Ultrasonography of pediatric urogenital emergencies: review of classic and new techniques.

AISE is a self-limiting disease, commonly seen in children under 10 years of age (mean, 6 years) [ 53 ]. Its etiology is unknown, but infection, allergic reaction, and angioedema are presumed [ 53 ]. AISE shows spontaneous regression, but recurrence is also seen, in up to 21% of cases [ 53 ]. The typical presentation is scrotal erythema and edema without tenderness [ 53 ]. Erythema and swelling can extend into the perineal and inguinal region in approximately 50% of cases. The rate of unilateral versus bilateral presentation varies across reports; the rate of bilateral presentation is 10%-100% [ 53 , 54 ]. Patients are usually afebrile, but systemic fever can be seen in up to one-third of cases [ 53 ]. Laboratory examinations show normal ranges, except for the possible presence of eosinophilia, supporting the theory of an allergic etiology [ 53 ]. Sonographic findings include scrotal wall thickening with a heterogeneous striated and edematous appearance ( Fig. 7A , B ) and hypervascularity ( Fig. 7C ) (called the fountain sign in bilateral cases), and possible inguinal lymphadenopathy [ 53 - 55 ]. However, these findings are non-specific, and ruling out other diseases is important. In AISE, morphology and vascularity are normal in the testis, epididymis, and spermatid cord [ 43 , 53 , 55 ].

In the pediatric population, urogenital emergencies are quite common, and may have serious consequences. They include testicular torsion, epididymitis, testicular appendage torsion, testicular trauma, acute idiopathic scrotal edema (AISE), ovarian torsion, and emergencies involving associations of urogenital anomalies such as Wunderlich syndrome. These diseases are diverse, and there are pitfalls in their diagnosis. Along with conventional ultrasonography (US), new techniques have been developed, such as contrast-enhanced US (CEUS), tissue elastography, and 3-dimensional sonography. CEUS is used off-label in children, but a recent review suggested that the use of US contrast agents is safe in children [ 1 ]. These new techniques are also presented in this review.

Ovarian torsion refers to a twisted vascular pedicle, which leads to vascular insult, resulting in ovarian ischemia and ultimately necrosis. Autoamputation can occur, especially in neonatal torsion [ 56 ]. This disastrous condition is also important in the pediatric field. Salvage rates in pediatric series vary across reports, ranging from only 0%- 27% in one report [ 57 ] to a majority of cases in another [ 58 ]. There appears to be significant individual variation in the time to infarction, and there is no clear golden time for surgery, in contrast to testicular torsion [ 57 ]. The age distribution is bimodal, with the two peaks occurring in infants and adolescents [ 59 ]. Ovarian torsion is much more common on the right side because of the smaller free pelvic space on the left side due to the sigmoid colon [ 60 ]. Torsion usually occurs in association with an ovarian mass. The mass is usually benign, typically an ovarian cyst or teratoma; the reported malignancy rate was only 1.8% in pediatric cases of ovarian torsion [ 61 ]. The most common sonographic findings are enlargement and heterogeneity [ 58 ]. A mass of >5 cm is 83% sensitive for ovarian torsion [ 59 ], although this finding is not specific. Ovarian hemorrhage is rare in prepubertal children because endometriosis and tubo-ovarian abscess are exceedingly rare. Thus, a hemorrhagic ovarian cyst suggests ovarian torsion [ 58 ], although false-positives have been reported [ 62 ]. In addition to cystic ovarian masses causing ovarian torsion, intraovarian cysts should be evaluated carefully. Peripherally located cysts ( Fig. 8A ), which are not true cysts and may be attributable to the transudation of fluid due to congestion, have a relatively high specificity of 74% [ 62 , 63 ]. Ovarian enlargement with multiple peripheral cysts can show a high positive predictive value (87.5%) and specificity (93.3%) [ 63 ]. The follicular ring sign, or perifollicular hyperechoic rim, has also been reported to have a high specificity (80%), and is seen starting in the early stage of torsion [ 64 ]. This sign should be differentiated carefully from the acoustic shadow artifact of normal follicles in terms of the following features: it is seen concentrically around the follicles and exhibits a perceptible thickness (1-2 mm) [ 64 ]. A transvaginal scan is recommended, if available, but this sign can also be detected on a transabdominal scan [ 64 ]. The intrafollicular fluid-debris level is an additional follicular feature with a high specificity (85%) [ 65 ]. Other classical signs include ovarian edema, abnormal ovarian position, free fluid in the pouch of Douglas, and the absence of ovarian vascularity ( Fig. 8C ) [ 58 , 63 , 66 - 70 ]. Venous flow is obstructed first, and arterial flow shows a “spiky” pattern. Both arterial and venous flow are then lost in the advanced stages [ 70 ]. The ability to make a diagnosis based on ovarian vascularity has considerable variation, with a positive predictive value of 19%-94% and a negative predictive value of 46%-100% [ 68 , 69 , 71 ]. There seem to be many factors affecting accuracy: dual supply from the uterine and ovarian arteries to the ovary, incomplete or intermittent torsion, the small size of vessels and low flow in children, and the deep location of the ovary. Moreover, the selected slice may not correctly reflect the vascularity of the entire ovary [ 72 ]. Recently, 3-dimensional assessment, which allows the evaluation of the whole ovary with quantitative vascular assessment, has been applied to ovarian torsion in adults [ 72 - 74 ], although this was performed with a transvaginal approach. Another solution could be CEUS. An animal study showed that the administration of contrast material enhanced the visualization of ovarian flow [ 75 ], and a case report showed decreased flow in a twisted ovary in a 6-year-old girl [ 76 ]. The whirlpool sign and a twisted pedicle have been reported to be useful and diagnostic ( Fig. 8B , Video clip 3 ) [ 66 , 77 , 78 ]. This is a direct finding of torsion; however, the utility of the whirlpool sign has not been fully evaluated in pediatric series, where a transvaginal approach is not applicable [ 58 ]. For example, Lee et al. [ 78 ] showed 87% accuracy in an adult series, but they used a transvaginal probe in 47 patients, with the exception of four patients who were virgins or pregnant. They also stated that it was difficult to identify the whirlpool sign by a transabdominal approach [ 78 ]. This limitation seems to have resulted in the claim by some authors that US is not reliable in the diagnosis or exclusion of ovarian torsion in the pediatric population [ 59 ], although other authors insist on the utility of the whirlpool sign with a transabdominal approach [ 77 ]. The US diagnosis of ovarian torsion is not straightforward, and it is affected greatly by the operator (60%- 100%) [ 69 ]. Thus, other modalities should be used in equivocal cases. Neonatal ovarian torsion should be considered separately because this condition usually occurs antenatally. Of patients with neonatal ovarian torsion, 91% had ovarian cysts on prenatal US [ 79 ]. US shows complex cystic masses, suggesting hemorrhage, with signs such as multi-septation, echogenic debris, and/or fluidfluid levels ( Fig. 9 ) [ 67 , 79 ]. Calcification can also be seen in some cases [ 79 ]. There are several pitfalls in the diagnosis of neonatal torsion. Half of the ovaries with torsion may show an extrapelvic location and could be misdiagnosed as appendicitis or as an abscess [ 67 ]. Moreover, a thickened wall can show an echogenic inner rim, mimicking duplication cysts ( Fig. 9A ) [ 79 ]. Another special condition of ovarian torsion is seen in ovarian hernia [ 80 - 84 ]. Ovarian hernia is commonly seen in infants, and the incidence of irreducible ovaries is 6%-7% for inguinal hernias in girls [ 83 ]. As the ovarian vascular pedicle is narrowed in the internal ring, the size of the ovary is relatively greater than the pedicle. This causes a predisposition for the ovary to twist [ 84 ]. Ovarian hernia has a risk of torsion, and it is necessary to evaluate the possibility of torsion, including vascularity. If torsion exists, this should be treated as an emergency [ 84 ]. Unlike deep in the pelvis, US with a high-frequency linear probe is useful in evaluating inguinal hernia. Ovarian hernia is readily recognized as an oval mass with small cysts on US [ 80 ]. The sonographic findings of twisted ovarian hernia include multiple cysts, ovarian enlargement, and heterogeneous hyperechogenicity [ 82 ]. A twisted pedicle and decreased vascularity can also be seen ( Fig. 10 ).

The US of pediatric urogenital emergencies is reviewed in this article. Although many pitfalls exist in making a correct diagnosis, knowledge of the correct approach can be of great help. New techniques, including elastography, 3-dimensional US, and CEUS, are also discussed here. These techniques should be used as additional tools for making correct diagnoses.

Testicular trauma causes hemorrhage and infarction of the parenchyma, ultimately leading to necrosis. In serious cases, disruption of the tunica albuginea can occur, also known as testicular rupture, accompanied by parenchymal protrusion. This is an indication for urgent surgery, and early surgical intervention improves long-term testicular function [ 14 ]. Sonographic findings include changes in echogenicity due to hemorrhage and ischemia, and irregular testicular contours and/or discontinuity of the tunica albuginea suggest testicular rupture ( Fig. 6A ). Although tunica albuginea breach per se was visualized in only 50% of cases of testicular rupture in one study, US showed a sensitivity of 100% and a specificity of 65% for testicular rupture [ 51 ]. CEUS has been found to show no significant defect in enhancement in cases of minor trauma, and weak, inhomogeneous, or patchy enhancement for severely fractured testicles. Hematomas have been found to show no enhancement [ 14 ]. Magnetic resonance imaging may be an alternative modality when the use of US results in an inconclusive diagnosis [ 52 ].

If atresia of the uterine cervix, vagina, or hymen is present, menstrual blood discharge is obstructed at menarche, leading to hematometra, also called menstrual molimina. Usually, atresia goes unnoticed until abdominal pain occurs. Thus, radiologists sometimes encounter cases of hematometra presenting with acute abdominal pain. US shows uterine dilatation with echogenic fluid ( Fig. 11 ), with or without cervical dilatation, according to the area of atresia [ 85 ]. Fluid-fluid levels can be seen in some cases ( Fig. 11 ). Uterine or vaginal atresia with Müllerian duct anomalies is frequently accompanied by renal anomalies. In particular, renal aplasia is highly predictive of an ipsilateral obstructive Müllerian anomaly, with this association found in more than 50% of cases [ 86 ]. The combination of unilateral renal aplasia, a duplicated uterus, and vaginal occlusion with Gartner pseudocyst was initially reported by Herlyn and Werner in 1971 (Herlyn-Werner syndrome) [ 87 ]. Wunderlich [ 88 ] reported the combination of renal agenesis and hemicervical atresia in 1976 (Wunderlich syndrome). In 1979, these cases were reported as Herlyn-Werner and Wunderlich syndromes [ 89 ]. These concepts are often combined as Herlyn-WernerWunderlich syndrome, although the claim has been made that such a syndrome does not exist [ 90 ]. Recently, the term obstructed hemivagina and ipsilateral renal anomaly has also been commonly used because this concept incorporates all kinds of uterine anomalies other than a duplicated uterus. Thus, the definition of syndromes is complex; however, the key fact is quite simple: there is an association of urogenital anomalies on the same side. The typical presentation of these syndromes is abdominal pain at menarche. This diagnosis is relatively easy for pediatric radiologists familiar with these anomalies. However, these cases are sometimes initially misdiagnosed, probably because it is not possible to predict whether patients will initially visit emergency rooms, physicians, surgeons, or pediatricians. Moreover, radiologists may not always be involved. Thus, these patients should be noted before symptoms with routine US. In patients with renal dysplasia, the importance of investigating hemiuterine atresia has been stressed [ 91 ]. In the neonatal period, the uterus is relatively large because of maternal and placental hormones, and is suitable for the investigation of uterine anomalies ( Fig. 12 ). However, the uterus becomes smaller after this period until adolescence and is difficult to see whether a uterine anomaly exists ( Fig. 13 ). Thus, in cases of renal dysplasia, especially renal aplasia, an investigation to determine whether uterovaginal anomalies are present is recommended in the neonatal period [ 92 ].