Multiparametric ultrasonography of the pediatric scrotum and in boys with undescended testes.

Due to its noninvasiveness and high resolving power, ultrasound examination is the examination of choice for the imaging of the structures of the pediatric scrotum. It allows to reveal changes impossible to find in the course of a clinical examination. Its significance has increased over the past few years due to the technological developments. The introduction of transducers with frequency of 10-17 MHz has improved the resolution of pediatric testes images as well as the resolution of the inguinal canals images, which has been of particular importance for the evaluation of undescended, retractile and abdominal testes. New diagnostic tools have also been introduced, such as 3D imaging or elastography, whose application has helped provide valuable additional information for the evaluation of pediatric testes, for treatment monitoring, and for post-surgical follow-up examinations. 3D imaging facilitates a more accurate evaluation of the location of an undescended testicle, testicular volume, and vascularization. Elastography may be used for the evaluation of focal lesions, post-ischemic lesions, unclear fluid spaces, undescended testes, and following orchiopexy.

Introduction

The basic diagnostic method for scrotal structures imaging is 2D examination allowing for the evaluation of a testicle's structure, size and – in the case of a measurements in three planes – estimating the volume. The increasingly sensitive Doppler scan may also be used, to detect low flow speed, which is of considerable importance for the evaluation of testes in young boys. The examination renders a very good image of the inguinal canal and its content, thus allowing to locate the testicle in the canal and determine its flows. It also reveals changes such as decrease in the size of an undescended testicle, or changes in its structure.

Despite such excellent imaging opportunities, we still need a tool helping to evaluate the condition of an undescended testicle prior to and following a surgical procedure, and to provide a prognosis on the function of the testes in the future. This proves difficult mainly due to the time which lapses before a testicle resumes its full function after the procedure. The general tendency is to evaluate the testicular volume, trying to translate it into the testicle's function. This can be accompanied by counting the vascular segments and the evaluating the flow spectrum. New diagnostic methods, such as sonoelastography and 3D ultrasonography have also emerged.

3D ultrasound (3DUS)

3D technology provides numerous interesting functions that may be used alongside the 2D examination. The image of an organ or a pathological structure is presented in many different planes. The coronal plane (for conditions such as undescended testes frequently unobtainable in a 2D scan) proves particularly significant, as it helps to determine more accurately the exact location of such a testicle in the inguinal canal itself or in an inguinal pouch where ectopic testes are sometimes found( (fig. 1).

Fig. 1

3D examination in three planes and slice plane, testicle in the inguinal canal, arrows – coronal plane

In a 3D examination the evaluation of a testicular volume or focal lesions is more accurate as we can map the exact shape of an area of interest. In an archived examination the measurements may be viewed repeatedly. The evaluation of a testicular volume in a 2D scan depends on the accurateness of measurements in the three planes, and they cannot be corrected in the archived examinations(. It is precisely the archiving of 3D examinations that has huge potential for standardizing examinations. It allows to recover a patient's full data in the future, to monitor changes, and to examine the correlation with other imaging modalities(.

Combining 3D option with power Doppler helps to deliver a more accurate qualitative and quantitative assessment of the vascularization of an organ and the changes occurring therein. It reveals pathologic vascularization and enables to calculate the vascularization index, i.e. the ratio of the number of vessels to a given volume, lesion or entire organ (fig. 2). The vascularization index has a huge diagnostic potential, since it allows to monitor, without any contrasting agents, all kinds of pathologies where vascularization changes occur. The vascularization index measurement may be significant for the evaluation of the health of testes following surgical procedures, torsions, as well as various ot her clinical conditions, including ones unrelated to the reproductive system. For normal testes the index tends not to exceed 10%, whereas in pathologic changes it amounts to 30%. In boys displaying cryptorchidism the vascularization index was lower in undescended testes, as well as in testes moved to the scrotal sac (fig. 3). In patients with testicular adrenal rest tumors (TART), the vascularization index decreased as treatment proceeded, possibly pointing to a decrease in the activity of the lesions(. However, before the method is standardized, further research on a larger patient group is necessary.

Fig. 2

3D examination, normal result. Measurement of the testicular volume and VI (vascularization index)

Fig. 3

VI in patients with undescended testes (1), following orchiopexy (2), and in control group (3)

Unfortunately, there also exist limitations of 3D scrotum examinations in children, including lack of patient's cooperation, poorer resolution than in 2DUS, the need for computer analysis, the smaller size of the regions of interest and of organs to be examined. Nonetheless, wherever the device allows, a 3D scan should be performed to accompany the 2D one.

Real-time sonoelastography (RTSE)

Elastography is an increasingly popular method applied in the ultrasound diagnostics, including the assessment of the scrotal structures. The publications so far have indicated a significant potential of elastography for the evaluation of focal lesions in the testicle and for their improved differentiation as well as for distinguishing inflammatory from mass lesions(. Moreover, they have also pointed to the potential for distinguishing unclear fluid lesions, e.g. hematoceles, from solid tumors(. The research however has mostly been concerned with adult men who are more prone to develop mass lesions which in children are much less prevalent. Hence, the application of elastography tends to be found useful for diagnosing other conditions.

A normal testicle tends to display homogenous structure of high stiffness (fig. 4). Focal lesions may be better isolated in the elastographic examination, as areas of even increased stiffness as compared to the normal testicular parenchyma (figs. 4, 5). In the case of such lesions, whether diffuse or focal, the normal parenchyma of the testicle displays intermediate stiffness(. A similar pattern may be found in conditions such as benign tumors, TART (fig. 5), teratomas, dermoid cysts and pseudotumors, hence elastography on its own is insufficient for the sake of differentiative diagnosis thereof(. In TART patients the stiffness of lesions and the remaining testicular parenchyma has been observed to even out which may be an evidence of a decrease in the stiffness of the tumor tissue. Elastography proves a more accurate method of finding post-ischemic and scarring lesions. Within no more than a few weeks after a torsion incident, whenever ischemia has taken place despite a surgical procedure, and unclearly marked lesions of inferior vascularization occur, elastography very sensitively detects them as areas of enhanced stiffness (fig. 6). It is similar in the case of post-traumatic regressive changes.

Fig. 4

2D image and elastography of a normal testicle (white arrow) and a fibrous pseudotumor (black arrow)

Fig. 5

TART (white arrows) in a patient with congenital adrenal hyperplasia

Fig. 6

Elastography of a testicle 3 weeks after a torsion incident. Scarring lesions of increased cohesion

Elastography may also help to confirm the presence of undescended testes in the abdominal cavity or in the inguinal canal, especially in the case of small, poorly differentiated structures (fig. 7). The examination of testes which have undergone orchiopexy may establish areas of increased stiffness inside the testes (fig. 8) or in the tissues surrounding them(.

Fig. 7

Elastography of a testicle located in the inguinal canal (white arrows), and in the abdominal cavity (black arrows)

Fig. 8

Elastography of a testicle 2 years after a right-side orchiopexy. Right testicle smaller, of heterogeneous elastographic structure, with areas of enhanced stiffness

The majority of the RTSE applications been mentioned here should only serve as initial observations in need of further research. Since the examination is relatively simple to perform, it may be used on children. Nonetheless, due to a child's anxiety and restlessness, certain limitations are likely to occur. Moreover, RTSE provides solely qualitative information on the compressibility of tissues, the information varying largely depending on examination technique.

Conclusion

The application of modern ultrasonography methods such as 3D imaging or elastography may provide a wealth of additional information for the sake of the assessment of pediatric testes, as well as in the course of treatment monitoring and post-surgical follow-up examinations. 3D examination facilitates a more accurate assessment of the location of an undescended testicle, testicular volume, as well as vascularization assessment, whereas elastography may be used for the evaluation of focal lesions, post-ischemic lesions, unclear fluid spaces, undescended testes, and testes having undergone an orchiopexy.