Ultrasonography of the scrotum

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Authors: Mikael Häggström; Authors of integrated Creative Commons article[1] [notes 1]

Sonography of a normal testis. The normal testis presents as a structure having homogeneous, medium level, granular echotexture. The mediastinum testis appears as the hyperechoic region located at the periphery of the testis as seen in this figure.[1]

Scrotal (or transscrotal) ultrasound is used in the evaluation of testicular pain, and can help identify solid masses.[2]

Planning

How soon

  • Signs of testicular torsion: Emergency
  • Other pain, or high suspicion of testicular cancer in a young patient: Within 1 week
  • Enlargement, suepected hydro-, varico- or spermatocele, palpable induration, control after infection: 2 weeks to 2 months[notes 2]

Imaging technique

For any scrotal examination, thorough palpation of the scrotal contents and history taking should precede the sonographic examination. Patients are usually examined in the supine position with a towel draped over his thighs to support the scrotum. Warm gel should always be used because cold gel can elicit a cremasteric response resulting in thickening of the scrotal wall; hence a thorough examination is difficult to be performed. A high resolution, near-focused, linear array transducer with a frequency of 7.5 MHz or greater is often used because it provides increased resolutions of the scrotal contents. Images of both scrotum and bilateral inguinal regions are obtained in both transverse and longitudinal planes. Color Doppler and pulsed Doppler examination is subsequently performed, optimized to display low-flow velocities, to demonstrate blood flow in the testes and surrounding scrotal structures. In evaluation of acute scrotum, the asymptomatic side should be scanned first to ensure that the flow parameters are set appropriately. A transverse image including all or a portion of both testicles in the field of view is obtained to allow side-to-side comparison of their sizes, echogenicity, and vascularity. Additional views may also be obtained with the patient performing Valsalva maneuver.[1]

Anatomy

Normal epididymal head. The epididymal head, usually iso- or slightly hyperechoic than the testis is seen located cephalad to the testis.[1]

At ultrasound, the normal testis has a homogeneous, medium-level, granular echotexture. The testicle is surrounded by a dense white fibrous capsule, the tunica albuginea, which is often not visualized in the absence of intrascrotal fluid. However, the tunica is often seen as an echogenic structure where it invaginates into the testis to form the mediastinum testis. In the testis, the seminiferous tubules converge to form the rete testes, which is located in the mediastinum testis. The rete testis connects to the epididymal head via the efferent ductules. The epididymis is located posterolateral to the testis and measures 6–7 cm in length. At sonography, the epididymis is normally iso- or slightly hyperechoic to the normal testis and its echo texture may be coarser. The head is the largest and most easily identified portion of the epididymis. It is located superior-lateral to the upper pole of the testicle and is often seen on paramedian views of the testis. The normal epididymal body and tail are smaller and more variable in position.[1]

The testis obtains its blood supply from the deferential, cremasteric and testicular arteries. The right and left testicular arteries, branches of the abdominal aorta, arise just distal to the renal arteries, provide the primary vascular supply to the testes. They course through the inguinal canal with the spermatic cord to the posterior superior aspect of the testis. Upon reaching the testis, the testicular artery divides into branches, which penetrate the tunica albuginea and arborize over the surface of the testis in a layer known as tunica vasculosa. Centripetal branches arising from the capsular arteries carry blood toward the mediastinum, where they divide to form the recurrent rami that carry blood away from the mediastinum into the testis. The deferential artery, a branch of the superior vesicle artery and the cremasteric artery, a branch of the inferior epigastric artery, supply the epididymis, vas deferens, and peritesticular tissue.[1]

Scrotal ultrasonography with Doppler of an 85 year old man with hydrocele, making the appendix of the testicle clearly distinctive as a 4 mm outpouching.

Four testicular appendages have been described: the appendix testis, the appendix epididymis, the vas aberrans, and the paradidymis. They are all remnants of embryonic ducts. Among them, the appendix testis and the appendix epididymis are usually seen at scrotal US. The appendix testis is a mullerian duct remnant and consists of fibrous tissue and blood vessels within an envelope of columnar epithelium. The appendix testis is attached to the upper pole of the testis and found in the groove between the testis and the epididymis. The appendix epididymis is attached to the head of the epididymis. The spermatic cord, which begins at the deep inguinal ring and descends vertically into the scrotum consists of vas deferens, testicular artery, cremasteric artery, deferential artery, pampiniform plexuses, genitofemoral nerve, and lymphatic vessel.[1]

Testicular size

Volume of both testicles combined
, on average ± standard error (ml)[3]
Age Testosterone level
Normal Decreased
51-60 33.7 ± 2.4 31.4 ± 3.2
61-70 31.0 ± 2.5 22.3 ± 2.
71-80 33.1 ± 2.7 19.1 ± 2.8
81-90 28.8 ± 2.1e 16.6 ± 3.1

The normal adult testis is an ovoid structure measuring 3 cm in anterior-posterior dimension, 2–4 cm in width, and 3–5 cm in length. Normal volume is 18 cm³ per testis on average (range 12 cm³ to 30 cm³.[4]

By 70 years of age, most men have developed a combination of decreased testicular size and decreased serum testosterone levels.[3] However, this does not occur in all men, and it is therefore of value to note a decreased volume regardless of patient age.

Intratesticular tumors

Main article: Ultrasonography of intratesticular tumors

Extratesticular tumors

Main article: Ultrasonography of extratesticular tumors

Inflammation

Epididymitis and epididymo-orchitis

Epididymo-orchitis in a 77 year-old man. (a) Transverse sonography shows enlargement of the epididymis with hypoechogenicity noted over the testis and epididymis associated with scrotal wall thickening. (b) Color Doppler sonography showed hyperemic change of the testis and epididymis, presenting as an “inferno” vascular flow pattern.[1]
Normal epididymis thickness
Head 10 - 12 mm[5]
Tail 2 - 5 mm[6]

Epididymitis and epididymo-orchitis are common causes of acute scrotal pain in adolescent boys and adults. The infection usually begins in the epididymal tail and spreads to the epididymal body and head. Approximately 20% to 40 % of cases are associated with orchitis due to direct spread of infection into the testis.[1]

At ultrasound, the findings of acute epididymitis include an enlarged hypoechoic or hyperechoic (presumably secondary to hemorrhage) epididymis [Fig. 20a]. Other signs of inflammation such as increased vascularity, reactive hydrocele, pyocele and scrotal wall thickening may also be present. Testicular involvement is confirmed by the presence of testicular enlargement and an inhomogeneous echotexture. Hypervascularity on color Doppler images [Fig. 20b] is a well-established diagnostic criterion and may be the only imaging finding of epididymo-orchitis in some men.[1]

Further workup

If epididymitis is visualized, the scrotum should also be scanned for any potential abscess formation.

Tuberculous epididymo-orchitis

Fig. 21. Tuberculous epididymo-orchitis. (a) Transverse sonography of a surgically proved tuberculous epididymitis shows an enlarged epididymis containing calcification and necrosis. (b) Composite image: Transverse sonography of the same patient shows multiple hypoechoic nodules in the left testis associated with surrounding reactive hydrocele.[1]

Although the genitourinary tract is the most common site of extra-pulmonary involvement by tuberculosis, tuberculous infection of the scrotum is rare and occurs in approximately 7% of patients with tuberculosis. At the initial stage of infection, the epididymis alone is involved. However if appropriate antituberculous treatment is not administered promptly, the infection will spreads to the ipsilateral testis. The occurrence of isolated testicular tuberculosis is rare. Clinically patients with tuberculous epididymo-orchitis may present with painful or painless enlargement of the scrotum, hence they cannot be distinguished from lesions such as testicular tumor, testicular infarction and may mimic testicular torsion..[1]

At ultrasound, tuberculous epididymitis is characterized by an enlarged epididymis with variable echogenicity. The presence of calcification, caseation necrosis, granulomas and fibrosis can result in heterogeneous echogenicity [Fig. 21a]. The ultrasound findings of tuberculous orchitis are as follow: (a) diffusely enlarged heterogeneously hypoechoic testis (b) diffusely enlarged homogeneously hypoechoic testis (c) nodular enlarged heterogeneously hypoechoic testis and (d) presence of multiple small hypoechoic nodules in an enlarged testis [Fig. 21b].[1]

Although both bacterial and tuberculous infections may involve both the epididymis and the testes, an enlarged epididymis with heterogeneously hypoechoic pattern favors a diagnosis of tuberculosis (Muttarak and Peh, 2006, as cited in Kim et al, 1993 and Chung et al, 1997). With color Doppler ultrasound, a diffuse increased blood flow pattern is seen in bacterial epididymitis, whereas focal linear or spotty blood flow signals are seen in the peripheral zone of the affected epididymis in patients with tuberculosis.[1]

Fournier gangrene

Fournier gangrene. (a) Transverse sonography image shows echogenic areas with dirty shadowing representing air in the perineum. (b) Gas presented as numerous, discrete, hyperechoic foci with reverberation artifacts are seen at scrotal wall.[1]

Fournier gangrene is a polymicrobial necrotizing fascitis involving the perineal, perianal, or genital regions and constitutes a true surgical emergency with a potentially high mortality rate. It usually develops from a perineal or genitourinary infection, but can arise following local trauma with secondary infection of the wound. 40–60% of patients are being diabetic. Although the diagnosis of Fournier gangrene is often made clinically, diagnostic imaging is useful in ambiguous cases.[1]

The sonographic hallmark of Fournier gangrene is presence of subcutaneous gas within the thickened scrotal wall. At ultrasound, the gas appears as numerous, discrete, hyperechoic foci with reverberation artifacts [Fig. 22]. Evidence of gas within the scrotal wall may be seen prior to clinical crepitus. The only other condition manifesting with gas at sonographic examination is an inguinoscrotal hernia. This can be differentiated from Fournier gangrene by the presence of gas within the protruding bowel lumen and away from the scrotal wall. (Levenson et al, 2008).[1]

Other benign lesions of the scrotum

Tubular ectasia

Fig. 23. Tubular ectasia of the testis. Honey-comb shaped cystic lesion at mediastinum testis.[1]
Fig. 24. Tubular ectasia of the testis . Lesion in the testis mimicking testicular tumor, but the microcystic appearance of this lesion is suggestive of tubular ectasia.[1]

The normal testis consists of several hundred lobules, with each lobule containing several seminiferous tubules. The seminiferous tubules of each lobule merge to form the straight tubes, which in turn converge to form the rete testis. The rete testis tubules, which lie within the mediastinum testis, are an anastomosing network of irregular channels with a broad lumen, which then empties into the efferent ductules to give rise to the head of the epididymis. Obstruction in the epididymis or efferent ductules may lead to cystic dilatation of the efferent ductules, which usually presents as an epididymal cyst on ultrasound. However, in the more proximal portion this could lead to the formation of an intratesticular cyst or dilatation of the tubules, so called tubular ectasia. Factors contributing to the development of tubular ectasia include epididymitis, testicular biopsy, vasectomy or an aging process. Clinically this lesion is usually asymptomatic. The ultrasound appearance of a microcystic or multiple tubular-like lesions located at the mediastinal testis [Fig. 23] and associated with an epididymal cyst in a middle-aged or elderly patient should alert the sonographer to the possibility of tubular ectasia. The differential diagnosis of a multicystic lesion in testis should include a cystic tumor, especially a cystic teratoma. A cystic teratoma is usually a palpable lesion containing both solid and cystic components; and the cysts are normally larger than that of tubular ectasia, which appear microcystic [Fig. 24]. Furthermore, the location of tubular ectasia in the mediastinum testis is also helpful in making the differential diagnosis.[1]

Testicular microlithiasis

Histologically, testicular microlithiasis refers to the scattered laminated calcium deposits in the lumina of the seminiferous tubules. These calcifications arise from degeneration of the cells lining the seminiferous tubules. At ultrasonography, microliths appear as tiny punctate echogenic foci, which typically do not shadow. Although minor microcalcification within a testis is considered normal, the typical US appearance of testicular microlithiasis is of multiple nonshadowing echogenic foci measuring 2–3 mm and randomly scattered throughout the testicular parenchyma [Fig. 25] (Dogra et al, 2003, as cited in Janzen et al, 1992). The clinical significance of testicular microlithiasis is that it is associated with increased risk of testicular malignancy, thus follow up of affected individuals with scrotal sonography is necessary to ensure that a testicular tumor does not develop.[1]

Testicular torsion

Fig. 26. Testicular torsion of the right testis. Absence of vascular flow and ill-defined hypoechoic lesions are seen in the testis.[1]

The normal testis and epididymis are anchored to the scrotal wall. If there is a lack of development of these attachments, the testis is free to twist on its vascular pedicle. This will result in torsion of the spermatic cord and interruption of testicular blood flow. Testicular torsion occurs most commonly at 12 to 18 years but can occur at any age. Torsion results in swelling and edema of the testis, and as the edema increases, testicular perfusion is further altered. The extent of testicular ischemia depends on the degree of torsion, which ranges from 180° to 720° or greater. The testicular salvage rate depends on the degree of torsion and the duration of ischemia. A nearly 100% salvage rate exists within the first 6 hours after the onset of symptoms; a 70% rate, within 6–12 hours; and a 20% rate, within 12–24 hours. Therefore testicular torsion is a surgical emergency and the role of ultrasound is to differentiate it from epididymitis as both disease presents with acute testicular pain clinically.[1]

There are two types of testicular torsion: extravaginal and intravaginal. Extravaginal torsion occurs exclusively in newborns. Ultrasound findings include an enlarged heterogeneous testis, ipsilateral hydrocele, thickened scrotal wall and absence of vascular flow in the testis and spermatic cord. The ultrasound findings of intravaginal torsion vary with the duration and the degree of rotation of the spermatic cord. Gray scale ultrasound may appear normal if the torsion is just occurred. At 4-6 hours after onset of torsion, enlarged testis with decreased echogenicity is seen. At 24 hours after onset, the testis appears heterogeneous due to vascular congestion, hemorrhage and infarction. As gray scale ultrasound is often normal during early onset of torsion, Doppler sonography is considered as essential in early diagnosis of testicular torsion. The absence of testicular flow at color and power Doppler ultrasound is considered diagnostic of ischemia, provided that the scanner is set for detection of slow flow, the sampling box is small and the scanner is adjusted for the lowest repetition frequency and the lowest possible threshold setting.[1]

Varicocele

Fig. 27. Varicocele. (a) Multiple tortuous tubular like structure are seen in the left scrotum. (b) Color Doppler sonography shows vascular reflux during Valsalva’s maneuver.[1]
Fig. 28. Intratesticular varicocele. (a) Dilated tubular structures are seen within the testis. (b) Presence of vascular reflux is noted during Valsalva’s maneuver.[1]

Varicocele refers to an abnormal dilatation of the veins of the spermatic cord due to incompetence of valve in the spermatic vein. This results in impaired blood drainage into the spermatic vein when the patient assumes a standing position or during Valsalva’s maneuver. Varicoceles are more common on the left side due to the following reasons (a) The left testicular vein is longer; (b) the left testicular vein enters the left renal vein at a right angle; (c) the left testicular artery in some men arches over the left renal vein, thereby compressing it; and (d) the descending colon distended with feces may compress the left testicular vein.[1]

The US appearance of varicocele consists of multiple, hypoechoic, serpiginous, tubular like structures of varying sizes larger than 2 mm in diameter that are usually best visualized superior or lateral to the testis [Fig. 27a]. Color flow and duplex Doppler US optimized for low-flow velocities help confirm the venous flow pattern, with phasic variation and retrograde filling during a Valsalva’s maneuver [Fig. 27b]. Intratesticular varicocele may appear as a vague hypoechoic area in the testis or mimics tubular ectasia. With color Doppler, this intratesticular hypoechoic area also showed reflux of vascular flow during Valsalva’s maneuver [Fig. 28].[1]

Undescended testis

Fig. 29. Undescended testis. (a) Normal testis in the scrotum. (b) Atrophic and decreased echogenicity of the contralateral testis of the same patient seen in the inguinal region.[1]

Normally the testes begin its descent through the inguinal canal to the scrotum at 36 weeks’ of gestation and completed at birth. Failure in the course of testes descent will result in undescended testes (Cryptorchidism).

Undescended testis is found in 4% of full-term infants but only 0.8% of males at the age of 1 year have true cryptorchidism. Although an undescended testis can be found anywhere along the pathway of descent from the retroperitoneum to the scrotum, the inguinal canal is the most common site for an undescended testis. Deviation of testis from the normal pathway of descent will result in ectopic testis that is commonly seen in pubopenile, femoral triangle and perineal regions.[1]

Besides infertility, undescended testes carry an increased risk of malignancy even for the normally located contralateral testis. The risk of malignancy is estimated to be as high as 10 times the normal individual with seminoma being the most common malignancy. The incidence of infertility is decreased if surgical orchiopexy is carried out before the 1-3 years but the risk of malignancy does not change. Because of the superficial location of the inguinal canal in children, sonography of undescended testes should be performed with a high frequency transducer. At ultrasound, the undescended testis usually appears small, less echogenic than the contralateral normal testis and usually located in the inguinal region [Fig. 29]. With color Doppler, the vascularity of the undescended testis is poor.[1]

Testicular appendiceal torsion

Fig. 30. Testicular appendiceal torsion. A hyperechoic lesion with surrounding vascularity is seen in the groove between the testis and epididymis.[1]

At sonography, the appendix testis usually appears as a 5 mm ovoid structure located in the groove between the testis and the epididymis. Normally it is isoechoic to the testis but at times it may be cystic. The appendix epididymis is of the same size as the appendix testis but is more often pedunculated. Clinically pain may occur with torsion of either appendage. Physical examination showed a small, firm nodule is palpable on the superior aspect of the testis and a bluish discoloration known as ‘‘blue dot’’ sign may be seen on the overlying skin. Torsion of the appendiceal testis most frequently involved in boys aged 7-14 years (Dogra and Bhatt 2004). The sonographic features of testicular appendiceal torsion includes a circular mass with variable echogenicity located adjacent to the testis or epididymis [Fig. 30], reactive hydrocele and skin thickening of the scrotum is common, increased peripheral vascular flow may be found around the testicular appendage on color Doppler ultrasound. Surgical intervention is unnecessary and pain usually resolves in 2 to 3 days with an atrophied or calcified appendages remaining.[1]

Conclusion

Ultrasound remains as the mainstay in scrotal imaging not only because of its high accuracy, excellent depiction of scrotal anatomy, low cost and wide availability, it is also useful in determining whether a mass is intra- or extra-testicular, thus providing us useful and valuable information to decide whether a mass is benign or malignant even though malignancy do occur in extratesticular tumors and vice versa. Furthermore, ultrasound also provides information essential to reach a specific diagnosis in patients with testicular torsion, testicular appendiceal torsion and inflammation such as epididymo-orchitis, Fournier gangrene etc, thus enabling us to avoid unnecessary operation.[1]

Notes

  1. For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Radlines:Authorship for details.
  2. NU Hospital Group, Sweden

References

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  4. [1]" By E. Nieschlag, Hermann M. Behre, H. van. Ahlen, Andrology: Male Reproductive Health and Dysfunction"
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