Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

Figure 13.1. Posterior urethral valves in an 11-year-old. The prostatic urethra is dilated and has a “spinning-top” configuration.

ablation; in addition to voiding cystourethrography, postoperative urodynamic studies are often helpful.

After birth, a voiding cystourethrogram should be diagnostic for posterior urethral valves (Fig. 13.1). Catheterization is easy in those with type 1 valves, but may not be possible with type 3 valves, depending on the central opening. The prostatic and membranous urethra are dilated, with an abrupt transition in caliber at the valve site. At times the valves are identified.

In many infants US detects a dilated posterior urethra during voiding and bilateral hydronephrosis (Fig. 13.2). Vesicoureteral reflux and hydronephrosis is associated with a dysplastic kidney in some. A thick, trabeculated bladder wall and diverticula develop eventually. Severe obstruction in a neonate can result in calyceal perforation and urinary ascites.

A retrograde urethrogram is not appropriate for detecting these valves; they tend to be effaced against the urethral wall, and obstruction is not detected. A voiding cystourethrogram is the examination of choice. In a search for posterior urethral valves, some radiologists remove the catheter while others leave it in place. Some believe that a catheter can obscure the valves.

Voiding cystourethrography in boys with severe posterior urethral valves identifies a trabeculated bladder body and smooth bladder

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base; bladder base trabeculations do not develop. A trabeculated bladder body evolves as a result of contractions due to parasympathetic (cholinergic) stimulation during voiding, while the bladder base relaxes due to sympathetic (adrenergic) stimulation and thus remains smooth.

Indications for percutaneous nephrostomy in neonates with posterior urethral valves include renal failure, severe infection, and, at times, evaluation of a dilated collecting system. Such diversion, however, is not without its own problems. Even if a proximal urinary tract diversion is performed, many neonafes tend to continue losing renal function. Diversion also results in a defunctionalized bladder and loss of bladder compliance. In general, primary valve ablation performed in infants prior to age 1 year results in better recovery of bladder function than those treated with urinary diversion, realizing that in some of these infants neither procedure halts progression of renal insufficiency.

Results of renal transplantation in children with end stage renal disease due to posterior urethral valves are similar to those obtained in children with nonobstructive renal disease. In either case, probably all children with contemplated renal transplantation should be studied for the presence of congenital posterior urethral valves; the presence of these valves has a role in graft function deterioration.

Anterior Valves

True anterior urethral valves are rare, with most believed to represent a fold that is part of a urethral diverticulum. Some of these valves are detected investigating prenatal hydronephrosis, while others manifest by voiding dysfunction later in life. Bladder rupture can develop in a neonate with anterior urethral valves.

A voiding cystourethrogram should detect these valves, although their imaging appearance is very similar to that of an anterior urethral diverticulum.

Stricture

Urethral strictures are distinct from posterior or anterior urethral valves. Identical congenital urethral strictures occasionally develop in relatives.

Diverticulum

A congenital urethral diverticulum originates from the anterior urethra and is associated with urethral obstruction. These diverticula have either a saccular appearance (and originate from the ventral urethral wall) or are diffuse (megalourethra).

A saccular diverticulum is a ventral outpouching in the midurethra; it is rare in the bulbous urethra, in which case cystic dilation of Cowper’s gland duct should be suspected. It contains a valve-like deformity in its distal end; as the diverticulum fills with urine, the distal end is elevated into the urethra and limits flow.

Clinically, a saccular diverticulum should be suspected with intermittent urinary obstruction swelling of the penis.

A voiding cystourethrogram should detect an abnormality but may not differentiate a diverticulum from anterior urethral valves.

Hypospadias

Hypospadias consists of an abnormal ventral urethral termination due to failure of urogenital fold fusion. Varying degrees of malposition are possible; at times a urethra even terminates in the perineum. The utricle tends to be

enlarged, with its size having a direct relationship to severity of hypospadias.

About 10% of boys with hypospadias have a familial history and have associated cryptorchidism; renal abnormalities are uncommon. A distal urethral malignancy occasionally develops in men with congenital hypospadias.

A voiding cystourethrogram aids in defining underlying anatomy.

Epispadias

Epispadias is part of the spectrum of pelvic abdominal wall failure-to-fuse anomalies. Failure of dorsal urethral closure results in epispadias. Various gradations occur ranging from failure of bladder neck closure to a defect in the distal urethra. The urethral sphincter is underdeveloped, and these boys have incontinence.

A blind epispadial sinus, or congenital prepubic sinus, is a congenital accessory urethra that does not communicate with the bladder. The underlying anatomy can be outlined with a fistulogram.

Megalourethra

Urethrography in a male infant with a megalourethra revealed crescent-shaped anterior urethral dilatation (2); associated abnormalities included prune-belly syndrome, absent corpus spongiosum, and bilateral undescended testes.

Testes

Anorchia/Cryptorchidism

Clinical

Scrotal agenesis is very rare. Among boys with a clinically impalpable testis, about one-fifth have an absent testis (anorchia) and the rest cryptorchidism. A minority of boys with anorchia have complete testicular agenesis along with epididymis and vas deferens, but a majority have blind-ending cord structures—also called a vanishing testis. The blind-ending cord in these boys with a vanishing testis terminates mostly in the inguinal canal, with a minority intraabdominally, in the superficial inguinal ring, or, least common, in the scrotum. Yet the diagnosis of agenesis is imprecise; some indi-

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viduals who have negative inguinal canal, and scrotal exploration have later developed an intraabdominal seminoma, presumably from an overlooked intraabdominal testis.

Cryptorchidism is more common than anorchia. Pathogenesis of cryptorchidism is unclear; it is probably part of an embryogenetic defect. These infants are also prone to develop renal agenesis, ureteral duplication and seminal vessel abnormalities. Normally at birth the testes are already descended into the scrotum. With clinical suspicion of an undescended testes, the primary question is: What is the location of the testis? Clinically, these infants can be subdivided into those with a nonpalpable testis and those with a palpable testis in an abnormal location. About 25% have a nonpalpable testis located in the abdomen or inguinal canal (and occasionally even distal to the external inguinal ring), while a palpable testis ranges in location from the inguinal canal, inguinal pouch, and high scrotal position, to even an unusual ectopic position. In most babies with cryptorchidism the testis descends shortly after birth, but an undescended testis persisting beyond the age of 1 year generally will not change position. By puberty, an undescended testis degenerates and has a low spermatogenesis rate.

A high scrotal testis is one located below the external inguinal canal; it can be manipulated to the upper scrotum, but then ascends. Some consider it to represent the mildest form of an undescended testis.A high scrotal testis tends to be smaller than the contralateral one. These boys have a higher prevalence of testicular torsion.

A nonpalpable testis is more common on the left side.

Bilateral cryptorchidism is found in about half of adults with Noonan’s syndrome. A high prevalence of undescended testis is found in Down syndrome. Premature infants are somewhat prone to having cryptorchidism. An association exists between cryptorchidism and epididymal abnormalities.

An undescended testis is prone to developing a malignancy, with the most common tumors being a seminoma and embryonal cell carcinoma. Metachronous tumors occur with bilateral cryptorchidism. The risk of malignancy increases even after orchiopexy, to the point that some surgeons advocate orchidectomy

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for postpubertal cryptorchid males. As an example of the risk for cancer, a 26-year-old man with Noonan’s syndrome had had bilateral orchiopexy for undescended testicles at 12 years of age, and now US confirmed a right testicular solid tumor and CT identified retroperitoneal adenopathy (3); orchiectomy revealed findings consistent with a seminoma.

Postpubertal males with cryptorchidism rarely have normal spermatogenesis; maturation arrest and seminiferous tubular atrophy are common. Bilateral dysgenesis is evident even with unilateral cryptorchidism because the risk of malignancy is also increased in the contralateral normally located testis and some investigators suggest a post-pubertal biopsy for carcinoma-in-situ.

Transverse testicular ectopia, consisting of an abnormal testicular descent resulting in a unilateral location of both testes, is extremely rare. It is usually associated with an inguinal hernia. The spermatic cord of the ectopic testis originates from its correct site. In such a situation, one testis is in the inguinal region and another in the ipsilateral scrotum.

An undescended testis can develop torsion later in life; an underlying neoplasm is associated with such torsion.

Imaging

Individuals operated on previously for cryptorchidism tend to develop microlithiasis (4); annual US surveillance is recommended for these patients with microlithiases.

Because of ease and ready availability, US is the current primary imaging modality in evaluating cryptorchidism. Ultrasonography correctly identifies over 90% of inguinal testes but only a minority of atrophic inguinal testes. Ultrasonography has a low yield if no testis is palpable or is intraabdominal in location or in those with an associated inguinal hernia. MRI should be considered for these infants.

Ultrasonography identifies an undescended testis as a smooth oval structure that is usually smaller than a normal testis.An enlarged lymph node has a similar appearance, and visualization of a linear echogenic mediastinum testis is helpful in differentiating between these two structures.

Computed tomography is limited in this condition. Especially in children, the lack of

surrounding fat makes testis detection difficult.

Magnetic resonance imaging is evolving as the preferred imaging modality for an undescended testis and its role will undoubtedly increase in the future. It localizes most undescended testes, including those in the abdomen. A current reasonable approach is to add either MR or US if the first study is inconclusive. A testis is hypointense on T1and hyperintense on T2-weighted signal intensity, although the T2weighted signal intensity is lower than usual with an atrophic or fibrotic testis. Most undescended testes are perivesical in location, with an occasional one outside the pelvis.

One promising technique is MR venography; imaging at various delayed venous phases after gadolinium infusion detects the contrastenhanced pampiniform venous plexus. This technique detected testes not identified with more conventional MRI (5).

Spermatic arteriography has been supplanted by noninvasive imaging.

Thermography has been suggested as an aid in detecting an undescended testis but is of limited use with an abdominal testis. It appears to have a role if a high undescended testis is suspected but is not palpable and not detected by US.

Therapy

In the past, therapy for an undescended testis included surgical exploration, supplanted later by subumbilical laparoscopy, and, more recently, transinguinal laparoscopy. One approach for a nonpalpable testis is initial abdominal laparoscopy; if vas deferens or spermatic vessels enter the internal inguinal ring, surgical exploration of the inguinal canal is performed, but if both vas deferens and spermatic vessels are absent or end blindly intraabdominally, a diagnosis of anorchia or vanishing testis is presumed.

Residual testicular and epididymal abnormalities persist in adults who are treated for an undescended testis in childhood. The cryptorchid testis is smaller in adults treated surgically when they were children. The fertility rate of adult men who underwent surgical correction of bilateral cryptorchidism as children is markedly reduced compared to those who had unilateral cryptorchidism; the resultant fertility

is independent of surgical timing. These adults tend to have an abnormal US echo pattern in the involved testes.

Polyorchidism

Polyorchidism is uncommon. It is a result of transverse division of the embryonic genital ridge. Bilateral polyorchidism is extremely rare.

These boys are at an increased risk for cryptorchidism, inguinal hernia, and testicular malignancy, at times uncommon ones such as a rete testis adenoma and an embryonal carcinoma.

An occasional polyorchid testis is detected by US.

Dysplasia

Cystic dysplasia is a rare congenital nonneoplastic condition resulting in multiple cysts in the mediastinum testes. The defect probably represents a lack of connection between rete testis tubules and efferent ductules.

Rete testis cystic dysplasia presents as a scrotal or abdominal tumor. Ipsilateral renal agenesis is found in some individuals, and whenever cystic dysplasia is detected, ipsilateral renal agenesis should be excluded. Other associated lesions include multicystic dysplastic kidney, duplication anomalies, and cryptorchidism. Multicystic epididymides and seminal vesicles have developed in association with polycystic renal disease.

Ultrasonography reveals multiple small cysts. The appearance is similar to that seen with a teratoma or even testicular microlithiasis.

Vas Deferens

Wolffian duct structures include the epididymis, vas deferens, seminal vesicles, and ejaculatory ducts. Malformations of these structures consist of cysts, agenesis, and partial atresia; an occasional one is associated with renal agenesis. Congenital absence of the vas deferens can be either bilateral or unilateral. In some, unilateral vas deferens agenesis is associated with unilateral renal agenesis (bilateral renal agenesis is incompatible with life), and a finding of vas deferens agenesis should lead to a renal study. Those with congenital unilateral

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vas deferens absence and infertility often have anomalies in the contralateral testes. An association exists between the absence of a vas deferens and cystic fibrosis; in fact, congenital bilateral vas deferens absence probably is a mild form of cystic fibrosis.

Four patterns were identified among men with vas deferens agenesis (6): bilateral agenesis (64%), bilateral agenesis associated with unilateral renal agenesis (3%), unilateral agenesis (15%), and unilateral agenesis with unilateral renal agenesis (18%). A cystic fibrosis mutation was detected in 64% of men with bilateral agenesis but in none with unilateral agenesis, and the latter condition thus presumably is due to a different pathogenetic pathway.

The absence of vas deferens is identified by endorectal US.

Other anomalies include an ectopic vas deferens and vas deferens duplications.

Abnormal wolffian duct development can result in an ectopic vas deferens insertion into the posterior bladder wall.

Splenogonadal Fusion

An unusual cause of a scrotal mass in boys is splenogonadal fusion. In this congenital entity, splenic tissue is located in the epididymis, tunica albuginea, or along the spermatic cord, almost always on the left side. Although usually found as a discrete tumor, occasionally varying amounts of splenic tissue extend from the splenic hilum inferiorly. Such continuous splenic tissue is associated with other systemic anomalies.

Many of these discrete splenic tumors are initially thought to represent a neoplasm. Consideration of splenogonadal fusion is important because at times a surgeon is able to dissect splenic tissue off the tunica albuginea.

Adrenal Rests

Testicular epididymal and adjacent structure adrenal rests derive from aberrant adrenal cortical tissue migrating into these structures during fetal development. Incidental adrenal rests are most common in newborns but generally involute with age. Hyperplasia of these adrenal rests leads to either focal tumors or diffuse testicular enlargement. In fact, a testicu-

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lar tumor in a male with congenital adrenal hyperplasia most often represents testicular adrenal rests. These testicular rests can change in size, at times rapidly. Most symptomatic ones are discovered in the pediatric age group, at times associated with precocious puberty. These solid, multiple, and usually bilateral tumors are believed to develop secondary to elevated adrenocorticotropic hormone (ACTH) levels and are also found in Addison’s disease and Cushing’s syndrome. A rare such adrenal rest develops a malignancy.

Most are located adjacent to the mediastinum testis. US reveals these predominantly intratesticular, often multiple, bilateral tumors to be mostly hypoechoic when small but often contain hyperechoic regions with growth (7); with color Doppler US they range from hypervascular, isovascular, to hypovascular relative to normal testis. Some contain a spoke-wheel pattern of converging vessels. They are isointense on T1and hypointense on T2-weighted MR images, tumor margins are well-defined and most show contrast enhancement (7). Their appearance suggests a neoplasm. With the presence of adrenal hyperplasia, whether these tumors should be investigated for a possible underlying malignancy remains an individual clinical decision.

Ultrasonography and MRI appear similar in detecting intratesticular adrenal rest tissue (8); MR showed 71% of testicular adrenal rests to be isointense and 29% slightly hyperintense to normal testicular tissue on T1weighted images; all were hypointense on T2-weighted images, and 85% enhanced diffusely postcontrast.

At times testicular vein sampling reveals elevated cortisol levels (compared with peripheral blood).

These tumors regress with glucocorticoid therapy.

Trauma

Urethra

Anterior pelvic arch fractures are usually associated with membranous urethral injury, while straddle injuries tend to involve the bulbous urethra. Associated bladder injury should also be suspected. A retrograde urethro-

Table 13.1. Classification of blunt urethral trauma

Type I: Posterior urethra intact but stretched

Type II: Partial or complete posterior injury with tear of membranous urethra above urogenital diaphragm

Type III: Partial or complete combined anterior/ posterior urethral injury with urogenital diaphragm disruption

Type IV: Bladder neck injury with extension into urethra

IVA: Injury to base of bladder with periurethral extravasation simulating a true type IV injury

Type V: Partial or complete anterior urethral injury

Source: Adapted from Goldman et al. (9).

gram should be obtained with any suspected urethral injury.

Urethral trauma ranges from incomplete to complete rupture. Blind bladder catheterization should be discouraged in such a setting to avoid converting a partial tear into complete rupture. A classification of injury to the anterior and posterior urethra is outlined in Table 13.1. Type IV injury is least common. A retrograde urethrogram should be diagnostic for a tear.

Although CT is not directly employed for urethral trauma, it is often obtained to evaluate pelvic structures, and it does provide indirect evidence of urethral injury. With type I injury the prostate is elevated, type II is associated with contrast extravasation above the urogenital diaphragm, and type III is associated with extravasation below the urogenital diaphragm. An MRI can establish the length of urethral injury and any prostatic displacement. The sequelae of urethral injury are stricture, impotence, and incontinence, the latter due to prior sphincter injury. Future impotence is suggested if MRI detects avulsion of the corpus cavernosum, separation of the corporeal body, and superior or lateral prostatic displacement. With both corpus cavernosum avulsion and prostatic displacement, the probability of permanent impotence is over 90%.

Strictures in boys with posttraumatic urethral disruption are almost always inferior to the verumontanum; stricture length tends to be overestimated during urethrography due to incomplete filling.

Smaller, less fibrous posttraumatic rectourethral fistulas tend to heal spontaneously after a double diversion; others require recon-