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A study of Craniospinal Imaging in Patients with Anorectal Malformation

Introduction: Anorectal malformations are commonly associated with craniospinal abnormalities like hydrocephalus, tethered cord syndrome, occult spinal dysraphism, syringomyelia, meningomyelocele and Arnold Chiari malformation. Aim of our study was to identify the incidence of craniospinal anomalies in patients with anorectal malformation and to analyse utility of Ultrasound and MRI as a screening tool in these patients to detect such anomalies. Material and Method: 52 infants male and female of anorectal malformation were included. All underwent ultrasonography of brain and spinal cord and 27 patients underwent MRI to detect craniospinal anomalies. Result: Out of 52 cases 38(73.07 %) were males and 14(26.93 %) were females. High type ARM (34.61 %) and Vestibular fistulas(19.23 %) were most common type in male & female child respectively. On ultrasonography in this series no craniospinal abnormality was found. On ultrasonography subarachnoid space was normal in all cases and central canal diameter was found <1cm in all cases. No abnormalities were detected in posterior fossa like cistermagna dilatation, dilated ventricles, Chiari Malformation. MRI spine was done 27 patients with high and low type malformation, but no abnormality was detected. Conclusion: Craniospinal anomaly and tethered cord are not frequently found in patients with anorectal malformation, in Northern Indian Population. As no association was found between craniospinal anomalies and anorectal malformation in the present study, the use of Ultrasonography and MRI as a screening tool is not recommended unless clinically indicated.


Introduction
Anorectal malformation is associated with maldevelopment of neighbouring structures arising from caudal cell mass. Various craniospinal abnormalities in theses patients are often unnoticed until manifest. The detrimental consequences of untreated craniospinal diseases are often irreversible.Various craniospinal abnormalities associated with anorectal malformation are hydrocephalus, tethered cord syndrome, occult spinal dysraphism, syringomyelia, Meningomyelocoele and Arnold Chiari malformation. T`hese anomalies are seen in as much as 46.5% neonates with anorectal malformation [1]. Apart from ultrasonography, MRI is a standard diagnostic tool for assessing craniospinal abnormalities but limitation of MRI in developing countries are poor cost effectiveness and need of anesthesia to perform the procedure in children. So, Ultrasonography plays role in screening for these craniospinal abnormalities in anorectal malformations [2]. This utilizes the advantages of ultrasound like cost effectiveness, easy availability, high resolution techniques and good soft tissue window in infants for visualization of brain and spinal cord. There are very few reports describing the incidence of such anomalies in Northern India.
Thus there is need of a study to evaluate the incidence of such anomalies and henceforth subsequent role of routine screening test for detection of craniospinal abnormalities associated with anorectal malformation.

Material and methods
This is a prospective study, conducted in Department of Surgery and Department of Radio diagnosis, in tertiary care hospital from January 2012 to December 2013.
Inclusion criteria: 52 infants, male and female, presenting with all varieties of anorectal malformation were included in this study. Exclusion criteria-The patients beyond infancy were excluded from the study (As soft tissue window is obliterated with ossification).

Method
Sonography is done by a consultant sonologist having experience in pediatric radiology and is done by high frequency probes [10 MHZ] under oral sedation with syrup promethazine/trichlorophos, the dose was given according to weight of child. Brain structures like lateral ventricles, third ventricles, corpus callosum, thalamus, posterior fossa and their related anomalies like hydrocephalus, Chiari malformation, corpus callosal agenesis, meningocele, encephelocele etc were seen. Spinal cord and vertebral column structures on ultrasonography were also analysed. Spinal cord, anterior and posterior subarachnoid spaces were seen as a hypo echoic structures and transverse process of spine, ribs are seen as hyper echoic structures. All images were saved as electronic documents and interpretation were done collectively by same sonologist. Plain X-ray anteroposterior and lateral views were performed in all patients to identify bony sacral anomalies. MRI spine was done in 27 consecutive patients, rest failed to undergo MRI due to financial restraints. Ethical committee approval was taken and statically analyses are done according to data collection and need of test on appropriate software with respect to identify the role of test as screening tool.

Results
Results are depicted in following tables.

ARM and subarachnoid space and central canal diameter on USG Spine
All neonates underwent ultrasonographic evaluation of spine for parameters like central canal diameter, subarachnoid space, termination of cord and for other significant abnormality is showing that on ultrasonography subarachnoid space is normal in all cases and central canal diameter is found <1cm in all 52 cases and no variation found between high type and low type anorectal malformation. No abnormality was detected in posterior fossa like cistermagna dilatation, dilated ventricles, Chiari Malformation etc.

Distribution of cases according to abnormality detected on MRI spine
MRI scan done in 27 patients. No abnormality was detected on MRI scanning.

Discussion
According to western literature craniospinal abnormalities especially spinal abnormalities are very common among patients with anorectal malformation; incidence is up to 46% [3][4][5][6][7]. In India it is up to 10% [8]. Some studies suggest that high resolution ultrasonography can detect craniospinal abnormalities efficiently but recently most of the studies suggest MRI as a routine investigation in patients with anorectal malformation because of high incidence of spinal abnormalities association with ARM [9]. In our series ultrasonography was performed in all cases, if altered or inconclusive; it was completed with Magnetic Resonance Image (MRI).
Among 52 patients, 18 patients had high type, 6 patients with intermediate type, 14 with low type, 10 with vestibular fistula, and 4 with cloaca. In this study No association was found in corpus callosum agenesis, brain parenchyma (Chiari malformation) and ventricles abnormality on ultrasonography of brain. This result is in contrast to western literature ,which says the incidence to be 8.3%[10]. In our study there is wide variation found in posterior cranial fossa diameter on ultrasonography of brain, it varied from 4.7cm to 6.1cm. Patients of lesser age have less posterior cranial fossa diameter and vice a versa. The reason for this discripency may be age of neonates. Despite of this variation in posterior cranial fossa diameter, no brain abnormalies were detected. So we can say that posterior cranial fossa diameter is insignificant in relation to cranialspinal anomalies associated with anorectal malformation. In this study the dimension of central canal diameter is <1cm in all the patients and no abnormalities were detected in subarachnoid space. In our study in 5.7% cases spinal cord terminates at T11-T12, in 86.5% cases spinal cord terminates at T12-L1, in 7.5% cases spinal cord terminates at L1-L2.the incidence of spinal cord termination is almost equal in both high and low variety and in accordance with the literature. In study of Suppiej A et al 33.8% incidence of tethered cord in anorectal malformation was seen [11]. Taskinen S et al showed 13.3% incidence of tethered cord in ARM [3].
According to world literature the incidence of spinal cord anomalies is in the range of 10%-40% in anorectal malformation, but in our study the incidence was 0%. As compared to other studies the incidence in our study is very contrast. In the study of Lisa H. Lowe et al [12] and Blaicher W, Prayer D et al [13]. USG brain was taken as a screening tool. According to Beek FJA et al ultrasound of the spinal cord and spine has been advocated as a screening method for patients with anorectal malformation [14]. Low lying cord (ending at L2) was found in 3 patients (7.6%), but had no sonological and MRI findings suggestive of Tethered cord were seen hence, this group needs a longer follow up to identify its importance.

Conclusion
Ultrasonography gives good anatomical details of cranial and spinal structures quite accurately during infantile period. In our study craniospinal anomaly and tethered cord are not frequently found in patients with anorectal malformation. Use of MRI along with USG adds no distinct advantage in craniospinal anomaly detection in patient with anorectal malformation. Decisions to go for craniospinal MRIs and USGs, routinely in patients with ARM should be preceded by evaluation of incidence in the proposed scenario and subject to positive clinical finding. Larger series for longer duration of follow up (especially for Tethered cord syndrome) are needed to further substantiate the fact.