Cryptorchidism

In humans, the testis develops in the abdomen and descends into the lower portion of the scrotum during the third trimester. When the testis is not found in its normal anatomical location, it can either be palpable elsewhere or be nonpalpable. When palpated outside the scrotum, the testis may be cryptorchid, ectopic or retractile, while a nonpalpable testis may be cryptorchid, atrophic or absent. Cryptorchidism occurs when the testis fails to descend into its normal postnatal location and may be found in the abdomen, in the inguinal canal, or at the external ring (prescrotal).

Cryptorchidism is a common disorder. The incidence of cryptorchidism in premature male infants is 9.2 -30%, and in full-term infants is 3.4 - 5.8%. In the majority of these patients (95% of premature and 75% of full term infants) the testis will descend spontaneously within the first year of life. In boys one year of age, the incidence of cryptorchidism is 0.8%, and remains constant through puberty and adulthood, ranging from 0.5% to 0.8%. In one third of patients, cryptorchidism occurs bilaterally. When unilateral, the right side is more often affected (right:left = 7:3). The most common location of the cryptorchid testis is the inguinal canal (72%), followed by prescrotal (20%) and abdominal (8%) locations. In the abdomen, the undescended testis may be located anywhere from the renal hilum to just inside of the internal ring.

The cryptorchid testis requires surgical correction, to avoid the complications associated with the undescended testis: the psychological impact of having abnormal external genitalia, infertility, malignant degeneration, torsion and bowel incarceration.

Psychological impact

Not having a full scrotum is a defect that is obvious to parents and patients and can be a significant source of psychological difficulties for both. Surgery to restore normal scrotal appearance (i.e. orchiopexy) is warranted to prevent the development of such psychopathological issues in children with cryptorchidism.

Infertility

Abnormal testicular descent interferes with normal production of spermatozoa. It has been observed that during the first six months of life the number of germ cells in the cryptorchid testis is comparable to that in the fully descended testis. However, subsequent to this, the number of spermatogonia in cryptorchid testis remains low and does not increase with age, indicating deficiency in gonocyte to spermatogonia transformation. As early as the second year of life, up to 40% of cryptorchid testis have completely lost their germ cells. The further and longer the testis is from its normal anatomical position, the greater the damage is to the seminiferous tubules. It is suggested that the temperature difference (as small as 1.5o C to 2.0 o C) which exists between the scrotum and the body is responsible for inhibiting spermatogenesis. Early orchiopexy has been shown to improve fertility parameters, but by no means restores it to normal.

Malignant degeneration

Abnormal descent also predisposes the testis to malignant degeneration. Approximately 10% of testicular cancers are associated with an undescended testis, and the incidence of malignant degeneration in an undescended testis has been reported to be 48 times greater than in the normal testis. Malignant degeneration usually occurs after puberty, even after patent. A hernial sac is found in over 90% of patients with an undescended testis. This may allow bowel and other viscera to descend out of the abdomen and become trapped in the scrotum, resulting in incarceration (see torsion testicular).

Treatment

Because of the high incidence of complications, early treatment including hormonal therapy, orchiopexy and orchiectomy, is important. Gonadotropin-releasing hormone (GnRH) and human chorionic gonadotropin (hCG) are currently used for hormonal therapy. While these hormones are very successful in treating the retractile testis, their success rate is relatively low (618%) in the treatment of the truly undescended testis. Because of the possibility of spontaneous descent, surgical intervention is usually delayed until after one year of age. Orchiopexy is usually performed in patients between 1 and 10 years of age, and orchiectomy is considered in patients after puberty. It was previously observed that after 32 years of age, the surgical risk outweighed the risk of malignancy and thus, surgical intervention was not indicated in these patients. However , with modern anaesthetic techniques, the surgical risk is markedly reduced and thus, orchiectomy may still be warranted especially in older adults with abdominal testis.

Diagnosis

The diagnosis of cryptorchidism can be difficult, owing to problems in differentiating the truly undescended testis from the absent or atrophic testis. A variety of radiological tests such as US (Fig.1), MRI, CT and angiography have been used to aid in locating the nonpalpable testis. With experience, the techniques of these radiological tests have been further refined and in the advantages and limitations recognized, suggesting specific roles in the evaluation of patients with nonpalpable testis.

Ultrasound

When searching for an undescended testis in infants and children using ultrasound (US), it is helpful first to examine the normally descended testicle and to then search for a comparable structure on the contralateral side. The undescended testis is usually oval in shape and has a homogeneous, hypoechoic echotexture. It is most frequently located distal to the external inguinal ring in the subcutaneous tissue anterior to the pubic tubercle in the superficial inguinal pouch. Because of good spatial resolution and freely selectable scanning planes (parallel to the course of the inguinal canal), high-resolution real-time ultrasound can reliably detect a testis located in the inguinal canal or between the external inguinal ring and the scrotal neck. Even very small (10 mm in diameter), rudimentary testicles can be recognized if they are located in this area. However, the intracanalicular localization of an ectopic testis is not precise. If the undescended testis is not found in the inguinal canal or at the base of the scrotum, the suprapubic, perineal, and femoral regions should be scanned. When the undescended testis is located cranial to the internal inguinal ring (i.e. abdominal), shadowing from bowel gas may make it difficult to distinguish the small testis from other abdominal structures. The abdominal cryptorchid testis is often not detectable on US, except when located just proximal to the internal ring of the inguinal canal.

Occasionally, it may be difficult to distinguish the testis from other structures in the groin on US. An inguinal hernia may be sometimes mistaken for a testis. However, by scanning during Valsalva maneouvre, coughing, or after deliberate evocation of the cremasteric reflex (stimulation of the skin on the inner side of the thigh), the two can be differentiated. The pars infravaginalis of the gubernaculum testis, which is hypoechoic and nodular in appearance, may be confused for an atrophic testis. The testis can be reliably distinguished from the gubernaculum by visualization of the mediastinum testis, which appears as a delicate hyperechoic intratesticular band. Besides identifying the location of extended to the kidneys when no testis is seen in the pelvis. Owing to the large field of view and superb definition of anatomical landmarks, exact localization of an undescended testis is accurate, and although precise differentiation between an undescended testis in the high scrotal location, superficial inguinal canal, or the inguinal canal. The diagnosis of an undescended testis can be made when an elliptical mass is demonstrated along the expected path of testicular descent. When the undescended testis is located in the abdomen, it is round in shape. The abdominal testis, when located close to the internal inguinal ring, can be seen lateral to the bladder or adjacent to the iliac vessels or psoas muscles. High abdominal testes may be more difficult to demonstrate on MR. When the undescended testis is in the inguinal canal, it is usually oval in shape. It is important to distinguish an undescended testis from an inguinal lymph node on MR images. Although the signal intensity of lymph nodes may be similar to that of the testis, differentiation between the two is based upon the characteristic signal intensity of the testis and internal structures (i.e. the mediastinum testis) and the expected location of the inguinal nodes (inferior to the inguinal ligament below the inguinal canal or adjacent to the femoral or iliac vessels) Although the presence or absence of the spermatic cord cannot always predict the location of an undescended testis, structures of the spermatic cord are helpful landmarks.

The ductus deferens and the testicular vessels are often traced in the spermatic cord to the level of the undescended testis. The ductus is rarely present caudal to an undescended testis. However, the presence of a blind ending ductus does not always imply absence of the testis because the embryological development of the gonads is independent from that of the ductal structures. When the undescended testis is located proximal to the external inguinal ring, an empty spermatic cord may be seen as a thin curvilinear structure extending distally to the scrotum. Another important landmark is the pars infravaginalis gubernaculi (PIG), the distal bulbous termination of the gubernaculum, which is always caudal to the undescended testis. The gubernaculum is a cordlike structure that guides the testis during descent. It is gelatinous in early fetal life and normally atrophies after the testis descends completely. When the testis fails to descend to the scrotum, the gubernaculum persists as a fibrotic remnant. The PIG is sometimes misdiagnosed as an undescended testis on imaging studies, and differentiation between the two is essential. This is achieved on MR images by identification of the characteristic signal intensities of the testis and the gubernaculum, and the presence or absence of the mediastinum testis.

Whereas the testis typically shows low signal intensity on T1-weighted images and high signal intensity on T2-weighted images, the gubernaculum demonstrates low signal intensity on both T1- and T2-weighted images. Signal intensity characteristics alone, however, are not sufficient to differentiate the gubernaculum from an atrophic undescended testis which also demonstrates low signal intensity on T2-weighted images. Identification of the mediastinum testis, which can be seen on MR images, allows a definitive diagnosis of undescended testis. MR imaging is highly accurate in localizing the testis as abdominal or canalicular. Besides identifying the location of the undescended testis, MR imaging may be useful in other situations. MRI can differentiate retractile and undescended testes, offering an alternative to hormonal testing. In the former, the volume and signal intensity of the testis are normal and the gubernaculum is well developed. In an undescended testis, however, the volume of the testis may be normal or small, the gubernaculum is usually not well developed, and the signal intensity of the testis may be lower than normal on T2-weighted images. Furthermore, MR imaging can reliably locate remnants of testicular regressio the scrotal sac or inguinal regions, the examination should be extended up to the renal hilus. When preparing children for evaluation of suspected undescended testes, ingestion of oral contrast material may be simplified by administering 500 ml of oral contrast at least one hour before the examination. Bolus injection of intravenous contrast material with prompt scanning is necessary to obtain optimal vascular enhancement for the detection of undescended testes. On CT examination, the undescended testis appears as an oval soft-tissue mass along the expected course of testicular descent (Fig.2). CT like MRI allows precise localization of the undescended testis as prescrotal, canalicular, or abdominal. While it may be more difficult to detect the abdominal testis than a prescrotal or canalicular testis, because the former can be confused with bowel loops, vessels, and lymph nodes, CT is superior to either US or MRI for that indication. CT can differentiate the undescended testis from inguinal lymph nodes which are located outside the spermatic cord, inferior to the inguinal ligament (below the inguinal canal), or adjacent to the femoral or iliac vessels, deep and lateral to the inguinal canal. Finally, the possibility of malignant degeneration should be considered when the undescended testes is larger than 2 cm in longest dimension observed on CT images or has heterogeneous enhancement.

Venography

For many years testicular venography was the most widely used diagnostic procedure in the evaluation of the suspected cryptorchid testis, and it reduced the need for surgical exploration. Three distinct findings have been reported in the literature: demonstration of the pampiniform plexus, the testicular parenchyma, and the blind-ending testicular vein. If a pampiniform plexus is demonstrated, it is most likely that a testicle is present. If there is a blind-ending testicular vein, it is most unlikely that a testicle is present.

Practical approach

In practice, US is most often used in the search for the undescended testis. MRI offers the advantages of noninvasiveness, excellent soft tissue contrast, a large field of view, multiplanar capability, free selection of imaging plane, and absence of ionizing radiation exposure (Fig.3) (Fig.4). More importantly, MRI is not limited by a large patient's habitus. MRI is highly accurate (94%) in locating undescended testes, a figure comparable to CT and slightly better than US, though an abdominal testis may escape detection on MR examination. MRI, however, is the preferred modality when testicular tumour in an undescended testis is suspected. The widespread availability of US and MR imaging have made CT a much less frequent choice for the detection of undescended testis. It should be remembered, however, that CT is as accurate as real-time sonography in the localization of a testis in the inguinal canal, and is superior for detection of abdominal testes. In one study which compared CT with high-resolution US for the localization of the nonpalpable, undescended testis, the accuracy of CT and US were 96% and 91%, respectively.

HH