Sacral Agenesis, Myelocystocele, and Cloacal Exstrophy

A number of complex anomalies involving the caudal spine have been described, some of which may come to the attention of the neurosurgeon.69,70 These may involve multiple organ systems and include imperforate anus, the VACTERL syndrome (vertebral anomalies, anal atresia, cardiac anomalies, tracheoesophageal fistula, esophageal atresia, renal and limb anomalies), the OEIS complex (omphalocele, cloacal exstrophy, imperforate anus, spinal deformities), and sacral agenesis. All of these conditions may coexist with the tethered cord syndrome.

Many consider these individual entities to reside along the spectrum of caudal regression syndrome, thus sharing similar embryologic mishaps. The severity of the anomaly determines the likely spinal pathology and the management. Simple imperforate anus is associated with hypertrophy of the filum terminale, and there may be no cutaneous stigmata of this condition. Screening with MRI is recommended. Sacral agenesis is suspected by flattening of the buttocks, shortening of the intergluteal cleft, and prominence of the iliac crest. The newborn with an omphalocele, ambiguous genitalia, and cloacal exstrophy may have an associated skin-covered lumbosacral mass, which may represent a myelocystocele or a lipomyelomeningocele. Myelocystocele may occur in association with these complex syndromes or in isolation. It is generally considered to be an extreme form of the common ventriculus terminalis, which is a normal anatomic variant seen often on MRI scans performed for unrelated indications. The central canal of the terminal spinal cord is massively dilated to form a huge cystic structure, which presents as a skin-covered lumbosacral mass. Fetal ultrasound may confuse a myelocystocele with a cystic myelomeningocele. The spinal cord is invariably tethered.

Sacral agenesis is associated with maternal diabetes. Pang has divided these cases into five types, based on the appearance of the sacrum.69 As a practical matter, one can divide these anomalies into those with a high conus and those with a low conus. High symmetrical sacral agenesis is correlated with a truncated, club-shaped conus ending around T11 or T12. Tethering is not present, although dural canal stenosis has been reported as the cause of delayed deterioration. The lower asymmetrical forms of sacral dysgenesis are more likely to have a low-lying tethered cord. Altogether, tethering is reported in 24% of children with anorectal malformations and as frequently as 43% in those with complex malformations.71 Mechanisms of tethering include myelocystocele, lipomyelomeningocele, and simple hypertrophy of the filum.

Initial management of infants with multisystem anomalies is usually nonneurosurgical and consists of colostomy, closure of an omphalocele, urinary diversion, and reconstruction for tracheoesophageal fistula. An MRI of the spine is obtained electively, when the infant is stable. Fetal MRI can also make the diagnosis.72 When the conus is at a normal level, neurosurgical intervention is usually not required. Those cases in which the conus is low-lying should undergo tethered cord release when the systemic condition permits. It is useful to perform the tethered cord release prior to reversing the colostomy, because the wound is protected from fecal contamination. Even infants with high motor levels should undergo prophylactic untethering, because improvement is possible.

Surgery is similar to that for other tethered cord syndromes. Surgery for myelocystocele consists of defining normal anatomy above the sac and amputating the sac and all of the tissue below the level of the last intact nerve roots with untethering (Fig. 7.22). The dural reconstruction may require a graft.

Patients who do not have tethering or who have undergone successful untethering procedures should remain with stable deficits. If new signs or symptoms appear, a repeat MRI should be performed to define retethering, syrinx formation, or dural constriction. Patients may require long-term management by neurosurgeons, pediatric general surgeons, urologists, and orthopedists.