Anterior sacral meningocele presenting as constipation.

Anterior sacral meningocele (ASM) is a rare form of spinal dysraphism in children. Usually asymptomatic, it can present as constipation, urinary problems or rarely neurological symptoms. High index of suspicion with careful clinical examination is necessary to make early diagnosis. Magnetic resonance imaging is the investigation of choice. We describe a successfully managed young child with ASM associated with rib and vertebral defects.

Introduction

Anterior sacral meningocele (ASM) is an anomaly where the meninges protrude into retroperitoneal and presacral space through an anterior sacral defect. Most of the cases present in adult age and diagnosis in childhood is rare. Common presentations include infection, meningitis and obstetric problems. We report a 19-month-old child with ASM presenting with constipation and urinary problems which improved after surgery through abdominal approach. Bilateral rib and vertebral defects seen in our patient have not been described in literature earlier.

Case Report

A 19-month-old female child presented to the hospital with complaints of constipation since 6 months of age and difficulty in passing urine for last 6 months. Parents had noticed lower abdominal fullness for last 1 year. The child was born out of non-consanguineous marriage between young parents at full term by an uncomplicated vaginal delivery. Antenatal ultrasound screening had not been performed. There was no history suggestive of birth asphyxia or trauma. The parents gave history of increasing constipation for which laxatives and enemas had been advised but did not provide relief. The child passed small amounts of urine at short intervals.

The child weighed 7.2 kg and other anthropometric parameters including head circumference were appropriate for age. Chest examination revealed multiple rib defects on both sides but air entry was normal without any added sounds. Abdominal examination revealed a cystic mass in the suprapubic region arising out of pelvis and reaching up to umbilicus. Digital rectal examination showed normal tone of the normally placed anus but a large cystic mass was felt posteriorly which precluded higher examination. Examination of the spine at the back did not show any bony defects. There was no neurological deficit.

Hematological investigations showed hemoglobin of 11.2 g/dL, TLC of 12,000 per cc and platelets of 117×103 per mm3. Kidney function tests were normal.

X-ray chest [Figure 1] showed multiple segmentation anomalies of cervicodorsal vertebrae along with fusion anomalies of ribs on both sides. Echocardiogram did not show any associated cardiac anomaly. Ultrasound of abdomen demonstrated a cystic lesion posterior to urinary bladder measuring 9×4 cm with well-defined dome shaped upper margin and tapering inferiorly. No internal echoes were seen within the lesion. Urinary bladder was pushed anteriorly. There was no evidence of hydroureteronephrosis. Barium enema demonstrated Scimitar sign along with increased presacral space, displacement of the rectum anteriorly and sigmoid colon to the right [Figure 2a and b]. Computed tomography [Figure 3a and b] showed an anterior sacral dysraphic defect with large cystic mass in presacral region displacing the urinary bladder anteriorly and to the right side. Posteriorly, mass was seen entering the spinal canal through large sacral bone defect. There was no hydrocephalus. Both the kidneys were displaced and rotated through their axis but there was no evidence of hydronephrosis.

Figure 1

Plain X-ray chest showing multiple segmentation anomalies of cervicodorsal vertebrae along with fusion anomalies of ribs on both sides

Figure 2

Barium enema showing a) Scimitar sign; and b) increased presacral space and displacement of rectum

Figures 3 (a,b)

Computed tomography showing anterior sacral meningocele with a) communication with the sacral defect; and b) displacement of urinary bladder to the left

An exploratory laparotomy was performed by a suprapubic transverse incision with intent to excise the meningocele from anterior route. A cystic lesion measuring about 8×4 was seen emerging within the leaves of sigmoid mesocolon from the anterior part of sacrum in the pelvis. The sigmoid colon was pushed to the right while urinary bladder was pushed to the left side [Figure 4]. The sac was dissected till the base. The sac was opened at the apex, clear cerebrospinal fluid (CSF) was aspirated and the sac was excised with watertight closure of the tapering base saving the nerve roots and controlling epidural veins. Closed dural defect was checked for leakage of CSF and hemostasis and then covered with local tissue. CSF was sent for culture and sac was sent for histopathological examination (HPE). The CSF culture was reported as sterile while HPE report showed fibrocollagenous and fibrofatty tissue with few entrapped blood vessels and occasional nerve fibers.

Figure 4

Operative photograph showing the anterior sacral meningocele with displacement of urinary bladder and sigmoid colon

There was no neurological deficit in the immediate postoperative period. There was no evidence of constipation, urinary complaints or hydrocephalus at 6 months of follow-up. Although the rib defects have not caused any clinical problem till now, the child remains in follow-up to manage if need arises.

Discussion

ASM is an exceedingly rare form of spinal dysraphism characterized by protrusion of dural sac anterior through a defect in the anterior aspect of sacrum.[12] These are labeled as Type 1B according to Nabors’ classification.[3] Very few cases have been described in early childhood.

ASMs mostly result from failure of fusion of the sacrum with subsequent herniation of the sacrum meninges into the sacral hollow. North et al.,[4] have classified the possible mechanisms leading to ASM as:

Congenital:

Sacral bone defect

Proliferation of arachnoid

Connective tissue disorders

Degenerative: Ischemic lesion

Traumatic: Nerve root avulsion or hemorrhage

Iatrogenic: During surgery

ASM may be associated with syndrome like Currarino syndrome which includes anorectal malformations, sacral bony defect and presacral mass; and Marfan's syndrome wherein the etiology may be disorder of collagen biosynthesis and structure at the dural level.[3] Bilateral multiple rib defects seen in the present case have not been described in the available English literature till now. Autosomal dominant transmission of the disease has been said to cause familial occurrence of ASM.[5-7]

Owing to occult nature, these lesions usually present later in life. These could present with constipation, urological symptoms or rarely neurological symptoms. More than three-fourth cases are seen in women of reproductive age who are more likely to have diagnosis of asymptomatic ASM during pelvic examination. In this group of patients, ASM may lead to infertility and difficult labor.

Young children mostly present with chronic constipation or retention of urine.[8] A child with constipation may be treated with laxatives for long periods or misdiagnosed as Hirschsprung's disease. This can be avoided by often ignored digital rectal examination. The cysts may become secondarily infected leading to meningitis[9] and to pyocele. Associated tethered cord could present with neurological signs.[10] Rarely, these can be occupied by epidermoid cyst[11] or could rupture into the rectum. ASM has been reported to be misdiagnosed as ovarian cyst at many occasions.[12]

Radiological investigations include plain and contrast radiographs, ultrasound, computed tomography and magnetic resonance imaging (MRI). ‘Scimitar’ sign, a smooth curved unilateral sacral defect simulating shape of Arabic sabre on plain X-ray, is considered to be pathognomonic of ASM.[13] Contrast enema, which may show displacement of rectum, sigmoid colon and urinary bladder, is now obsolete for diagnosis. Abdominal and spinal sonography should be the first diagnostic investigation and can diagnose ASM and differentiate it from other cystic lesions in the pelvis.[14] Imaging for screening for ASM and presacral teratoma should be directed at identifying the presacral mass rather than sacral bony defect. Thus computed tomography or MRI is recommended as the screening modality.[15] Computed tomography, diagnostic in the present case, has been replaced by MRI as the radiological investigation of choice.

Good clinical examination and radiological investigations should be able to differentiate ASM from other causes of cystic presacral masses in children which include a) sacrococcygeal teratoma (Altman type 4); b) tumors like dermoid, lipomas, neuroblastoma; c) neuroectodermal cyst; d) rectal duplication cyst; e) ovarian cyst and f) pelvic kidney among others.

Surgery is the mainstay for management of ASM. Surgery should aim to obliterate the communication between meningocele and the spinal subarachnoid space; to decompress the pelvic structures by meningocele excision; and to untether the spinal cord, if necessary.[1617] Standard approach for ASM is through posterior sacral laminectomy. This route permits ligation of the base, to disrupt its connection with the thecal sac and also manage tethered cord if present. Dural fibrin patch may be used to close the open defect.[18] One has to be careful to preserve nerve roots in the vicinity to prevent post operative neurological complications.

An open anterior transperitoneal abdominal approach was used in our case as the large ASM was reaching up to the umbilicus and had a large neck. Anticipated difficulty in managing the large ASM, excellent exposure available, and previous experience of this approach guided in preferring this approach. Limitation of this procedure is the management of caudal spinal cord anomalies as deep pelvic dissection is difficult.[1920]

Laparoscopic approach for surgical management of ASM is increasingly being used.[2122] This is especially useful for narrow-based ASM which may be suture ligated. A posterior sagittal approach may be useful in management of ASM associated with anorectal malformations in Currarino syndrome.[2324]