twist to the spermatic cord.19 Although relatively uncommon in comparison with epididymitis, epididymo-orchitis, and testicular neoplasm, this condition requires rapid diagnosis to salvage a viable testis by means of prompt surgery. Testicular torsion can occur at any age but is most common in neonates and adolescents. The gubernaculum is not attached to the scrotal wall in neonates, so the testis is more susceptible to torsion (extravaginal torsion).19 The "bell-and-clapper" deformity, an abnormal reflection of the processus vaginalis resulting in a narrowed testicular bare area, also increases the chance of torsion. Because fixation of the testis to the posterior scrotal wall is incomplete, due to the reduced bare area, the testis falls forward and rotates within the tunica vaginalis (intravaginal torsion). This occurs more commonly than extravaginal torsion. Because the lesion is usually bilateral, surgical treatment of unilateral testicular torsion calls for contralateral orchiopexy.

The clinical onset of testicular torsion may occur during sleep, following trauma, or spontaneously. Immediate and intense pain is usually followed by swelling of the ipsilateral scrotum. Acute torsion occurs when patients present within 24 hours of symptomatic onset. Subacute or missed torsion refers to presentation from one to 10 days after the initial attack; if symptoms persist for a longer period, patients are diagnosed with chronic torsion. Testicular salvage depends on the degree and duration of torsion. The salvage rate of the testis is 80% to 100% if surgery is performed within five hours after onset of pain.5

The gray-scale ultrasound features of testicular torsion depend on its duration. In the acute phase, ultrasound shows an enlarged testis with diffuse hypoechoes. An enlarged hypoechoic epididymis, reactive hydrocele, and scrotal wall thickening are also observed. If torsion persists and infarction is established, necrosis and hemorrhage produce areas of heterogeneity. Although these ultrasound findings cannot differentiate testicular torsion from acute epididymo-orchitis, color Doppler reveals the difference; flow within the affected testis is reduced or absent compared with the contralateral asymptomatic testis.

In color Doppler ultrasound examination, blood flow in both symptomatic and asymptomatic testes should be compared to ensure that the equipment can detect normal testicular blood flow.18-20 A testis with incomplete torsion may retain some flow, but the peak systolic velocities will still be lower than normal.20 In cases of missed torsion where there is hyperemia of the scrotal covering via flow through the dartos, color Doppler ultrasound demonstrates increased flow in the peritesticular tissues and lack of intratesticular flow (Figure 6).19,20

Ultrasound is the imaging modality of choice for evaluating patients with blunt scrotal trauma. Lacerated or fragmented testes require surgery, while small hematoceles are generally treated conservatively. Untreated testicular injury produces a variety of complications, including testicular atrophy, secondary infection, and prolonged patient discomfort.3,18

Irregular or indistinct tunica albuginea indicates testicular rupture. Ultrasound features of intratesticular hematoma vary with time. Acute hematoma is heterogeneous, often with increased echogenicity. As resolution occurs, the lesions become hypo- to anechoic and may contain septations. The history of recent trauma will differentiate a hematoma from a tumor. Follow-up ultrasound should still be performed, however, because 10% to 15% of patients with testicular tumors seek medical attention only after scrotal trauma.

The appearance of a hematoma changes rapidly with time, whereas tumors remain unchanged for several weeks. When a concomitant hematocele is present, as is often the case, determination of testicular fracture can be difficult. High-frequency 7.5-MHz transducers sometimes limit depth penetration of the entire scrotum. Low-frequency 3.5 to 5-MHz transducers should be used instead to identify the testis for patients with large hematocele.18-20 Hematocele is viewed as a complex fluid collection, containing numerous echoes (Figure 7). It becomes less echogenic over time and frequently contains septations.4,16,21

Prof. Muttarak is a professor of radiology at Chiang Mai University, Chiang Mai, Thailand.

References

  1. Entwisle KG, Ayers AB. Imaging of the scrotum and testes. Imaging 1992;4:107-116.
  2. Hendrikx AJM, Dang CL, Vroegindeweij D, Korte JH. B-mode and colour-flow duplex ultrasonography: a useful adjunct in diagnosis scrotal diseases? Br J Urol 1997;79:58-65.
  3. Muttarak M. Anatomy and diseases of the scrotum. J Hong Kong Coll Radiologists 2000;3(1):83-93.
  4. Krone KD, Carroll BA. Scrotal ultrasound. Radiol Clin N Am 1985;23:121-139.
  5. Feld R, Middleton WD. Recent advances in sonography of the testis and scrotum. Radiol Clin N Am 1992;30:1033-1051.
  6. Nachtsheim DA, Scheible FW, Gosink B. Ultrasonography of testis tumors. J Urol 1983;129:978-981.
  7. Hamm B. Differential diagnosis of scrotal masses by ultrasound. Eur Radiol 1997;7:668-679.
  8. Fowler RC, Chennells PM, Ewing R. Scrotal ultrasonography: a clinical evaluation. Br J Radiol 1987;60:649-654.
  9. Horstman WG, Melson GL, Middleton WD, Andriole GL. Testicular tumors: findings with color Doppler US. Radiology 1992;185:733-737.
  10. Ferry JR, Harris NL, Young RH, et al. Malignant lymphoma of the testis, epididymis, and spermatic cord. Am J Surg Path 1994;18:376-390.
  11. Mazzu D, Jeffrey RB, Ralls PW. Lymphoma and leukemia involving the testicles: findings on gray-scale and color Doppler sonography. AJR 1995;164:645-647.
  12. Eskey CJ, Whitman GJ, Chew FS. Malignant lymphoma of the testis. AJR 1997;169:822.
  13. Glazer HS, Lee JKT, Melson GL, McClennan BL. Sonographic detection of occult testicular neoplasms. AJR 1982;138:673-675.
  14. Grantham JG, Charboneau JW, Jame EM, et al. Testicular neoplasms: 29 tumours studied by high resolution ultrasound. Radiology 1985;157:775-780.
  15. Subramanyam BR, Horii SC, Hilton S. Diffuse testicular disease: sonographic features and significance. AJR 1985;145:1221-1224.
  16. Black JAR, Patel A. Sonography of the abnormal extratesticular space. AJR 1996;167:507-511.
  17. Subramanyam BR, Balthazar EJ, Raghavendra BN, et al. Sonographic diagnosis of scrotal hernia. AJR 1982;139:535-538.
  18. Berman JM, Beidle TR, Kunberger LE, Letourneau JG. Sonographic evaluation of acute intrascrotal pathology. AJR 1996;166:857-861.
  19. Sidhu PS. Clinical and imaging features of testicular torsion: role of ultrasound. Clin Radiol 1999;54:343-352.
  20. Stavros T, Rapp C, McGrath J. Color duplex sonography of acute scrotal pain. In: Bluth EI, Arger PH, Benson CB, et al, eds. Ultrasound: a practical approach to clinical problems. New York: Thieme, 2000:135-152.
  21. Hricak H, Jeffrey RB. Sonography of acute scrotal abnormalities. Radiol Clin N Am 1983;21:595-603.

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