Congenital spinal lipomas: Role of prophylactic surgery.

INTRODUCTION: Congenital spinal lipomas constitute an important group of lesions causing tethered cord syndrome. Management of these lesions is challenging and role of prophylactic surgery for these lesions is still controversial. Hence, current study was undertaken with the aim to evaluate the role of prophylactic surgery in the management of these lesions.
MATERIALS AND METHODS: A total of 147 consecutive patients, treated over a period of 10 years (January 2001-December 2010), are retrospectively analyzed.
RESULTS: In our study, 93 patients had conus lipomas, 26 had filum lipomas and 28 had only lipomeningomyelocele. Boys and girls were almost equally represented. The age of patients at the time of surgery ranged from 15 days to 34 years with an average of 62 months (5.2 years). Neurological deficits were present in 101 (68) patients. The patients with neurological deficits were older in comparison to those neurologically intact (average age 6.2 versus 2.8 years, respectively). Difference in age between the two groups was statistically significant (P value 0.03). Neurological deterioration was observed in 8 (5) patients following surgery, out of which six patients developed transient deterioration and only two, had persisting deficits. None of the neurologically asymptomatic patients developed persistent neurological deficits. In the symptomatic group, nine patients (9) showed improvement in neurological status after surgery.
CONCLUSIONS: In author's view, prophylactic surgery for congenital spinal lipomas is safe and effective. However, a well designed randomized controlled trial, to definitely and objectively prove the usefulness of prophylactic surgery is needed.

Introduction

Spinal lipomas associated with dysraphism constitute an important and common cause of tethered cord syndrome[1-4] and can lead to progressive neurological deterioration as the child grows older. Tethering of the cord, roots or filum and the compression produced by the presence of lipomas is considered responsible for the development of the neurological symptoms.[56]

These lesions occur due to abnormal embryologic development that was explained in detail by Mclone and Naidich.[7] An aberration in embryological development between 25th and 48th postovulation day leads to the development of congenital spinal lipomas. These lesions occur due to a brief dysjunction in the timing of separation and simultaneous fusion of cutaneous ectoderm and neurectoderm. The cutaneous ectoderm closes slightly before closure of the neural tube. The paraxial mesenchyme enters through the transient gap in the neural tube, and under the inductive influence of the neural placode, forms fat.[8]

The incidence of congenital spinal lipomas is in the range of 0.4–0.8/100000.[19] These children present with varied clinical manifestations. The diagnosis can be made at birth or shortly thereafter due to the presence of cutaneous stigmata, however, its diagnosis may be elusive and these children may be diagnosed at a later age due to various neurological, cutaneous, or orthopedic abnormalities.

Management of congenital spinal lipomas is challenging. Surgery remains the standard treatment. However, literature regarding the role of prophylactic surgery is scanty and very few studies[110-13] favor prophylactic surgery. This study was conducted to analyze the clinical manifestations, radiological findings, outcome following surgery, and also to evaluate the role of prophylactic surgery in the management of these lesions.

Materials and Methods

A total of 147 consecutively treated patients with spinal cord lipomas associated with spinal dysraphism, over a period of 10 years extending from January 2001 through December 2010 were retrospectively analyzed. Patient's admission records, neuroimaging, operation records, and outpatient files were used to collect the data.

Results

Patient characteristics

Boys and girls were almost equally represented in the study group, 75 versus 72, respectively. At the time of surgery, age of the patients ranged from 15 days to 34 years with an average of 62 months (5.2 years). Follow up of the patients ranged from 6 months to 62 months with an average of 23 months.

Symptoms and signs

The various clinical manifestations included presence of neurological deficits, cutaneous and orthopedic abnormalities. Presence of neurological deficits was the commonest presentation observed in 101 (69) patients, whereas 46 (32) had nonneurological manifestations. The group of patients presenting with neurological deficits were older (average age 75 months) as compared with the group without neurological deficits (average age 34 months). The difference in age of presentation between these two groups was statistically significant (P value 0.03). Using receiver operating curve (ROC), an age cut off of 21 months was found; the odds ratio of having neurological deficits at presentation was 4.1 in children older than 21 months when compared with children younger than 21 months (P value 0.04).

Neurological manifestations

One hundred one patients were symptomatic neurologically. Neurological deficits included weakness of lower limbs, sensory impairment, and bladder and bowel dysfunction, either alone or in different combinations. Forty-five patients had weakness as the sole neurological manifestation. Eighteen patients had weakness associated with bladder and bowel involvement. In 16 patients, impairment of motor, sensory as well as bladder and bowel functions was present. Another 16 patients had alterations in bladder and bowel functions as the sole neurological deficit [Table 1].

Table 1

Neurological manifestations

Cutaneous manifestations

Different cutaneous stigmata of spinal dysraphism were present in 111 (76) patients. Lipomeningomyelocele (LipoMMC) or subcutaneous lipoma was the commonest cutaneous manifestation present in 83 (56) patients [Table 2].

Table 2

Cutaneous manifestations

Orthopedic manifestations

Orthopedic abnormalities were observed in 59 (40) patients. Scoliosis was the commonest manifestation, noticed in 29 patients. Other manifestations included congenital talipes equinovarus congenital talipes equinovarus (CTEV), flat foot, coxa vera deformity of legs, and sprengel's deformity of scapula.

Neuroimaging

Magnetic resonance imaging (MRI) evaluation was carried out as part of diagnostic workup in all patients. Low lying tethered cord was present in all the patients. Thirty-five patients had syringomyelia and twenty-one had associated split cord malformation. Other common associated findings included chiari malformation and hydrocephalus [Table 3].

Table 3

Radiological findings

Operative procedure

Patients were taken up for surgery after preoperative diagnostic evaluation. In all cases, the aim was to decompress and to release tethering, as well as to rebuild the dural canal. LipoMMC sac when present was defined on all sides. Laminotomy was carried out proximal to the bony defect. LipoMMC sac or subcutaneous lipoma was completely excised. Conus lipoma was totally or near totally excised. Conus was reconstituted after excision of conus lipoma with multiple pial sutures. Filum terminale was identified and resected in all the patients. Filum lipoma when present was excised. Dura closure was carried out primarily in a watertight fashion. Laminoplasty was done with multiple nylon sutures. Incision was then closed in multiple layers.

Depending upon the intraoperative findings, spinal lipomas were then classified as described below.

Spinal lipomas

(A) Lipomyelomeningocele [Figure 1a and b]

Figure 1

Representative MRI images of LipoMMC (a,b), dorsal conus (c,d), transitional conus (e,f), and terminal conus lipoma (g,h)

A total of 83 patients had LipoMMC. Its associations included conus lipoma in 47 patients and filum lipoma in 8 patients. In 28 patients, lipoMMC was the sole lipomatous lesion. Ten patients had split cord malformation split cord malformation (SCM) and eighteen had associated syrinx.

(B) Conus lipoma [Figure 1c–h]

Ninety-three patients had conus lipoma. These lesions were further classified as dorsal conus lipoma in 38 patients, transitional conus lipoma in 32 and the rest 23 had terminal conus lipoma. Associations of conus lipomas included lipoMMC in 47, filum lipoma in 8, split cord malformation in 12, and syringomyelia in 23.

(C) Filum lipoma

Twenty-six patients had filum lipoma. It was associated with conus lipoma in eight, LipoMMC in eight, syrinx in eight, and SCM in nine patients.

Immediate postoperative complications

Eleven (7) patients developed wound-related complications [Table 4] and were managed conservatively. One child developed pneumonia and septicemia after surgery, probably due to aspiration and expired 7 days after surgery.

Table 4

Immediate postoperative complications

Neurological outcome

One hundred one patients had neurological deficits at the time of admission. Nine (9) patients showed improvement in muscle power postoperatively. Postoperative deterioration in power was observed in eight (5) patients, out of which two patients had persistent deficits, whereas in the rest six patients, the deficits resolved over a period of 2–3 weeks [Table 5]. Five of these patients had preexisting deficits, whereas, three patients were neurologically intact preoperatively and in all these three patients, the neurological deficits recovered completely. Thus, the risk of developing transient neurological deficits in patients undergoing prophylactic surgery was 6.5% (3 out of 46 patients).

Table 5

Effect of surgery on neurological outcome

Both patients with persistent deficits had transitional conus lipoma and both were previously operated at another hospital and underwent second surgery at our institute.

Follow-up

Follow-up period ranged from 6 to 62 months with an average of 23 months. Nine (9) patients showed improvement in neurological status following surgery during follow-up. Out of these nine patients, three patients with lower limb weakness associated with urinary and fecal incontinence showed improvement in both motor and bladder/bowel functions and regained bladder/bowel control. Two patients with weakness as the only manifestation, improved postoperatively. Another two patients with motor, sensory and bladder/bowel symptoms had improvement in motor and bladder and bowel functions, and two patients with motor and sensory complaints had improvement in motor and sensory functions postoperatively.

Discussion

Congenital spinal lipomas constitute a heterogenous group. Different terms have been coined in the literature for these lesions. Pierre-Kahn et al.[1] used the term lumbosacral lipomas and subdivided them into lipomas of conus and lipomas of filum. They used the term lipomyelomeningocele for meningocele, which was associated with subcutaneous lipoma. Chapman[2] categorized conus lipomas into dorsal, caudal, and transitional types. In the present study, congenital spinal lipomas have been categorized into: conus lipomas, lipomyelomeningocele, and filum lipomas. Conus lipomas are further subdivided into: dorsal, terminal, and transitional types.

In the natural course of these lesions, the chances of developing neurological deficits increase with increasing age at presentation. This fact has been substantiated by different studies.[1-101314] In a study carried out by Pierre- Kahn et al.,[1] the average age of patients presenting with cutaneous abnormalities was 9 months as compared with 6.4 years for the whole group. Dorward et al.[10] have also shown that children presenting after 3 years of age were more likely to be having neurological deficits as compared with those younger. In a study by Kasliwal and Mahapatra,[13] the group of patients with neurological deficits (mean age 5.5 years) were older compared with those without deficits (mean age 2 years). In current study also, at the time of admission, the group of patients with neurological deficits were older than the neurologically intact patients (6.2 years versus 2.8 years, respectively). This difference in presentation between the two subgroups (with and without neurological deficits), separated by the age gap, can be seen as a reflection of the natural history of patients with spinal lipomas. Similar observations have been made by Kasliwal and Mahapatra in their study.[13] But it is also possible that these two groups are completely different from each other as far as disease progression and natural history is concerned,[10] thereby considering them to represent same group of patients, at different points along the natural course of the disease might not be appropriate.

The incidence of preoperative neurological deficits in patients with spinal lipomas varies from 23 to 75%[1–9, 13–19] in different studies. In a study conducted by Pierre-Kahn et al.,[1] 57% of patients had neurological deficits at the time of presentation. Kasliwal and Mahapatra[13] reported that 70% of patients had neurological deficits at the time of presentation. In our study, 69% patients had preoperative neurological deficits, motor weakness being the most common manifestation.

In literature, the incidence of postoperative neurological deterioration has ranged from 1.6 to 7%.[11113-17] In our study, the risk of developing persistent neurological deterioration after surgery was 2% (2/101) among the patients presenting with neurological deficits. None of the neurologically intact patients developed permanent neurological deficits as a result of surgery. Thus the overall risk of developing permanent neurological deficits as a result of surgery was 1.2%.

There has not been a consensus over the concept of prophylactic surgery for asymptomatic spinal lipomas. Various authors have raised concerns regarding the usefulness and safety of prophylactic surgery,[1913-20] particularly in the context of certain types of spinal lipomas.[116] The argument most commonly offered against prophylactic surgery is that it does not have any preventive effect upon the development of late neurological deficits in these patients and they continue to deteriorate at the same rate irrespective of whether surgery is performed or not.[6914] However, there are studies[1411] in the literature which have shown that prophylactic surgery in addition to being safe also offers longer progression free survival in comparison to conservative treatment. In our study also, none of the asymptomatic patients developed persistent neurological deficits. And none of the patients developed neurological deterioration during follow up. In patients who have already developed neurological deficits, surgical intervention has a definitive role in stabilizing and to some extent improving these deficits. Also early surgery must be contemplated to prevent further deterioration. In our study, nine patients (9 of the patients with preoperative neurological deficits) had improvement in neurological function after surgery and none of the patients developed late neurological deficits during follow up.

The conservative treatment for asymptomatic patients with spinal lipomas has its own drawbacks. Close monitoring of these children managed conservatively may not be possible in developing countries. Moreover, an expert neurosurgeon and urologist may not be available for all the patients. Aesthetic concern also remains an important issue and performing surgery on patients after development of neurological deficits may not give good results.

Surgical treatment for spinal lipomas has been shown to be safe in different studies.[41113] It is effective also in prolonging the progression free survival.[1411] In our study also, none of the asymptomatic patients developed persistent neurological deficits after surgery and none deteriorated during follow up.

Conclusions

Congenital spinal lipomas are an important cause of tethered cord syndrome. Prophylactic surgery for asymptomatic congenital spinal lipomas remains a debatable issue. In the literature one finds both proponents and opponents of prophylactic surgery. Conservative management of these lesions is associated with many drawbacks. Today, with better understanding of the anatomy of spinal lipomas and with advances in microneurosurgical techniques, surgery for these lesions is safer. Over the past decade, there has been accumulating evidence in favor of prophylactic surgery. Based upon the results of our study, authors favor and recommend prophylactic surgery, which is safe and useful.[21-24] However, a well designed randomized controlled trial, to definitely and objectively prove the usefulness of prophylactic surgery as well as to identify specific subgroups that would benefit the most from prophylactic surgery for spinal lipomas is the need of the hour.