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The role of magnetic resonance imaging in fetal renal anomalies
International Journal of Gynecology and Obstetrics 111 (2010) 209–212
Contents lists available at ScienceDirect
International Journal of Gynecology and Obstetrics j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i j g o
CLINICAL ARTICLE
The role of magnetic resonance imaging in fetal renal anomalies Prerna Gupta a,⁎, Sunesh Kumar a, Raju Sharma b, Ankur Gadodia b, Kallol K. Roy a, Jai B. Sharma a a b
Department of Obstetrics and Gynecology, All India Institute of Medical Sciences, New Delhi, India Department of Radio Diagnosis, All India Institute of Medical Sciences, New Delhi, India
a r t i c l e
i n f o
Article history: Received 15 May 2010 Received in revised form 9 July 2010 Accepted 24 August 2010 Keywords: Congenital anomaly Fetus Magnetic resonance imaging Ultrasound Urinary system
a b s t r a c t Objective: To evaluate the role of magnetic resonance imaging (MRI) in fetuses with suspected renal anomalies after ultrasonography. Methods: Eighty-six consecutive singleton fetuses with suspected malformation after ultrasound underwent MRI at the All India Institute of Medical Sciences, New Delhi, India, from January 1, 2005, to July 31, 2008. The study group comprised 27 fetuses with suspected renal anomaly on ultrasound. The MRI findings were compared with the sonographic findings, and their impact on management was assessed. Postpartum imaging, autopsy, or surgical findings were taken as the gold standard of assessment and diagnosis. Results: The sonographic findings in 19 (70.4%) cases were confirmed by MRI; additional findings were obtained with MRI in 7 (25.9%) cases, 3 (11.1%) of which resulted in a change in postnatal management. Additional information was also provided by MRI for 5 (50.0%) of the 10 fetuses with oligohydramnios. The MRI diagnosis was incorrect—compared with ultrasound and gold standard—for 2 (7.4%) fetuses. Conclusion: Ultrasound is the imaging modality of choice for the diagnosis of fetal renal anomalies; fetal MRI is a useful adjunct, especially when ultrasound is inconclusive owing to oligohydramnios. © 2010 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved.
1. Introduction Genitourinary anomalies constitute 14%–40% of anomalies detected during prenatal sonography [1,2]. Ultrasound is an excellent modality for evaluating the fetal urinary tract [3], but may be limited because of fetal position, maternal obesity, overlying bone, and oligohydramnios— which is commonly associated with fetal uropathies. Magnetic resonance imaging (MRI) as a complementary modality is becoming more popular in such settings [3–6] because it enables the fetus to be viewed in multiple planes, irrespective of fetal lie, and has excellent contrast resolution. However, there have been only a small number of studies on a limited number of patients with regard to the role of MRI in detecting and managing fetal uropathies [7–11]. The aim of the present study was to evaluate the role of MRI in detecting sonographically suspected renal anomalies and its impact on management of the condition/parental counseling. 2. Materials and methods A prospective study was conducted at the All India Institute of Medical Sciences, New Delhi, India, from January 1, 2005, to July 31, 2008. Eighty-six consecutive singleton fetuses with suspected malformation following ultrasound underwent MRI. Of these fetuses,
⁎ Corresponding author. Department of Obstetrics and Gynecology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110029, India. Tel.: + 91 9868636821; fax: + 91 1126862663. E-mail address: [email protected] (P. Gupta).
27 had suspected renal anomalies on ultrasound and formed the study group. Mothers of fetuses with contraindication to MRI were excluded from the study. Sonography was performed using Ultramark HDI 1500 (Philips Medical System, Bothell, WA, USA); MRI was carried out with a 1.5-T Sonata (Siemens, Erlanger, Germany) or Avanto (Siemens, Erlanger, Germany) scanner. The scanners were used based on availability at the time of scanning, with Avanto preferred to Sonata. T1- and T2weighted sequences were obtained in multiple orthogonal planes with regard to fetal orientation. Half-Fourier acquisition single-shot turbo spin-echo and true fast imaging with steady-state precession were used in an optimum fashion. Contrast agents and maternal sedation were not used, and all MRI studies were assessed by the same radiologist (RS)—who was blinded to the sonography results. Fetal autopsy, neonatal imaging, or postnatal surgical findings were taken as the gold standard of assessment. Magnetic resonance imaging was considered to have influenced management if subsequent treatment was affected by the MRI findings. The study was approved by the institutional ethics committee, and informed consent was obtained from the mothers of all fetuses. 3. Results In total, 86 fetuses were included in the study, of which 27 had suspected renal anomalies on ultrasound and formed the study group (mean gestational age 27 weeks [range 18–37 weeks]) (Table 1). In the 40.7% of fetuses that were younger than 24 weeks of gestation, MRI diagnosis was also used in the decision on whether to terminate pregnancy. A total of 10 (37%) cases were associated with severe
0020-7292/$ – see front matter © 2010 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ijgo.2010.07.024
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P. Gupta et al. / International Journal of Gynecology and Obstetrics 111 (2010) 209–212
Table 1 Distribution of anomalies (n = 27). Diagnosis
Number (percentage)
Pelviureteric junction obstruction Recessive polycystic kidney disease Multicystic dysplastic kidney Cystic dysplastic kidney Bilateral renal agenesis Unilateral renal agenesis Posterior urethral valvea Severe oligohydramnios Duplex kidney
9 (33.3) 5 (18.5) 3 (11.1) 2 (7.4) 2 (7.4) 2 (7.4) 2 (7.4) 2 (7.4) 1 (3.7)
a
One case of posterior urethral valves had associated cystic dysplastic kidney.
Table 2 Impact of magnetic resonance imaging on genitourinary anomalies.a Genitourinary anomalies
Number of cases
Additional information provided Changes to counseling Diagnosis changed Management changed Confirmation of diagnosis
7 (25.9) 2 (7.4) 3 (11.1) 3 (11.1) 19 (70.4)
a
Fig. 1. Magnetic resonance urography image showing gross hydronephrosis of bilateral kidneys (right side more than left). No ureteral dilatation was seen, indicative of pelviureteric junction obstruction.
Values are given as number (percentage).
oligohydramnios. Magnetic resonance imaging was technically satisfactory in all cases. The gold standards of fetal autopsy, neonatal imaging, and postnatal surgery were performed in 11, 14 (12 ultrasound and 2 MRI), and 2 cases, respectively. Ultrasound findings were confirmed by MRI in 19 (70.4%) cases, which were also confirmed by postnatal examination (Table 2). In 7 (25.9%) cases, MRI provided additional findings, which resulted in a change in postnatal management in 3 (11.1%) cases. There were 2 (7.4%) cases in which MRI diagnosis was incorrect compared with ultrasound findings, and 1 case of duplex kidney was missed on both ultrasound and MRI. Based on the gold standard of assessment, fetal hydronephrosis and pelviureteric junction (PUJ) obstruction were present in 9 (33.3%) cases (Table 3). The diagnosis following fetal sonography was correct for 8 of these cases, whereas the diagnosis following fetal MRI was correct for all 9. In 2 fetuses with PUJ obstruction, MRI diagnosis resulted in a change in postnatal management. For 1 case of severe PUJ obstruction—which had been incorrectly diagnosed as a non-specific abdominal cyst following fetal ultrasound—MRI was used to diagnose gross right hydronephrosis correctly, and early postnatal surgery was planned. In another case of bilateral PUJ obstruction, magnetic resonance urography revealed more hydronephrosis on the right side than on the left, resulting in early postnatal surgery (Fig. 1).
According to gold-standard assessment, there were 10 fetuses with cystic renal disease (5 with autosomal recessive polycystic kidney disease [ARPKD]), 3 with multicystic dysplastic kidney (MCKD), and 2 with cystic dysplasia). Nine were correctly diagnosed via ultrasound, whereas all 10 were correctly diagnosed using MRI. In the cases of ARPKD, MRI showed bilateral enlarged kidneys as areas of high signal intensity on T2-weighted images (Fig. 2), whereas it revealed multiple non-communicating cysts that were separate from the pelvicalyceal system in the cases of MCKD (Fig. 3). Magnetic resonance imaging did not have any advantage over ultrasound in diagnosing ARPKD and MCDK. In 1 case of MCDK diagnosed following ultrasound, MRI revealed an additional finding of colpocephaly but, because there was associated agenesis of the other kidney, management of the condition was not changed. In 1 case, ultrasound at 24 weeks revealed only posterior urethral valves, whereas MRI also demonstrated cystic dysplasia of the kidneys, resulting in a decision to terminate the pregnancy. Two fetuses had bilateral renal agenesis, which—in each case— was correctly diagnosed with both ultrasound and MRI. Severe oligohydramnios was present, and MRI provided better visualization compared with ultrasound, revealing empty renal fossa (Fig. 4). Two fetuses with unilateral renal agenesis were incorrectly diagnosed as having small hypoplastic kidney following MRI.
Table 3 Additional findings and missed diagnoses of urinary anomalies following MRI. USG diagnosis
Additional finding with MRI
Oligohydramnios
Comments
Bilateral hydronephrosis
PUJ obstruction (right side more than left) Right hydronephrosis (PUJ obstruction) Mild bilateral hydronephrosis Confirmed normal anatomy Dysplastic kidney
Present (n = 1)
Severe hydronephrosis more on right side; early postnatal surgery planned (management changed) Confirmed anatomic location (diagnosis and postnatal management changed)
Right-sided cyst Mild polyhydramnios Severe oligohydramnios (n = 2) Posterior urethral valve; decreased liquor Absent unilateral kidney Left multicystic kidney; right renal agenesis Right hydronephrosis
Both kidneys observed Left multicystic kidney; right hypoplastic kidney Duplex moiety
Absent
Absent Present (n = 1)
Additional finding (diagnosis changed) Important in counseling Cystic dysplastic kidney associated with poor outcome in PUV observed (management changed) Incorrect diagnosis Missed diagnosis of right renal agenesis
Absent
Duplex kidney
Absent Present (n = 2) Present (n = 1)
Abbreviations: MRI, magnetic resonance imaging; PUJ, pelviureteric junction obstruction; USG, ultrasonography.
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211
Fig. 2. A 28-week-old fetus with autosomal recessive polycystic kidney disease (ARPKD). A. Ultrasound showing enlarged hyperechoic kidneys. B. Axial T2-weighted magnetic resonance image showing bilaterally enlarged hyperintense kidneys. The findings indicate ARPKD.
Fig. 3. A 30-week-old fetus with multicystic dysplastic kidney (MCKD). A. Ultrasound showing unilateral enlarged kidney with multiple peripherally arranged cysts of varying size. B. Axial T2-weighted image showing multiple hyperintense cysts in an enlarged kidney, indicative of MCKD.
The renal anomalies were not compatible with life in 10 cases (5 cases of ARPKD, 2 cases of cystic dysplastic kidney, 2 cases of bilateral renal agenesis, and 1 case of unilateral renal agenesis with contralateral MCKD). In 1 case of ARPKD and 1 case of bilateral renal agenesis, there was a signal void in the region of the bladder. In the other cases, either the bladder was not seen or the bladder was observed with bright signal intensity on T2-weighted images. Magnetic resonance imaging provided additional information in 5 (50.0%) of the 10 cases in which oligohydramnios was present (Table 3); in 2 fetuses with anhydramnios, ultrasonography was
inconclusive and MRI was performed to rule out renal anomalies (Fig. 5). Normal kidneys were identified via MRI in both cases.
4. Discussion Ultrasonography is the primary imaging modality for fetal evaluation, and its availability and low cost make it the ideal screening method for low-risk populations. Fetal MRI is also a safe and robust technique in cases of equivocal sonographic findings [12,13].
Fig. 4. A 28-week-old fetus with bilateral renal agenesis. A. Ultrasound showing severe oligohydramnios. Bilateral kidneys were not visualized. B. T2-weighted coronal magnetic resonance image showing severe oligohydramnios and absence of kidneys.
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kidney following MRI, and 1 case of bilateral hypoplastic kidney was incorrectly diagnosed as bilateral renal agenesis. In the present study, there were 10 cases of lethal renal anomalies; there was a signal void in the bladder region with MRI in only 2 of these cases (1 ARPKD and 1 bilateral renal agenesis). However, a signal void in the region of the pelvicalyceal system was observed in all cases in a study by Hawkins et al. [17]. Thus, further studies are required to validate the role of signal voids in the bladder with regard to identifying lethal renal anomalies. Ultrasound is the first-choice screening method for evaluating fetal renal anomalies. Magnetic resonance imaging has a definite supplemental role when sonographic findings are inconclusive, particularly when oligohydramnios is present. Conflict of interest The authors have no conflicts of interest. References Fig. 5. T2W MR image showing normal anatomy in a case associated with severe oligohydramnios.
Congenital renal anomalies are often associated with oligohydramnios, which can make sonographic evaluation difficult, whereas fetal MRI is not significantly affected by diminished amniotic fluid. On T2-weighted images, fetal kidneys are seen as oval structures with intermediate signal intensity on either side of the spine [14,15]. The presence of urine enables easy visualization of the renal collecting system as high-signal structures in the middle of the kidney. Several reports have been published regarding the role of MRI in the detection and management of central nervous system and thoracic anomalies, but only a small number of case series have been published on the use of MRI in the evaluation of fetal uropathies [7–11]. Prenatal detection of fetal uropathy is associated with a mortality rate of 20%–50%, and associated anomalies have been found in 3%–26% of fetuses [16]. In the present study, MRI provided additional information in 7 (25.9%) cases, in 3 (11.1%) of which it led to a change in postnatal management. These results are comparable to those of Cassart et al. [8] and Alamo et al. [10], who reported that additional information was provided by MRI in 29%–33% of cases. The range of rates in these studies may have been due to unequal distribution of pathologies. Magnetic resonance imaging provided additional information in 50.0% of cases associated with oligohydramnios, which is similar to the 41.7% (in addition to the 30.0% in cases with normal levels of amniotic fluid) reported by Poutamo et al. [7]. Thus, MRI can have a definite supplemental role when oligohydramnios is present. Compared with ultrasound, MRI enabled better visualization of the 2 fetuses with bilateral renal agenesis and severe oligohydramnios, which is consistent with the results of previous studies [6–8]. However, MRI might not enable a definitive diagnosis in cases of suspected renal agenesis and poor visibility—in the present study, 2 cases of unilateral agenesis were incorrectly diagnosed as hypoplastic
[1] Filly RA, Feldstein VA. Fetal genitourinary tract. In: Callen PW, editor. Ultrasonography in Obstetrics and Gynecology. Philadelphia: Saunders; 2000. p. 515–50. [2] The urinary tract and adrenal glands. In: Romero R, Pilu G, Jeanty P, Ghidini A, Hobbins JC, editors. Prenatal Diagnosis of Congenital Anomalies. Norwalk: Appleton & Lange; 1988. p. 255–300. [3] Sivit CJ, Hill MC, Larsen JW, Kent SG, Lande IM. The sonographic evaluation of fetal anomalies in oligohydramnios between 16 and 30 weeks gestation. AJR Am J Roentgenol 1986;146(6):1277–81. [4] Kubik-Huch RA, Huisman TA, Wisser J, Gottstein-Aalame N, Debatin JF, Seifert B, et al. Ultrafast MR imaging of the fetus. AJR Am J Roentgenol 2000;174(6): 1599–606. [5] Levine D. Magnetic resonance imaging in prenatal diagnosis. Curr Opin Pediatr 2001;13(6):572–8. [6] Breysem L, Bosmans H, Dymarkowski S, Schoubroeck DV, Witters I, Deprest J, et al. The value of fast MR imaging as an adjunct to ultrasound in prenatal diagnosis. Eur Radiol 2003;13(7):1538–48. [7] Poutamo J, Vanninen R, Partanen K, Kirkinen P. Diagnosing fetal urinary tract abnormalities: benefits of MRI compared to ultrasonography. Acta Obstet Gynecol Scand 2000;79(1):65–71. [8] Cassart M, Massez A, Metens T, Rypens F, Lambot MA, Hall M, et al. Complementary role of MRI after sonography in assessing bilateral urinary tract anomalies in the fetus. AJR Am J Roentgenol 2004;182(3):689–95. [9] Caire JT, Ramus RM, Magee KP, Fullington BK, Ewalt DH, Twickler DM. MRI of fetal genitourinary anomalies. AJR Am J Roentgenol 2003;181(5):1381–5. [10] Alamo L, Tarek L, Pierre S, Reto M, Yvan V, Maria-Chiara O, et al. Fetal MRI as complement to US in the diagnosis and characterization of anomalies of the genito-urinary tract. Eur J Radiol 2009 [Electronic publication ahead of print]. doi: 19643559. [11] Barseghyan K, Jackson HA, Chmait R, De Filippo RE, Miller DA. Complementary roles of sonography and magnetic resonance imaging in the assessment of fetal urinary tract anomalies. J Ultrasound Med 2008;27(11):1563–9. [12] Garden AS, Griffiths RD, Weindling AM, Martin PA. Fast-scan magnetic resonance imaging in fetal visualization. Am J Obstet Gynecol 1991;164(5 Pt 1):1190–6. [13] Baker PN, Johnson IR, Harvey PR, Gowland PA, Mansfield P. A three-year follow-up of children imaged in utero with echo-planar magnetic resonance. Am J Obstet Gynecol 1994;170(1 Pt 1):32–3. [14] Hörmann M, Brugger PC, Balassy C, Witzani L, Prayer D. Fetal MRI of the urinary system. Eur J Radiol 2006;57(2):303–11. [15] Martín C, Darnell A, Durán C, Bermúdez P, Mellado F, Rigol S. Magnetic resonance imaging of the intrauterine fetal genitourinary tract: normal anatomy and pathology. Abdom Imaging 2004;29(3):286–302. [16] Cusick EL, Didier F, Droulle P, Schmitt M. Mortality after an antenatal diagnosis of foetal uropathy. J Pediatr Surg 1995;30(3):463–6. [17] Hawkins JS, Dashe JS, Twickler DM. Magnetic resonance imaging diagnosis of severe fetal renal anomalies. Am J Obstet Gynecol 2008;198(3) 328.e1–5.
Contents lists available at ScienceDirect
International Journal of Gynecology and Obstetrics j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i j g o
CLINICAL ARTICLE
The role of magnetic resonance imaging in fetal renal anomalies Prerna Gupta a,⁎, Sunesh Kumar a, Raju Sharma b, Ankur Gadodia b, Kallol K. Roy a, Jai B. Sharma a a b
Department of Obstetrics and Gynecology, All India Institute of Medical Sciences, New Delhi, India Department of Radio Diagnosis, All India Institute of Medical Sciences, New Delhi, India
a r t i c l e
i n f o
Article history: Received 15 May 2010 Received in revised form 9 July 2010 Accepted 24 August 2010 Keywords: Congenital anomaly Fetus Magnetic resonance imaging Ultrasound Urinary system
a b s t r a c t Objective: To evaluate the role of magnetic resonance imaging (MRI) in fetuses with suspected renal anomalies after ultrasonography. Methods: Eighty-six consecutive singleton fetuses with suspected malformation after ultrasound underwent MRI at the All India Institute of Medical Sciences, New Delhi, India, from January 1, 2005, to July 31, 2008. The study group comprised 27 fetuses with suspected renal anomaly on ultrasound. The MRI findings were compared with the sonographic findings, and their impact on management was assessed. Postpartum imaging, autopsy, or surgical findings were taken as the gold standard of assessment and diagnosis. Results: The sonographic findings in 19 (70.4%) cases were confirmed by MRI; additional findings were obtained with MRI in 7 (25.9%) cases, 3 (11.1%) of which resulted in a change in postnatal management. Additional information was also provided by MRI for 5 (50.0%) of the 10 fetuses with oligohydramnios. The MRI diagnosis was incorrect—compared with ultrasound and gold standard—for 2 (7.4%) fetuses. Conclusion: Ultrasound is the imaging modality of choice for the diagnosis of fetal renal anomalies; fetal MRI is a useful adjunct, especially when ultrasound is inconclusive owing to oligohydramnios. © 2010 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved.
1. Introduction Genitourinary anomalies constitute 14%–40% of anomalies detected during prenatal sonography [1,2]. Ultrasound is an excellent modality for evaluating the fetal urinary tract [3], but may be limited because of fetal position, maternal obesity, overlying bone, and oligohydramnios— which is commonly associated with fetal uropathies. Magnetic resonance imaging (MRI) as a complementary modality is becoming more popular in such settings [3–6] because it enables the fetus to be viewed in multiple planes, irrespective of fetal lie, and has excellent contrast resolution. However, there have been only a small number of studies on a limited number of patients with regard to the role of MRI in detecting and managing fetal uropathies [7–11]. The aim of the present study was to evaluate the role of MRI in detecting sonographically suspected renal anomalies and its impact on management of the condition/parental counseling. 2. Materials and methods A prospective study was conducted at the All India Institute of Medical Sciences, New Delhi, India, from January 1, 2005, to July 31, 2008. Eighty-six consecutive singleton fetuses with suspected malformation following ultrasound underwent MRI. Of these fetuses,
⁎ Corresponding author. Department of Obstetrics and Gynecology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110029, India. Tel.: + 91 9868636821; fax: + 91 1126862663. E-mail address: [email protected] (P. Gupta).
27 had suspected renal anomalies on ultrasound and formed the study group. Mothers of fetuses with contraindication to MRI were excluded from the study. Sonography was performed using Ultramark HDI 1500 (Philips Medical System, Bothell, WA, USA); MRI was carried out with a 1.5-T Sonata (Siemens, Erlanger, Germany) or Avanto (Siemens, Erlanger, Germany) scanner. The scanners were used based on availability at the time of scanning, with Avanto preferred to Sonata. T1- and T2weighted sequences were obtained in multiple orthogonal planes with regard to fetal orientation. Half-Fourier acquisition single-shot turbo spin-echo and true fast imaging with steady-state precession were used in an optimum fashion. Contrast agents and maternal sedation were not used, and all MRI studies were assessed by the same radiologist (RS)—who was blinded to the sonography results. Fetal autopsy, neonatal imaging, or postnatal surgical findings were taken as the gold standard of assessment. Magnetic resonance imaging was considered to have influenced management if subsequent treatment was affected by the MRI findings. The study was approved by the institutional ethics committee, and informed consent was obtained from the mothers of all fetuses. 3. Results In total, 86 fetuses were included in the study, of which 27 had suspected renal anomalies on ultrasound and formed the study group (mean gestational age 27 weeks [range 18–37 weeks]) (Table 1). In the 40.7% of fetuses that were younger than 24 weeks of gestation, MRI diagnosis was also used in the decision on whether to terminate pregnancy. A total of 10 (37%) cases were associated with severe
0020-7292/$ – see front matter © 2010 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ijgo.2010.07.024
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Table 1 Distribution of anomalies (n = 27). Diagnosis
Number (percentage)
Pelviureteric junction obstruction Recessive polycystic kidney disease Multicystic dysplastic kidney Cystic dysplastic kidney Bilateral renal agenesis Unilateral renal agenesis Posterior urethral valvea Severe oligohydramnios Duplex kidney
9 (33.3) 5 (18.5) 3 (11.1) 2 (7.4) 2 (7.4) 2 (7.4) 2 (7.4) 2 (7.4) 1 (3.7)
a
One case of posterior urethral valves had associated cystic dysplastic kidney.
Table 2 Impact of magnetic resonance imaging on genitourinary anomalies.a Genitourinary anomalies
Number of cases
Additional information provided Changes to counseling Diagnosis changed Management changed Confirmation of diagnosis
7 (25.9) 2 (7.4) 3 (11.1) 3 (11.1) 19 (70.4)
a
Fig. 1. Magnetic resonance urography image showing gross hydronephrosis of bilateral kidneys (right side more than left). No ureteral dilatation was seen, indicative of pelviureteric junction obstruction.
Values are given as number (percentage).
oligohydramnios. Magnetic resonance imaging was technically satisfactory in all cases. The gold standards of fetal autopsy, neonatal imaging, and postnatal surgery were performed in 11, 14 (12 ultrasound and 2 MRI), and 2 cases, respectively. Ultrasound findings were confirmed by MRI in 19 (70.4%) cases, which were also confirmed by postnatal examination (Table 2). In 7 (25.9%) cases, MRI provided additional findings, which resulted in a change in postnatal management in 3 (11.1%) cases. There were 2 (7.4%) cases in which MRI diagnosis was incorrect compared with ultrasound findings, and 1 case of duplex kidney was missed on both ultrasound and MRI. Based on the gold standard of assessment, fetal hydronephrosis and pelviureteric junction (PUJ) obstruction were present in 9 (33.3%) cases (Table 3). The diagnosis following fetal sonography was correct for 8 of these cases, whereas the diagnosis following fetal MRI was correct for all 9. In 2 fetuses with PUJ obstruction, MRI diagnosis resulted in a change in postnatal management. For 1 case of severe PUJ obstruction—which had been incorrectly diagnosed as a non-specific abdominal cyst following fetal ultrasound—MRI was used to diagnose gross right hydronephrosis correctly, and early postnatal surgery was planned. In another case of bilateral PUJ obstruction, magnetic resonance urography revealed more hydronephrosis on the right side than on the left, resulting in early postnatal surgery (Fig. 1).
According to gold-standard assessment, there were 10 fetuses with cystic renal disease (5 with autosomal recessive polycystic kidney disease [ARPKD]), 3 with multicystic dysplastic kidney (MCKD), and 2 with cystic dysplasia). Nine were correctly diagnosed via ultrasound, whereas all 10 were correctly diagnosed using MRI. In the cases of ARPKD, MRI showed bilateral enlarged kidneys as areas of high signal intensity on T2-weighted images (Fig. 2), whereas it revealed multiple non-communicating cysts that were separate from the pelvicalyceal system in the cases of MCKD (Fig. 3). Magnetic resonance imaging did not have any advantage over ultrasound in diagnosing ARPKD and MCDK. In 1 case of MCDK diagnosed following ultrasound, MRI revealed an additional finding of colpocephaly but, because there was associated agenesis of the other kidney, management of the condition was not changed. In 1 case, ultrasound at 24 weeks revealed only posterior urethral valves, whereas MRI also demonstrated cystic dysplasia of the kidneys, resulting in a decision to terminate the pregnancy. Two fetuses had bilateral renal agenesis, which—in each case— was correctly diagnosed with both ultrasound and MRI. Severe oligohydramnios was present, and MRI provided better visualization compared with ultrasound, revealing empty renal fossa (Fig. 4). Two fetuses with unilateral renal agenesis were incorrectly diagnosed as having small hypoplastic kidney following MRI.
Table 3 Additional findings and missed diagnoses of urinary anomalies following MRI. USG diagnosis
Additional finding with MRI
Oligohydramnios
Comments
Bilateral hydronephrosis
PUJ obstruction (right side more than left) Right hydronephrosis (PUJ obstruction) Mild bilateral hydronephrosis Confirmed normal anatomy Dysplastic kidney
Present (n = 1)
Severe hydronephrosis more on right side; early postnatal surgery planned (management changed) Confirmed anatomic location (diagnosis and postnatal management changed)
Right-sided cyst Mild polyhydramnios Severe oligohydramnios (n = 2) Posterior urethral valve; decreased liquor Absent unilateral kidney Left multicystic kidney; right renal agenesis Right hydronephrosis
Both kidneys observed Left multicystic kidney; right hypoplastic kidney Duplex moiety
Absent
Absent Present (n = 1)
Additional finding (diagnosis changed) Important in counseling Cystic dysplastic kidney associated with poor outcome in PUV observed (management changed) Incorrect diagnosis Missed diagnosis of right renal agenesis
Absent
Duplex kidney
Absent Present (n = 2) Present (n = 1)
Abbreviations: MRI, magnetic resonance imaging; PUJ, pelviureteric junction obstruction; USG, ultrasonography.
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Fig. 2. A 28-week-old fetus with autosomal recessive polycystic kidney disease (ARPKD). A. Ultrasound showing enlarged hyperechoic kidneys. B. Axial T2-weighted magnetic resonance image showing bilaterally enlarged hyperintense kidneys. The findings indicate ARPKD.
Fig. 3. A 30-week-old fetus with multicystic dysplastic kidney (MCKD). A. Ultrasound showing unilateral enlarged kidney with multiple peripherally arranged cysts of varying size. B. Axial T2-weighted image showing multiple hyperintense cysts in an enlarged kidney, indicative of MCKD.
The renal anomalies were not compatible with life in 10 cases (5 cases of ARPKD, 2 cases of cystic dysplastic kidney, 2 cases of bilateral renal agenesis, and 1 case of unilateral renal agenesis with contralateral MCKD). In 1 case of ARPKD and 1 case of bilateral renal agenesis, there was a signal void in the region of the bladder. In the other cases, either the bladder was not seen or the bladder was observed with bright signal intensity on T2-weighted images. Magnetic resonance imaging provided additional information in 5 (50.0%) of the 10 cases in which oligohydramnios was present (Table 3); in 2 fetuses with anhydramnios, ultrasonography was
inconclusive and MRI was performed to rule out renal anomalies (Fig. 5). Normal kidneys were identified via MRI in both cases.
4. Discussion Ultrasonography is the primary imaging modality for fetal evaluation, and its availability and low cost make it the ideal screening method for low-risk populations. Fetal MRI is also a safe and robust technique in cases of equivocal sonographic findings [12,13].
Fig. 4. A 28-week-old fetus with bilateral renal agenesis. A. Ultrasound showing severe oligohydramnios. Bilateral kidneys were not visualized. B. T2-weighted coronal magnetic resonance image showing severe oligohydramnios and absence of kidneys.
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kidney following MRI, and 1 case of bilateral hypoplastic kidney was incorrectly diagnosed as bilateral renal agenesis. In the present study, there were 10 cases of lethal renal anomalies; there was a signal void in the bladder region with MRI in only 2 of these cases (1 ARPKD and 1 bilateral renal agenesis). However, a signal void in the region of the pelvicalyceal system was observed in all cases in a study by Hawkins et al. [17]. Thus, further studies are required to validate the role of signal voids in the bladder with regard to identifying lethal renal anomalies. Ultrasound is the first-choice screening method for evaluating fetal renal anomalies. Magnetic resonance imaging has a definite supplemental role when sonographic findings are inconclusive, particularly when oligohydramnios is present. Conflict of interest The authors have no conflicts of interest. References Fig. 5. T2W MR image showing normal anatomy in a case associated with severe oligohydramnios.
Congenital renal anomalies are often associated with oligohydramnios, which can make sonographic evaluation difficult, whereas fetal MRI is not significantly affected by diminished amniotic fluid. On T2-weighted images, fetal kidneys are seen as oval structures with intermediate signal intensity on either side of the spine [14,15]. The presence of urine enables easy visualization of the renal collecting system as high-signal structures in the middle of the kidney. Several reports have been published regarding the role of MRI in the detection and management of central nervous system and thoracic anomalies, but only a small number of case series have been published on the use of MRI in the evaluation of fetal uropathies [7–11]. Prenatal detection of fetal uropathy is associated with a mortality rate of 20%–50%, and associated anomalies have been found in 3%–26% of fetuses [16]. In the present study, MRI provided additional information in 7 (25.9%) cases, in 3 (11.1%) of which it led to a change in postnatal management. These results are comparable to those of Cassart et al. [8] and Alamo et al. [10], who reported that additional information was provided by MRI in 29%–33% of cases. The range of rates in these studies may have been due to unequal distribution of pathologies. Magnetic resonance imaging provided additional information in 50.0% of cases associated with oligohydramnios, which is similar to the 41.7% (in addition to the 30.0% in cases with normal levels of amniotic fluid) reported by Poutamo et al. [7]. Thus, MRI can have a definite supplemental role when oligohydramnios is present. Compared with ultrasound, MRI enabled better visualization of the 2 fetuses with bilateral renal agenesis and severe oligohydramnios, which is consistent with the results of previous studies [6–8]. However, MRI might not enable a definitive diagnosis in cases of suspected renal agenesis and poor visibility—in the present study, 2 cases of unilateral agenesis were incorrectly diagnosed as hypoplastic
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