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Case Report |
Department of Radiology, Stanford University Medical Center, 875 Blake Wilbur Dr., Stanford, CA 94305-5826.
Received April 9, 2004;
accepted after revision May 4, 2004.
Address correspondence to D.M. Ikeda
(dikeda{at}stanford.edu).
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To stage the known cancer, we performed contrast-enhanced MRI on a 1.5-T scanner (Signa, GE Healthcare) as previously described [2], including a T1-weighted axial sequence (TR/TE, 300/16) with a 5-mm thickness to evaluate for adenopathy. A comprehensive diagnostic breast MRI examination [3] was performed, beginning with a dynamic scanning sequence consisting of rapid 3D volume spiral MRI during administration of an IV gado-pentetate dimeglumine (Magnevist, Berlex Laboratories) bolus at a dose of 0.1 mmol/kg to characterize initial contrast enhancement, followed by a contrast-enhanced high-resolution 3D acquisition (3D acquisition, spectral-spatial radiofrequency pulses, on-resonance magnetization transfer) to characterize the lesion morphology on thin sections [2]. Finally, a second dynamic spiral sequence was used to record contrast washout from abnormally enhancing lesions.
On contrast-enhanced MRI, the known invasive lobular cancer appeared irregular in shape in the lower breast with a rapid initial enhancement and a late plateau. MRI also revealed an 8-mm oval smooth upper breast mass near a blood vessel with rapid initial enhancement and late washout on the dynamic scans, possibly representing a lymph node. Because MRI did not conclusively show a fatty hilum, the resulting differential diagnosis was a second carcinoma [4]. When correlated to the diagnostic mammogram, this finding was thought to correspond to the lymph node seen on the diagnostic mammogram and sonogram. It was thought that the mass found on MRI was a lymph node because it correlated in size, location, and surrounding tissue with the mammography and sonography. However, an absolute correlation was requested because invasive lobular cancer had been diagnosed in the lower breast, and invasive lobular cancer is more difficult to diagnose on MRI than invasive ductal cancer.
To correlate the sonography and MRI findings, we placed the patient prone in a vertically open 0.5-T MRI scanner (Signa-FP, GE Healthcare) and positioned in a dedicated open breast coil. Using methods previously described for MRI-guided preoperative freehand needle localization [5], areas of architecture on the axial T1-weighted fast spin-echo images were used to show the location of the upper breast mass and were correlated directly to the previous diagnostic axial T1-weighted and reformatted contrast-enhanced images (Fig. 1B). While the patient remained in the coil, a fiducial marker was placed on the skin at the location that would have been selected for needle placement had the mass been targeted for biopsy (Fig. 2A). A repeat unenhanced axial T1-weighted fast spin-echo image confirmed the location of the fiducial marker relative to the expected location of the mass (Fig. 1C).
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With the patient remaining motionless and prone in the breast coil, the patient, table, and coil were moved together out of the magnet room into an anteroom. The location of the fiducial marker was noted, marked on the skin with ink, and removed (Figs. 2A and 2B). A sonography scanner was brought in, and a 7.5-MHz linear array transducer was placed through the open breast coil to scan directly over the marked location in the axial plane (Fig. 2C). The breast was stabilized by a hand placed on its medial side, directly opposite the transducer as needed. Sonography showed a normal intramammary lymph node, with a hypoechoic cortex and an echogenic fatty hilum. The lymph node was at the expected depth and was the same size as the MRI-detected finding, and was at the border of fat and strands of glandular tissue as seen on MRI. It was adjacent to a blood vessel, also seen on the MR image and mammogram, showing that the sonographic, MRI, and mammographic findings were the same, excluding the presence of a second cancer.
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Excisional biopsy of the invasive lobular cancer and an axillary sentinel lymph node dissection were performed. Six months later, follow-up mammography and sonography again showed the lymph node in the upper breast. No other masses were identified.
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Non-MRI-guided sonography has been shown to have a low (23%) rate of
detecting MRI-identified lesions. In addition, the frequency of cancer
diagnosis after biopsy is significantly higher in lesions visible on MRI and
sonography than on MRI alone (43% vs 14%)
[6], highlighting the need for
accurate MRI-guided sonography when correlation of MRI and sonographic
findings is unclear.
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In our facility, MRI-guided preoperative needle localization of suspicious findings is always followed by preoperative craniocaudal and mediolateral mammograms that are marked for the surgeon. This is especially important for MRI findings thought to correlate to mammographic or sonographic findings, because the post-MRI-localization mammogram or sonogram occasionally yields unexpected results. In rare cases, the sonographic or mammographic finding does not correlate to findings at the tip of the wire deployed under MRI guidance, and a second needle or hookwire must be placed into the sonographic or mammographic finding by conventional methods. A more worrisome scenario would arise if an MRI finding was mistakenly thought to correlate to a sonographic finding and was excised after a songraphically guided preoperative needle localization, leaving the MRI-detected finding in the breast. Our technique of direct correlation of MRI and sonography by scanning through the open coil prevents such occurrences. However, this technique does not eliminate the need for MRI-guided biopsy, because some MRI-detected lesions may not be detected on sonography.
Another way to correlate mammographic, sonographic, and MRI findings before excisional biopsy would be to localize the sonographic or mammographic finding with an MRI-compatible wire and to perform contrast-enhanced breast MRI after localization. The problem with this scenario is in scheduling the postlocalization MRI to include enough time and personnel for an add-on MRI-guided preoperative needle localization if the conventionally localized findings do not correlate to the suspicious abnormally enhancing lesion(s).
Our technique is an improvement of that described by Obdeijn et al. [7], in which sonography was performed after an abnormal MRI finding. Our technique performs both examinations without changing the orientation of the breast within the breast coil, allowing direct correlation of the findings.
A technique to correlate mammographic and sonographic findings was described by Meyer et al. [8]. They placed a suspect lesion in the aperture of a fenestrated mammographic compression plate used for preoperative needle localization and performed sonography though the aperture at a location shown on the mammogram. Piron et al. [1] are developing an analogous technique for use in correlating imaging techniques during tissue biopsy, because some fenestrated compression plates designed for MRI-guided preoperative needle localization or percutaneous biopsy have apertures wide enough to accommodate the ultrasound transducer.
In contrast to that described by Piron et al. [1], our technique does not use a fenestrated compression plate to hold the breast but instead scans the uncompressed breast through the open MRI breast coil. The advantages of this method are that no new equipment or materials are needed and that the lesions that might be blocked by the fenestrated plate are more easily accessed. A limitation shared by both methods is the inability to visualize lesions high in the axilla or close to the chest wall because the breast coil housing blocks access to these portions of the breast. The ultrasound beam might access some of these difficult lesions by the operator's angling of the transducer around the breast coil housing toward the lesion. A second limitation is evaluation of lesions near the nipple, where transducer contact may be limited by the small amount of breast tissue located anteriorly.
In summary, we have described an in vivo technique for correlating sonographic and MRI findings when results of traditional visualization techniques are uncertain. The need for this technique may be rare and performing sonographic scanning through the MRI coil is costly because of use of magnet time. However, when the correlation of the findings of MRI and other imaging techniques are uncertain, direct correlation is less invasive and less costly than performing a biopsy when the mass is benign, as in this case. When the mass is malignant, this technique may help avoid miscorrelation of MRI and sonographic findings.
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