Decompression of idiopathic lumbar epidural - Semantic Scholar

J Neurosurg Spine 4:24–30, 2006

Decompression of idiopathic lumbar epidural lipomatosis: diagnostic magnetic resonance imaging evaluation and review of the literature YOSHINORI ISHIKAWA, M.D., YOICHI SHIMADA, M.D., NAOHISA MIYAKOSHI, M.D., TETSUYA SUZUKI, M.D., MICHIO HONGO, M.D., YUJI KASUKAWA, M.D., KYOJI OKADA, M.D., AND EIJI ITOI, M.D. Department of Orthopedic Surgery, Akita University School of Medicine, Akita, Japan Object. Idiopathic symptomatic spinal epidural lipomatosis (SEL) is a rare condition, and few reports have discussed diagnostic imaging criteria. To evaluate factors relating to its clinical symptoms, correlations between clinical features and the presence of spinal epidural fat were investigated, and the literature concerning idiopathic SEL was reviewed. Methods. Morphological gradings of epidural fat were evaluated in seven patients with idiopathic SEL by using magnetic resonance (MR) imaging. In addition, body mass index (BMI), the number of involved vertebral levels, grade, and preoperative Japanese Orthopaedic Association (JOA) score were analyzed. Surgery resulted in symptomatic relief, with a mean JOA score recovery rate of 67.4%. Grading of epidural fat tended to display a slight negative correlation with preoperative JOA score, whereas a strong significant positive correlation was found between the number of involved vertebral levels and BMI. Conclusions. The number of involved vertebral levels and obesity are strongly correlated, whereas severity of dural compression is not always significantly associated with neurological complications. These results indicate that epidural fat of the lumbar spine contributes to neurological deficits. In addition, weight-reduction therapy appears to decrease the number of vertebral levels involved. Magnetic resonance imaging–based grading is helpful for the diagnosis and evaluation of idiopathic lumbar SEL. Moreover, symptoms and neurological findings are important for determining the surgical approach.

KEY WORDS • spinal epidural lipomatosis • lumbar spine • magnetic resonance imaging • surgical decompression

epidural lipomatosis is defined as the accumulation of normal unencapsulated fat in the extradural space and is known to require long-term corticosteroid therapy or endocrinopathy.2,8,11,18–21,24,29,32,33,40 As an uncommon complication even with the use of corticosteroid therapy,20,32 SEL causing neurological deficits occurs more frequently in the thoracic than the lumbar spine.21,29 Furthermore, ‘idiopathic” SEL as a cause of neurological deficits is extremely rare compared with cases resulting from corticosteroid therapy or endocrinopathy. To date, only 48 cases of symptomatic idiopathic SEL for the whole spine and only 33 cases specific to the lumbar spine have been reported sporadically in the English-language literature,2–8,10,11,13,14,16,21–25,28–42 and and only small reviews have

S

PINAL

Abbreviations used in this paper: BMI = body mass index; JOA = Japanese Orthopaedic Association; MR = magnetic resonance; SD = standard deviation; SEL = spinal epidural lipomatosis.

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been conducted.5,11,22,29,30,32–34 We have undertaken surgery in seven consecutive patients with idiopathic lumbar SEL, representing the largest series of such cases in the literature. The clinical and imaging features are discussed herein, along with a review of previously reported cases. Clinical Material and Methods Patient Population Between 1994 and 2004, seven patients (five men and two women) underwent decompressive surgery for lumbar idiopathic SEL at our institution (Table 1). Their mean age was 65.7 years (range 43–77 years) and their mean BMI was 27.1 kg/m2 (range 22.9–31.3 kg/m2). No patient had a history of corticosteroid therapy or Cushing disease, and three patients were receiving treatment for diabetes. All patients presented with neurological deficits in the lower extremities, with intermittent claudication as seen in cauda equina syndrome. The SEL involved one to five J. Neurosurg: Spine / Volume 4 / January, 2006

Idiopathic spinal epidural lipomatosis TABLE 1

Summary of patient characteristics* Case No. Variable

1

2

age (yrs), sex BMI (kg/m2) history of diabetes mellitus involved level no. of involved levels concomitant disease

66, M 23.3 yes L4–5 1 none

72, M 22.9 no L3–S1 3 disc hernia

3

67, M 27.1 yes L2–S1 4 none

4

5

6

77, M 28.3 no L1–S1 5 spondylolisthesis

63, F 28.9 yes L2–S1 4 spondylolisthesis

72, M 31.3 no L1–S1 5 none

7

Mean (SD)

43, F 65.7 (11.0) 28.4 27.1 (3.1) no — L2–S1 — 4 3.7 (1.4) none —

* — = not applicable.

lumbar intervertebral levels, as shown on MR images. Nonsteroidal antiinflammatory drugs and weight-reduction therapies were prescribed for each patient on an outpatient basis, but neither of these conservative treatments proved effective. All patients subsequently underwent bilateral fenestration or partial laminectomy with epidural fat debulking. In addition, a herniotomy was performed in one patient with lumbar disc herniation, and posterolateral spinal fusion was undertaken in two patients with spondylolisthesis at the level of fat debulking. Clinical Evaluation

Clinical investigations of back or leg symptoms and neurological status were performed before and after surgery by using the JOA scale for lumbar disease (Table 2; full normal score 29 points).15 The JOA recovery rate was calculated as proposed by Hirabayashi, et al.,12 as follows: (postoperative JOA score 2 preoperative JOA score)/ (29 2 preoperative JOA score) 3 100. The distance the patient was able to walk was also recorded to determine the severity of intermittent claudication. Magnetic Resonance Imaging–Based Grading System

The morphological features of epidural fat from L1–2 through L5–S1 that were discernable on MR images were evaluated using the grading system for lumbar SEL proposed by Naka, et al.27 The grading system uses three sagittal and three axial grades derived using T1-weighted MR images, as explained in the captions of Figs. 1 to 3. These grades represent the severity of dural compression in patients with or without concomitant lumbar disease, as used to evaluate the severity of cauda equina syndrome. When one level showed the “Y” sign (Fig. 3), axial grading was considered to be Grade 3 in this study. The “Y” sign, as reported by Kuhn, et al.,20 is a Y-shaped dural sac compressed by severe accumulation of epidural fat. Statistical Analysis

All data are presented as means 6 SDs. Statistical differences between variables were compared using twogroup paired t-tests. To evaluate factors affecting preoperative symptoms, the correlations between BMI, number of involved vertebral levels, total score of axial and sagittal epidural fat grades, and preoperative JOA score were analyzed using Spearman rank correlations or Pearson correlation coefficients, as appropriate. Correlations between variables were estimated according to the correlation coefJ. Neurosurg: Spine / Volume 4 / January, 2006

ficient (absent, r # 0.2; weak, 0.2 , r # 0.4; moderate, 0.4 , r # 0.7; or strong, r . 0.7). Probability values less than 0.05 were considered statistically significant. TABLE 2 Evaluation system for treatment of low-back disorders devised by the JOA Physiological Test Criteria

subjective symptoms low-back pain none occasional mild frequent mild or occasional severe frequent severe leg pain &/or numbness* none occasional mild frequent mild or occasional severe frequent severe walking capacity normal able to walk .500 m w/ leg pain &/or numbness able to walk 100–500 m able to walk ,100 m clinical signs straight leg raising test .70˚ (normal) 30–70˚ ,30˚ motor function* normal slight weakness (good) severe weakness (, good) sensory function normal slight disturbance severe disturbance bladder function normal mild dysuria severe dysuria restriction of activities of daily living† turn over while lying standing up washing face half-sitting posture sitting lifting running total for healthy individuals

Score

3 2 1 0 3 2 1 0 3 2 1 0 2 1 0 2 1 0 2 1 0 0 23 26 2 2 2 2 2 2 2 29

* Evaluated using manual muscle testing. † Activity impossible = 0; difficult = 1; easy = 2.

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Y. Ishikawa, et al.

FIG. 1. Sagittal grading of epidural fat on T1-weighted MR images. Left: Grade 1 was defined as epidural fat observed within the border between the anterosuperior edges of the upper and lower neighboring neural arches. Center: Grade 2 was defined as fat observed over the border at the middle but not at the edges of neural arches on both sides. Right: Grade 3 was defined as fat observed over the border at the edges of neural arches on at least one side.

Results Table 3 summarizes overall outcomes for the seven patients. Surgery provided all of them with symptomatic relief to some degree. The mean postoperative JOA score (24 6 3.6) was significantly improved compared with preoperative JOA score (14 6 5.2; p = 0.0023). The mean recovery rate was 67.4 6 20.7% in all patients: 71.3 6 13.9% with concomitant disease and 64.5 6 26.5% without concomitant disease. The mean preoperative distance the patients were able to walk was 185 6 150 m. Postoperatively, all patients displayed significant recovery of walking ability to more than 500 m (p , 0.0001). In almost all patients, a fat accumulation of Grade 2 or 3 was observed on both sagittal and axial MR images. Grading of epidural fat tended to show moderate negative correlations with preoperative JOA score, but no significant relationship was identified (Table 4). Midsagittal canal diameters represented by the mean (SD) from L1–2 to L5–S1 were 18.4 (2.0), 18.2 (1.0), 17.9 (0.7), 16.7 (3.5), and 18.3 mm (3.7), respectively, and they had no significant correlation with preoperative or postoperative JOA score (p . 0.05). A strong positive correlation was identified between the number of involved vertebral levels and BMI; however, correlations between preoperative JOA score and BMI or the number of involved vertebral levels were absent or weak.

grades of epidural fat using MR images were assigned as Grade 3 on sagittal and as Grade 1 on axial views (Fig. 4). Partial laminectomies with fat debulking were performed at L3–4, L4–5, and L5–S1. Numerous small vessels and strings were observed intraoperatively in the epidural fat. The histopathological diagnosis was proliferation of normal fat. The patient reported symptomatic relief immediately after surgery and was able to walk normally. His postoperative JOA score was 29; thus, his recovery rate was 100%.

Illustrative Case Case 3

The patient was a 67-year-old man with diabetes and a BMI of 27.1 kg/m2. He complained of intermittent claudication when walking a distance of 200 m, and his preoperative JOA score was 20. His MR images revealed that the dural sac tapered off at and below the level of L3–4 by compression due to SEL. Morphological MR imaging 26

FIG. 2. Axial appearance of epidural fat on T1-weighted MR images. Fat accumulation at each intervertebral disc level from L1–2 to L4–5 was classified as follows: absent (upper left), concave (upper right), flat (lower left), or convex (lower right).

J. Neurosurg: Spine / Volume 4 / January, 2006

Idiopathic spinal epidural lipomatosis

FIG. 3. The Y-shaped sign (left) and the circumferential type (right) for the L5–S1 disc level was also evaluated using MR imaging. Between examined lumbosacral levels, Grade 1 was considered present for two or fewer flat types, Grade 3 for two or more convex and/or circumferential types or the “Y” sign, and Grade 2 for fat accumulation more than in Grade 1 but less than in Grade 3.

Discussion

Treatment Parameters

Characterized by abnormal accumulation of unencapsulated fat in the spinal epidural space, SEL usually occurs as a complication of long-term corticosteroid therapy.18 Idiopathic SEL was first reported by Badami and Hinck2 in 1982. Haddad, et al.,11 first hypothesized that idiopathic SEL was a byproduct of obesity, with the gradual overgrowth of epidural fat resulting in compression of the spinal cord and nerves. Compared with SEL secondary to corticosteroid therapy, idiopathic SEL is extremely rare, and to the best of our knowledge, only 48 cases of wholespine and only 33 cases for the lumbar SEL have been reported in the English-language literature.2–8,10,11,13,14,16,21–25, 28–42 These reported cases are summarized in Table 5 and in Fig. 5. A comparison of these and the present seven cases indicated that the main lesion in idiopathic SEL is located more frequently in the lumbar spine than in the thoracic spine (40 in the lumbar and 13 in the thoracic spine) and shows two peaks, differing from the smaller idiopathic series reported by Kumar, et al.,21 Payer, et al.,29 or Robertson, et al.33 Confirming previous reports of SEL in the lumbar spine, a strong male preponderance was identified (32 men, eight women, and one unknown).33,37

Spinal epidural lipomatosis is known to be related to obesity.11,21,24,33 The present study also revealed a strong correlation between BMI and epidural fat accumulation. The suggestion has been made that SEL is strongly associated not only with subcutaneous fat4 but also with visceral fat and lifestyle-related diseases.17 Thus, if no acute progression of symptoms occurs, weight-reduction diet therapy should be attempted for the initial treatment of idiopathic SEL.4,5,11,29 Borstlap, et al.,5 reported reduction of the “Y” sign as seen on MR imaging and clinical improvements after weight-reduction diet therapy. The effects of lumbar epidural lipomatosis are expected to be reversible in obese patients after weight-reduction therapy (Table 6).4,5,11,30,31,33,41 The present results indicate that spinal epidural fat is correlated with obesity, but no case of postoperative recurrence has been reported. Further follow-up studies and reevaluation using MR imaging are warranted. Decompressive surgery with fat debulking should be considered when diet therapy proves unsuccessful or when the patient suffers acute neurological deterioration. All patients in the present study and those described in the relevant literature achieved symptomatic relief after lumbar surgery (Table 6). The mean JOA recovery rate of 67.4%

TABLE 3 Summary of outcomes in patients with idiopathic SEL* Case No. Variable

1

2

3

4

5

6

7

Mean (SD)

preop JOA score postop JOA score recovery rate preop walking distance (m) grade sagittal axial total “Y” sign

15 20 35.7 500

11 26 83.3 100

20 29 100.0 200

13 22 56.3 140

17 26 75.0 200

4 19 60.0 120

16 24 61.5 40

14 (5.2) 24 (3.6) 67.4 (20.7) 186 (149.5)

3 1 4 no

2 3 5 no

3 1 4 no

3 3 6 yes

3 2 5 no

3 3 6 yes

2 2 4 no

2.7 (0.5) 2.1 (0.9) 4.9 (0.9) —

* — = not applicable.


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Y. Ishikawa, et al. TABLE 4 Correlation between variables and fat grade*

Variable

preop JOA score BMI no. of involved levels

Preop JOA Score

— — —

Total Grade

BMI

No. of Involved Levels

20.036† — —

20.225† 0.835‡§ —

20.680† 0.416† 0.693†

(sagittal 1 axial)

* — = not applicable. † Spearman correlation coefficient (r). ‡ Pearson correlation coefficient (r). § p , 0.05.

in our patients was equivalent to or less than rates measured after surgery in cases of other concomitant diseases of the lumbar spine.9,43 These results probably indicate that epidural fat acts as a contributing factor for spinal canal narrowing and makes the nerve root vulnerable to damage. Conversely, spinal canal stenosis caused solely by excessive soft epidural fat damages nerve roots softly and slowly. The longer duration of nerve root constriction may cause the relatively lower recovery rate.26 The relatively higher recovery rate in cases involving concomitant disease may be due to preoperative lumbar pain and the subacute progression of stenosis. Subacute symptoms and severe

pain would tend to result in earlier treatment and thus less deterioration of the nerve root. Further examination of fat quantity and correlations between preoperative duration of symptoms and JOA score are needed to clarify these matters. Imaging Recommendations

The present study employed Naka’s grading system27 and Kuhn’s “Y” sign20 to evaluate lumbar SEL. Naka’s grading system is simple and easy to understand. Observing the lumbar epidural fat, Kuhn, et al., reported the Y-shaped image as a specific sign of lumbar thecal compression on axial T1-weighted MR images and postmyelographic computerized tomography scans in cases of symptomatic lumbar SEL.20 Using these imaging criteria allowed semiquantitative evaluation of the severity of lumbar SEL. The results of the present study demonstrated that morphological grades of epidural fat accumulation in the lumbar spine tended to display a moderate, negative correlation with JOA score, but no statistically significant relationship was found. Postoperative neurological status was determined by numerous factors, including preoperative duration of symptoms and neurological status;26 the influence of concomitant lumbar disease is also a possibility, as mentioned previously. Kornberg and Rechtine19

FIG. 4. The morphological grading of epidural fat as determined on MR imaging was Grade 3 on a sagittal sequence (left) and Grade 1 on axial sequences (upper, L3–4; center, L4–5; and lower, L5–S1).

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Idiopathic spinal epidural lipomatosis TABLE 5 Summary of 40 cases of idiopathic lumbar SEL stratified by age and sex*

TABLE 6 Summary of treatment results stratified by type in 40 cases of idiopathic lumbar SEL*

Variable

Men

Women

Total

no. of cases age (yrs) mean (SD) range

32

8

40

Variable

WL

L

L1F

L1E

54.4 (12.1) 32–77

56.6 (14.1) 29–71

54.8 (12.4) 29–77

no. of treatments no. of improved cases

11 8

22 19

6 6

1 1

* This table includes our seven patients.

reported that the patients who were likely to undergo operative treatment for lumbar canal stenosis had a canal diameter of less than 16 mm.1 Mean canal diameters in our series were relatively larger. These differences might indicate that the symptoms in our series were mainly provoked by SEL, whereas severity of dural compression and postoperative neurological condition are not always significantly correlated.19,26 According to the present results, MR imaging–based grading appears to be useful for making a diagnosis of idiopathic lumbar SEL, but symptoms and neurological findings are also important factors in determining the surgical approach. When treating patients with thoracic or cervical lesions, we should be careful not to rely on the generalization that the degree of dural sac compression caused by fat is not predictive of the extent of neurological deficit. In the clinical setting, subclinical lumbar canal stenosis due to degeneration is frequently observed in elderly individuals. Distinguishing pure SEL from the combination of SEL and lumbar canal stenosis in elderly patients is therefore sometimes difficult. We think that our grading system is useful for making a diagnosis easily, with or without the presence of abnormal fat accumulation, for predicting the symptoms of patients with lumbar SEL. Further observational studies involving larger patient populations are warranted to clarify the clinical characteristics of SEL.

FIG. 5. Graph showing the distribution of idiopathic SEL by spinal level, with sex ratio at each level. The majority of cases of idiopathic SEL involve the midthoracic and lower lumbar vertebral levels, representing two peaks.


Treatment Type

* Includes our seven patients. Abbreviations: WL = weight loss; L = laminectomy; L 1 F = laminectomy plus fusion; L 1 E = laminectomy plus endoscopy.

Conclusions We have described seven consecutive cases of symptomatic idiopathic lumbar SEL treated using surgical decompression. All patients experienced symptomatic relief after surgery. The MR imaging grading of epidural fat correlated moderately with preoperative symptoms. Lumbar spinal epidural fat is a factor in neurological deficits, and MR imaging grading is helpful for the diagnosis and evaluation of idiopathic lumbar SEL. In addition, symptoms and neurological findings are important for determining surgical indications. References 1. Amundsen T, Weber H, Lilleas F, Nordal HJ, Abdelnoor M, Magnaes B: Lumbar spinal stenosis. Clinical and radiologic features. Spine 20:1178–1186, 1995 2. Badami JP, Hinck VC: Symptomatic deposition of epidural fat in a morbidly obese woman. AJNR Am J Neuroradiol 3: 664–665, 1982 3. Bednar DA, Esses SI, Kucharczyk W: Symptomatic lumbar epidural lipomatosis in a normal male. A unique case report. Spine 15:52–53, 1990 4. Beges C, Rousselin B, Chevrot A, Godefroy D, Vallee C, Berenbaum F, et al: Epidural lipomatosis. Interest of magnetic resonance imaging in a weight-reduction treated case. Spine 19: 251–254, 1994 5. Borstlap AC, van Rooij WJ, Sluzewski M, Leyten AC, Beute G: Reversibility of lumbar epidural lipomatosis in obese patients after weight-reduction diet. Neuroradiology 37:670–673, 1995 6. Fan CY, Wang ST, Liu CL, Chang MC, Chen TH: Idiopathic spinal epidural lipomatosis. J Chin Med Assoc 67:258–261, 2004 7. Flores A, Sonntag VKH, Dickman CA: Idiopathic spinal epidural lipomatosis: Report of two cases and review of the literature. BNIQ 11:22–25, 1995 8. Frank E: Endoscopic suction decompression of idiopathic epidural lipomatosis. Surg Neurol 50:333–335, 1998 9. Fujitani M, Hasegawa K, Anbo H, Matsuno S, Kaneda K: [A study of reoperated cases for lumbar spinal stenosis.] Orthop Surg Traumatol 42:1415–1423, 1999 (Jpn) 10. Gero BT, Chynn KY: Symptomatic spinal epidural lipomatosis without exogenous steroid intake. Neuroradiology 31:190–192, 1989 11. Haddad SF, Hitchon PW, Godersky JC: Idiopathic and glucocorticoid-induced spinal epidural lipomatosis. J Neurosurg 74: 38–42, 1991 12. Hirabayashi K, Miyakawa J, Satomi K, Maruyama T, Wakano K: Operative results and postoperative progression of ossification among patients with ossification of cervical posterior longitudinal ligament. Spine 6:354–364, 1981 13. Hogg JP, Shank T, Gingold M, Bodensteiner J, Schochet SS,

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Manuscript received June 28, 2005. Accepted in final form October 12, 2005. Address reprint requests to: Yoshinori Ishikawa, M.D., Department of Orthopedic Surgery, Akita University School of Medicine, 1-1-1 Hondo, Akita 010-8543, Japan. email: [email protected].
