Introduction 1 2 3 4 2 3 5 6 7 8 12 13 15 Materials and methods During a 7-year period, 880 boys referred to the Department of Paediatric Surgery, Erasmus MC-Sophia Children’s Hospital, Rotterdam, underwent primary surgery for UDT. US was performed in 137 of these children with 156 NPT. Prior to US the patients were clinically examined by a general practitioner, a paediatrician, a urologist or, in most cases, by a paediatric surgeon. Clinical examination by a paediatric surgeon was with the boy in the supine position, the lower half of the body undressed. The examiner placed the index finger and thumb of the right hand on either side of the inguinal canal, thus preventing testes lying distally from the inguinal canal from withdrawing into the inguinal region during palpation of the scrotum. With the examiner standing on the right side of the patient, the inguinal region was then examined with the fingertips of a warm left hand. If there seemed to be no palpable testis, an attempt was made to empty the inguinal canal by carrying out an ironing movement with the fingertips stroking in the direction of the scrotum. This may reveal a palpable testis at the level of the exit of the inguinal canal, immediately shooting back deep into the inguinal canal. If no testis could be located at all, the perineum, the base of the penis and the thigh were closely examined to exclude an ectopic testis. US was performed using an Ultramark 9 HDI unit (Advanced Technology Laboratories, Bothell, Wash.) with a high-frequency, broadband, 7–10-MHz linear array transducer or a Philips ATL HDI 5000 unit, also with a high-frequency, broadband, 5–12-MHz linear array transducer. US was performed by eight different paediatric radiologists. After US all boys were clinically re-examined by a paediatric surgeon and again on the operating table when under anaesthesia. Subsequently, all boys underwent surgery and testicular position and other operative findings were assessed intraoperatively. 16 All US findings were compared with intraoperative findings. Results Eligible for this study were 137 boys with 156 NPT. Excluded from analysis were two with Müllerian inhibitory factor deficiency syndrome, implying abnormal testis position. The ages of the remaining 135 boys ranged from 4 weeks to 16.2 years. Of the remaining 152 NPT, 70 were left-sided, 48 right-sided and 17 bilateral. Four patients (four NPT) had been referred to the radiologist by a general practitioner and 24 patients (30 NPT) by a paediatrician. Most patients, 107 with 118 NPT, were first diagnosed by a paediatric surgeon before being referred to the radiologist. All boys were seen by a paediatric surgeon after the US examination for re-examination and to discuss therapy determined by the US findings. With knowledge of the US results, 28% of the NPT previously diagnosed as not palpable now appeared to be palpable. Three of the four NPT (75%) in patients first seen by a general practitioner were palpable when re-examined by a paediatric surgeon, as was the case for 18 of 30 NPT (60%) referred by a paediatrician. Of the NPT first examined by a paediatric surgeon, 18% were palpable on re-examination with knowledge of the US results. US was able to locate 103 of 152 NPT (68%): 16 were found in the abdomen and 87 in an inguinal position; therefore 49 could not be found. Comparing the US results with the surgical findings, there was a 100% positive predictive value (PPV) for the 16 abdominal testes seen on US; all were indeed found abdominally. Nevertheless, 14 viable abdominally located testes were missed by US. At surgery, all these testes were found in the lower abdomen—on the iliopsoas muscle, in the pelvis, or close to the internal inguinal ring. US located 87 inguinal testes, 84 of which were indeed found in the inguinal region (97% PPV); the other three were viable and found intraabdominally. Thirty-five of the NPT were defined as small, atrophic or vanished at operation. Ultimately, US failed to locate 49 NPT. Nevertheless, 16 of these at surgery appeared to be viable, with 14 located intraabdominally and two in the inguinal region. Two atrophic testes were found in the abdomen. A further 22 atrophic testes were found inguinally or scrotally. Anorchia was present in nine boys. 1 Fig. 1 Ultrasound findings in 152 nonpalpable testes in relation to findings at operative exploration  Discussion 17 18 1 2 19 20 4 21 7 21 27 3 28 30 24 26 28 30 26 27 30 3 7 21 22 26 29 23 25 30 1 Table 1 n.a. Reference Study design n Located by US Located “true” NPT a a Re-examination Remarks Advice in NPT Positive Negative Testes palpable Previous examiner 22 Retrospective/medical charts 55 28/55 (51%) n.a. 84 100 67 n.a. – US 29 Prospective/cohort 62 37/62 (60%) n.a. 76 100 0 n.a. Vanished not included in accuracy and predictive values Laparoscopy 3 Retrospective/medical charts 66 12/66 (18%) 0/21 (0%) b b b 45/66 (68%) Referring physician 82% US ordered by referring physician; 93% US performed elsewhere Laparoscopy 23 Retrospective/medical charts 170 111/170 (65%) n.a. b b b n.a. – US 21 Prospective/cohort 74 48/74 (65%) 16/29 (55%) b b b 45/74 (61%) Referring physician Only nubbins palpable on re-examination US 24 Prospective/cohort 21 13/21 (62%) n.a. 76 92 50 n.a. US twice and blind to physical examination US → MRI 30 Retrospective/medical charts 22 5/12 (42%) 3/7 (43%) 58 100 29 13/22 (59%) Referring physician – Laparoscopy 7 Prospective/cohort 45 45/45 (100%) 6/8 (75%) 93 93 – 36/45 (80%) Referring physician Physical examination and US blind to each other US 26 Prospective/cohort 38 17/38 (45%) 1/18 (6%) 61 88 38 1/21 (5%) Expert US blind to physical examination US if obese 20/41 (49%) Referring physician 28 Prospective/cohort 14 2/14 (14%) n.a. 21 100 8 n.a Surgery blind to US Laparoscopy 27 Prospective/cohort 69 61/69 (88%) 4/12 (33%) 99 100 88 n.a  US 25 Prospective/cohort 23 15/23 (65%) n.a. 91 91 75 n.a. US and CT blind to each other US a b An important message emerging from these articles is the very high PPV of US and the importance of thorough examination by a physician with experience in small genital examination. More than two-thirds of testes of referred patients were palpable on examination by experienced physicians. Many US investigations could have been avoided if patients had first been referred to an expert. The (paediatric) radiologist’s experience is also vital and US should be undertaken in the hospital where further treatment will be given. 2 7 29 Fig. 2 Flow chart representing the diagnostic and therapeutic approach in boys with NPT  In summary, we found 97% sensitivity of US for viable inguinal testes and 48% sensitivity for viable abdominal testes. When US located a testis it was also found at that site during surgery in 97% of NPT (PPV 97%). In our study, only three viable testes were not located correctly, being in the inguinal canal at US and within the abdomen at surgery. This can be explained by the fact that there was a patent internal inguinal ring with a mobile testis. More than two-thirds of NPT could be localized with US. Approximately one-third of NPT that were not found with US appeared to be viable at surgery. Of 34 testes considered nonpalpable by a general practitioner or paediatrician, 21 (62%) were palpable on re-examination by a paediatric surgeon after US. In contrast, of 118 testes considered nonpalpable by a paediatric surgeon, only 21 (18%) were palpable on re-examination. Conclusion 2