| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
1 All authors: Department of Radiology, Thomas Jefferson University Hospital, 111 S. 11th St., Philadelphia, PA 19107.
Received April 29, 2002;
accepted after revision June 13, 2002.
Address correspondence to M. E. Schweitzer.
Abstract
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
MATERIALS AND METHODS. MR images of the lumbar spine obtained at 1.5
T of 307 consecutive outpatients (191 female, 116 male) were reviewed on the
basis of MR imaging signal characteristics for the presence, degree, size, and
location of presumed subcutaneous posterior soft-tissue edema and fluid
collections. The patients were divided into three weight groups (<70,
70-85, or > 85 kg) and two age groups (<50 or 
50 years old). Edema
was graded on a scale of 0-5 according to its length relative to the vertebral
bodies. When present, the fluid collection volumes were calculated. The
vertical epicenter of the signal abnormality was noted by vertebral body
level.
RESULTS. Lumbar soft-tissue edema was seen in 121 patients (39%), and discrete fluid collections were seen in 53 patients (17%). Both degree of edema and volume of fluid collection were associated with increasing weight (p < 0.001 and p = 0.002, respectively) and increasing age (p < 0.001 and p = 0.01, respectively). The degree of edema in females was significantly greater than in males (p = 0.003). However, the sex of the patient did not correlate with frequency of fluid collections (p = 0.12) or volume of collections (p = 0.08). The mean epicenters of edema in females and males were at similar levels (L3.4 and L3.9, respectively, p = 0.54).
CONCLUSION. The severity of posterior lumbar subcutaneous edema and the volume of fluid collections on MR imaging are associated with increased weight.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Cooper et al. [2] reported that lumbar edema accumulated at the subcutaneous fascia plane on CT. To our knowledge, no prior reports in the literature scientifically describe lumbar soft-tissue edema on MR imaging or evaluate the relation of the edema and the patient's body habitus. Consequently, in this study we investigated the correlation of body weight and the posterior lumbar and sacral subcutaneous edema or fluid collections seen on MR imaging.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
The final study population consisted of 307 patients, of whom 191 were female and 116 were male (age range, 13-90 years; mean age ± SD, 50.3 ± 15.7 years). The demographic data of the patient population are listed in Table 1. This research project was approved by the institutional review board of our hospital.
|
Imaging Technique
Imaging was performed on a 1.5-T MR imaging unit (Signa; General Electric
Medical Systems, Milwaukee, WI) with a dedicated spine coil. Although imaging
was performed in several planes, the subcutaneous posterior lumbar soft-tissue
edema was evaluated primarily on fat-saturated sagittal T2-weighted fast
spin-echo images. In cases of inadequate fat saturation, which sometimes was
seen in sacral subcutaneous soft tissue, the T1-weighted
non—fat-saturated images were used to confirm the presence and extent of
the edema. The MR imaging parameters were as follows: echo-train length, 8; TR
range/TE range for sagittal T2-weighted sequences, 3100-4000/80-90; TR/TE for
sagittal T1-weighted sequences, 400/9. The following parameters were the same
for all pulse sequences: section thickness, 4.0 mm; intersection gap, 1.0 mm;
matrix, 512 x 192; and field of view, 30 x 30 cm.
Image Analysis
The lumbar MR images were retrospectively reviewed by one radiologist for
the presence, degree, and location of subcutaneous posterior softtissue
edema-like signal (for simplicity, the term "edema" is used for
the remainder of the text). Lumbar edema was graded on a scale of 0-5
according to its length relative to the vertebral bodies on sagittal images:
0, no edema; 1, less than the height of one vertebra; 2, equal to or longer
than the height of one vertebra but not reaching the adjacent end plate of the
next vertebra; 3, spanning the height of two vertebrae; 4, equal to or longer
than two vertebrae, but less than grade 5; and 5, spanning three vertebrae or
longer. When a patient had multiple foci of edema, the sum of the length was
used to categorize the degree of edema. Sacral edema was also graded in a
similar fashion on a scale of 0-5 using the height of S1 as a reference. In
some patients who had edema, well-marginated discrete accumulations of
homogeneous T2 hyperintensity could also be identified, which we labeled
"fluid collection." When present, the size of the fluid collection
was measured in three dimensions, and the volume was calculated as the product
of three dimensions multiplied by 0.5, assuming an ellipsoid shape. In cases
of multiple collections, the volumes were summed. The vertical epicenter of
edema was noted on a scale of 1-5 corresponding to the lumbar vertebral body
levels, or as 1.5, 2.5, 3.5, or 4.5 if the epicenter was at the intervetebral
disk level.
For purposes of data analysis, we divided the patients into three groups
based on body weight: group 1, less than 70 kg, consisted of 102 patients;
group 2, 70-85 kg, had 102 patients; and group 3, greater than 85 kg,
contained 103 patients. The patients were also divided into two groups based
on age (< 50 years old, 155 patients; 50 years old, 152 patients). The
mean degree of edema in each group of patients was calculated as the summation
of the products of each degree of edema and the number of patients in that
degree category, then divided by the total number of patients in that group.
For dichotomous dependent variables including the presence or absence of edema
or discrete volume of collection in different weight, age, or sex groups,
chi-square tests were computed. For ordinal and non-normally-distributed
continuous variables, including the degree of edema and the volume of fluid
collections in different weight, age, or sex groups, Mann-Whitney U
tests and Kruskal-Wallis tests were calculated. To analyze whether the effect
of weight was independent of sex and age, two-way parametric analyses of
variance were calculated separately for males and females. Although the
dependent variables were not normally distributed, parametric analysis of
variance is robust for violations of normality provided sample sizes are equal
[3]. A p value of less
than 0.05 was defined as statistically significant.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
|
The mean body weight of our patient populaton was 78.5 kg (range, 45.5-145.0 kg), and the mean age was 50.3 ± 15.7 years (range, 13-90 years). Among the overall population, 121 patients (39.4%) had lumbar edema. The percentage of patients who had lumbar edema increased significantly from 22.5% in weight group 1 to 33.6% in weight group 2 and 59.2% in weight group 3 (p < 0.0001). The degree of lumbar edema also significantly increased in the heavier weight group (p < 0.0001). Among the patients with edema, 53 patients (43.8%) had lumbar fluid collections. Similarly, the percentage of patients having fluid collections also significantly increased with body weight from 9.0% in group 1 to 15.7% and 27.2% in groups 2 and 3 (p = 0.002). Furthermore, fluid collection volume significantly increased in the heavier weight group as well (p < 0.05). The values of mean degree of edema and volumes of fluid collections in each weight group and statistical data are presented in Table 2. Figures 2,3,4 illustrate the various degrees of edema in three patients from different weight groups.
|
|
|
|
The percentage of patients who had lumbar edema (31.0%) or fluid collections (12.3%) in the younger age group was significantly lower than that in the older age group (48.0% and 22.4%, respectively; p = 0.003 and 0.02). The degree of lumbar edema and the volume of fluid collection also increased with age (p < 0.001 and p = 0.01, respectively) (Table 3). The frequency of lumbar edema in females (46%) was significantly greater than in males (29%) (p = 0.005). The degree of edema was also more severe in females than in males. However, no correlation of sex with the frequency (p = 0.12) or volume of fluid collections was seen. The degree of soft-tissue edema and volume of fluid collections in both sexes are summarized in Table 4.
|
|
In the sacral region, 92 patients (30%) had subcutaneous soft-tissue edema, and eight patients (3%) had fluid collections. Similarly, the percentage of patients with edema and the degree of edema were associated with increasing weight (p < 0.001, and p = 0.001, respectively). The percentage of patients with a fluid collection, however, did not increase with body weight (p = 0.41) (Table 2). Both the percentage of patients with edema and the degree of edema significantly increased in the older age group (p = 0.0008, and p = 0.001, respectively). However, the frequencies of fluid collections were not significantly different between the two age groups (p = 0.98) (Table 3). A significantly greater percentage of female patients than male patients had sacral edema (p = 0.02). The degree of edema in females was also more severe than that in males (p = 0.02). However, similar to the lumbar spine, the percentage of patients with a fluid collection was not significantly different in the female or male groups (p = 0.45). No significant difference was found in fluid collection volume between male and female groups (Table 4).
In both the female and the male groups, the degree of edema increased with heavier weight, independently of age, at either the lumbar or the sacral region (all, p < 0.05).
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Cooper et al. [2] reported the manifestations of posterior lumbar edema on CT. Those authors noted that lumbar edema accumulated at the subcutaneous fascia plane. In our study, the posterior lumbar soft-tissue edema was observed in this fibrous plane and in the deep fat layer. Anatomically, trunk subcutaneous soft tissue (adipose tissue) is separated by the subcutaneous fascia into superficial and deep adipose layers [2, 4,5,6]. The subcutaneous fascia fuses medially with the deep lumbar fascia. The superficial adipose layer is contained within uniform and compact fascial septa, whereas the deep adipose layer is contained within a relatively loose, less organized, and more widely spaced fascial septum. The thickness of the deep adipose compartment is variable at the trunk and contributes significantly to total mass and overall body contour [4]. The observed accumulation of edema in the deep fat layer in heavier patients may be because this layer of fat is loosely packed and is thicker in obese patients.
Physiologically, extracellular edema has two general causes: abnormal leakage of fluid from the plasma to the interstitial spaces across the capillaries, and failure of the lymphatics to return fluid from the interstitium back into the blood [7]. Many conditions can cause fluid accumulation in the interstitium by means of increased capillary pressure, decreased plasma protein, increased capillary permeability, and blockage of lymph return [7].
In obese patients, soft-tissue edema may occur for the following reasons. First, elevated intraabdominal pressure has been shown in obese patients [8, 9]. The elevated abdominal pressure produces increased inferior vena cava pressure [10, 11] and, presumably, increased peripheral venous and capillary pressure; as a result, filtration into the interstitium increases. Increased abdominal pressure likely also impedes lymphatic drainage in the abdominal lymph channels. Because the lumbar subcutaneous lymph joins the abdominal lymphatics, they could also be affected. Second, obesity is associated with expanded circulatory volume [12], which in turn could translate to increased intravascular pressure. Third, capillary permeability to albumin increases in overweight women with swelling syndrome [13]. This mechanism may also contribute to the soft-tissue edema seen in our obese patients. Fourth, in obese patients, the cutaneous vasoconstrictive response to sympathetic activation is reduced, which may result in increased peripheral capillary blood flow and capillary permeability [14]. Fifth, obesity is associated with glomerulopathy, nephrotic syndrome [15, 16], and related hypoalbuminemia. Although we did not have direct measurements of serum albumin levels, potentially lumbar soft-tissue edema results from the low intravascular albumin and decreased colloid osmotic pressure. Sixth, slowed lymphatic drainage was found in patients who had lipedema—an entity of leg edema in obese patients [17]. However, whether this mechanism also applies to the soft tissue of the back in obese patients remains to be elucidated. Finally, in obese individuals external intermittent compression of the lymph vessel related to muscular contraction and body movement may be decreased, thereby minimizing lymph flow.
Our study showed that both the degree of the posterior lumbar soft-tissue edema and the frequency of fluid collections increased significantly in older patients. Advanced age and greater body weight were independently associated with soft-tissue edema. Other factors besides obesity likely also contributed to the edema in older patients. One practical explanation is that older patients tend to have more coexisting medical problems such as cardiac or renal dysfunction than younger patients. In these conditions, patients may be volume overloaded, and venous circulation may be impaired. In addition, the plasma protein level may also decrease because of renal insufficiency. As a result, lumbar soft-tissue edema occurs. Second, in elderly patients, physical activity is presumably less than in a young population, and lymphatic and venous return related to adjacent tissue pumping decreases. In this preliminary and retrospective study, unfortunately, these relevant data were not recorded at the time that MR imaging was performed. A study designed to collect these clinical data and to measure lean body mass and truncal obesity may in the future clarify these results.
The fact that females had a higher frequency of edema than males can probably be explained simply by their greater adipose tissue content, particularly in the loose deep trunk fat layer, provided comparison is made with males having the same body weights and heights. Male patients generally have greater lean body mass than females. This hypothesis can be tested by correlation of edema with the subcutaneous fat thickness in the posterior lumbar soft tissue, comparing female and male patients. This correlation was not accomplished, however, because the data were not collected at the time that MR imaging was performed. The compression of posterior lumbar subcutaneous fat with the patient in the supine position precluded precise measurement of the fat thickness, and in some patients the extreme posterior fat was not included in the field of view.
Posterior lumbar soft-tissue edema seen in obese patients without other abnormal findings in proximity may be explained by the patients' body habitus. However, readers should be cautious in applying these results to clinical practice. Careful scrutiny of the adjacent structures such as osseous spine, paraspinal musculature, and skin should be performed before one attributes the posterior lumbar and sacral edema only to the body habitus. In one of our female patients (body weight, 55 kg), diffuse paraspinal muscular edema coexisted with severe posterior lumbar soft-tissue edema. This edema was related to the patient's known diagnosis of polymyositis (Fig. 5).
|
We acknowledge several limitations to this study. First, the subjects were not healthy volunteers. Instead, we selected patients from an outpatient imaging center. We assume that this population is generally mobile and less likely to have debilitating conditions than inpatients. In addition, this group represents patients typically seen clinically. Second, the degree of obesity was not directly measured. Instead, weight was used as a reference for the degree of obesity. Factors such as height of the patient and fat distribution were not directly incorporated into the data analysis. In future studies, direct analysis of the relation of edema and obesity can be performed by collecting data such as height, skin fold thickness, and anthropometric measurements as well as body weight. Third, we presume the abnormal edema-like signal was edema or discrete fluid collections, on the basis of the MR imaging signal characteristics. The precise nature of this abnormal signal remains unclear. Sonographic evaluation of these areas and examination of the aspirates from the fluid collections seen on MR imaging may elucidate this issue. These evaluations were not performed in our observational study.
In summary, we conclude that lumbosacral subcutaneous soft-tissue edema is associated with increased body weight, female sex, and older age. Because body weight reflects the degree of obesity in patients with similar height, we postulate that the underlying risk factor is obesity.
Acknowledgments
We thank William Morrison for his assistance in printing the figures.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  H. Lakadamyali, N. C. Tarhan, T. Ergun, B. Cakir, and A. M. Agildere STIR Sequence for Depiction of Degenerative Changes in Posterior Stabilizing Elements in Patients with Lower Back Pain Am. J. Roentgenol., October 1, 2008; 191(4): 973 - 979. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
