Normal Development and Anatomy

Until the seventh week of gestation, the embryos of both sexes undergo identical development. During this time, genital ridges form on both sides of the midline. These ridges are composed of mesenchyme, and extend from the sixth thoracic to the second sacral segments. They are covered by proliferating mesothelium that subsequently forms the primitive sex cords. The primordial germ cells that form in the wall of the yolk sac migrate along the hindgut and dorsal mesenteric root into the genital ridge.

Under the influence of testis-determining factor (encoded by the Y chromosome), the primitive “indifferent” gonad begins to form testicular elements beginning at 42 to 44 days of gestation. Sertoli cells that are derived from coelomic epithelium aggregate around the germ cells in the form of “sex cords.” The primitive sex cords form the seminiferous tubules. Therefore, the seminiferous tubules contain elements from 2 distinct cell lines. The mesothelium gives rise to the Sertoli or supporting cells, whereas the germ cells become the spermatogonia. The mesenchyme between the seminiferous tubules differentiates into the Leydig (interstitial) cells. Testicular descent into the pelvis occurs between the 7th and 12th weeks, and descent through the inguinal canal begins at approximately 36 weeks.¹

Under the influence of testosterone secreted by the Leydig cells, the embryonic mesonephric ducts differentiate into the epididymis, vas deferens, seminal vesicles, and ejaculatory ducts. The mesonephros is a common factor in renal and internal genital organ development, and alterations during this early phase of embryogenesis likely account for combined anomalies of these structures. The Sertoli cells secrete Müllerian inhibiting factor, which causes the paramesonephric ducts (Müllerian ducts) to regress. Normal rudimentary structures derived from the paramesonephric ducts include the appendix testis and the prostatic utricle.^2,3

The testis consists of seminiferous tubules separated by thin fibrous septa. The tunica albuginea is a dense fibrous capsule that surrounds the testis. The tunica vaginalis is a flattened layer of mesothelium that covers the tunica albuginea. The seminiferous tubules coalesce posteriorly to form larger ducts (the tubuli recti), which drain into the rete testis. The rete testis forms efferent ductules that penetrate through a thickened area of the tunica albuginea to form the head of the epididymis. Within the epididymis, the ductules converge to form a single tubule that exits the epididymis as the vas deferens. The thickened portion of the tunica albuginea at the head of the epididymis invaginates into the testis to form the mediastinum testis, which is the site of entry for the testicular ducts, nerves, and vessels. The Sertoli cells aid spermatogenesis by providing a support structure for maturing germ cells and by facilitating phagocytic removal of degenerating germ cells. The space between the seminiferous tubules consists of connective tissue, lymphatics, blood vessels, mast cells, and Leydig cells. The Leydig cells are the principal source of testosterone production.

With sonography, the normal testis has moderate echogenicity and a homogeneous slightly granular echotexture (Figure 54-1). The mediastinum testis appears as an echogenic line that emanates from the posterior aspect of the testis. The epididymis usually has equal or slightly greater echogenicity than that of the testis.

With MRI, the normal testis has homogeneous intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images. The tunica albuginea appears as a low-signal intensity band surrounding the testis. The mediastinum testis forms a low-signal intensity band along the posterior margin of the testis. The epididymis is isointense or mildly hypointense on T1-weighted images, and hypointense to the testis on T2-weighted images. The normal testis measures approximately 15 mm in length at birth, 20 mm at 4 to 10 years of age, 30 mm at 12 to 13 years, and 40 mm in teenagers.

The appendix testis is a vestigial remnant of the mesonephric and Müllerian duct systems. When outlined by fluid in the tunica vaginalis, the appendix testis is visible as a small nodule arising from the surface of the upper pole of the testis in the groove between the testis and the head of the epididymis (see Figure 54-28). The normal appendix testis is 1 to 7 mm in diameter and has an oval or pedunculated configuration. The appendix epididymis is attached to the head of the epididymis; it is not identifiable on imaging studies unless pathologically enlarged.

The testicular artery enters the posterosuperior aspect of the testis, where it divides into branches along the testicular surface. This vascular layer of capsular arteries is the tunica vasculosa. Vessels from the tunica vasculosa extend into the mediastinum, and then into the testicular parenchyma in a linear fashion. These normal intratesticular vessels are visible on longitudinal color Doppler images as multiple parallel linear vascular structures (Figure 54-2). In about half of normal individuals, 1 or more transmediastinal arteries enter the mediastinum and course through the gland. A transmediastinal artery appears as a hypoechoic linear band on grayscale images and has arterial characteristics on color Doppler. Normal intratesticular arteries have low-impedance waveforms on spectral Doppler analysis, with prominent end-diastolic flow velocity (Figure 54-3).

Congenital Anomalies

Testis

Testicular Exstrophy

Congenital extrusion of 1 or both testes outside the scrotum is 1 of the rarest testicular anomalies. This clinically obvious condition does not require imaging studies for diagnosis. Sonography of the urinary system is usually indicated for these infants to detect additional anomalies.^4,5

Transverse Testicular Ectopia

Transverse (or crossed) testicular ectopia refers to the presence of both testes in 1 side of the scrotum, each with an intact ipsilateral blood supply, epididymis, and vas. The ectopic gonad is located in the same canal as the normally descended testis. This is an uncommon malformation.⁶ The most frequent associated anomalies are inguinal hernias (98%) and persistent Müllerian duct syndrome (30%) (i.e., persistence of Müllerian duct structures, such as the uterus, fallopian tubes, and upper two-thirds of vagina, in otherwise normally virilized males). Transverse testicular ectopia should be considered as a possibility when there is a unilateral inguinal hernia that is associated with a nonpalpable contralateral testis. Sonography confirms the testicular anatomy.⁷

Retractile Testes

Retractile, or migratory, testes are common during childhood. Most children with this finding are between 2 and 7 years of age. An otherwise normal testis slides back and forth through the external inguinal ring, between the scrotum and the distal aspect of the inguinal canal. Forceful cremaster contraction is the usual mechanism for retraction. Return to the scrotum occurs after muscle relaxation or manual manipulation. Testicular retraction usually resolves spontaneously by puberty. Surgical treatment is rarely required. This typically self-limited abnormality needs to be differentiated clinically and radiographically from true cryptorchidism. Real-time sonography is particularly helpful. Gentle manipulation of the testis with the ultrasound transducer during real-time observation often induces retraction and reduction in children with retractile testes.⁸

Cryptorchidism

Cryptorchidism, or undescended testis, refers to a testis that is located outside of the scrotum. The anomalous location is typically along the normal path of developmental testicular descent. The frequency of this abnormality is inversely proportional to the birth weight of the infant. Cryptorchidism occurs in approximately 3% of term infants, 30% of premature infants, 70% of infants less than 1800 g, and 100% of infants less than 900 g.^9,10 Because spontaneous correction occurs in most children, the frequency of undescended testis decreases to below 1% by the age of 1 year. There is a fourfold increased risk for cryptorchidism in the sibling of an affected child; most evidence points to a multifactorial mode of inheritance. There is an increased frequency of urinary tract anomalies (e.g., renal agenesis, ectopic kidney, ureteropelvic junction obstruction, and hypospadias) and congenital anomalies of the central nervous system in patients with cryptorchidism.¹¹ Cryptorchidism, sometimes bilateral, occurs in approximately 12% of children with posterior urethral valves.^12–16

Normal development and maturation of the testis requires an intrascrotal location. Cryptorchidism can lead to infertility. It is also associated with an increased risk of testicular cancer, most commonly seminoma. The clinical presentation of testicular malignancy in these patients is usually after puberty. The incidence of testicular malignancy in an undescended testis is up to 48 times as high as that of a normal testis.¹⁰ Malignancy is approximately 4 times more common with an intra-abdominal testis than with an inguinal testis.¹⁷ In patients with unilateral cryptorchidism, the normal contralateral testis is also at increased risk for malignancy. In addition, patients with surgically corrected cryptorchidism remain at increased risk for testicular cancer. The possibility of malignant degeneration should be considered when an undescended testis is enlarged or irregular. Germ cell tumors and torsion have also been reported in intra-abdominal testes.^18,19

The classification of undescended testis is as follows: (1) prescrotal retention—the testis is located in the superior aspect of the scrotum, below the inguinal canal and above the scrotal pouch. Prescrotal retention is the most common type of cryptorchidism. (2) Inguinal retention (canalicular testis)—the testis rests within the inguinal canal, between the internal and external rings. (3) Intra-Abdominal retention—the testis is within the retroperitoneum, between the lower pole of the kidney and the internal inguinal ring. The most common location on an intra-abdominal testis is adjacent to the internal inguinal ring, posterior to the abdominal wall muscles and adjacent to the iliac vessels. (4) Ectopic testis—the testis is in a location outside of the pathway of descent into the scrotum. The most common locations of ectopic testis are the perineum, femoral canal, superficial inguinal pouch, suprapubic area, and the contralateral scrotal pouch.

Physical examination of the child with cryptorchidism demonstrates a hypoplastic, empty scrotum. The undescended testis may be palpable in the inguinal canal or in a prescrotal location; however, up to 30% of cryptorchid testes are nonpalpable. In those with cryptorchidism and no palpable testes, the location is within the inguinal canal in approximately 80% and intra-abdominal in 20%. A relatively mild form of cryptorchidism is termed a “gliding testis,” in which a testis can be pushed into the scrotum by external manipulation, but retracts into the inguinal canal when released. In those with unilateral cryptorchidism, the right testicle is affected twice as often as the left. About one-fourth of patients with cryptorchidism have bilateral involvement.

A palpable mass in the inguinal canal of a patient with an empty scrotum needs to be differentiated from a lymph node or hernia. In addition to cryptorchidism, the differential diagnosis in a child with an empty scrotum and no palpable testis includes agenesis of the testis and testicular ectopia. In prepubertal boys, clinical differentiation between bilateral cryptorchidism and bilateral testicular agenesis can be achieved with measurement of serum Müllerian inhibiting substance (anti-Müllerian hormone).^20–25

The initial imaging modality for the evaluation of a child with suspected cryptorchidism is sonography. If the findings are equivocal or the testis cannot be located with sonography, MRI or CT can be performed. MRI offers the advantage of a lack of ionizing radiation, and is reported to have an accuracy of 94% for locating undescended testes.²⁶ CT is of approximately equal sensitivity to sonography and MRI for the detection of a testis within the inguinal canal, and is the superior technique for the demonstration of an intra-abdominal location.^24,27 Many patients with cryptorchidism, particularly those with a suspected intra-abdominal testis, are evaluated with laparoscopy.

With sonography, an undescended testis is oval, has a homogeneous echotexture, and is isoechoic to the normal intrascrotal testis (Figure 54-4). A testis in the inguinal canal is hypoechoic relative to subcutaneous fat. With high-resolution imaging, the mediastinum testis can frequently be visualized as a hyperechoic thin intratesticular band; this is an important characterizing feature (Figure 54-5). The undescended testis frequently is mildly hypoplastic, particularly if first discovered in an older child.

An inguinal lymph node can mimic an undescended testis. Most often, a node can be differentiated from a testis by observation of the shape, lack of a mediastinum testis, and lower echogenicity than that of a testis. Color Doppler imaging also helps by demonstrating typical hilar blood flow in a lymph node (Figure 54-6). Intra-Abdominal structures bulging into an inguinal hernia can be differentiated by observing motion with the Valsalva maneuver, lack of the homogeneous hypoechoic appearance of a testis, and visualization of peristalsis or gas in herniated bowel. If a testis cannot be identified in the scrotum or inguinal canal, the sonographic examination should be extended to evaluate the lower abdomen and pelvis adjacent to the internal inguinal ring, as well as the suprapubic, perineal, and femoral areas.

MRI demonstrates an undescended testis as an oval or round structure that is of intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images (Figure 54-7). An undescended testis in the inguinal canal usually has an oval configuration, whereas a more rounded shape typically occurs with an intra-abdominal location. The mediastinum testis produces a low-signal intensity internal stripe. Visualization of the mediastinum testis is helpful in the differentiation from inguinal lymph nodes, which have similar signal intensities as a testes. In addition, lymph nodes tend to be located inferior to the inguinal ligament or adjacent to the femoral or iliac vessels.

The inguinal canal is an important anatomic landmark for the localization of an undescended testis. Often, the ductus deferens and testicular vessels can be traced within the spermatic cord to the level of the undescended testis. The ductus rarely extends caudal to the undescended testis. However, when the undescended testis is located proximal to the external inguinal ring, an empty spermatic cord may be seen as a thin structure extending to the scrotum.

The gubernaculum is sometimes visible on MR imaging of patients with an undescended testis. The pars infravaginalis gubernaculum is the distal bulbous termination of the gubernaculum. It is always located caudal to the undescended testis. The gubernaculum is a gelatinous cord-like structure that guides the testis during descent in fetal life. It normally atrophies after the testis descends completely. With cryptorchidism, the gubernaculum persists as a fibrotic remnant. Although both the gubernaculum and the testis produce low signal intensity on T1-weighted images, the gubernaculum is hypointense on T2-weighted images and does not have the linear internal band that is usually visible in a testis (due to the mediastinum testes).²⁸

Testicular regression refers to an undescended testis that is composed of fibrous scar, with hemosiderin deposition and calcification. MRI shows an atrophic cord that approaches the base of an empty scrotum. Remnant cord structures and a fibrotic nodule containing hemosiderin and calcification are demonstrated on T2-weighted images as irregular tissue of low signal intensity.

CT demonstrates an undescended testis as a round or oval soft tissue attenuation mass somewhere along the course of testicular descent. As with MRI and sonography, differentiation from inguinal lymph nodes is important. The attenuation values and enhancement characteristics do not allow differentiation. However, lymph nodes are located outside the spermatic cord, and most are inferior to the inguinal ligament. An intra-abdominal testis may be difficult to differentiate from a lymph node, fluid-filled bowel, or other normal structure. The absence of a normal spermatic cord in the ipsilateral inguinal canal is an important characteristic of cryptorchidism that can frequently be observed with CT. An infarcted intra-abdominal testis may be demonstrated on CT as a calcified mass. The gubernaculum is sometimes visible as a linear soft-tissue attenuation structure inferior to an inguinal testis (Figure 54-8).

Testicular venography can be used in the evaluation of patients with suspected intra-abdominal cryptorchidism; however, it is rarely indicated because of the availability of laparoscopy and modern cross-sectional imaging techniques. Accurate localization of the testicle is possible if the testicular parenchyma is visualized on venography. If the testicle itself is not visible, opacification of the pampiniform plexus indicates that the testis is likely to be present. If there is a blind-ending testicular vein, the testis is usually absent. In a significant minority of patients, the examination is technically unsuccessful, due to failure of identification of the origin of the testicular vein or the presence of valves that interfere with retrograde opacification of the vein.^29,30

Spontaneous descent of a cryptorchid testis is common. Orchidopexy is usually reserved for children with persistent cryptorchidism between 6 and 15 months of age; there is a substantial risk of germ cell neoplasia after this age. The lifetime risk of developing testicular cancer in men with a history of cryptorchidism is 3% to 5%. This compares with an approximate risk of 0.3% to 0.7% for men in the general population, varying somewhat with race, nationality, and genetic profile.^20–22,31

Splenic-Gonadal Fusion

Cryptorchidism is frequently present in patients with splenic-gonadal fusion. This anomaly is related to the close proximity during weeks 6 to 8 of embryogenesis of the developing left gonad to the left dorsal mesogastrium from which the spleen forms. As the left gonad subsequently descends, a small focus of splenic tissue may accompany the gonad, resulting in an aberrant focus of splenic tissue. Sometimes, a band of tissue extends from the normal spleen to the gonad. Despite the left-sided nature of this anomaly, some males with splenic-gonadal fusion have bilateral cryptorchidism.³²

Splenic-gonadal fusion is 9 times more common in males than in females. Other developmental anomalies occur in up to 20% of these patients: micromastia, limb defects, congenital heart disease, imperforate anus, spina bifida, diaphragmatic hernia, and hypospadias. These associations presumably reflect shared temporal patterns of development during embryogenesis. Splenicgonadal fusion is frequently asymptomatic and is discovered incidentally during gonadal surgery. Affected males occasionally report pain. In some patients with splenicgonadal fusion, the diagnosis is suggested by visualization of a “tail” between the spleen and the left gonad on sulfur colloid scintigraphy. The splenic focus adjacent to the gonad may also be visualized with scintigraphy, if it is of sufficient size.^33–35

Agenesis and Hypoplasia

Absence of 1 or both testes in otherwise normal phenotypic males is identified in up to 35% of patients evaluated for a nonpalpable testis.^36,37 Potential causes of an absent testis are fetal torsion, an in utero vascular insult, and true agenesis. Unilateral testicular agenesis (monorchidism) sometimes occurs as a familial process or in association with chromosome 18q syndrome. Bilateral testicular agenesis (anorchidism) is a component of chromosome 46,XY gonadal dysgenesis.

A hypoplastic (rudimentary) testis in an otherwise normal individual is nearly always unilateral. Bilateral testicular hypoplasia can be familial and is sometimes identified in association with micropenis. Syndromes that are associated with hypoplastic or dysplastic testes include the chromosomal syndromes XXXY, XXYY, and 18p, chromosome XY gonadal dysgenesis, Klinefelter syndrome, and Denys-Dash syndrome.

Polyorchidism

Polyorchidism is a very rare congenital lesion.³⁸ The super-numerary testis is in the scrotum in approximately 75% of these patients, in the inguinal canal in 20%, and in the retroperitoneum in 5%. Approximately 5% of instances of polyorchidism are bilateral. The most common pattern is a duplicated or bifid testis that is surrounded by a single tunical albuginea and is served by a single epididymis and a single vas deferens. Less commonly, there is complete duplication of the testis, epididymis, and vas. The clinical presentation of polyorchidism is that of an apparent scrotal mass by palpation.

The patient with a palpable scrotal or testicular mass is usually evaluated with sonography. Polyorchidism is indicated by a bifid appearance of the testis or the presence of 2 structures that have the echo character of testicular tissue. The 2 components may be symmetric or 1 may be dominant. The status of the epididymis-ductus deferens complex should also be evaluated. Patients with polyorchidism are also effectively imaged with MR; T2-weighted images are usually most beneficial for demonstrating testicular anatomy.^39–42

Cystic Dysplasia of the Testes

Cystic dysplasia is a benign congenital cystic lesion of the testis that is distinct from acquired cystic ectasia of the rete testis that occurs in adults. The lesion is characterized by multiple irregular cystic spaces in the mediastinum of the testis. The pathogenesis likely involves an early insult of mesonephric duct development; this lesion is often associated with ipsilateral abnormalities of the Wolffian duct and ureter. Cystic dysplasia is in the differential diagnosis of a testicular cyst in an infant or child (Table 54-6). Congenital cystic dysplasia is associated with ipsilateral renal agenesis and renal dysplasia. Most patients present with otherwise asymptomatic scrotal swelling.⁴³

Sonography of cystic dysplasia shows multiple anechoic cysts extending out from the mediastinum testis into the testicular parenchyma. There are usually manifestations of pressure atrophy of the parenchyma. Typically, the cysts are small (2 to 3 mm) and variable in size. The lesion frequently has a multilobulated configuration and is located in the region of the rete testis. The normal rete testis is demonstrated on sonography as an echogenic structure extending from the mediastinum testis to the epididymal head. The ipsilateral kidney may be absent or dysplastic.^44–46

Adrenal Rest

Aberrant adrenocortical cells in the testis can enlarge in response to high levels of circulating adrenocortical hormone. This can occur in association with congenital adrenal hyperplasia, Addison disease, Cushing syndrome, and adrenogenital syndrome. Adrenal rests secrete cortisol and diminish in size with the administration of prednisone. On sonography, an adrenal rest appears as a small hypoechoic mass; fibrosis may produce areas of increased echogenicity. The lesions are usually located adjacent to the mediastinum testis. Most often (at least 80%), there are multiple and bilateral foci. There is considerable overlap in the histologic findings of adrenal rest and Leydig cell tumor. Features that favor the former include bilaterality, shrinkage in response to steroid therapy, and absence of Reinke crystals.^47–51

Prostate

Prostatic Utricle

The normal prostatic utricle is a rudimentary embryological remnant that is located in the midline of the prostate and communicates with the posterior urethra at the level of the midportion of the verumontanum. The superior aspect of the prostatic utricle is a remnant of the Müllerian duct, whereas the caudal portion arises from the Müllerian duct, Wolffian duct, and epithelium of the urogenital sinus.

The prostatic utricle is a relatively large structure during early embryonic development, and normally undergoes subsequent involution in males. Persistence of a prominent utricle is likely related to local hormonal effects, such as deficiency of 5 α-reductase. Involution of the Müllerian structures, including the prostatic utricle, is induced by Müllerian inhibitory factor, which is secreted by cells in the developing testes beginning at approximately 8 weeks of gestational age. Male children who were not exposed to normal levels of Müllerian inhibitory factor in utero have a spectrum of genital developmental characteristics that ranges from normal to pseudohermaphroditism. There is an increased prevalence of prostatic utricle enlargement in patients with hypospadias. Other associated anomalies are ambiguous genitalia, cryptorchidism, and congenital urethral polyp. Many individuals with a small remnant prostatic utricle have otherwise normal genitourinary anatomy.

A congenitally enlarged prostatic utricle is also termed utriculus masculinus or utricle cyst. If there is an attached cervix or uterus, it is termed a vagina masculina. An enlarged prostatic utricle is usually asymptomatic. Occasional patients suffer persistent or recurrent urinary tract infections. Postvoid dribbling can occur if urine refluxes into the cyst during micturition.

A dilated prostatic utricle is demonstrated on urethrography as a dorsal midline tubular structure that communicates with the posterior urethra (see Figure 44-62 in Chapter 44). The cranial end has a rounded, dome shape. In patients with ambiguous genitalia, there may be a cervical indentation on the “fundus” of the utricle; the anomaly is then considered a vagina masculina. The neck of a prostatic utricle as it enters the urethra is thin. Prostatic utricle can sometimes be appreciated on sonography as a cystic structure in the prostate or posterior to the bladder (Figure 54-9). A perineal approach sometimes facilitates the sonographic visualization of a small lesion. Rarely, imaging studies show a calculus in the cavity. A Müllerian duct cyst has a similar imaging appearance as prostatic utricle, although the latter more often is associated with hypospadias or another anomaly of the external genitalia.^52–54

The morphology of prostatic utricle can be categorized according to a grading system. Grades 0 to II open in the center of the verumontanum, whereas the rare grade III lesion opens into the bulbous urethra. Grade 0 does not extend above the verumontanum, grade I extends above the verumontanum, but below the bladder neck, and grade II extends superior to the bladder neck.⁵⁵

Müllerian Duct Cyst

Müllerian duct cyst is a congenital unilocular midline cyst that is located along the base of the prostate. The embryological basis of this anomaly apparently involves accumulation of secretions in a remnant of the Müllerian duct. This anomaly is anatomically and embryologically distinct from a congenitally enlarged prostatic utricle, although the imaging features are similar. Unlike prostatic utricle, there is no association between Müllerian duct cyst and other genitourinary anomalies. As with other prostatic cysts, a large Müllerian duct cyst can cause bladder outlet obstruction. Müllerian duct cyst is best demonstrated with sonography or MR. The cyst usually extends cephalad to the prostate gland. Only rarely does the lesion communicate with the urethra to allow visualization during urethrography. Although most often located in the prostate, a Müllerian duct cyst can occur anywhere along the path of Müllerian duct regression, from the scrotum to the utricle.^52,56–58

Seminal Vesicles

Agenesis, Duplication, and Ectopia

The embryonic seminal vesicles arise as outpouchings from the Wolffian ducts at approximately 13 weeks gestation. The anterior ends of the Wolffian ducts later dilate to form the ampulla of the vas deferens. Seminal vesicle agenesis can be unilateral or bilateral. Unilateral agenesis may occur in association with ipsilateral renal agenesis or congenital absence of the vas deferens. Seminal vesical duplication can also occur. Ectopia of the seminal vesicle is sometimes associated with ipsilateral renal agenesis or with an ipsilateral ectopic ureter that enters a common duct that drains both the ureter and the seminal vesicle. The diagnosis of seminal vesicle agenesis, duplication, or ectopia can usually be established with CT or MR.

Congenital Cyst

A congenital seminal vesicle cyst is lined by stratified or low cuboidal epithelium. The fluid component contains spermatozoa, leukocytes, erythrocytes, and epithelial cells. Congenital seminal vesicle cyst can occur in otherwise normal patients, but there is often an associated ipsilateral urinary tract anomaly such as renal agenesis, renal dysgenesis, blind-ending ureter, or (rarely) polycystic kidney disease.^59,60 The most common embryological mechanism is failure of development of the ureteric bud (hence the association with renal agenesis), which in turn causes maldevelopment of the mesonephric duct, atresia of the ejaculatory duct, and cyst formation due to seminal vesicle obstruction. Patients with agenesis of the vas deferens sometimes have cystic changes in the ipsilateral seminal vesicle. A small cyst is usually asymptomatic. A large cyst or multiple smaller cysts can result in urinary frequency, voiding dysfunction, recurrent epididymitis, or hemospermia.⁶¹

Most congenital seminal vesicle cysts are detectable with sonography. The lesion usually has well-defined walls and anechoic contents (Figure 54-10). Larger cysts can also be demonstrated on CT and MR. Hemorrhage within a seminal vesicle cyst can lead to a hyperintense character on T1-weighted MR. A complete imaging evaluation of the remainder of the urinary tract is required for these patients to detect associated anomalies.^62–64

Vas Deferens

Agenesis

Agenesis of the vas deferens, while a congenital lesion, is usually not discovered until adult life. The patient may present with infertility or a reduced volume of ejaculate. Congenital absence of the vas deferens is bilateral in approximately 80% of affected individuals, and approximately 80% of those with bilateral involvement have a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. These mutations are much less common in patients with unilateral absence of the vas deferens. Patients with bilateral or unilateral congenital absence of the vas deferens often have associated genitourinary system anomalies, such as renal agenesis, ectopic kidney, horseshoe kidney, multicystic dysplastic kidney, or polycystic kidneys. A rare combination of vas deferens agenesis, renal agenesis, ureteral ectopia into a cystic seminal vesicle, and hemivertebra has been reported.⁶⁵

Persisting Mesonephric Duct

Persisting mesonephric duct (“congenital vasoureteral communication”) is a rare anomaly in which the vas deferens joins with the distal portion of the ureter. The resulting common channel (i.e., the persisting mesonephric duct) drains into the bladder or posterior urethra; the most common site is at the base of the bladder. The anomaly can be unilateral or bilateral. The ipsilateral kidney is hypoplastic or dysplastic and there is aplasia of the ipsilateral seminal vesicle. Other potential associated anomalies include ureteral obstruction, ureteropelvic junction obstruction, hypospadias, urethral duplication, ectopic kidney, and anorectal malformations. Voiding cystourethrography in patients with persisting mesonephric duct usually demonstrates ipsilateral vesicoureteral reflux. The diagnosis is established by noting reflux into the vas deferens.^66–68

Extratesticular Scrotal Fluid Collections

Hydrocele

Hydrocele is the most common cause of scrotal enlargement. A hydrocele is an abnormal accumulation of fluid between the parietal and visceral layers of the tunica vaginalis testis. The lesion can be unilateral or bilateral. The fluid usually collects anterior and lateral to the testis, due to the posterior attachment of the testis to the epididymis and scrotal wall. The fluid in a hydrocele may be simple (serous) or complex (e.g., hematocele or pyocele). Simple hydroceles are anechoic on sonography; some contain low-level echoes due to fibrin bodies or cholesterol crystals. Complex hydroceles contain internal echoes and septations (Figure 54-11). A chronic lesion may calcify.

Hydroceles are congenital or acquired, and communicating or noncommunicating. Most congenital hydroceles are communicating. A reactive or acquired hydrocele results from passage of fluid into the tunica vaginalis and/or impaired fluid absorption, and is noncommunicating. Common causes of an acquired hydrocele are an adjacent inflammatory process, trauma, testicular torsion, and neoplasm.

A congenital hydrocele is due to failure of normal closure of the process vaginalis. Serous fluid from the peritoneal cavity accumulates within the scrotum. This is termed a communicating hydrocele (Figure 54-12). Approximately 6% of full-term male infants have a congenital hydrocele, and 90% of infantile hydroceles resolve spontaneously, most often by 1.5 years of age. The great majority of individuals with a patent process vaginalis do not develop clinically identifiable hydroceles, however. The process vaginalis is open in more than 80% of infants at birth; patency persists in 15% to 30% of adults. Spontaneous closure of the process vaginalis is most common in the first year of life, but occasionally occurs much later.⁶⁹

Congenital hydroceles can be classified according to the location: scrotal, spermatic cord, inguinal-scrotal, and abdominal-scrotal. Retained loculated fluid within 1 or more unobliterated segments of the process vaginalis is termed a spermatic cord hydrocele.⁷⁰

Abdominoscrotal Hydrocele

Abdominoscrotal hydrocele is an uncommon type of congenital hydrocele, in which an encysted fluid collection of the scrotum and inguinal canal bulges into the peritoneal cavity via the deep inguinal ring. Cryptorchidism can occur in association with this lesion. Abdominoscrotal hydrocele can be confused clinically with an indirect inguinal hernia. Hydronephrosis and lower extremity edema can occur due to mass effect. Imaging with sonography, CT, or MRI shows a cystic, dumbbell-shaped mass with a thin well-defined capsule. The mass occupies the scrotum and inguinal canal, and bulges into the peritoneal cavity.^71–73

Spermatic Cord Hydrocele

A spermatic cord hydrocele is a loculated fluid collection in the inguinal canal due to failure of obliteration of 1 or more segments of the process vaginalis. The lesion is usually located near the inguinal ring. The most common form of spermatic cord hydrocele is the encysted hydrocele, which is a cyst of the inguinal canal that does not communicate with the peritoneum or the tunica vaginalis. The much less common funiculocele (funicular hydrocele) is a spermatic cord hydrocele that communicates with the peritoneum at the internal inguinal ring.

With sonography, a spermatic cord hydrocele is anechoic and is associated with the spermatic cord. There is a well-defined wall (Figure 54-13). When the cyst abuts the testis, it can “cap” the testis, but does not surround it; this allows differentiation from the more common intrascrotal hydrocele. Differentiation from an epididymal cyst or spermatocele can be achieved if the mass is shown to be extrinsic to the epididymis.^74,75

Hematocele

A hematocele is an accumulation of blood between the parietal and visceral layers of the tunica vaginalis. This most often occurs due to trauma, but can also be identified with testicular torsion, infarct, and neoplasm. With sonography, the hemorrhagic nature of the fluid can usually be appreciated as fine internal echoes, although an anechoic appearance similar to that of a hydrocele is sometimes encountered. If the hematocele is long-standing, irregular thick septations may be present. The MRI appearance of a hematocele varies according to the age of the hemorrhage. An acute lesion has relatively low signal intensity on T1-weighted images and a subacute lesion has high signal intensity.

Pyocele

An accumulation of infected fluid between the layers of the tunica vaginalis is termed a pyocele. The clinical presentation includes scrotal swelling and redness, in a patient with pain, fever, and leukocytosis. Imaging studies demonstrate a complex fluid collection, with multiple septations. Debris is usually demonstrable within the fluid. On MRI, the fluid of a pyocele produces higher signal intensity on T1-weighted images than does the clear fluid on a hydrocele. Likewise, the attenuation value of the fluid on CT is higher than that of clear fluid. MR or CT with contrast shows inflammatory enhancement. The scrotal wall is thickened.¹⁰

Spermatocele

A spermatocele is a retention cyst of the small tubules that connect the rete testes to the head of the epididymis. This is usually an acquired lesion that develops in association with pathology that obstructs the sperm pathway, such as epididymitis.⁷⁶ A spermatocele presents as a painless cystic mass in the region of the head of the epididymis. Acute symptoms may occur in the rare instance of torsion of a spermatocele.⁷⁷ The lesion is lined by epithelium and is filled with fluid that contains cellular debris, dead spermatozoa, and lipids.

Epididymal Cyst

A cyst of the epididymis can be a simple cyst that contains clear fluid or a spermatocele that contains cellular debris and fat globules. Spermatoceles tend to be located in the epididymal head, whereas simple cysts can arise anywhere in the epididymis. Epididymal cyst occurs in approximately 5% of normal males, and is often a congenital lesion. In utero exposure to diethylstilbestrol is associated with increased incidence of epididymal cyst. Other reported genitourinary malformations in male infants related to diethylstilbestrol exposure include microphallus, cryptorchidism, and testicular hypoplasia. In some patients, epididymal cyst is acquired due to a prior episode of trauma or epididymitis.⁷⁸

The differential diagnosis of a cystic mass in the region of the epididymis includes spermatocele, loculated hydrocele, and epididymal cyst. If the cyst is large, the imaging findings and clinical examination may not allow differentiation between these lesions. Sonography usually shows a well-defined anechoic cyst, sometimes with loculations (Figure 54-14). The extratesticular location and cystic composition are easily documented with sonography (Figure 54-15). Differentiation from a hydrocele is straightforward, in that a hydrocele surrounds the testis, whereas spermatocele, loculated hydrocele, and epididymal cyst abut the testis and cause inferior displacement (Table 54-1).

Inguinal Hernia

Most pediatric inguinal hernias are due to failure of the peritoneal pouch to obliterate, resulting in a persistent communication between the peritoneal sac and the tunica vaginalis. This is an indirect inguinal hernia. The most common herniated structures are fluid, bowel, and omentum. Rare contents of the hernia sac are ovary, appendix, and bladder. A direct inguinal hernia is an acquired lesion that is uncommon in children. The herniation of a direct inguinal hernia occurs medial to the epigastric vessels.

The inguinal canal is lined by the aponeuroses of the external oblique, internal oblique, and transversus abdominis muscles. The external (or superficial) inguinal ring is a triangular opening in the aponeurosis of the external oblique muscle located at the level of the upper margin of the symphysis pubis. The internal (or deep) iliac ring is an oval gap in the transversalis fascia. It is located lateral to the inferior epigastric vessels and inferomedial to the transversus abdominis muscle. The normal structures in the inguinal canal of males are the spermatic cord, vas deferens, testicular artery, pampiniform plexus, and genital branch of the genitofemoral nerve. In females, the round ligament of the uterus and the ilioinguinal nerve to the labia majora pass through the inguinal canal.⁷⁵

The prevalence of inguinal hernia in the pediatric population is 10 to 20 per 1000. Approximately 30% of these patients present during the first 6 months of life. Approximately 7% of premature infants have a hernia, 85% of which are males.⁷⁹ Clinically evident hernias can develop in previously asymptomatic patients with ascites or after placement of a ventriculoperitoneal shunt.⁸⁰ Inguinal hernias are more frequent on the right side and 10% are bilateral. Contralateral patency of the processus vaginalis is as high as 40% to 50% in children with a unilateral inguinal hernia.⁸¹ Approximately 7% of children who undergo unilateral hernia repair subsequently develop a clinical hernia on the opposite side.⁸¹ Incarceration occurs more frequently in the first year of life.

Sonography shows an inguinal hernia as distention of the inguinal canal with soft tissue or bowel via an enlarged internal inguinal ring. Herniated omentum often has an echogenic character on sonography. Herniated bowel can be collapsed or fluid-filled (Figure 54-16). Careful observation for peristaltic motion is useful for the detection of herniated intestine. Small echogenic bubbles of air are sometimes visible. The adjacent soft tissues are often somewhat hyperemic on Doppler evaluation. A hydrocele often accompanies an inguinal hernia, particularly in infants and young children. The testis is normal. On standard radiographs, an inguinal hernia appears as soft tissue fullness, sometimes containing bowel gas (see Chapter 39).

In some cases, a fluid-filled hernia sac has a sonographic appearance that mimics that of a hydrocele of the inguinal canal or spermatic cord. However, the fluid of a hernia does not envelop the testis, as does an inguinalscrotal hydrocele. The most common form of spermatic cord hydrocele, the encysted hydrocele, appears as an oval cyst that contains clear fluid and lacks communication with the abdomen. A funicular hydrocele does extend into the abdomen via an enlarged internal ring; differentiation is based on the cystic character and lack of peristalsis.

Varicocele

A varicocele is abnormal dilation of the veins of the pampiniform plexus. Varicocele occurs in 10% to 15% of adolescent males. Although there is incomplete elucidation of the pathogenesis of this lesion, implicated factors for idiopathic varicocele include incompetent valves within the ipsilateral testicular vein and abnormal flow in collateral vessels. Compression of the left renal vein between the aorta and the superior mesenteric artery (the nutcracker phenomenon) is a potential cause of secondary varicocele. There is also an association with retroaortic left renal vein, presumably due to impaired drainage and elevated pressure in the renal vein. A renal tumor is an uncommon, but clinically important, potential cause of secondary varicocele. There appears to be a high concurrence of idiopathic varicocele and valvar incompetence of the saphenofemoral junction, which may impart an elevated risk for eventual lower extremity venous insufficiency.⁸²

Varicoceles most often become clinically evident between the ages of 10 and 15 years. Approximately 98% of patients with a clinically evident varicocele have a left-sided lesion or bilateral lesions. A varicocele increases in size when the patient assumes the standing position and during the Valsalva maneuver.

Sonographic examination demonstrates a varicocele as multiple dilated serpiginous veins in the spermatic cord and around the epididymis (Figure 54-17). Flow within these veins is slow; slow flow settings are required for detection with Doppler studies. Evaluation of the left renal vein in a patient with a varicocele often demonstrates narrowing at the point where the vein passes between the aorta and superior mesenteric artery, dilation of the vein proximal to this point, and elevation of peak systolic velocity in the narrowed segment (i.e., the nutcracker phenomenon). If the left testicular vein is visible arising from the renal vein, Doppler shows retrograde flow during the Valsalva maneuver. While typically used for evaluating patients with a palpable scrotal abnormality, sonography also has a high sensitivity (>90%) for the detection of sub-clinical varicoceles.^83,84

The indications for treatment of a varicocele in the pediatric age group are not straightforward. The most important indication for treatment in adults is infertility. However, delayed treatment can lead to testicular atrophy. Generally accepted indications for treatment in young patients include a clinical grade III, a testicular volume of greater than 3 mL below that of the normal testis, and veins within the lesion that are greater than 3 mm in diameter. Documentation of retrograde flow within the spermatic vein is an additional sign that can be achieved with venography or Doppler sonography; however, this finding alone is insufficient for the diagnosis of varicocele, as up to half of normal individuals have retrograde flow during the Valsalva maneuver. The presence of retrograde flow even without the Valsalva maneuver may indicate a more severe lesion in the adolescent patient.

The Acute Scrotum

Common causes of acute scrotal pain include trauma, acute epididymitis, acute epididymo-orchitis, testicular torsion, torsion of the appendix testis, and torsion of the appendix epididymis. In a typical pediatric emergency department, approximately 15% of boys who present with an acute scrotum have testicular torsion, 45% have torsion of an appendix of the testis, and 35% have epididymitis. Accurate distinction between these lesions can usually be made on the basis of the clinical findings, supplemented as appropriate with diagnostic imaging studies. Sonography is the imaging study of choice for most patients with acute scrotal pain (Table 54-2). In some instances, surgical exploration is required for a definitive diagnosis and timely therapy.^85–87