(Radiographics. 2002;22:189-216.)
© RSNA, 2002
From the Archives of the AFIP
Tumors and Tumorlike Lesions of the Testis: Radiologic-Pathologic Correlation1
Paula J. Woodward, MD,
Roya Sohaey, MD,
Michael J. O’Donoghue, LCDR, MC USNR and
Douglas E. Green, MD
1 From the Departments of Radiologic Pathology (P.J.W.) and Genitourinary Pathology (M.J.O.), Armed Forces Institute of Pathology, 6825 16th St, NW, Bldg 54, Rm M-121, Washington, DC 20306-6000; Department of Radiology, Oregon Health Sciences University, Portland (R.S.); and Department of Radiology, University of Utah, Salt Lake City (D.E.G.). Received July 12, 2001; revision requested August 15 and received September 19; accepted September 20. Address correspondence to P.J.W. (e-mail: woodward@afip.osd.mil).
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Abstract
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Testicular carcinoma represents only 1% of all neoplasms in men, but it is the most common malignancy in the 15–34-year-old age group. Germ cell tumors constitute 95% of all testicular tumors. Germ cell tumors are a varied group of neoplasms whose imaging features reflect their underlying histologic characteristics. Seminomas are generally well-defined homogeneous lesions, whereas the nonseminomatous tumors (embryonal carcinoma, yolk sac tumor, choriocarcinoma, teratoma, and mixed germ cell tumor) have a much more varied appearance. Germ cell tumors follow a predictable pattern of spread via the lymphatic drainage to the retroperitoneal nodes. Choriocarcinoma, which has a proclivity for early hematogenous spread, is a notable exception. Testicular tumors may also arise from the sex cords (Sertoli cells) and stroma (Leydig cells). Although 90% of these tumors are benign, there are no reliable imaging criteria to differentiate them from malignant masses. Some benign testicular masses can be recognized, obviating an unwarranted orchiectomy. A dilated rete testis is a normal variant and appears as a series of small tubules near the mediastinum testis. Other benign lesions that can be suspected on the basis of imaging findings and history include intratesticular cysts, epidermoid cysts, congenital adrenal hyperplasia, and sarcoidosis.
© RSNA, 2002
Index Terms: Germ cell neoplasm, 847.313, 847.329 • Seminoma, 847.329 • Teratoma, 847.313 • Testis, cysts, 847.311 • Testis, neoplasms, 847.313, 847.329, 847.34
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LEARNING OBJECTIVES FOR TEST 6
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After reading this article and taking the test, the reader will be able to:
- Describe the pathogenesis and risk factors for testicular carcinoma.
- Delineate the common sites and pattern of spread of metastatic disease.
- Recognize which clinical conditions and imaging findings can be used to help differentiate benign from malignant masses.
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Introduction
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Testicular carcinoma is the most common malignancy in young men and boys 15–34 years of age (1). Overall, however, it is a relatively rare tumor, constituting only 1% of all malignant neoplasms in men. Testicular tumors can be further categorized into germ cell and non–germ cell tumors. Germ cell tumors arise from spermatogenic cells and constitute 95% of testicular neoplasms. They are almost uniformly malignant. Non–germ cell primary tumors of the testis derive from the sex cords (Sertoli cells) and stroma (Leydig cells). These tumors are malignant in only 10% of cases. Nonprimary tumors such as lymphoma, leukemia, and metastases can also manifest as testicular masses (1) (Table 1).
An unexplained increase in the prevalence of testicular carcinoma has been noted, with a 100% increase in the number of reported cases since 1936. A similar trend has also been reported in several northern European countries (1). In the United States, the projected number of new cases for 2001 is 7,200 (2). Ninety percent of patients presenting with testicular carcinoma are white, whereas only 3% of men with these tumors are African-American (3). The peak prevalence of testicular tumors occurs in the 25–35-year-old age group. A secondary peak prevalence occurs among men 71–90 years of age, with lymphoma and metastasis accounting for most cases. A third, lesser peak occurs among infants, with a rapid decline to a nadir for boys 10 years of age (1). Despite the increase in the number of cases, survival rates for patients with testicular carcinoma have increased from 79% to 95% over the past 30 years (2).
Testicular neoplasia can manifest in a variety of ways. The most common manifestation is a painless scrotal mass. Other symptoms include a sensation of heaviness or fullness in the lower abdomen or scrotum. Pain is a much less common presenting symptom, reported by approximately 10% of patients (1). In some cases, testicular neoplasia may initially be misdiagnosed as orchitis. Tumors may undergo regression, necrosis, and scarring (so-called burned-out germ cell tumors), and therefore some patients may have normal or small testes at presentation. This subgroup of patients, along with those who have an aggressive histologic tumor type, may present with metastases (4). A small minority of patients with hormonally active tumors may present with endocrine abnormalities, most commonly gynecomastia (1).
Radiologists are often involved in the initial work-up and evaluation of a scrotal mass as well as in the staging of a known tumor. In this article, the classification, biologic behavior, and staging of testicular tumors are reviewed. Conditions that may mimic neoplasms are also discussed. The discussion emphasizes recognition of the imaging features of the various tumors and tumorlike lesions of the testis, with the goal of preventing a needless orchiectomy.
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Embryologic Development
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Although the sex of an embryo is chromosomally determined at the time of fertilization, there is no morphologic male or female sexual differentiation until the 7th week of development. Until that time, embryos of both sexes develop along identical lines. This period is often called the "indifferent stage." The undifferentiated gonad is composed of three different cell types: mesenchyme, mesothelium, and germ cells. During the indifferent stage, genital ridges form on both sides of the midline from condensation of mesenchyme. These ridges extend from the sixth thoracic to the second sacral segments of the developing embryo and are covered by proliferating mesothelium (coelomic epithelium). Subsequent proliferation and inward fingerlike migration of these cells form the primitive sex cords. The third component of the developing gonad is the primordial germ cells. The germ cells form in the wall of the yolk sac and then migrate along the hindgut and dorsal mesenteric root into the genital ridge. Once they arrive at the genital ridge, they are incorporated into the primitive sex cords (Fig 1) (5,6).
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Figure 1a. Testicular embryology. (a) Drawing of a 6-week-old embryo depicts migration of the primordial germ cells (purple dots) from the yolk sac, along the hindgut, and into the genital ridges. (b) Cross-sectional drawing through the midabdomen shows the genital ridges. There is inward extension of the proliferating mesothelium forming the primitive sex cords. The primordial germ cells are being incorporated into these developing sex cords. (c) Cross-sectional drawing of a further stage of development shows the sex cords and incorporated germ cells in the developing seminiferous tubules.
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Figure 1b. Testicular embryology. (a) Drawing of a 6-week-old embryo depicts migration of the primordial germ cells (purple dots) from the yolk sac, along the hindgut, and into the genital ridges. (b) Cross-sectional drawing through the midabdomen shows the genital ridges. There is inward extension of the proliferating mesothelium forming the primitive sex cords. The primordial germ cells are being incorporated into these developing sex cords. (c) Cross-sectional drawing of a further stage of development shows the sex cords and incorporated germ cells in the developing seminiferous tubules.
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Figure 1c. Testicular embryology. (a) Drawing of a 6-week-old embryo depicts migration of the primordial germ cells (purple dots) from the yolk sac, along the hindgut, and into the genital ridges. (b) Cross-sectional drawing through the midabdomen shows the genital ridges. There is inward extension of the proliferating mesothelium forming the primitive sex cords. The primordial germ cells are being incorporated into these developing sex cords. (c) Cross-sectional drawing of a further stage of development shows the sex cords and incorporated germ cells in the developing seminiferous tubules.
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Further development of the undifferentiated gonad into a testis requires the presence of a Y chromosome. The gene for a testis-determining factor has been localized on the short arm of the Y chromosome. Under the influence of the testis-determining factor, the primitive sex cords form the seminiferous tubules. These tubules are from two distinct cell lines: (a) those from the mesothelium are the Sertoli or supporting cells and (b) those from the migrated germ cells become the spermatogonia. The mesenchyme between the developing seminiferous tubules differentiates into the interstitial (Leydig) cells. A thick fibrous capsule, the tunica albuginea, forms along the surface of the primitive testis (Fig 1) (5,6).
At approximately 8 weeks gestational age, the Leydig cells begin to secrete testosterone. Under this hormonal influence, the mesonephric (wolffian) ducts differentiate into the epididymis, vas deferens, seminal vesicles, and ejaculatory ducts. In addition, the Sertoli cells secrete müllerian-inhibiting factor, which causes the paramesonephric (müllerian) ducts to regress. Between the 7th and 12th weeks, the testes contract and become more ovoid as they descend into the pelvis. They remain near the deep inguinal ring until the 7th month, when they begin their descent through the inguinal canal into twin scrotal sacs (5,6).
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Anatomy and Histologic Characteristics
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The adult testis consists of densely packed seminiferous tubules, which are separated by thin fibrous septa and surrounded by a fibrous capsule, the tunica albuginea. The tunica albuginea is covered by a flattened layer of mesothelium, the tunica vaginalis. The seminiferous tubules come together posteriorly to form larger ducts, the tubuli recti, which drain into the rete testis at the testicular hilum. The rete testis converges posteriorly to form 15–20 efferent ductules that penetrate through a thickened area of the tunica albuginea to form the head of the epididymis (Fig 2). This area of thickened tunica albuginea invaginates into the testis and forms the mediastinum testis. The ducts, nerves, and vessels enter and exit the testis through the mediastinum testis. Once in the epididymis, the efferent ductules converge to form a single convoluted tubule in the body and tail that exits the epididymis as the vas deferens.
In a normal adult testis, there are 200–300 lobules, each of which contains 400–600 seminiferous tubules. Each tubule is 30–80 cm long; thus, the total estimated length of all seminiferous tubules is 300–980 meters (1). As mentioned, the seminiferous tubules are composed of two cell types: germ cells and Sertoli cells. The predominant cell population is the spermatogenic germ cells in various stages of development. The spermatogonia are the first cells in spermatogenesis and lie adjacent to the basement membrane. These cells mature into spermatocytes, spermatids, and finally spermatozoa as they migrate toward the center of the tubule. The Sertoli cells are nondividing cells that extend from the basement membrane to the lumen of the tubule. They aid in spermatogenesis by providing a support structure for maturing germ cells and by removing degenerating germ cells by means of phagocytosis. The tight junctions that Sertoli cells form with one another are responsible for the blood-testis barrier (1). The space between the seminiferous tubules is the interstitium, which is derived from the mesenchyme. The interstitium includes the connective tissue, lymphatics, blood vessels, mast cells, and Leydig cells (Fig 3). Leydig cells are the principal source of testosterone production in men (1).
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Figure 3. Normal testis histologic characteristics. High-power photomicrograph (original magnification, x200; hematoxylin-eosin stain) shows seminiferous tubules lined with spermatogenic cells in various stages of development. Several Sertoli cells with pale-staining oval nuclei can also be seen (straight arrows). Within the interstitium are connective tissue, blood vessels, and scattered Leydig cells (curved arrows).
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Imaging Evaluation of the Testis
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Ultrasonography (US) is the primary imaging modality for investigating testicular lesions. It is easily performed and has been shown to be nearly 100% sensitive in the identification of scrotal masses. Intratesticular versus extratesticular pathologic conditions can be differentiated with 98%–100% sensitivity (7–9). Sonography of the scrotum should be performed with the highest frequency transducer that gives adequate penetration (5–10 MHz).
On sonograms, the normal testis has a homogeneous, medium-level, granular echotexture. The covering tunica albuginea is generally not seen as a separate structure; however, where it invaginates to form the mediastinum testis, it can be seen as an echogenic line emanating from the posterior aspect of the testis (Fig 4). The epididymis is isoechoic or slightly hyperechoic compared with the testis.
When a palpable mass is evaluated with US, the primary goal is localization of the mass (intratesticular or extratesticular) and further characterization of the lesion (cystic or solid). With rare exception, solid intratesticular masses should be considered malignant. The sonographic appearance of tumors reflects their gross morphology and underlying histologic characteristics. Most testicular tumors are hypoechoic compared with the surrounding parenchyma. Others can be heterogeneous, with areas of increased echogenicity, calcifications, and cyst formation (7–16). Larger tumors tend to be more vascular than smaller tumors; however, the use of color Doppler US to investigate suspected tumors is not particular helpful in adults (17). Color Doppler US has, however, proved to be helpful in prepubertal boys when the gray-scale findings are subtle and may help identify an isoechoic mass (18).
Since US is easily performed, inexpensive, and highly accurate, magnetic resonance (MR) imaging is seldom needed for diagnostic purposes. MR imaging can, however, be a useful problem-solving tool in the rare cases in which the results of US are inconclusive (19), and it is particularly helpful in the evaluation of cryptorchidism (20,21).
The MR imaging examination should be performed with a surface coil. These coils have superior signal-to-noise ratios that permit high-resolution imaging. With the patient supine, a towel is placed under the scrotum to raise it from between the thighs. The penis is positioned on the abdomen out of the area of interest. A second towel is draped over the scrotum, and the coil is placed on the towel. The towels should be warm to reduce scrotal muscular contractions that would degrade the images. In patients with suspected cryptorchidism, the abdomen and pelvis may also need to be evaluated. For this purpose, a head coil is employed for infants and small children and a torso coil for older boys.
We routinely obtain axial and coronal spin-echo T1-weighted images (400–600-msec repetition times, minimal 10-msec echo time, 3-mm section thickness, 0.5-mm interval, 128 x 256 matrix, and two excitations). Axial, coronal, and sagittal fast spin-echo T2-weighted images are then acquired (4,000–6,000-msec repetition times, 140-msec echo time, 3-mm section thickness, 0.5-mm interval, 256 x 256 matrix, 12–14 echo train length, two to four excitations). Superior and inferior saturation bands are applied to eliminate ghosting artifacts from blood flow along the phase-encoding axis. Although not generally needed, gadolinium contrast material can be administered to help characterize indeterminate scrotal masses (22). For staging purposes, T1-weighted axial images of the abdomen should be obtained to search for adenopathy.
The normal testis has homogeneous intermediate signal intensity on T1-weighted images and high signal intensity (slightly less than that of fluid) on T2-weighted images. The tunica albuginea appears as a thin low-signal-intensity band surrounding the testis with both pulse sequences. The internal architecture of the testis is better seen on T2-weighted images. Thin low-signal-intensity septa can be seen radiating back toward the mediastinum testis, which forms a band along the posterior margin of the testis (Fig 5). The epididymis is isointense or slightly hypointense relative to the testis on T1-weighted images and hypointense on T2-weighted images.
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Figure 5a. Normal testes. (a) T1-weighted MR image of the scrotum shows the uniform intermediate signal intensity of the testes. (b) T2-weighted fat-suppressed MR image taken at a slightly inferior plane shows the hyperintense testicular parenchyma and the well-defined hypointense tunica albuginea and mediastinum testis (arrows). There are also bilateral hydroceles (with that on the right being greater than that on the left).
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Figure 5b. Normal testes. (a) T1-weighted MR image of the scrotum shows the uniform intermediate signal intensity of the testes. (b) T2-weighted fat-suppressed MR image taken at a slightly inferior plane shows the hyperintense testicular parenchyma and the well-defined hypointense tunica albuginea and mediastinum testis (arrows). There are also bilateral hydroceles (with that on the right being greater than that on the left).
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In general, testicular tumors are isointense relative to normal testicular tissue on T1-weighted images and hypointense on T2weighted images. They can, however, be heterogeneous in signal intensity, an appearance that suggests the presence of calcifications, necrosis, or hemorrhage (23,24).
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Germ Cell Tumors
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Intratubular germ cell neoplasia is thought to be the precursor of most germ cell tumors. It is the testicular equivalent of carcinoma in situ. Fifty percent of patients with intratubular germ cell neoplasia will develop an invasive tumor in 5 years (1). The prevailing theory of development is that these abnormal cells develop either along a unipotential gonadal line and form seminoma or along a totipotential cell line and form nonseminomatous tumors. The totipotential cells may remain largely undifferentiated (embryonal carcinoma) or develop toward embryonic differentiation (teratoma) or extraembryonic differentiation (yolk sac tumors, choriocarcinoma). Because these totipotential cells can develop along several pathways at once, multiple histologic types often occur together, yielding a mixed germ cell tumor (25,26). For clinical purposes, germ cell tumors are divided into two groups: seminomatous and nonseminomatous germ cell tumors.
Patterns of Spread
Metastases can spread by both lymphatic and hematogenous routes. Direct extension through the tunica albuginea with involvement of the scrotal skin is a rare and late finding (1). Most germ cell tumors spread first via the lymphatics rather than hematogenously. A notable exception is choriocarcinoma, which has a proclivity for early hematogenous spread. Lymphatic involvement occurs in a predictable step-wise fashion. Knowledge of this well-defined pathway of lymphatic spread is the basis for modern surgical treatment. More conservative dissections of retroperitoneal lymph nodes spare the sympathetic nerves involved in emission (movement of semen into the posterior urethra) and antegrade ejaculation (3).
Testicular lymphatic drainage follows the testicular veins. For the right testis, the first-echelon nodes are in the interaortocaval chain at the second lumbar vertebral body. For the left testis, the first-echelon nodes are in the left paraaortic nodes in an area bounded by the renal vein, aorta, ureter, and inferior mesenteric artery (Fig 6). Some crossover of lymphatic involvement can occur in a right-to-left fashion following the normal drainage pattern to the cisterna chyli and thoracic duct. From the thoracic duct, tumor can spread to the left supraclavicular nodes and subsequently to the lungs. Left-to-right crossover is rare (3,27). As the volume of tumor increases, it may spread from the first-echelon nodes to involve the common, internal, and external iliac nodes. Tumor within the epididymis can spread directly to the external iliac nodes. Skin involvement may lead to direct spread to the inguinal nodes. For this reason, a transscrotal surgical approach is contraindicated. Orchiectomy, the first line treatment for all testicular tumors, is therefore performed through an inguinal approach (3).
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Figure 6a. Patterns of lymphatic tumor spread. Abdominal computed tomographic (CT) scans from two different cases demonstrate testicular metastases to the first-echelon nodes from a left-sided (a) and right-sided (b) testicular tumor.
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Figure 6b. Patterns of lymphatic tumor spread. Abdominal computed tomographic (CT) scans from two different cases demonstrate testicular metastases to the first-echelon nodes from a left-sided (a) and right-sided (b) testicular tumor.
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Distant organ metastases result from hematogenous spread. Hematogenous spread can occur late in the disease process for any germ cell tumor, but it is the primary mode of spread for choriocarcinoma. Pulmonary metastases are the most common for all germ cell tumors, followed by liver, brain, and bone metastases (28). Brain metastases are particularly common with choriocarcinoma (1). Of important note, germ cell tumor metastases may have histologic characteristics that are different than those of the primary testicular tumor, indicating the totipotential nature of the germ cells (1).
Staging
There are numerous staging systems in current use, which makes comparison of studies difficult. Many now advocate using the TNM (tumor, node, metastasis) classification set forth by the American Joint Committee on Cancer (Table 2) (29). This scheme takes into account the local extent of the tumor, lymph node size, presence of distant metastases, and serum markers. In general clinical practice, patients are often classified as having low-stage or advanced-stage disease. In low-stage disease, the tumor is confined to the testis, epididymis, or spermatic cord (T1–T3) and mild to moderate adenopathy (N1 and N2) may also be present. Advanced-stage disease includes tumors that invade the scrotal wall (T4), significant retroperitoneal adenopathy (N3), or visceral metastases (M1) (3).
Tumor Markers
Tumor markers have a well-established role in the diagnosis, staging, prognosis, and follow-up of germ cell tumors. Although there are many tumor markers that may be abnormal, only three are of clinical use: 
-fetoprotein, human chorionic gonadotropin, and, to a lesser degree, lactate dehydrogenase.
Alpha-fetoprotein is a protein produced early in gestation by the fetal liver, gastrointestinal tract, and yolk sac. Not surprisingly, the level of -fetoprotein is elevated in yolk sac tumors and mixed germ cell tumors with yolk sac elements. In rare cases, it may be elevated in teratomas with enteric mucous glands or nests of hepatoid cells. Human chorionic gonadotropin is a glycoprotein produced by the syncytiotrophoblasts of the developing placenta, and its level is elevated in tumors containing syncytiotrophoblasts (seminomas or choriocarcinomas). The levels of one or both of these tumor markers will be elevated in more than 80% of patients with nonseminomatous germ cell tumors at the time of diagnosis (1,3,30). Obtaining serial serum levels of these tumor markers helps quantify response to treatment and helps predict recurrence before it becomes radiologically evident. Lactate dehydrogenase is produced by multiple organs throughout the body and is a much less specific marker. It does, however, correlate with the bulk of the disease and is used in staging.
Seminoma
Seminoma is the most common pure germ cell tumor. It accounts for 35%–50% of all germ cell tumors. The rather large percentage ranges for both seminomas and mixed germ cell tumors stem from differences in pathologic reporting. Approximately 15% of seminomas have syncytiotrophoblasts, which has led to inconsistencies in classification. Clinically, however, the presence of syncytiotrophoblasts does not affect the overall good prognosis for patients with these tumors (25).
Seminomas, in comparison with nonseminomatous tumors, occur in a somewhat older population, with an average patient age of 40.5 years. Approximately 75% of patients present with disease limited to the testis, 20% have retroperitoneal adenopathy, and 5% have extranodal metastases (1).
Seminomas range in size from a small well-defined lesion to large masses that totally replace the testicle. At histologic analysis, the cellular morphology of seminomas resembles that of primitive germ cells. The cells are relatively uniform with clear cytoplasm and an associated lymphoid infiltrate (Fig 7).
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Figure 7. Seminoma. High-power photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows sheets of tumor cells with pale-staining cytoplasm separated by delicate stroma containing a lymphocytic infiltrate (arrows).
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The imaging characteristics of seminomas reflect their uniform cellular nature. On US images, these tumors are generally uniformly hypoechoic, and on MR images, they are homogeneously hypointense on T2-weighted images (Figs 8, 9). Larger tumors may be more heterogeneous. Seminomas can be lobulated or multinodular; however, these nodules are most commonly in continuity with one another. In rare cases, true multifocal nodules can be seen (Fig 10). Bilateral tumors are also rare, occurring in 2% of patients, and are almost always asynchronous (1).
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Figure 8a. Large seminoma. (a) Longitudinal US image of the left testis shows a homogeneously echogenic, enlarged left testis with no normal remaining parenchyma. (b) Photograph of the gross specimen shows a lobulated soft-tissue mass that completely replaces the normal testis.
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Figure 8b. Large seminoma. (a) Longitudinal US image of the left testis shows a homogeneously echogenic, enlarged left testis with no normal remaining parenchyma. (b) Photograph of the gross specimen shows a lobulated soft-tissue mass that completely replaces the normal testis.
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Figure 9a. Single small seminoma. (a) Transverse US image shows a well-marginated uniform hypoechoic mass in the posterior aspect of the testis (cursors). (b) On a T2-weighted image, the mass (arrow) is hypointense relative to the normal parenchyma. (c) Photograph of the gross specimen shows a well-circumscribed tan tumor. Scale is in centimeters.
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Figure 9b. Single small seminoma. (a) Transverse US image shows a well-marginated uniform hypoechoic mass in the posterior aspect of the testis (cursors). (b) On a T2-weighted image, the mass (arrow) is hypointense relative to the normal parenchyma. (c) Photograph of the gross specimen shows a well-circumscribed tan tumor. Scale is in centimeters.
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Figure 9c. Single small seminoma. (a) Transverse US image shows a well-marginated uniform hypoechoic mass in the posterior aspect of the testis (cursors). (b) On a T2-weighted image, the mass (arrow) is hypointense relative to the normal parenchyma. (c) Photograph of the gross specimen shows a well-circumscribed tan tumor. Scale is in centimeters.
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Figure 10a. Multifocal seminomas. (a) Longitudinal US image of the right testis shows two hypoechoic nodules within the testis (arrows). More lesions were seen in other planes. Also note multiple nonshadowing punctate calcifications scattered throughout the parenchyma. (b) Photograph of serial sections through the gross specimen shows multiple masses.
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Figure 10b. Multifocal seminomas. (a) Longitudinal US image of the right testis shows two hypoechoic nodules within the testis (arrows). More lesions were seen in other planes. Also note multiple nonshadowing punctate calcifications scattered throughout the parenchyma. (b) Photograph of serial sections through the gross specimen shows multiple masses.
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Seminoma is extremely radiosensitive, and its treatment is a true success story. Radiation therapy for low-stage tumors is very effective, resulting in a 5-year survival rate of 95%. Patients with advanced stage disease receive chemotherapy, which may be followed by radiation therapy (3).
Nonseminomatous Germ Cell Tumors
Embryonal Carcinoma.—
This tumor is composed of primitive anaplastic epithelial cells that resemble early embryonic cells. It is the second most common histologic type of testicular tumor after seminoma. Embryonal carcinoma is present in 87% of mixed germ cell tumors, although in its pure form, it accounts for only 2%–3% of all testicular tumors (1). Embryonal carcinoma occurs in a younger population than does seminoma, as it is seen most often in men aged 25–35 years. Embryonal carcinoma is often smaller than seminoma at the time of presentation but tends to be more aggressive in behavior. The tunica albuginea may be invaded, and the borders of the tumor are less distinct, often blending imperceptibly into the adjacent parenchyma. As expected, embryonal carcinomas are often more heterogeneous and ill-defined than seminomas on US images (Fig 11). Treatment for all the nonseminomatous tumors is similar and is discussed in the Mixed Germ Cell Tumor section of this article.
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Figure 11a. Embryonal carcinoma in a 23-year-old man. (a) Longitudinal US image of the left testis shows a small, irregular heterogeneous mass that forms an irregular margin with the tunica albuginea (cursors). (b) Photograph of the bivalved testis shows the tumor (arrows). (c) High-power photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a papillary tumor consisting of anaplastic cells with overlapping nuclei and ill-defined borders.
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Figure 11b. Embryonal carcinoma in a 23-year-old man. (a) Longitudinal US image of the left testis shows a small, irregular heterogeneous mass that forms an irregular margin with the tunica albuginea (cursors). (b) Photograph of the bivalved testis shows the tumor (arrows). (c) High-power photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a papillary tumor consisting of anaplastic cells with overlapping nuclei and ill-defined borders.
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Figure 11c. Embryonal carcinoma in a 23-year-old man. (a) Longitudinal US image of the left testis shows a small, irregular heterogeneous mass that forms an irregular margin with the tunica albuginea (cursors). (b) Photograph of the bivalved testis shows the tumor (arrows). (c) High-power photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a papillary tumor consisting of anaplastic cells with overlapping nuclei and ill-defined borders.
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Yolk Sac Tumor.—
The totipotential germ cells that differentiate toward extraembryonic fetal membranes give rise to yolk sac tumors, also known as endodermal sinus tumors. Yolk sac tumors account for 80% of childhood testicular tumors, with most cases occurring before the age of 2 years (21). In its pure form, yolk sac tumor is rare in adults; however, it is present in 44% of adult cases of mixed germ cell tumor. Alpha-fetoprotein is normally produced by the embryonic yolk sac, and thus serum -fetoprotein levels are elevated in greater than 90% of patients with yolk sac tumor (1). Imaging findings are nonspecific,especially in children, in whom the only finding may be testicular enlargement without a defined mass (Fig 12) (18,21).
Treatment of yolk sac tumors in adults does not differ from that of other nonseminomatous tumors. Treatment in the pediatric population is somewhat controversial. If the yolk sac tumor is confined to the testis at the time of orchiectomy (as it is in over 80% of cases) and if the serum level of -fetoprotein is not elevated, the patient can be closely monitored without further therapy and the prognosis is excellent. If relapse occurs, chemotherapy is the treatment of choice. The lungs are the most common site of recurrent disease (1,3).
Teratoma.—
After yolk sac tumor, teratoma is the second most common testicular tumor in children. Generally, teratomas occur in children less than 4 years of age. In its pure form, teratoma is rare in adults; however, teratomatous elements occur in approximately half of all adult cases of mixed germ cell tumor (1). Teratoma is a complex tumor, showing disorderly arrangement of adult and fetal tissues, with all three germ layers (endoderm, mesoderm, and ectoderm) involved (Fig 13). These tumors are subclassified into mature, immature, and those with malignant areas (1). Dermoids, which are the most common teratomatous lesion in the ovary, constitute only a small minority of testicular teratomas.
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Figure 13. Mature teratoma. Medium-power photomicrograph (original magnification, x70; hematoxylin-eosin stain) shows a cystic structure on the right lined by ciliated epithelium that resembles respiratory epithelium (arrowheads). Densely staining bone (curved arrow) and mucin-producing glandular structures (straight arrows) are also seen.
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The complex nature of this tumor is reflected in its sonographic appearance. Teratomas generally form well-circumscribed complex masses. Cysts are a common feature and may be anechoic or complex, depending on the cyst contents (ie, serous, mucoid, or keratinous fluid) (Fig 14). Care must be taken in differentiating teratomas from benign cysts within the testis. Cartilage, calcification, fibrosis, and scar formation result in echogenic foci that may or may not shadow (Fig 15).
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Figure 14a. Mature teratoma in a 22-year-old man. (a) Longitudinal US image of the right testis shows a multilocular cystic mass. The cysts vary in appearance from anechoic to echogenic. (b) Photograph of the gross specimen shows multiple cysts within the tumor.
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Figure 14b. Mature teratoma in a 22-year-old man. (a) Longitudinal US image of the right testis shows a multilocular cystic mass. The cysts vary in appearance from anechoic to echogenic. (b) Photograph of the gross specimen shows multiple cysts within the tumor.
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Figure 15a. Immature teratoma with malignant areas. (a) Transverse US image of the left testis shows a very heterogeneous, ill-defined mass with solid hyperechoic areas and small cysts. (b) Photograph of the gross specimen shows a glistening, variegated mass with areas of fibrosis and hemorrhage.
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Figure 15b. Immature teratoma with malignant areas. (a) Transverse US image of the left testis shows a very heterogeneous, ill-defined mass with solid hyperechoic areas and small cysts. (b) Photograph of the gross specimen shows a glistening, variegated mass with areas of fibrosis and hemorrhage.
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The biologic behavior of teratomas is quite variable, depending on the pubertal status of the testis. In prepubertal testes, pure teratomas are considered benign even when they are histologically immature (31,32). This benign behavior has led some investigators to recommend a testis-sparing tumor enucleation rather than orchiectomy (32). However, such conservative treatment is not an option for teratomas in postpubertal testes. Of important distinction, every element in a postpubertal testicular teratoma (mature or immature) can metastasize, irrespective of its histologic characteristic. Furthermore, the metastases may contain nonteratomatous germ cell elements. We stress that mature teratoma should not be equated with benignity (1).
It is controversial whether epidermoid cyst should be discussed with teratoma, since the histogenesis of this lesion is uncertain. Epidermoid cysts may result from monodermal development of a teratoma, or, alternatively, they may be the result of squamous metaplasia of surface mesothelium. Epidermoid cysts are composed of keratinizing, stratified, squamous epithelium with a well-defined fibrous wall. They are one of the few benign intratesticular masses and, unlike mature teratoma, have no malignant potential (1).
Epidermoid cysts constitute approximately 1% of testicular tumors. Although pathologically these lesions are true cysts, they are filled with cheesy laminated material that appears solid on radiologic images (1). The laminated morphology is often reflected in imaging studies. On US images, epidermoid cysts are well-circumscribed, round to slightly oval masses with a hyperechoic wall that is sometimes calcified. The mass may be hypoechoic, but the laminations often give rise to an "onion-skin" or ringed appearance (Fig 16) (33,34). On MR images, epidermoid cysts have a similar "target" appearance, with a low-signal-intensity capsule. The layers of keratinized material within the lesion are rich in water and lipid and appear as areas of high signal intensity on both T1- and T2-weighted images (Fig 17) (33).
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Figure 16a. Epidermoid cyst. (a) Longitudinal US image of the right testis shows a well-defined, hypoechoic mass with prominent concentric rings (arrow). (b) Photograph of the gross specimen shows laminated layers of keratinized material.
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Figure 16b. Epidermoid cyst. (a) Longitudinal US image of the right testis shows a well-defined, hypoechoic mass with prominent concentric rings (arrow). (b) Photograph of the gross specimen shows laminated layers of keratinized material.
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Figure 17a. Epidermoid cyst. (a) Transverse US image of the right testis shows a well-circumscribed lesion with a hyperechoic, partially calcified wall (arrow). (b, c) Axial T1-weighted (b) and T2-weighted (c) MR images demonstrate a laminated, "target" appearance of the lesion (arrow). (d) Photograph of the bivalved testis and mass shows the cheesy, laminated material within the cyst.
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Figure 17b. Epidermoid cyst. (a) Transverse US image of the right testis shows a well-circumscribed lesion with a hyperechoic, partially calcified wall (arrow). (b, c) Axial T1-weighted (b) and T2-weighted (c) MR images demonstrate a laminated, "target" appearance of the lesion (arrow). (d) Photograph of the bivalved testis and mass shows the cheesy, laminated material within the cyst.
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Figure 17c. Epidermoid cyst. (a) Transverse US image of the right testis shows a well-circumscribed lesion with a hyperechoic, partially calcified wall (arrow). (b, c) Axial T1-weighted (b) and T2-weighted (c) MR images demonstrate a laminated, "target" appearance of the lesion (arrow). (d) Photograph of the bivalved testis and mass shows the cheesy, laminated material within the cyst.
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Figure 17d. Epidermoid cyst. (a) Transverse US image of the right testis shows a well-circumscribed lesion with a hyperechoic, partially calcified wall (arrow). (b, c) Axial T1-weighted (b) and T2-weighted (c) MR images demonstrate a laminated, "target" appearance of the lesion (arrow). (d) Photograph of the bivalved testis and mass shows the cheesy, laminated material within the cyst.
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Although the radiologic appearance of epidermoid cysts is characteristic, it is not pathognomonic. Teratomas and other malignant tumors may have a similar appearance, and great care should be taken in evaluating the mass for any irregular borders, which would suggest a malignant lesion. Because carcinoma cannot be completely excluded, orchiectomy is usually performed. However, if the lesion has been thoroughly evaluated and if there is a strong likelihood that it is an epidermoid cyst, some investigators have suggested performing a testis-sparing enucleation rather than orchiectomy (33,35).
Choriocarcinoma.—
Choriocarcinoma is a rare germ cell tumor. In its pure form, it is seen in less than 1% of patients, but it occurs in mixed germ cell tumors in 8% of cases. It develops in patients in the 2nd and 3rd decades of life and is a highly malignant tumor composed of an admixture of cytotrophoblastic and syncytiotrophoblastic cells. Often, there is early widespread metastasis, and patients may present with symptoms referable to their metastases rather than a palpable testicular mass. Sites of metastases include the lung, liver, gastrointestinal tract, and brain (1). The primary tumor and metastases are often hemorrhagic. The levels of human chorionic gonadotropin are elevated and cause gynecomastia in 10% of cases (Fig 18). Choriocarcinoma has the worst prognosis of any of the germ cell tumors, with death usually occurring within 1 year of diagnosis (31). Patients with mixed germ cell tumors with choriocarcinoma fair better than those with pure choriocarcinoma tumors, but a very high level of human chorionic gonadotropin (>50,000 IU/L) portends a poor prognosis with a 5-year survival rate of 48% (3).
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Figure 18a. Metastatic choriocarcinoma. (a) Longitudinal US image shows an isoechoic mass in the inferior pole of the right testis (cursors). It appears to invade the tunica albuginea. (b) High-power photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows pale-staining cytotrophoblasts (C) surrounded by syncytiotrophoblasts (arrows) along the advancing edge. (c) Chest CT scan (lung windows) shows multiple pulmonary nodules. Gynecomastia is also noted. (d) Unenhanced brain CT scan shows a hemorrhagic metastasis with surrounding edema (arrow).
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Figure 18b. Metastatic choriocarcinoma. (a) Longitudinal US image shows an isoechoic mass in the inferior pole of the right testis (cursors). It appears to invade the tunica albuginea. (b) High-power photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows pale-staining cytotrophoblasts (C) surrounded by syncytiotrophoblasts (arrows) along the advancing edge. (c) Chest CT scan (lung windows) shows multiple pulmonary nodules. Gynecomastia is also noted. (d) Unenhanced brain CT scan shows a hemorrhagic metastasis with surrounding edema (arrow).
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Figure 18c. Metastatic choriocarcinoma. (a) Longitudinal US image shows an isoechoic mass in the inferior pole of the right testis (cursors). It appears to invade the tunica albuginea. (b) High-power photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows pale-staining cytotrophoblasts (C) surrounded by syncytiotrophoblasts (arrows) along the advancing edge. (c) Chest CT scan (lung windows) shows multiple pulmonary nodules. Gynecomastia is also noted. (d) Unenhanced brain CT scan shows a hemorrhagic metastasis with surrounding edema (arrow).
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Figure 18d. Metastatic choriocarcinoma. (a) Longitudinal US image shows an isoechoic mass in the inferior pole of the right testis (cursors). It appears to invade the tunica albuginea. (b) High-power photomicrograph (original magnification, x100; hematoxylin-eosin | |
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Abstract
LEARNING OBJECTIVES FOR TEST...
