DOI: 10.1148/rg.275065172
RadioGraphics 2007;27:1239-1253
© RSNA, 2007
US–MR Imaging Correlation in Pathologic Conditions of the Scrotum1
Woojin Kim, MD,
Mark A. Rosen, MD, PhD,
Jill E. Langer, MD,
Marc P. Banner, MD,
Evan S. Siegelman, MD, and
Parvati Ramchandani, MD
1 From the Department of Radiology, Hospital of the University of Pennsylvania, 1 Silverstein, 3400 Spruce St, Philadelphia, PA 19104. Recipient of a Certificate of Merit award for an education exhibit at the 2005 RSNA Annual Meeting. Received September 22, 2006; revision requested October 24 and received December 6; accepted December 6. W.K. is a principal in iVirtuoso, Baltimore, Md; J.E.L. is a consultant to Bio-Imaging Technologies, Newtown, Pa; all other authors have no financial relationships to disclose.
Address correspondence to W.K. (e-mail: woojinrad{at}gmail.com).
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Abstract
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Ultrasonography (US) is usually the initial imaging modality for evaluation of pathologic conditions of the scrotum. However, magnetic resonance (MR) imaging can be useful as a problem-solving tool when sonographic findings are equivocal. MR imaging allows characterization of scrotal masses as intratesticular or extratesticular and can demonstrate various types of lesions and tissue, including cysts or fluid, solid masses, fat, and fibrosis. MR imaging may be of value when the location of a scrotal mass is uncertain or when US does not allow differentiation between a solid mass and an inflammatory or vascular abnormality. Gadolinium-enhanced MR imaging can help differentiate between a benign cystic lesion and a cystic neoplasm. Gadolinium-enhanced imaging can also be used to demonstrate areas of absent or reduced testicular perfusion, such as in segmental testicular infarct. Finally, MR imaging can demonstrate an intraabdominal undescended testis, which can be difficult to detect with US, and is superior to US in differentiation between an undescended testis and testicular agenesis.
© RSNA, 2007
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LEARNING OBJECTIVES FOR TEST 1
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After reading this article and taking the test, the reader will be able to:- Describe the US features of various pathologic conditions of the scrotum.
- Identify the MR imaging findings that correlate with the US features.
- Discuss the role of MR imaging as an adjunct to US in evaluation of scrotal lesions.
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Introduction
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Ultrasonography (US) performed by using a high-frequency transducer with color Doppler analysis is the initial imaging modality of choice when evaluating scrotal disease. US can suggest a specific diagnosis for a wide variety of intrascrotal diseases, appropriately guiding treatment (1–4). However, magnetic resonance (MR) imaging can be useful as a problem-solving tool when sonographic findings are equivocal or suboptimal (5–7). When used properly, MR imaging can decrease the overall number of unnecessary surgical procedures and reduce cost (8).
In this pictorial review, sonographic findings of a wide variety of scrotal lesions are presented and correlated with their MR imaging appearances, emphasizing those features that can help establish a specific diagnosis. Unless otherwise specified, both the US and MR imaging examples are from the same patient. The imaging findings of intratesticular tumors, benign intratesticular lesions, extratesticular tumors, inflammatory and ischemic lesions, and conditions such as hematoma and undescended testis are presented. Recommendations for when MR imaging can or should be used as an adjunctive imaging modality in the evaluation of known or suspected scrotal disease are also discussed.
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Technique
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US examination of the scrotum is performed with the patient placed in a supine position with a towel draped over his thighs to support the scrotum. A high-resolution, near-focused, linear-array transducer with a frequency of 7.5 MHz or greater is used. Transverse and longitudinal gray-scale imaging of the scrotum and inguinal regions bilaterally is performed. Color Doppler examination is subsequently performed, optimized to be sensitive to low-velocity flow. This is accomplished by having low pulse repetition frequency and a low wall filter with appropriate color gain settings (generally over 80%). When examining the acute scrotum, the asymptomatic side should be scanned first to ensure that the flow parameters are set appropriately (1). A transverse image including all or a portion of both testicles in the field of view is also obtained to allow side-to-side comparison of their sizes, echogenicity, and vascularity. More detailed descriptions of scanning techniques have been given previously (1).
For MR imaging, a 1.5-T unit is used at our institution. Similarly to US, a folded towel is placed between the patient’s legs to elevate the scrotum and penis. A 5-inch (13-cm) local surface coil is used. The typical imaging protocol consists of large field-of-view axial pelvic imaging to assess the inguinal canal and bowel for hernias and ascites. The origins of the renal vessels are included to allow evaluation of the lymph node drainage of the testicles. A high-resolution T2-weighted fast spin-echo sequence (field of view = 10–12 cm, imaging matrix = 256 x 256) is used in the axial, sagittal, and coronal planes to image the scrotum. A high-resolution axial T1-weighted spoiled gradient-echo sequence is also used to identify hemorrhage.
Gadolinium-enhanced imaging is not routinely used but can be performed in selected instances. Use of contrast material can aid in differentiating between a benign cystic lesion and a cystic neoplasm. Gadolinium-enhanced imaging can also be used to assess for areas of absent or reduced testicular perfusion, such as in segmental testicular infarct. When gadolinium-enhanced imaging is indicated, we use a fat-saturated T1-weighted spoiled gradient-echo sequence. We obtain fat-saturated pre- and postgadolinium T1-weighted spoiled gradient-echo images in the axial and coronal planes.
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Normal Appearances of the Epididymis and Testis
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The normal adult testis is ovoid and measures 3 cm in anterior-posterior dimension, 2–4 cm in width, and 3–5 cm in length. Each testis normally weighs between 12.5 and 19 g. Both the size and weight of the testes normally decrease with age. At US, the normal testicle is slightly echogenic with homogeneous echotexture. The testicle is surrounded by a fibrous band, 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. The epididymis is located posterolateral to the testis and measures 6–7 cm in length. At sonography, it is iso- to hyperechoic to the normal testis and has equal or diminished vascularity. The head is the largest and most easily identified portion of the epididymis. It lies superior and 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 (1,4).
At MR imaging, the normal testis has a homogeneous appearance, with intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images relative to skeletal muscle. The relatively high signal intensity of the testis on T2-weighted images allows excellent contrast from solid lesions, which invariably have lower signal intensity on T2-weighted images. T1-weighted images are useful for depicting increased signal intensity in certain tissues, such as fat and methemoglobin. The tunica albuginea appears as low signal intensity on T1- and T2-weighted images. The epididymis has signal intensity characteristics similar to testicular parenchyma on T1-weighted images but lower signal intensity on T2-weighted images (9).
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Imaging Evaluation of Scrotal Mass or Enlargement
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One of the primary indications for scrotal imaging is to evaluate for the presence of intratesticular tumor in the setting of scrotal enlargement or a palpable abnormality at physical examination. The presence of a solitary intratesticular solid mass is highly suspicious for malignancy. Primary intratesticular malignancy can be divided into germ cell tumors and non–germ cell tumors. Germ cell tumors are further categorized as either seminomas or nonseminomatous tumors. The non–germ cell neoplasms of the testis include Leydig cell and Sertoli cell tumors.
Conversely, the vast majority of extratesticular lesions are benign. One of the most common solid extratesticular masses encountered is the adenomatoid tumor. Other common benign extratesticular conditions that may manifest as scrotal enlargement include hydrocele, varicocele, and epididymal cysts. Hence, when a scrotal mass is identified, the primary goal of imaging is to determine whether the lesion is intra- or extratesticular. US remains the initial imaging modality of choice for this purpose. The accuracy of sonography approaches 100% in the ability to distinguish intratesticular from extratesticular disease (10). When the exact location of a scrotal lesion is not clearly established with sonography, MR imaging may be used as a secondary modality to localize the lesion with respect to the testis.
Imaging of nodal metastases plays an important role in treatment planning for patients with primary scrotal malignancy (11). The primary site of nodal drainage is to the paraaortic lymph nodes near the renal hila. Evaluation of the retroperitoneum should be performed when a testicular malignancy is diagnosed or suspected. The lymphatic drainage of the epididymis and spermatic cord is to the internal and external iliac nodal chains. The scrotal wall drains to the inguinal nodes. Thus, these lower pelvic lymph nodes can be involved when there has been invasion of tumor outside the testicular parenchyma.
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Malignant Testicular Tumors
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Seminoma
Approximately 95% of malignant testicular tumors are germ cell tumors, of which seminoma is the most common histologic subtype. Compared to the nonseminomatous germ cell tumors, seminoma occurs in an older patient population, with a mean age of approximately 40 years (5). These tumors carry a favorable prognosis due to their sensitivity to radiation and chemotherapy.
At scrotal sonography, a hypoechoic and typically homogeneous intratesticular mass is present, often with lobulated margins, which may simulate multifocal masses (Fig 1a); true multifocal tumors are rare (1,5,12). Compared with non-seminomatous tumors, seminomas are less likely to demonstrate calcification or cystic areas. Unless they are quite large, seminomas are generally more homogeneous in echotexture than are non-seminomatous tumors. At MR imaging, seminoma is usually homogeneous in appearance and relatively isointense to the normal testicular parenchyma on T1-weighted images and hypointense on T2-weighted images (Fig 1b, 1c) (9). However, MR imaging does not allow reliable differentiation between different subtypes of testicular neoplasms.
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Figure 1a. Seminoma in a 31-year-old man with the chief symptom of right testicular swelling. He reported sudden onset of testicular pain with scrotal swelling and erythema 3 months earlier, for which he was treated with 5 weeks of antibiotic therapy. (a) Sagittal sonogram of the right testicle shows a hypoechoic and relatively homogeneous, multi-nodular, solid intratesticular mass. No calcifications or cystic areas are noted. (b) Axial T2-weighted image shows that the tumor has homogeneous low signal intensity. (c) Gadolinium-enhanced MR image shows heterogeneous enhancement of the tumor with areas of necrosis.
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Figure 1b. Seminoma in a 31-year-old man with the chief symptom of right testicular swelling. He reported sudden onset of testicular pain with scrotal swelling and erythema 3 months earlier, for which he was treated with 5 weeks of antibiotic therapy. (a) Sagittal sonogram of the right testicle shows a hypoechoic and relatively homogeneous, multi-nodular, solid intratesticular mass. No calcifications or cystic areas are noted. (b) Axial T2-weighted image shows that the tumor has homogeneous low signal intensity. (c) Gadolinium-enhanced MR image shows heterogeneous enhancement of the tumor with areas of necrosis.
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Figure 1c. Seminoma in a 31-year-old man with the chief symptom of right testicular swelling. He reported sudden onset of testicular pain with scrotal swelling and erythema 3 months earlier, for which he was treated with 5 weeks of antibiotic therapy. (a) Sagittal sonogram of the right testicle shows a hypoechoic and relatively homogeneous, multi-nodular, solid intratesticular mass. No calcifications or cystic areas are noted. (b) Axial T2-weighted image shows that the tumor has homogeneous low signal intensity. (c) Gadolinium-enhanced MR image shows heterogeneous enhancement of the tumor with areas of necrosis.
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Nonseminomatous Germ Cell Tumor
Histologically, the presence of any nonseminomatous cell types in a testicular germ cell tumor classifies it as a nonseminomatous tumor, even if the seminomatous cell type predominates. These subtypes include yolk sac tumor, embryonal cell carcinoma, teratocarcinoma, teratoma, and choriocarcinoma. At US, nonseminomatous tumors tend to be more heterogeneous in echotexture with irregular or ill-defined margins. Nonseminomatous tumors are more likely to have cystic areas and echogenic foci than seminomas (Fig 2a). The echogenic foci can be due to calcification, hemorrhage, or fibrosis (1). At MR imaging, when compared to the normal testis, these tumors are usually iso- to hyperintense on T1-weighted images and hypointense on T2-weighted images (9). The overall heterogeneous appearance is mostly due to the presence of mixed cell types, hemorrhage, and necrosis (Fig 2b).
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Figure 2a. Nonseminomatous germ cell tumor in a 24-year-old man with painless scrotal swelling. (a) Sagittal US image shows a large, heterogeneous intratesticular tumor with cystic areas. (b) Sagittal gadolinium-enhanced T1-weighted image shows heterogeneous enhancement of the tumor with lack of enhancement centrally due to necrosis. These imaging findings are typical of nonseminomatous germ cell tumors.
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Figure 2b. Nonseminomatous germ cell tumor in a 24-year-old man with painless scrotal swelling. (a) Sagittal US image shows a large, heterogeneous intratesticular tumor with cystic areas. (b) Sagittal gadolinium-enhanced T1-weighted image shows heterogeneous enhancement of the tumor with lack of enhancement centrally due to necrosis. These imaging findings are typical of nonseminomatous germ cell tumors.
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Spontaneous Regression in Primary Germ Cell Testicular Tumors
On occasion, primary testicular tumors may undergo spontaneous regression. These lesions are usually termed "burnt-out" germ cell tumors. Spontaneously regressed testicular tumors often demonstrate little or no remaining viable tumor, with mostly scarring and fibrosis found at histologic analysis after orchiectomy. Burnt-out germ cell tumors usually arise from testicular teratocarcinomas or choriocarcinomas that rapidly outgrow their blood supply with subsequent regression, necrosis, and scarring. While teratocarcinoma and choriocarcinoma are the tumors most likely to undergo spontaneous regression, all germ cell tumors, including seminomas, may undergo this phenomenon (13). It is thought that "primary" retroperitoneal germ cell tumors may in fact represent metastases from primary testicular germ cell tumors, which then spontaneously regressed.
At scrotal US, regressed germ cell tumors appear as a hypoechoic or ill-defined, intratesticular calcified lesion (Fig 3a) (1,5,12). At MR imaging, T2-weighted images demonstrate a focal low-signal-intensity area of distortion of the normal testicular architecture, without a visible mass (Fig 3b). The appearance can resemble segmental infarction.
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Figure 3a. Burnt-out seminoma in a 24-year-old man with left flank pain, for which computed tomography of the abdomen and pelvis was performed. The presence of necrotic lymph nodes in the left paraaortic region prompted further evaluation. (a) Sagittal sonogram shows an ill-defined, intratesticular calcified lesion (arrow) with posterior acoustic shadowing. (b) Sagittal T2-weighted image shows a focal area of low-signal-intensity scarring (arrow) without a visible mass. The lesion was found to be a burnt-out seminoma.
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Figure 3b. Burnt-out seminoma in a 24-year-old man with left flank pain, for which computed tomography of the abdomen and pelvis was performed. The presence of necrotic lymph nodes in the left paraaortic region prompted further evaluation. (a) Sagittal sonogram shows an ill-defined, intratesticular calcified lesion (arrow) with posterior acoustic shadowing. (b) Sagittal T2-weighted image shows a focal area of low-signal-intensity scarring (arrow) without a visible mass. The lesion was found to be a burnt-out seminoma.
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Benign Testicular Lesions
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Tunica Albuginea Cyst
Tunica albuginea cysts typically manifest as small (2–5 mm) palpable masses, most commonly along the upper anterior or lateral aspect of the testicle, and can be single or multiple. Their origin is uncertain, but they are thought to arise from mesothelial cells (14,15). At US, these extratesticular cysts appear as a small, peripherally located, anechoic lesion within the layers of the tunica. Larger lesions may compress the testicular parenchyma and simulate an intratesticular mass (15). Less commonly, these lesions have internal echoes and raise concern for a neoplasm (Fig 4a) (15). At MR imaging, regardless of size, the signal intensity of these cysts follows that of fluid with all pulse sequences (Fig 4b). When sonographic results are equivocal, MR with multiplanar imaging can, in addition, demonstrate the paratesticular location (9).
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Figure 4a. Tunica albuginea cyst in a 36-year-old man. (a) US image shows a small, peripherally located testicular lesion (arrow) with internal echoes. (b) On a coronal T2-weighted image, the lesion (arrow) is isointense relative to fluid. The lesion was isointense to fluid with all pulse sequences, a finding that confirmed its cystic nature. The presence of this pathognomonic finding obviated any further intervention.
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Figure 4b. Tunica albuginea cyst in a 36-year-old man. (a) US image shows a small, peripherally located testicular lesion (arrow) with internal echoes. (b) On a coronal T2-weighted image, the lesion (arrow) is isointense relative to fluid. The lesion was isointense to fluid with all pulse sequences, a finding that confirmed its cystic nature. The presence of this pathognomonic finding obviated any further intervention.
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Testicular Cyst
Simple cysts are usually nonpalpable and thus are detected incidentally and require no treatment when discovered. Similar to cysts elsewhere in the body, they are usually well-defined and anechoic with enhanced through transmission and an imperceptible wall (Fig 5a) (15,16). At MR imaging, the lesion follows the signal characteristics of fluid with all pulse sequences (Fig 5b). Careful inspection is warranted to differentiate these from cystic testicular neoplasms, such as cystic teratoma (9). Contrast-enhanced MR imaging aids in this diagnosis by demonstrating lack of solid enhancement in these lesions.
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Figure 5a. Intratesticular cyst in a 50-year-old man. (a) US image shows a right-sided 17-mm-diameter intratesticular cyst. (b) T2-weighted image shows that the lesion (arrow) has the characteristic high signal intensity of fluid. The surrounding thin rim of testicular parenchyma enables diagnosis of an intratesticular cyst. However, note that there is some overlap in imaging appearances of an intratesticular cyst and a tunica albuginea cyst. No further intervention was performed.
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Figure 5b. Intratesticular cyst in a 50-year-old man. (a) US image shows a right-sided 17-mm-diameter intratesticular cyst. (b) T2-weighted image shows that the lesion (arrow) has the characteristic high signal intensity of fluid. The surrounding thin rim of testicular parenchyma enables diagnosis of an intratesticular cyst. However, note that there is some overlap in imaging appearances of an intratesticular cyst and a tunica albuginea cyst. No further intervention was performed.
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Dilated Rete Testis
Dilated rete testis represents dilated testicular mediastinal tubules, a benign condition thought to result from partial or complete obliteration of the efferent ducts. It is often bilateral, is frequently associated with spermatocele, and is more common in men over the age of 55 years (15). At sonography, it appears as multiple small cystic or tubular anechoic structures that replace and enlarge the mediastinum (Fig 6a) (15,17,18). The geographic shape, lack of mass effect, and lack of internal flow are helpful to distinguish this benign condition from a partially cystic tumor (15,17). At MR imaging, the cystic dilatation or ectasia of multiple small tubules of the rete testis appears hyperintense on T2-weighted images (Fig 6b). After administration of gadolinium contrast material, no internal enhancement is seen. Its characteristic appearance at MR imaging with lack of enhancement can aid in diagnosis (9).
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Figure 6a. Dilated rete testis in a 44-year-old man. (a) Sonogram shows multiple small, cystic or tubular, anechoic structures that replace and enlarge the testicular mediastinum. (b) On a T2-weighted image, the lesion has high signal intensity.
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Figure 6b. Dilated rete testis in a 44-year-old man. (a) Sonogram shows multiple small, cystic or tubular, anechoic structures that replace and enlarge the testicular mediastinum. (b) On a T2-weighted image, the lesion has high signal intensity.
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Epidermoid Inclusion Cyst
The most common benign intratesticular neoplasm is an epidermoid inclusion cyst. This relatively uncommon benign tumor is of germ cell origin but contains only ectodermal tissue. It typically manifests in younger men and adolescents as a painless, palpable mass and is most commonly 1–3 cm at discovery (19). Unlike germ cell neoplasms, epidermoid inclusion cyst can be treated with enucleation rather than orchiectomy.
The most common sonographic appearance is a lesion with concentric alternating rings of low and high echogenicity, which represent layers of keratinized squamous epithelium. This has also been termed the onion ring pattern and represents the classic appearance for an epidermoid inclusion cyst. No flow is demonstrated at color Doppler imaging, thus providing a clue to the diagnosis (Fig 7a) (1,19,20). At MR imaging, a similar onion ring appearance with alternating bands of high and low T2 signal intensity can be revealed (Fig 7b).
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Figure 7a. Epidermoid inclusion cyst in a 26-year-old man with a 2-year history of a palpable mass in the left testicle without interval change. (a) Sagittal sonogram shows a testicular lesion with concentric rings of alternating low and high echogenicity but without vascularity. These findings represent the classic onion ring appearance of an epidermoid inclusion cyst. (b) On a sagittal T2-weighted image, the lesion has a similar appearance, with alternating bands of high and low signal intensity.
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Figure 7b. Epidermoid inclusion cyst in a 26-year-old man with a 2-year history of a palpable mass in the left testicle without interval change. (a) Sagittal sonogram shows a testicular lesion with concentric rings of alternating low and high echogenicity but without vascularity. These findings represent the classic onion ring appearance of an epidermoid inclusion cyst. (b) On a sagittal T2-weighted image, the lesion has a similar appearance, with alternating bands of high and low signal intensity.
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Other described sonographic appearances include a target appearance, where there is an echogenic center surrounded by a halo, a well-defined mass with a rim of calcification, and a solid mass with a hyperechoic rim. Atypical appearances can also be seen where the inclusion cyst resembles a simple cyst (anechoic at US, simple fluid appearance on T1- and T2-weighted images). No matter the imaging appearance, epidermal inclusion cysts should not demonstrate internal flow at Doppler sonography nor enhancement after administration of gadolinium contrast material (9).
Leydig Cell Hyperplasia
Leydig cell hyperplasia is a rare, benign condition characterized by multiple small testicular nodules, frequently bilateral. Various conditions have been associated with Leydig cell hyperplasia, including cryptorchidism, congenital adrenal hyperplasia, human chorionic gonadotropin (hCG)–producing germ cell tumors, Klinefelter syndrome, and exogenous hCG therapy. The sonographic appearance can be variable, with both hypoechoic and hyperechoic appearances having been described (Fig 8a). At MR imaging, multiple small (1–6-mm) nodules are seen, which are hypointense on T2-weighted images (Fig 8b). There may be mild enhancement after administration of gadolinium contrast material (9).
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Figure 8a. Leydig cell hyperplasia in a 44-year-old man. (a) US image of the left testicle shows several small, hypoechoic intratesticular lesions (arrows). Similar lesions were noted in the contralateral testis. (b) T2-weighted image shows that the lesions are hypointense (arrow). Leydig cell hyperplasia was demonstrated with biopsy.
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Figure 8b. Leydig cell hyperplasia in a 44-year-old man. (a) US image of the left testicle shows several small, hypoechoic intratesticular lesions (arrows). Similar lesions were noted in the contralateral testis. (b) T2-weighted image shows that the lesions are hypointense (arrow). Leydig cell hyperplasia was demonstrated with biopsy.
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The differential diagnosis for multiple nodular lesions includes lymphoma, leukemia, metastatic disease, granulomatous disease, and bilateral primary testicular neoplasm. MR imaging may demonstrate greater extent of disease (including bilaterality) relative to that shown with sonography (21). When bilateral multifocal masses are identified, the possibility of benign Leydig cell hyperplasia should be considered, as this gives the urologist the option of performing a surgical biopsy rather than orchiectomy to exclude malignancy.
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Extratesticular Tumors
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Adenomatoid Tumor
Adenomatoid tumors are benign, solid extratesticular lesions that can originate from the epididymis, tunica vaginalis, or spermatic cord. They are the most common tumor of the epididymis and occur more often in the lower pole than in the upper pole by a ratio of 4:1. Usually an incidental finding, adenomatoid tumors manifest as a painless scrotal mass, with the majority diagnosed in patients aged 20–50 years (22). They are typically unilateral and occur more frequently on the left side. When they grow noninvasively into the testicular parenchyma, they can simulate intratesticular disease.
At US, they appear as a solid extratesticular mass with variable echogenicity (Fig 9a) (1,23, 24). Commonly, MR imaging demonstrates low signal intensity relative to the testicular parenchyma on T2-weighted images (Fig 9b). MR imaging can aid in determining the paratesticular origin of the lesion. Adenomatoid tumors enhance after administration of gadolinium contrast material. Slow or decreased enhancement relative to the normal testis may also suggest a benign origin (7), although this finding can be variable.
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Figure 9a. Adenomatoid tumor in a 35-year-old man with a palpable abnormality in the left side of the scrotum. He had felt the abnormality for more than 1 year without interval change. (a) Sagittal sonogram shows a solid mass with slightly heterogeneous echogenicity (arrow). At the time of imaging, it was uncertain whether the mass was an intra- or extratesticular tumor. (b) On a T2-weighted image, the lesion (arrow) has low signal intensity. The mass grows noninvasively along the testicular mediastinum without invasion of the parenchyma. This finding and the presence of a small cleft at the testicular margin were suggestive of an extratesticular location.
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Figure 9b. Adenomatoid tumor in a 35-year-old man with a palpable abnormality in the left side of the scrotum. He had felt the abnormality for more than 1 year without interval change. (a) Sagittal sonogram shows a solid mass with slightly heterogeneous echogenicity (arrow). At the time of imaging, it was uncertain whether the mass was an intra- or extratesticular tumor. (b) On a T2-weighted image, the lesion (arrow) has low signal intensity. The mass grows noninvasively along the testicular mediastinum without invasion of the parenchyma. This finding and the presence of a small cleft at the testicular margin were suggestive of an extratesticular location.
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Epididymal Cystadenoma
Papillary cystadenoma of the epididymis is a benign epithelial neoplasm. It is seen in up to 60% of men with von Hippel–Lindau disease. Although the sporadic variety is usually seen in middle-aged men, it occurs earlier in patients with von Hippel–Lindau disease (22). The sonographic appearance can be variable. Commonly, it will have a solid appearance with few cystic spaces (Fig 10a). Alternatively, it can appear as a multiloculated cystic lesion with small papillary projections (15,25).
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Figure 10a. Epididymal cystadenoma in a 31-year-old patient with a history of von Hippel–Lindau disease who presented with bilateral epididymal masses. (a) US image shows a solid, hypoechoic epididymal lesion with few cystic spaces (arrow). (b) Axial gadolinium-enhanced T1-weighted image shows the rim-enhancing mass (arrow) within the epididymis.
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Figure 10b. Epididymal cystadenoma in a 31-year-old patient with a history of von Hippel–Lindau disease who presented with bilateral epididymal masses. (a) US image shows a solid, hypoechoic epididymal lesion with few cystic spaces (arrow). (b) Axial gadolinium-enhanced T1-weighted image shows the rim-enhancing mass (arrow) within the epididymis.
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In patients with von Hippel–Lindau disease, sonographic criteria for diagnosis of epididymal cystadenoma consist of (a) a predominantly solid epididymal mass larger than 10 x 14 mm and (b) slow growth (23). Most are treated conservatively with serial US to monitor lesion growth. At MR imaging, a cystic mass with septations or mural nodules can be seen (Fig 10b). The internal architecture of the lesion can be demonstrated at gadolinium-enhanced T1-weighted imaging.
Lipoma
Lipoma is the most common benign tumor of the spermatic cord and can occur at any age (15,22). At US, it is a well-defined, homogeneous, hyperechoic paratesticular lesion of varying size (Fig 11a) (23). At MR imaging, lipoma appears uniform and follows fat signal intensity with all sequences, including fat-suppressed sequences, thus confirming the diagnosis (Fig 11b) (9).
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Figure 11a. Lipoma in a 71-year-old man with a right-sided scrotal mass. The possibility of a hernia was considered. (a) Transverse US image of both testes shows a large, well-defined, homogeneous, hyperechoic, right-sided paratesticular lesion (arrow). No hernia was seen. (b) On a T1-weighted image, the lesion (arrow) has high signal intensity. The lesion had low signal intensity on fat-saturated T2-weighted images and followed the signal intensity of fat with all pulse sequences, findings consistent with a lipoma.
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Figure 11b. Lipoma in a 71-year-old man with a right-sided scrotal mass. The possibility of a hernia was considered. (a) Transverse US image of both testes shows a large, well-defined, homogeneous, hyperechoic, right-sided paratesticular lesion (arrow). No hernia was seen. (b) On a T1-weighted image, the lesion (arrow) has high signal intensity. The lesion had low signal intensity on fat-saturated T2-weighted images and followed the signal intensity of fat with all pulse sequences, findings consistent with a lipoma.
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Fibrous Pseudotumor
Fibrous pseudotumor is a benign, reactive fibrous proliferation of paratesticular tissue. It can grow up to 8 cm in diameter and therefore can mimic a neoplasm. It most commonly arises from the tunica vaginalis. The sonographic appearance is nonspecific (15,23), and calcification is common (Fig 12a). The lesion can dislodge and become freely mobile within the scrotal sac; such a lesion is known as a "scrotal pearl." At MR imaging, owing to the presence of fibrosis, the lesion has low signal intensity on both T1- and T2-weighted images (Fig 12b) with variable enhancement.
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Figure 12a. Fibrous pseudotumor in a 31-year-old man with a palpable abnormality in the right testicle. (a) Sagittal sonogram shows a small hypoechoic lesion (arrow) in the periphery of the testicle. The lesion has a central focus of high echogenicity, which may represent calcification. (b) On a T2-weighted image, the lesion (arrow) has low signal intensity. The lesion also had low signal intensity on T1-weighted images, findings compatible with calcification or fibrous tissue.
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Figure 12b. Fibrous pseudotumor in a 31-year-old man with a palpable abnormality in the right testicle. (a) Sagittal sonogram shows a small hypoechoic lesion (arrow) in the periphery of the testicle. The lesion has a central focus of high echogenicity, which may represent calcification. (b) On a T2-weighted image, the lesion (arrow) has low signal intensity. The lesion also had low signal intensity on T1-weighted images, findings compatible with calcification or fibrous tissue.
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Inflammatory or Ischemic Conditions
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Epididymo-orchitis
Epididymitis and epididymo-orchitis are common causes of acute scrotal pain in young males. Most cases are caused by sexually transmitted disease or retrograde spread of bacterial infections from the urinary bladder. The infection usually begins in the tail of the epididymis and spreads to the body and head. Approximately 20%–40% of cases of epididymitis are associated with orchitis, which is thought to be due to direct extension of infection into the testicular parenchyma (26).
At US, the findings of acute epididymitis include low echogenicity or rarely high echogenicity (if there is coexisting hemorrhage) with enlargement and hypervascularity of the entire epididymis or a focal region. Similarly, diffuse inflammation of the testis causes enlargement, heterogeneous echogenicity (Fig 13a), and hypervascularity (Fig 13b). Hypervascularity on color Doppler images is a well-established diagnostic criterion and may be the only imaging finding of epididymo-orchitis in some men (26). Associated findings, such as reactive hydrocele or pyocele and scrotal wall edema, can further support the diagnosis.
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Figure 13a. Epididymo-orchitis in a 52-year-old man. (a) Sagittal sonogram of the left epididymis (arrow) and testis shows heterogeneous low echogenicity and enlargement. (b) Color Doppler image shows hypervascularity. (c) Axial gadolinium-enhanced fat-saturated T1-weighted image, obtained in another patient, shows an abnormally enhancing and enlarged epididymis with a surrounding rim of fluid (arrow).
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Figure 13b. Epididymo-orchitis in a 52-year-old man. (a) Sagittal sonogram of the left epididymis (arrow) and testis shows heterogeneous low echogenicity and enlargement. (b) Color Doppler image shows hypervascularity. (c) Axial gadolinium-enhanced fat-saturated T1-weighted image, obtained in another patient, shows an abnormally enhancing and enlarged epididymis with a surrounding rim of fluid (arrow).
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Figure 13c. Epididymo-orchitis in a 52-year-old man. (a) Sagittal sonogram of the left epididymis (arrow) and testis shows heterogeneous low echogenicity and enlargement. (b) Color Doppler image shows hypervascularity. (c) Axial gadolinium-enhanced fat-saturated T1-weighted image, obtained in another patient, shows an abnormally enhancing and enlarged epididymis with a surrounding rim of fluid (arrow).
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Scrotal trauma also results in enlargement and hyperemia of the epididymis and should be considered in the differential diagnosis. Diffuse heterogeneous echogenicity of the testis is not specific for orchitis and can be seen with leukemia, lymphoma, metastasis, and infarction. Leukemia, lymphoma, metastasis, and mumps usually demonstrate bilateral involvement, while other infectious conditions usually have unilateral involvement. However, given the difficulty in differentiating between these entities with imaging findings alone, follow-up to resolution is recommended if the diagnosis is uncertain (1).
At MR imaging, epididymo-orchitis generally demonstrates heterogeneous areas of low signal intensity on T2-weighted images. The epididymis may be enlarged and hyperenhancing on contrast-enhanced T1-weighted images (Fig 13c). Inhomogeneous enhancement of the testis with hypointense bands may also be seen.
Segmental Infarct
Segmental infarct of the testicle is relatively rare and has been reported in patients at risk for small vessel ischemic disease, such as those with underlying vasculitis, sickle cell disease, and hypercoagulable states (27,28). It is also an uncommon complication of epididymo-orchitis, scrotal trauma, and inguinal hernia repair (29). At US, the infarct appears as a wedge-shaped or geographic area of low echogenicity with its vertex directed toward the testicular mediastinum (Fig 14a). In general, there is absent or diminished flow on color Doppler images.
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Figure 14a. Segmental infarct in a 54-year-old man with right-sided scrotal pain. His history was significant for repair of a muscle injury in the right groin; the repair involved repositioning of the spermatic cord. (a) Sonogram shows a geographic area of low echogenicity (arrow). (b) On a gadolinium-enhanced T1-weighted image, the abnormal area (arrow) does not demonstrate enhancement.
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Figure 14b. Segmental infarct in a 54-year-old man with right-sided scrotal pain. His history was significant for repair of a muscle injury in the right groin; the repair involved repositioning of the spermatic cord. (a) Sonogram shows a geographic area of low echogenicity (arrow). (b) On a gadolinium-enhanced T1-weighted image, the abnormal area (arrow) does not demonstrate enhancement.
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On T1-weighted MR images, infarcts may appear isointense to testicular parenchyma. Hemorrhagic infarcts demonstrate foci of high signal intensity on T1-weighted images. On T2-weighted images, the signal intensity is variable but the infarct usually appears as an area of low signal intensity. Rim enhancement can be seen on gadolinium-enhanced images. MR imaging can aid in diagnosis when US results are not definitive by confirming that the visualized abnormality is segmental rather than masslike, with demonstration of a wedge-shaped abnormality on T2-weighted and gadolinium-enhanced T1-weighted images (Fig 14b).
Tuberculous Epididymo-orchitis
The genitourinary tract is the most common site of extrapulmonary involvement by tuberculosis. At US, there is enlargement of the epididymis with variable echogenicity. The presence of caseation necrosis, granulomas, fibrosis, and calcifications can cause heterogeneous echogenicity (Fig 15a) (1,30). Orchitis has a similar appearance, but the presence of multiple small hypoechoic nodules has also been described (31). At MR imaging, heterogeneous abnormal signal intensity can be seen on T2-weighted images (Fig 15b).
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Figure 15a. Tuberculous epididymo-orchitis in a 70-year-old man. (a) Sonogram shows multiple small hypoechoic nodules (arrow), which represent tuberculous epididymo-orchitis. (b) T2-weighted image shows heterogeneous abnormal signal intensity (arrows) bilaterally.
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Figure 15b. Tuberculous epididymo-orchitis in a 70-year-old man. (a) Sonogram shows multiple small hypoechoic nodules (arrow), which represent tuberculous epididymo-orchitis. (b) T2-weighted image shows heterogeneous abnormal signal intensity (arrows) bilaterally.
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Sarcoidosis
Sarcoidosis can rarely involve the genitourinary tract. In general, it affects the epididymis more commonly than the testis. While it can manifest as a solitary lesion, it is more commonly seen as multiple small bilateral lesions (22). At US, testicular lesions are hypoechoic (Fig 16a). Epididymal involvement by sarcoidosis results in enlargement. At MR imaging, low-signal-intensity intratesticular lesions can be seen on T2-weighted images (Fig 16b); the lesions enhance after contrast material administration.
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Figure 16a. Sarcoidosis in a 30-year-old man with bilateral enlargement of the epididymides and testes. The patient had a history of sarcoidosis. (a) Sonogram shows multiple hypoechoic intratesticular lesions. (b) On a T2-weighted image, the lesions have low signal intensity.
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Figure 16b. Sarcoidosis in a 30-year-old man with bilateral enlargement of the epididymides and testes. The patient had a history of sarcoidosis. (a) Sonogram shows multiple hypoechoic intratesticular lesions. (b) On a T2-weighted image, the lesions have low signal intensity.
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Hidradenitis Suppurativa
Hidradenitis suppurativa is a chronic condition characterized by swollen, inflamed, and painful lesions in regions of the body containing apocrine glands, such as the axilla and groin. When the scrotum is involved in cases of inguinal hidradenitis, US demonstrates nonspecific scrotal skin thickening (Fig 17a). At MR imaging, skin thickening with high signal intensity, which signifies the presence of edema, is seen on T2-weighted images (Fig 17b); enhancement is also seen (Fig 17c). The underlying testis is typically uninvolved and appears normal. However, imaging studies can demonstrate a complicating fistula or abscesses.
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Abstract
LEARNING OBJECTIVES FOR TEST...
