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Original Report |
1 Department of Radiology, Gunma Cancer Center, 617-1 Takabayashi-nishi-cho,
Ota-shi, Gunma 373-8550, Japan.
2 Present address: Department of Radiology, Dokkyo University School of
Medicine, Koshigaya Hospital, 2-1-50, Minamikoshigaya, Koshigaya-shi, Saitama,
343-8555, Japan.
3 Department of Surgery, Gunma Cancer Center, Ota-shi, Gunma 373-8550,
Japan.
4 Department of Pathology, Gunma Cancer Center, Ota-shi, Gunma 373-8550,
Japan.
Received July 12, 2001;
accepted after revision January 22, 2002.
Supported in part by Grant-in-Aid for Cancer Research 10-25 from the
Ministry of Health and Welfare.
Abstract
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CONCLUSION. The MR imaging findings in mucinous carcinomas include dynamic curves of the gradually enhancing type and a very high signal intensity on T2-weighted images compared with other histologic types of invasive ductal carcinoma. These findings appear to be useful for diagnosis.
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Several reports have been published regarding the mammographic findings of mucinous carcinomas of the breast [1, 3, 4]. To our knowledge, little has been published on the MR imaging characteristics of these tumors. We report on the findings in eight patients with mucinous carcinoma of the breast in whom the architectural features and enhancement patterns on MR imaging were investigated.
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In making the pathologic diagnosis, we followed the standards laid down by the Japanese Breast Cancer Society in its General Rules for Clinical and Pathological Recording of Breast Cancer [5]. We identified the pathologic subtype for patients 1-5 as the pure type of mucinous carcinoma and that for patients 6-8 as a mixed type (Table 1). In patient 6, less than half of the tumor was solid tubular carcinoma, and the component of mucinous carcinoma was surrounded by that of solid tubular carcinoma. In patients 7 and 8, tumor was composed in small part of papillotubular carcinoma.
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We performed all MR imaging on a 1.5-T machine (Signa Advantage 4.8; General Electric Medical Systems, Milwaukee, WI) using a commercially available breast coil (Bilateral Breast Coil, General Electric Medical Systems). The patients lay in the prone position during the procedure. After axial localizer images of the affected breast were obtained, sagittal fat-saturated spoiled gradient-echo images (TR/TE, 60/5; flip angle, 45°; matrix, 512 x 256; thickness, 5 mm; gap, 1 mm; acquisitions, 2) were obtained. In addition, sagittal fat-saturated T2-weighted fast spin-echo images (4800/154; matrix, 512 x 256; thickness, 5 mm; gap, 1 mm; acquisitions, 2) were obtained. On the basis of the findings in the unenhanced images, four contiguous sagittal sections of 5-mm thickness were selected for dynamic MR imaging with spoiled gradient-recalled echo imaging (84.5/4.2; flip angle, 60°; thickness, 5 mm; matrix, 256 x 192; acquisition, 1). Gadopentetate dimeglumine (Magnevist; Schering, Berlin, Germany) was administered IV as a bolus injection at a dose of 0.1 mmol/kg body weight over 10 sec, followed by flushing with 20 mL of saline via an extension tube.
Serial dynamic MR images were obtained before injection of the contrast agent and at 30, 60, and 90 sec after the start of injection. In two patients, dynamic images were obtained up to 3 min after the start of the injection. Thereafter, sagittal fat-saturated fast multiplanar spoiled gradient-recalled echo images of the entire affected breast were obtained (434/4.2; flip angle, 60°; matrix, 256 x 192; thickness, 4 or 5 mm; gap, 1 mm; acquisition, 1). The field of view was 26 cm in all sequences.
Interpretation of the MR imaging findings was based on the evaluation of the internal signal intensity, internal structure, and border characteristics of the breast mass by four radiologists working in consensus. Time-signal intensity curves on the serial dynamic images were also obtained. The contrast enhancement ratio at each time point was calculated from the signal intensity in the regions of interest established at the same positions in all tumors. A time-signal intensity curve was drawn by plotting the time along the horizontal axis and the contrast enhancement ratio along the vertical axis. Contrast enhancement ratio was calculated using the following equation: Contrast enhancement ratio (%) = [(signal intensity after contrast enhancement - signal intensity before contrast enhancement) / signal intensity before contrast enhancement] x 100.
To investigate the similarities and differences between mucinous carcinomas and other histologic types of breast carcinoma, we visually evaluated the signal intensity of the tumor on fat-saturated T2-weighted fast spin-echo MR images obtained during the same period in 121 patients having breast cancer of different histologic types. Visual evaluation determined whether the signal intensity of the tumor was lower than, equivalent to, or higher than that of the surrounding mammary gland tissues and whether the signal was stronger and almost the same as water (very high).
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Figure 1 shows the time-signal intensity curve for the seven of eight patients in our study who underwent dynamic MR imaging. Dynamic study was not performed in patient 7. In patients 1-4, the contrast enhancement ratio after 60 sec was less than 100%, and slow contrast development was observed (Kuhl's type I) [6]. In patients 5 and 8, the curve plateaued after the initial upstroke (Kuhl's type II). In one patient with the mixed type of the tumor (patient 6), areas of mucinous carcinoma exhibited a flat pattern (Kuhl's type II), and areas not affected by the mucinous carcinoma showed a washout time curve (Kuhl's type III).
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Figure 2A,2B,2C,2D,2E,2F shows the MR images and pathologic findings for patient 2. The tumor extended from the upper left outer quadrant. It was lobular with irregular borders. On the T1-weighted images (Fig. 2A), the signal intensity in the tumor was the same as that of the normal mammary gland, but signal intensity was markedly higher on the T2-weighted images (Fig. 2B). On dynamic MR imaging, peripheral tumor enhancement was noted early, and the tumor interior came to be visualized with the passage of time (Figs. 2C,2D,2E). At histopathologic examination, tumor cells appeared to be floating in the mucin substrate (Fig. 2F), and mucinous carcinoma of the pure type was diagnosed.
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Figure 3A,3B,3C,3D,3E shows MR images of patient 6. The tumor was confined within the upper right outer quadrant, and the longest diameter was 45 mm. In T2-weighted images, a low-signal region was observed around a core of high intensity (Fig. 3B). The high-signal region represented mucinous carcinoma of the pure type, whereas the low-signal region represented solid-tubular carcinoma. On dynamic MR imaging, the areas of mucinous carcinoma showed a flat pattern. The areas not affected by mucinous carcinoma, on the other hand, exhibited a washout time course (Figs. 1 and 3C,3D,3E).
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Visual Evaluation of Signal Intensity in T2-Weighted Images
We visually evaluated the signal intensity in each tumor on fat-saturated
T2-weighted images in 121 patients with other histologic types of breast
carcinoma. The histologic types we identified included invasive ductal
carcinoma (n = 115), medullary carcinoma (n = 1), and
lobular carcinoma (n = 5). Although all eight tumors of mucinous
carcinoma showed very high signal intensity on T2-weighted images, very high
signal intensity was noted in the tumors of only two patients with invasive
ductal carcinoma. In both patients, marked degenerative necrosis was observed
inside the tumor at histopathologic examination, which was thought to
correlate with the very high signal intensity on T2-weighted images.
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Consistent with our results, other reports indicate that the time—signal intensity curves obtained from dynamic contrast-enhanced MR imaging of mucinous carcinomas exhibit a gradually enhancing pattern [9, 10]. One reason for the observation of a gradually enhancing pattern in the time—signal intensity curves in mucinous carcinomas is the presence of a large amount of mucus in the tumors: diffusion of the contrast medium through the entire tumor takes time [10]. According to one report, contrast patterns were not observed at all in mucinous carcinomas having little vascularity [11]. On the other hand, gradually enhancing contrast patterns on dynamic contrast-enhanced MR imaging have also been reported in breast cancers of other histologic types [10]. Breast carcinoma with a large fibrous component and tumors rich in intraductal components are believed to exhibit a gradually enhancing contrasting pattern [10].
In our study of mucinous carcinomas of the mammary gland, the signal intensity on T1-weighted images varied from low intensity to high intensity. Mucin, in particular, is believed to affect signal intensity on T1-weighted images because of its protein content, and mucin-containing tumors in other organs, such as mucin-producing ovarian tumors, also exhibit diverse signal intensities on T1-weighted images, depending on the differences in the protein concentrations in the tumors.
Mucinous carcinoma is generally believed to exhibit high signal intensity on T2-weighted images because of its large mucin component. In all patients examined in our study, mucinous carcinoma showed a very high signal intensity on the T2-weighted images. In patient 6, the solid tubular carcinoma part of the tumor showed low signal intensity, whereas the mucinous carcinoma part exhibited very high signal intensity. Patients 7 and 8 were diagnosed as having a mixed type of mucinous carcinoma; however, the signal on the T2-weighted images showed very high intensity—the same as was seen in the tumor of pure type. In these two patients, the component of papillotubular carcinoma was slight, and it was thought not to affect signal intensity. Entities exhibiting high signal intensity on T2-weighted images include cysts, such as simple cysts, intracystic carcinoma, and intracystic papilloma; tumors containing mucus, such as mucinous carcinoma and mucocele; and lesions with large moisture content, such as necrosis, edema, and abscess. Kuwabara [12] suggested that low intensity is never noted in the tumor on T2-weighted images when there is a cyst, abscess, mucinous carcinoma, phyllodes tumor, or medullary carcinoma, and this finding may be useful for the diagnosis by exclusion. Our evaluation of the signal intensity of 115 other mammary gland tumors on T2-weighted images revealed that only two invasive ductal carcinomas exhibited very high intensity, which was associated with severe degenerative necrosis.
In conclusion, we found that mucinous carcinomas of the mammary gland are seen as lobular tumors on MR imaging. Their dynamic time—signal intensity curves exhibit the gradually enhancing type of contrast pattern or plateau pattern after initial upstroke. These tumors show very high signal intensity (the same as water) on T2-weighted images. We believe that these findings are useful for the diagnosis of mucinous carcinoma.
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