Selection of operative approach in children with Currarino syndrome

To summarize the experience of surgical treatment of children diagnosed with Currarino syndrome, with an emphasis on the selection of an optimal operative approach. The clinical materials of patients diagnosed with Currarino syndrome were recorded. Special attention was given to the operative management, particularly the different routes for operation. The type of ARM was the critical point. The Rintala score was used for the evaluation of bowel function. The medical records of 26 patients were reviewed. Seven were male, and 19 were female, with a mean age of 19.38 ± 13.80 months. The standard posterior sagittal approach (SPS) group included three perineal fistulae, one anal stenosis, one retraction of the rectum after anoplasty for vestibular fistula, one ARM with no fistula, one rectourethral fistula, and one cloaca. In the limited posterior sagittal approach (LPS) group, there were 13 perineal fistulae, one displacement of the rectum, and one retraction of the rectum after anoplasty for the vestibular fistula. In addition, the transanal approach (TA) and anterior sagittal approach (AS) were also used. The mean follow-up time was 39.48 ± 26.84 m. The Rintala score was 16.74 ± 2.93. For a perineal fistula, SPS or LPS should be used to reach anoplasty and remove the presacral mass. For a vestibular fistula, the AS or LPS should be chosen. For anal stenosis, SPS or LPS should be used.


Introduction
Currarino syndrome is a rare triad consisting of sacral dysgenesis, presacral mass, and anorectal malformation (ARM), and it is transmitted in an autosomal dominant mode in half of the cases with variable expressivity [1]. Clinically, it can present as an imperforate anus at birth, abdominal distension, constipation, obstipation from anorectal stenosis or extrinsic compression from a presacral mass, or acute or recurrent meningitis [2,3]. Operative management of Currarino syndrome includes resection of the presacral mass and rectifying the ARM. Treatment by the anterior sagittal approach (AS), posterior sagittal approach (PS) or transanal approach (TA) may be used with the cooperation of pediatric and neurological surgeons for optimal results [4][5][6]. The standard posterior sagittal approach (SPS) is the most common approach in case reports [7,8], which requires a full posterior sagittal incision running from the lower sacrum toward the base of the scrotum in the male or to the single perineal orifice in a female. Additionally, the limited posterior sagittal approach (LPS) may be used [9], which requires a minimal posterior sagittal incision. However, there has been no study on choosing the optimal one. The reason includes that Currarino syndrome is rare, and delayed or missed diagnosis is common.
Our hospital is a tertiary hospital in Asia, and Currarino syndrome is more common than in Europe or America. This study reviewed the materials of children diagnosed with Currarino syndrome in our institute. We paid particular attention to how to choose the optimal operative approach.

Methods
From January 2008 to September 2021, the clinical materials of children diagnosed with Currarino syndrome in our department were retrospectively studied. Clinical data were extracted from the case records. The case history, clinical manifestations, imaging findings, surgical treatment, pathology, and results were summarized. The study was conducted under the ethical standards of the ethical committee of our hospital.
Special attention was given to operative management, particularly the different routes for operation. The type of ARM was the critical point. Meanwhile, the size of the mass, its relation to the spinal canal, and coexisting megacolon were the other factors we should consider.

For perineal fistula
The child was positioned in a lithotomy position. The center of the external sphincter was mapped using an electrical stimulator, and usually, an LPS incision was made (Fig. 1). After splitting the posterior sphincter around the rectum, the presacral space was exposed for mass resection. Small and low presacral masses could be resected through the approach, while large and high presacral masses need an SPS incision.

For anal stenosis
The child was positioned in a lithotomy position. A PS incision was made to expose the presacral mass (Fig. 2). After the removal of the mass, the posterior wall of the stenotic anus was brought out to incise the ring vertically and suture transversely.

For rectourethral fistula
The child was placed in the prone position. The center of the external sphincter was mapped using an electrical stimulator. The SPS incision separates the muscle complex and levator muscles in the midline. Then, the rectum was located. After removing the presacral mass, the distal rectum was exposed to mend the fistula. Then, the rectum was pulled out to finish the anoplasty.

For ARM with no fistula
The child was placed in the prone position. The blind end of the rectum was usually located at the level of the bulbar urethra and was easily reachable from the SPS approach. The rectum must be carefully separated from the urethra because the two structures share a common wall. Resection of the presacral mass was performed before this. Then, the anoplasty was performed as described for the rectourethral fistula.

For vestibular fistula
The child was positioned in a lithotomy position. The center of the external sphincter was mapped using an electrical stimulator externally. The midline incision was made at the site of the proposed anal orifice and extended anteriorly (AS) for resection of the presacral mass and anoplasty.

For the cloaca
First, cystoscopy and vaginoscopy should be performed for surgical planning. The position of the rectum must be carefully checked to determine whether it can be reached from a posterior sagittal incision or will require a laparotomy or laparoscopy. The repair of cloacal malformations with a less than 3 cm common channel can be performed through an SPS alone, usually using a total urogenital mobilization technique. Long common-channel cloacas are less predictable and frequently require vaginal replacement and reconstructive urological expertise. The presacral mass should be resected with mobilization of the rectum.

For megacolon
The grossly dilated rectum and sigmoid could be mobilized with laparotomy or laparoscopy. The proximal colon was retracted to the position of the anus without tension. Distal dissection was performed 1 cm above the dentate line. The anterior rectum was mobilized at the submucosal plane. The posterior rectum was mobilized at full thickness together with the presacral mass, which always had adhesion to the posterior wall of the rectum. After resection of the dilated colon, the proximal colon was anastomosed to the anus.

For spinal cord malformation
An asymptomatic small anterior sacral meningocele or lipoma should be managed conservatively. Then, a moderate or large lesion should be offered for repair in the same session when revising the ARM. Attendance by a neurosurgeon during the operation is necessary.

Time for enterostomy
Enterostomy was suggested for patients with a previous surgical history to ensure wound healing. As for a presacral mass connected with the spinal canal, enterostomy was obligatory to prevent a fatal CNS infection.
The follow-up was conducted in the outpatient department or by phone. The Rintala bowel function score was used to evaluate bowel function [10]. The patients were divided into three categories for bowel function recovery: ≥ 17 indicated normal bowel function, 12-16 indicated mild bowel dysfunction, and < 12 indicated severe bowel dysfunction.
Continuous variables are presented as the mean and standard deviation. Categorical variables are presented as frequencies and percentages.

Results
The medical records of 26 patients were reviewed and are listed in table one. Seven were male, and 19 were female, with a mean age of 19.38 ± 13.80 months (ranging from 2 to 47 months) ( Table 1).
The anorectal malformations included 17 perineal fistulae, four vestibular fistulae, two anal stenoses, one ARM with no fistula, one rectourethral fistula, and one cloaca. X-rays of the sacrum, barium enema, ECG, pelvic ultrasound, and MRI of the pelvis and spine were given as regular preoperative examinations to exclude accompanying anomalies. Megacolon was found in seven patients.
The PS was taken in 23 cases. The SPS was taken in eight cases, and LPS was taken in another 15 patients. The SPS group included three perineal fistulae, one anal stenosis, one retraction of the rectum after anoplasty for vestibular fistula, one ARM with no fistula, one rectourethral fistula, and one cloaca. In the LPS group, there were 13 perineal fistulae, one displacement of the rectum, and one retraction of the rectum after anoplasty for the vestibular fistula. TA was used in one patient with megacolon and presacral mass after anoplasty for perineal fistula. AS was used in one vestibular fistula. A transdural approach was chosen for one patient with an infective fistula between the presacral mass and the spinal canal. Eight of the patients had an enterostomy before they came to us. Eight patients underwent ileostomy in our department. The other ten patients had no ostomy. The stoma was closed three months after the radical surgery.
The mean follow-up time was 39.48 ± 26.84 m, ranging from 6 to 145 m. The bowel function score (BFS) was noted regarding the ability to hold back defecation, feeling/reporting the urge to defecate, and the frequencies of defecation, soiling, fecal accidents, constipation, and social problems. The Rintala score was 16.74 ± 2.93, ranging from 12 to 20. Fourteen patients (14/26, 53.8%) had normal bowel function (BFS ≥ 17), and no patient had severe bowel dysfunction (BFS < 12). Four patients needed oral oxidation or enema to defecate for constipation.

Discussion
Patients with Currarino syndrome can present with a spectrum of anomalies, including a congenital sacral anomaly associated with a presacral mass and an ARM, usually anorectal stenosis [11]. In this study, perineal fistula prevailed (17/26, 65.4%), which was similar to a recently reported large group [8]. Other anomalies included anal stenosis (2/26, 7.7%), rectourethral fistula (1/26, 3.8%), an    The expressivity of this triad is variable, and the clinical manifestation is a complex spectrum of it. Constipation is the most commonly reported symptom. In our 26 cases, 16 patients in this study came for intractable constipation, with eight of them having already undergone anoplasty elsewhere. In addition, the other complaints were untreated presacral mass, retraction of the rectum after anoplasty, and infection of the presacral mass or infective presacral fistula. Therefore, the complexity of the clinical manifestation is a major challenge to its management.
The management of Currarino syndrome generally consists of the treatment of anorectal malformations and presacral masses. The principle of the surgical procedure was to correct the ARM and excise the presacral cyst [8]. Regarding ARM, SPS was used to repair a high-type ARM (rectourethral fistula), while LPS was the technique of choice for the more common low types (perineal/vestibular fistula/anal stenosis) [12]. AS and TA have also been reported [3,5]. The AS was used for the vestibular fistula, and the TA was used for anal stenosis with low and small presacral masses. Twenty-three patients used the PS in our study, including eight SPS and 15 LPS. SPS is the classic route to remove the presacral mass and complete the anoplasty with adequate exposure. LPS only needs to split parts of the external muscle complex and ani levator, which hurts a little to the neurovascular structure around the anus. In our study, all patients with a high-type ARM chose SPS. Patients with low-type ARM commonly chose LPS. In five patients who presented with a low-type ARM, we chose an SPS incision when the diameter of the presacral mass was larger than 5 cm or the position of the normal rectum was high.
Regarding low-type ARM, anal stenosis is a rare condition. A dilatation program can be instituted if the lumen permits the passage of a dilator, while others with tiny lumens should undergo colostomy after birth. We have tried to bring out the stenotic anus to incise the ring vertically and suture transversely. However, this may not always be feasible. Then, proper mobilization via PS is recommended [13,14].
When a presacral mass is to be excised, it can usually be done in the same sitting as repairing the ARM. Care should be taken during the dissection of the posterior attachments of the mass, when an anterior projection of the thecal sac may be encountered. When anterior sacral meningoceles occur, the traditional practice is to repair the meningocele before correcting the ARM. Currently, many pediatric surgeons excise the sac in the same session when using the PS [7,8]. There were seven presacral teratomas accompanied by anterior meningoceles in this group, and six of them were excised using the PS. The other patient with megacolon after anoplasty for perineal fistula was resected using the TA, but there was CSF leakage after the operation, which may be due to inadequate exposure. A transdural route taken from a sacral laminectomy allows for the excision of the intradural epidermoid and closure of the presacral fistula or meningocele pedicle [15]. There was a five-month-old girl with a presacral fistula between the teratoma and the spinal canal. A transdural route was taken to close the fistula at first, and excision of the teratoma followed through an arc incision. A tethered spinal cord is common in Currarino syndrome, but its contribution to the symptoms is not clear and has never been confirmed. Therefore, there is no great indication for prophylactic spinal cord detethering. Moreover, it depends on neurosurgical staff and the local experiences of pediatric neurosurgeons. If there is worsening bowel function, urinary symptoms, or deterioration in the movement or sensation of the lower limbs, cord detethering should be considered. PS is a common approach for treating ARM and presacral mass, but in situations where spinal cord malformation is symptomatic, it is not always available. The transdural approach is separated from the PS and can keep the CNS infection to a minimum without an enterostomy. In our series, two cases underwent detethering of the spinal cord in the transdural approach, one for a fistula between the presacral mass and spinal canal and the other for the parent's request. In addition to the transdural approach, an extended PSARP posterior to the sacrum (posterior sagittal transsacral and perineal [PSSP] approach) that allows simultaneous treatment of ARM, tumor, and neurological anomalies was also reported [16]. In cases with an enterostomy, PSSP is also available.
Seven patients in this group were complicated by megacolon, and five of them used the LPS incision. One of the other two patients used the TA approach, and the other one used the AS approach. TA is not as good for the exposure of the presacral mass, so for a larger mass (> 5 cm) or one connecting with the spinal canal, LPS or SPS may be the favorite choice. The other patient with a vestibular fistula used the AS approach, and when the presacral mass was more significant than 5 cm, a backward extension of the incision was needed.
Sixteen cases in this group had a stoma during the treatment. Six patients underwent colostomy after birth. One patient received an ileostomy in a local hospital for intractable constipation. Another case adopted colostomy due to CNS infection after removing the presacral mass. Eight cases received ileostomy in our department after removing the presacral mass and anoplasty to prevent CNS infection and ensure incision healing. The other ten cases did not have a stoma. Palliative surgery is initially performed in an infant born with an ARM to divert the colon and allow the patient to mature before definitive surgery. The initial palliative surgery of an imperforate anus includes a colostomy to enable enteric contents to evacuate, while an additional stoma is created for the distal colon [12]. We prefer to choose the terminal ileum for the stoma because it is easier to operate in and will not influence the pelvic cavity. An ileostomy is suggested for cases with a severe scar in the anus or connection with the neural canal.
In the follow-up, particular attention should be given to bowel function, and, if present, constipation should be treated [17]. Four patients in this group suffered from constipation and needed oral oxidation or enema to defecate. Follow-up for most patients has shown favorable postoperative bowel functional outcomes.
There were 12 cases in this study that came to us with unfavorable results of ARM operation and/or undiagnosed/ untreated presacral mass due to lack of experience. Delayed or missed diagnosis is common with undiagnosed presacral mass at centers having no or limited experience in detecting and treating those cases. The lack of proper imaging examination leads to misdiagnoses and insufficient repair requiring reoperation. Better knowledge of the different clinical signs and symptoms of Currarino syndrome enhances appropriate imaging and prompt diagnosis of this condition. The possibility of Currarino syndrome should be considered for patients with intractable chronic constipation, especially when an abnormal sacrum is seen in a pelvic radiograph [18]. Pelvic radiography may show evidence of the sacral anomaly, typically with preservation of the first sacral vertebra and asymmetric dysplasia of the distal sacrum, which is shaped like a sickle or scimitar. Some authors have suggested that such sacral abnormalities are pathognomonic for Currarino syndrome [19]. In lateral X-ray, there is no space between the rectum and sacrum in a normal condition, so when there is a wide space, a presacral mass should be precluded. Patients with an ARM must undergo multiple radiologic examinations including a vertebral radiograph to evaluate for vertebral anomalies, abdominal and pelvic ultrasound to evaluate for urogenital abnormalities, an MRI of the pelvis and spine to evaluate the complexity of the malformation, and a colostogram to observe the colon form and underlying fistulous tract from the rectum to either the bladder or urethra [20]. Then a protocol with rational timing of multidisciplinary surgical procedures may help to avoid undesirable outcomes.

Conclusions
For a perineal fistula, SPS or LPS could be used to reach an anoplasty and remove the presacral mass. For a vestibular fistula, the AS or LPS should be chosen. For anal stenosis, SPS or LPS should be used. TA is not as good for the exposure of the presacral mass, so for a larger mass (> 5 cm) or one connecting with the spinal canal, LPS or SPS may be the favorite choice. A transdural route allows for the excision of