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Genitourinary Imaging |
1 Departments of Radiology (S.P., P.M.T.P., C.S.P.v.R.)
2 Gynecology (J.B.T.), Leiden University Medical Center, the Netherlands.
| Abstract |
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MATERIALS AND METHODS: Dynamic contrast-enhanced MR imaging of cervical carcinoma was performed in 82 consecutive patients with stage I or IIA disease who were referred for radical hysterectomy. The maximum slope and amplitude of dynamic first-pass contrast enhancement were quantified. These parameters were correlated with histologic measures of tumor aggressiveness (tumor invasion depth, pelvic lymph node status).
RESULTS: The analysis was based on tumors in 62 patients: 30 aggressive and 32 relatively nonaggressive tumors. Twenty patients were excluded from analysis owing to insufficient surgical data, tumor too small for accurate assessment, or technical problems. There were no significant differences between aggressive and nonaggressive tumors in terms of the first-pass contrast-enhancement parameters of slope (2.0 vs 2.1 arbitrary signal intensity units per second, P > .5) or amplitude (24.8 vs 27.8 arbitrary units, P > .2).
CONCLUSION: Dynamic contrast-enhanced MR imaging does not facilitate differentiation between aggressive and nonaggressive tumors and therefore has no clinical role in assisting in treatment decisions in patients who are candidates for radical hysterectomy.
Index terms: Magnetic resonance (MR), treatment planning, 854.32, 854.33 Uterine neoplasms, 854.32 Uterine neoplasms, metastases, 992.33 Uterus, MR, 854.121412, 854.12143
| Introduction |
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It has recently been reported that MR imaging contrast agents and dynamic MR imaging may play roles in this respect. Hawighorst et al (7) observed that the tumors associated with a more pronounced degree of tumor angiogenesis have a markedly shorter exchange rate constant; that is, such tumors show more rapid first-pass contrast agent enhancement at dynamic MR imaging. Because tumor angiogenesis has been implicated as a predictor for tumor recurrence (8), fast and/or intense first-pass contrast enhancement of a tumor would correspond to more aggressive behavior (7,9). In theory, dynamic MR imaging could be used for the preoperative identification of aggressive tumor types, which could then be treated with primary radiation therapy. Dynamic MR imaging could thus help prevent unnecessary surgery in patients who, on the basis of conventional International Federation of Gynecology and Obstetrics (FIGO) staging criteria, would undergo surgery. The purpose of this study was to validate this hypothesis.
We undertook a study to determine whether such use of dynamic MR imaging would be feasible in clinical practice. We assessed whether, in the group of patients who were eligible for primary surgical treatment, contrast-enhanced dynamic MR imaging could be used for reliable determination of which patients had more aggressive cervical carcinomas, that is, tumors that, according to generally accepted criteria, should be treated with radiation therapy.
| MATERIALS AND METHODS |
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15 mm or <15 mm), the presence of pelvic metastatic lymph node involvement, or both. These two criteria are generally accepted as indicative of the risk for tumor recurrence (5,6). The analysts of the histopathologic material were blinded to the MR imaging data. We then analyzed whether dynamic contrast-enhanced MR imaging could help distinguish, before surgery, patients at high risk on the basis of the quantification of first-pass contrast enhancement. The MR imaging results did not play a role in the decision about the type of treatment. The study was approved by the ethical review board of our institution, and informed consent was obtained from all patients.
Patients
The study group comprised 82 consecutive patients aged 2885 years (mean age, 47.9 years) who were referred to the gynecology department at our hospital from February 1995 to July 1997 with histologically proved invasive cervical carcinoma, and who, on the basis of clinical FIGO staging, were to undergo surgical treatment (clinical stages IA, IB, IIA).
MR Imaging Protocol
MR imaging was performed with a 1.5-T system (Gyroscan NT-15; Philips Medical Systems, Best, the Netherlands) equipped with a body coil. For dynamic MR imaging, two contiguous, transverse, 7-mm-thick sections were obtained through the cervical tumor, with a temporal resolution of one image every two seconds. A T1-weighted fast gradient-recalled-echo sequence was used (15/7 [repetition time msec/echo time msec]; flip angle, 40°; one signal acquired; matrix size, 256 x 128; field of view, 45 cm). A bolus of 0.1 mmol of gadopentetate dimeglumine (Magnevist; Berlex-Schering, Berlin, Germany) per kilogram of body weight was manually injected; a flush with saline solution was delivered after the fourth gradient-recalled-echo sequence. The contrast-enhanced dynamic images were subtracted from the third unenhanced dynamic image (in which the spins had reached equilibrium saturation after having been exposed to the repetitive
pulses in the gradient-recalled-echo sequence). The imaging protocol included acquisition of T2-weighted fast spin-echo images in the transverse and sagittal planes (2,500/120 [effective echo time]; echo train length, 18; matrix, 256 x 256; field of view, 22 cm; no fat suppression; eight signals acquired).
Quantification of First-Pass Contrast Enhancement
By using the morphologic information provided by the T2-weighted images, regions of interest were drawn on the unenhanced dynamic MR images inside the cervical carcinoma and skeletal muscle (gluteal muscles). The timesignal intensity curves in the regions of interest were computed and were displayed graphically. All curves had a fast, approximately linear rise followed by a second phase of a plateau without substantial washout (Figure). We used automated computer software to record the following parameters at the quantification of the first-pass curves: (a) maximum slope of contrast enhancement (a linear fit on the signal intensity curve derived from four subsequent images was used to reduce the influence of random noise; the linear fit was based on the least-squares analysis method) and (b) amplitude of contrast enhancement (the maximum signal intensity reached in the subtracted image). The maximum slope and the amplitude were expressed in arbitrary signal intensity units per second and arbitrary signal intensity units, respectively. To eliminate variations due to differences in contrast agent injection velocity, heart rate, and cardiac output, we constructed an additional data set in which the values of the maximum slope and the amplitude were scaled to the corresponding values derived from normal skeletal muscle. This was accomplished by dividing the slope and amplitude values of the cervical carcinoma by the corresponding values of normal skeletal muscle in the same patient. All measurements were made by an observer (C.S.P.v.R.) who was unaware of the surgical-histopathologic findings.
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15 mm) and the presence of lymph node metastases, we formed two subgroups: relatively nonaggressive tumors (tumor invasion depth < 15 mm, no lymph node metastases) and aggressive tumors (tumor invasion depth
15 mm, presence of lymph node metastases, or both). For each tumor, we recorded maximum slope and amplitude for the absolute tumor signal intensity values and for the relative tumor values (ie, scaled to normal skeletal muscle). We used two-tailed unpaired Student t tests to test for significant differences between the two subgroups, with a P value of .05 or less indicative of such differences. | RESULTS |
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Twenty patients were excluded from the analyses (Table 2). Although MR imaging was performed in all 82 patients, dynamic contrast-enhanced MR imaging was not completed in three due to technical problems. In the 12 patients with stage IA disease, no tumor could be visualized on the T2-weighted MR images. The five patients in whom tumor aggressiveness could not be assessed because of insufficient data were also excluded from the analysis. Overall, a correlation between dynamic MR imaging results and tumor aggressiveness could be established in 62 patients, including 32 with nonaggressive tumors and 30 with aggressive tumors (Table 1).
The first-pass dynamic contrast-enhancement parameters in these 62 patients are summarized in Table 3. Faster and more intense first-pass contrast-enhancement was seen in tumor than in skeletal muscle in all 62 patients (Figure). There was a significant difference between the absolute slope and amplitude mean values for tumor and skeletal muscle (slope, 2.1 arbitrary units per second ± 0.8 vs 0.4 units per second ± 0.2, P << .001; amplitude, 26.4 units ± 9.3 vs 4.2 units ± 2.2, P << .001). We found no differences between aggressive and nonaggressive tumors in terms of absolute maximum slope (2.0 units per second ± 0.7 vs 2.1 units per second ± 0.9, P > .5) or amplitude (24.8 units ± 7.7 vs 27.8 units ± 10.5, P > .2) or in terms of relative values scaled to skeletal muscle (slope, 6.0 units per second ± 3.6 vs 5.5 units per second ± 3.6, P > .5; amplitude, 9.8 units ± 9.3 vs 7.6 units ± 6.9, P > .5). Dynamic MR images, therefore, reliably showed the difference between tumor tissue and muscle but did not allow differentiation between aggressive and nonaggressive tumors in our patient group.
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| DISCUSSION |
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Our results, however, showed no such relationship between biologic aggressiveness of cervical carcinoma and dynamic parameters of contrast-enhanced MR imaging. The dynamic parameters of slope and amplitude did not correlate with the histologic parameters of tumor invasion depth or presence of pelvic lymph node metastases, both of which are strong predictors of tumor recurrence and survival in patients with cancer of the uterine cervix and are established predictors of tumor aggressiveness (5,6,12,13). This corroborates the findings of Wiggins et al (11), who, in a histologic study with 29 patients, found no correlation between microvessel count (a measure of tumor angiogenesis) and nodal status, parametrial involvement, or depth of invasion.
One possible explanation for this apparent discrepancy may be related to insufficient accuracy of the MR imaging method used for reflecting the extent of angiogenesis. As is apparent from the Figure, however, there was a significant difference in slope and amplitude values between tumor and muscle, which indicates that our MR imaging method was, in fact, sensitive enough to demonstrate angiogenesis. One cannot exclude the theoretic possibility, however, that our MR imaging method could not accurately demonstrate true differences in angiogenesis between the various cases of cervical carcinoma. Hawighorst et al (7) have shown such accuracy for MR imaging. The patient population in the study by Hawighorst et al was less homogeneous than the population in our study, however, because there was a larger proportion of patients with more advanced disease (71% had a FIGO stage IIBIVA tumor).
It is possible that the association between angiogenesis and dynamic contrast-enhancement MR imaging findings is not simple but rather is complex. Angiogenesis, on the one hand, may be defined as the division rate of vascular cells or the spatial density of capillaries. Timesignal intensity curves measured with MR images, on the other hand, represent an interaction between specific blood flow, heterogeneity of flow, diffusion constants in the assessed tissues, spatial variability of these constants, and volumes of distribution of the enhancing agent. A more in-depth review of this topic has been provided by Verstraete et al (10).
Another tentative explanation might be that the hypothesis of a correlation between angiogenesis and the risk of tumor recurrence does not hold true, at least not in the individual patient who is generally considered for radical surgical resection. Dinh et al (8) indeed found a correlation between angiogenesis and recurrence, but on closer inspection, the reported significance of this correlation may be due to the presence of a single outlier; in addition, their study may lack statistical power because of the small number of subjects (n = 22). These observations cast doubt on the purported correlation between angiogenesis and recurrence.
Our conclusion, therefore, is that although dynamic contrast-enhanced MR imaging results reflect the degree of angiogenesis, they cannot be used to determine clinical treatment in the individual patient. In patients who are candidates for radical hysterectomy, one cannot use the dynamic parameters of contrast-enhancement slope and amplitude as tools to help predict tumor aggressiveness in cases of cervical carcinoma.
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Address reprint requests to S.P., Cardington House, Sunning Ave, Sunningdale, Berkshire, SL5 9PW England.
Abbreviation: FIGO = International Federation of Gynecology and Obstetrics
Author contributions: Guarantor of integrity of entire study, S.P.; study concepts, S.P., P.M.T.P.; study design, S.P., P.M.T.P., J.B.T.; definition of intellectual content, S.P.; literature research, S.P., C.S.P.v.R.; clinical studies, J.B.T.; data acquisition, C.S.P.v.R., J.B.T., S.P., P.M.T.P.; data analysis, S.P., P.M.T.P.; statistical analysis, S.P., P.M.T.P.; manuscript preparation, S.P., P.M.T.P.; manuscript editing, C.S.P.v.R., S.P., P.M.T.P.; manuscript review, S.P., P.M.T.P., J.B.T.
Received April 7, 1998;
revision requested May 19, 1998; revision received June 12, 1998;
accepted August 10, 1998.
| References |
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