Lipomeningocele

Lipomeningocele is an abnormality of the spine characterized by a low-lying conus medullaris, infiltrated with fatty tissue, which extends through a bony dysraphic defect and into the subcutaneous tissues. It is thought to occur as a result of an abnormality of secondary neurula-tion of the caudal cell mass, whereby pluripo-tential mesenchymal cells fail to regress and may lead to lipomas, hamartomas and teratomas in the lumbosacral region. The lipoma is invariably covered by skin but may have pigmentation, hair or cutaneous dimples on it. They often lie asymmetrically across the midline in the lumbosacral region and can reach a very large size. Intradurally, the lipoma may be attached to the dorsal surface of the cord or it may be inserted into the terminal end of the conus. The lipoma may enlarge in infancy or may be associated with obesity. Although uncommon, lipomeningoce-les may be associated with other developmental anomalies, including syringomyelia, Chiari malformation and anal and genitourinary malformations. The lesion is considered to lead to tethering of the spinal cord, thereby producing symptoms.

The cutaneous abnormality is frequently obvious at birth but, in the past, has not always been recognized for what it is. Progressive, often asymmetrical neurological deterioration in the legs is a common mode of presentation, as well as discrepancies in foot size and leg length in older children. Bladder and bowel dysfunctions are also frequent complaints. As with other forms of dysraphism, pain tends to be a feature in adulthood. Similarly, acute neurological deterioration has been described.

The approach to treatment of lipomeningo-cele depends largely upon the perceived natural history of the condition. Arguments in favor of prophylactic untethering include the fact that many infants appear to be neurologically normal, whereas most adolescents and adults present with some neurological deficits. In one study [15], all children were symptomatic by the age of 4 years. The condition therefore appears to carry a high risk of progressive deterioration, while the risks of surgery remain relatively low. Once neurological deficits or orthopedic deformity have occurred, they tend not to be reversible, even with surgery, and there is a background risk of acute deterioration and paraplegia without surgery. For these reasons, many neurosurgeons consider untethering the cord before the age of 6 months or do so as soon as the lesion is recognized thereafter [16,17]. Counter to this argument is the fact that not all children with lipomeningoceles do deteriorate as demonstrated by the occasional unsuspected adult presentation; that surgery does carry some risk of neurological damage; and that acute paraplegia in the absence of any preceding symptoms is rare. Added to this is the frequent problem of re-tethering after surgery. There has therefore been a reappraisal of the need for early prophylactic untethering and consideration of surgery only at the onset of the development of symptoms. This requires close and regular assessment of all patients with lipomeningoce-les, to detect any neurological change [18,19]. There is little argument over the place of surgery in preventing further deterioration in those presenting with progressive neurological deficits. Recently, Chumas [20] has summarized these arguments and emphasized the need for long-term follow-up of all these patients if a consensus is to be achieved.

Pre-operative assessment requires careful neurological examination of the legs and uro-dynamic assessment. MRI in the sagittal plane clearly demonstrates the lesion (Fig. 27.2a) and will also show an associated hydromyelia. Axial images reveal the relationship of the lipoma to the cord itself (Fig. 27.2b).

Surgery is aimed at untethering the spinal cord, reducing the bulk of the lipoma and reconstituting the dura to enable the conus to lie freely. This may require a dural patch to try to

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