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1
Department of Radiology, Queen Mary Hospital, 102 Pokfulam Rd., Hong
Kong.
2
Department of Surgery, Division of Pediatric Surgery, the University of Hong
Kong, Hong Kong.
Received May 25, 2000;
accepted after revision October 25, 2000.
Address correspondence to W. W. M. Lam.
Abstract
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SUBJECTS AND METHODS. Routine MR imaging and MR venography were performed in 34 patients presenting with impalpable testis. MR venography was performed by dynamic injection of gadopentetate dimeglumine bismethylamide with images taken at delayed venous phases. The site of the testis was determined by detection of the contrast-enhanced pampiniform venous plexus.
RESULTS. A total of 44 impalpable testes were examined. Twenty-six hypoplastic canalicular testes, two testes at pelvic skinfold, four atrophic testes in the scrotum, and five intraabdominal testes were detected on both routine MR imaging and MR venography. Five "vanishing" testes in the scrotum and two at the groin region were detected by MR venography but not on MR imaging.
CONCLUSION. Gadolinium-infusion MR venography is superior to MR imaging in the detection of atrophic testes. The method is a useful adjunct in patients with negative MR imaging findings.
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MR Imaging Techniques
MR imaging was performed with a 1.5-T superconducting whole-body imager
(Signa Horizon Echo-speed; General Electric Medical Systems, Milwaukee, WI). A
head coil was used for neonates and infants (< 1 year old). Older children
were imaged with a body coil. A sagittal spin-echo localizer (TR/TE, 500/9),
coronal and axial T2-weighted fat-saturation fast spin-echo sequences
(4000/102; excitations, 4; thickness, 4 mm; matrix size, 192 x 256), and
axial T1-weighted spin-echo sequences (600/9; excitations, 2; thickness, 4 mm;
matrix size, 192 x 256) were performed.
MR Venogram Techniques
Sagittal T1-weighted fast gradient-echo localizer images (12/1.1; flip
angle, 40°) were acquired first. A three-dimensional fast spoiled
gradient-recalled echo-pulse sequence (10.2/1.9; flip angle, 60°; number
of partitions, 28; partition thickness, 2 mm; matrix size, 256 x 128;
field of view, 20-30 cm; receiver bandwidth, 32kHz) was obtained in the
coronal plane. The acquisition time was about 28-35 sec, depending on the
number of slices included. Flow compensation and presaturation pulses were not
used.
Non—breath-hold dynamic three-dimensional images were obtained simultaneously after an IV bolus injection of gadolinium chelate. The dose of contrast material was set at 0.4 mmol of gadopentetate dimeglumine bismethylamide (Omniscan; Nycomed, Torshov, Norway) per kilogram of body weight if the body weight was less than 10 kg. A dose of 0.3 mmol per kilogram of body weight was given for children who were heavier than 10 kg of body weight. The injections were performed by hand via 22-gauge angiographic catheters. If the calculated volume of contrast material was less than 10 mL, a 1:1 dilution of contrast material to saline was used to increase the column of contrast material entering the vessels. The overall injection time was less than 1 min. Dynamic three-dimensional images were obtained at the start of injection of contrast material and then at 1, 2, 3, 4, and 5 min after the start of contrast injection. The overall scanning time of MR venography was about 5-7 min, including the preparation time.
Sedation
Patients younger than 5 years old received an oral sedative (chloral
hydrate, 50 mg/kg of body weight). An IV sedative (midazolam, 0.2-0.5 mg/kg of
body weight) was added if oral sedation was inadequate. Vital signs of
patients were carefully monitored during and after the examination.
Image Analysis
The testis was detected by enhancement of the pampiniform venous plexus at
different time intervals on MR venography sequences. Both the source images
and reconstructed images were reviewed. The images were reconstructed with the
Advantage Windows workstation (General Electric Medical Systems). Multiplanar
volume reconstruction post-processing software was used. Two radiologists
reviewed the MR images first, and then they reviewed the MR venograms
separately on the workstation without knowing the name of patients. In case of
disagreement between the two radiologists, they reviewed the MR venograms and
MR images together. A decision was reached by consensus. The findings of MR
imaging and MR venography were reported separately in each individual
patient.
The location of the testis was determined on MR imaging by the identification of focus of hyperintense signal on T2-weighted sequences and hypointense signal on T1-weighted sequences. On MR venograms, the location of the testis was determined by the detection of a bright linear enhanced pampiniform venous plexus. The testis was described as hypoplastic if its size was similar or slightly smaller than the normal one. Atrophic testis was considered if the size of the testis was small or reduced to a remnant. "Vanishing" testis was defined if blind-ending vas deferens and spermatic vessels were detected in the absence of the testis itself. In our study, vanishing testis was diagnosed if the bright linear enhanced pampiniform venous plexus was identified on the MR venography, but the testis could not be identified on T1- and T2-weighted sequences. If both MR venography and T1- and T2-weighted MR imaging failed to identify the testis and the pampiniform venous plexus, the testis was considered unidentified.
The imaging findings were correlated with surgical exploration or laparoscopic findings. The surgeons were aware of the imaging findings, and the surgical approach was planned according to the MR imaging and MR venography findings. Statistical analysis of the diagnostic difference between MR venography and MR imaging was performed by the chi-square test. Any p value less than 0.05 was considered statistically significant.
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On MR venography, the testis appears hypointense. The contrast-enhanced pampiniform venous plexus and the testicular vein appear as a bright line near the epididymis and then along the spermatic cord (Fig. 3A,3B). Another signal void line adjacent to the bright line could be caused by chemical shift artifact due to the remnant of a gubernaculum testis. A rim of contrast enhancement is detected around the testis (Fig. 1A,1B), giving rise to a rim or "hook" sign. This sign may represent vessels surrounding the testicular capsule. In our study, we found that the best timing for maximal enhancement of the pampiniform venous plexus was between 3 and 4 min after the injection of contrast media.
There was no discordance between the two radiologists in the interpretation of MR imaging findings. The two radiologists had discordant MR venography findings on initial interpretation in five (14.7%) of 34 patients. The eventual results on MR venography of these five patients were decided by consensus. Final diagnosis was determined by surgical exploration or laparoscopy. The sensitivities of MR imaging and MR venography were 84% and 100%, respectively. The specificities of both were 100%. The p value of the diagnostic difference between MR venography and MR imaging was less than 0.05 with the chi-square test; this difference was statistically significant.
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Although proper and adequate surgical exploration is likely to differentiate the various kinds of impalpable testes, the accuracy ranges from 88% to 100%, depending on the expertise of the surgeons [9, 10]. In a number of reported instances, patients with absent testes at previous surgeries were subsequently found to have testes present [11]. X-ray arteriography and venography require general anesthesia and are invasive and difficult to perform in infants. Sonography avoids the use of ionizing radiation and permits examination without sedation. Sometimes sonography can be difficult to perform in an un-cooperative unsedated patient. Moreover, imaging testis cephalic to the internal inguinal ring is difficult on sonography. Komine et al. [12] reported a sensitivity of 82.6%, a specificity of 100%, and an accuracy of 84.6% on sonography. Wolverson et al. [13] showed 94% sensitivity on CT, 88% sensitivity on sonography, and 100% specificity on both modalities, but their subjects were 3-23 years old, with 80% being 5 years or older. Because the body fat in a neonate or infant is relatively less than that in an older child, the accuracy of CT would be reduced. Another disadvantage of CT lies in the use of ionizing radiation. Maghnie et al. [14] reported that neither sonography nor MR imaging is currently sensitive enough to stand alone as a screening modality for impalpable testis because the two modalities used separately each give a useful result of 76%. Their combined specificity compared with surgical findings was 95%. Kier et al. [15] reported that MR imaging is not sensitive enough to allow complete exclusion of diagnosis of an undescended testis; thus, failure to localize a testis with MR imaging should not defer laparoscopy or surgical exploration.
The sensitivity of MR imaging in our study was 84% and was comparable to that reported in the literature (63-88%) [14, 15]. The ectopic testis is identified by the presence of characteristic bright signal on T2-weighted images and by a linear low-signal structure that represents the remnant of the gubernaculum testis. A limitation of MR imaging is that it cannot image the testis if a testis is absent or has vanished. In testicular atrophy, the normal testicular bright signal may be changed or lost, and this change would make it difficult to differentiate the atrophied testis from surrounding tissues. In vanishing testis, the testis is absent with only a blind-ended vas deferens and spermatic vessels remaining. Identifying its vascular supply is the most reliable method of locating the testis. Laparoscopy provides direct visualization of the testicular vessels and has been reported to be a sensitive method for locating the testis [4, 16]. Similar to laparoscopy, gadolinium-infusion MR venography is intended to localize the pampiniform venous plexus instead of imaging the testis itself, but this modality is noninvasive and can be performed preoperatively without general anesthesia.
If the testis could not be found on MR imaging, the cause could be vanishing testis or intraabdominal testis that was unidentified or obscured by the bowels. It is essential to differentiate this cause because an error will risk leaving an intraabdominal testis, which has significant risk of malignant degeneration. In our center, if the testis could not be found on any imaging modalities such as sonography, CT, or MR imaging, the surgeon proceeded to laparoscopy and then to surgical exploration if the testis could not be identified by laparoscopy at the groin and lower abdomen. In our study, MR venography could accurately identify the spermatic vessels even when the testis was absent. MR venography is therefore superior to routine MR imaging for the localization of vanishing testes and helps to guide the site of entrance of the laparoscope and the choice of operation. Unplanned groin exploration may be detrimental to the outcome of surgery for intraabdominal testis. Groin exploration could jeopardize the effectiveness of the alternate procedure of microvascular orchidopexy by disrupting tissue planes.
To obtain quality images, an adequate dose of contrast material is important. Besides the dose, the actual volume of contrast material entering the vessels is important. We found that both the source images and multiplanar volume reconstruction postprocessing images could show the spermatic vessels clearly. However, during the interpretation of images, radiologists should be careful to differentiate the spermatic vessels from other vessels present at the groin and scrotal regions. The spermatic vessels should be draining from the groin or scrotal region to the abdomen via the inguinal canal (Fig. 5A,5B,5C). The external pudendal vein should not be mistaken for the spermatic vessel because the external pudendal vein runs horizontally across the groin region from the great saphenous vein to the penis (Fig. 5A,5B,5C). The external pudendal vein and the spermatic vessel can be better differentiated on source images than on multiplanar volume reconstruction postprocessing images. We also found that the rim enhancement at skinfolds around the scrotum and penis and the enhancement of dorsal veins at the penis might create some problems in the identification of the spermatic vessels. Because the penis is usually deviated to the side of scrotum in which the testis is absent, it will obscure the spermatic vessels and thus make interpretation difficult. We recommend stabilization of the penis to the midline of the lower pelvis to avoid the confusion created by the enhancement of dorsal veins and the skinfold.
In our few patients with intraabdominal testes, the testes were mainly located near the inguinal canal and next to the bladder. We found that it was more difficult to detect the enhanced pampiniform venous plexus in that region because of enhancement of adjacent vessels such as the external iliac vessels. By adjusting different angles of rotation and different slice thicknesses with multiplanar volume reconstruction postprocessing, the adjacent vessels can be avoided (Fig. 4A,4B,4C). So far, we have no experience in detecting high intraabdominal testis. Because of the enhancement of abundant bowel vessels, we suspect that the detection of spermatic vessels would be problematic in the abdomen. The usefulness of MR venography in such cases has yet to be determined.
In our study, we had not referred our patients to sonography; thus, we could not compare the findings on MR imaging and MR venography with those on sonography. However, in comparison with the studies of Komine et al. [12] and Wolverson et al. [13], our sensitivity of MR imaging (84%) was comparable to that of sonography (82-88%). In our opinion, if the testicular tissue is present, MR imaging or sonography may provide similar results. Because sonography is easily available and without irradiation, it may be considered the first line of investigation. However, in cases of vanishing testis, because the testicular tissue is not present, MR venography is clearly better than MR imaging or sonography in identifying the testis.
In summary, gadolinium-infusion MR venography is a noninvasive, safe, and accurate method for the localization of impalpable testis. It is recommended as an adjunctive method for localization of impalpable testis when MR imaging or sonographic findings are negative.
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