The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 89, Issue 11

Scientific Articles | November 01, 2007

Magnetic Resonance Imaging of Renal Abnormalities in Patients with Congenital Osseous Anomalies of the Spine

Anthony I. Riccio, MD¹; James T. Guille, MD²; Leslie Grissom, MD³; T. Ernesto Figueroa, MD³

¹ Naval Medical Center of San Diego, 34800 Bob Wilson Drive, Building 1, Suite 112, San Diego, CA 92134
² Brandywine Institute of Orthopaedics, 600 Creekside Drive, Suite 611, Pottstown, PA 19464. E-mail address: guille@brandywineortho.com
³ Alfred I. duPont Hospital for Children, 1600 Rockland Road, P.O. Box 269, Wilmington, DE 19899

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Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.

Investigation performed at the Alfred I. duPont Hospital for Children, Wilmington, Delaware

The Journal of Bone and Joint Surgery, Incorporated

J Bone Joint Surg Am, 2007 Nov 01;89(11):2456-2459. doi: 10.2106/JBJS.F.01267

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Abstract

Background: Patients with congenital osseous anomalies of the spine are known to have a high prevalence of abnormalities in the renal system and of the spinal cord. Today, the screening tools of choice to detect these abnormalities include ultrasonography of the kidneys and collecting system and magnetic resonance imaging of the spine. A single screening tool that can identify both renal and intraspinal anomalies would be ideal.

Methods: Imaging studies of all patients with a congenital osseous anomaly of the spine seen at our institution during a ten-year period were retrospectively reviewed. Only patients who had had both a sonogram of the renal system and a magnetic resonance imaging study of the entire spine were included in the investigation. All studies were reviewed blindly by a pediatric radiologist for this study.

Results: One hundred and fifty-three patients met the criteria for inclusion in the study. Forty-one patients (27%) had a total of forty-seven renal abnormalities noted on both the sonogram and the magnetic resonance imaging scan. In no instance was a renal anomaly seen on one study and not on the other.

Conclusions: When properly performed, screening magnetic resonance imaging scans of the spine can show renal abnormalities, thus obviating the need for a separate screening renal ultrasound study.

Level of Evidence: Diagnostic Level IV. See Instructions to Authors for a complete description of levels of evidence.

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It has been said that a congenital osseous anomaly of the spine is just the tip of the iceberg, referring to the fact that as many as 61% of patients with vertebral anomalies have one or more associated anomalies in other organ systems, many of which may be medically important¹. Renal, cardiac, and intraspinal abnormalities are the most common of these associated anomalies. The relationship between congenital vertebral abnormalities and anomalies involving these other organ systems is well understood because organogenesis and the development of the vertebral elements occur concurrently during the sixth week of embryogenesis, at which time a single insult or developmental deviation may affect the formation and development of multiple organ systems.

The prevalence of genitourinary abnormalities in patients with congenital spine deformities reportedly ranges from 13% to 37%^2-4. Furthermore, Basu et al. demonstrated that, although most of these renal anomalies are benign, approximately one-third of patients with congenital scoliosis require some form of urologic intervention⁵. Screening of the renal system is therefore mandatory in the presence of congenital vertebral anomalies. Initial screening recommendations were made by MacEwen et al., who determined that, because of the high rate of renal anomalies, all patients with congenital scoliosis should undergo intravenous pyelography to identify kidney and collecting system defects². In 1987, Drvaric et al. showed that renal ultrasonography is an acceptable noninvasive screening alternative to intravenous pyelography³. Currently, ultrasonography is the preferred method for screening for genitourinary abnormalities at most centers, with intravenous pyelography and nuclear scans reserved for more in-depth evaluation if an abnormality is detected^3,4.

In addition to renal abnormalities, patients with congenital scoliosis demonstrate a high prevalence of concurrent neural axis anomalies^6-12. While myelography was once considered the gold standard for evaluation of these intraspinal anomalies^7,9,10, magnetic resonance imaging of the spine currently is the screening tool of choice. Although most intraspinal anomalies tend to be occult, the prevalence of neural axis defects is substantial, as high as 37% in patients with congenital scoliosis⁸. Accordingly, several authors have recommended magnetic resonance imaging of the entire spine, from the occiput to the sacrum, as part of the initial evaluation of all patients with a congenital spinal deformity^11,12.

Although not commonly used as a renal screening modality by orthopaedic surgeons, magnetic resonance imaging is frequently employed by urologists for evaluation of the urogenital system. Because our initial evaluation of a congenital spinal deformity includes screening for both renal and intraspinal anomalies, we believed that it would be cost-effective and efficient to screen both systems with use of a single imaging tool. The present study was undertaken to determine if magnetic resonance imaging is an acceptable screening modality for renal abnormalities in patients with congenital vertebral anomalies. If this were the case, the need for a screening sonogram in patients undergoing evaluation for intraspinal defects would be obviated.

Materials and Methods

Materials and Methods | Results | Discussion | References

After institutional review board approval was obtained, the medical records and imaging studies of all patients seen at our hospital between 1994 and 2004 with the diagnosis of a congenital anomaly of the spine were reviewed retrospectively. We included patients with congenital scoliosis, congenital kyphosis, congenital kyphoscoliosis, congenital fusion of the cervical vertebrae, and/or congenital scoliosis with congenital fusion of the cervical vertebrae. Patients with sacral agenesis and myelomeningocele were excluded. Two hundred and sixty-six patients were identified.

Of the 266 patients, 153 (58%) had had both spinal magnetic resonance imaging and renal sonography performed. Thirty-two patients (12%) had had sonography only, twenty-five patients (9%) had had magnetic resonance imaging only, and fifty-six patients (21%) had not had any imaging studies of the renal system. The study group comprised the 153 patients who had had both studies. There were eighty-seven girls (57%) and sixty-six boys (43%). The average age at the time that the sonography was performed was 6.3 years (range, two weeks to 18.4 years). The average age at the time that the magnetic resonance imaging was performed was 8.1 years (range, three weeks to 19.2 years). One hundred patients (65%) had congenital scoliosis, seven (5%) had congenital kyphosis, ten (7%) had congenital kyphoscoliosis, twenty-six (17%) had congenital fusion of the cervical vertebrae, and ten (7%) had congenital scoliosis with congenital fusion of the cervical vertebrae.

Standard renal ultrasonography was performed to identify renal abnormalities. The magnetic resonance imaging scans were performed with a 1.5-T 11.0 Excite imaging system (General Electric, Milwaukee, Wisconsin) with use of a phased-array spine coil with the patient supine. The entire spine was scanned from the base of the skull to the coccyx. Sagittal and coronal 48-cm field-of-view T2-weighted pilot images were acquired, from which sagittal and axial T1-weighted and T2-weighted images of the spine were prescribed. The parameters for the axial images included a 5 to 8-mm slice thickness and a 16-cm field of view, and an anterior saturation band was used. The magnetic resonance imaging studies had been ordered with the intent to screen for intraspinal abnormalities. However, during these studies, the kidneys were routinely visualized and associated renal anomalies could be diagnosed.

All renal ultrasound and magnetic resonance imaging scans of the study group were obtained, and all patient identifiers were removed. These studies were then reviewed, in random order, by a pediatric radiologist who was blinded to the patient's identity and the diagnosis. The radiologist was instructed to review the coronal, sagittal, and axial magnetic resonance images for both intraspinal and renal anomalies. The results of the radiologist's assessments of the renal sonogram and the spinal magnetic resonance imaging scan were then compared for each patient to determine any discrepancy in diagnosis.

Results

Materials and Methods | Results | Discussion | References

One hundred and twelve patients had no renal abnormality noted on either the magnetic resonance imaging scan or the sonogram. There was a 100% concordance between the renal sonograms and the spinal magnetic resonance imaging scans with regard to the diagnosis of the absence of renal abnormality. A total of forty-seven renal abnormalities in forty-one patients (27%) were identified (Table I). Twenty-five (61%) of these patients were girls, and sixteen (39%) were boys. The most common renal anomaly identified in this series was the unilateral absence of a kidney, seen in eleven patients (27%). The abnormalities were identified on both the magnetic resonance imaging scan and the sonogram of all forty-one patients. There was a 100% concordance between the sonograms and magnetic resonance images with regard to the diagnosis of the abnormalities, and in no case was an abnormality seen on one study but not on the other.

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TABLE I Renal Abnormalities

	No.
Solitary kidney	11
Hydronephrosis	6
Renal cyst	4
Small kidney	4
Extrarenal pelvis	4
Bifid collecting system	3
Horseshoe kidney	3
Malrotated kidney	3
Crossed-fused ectopia	2
High kidney	2
Pelvic kidney	2
Duplication	1
Malformed kidney	1
Pelviectasis	1
Total	47

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TABLE I Renal Abnormalities

	No.
Solitary kidney	11
Hydronephrosis	6
Renal cyst	4
Small kidney	4
Extrarenal pelvis	4
Bifid collecting system	3
Horseshoe kidney	3
Malrotated kidney	3
Crossed-fused ectopia	2
High kidney	2
Pelvic kidney	2
Duplication	1
Malformed kidney	1
Pelviectasis	1
Total	47

A renal abnormality was found in twenty-one (21%) of the 100 patients with congenital scoliosis, three of the seven with congenital kyphosis, two of the ten with congenital kyphoscoliosis, thirteen (50%) of the twenty-six with congenital fusion of the cervical vertebrae, and two of the ten with congenital scoliosis and congenital fusion of the cervical vertebrae.

Of the 266 patients who had been initially identified by our review, 210 had had either a magnetic resonance imaging scan or a sonogram, or both. Fifty-six (27%) of these patients had a renal abnormality seen on either one or both of the studies.

Discussion

Materials and Methods | Results | Discussion | References

The embryology of congenital scoliosis has been studied extensively. Dysplastic vertebrae resulting from an abnormal mesenchymal mold develop during the fifth to eighth weeks of intrauterine development, although the specific etiology of such abnormalities remains a mystery^13,14. Most congenital vertebral anomalies are spontaneous occurrences, unrelated to any identifiable causative event or agent during the gestational period. While research has shown an association between congenital spinal deformities and prenatal exposure to carbon monoxide or hypobaric hypoxia in mice, the clinical implications for humans remain unknown^15,16.

The prevalence of genitourinary anomalies in the presence of congenital spinal deformity is reportedly 13% to 37%, with the genitourinary problems ranging from an asymptomatic solitary kidney to obstructive uropathy with hydronephrosis^3,17,18. Arrest of metanephric tissue growth resulting in unilateral absence of a kidney is the most commonly associated renal abnormality; however, abnormal fusion of the primitive renal cell masses (causing a horseshoe kidney or crossed-fused ectopia) and improper migration of the renal cell masses (causing ectopia or malrotation) may occur between the fifth and eighth weeks of embryonic life. As noted earlier, one-third of all patients with congenital scoliosis and a renal anomaly may require some form of urologic intervention⁵. To our knowledge, no study has demonstrated a correlation between the level of the spinal curve or the type of vertebral deformity and the prevalence or type of genitourinary abnormality^17,19.

To date, few authors have been able to correlate the type and location of the renal abnormality with the type and location of the congenital spine anomaly^2,17,20,21. Tori and Dickson found the highest rates of renal anomalies in their patients with hemivertebra(e) in the cervical and upper thoracic spine¹⁸. In the present series, patients with congenital fusion of the cervical vertebrae had the highest prevalence of renal anomalies (50%), but we were unable to find any absolute association between the type and location of the renal abnormality and the type and location of the congenital spine anomaly. Rai et al. found a significant association (p = 0.04) between the presence of renal and costal abnormalities; the importance of that finding is unknown²⁰.

Because the neural axis and vertebral elements develop simultaneously, intraspinal anomalies are commonly associated with congenital osseous spinal deformity. Presently, there are no clear recommendations for screening for intraspinal anomalies in children with a congenital osseous spinal deformity. Prahinski et al. found a high prevalence of occult intraspinal anomalies in a consecutive series of patients with congenital scoliosis, but reported that the presence of such anomalies correlated poorly with the findings of the physical examination and on spinal radiographs¹¹. They concluded that further study is needed before screening magnetic resonance imaging can be considered mandatory; however, they stated that it was their own practice to perform magnetic resonance imaging for all patients presenting with congenital scoliosis. Bradford et al. performed spinal magnetic resonance imaging for forty-one patients with congenital spinal deformities and found intraspinal anomalies in sixteen patients, nine of whom had no evidence of neurologic abnormality on physical examination⁸. Interestingly, of the nine patients with occult lesions, four required neurosurgical intervention. These authors recommended screening spinal magnetic resonance imaging for patients with congenital scoliosis who present with neurologic findings, a cutaneous hairy patch over the spine, lumbosacral kyphosis, radiographic evidence of diastematomyelia, or a congenital vertebral bar with a contralateral hemivertebra, as well as for all patients undergoing a spinal stabilization procedure. More recently, screening magnetic resonance imaging was recommended for all patients with congenital spinal deformity because of the high prevalence of intraspinal anomalies even in the absence of clinical or radiographic findings^5,12.

We were surprised to find that fifty-six patients (21%) who were seen at our institution with a congenital osseous anomaly of the spine had not been screened for a renal anomaly, as we had thought that this concept was well established in the literature and especially since one of the first clinical research reports on the subject was from our institution more than thirty years ago². The present study demonstrated a 27% prevalence of urologic abnormalities in a series of 210 patients with congenital spinal deformities. In the group of 153 patients with both magnetic resonance images and renal sonograms, a 100% correlation was found between these two modalities with regard to the detection and characterization of renal abnormalities. The absence of urologic deformity also was determined successfully, with a 100% correlation between the two modalities. Therefore, screening for urologic deformity may be successfully accomplished with magnetic resonance imaging being performed to detect intraspinal anomalies in patients with congenital spinal deformities. This would obviate the need for screening renal ultrasonography for such patients. It is recognized that a renal sonogram may be required for further or serial evaluation, in consultation with a urologist, of a renal anomaly detected with screening magnetic resonance imaging.

A dilemma that arises in view of the results in the present study concerns the administration of a sedative agent to allow performance of a magnetic resonance imaging study of an infant or young child. A renal sonogram can be performed on an individual of any age without the need for sedation. This makes this imaging option attractive for very young children, who otherwise would require sedation for magnetic resonance imaging. However, as some renal abnormalities are life-threatening, evaluation of the urinary tract should not be withheld until the child is old enough to have a magnetic resonance imaging study done without sedation. Cost is another obvious concern because magnetic resonance imaging is substantially more expensive and time-consuming than renal ultrasonography. These concerns, while legitimate, will be less important if the orthopaedic literature continues to demonstrate that the risk of occult intraspinal anomalies requiring intervention is high enough to mandate magnetic resonance imaging for screening of all patients with congenital spinal deformities, regardless of cost or concerns about sedation. Clearly, patients who are diagnosed with a congenital spinal deformity at an age at which they can undergo magnetic resonance imaging without sedation can be screened adequately for both renal and intraspinal anomalies with the magnetic resonance imaging. ?

References

Materials and Methods | Results | Discussion | References

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Drvaric DM, Ruderman RJ, Conrad RW, Grossman H, Webster GD, Schmitt EW. Congenital scoliosis and urinary tract abnormalities: are intravenous pyelograms necessary? J Pediatr Orthop. 1987;7: 441-3.7441 1987 [CrossRef]

Albanese SA, Coren AB, Weinstein MP, Cady RB, Lubicky JP. Ultrasonography for urinary tract evaluation in patients with congenital spine anomalies. Clin Orthop Relat Res. 1988;228: 302-6.228302 1988 [PubMed]

Basu PS, Elsebaie H, Noordeen MH. Congenital spinal deformity: a comprehensive assessment at presentation. Spine. 2002;27: 2255-9.272255 2002 [PubMed][CrossRef]

Belmont PJ, Kuklo TR, Taylor KF, Freedman BA, Prahinski JR, Kruse RW. Intraspinal anomalies associated with isolated congenital hemivertebra: the role of routine magnetic resonance imaging. J Bone Joint Surg Am. 2004;86: 1704-10.861704 2004 [PubMed]

Blake NS, Lynch AS, Dowling FE. Spinal cord abnormalities in congenital scoliosis. Ann Radiol (Paris). 1986;29: 377-9.29377 1986 [PubMed]

Bradford DS, Heithoff KB, Cohen M. Intraspinal abnormalities and congenital spine deformities: a radiographic and MRI study. J Pediatr Orthop. 1991;11: 36-41.1136 1991 [PubMed][CrossRef]

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Rivard CH, Narbaitz R, Uhthoff HK. Time of induction of congenital vertebral malformations in human and mouse embryo. Orthop Rev. 1979;8: 135-9.8135 1979

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Farley FA, Loder RT, Nolan BT, Dillon MT, Frankenburg EP, Kaciroti NA, Miller JD, Goldstein SA, Hensinger RN. Mouse model for thoracic congenital scoliosis. J Pediatr Orthop. 2001;21: 537-40.21537 2001 [PubMed][CrossRef]

Kalamchi A, MacFarlane R. Renal abnormalities in congenital scoliosis—correlation of its incidence to the type and level of spinal deformity. Jefferson Orthop J. 1979;8: 70-4.870 1979

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Topics

congenital anomaly of the kidney ; kidney ; congenital scoliosis ; spine ; vibration ; spinal deformities ; ultrasonography of kidney

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Anthony I. Riccio, James T. Guille, Leslie Grissom, T. Ernesto Figueroa; Magnetic Resonance Imaging of Renal Abnormalities in Patients with Congenital Osseous Anomalies of the Spine. The Journal of Bone & Joint Surgery. 2007 Nov;89(11):2456-2459.

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