Lipomas of the Spinal Cord Associated with Spinal Dysraphism

The term lipomyelomeningocele refers to a congenital lesion of the meninges or spinal cord plus meninges and the presence of benign fat, both of which exist with a dysraphic spinal column. Depending on the classification system used, these lesions may be divided into as many as five subtypes as they appear on neuroimaging.2 In general, a lipomyelomeningocele is recognized on MRI as a caudally descended conus medullaris invested in fat. Arai et al, using conventional myelogram and MRI, define lipomyelomeningocele as a "low lying tethered spinal cord [that] enters a subcutaneous cystic meningeal sac and terminates in the lipomatous mass on the wall of the meningeal sac."2 The lipoma and meningocele may appear together or on opposite sides of the spinal canal. The asymmetric variety is less common and is generally associated with more severe deformities of the sacrum and lower extremities.23 Lipomyelomeningoceles may also be associated with a "syringomyelia, tethered spinal cord, dermal sinus tract, dermoid tumor, menigocele manqué, diastematomyelia, and neurenteric cyst."23 Greater than 90% of these lesions will present with lumbosacral cutaneous anomalies such as "dermal sinus tracts, atretic meningocele, hemangioma, and focal hirsutism."23 As such, there is generally little difficulty in making the diagnosis.

Lipomyelomeningoceles are not uncommon, and there is a female-to-male predominance of approximately 1.5:1.23 They are thought to result from mistakes in posterior canalization between days 28 and 48 of embryogenesis.23 Their histology is similar to other types of lipomatous tumors, with the lipoma-tous portion made up of mature adipocytes.

Most patients experience symptom onset early in life and many are diagnosed in utero using ultrasound. Of those not recognized or treated at birth, clinical manifestations generally progress slowly over months to years and may include motor weakness and sensory changes in the lower extremities, bladder incontinence, and pain.2,3,23 Lipomyelomeningoceles may present with both upper and lower motor neuron signs, and "asymmetrical weakness of the feet and legs is a hallmark of this condition."23 The acuity and degree of impairment depends on the nature of the lesion, but most authors agree that neurologic deterioration, over time, is assured in these patients.

Controversy exists regarding the timing of surgical repair in asymptomatic patients. The likelihood that patients will develop neurologic problems is high (88%), given a long enough period of follow-up, whereas the risk of complications during operative procedures is less than 10%.2,3,23 It is important in surgical planning to know whether the tethered cord lies within the spinal canal. The goals of surgery are to remove as much of the lipoma as possible while preserving nervous tissues, release the tethered cord, and attempt to prevent re-tethering.2,23 Refer to Management of Spinal Cord Lipomas and Lipomyelomeningoceles23 for further details on operative approaches.

Compared with intradural or intramedullary lipomas and lipomas of the filum terminale (discussed later), the prognosis for patients with lipomyelomeningoceles is not as favorable. In the report by Bulsara et al,3 only 29% of patients with lipomyelomeningocele had improved motor function postoper-atively, and there was very little improvement (7%) in bladder function or sensation. There was also little reported significant improvement in bowel function, pain, or scoliosis. They did note, however, that "younger patients tended to have better motor outcomes."3 It has been stated that "the longer and more complete the deficit [in motor, sensory, or bowel or bladder function], the less likely it is to resolve following surgical intervention."23 This would suggest that patients with lipomyelomeningoceles should be operated on early in the hopes of avoiding neurologic deterioration. It may also be concluded that early detection of these cases, by way of recognition of cutaneous stigmata, is critical to good clinical outcomes in this patient population.3

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