CONGENITAL LUMBOSACRAL LIPOMAS

Congenital lumbosacral lipomas can be responsible for progressive defe cts. The general feeling is that tethering of roots, filum, or cord pr obably explains this evolution, and that untethering of these structur es could prevent late deterioration. Like the vast majority of neurosu rgeons, we too have routinely and systematically operated on lumbosacr al lipomas, even in the absence of neurological deficits. This policy stemmed from our belief that spontaneous neurological deterioration wa s frequent, recovery from preoperative deficits rare, and surgery both efficient and benign in nature. After 22 years of experience, we felt that it was necessary to review our series of 291 lipomas (38 lipomas of the filum and 253 of the conus) operated on from 1972 to 1994. To reassess the value of prophylactic surgery, we attempted an accurate e valuation of (1) the risk of pathology, (2) the risks involved in surg ery, (3) the postoperative outcome with respect to preoperative defici ts, and (4) the postoperative outcome in asymptomatic patients at 1 ye ar and at maximum follow-up. Special attention was paid to 93 patients whose postoperative follow-up was more than 5 years (average 8.7, med ian 8, range 5-23 years). Of these 93 patients, 39 were asymptomatic p reoperatively (7 with lipoma of the filum and 32 with lipoma of the co nus). Lipomas of the filum and of the conus are entirely different les ions and were studied separately. In 6 cases prenatal diagnosis had be en possible. The mean age at surgery was 6.4 years. Low back skin stig mata were present in 89.4% of cases. Preoperative neurological deficit s existed in 57% of the patients and were congenital in 22%. Clinical signs and symptoms recorded were pain in 13.3% of the patients and/or neurological deficits affecting sphincter (52%), motor (27.6%) and sen sory (22.4%) functions. Deficits were progressive in 22.4% of cases, s lowly progressive in 58.8% of these and rapidly progressive in the rem aining 41.2%. In 36 patients (13.2%) the lipomas were seen to grow eit her subcutaneously or intraspinally. Among these patients, 21 were inf ants, 2 were obese adolescents, and 10 were pregnant women. The metabo lism of the fat within the lipomas was studied in Il patients and foun d to be similar to that at other sites. Lipomas were associated with v arious other malformations, either intra-or extraspinal. These associa ted anomalies were rare in the case of lipomatous filum (5.2%) but fre quent with lipomas of the conus, except for intracranial malformations (3.6%). Therapeutic objectives were spinal cord untethering and decom pression, sparing of functional neural tissue and prevention of reteth ering. Procedures used to achieve these goals were subtotal removal of the lipoma, intraoperative monitoring, duroplasty, and sometimes clos ure of the placode. Histologically, lipomas consisted of normal mature fat. However, 77% of them also included a wide variety of other tissu es, originating from ectoderm, mesoderm, or entoderm. This indicates t hat lipomas are either simple or complex teratomas. The results of the study are as follows. (1) Surgery was easy and safe when performed fo r treatment of lipomas of the filum (no complications), but difficult and hazardous in the case of lipomas of the conus (20% local, 3.9% neu rological complications). (2) All types of deficit could be improved b y surgery, which was beneficial in all cases of lipoma of the filum an d 50% of cases of lipoma of the conus. (3) In asymptomatic patients lo ng-term surgical results depended on the anatomical type of the lipoma . They were excellent in lipomas of the filum. In lipomas of the conus they were good in the short term but eroded with time. At more than 5 years of follow-up only 53. 1% of the patients were still free of sym ptoms. (4) Reoperations were performed in 16 patients (5.5%), 5 (31.2% ) of whom improved postoperatively, while in 7 (43.7%) progression sto pped, in 3 (18.7%) deterioration continued and in 1 (6.2%) the conditi on was worse after surgery. (5) The natural history of the malformatio n, that is to say the risk of spontaneous aggravation, has only been e valuated in hospital inpatients, so that the true level of risk remain s unknown. This means we cannot interpret the actuarial curve followin g surgery for asymptomatic lipoma of the conus. In conclusion, there a re two different types of lipoma: lipoma of the filum, for which surge ry is harmless and beneficial in both the short and the long term, and lipoma of the conus, for which surgery involves considerable risks an d is of questionable benefit in the long term. This raises the questio n as to whether prophylactic surgery is indicated for patients with as ymptomatic lipomas of the conus, and whether the outcome is any better than it would be if the lipoma were left to take its natural course. The lack of basic information remains a stumbling block to management of these patients. Until this is remedied, we are unable to recommend prophylactic surgery in patients with asymptomatic lipomas of the conu s.