Pearls and pitfalls in breast MRI

Abstract

At our academic institution, we have noticed repeated examples of both false-positive and false-negative MR diagnoses in breast cancer. The most common diagnostic errors in interpreting MRI of the breast are discussed in this review and experience-based advice is provided to avoid similar mistakes. The most common reasons for false-positive diagnoses are misinterpretation of artefacts, confusion between normal enhancing structures and tumours and, above all, insufficient use of the American College of Radiology breast imaging reporting and data system lexicon, whereas false-negative diagnoses are made as a result of missed tiny enhancement, a background-enhancing breast, or enhancement interpreted as benign rather than malignant.

Figure 1

Pseudo-enhancement due to a subtraction artefact. (a) At level “a”, a pseudo-enhancement is seen on the subtraction image due to subtraction between a mass in hypersignal on the (b) axial fat-saturated T₁ weighted image after contrast and the fat in hyposignal on the (c) axial fat-saturated T₁ weighted image before contrast. (d) At level “b”, 6 mm lower, the feature is inverted with a hyposignal on the subtraction image due to subtraction between fat in hyposignal on the (e) axial fat-saturated T₁ weighted image after contrast and the mass in hypersignal on the (f) axial fat-saturated T₁ weighted image before contrast. Pseudo-enhancement of the mass is due to its movement in a coronal plane between sequences before and after intravenous contrast.

Figure 2

Normal enhancing breast structures. (a) On the subtracted axial image of the left breast, four enhancing structures are seen: two are linear and two are nodular. (b) On the T₂ weighted image, the two nodules have a location within fat and a hypersignal highly suggestive of lymph nodes, and the two linear structures are suggestive of vessels with one in hypersignal (arrow) and the other in hyposignal (double arrows) because of a difference in velocities.

Figure 3

Invasive breast cancer with morphological findings better seen on native images. (a) On the subtracted axial slice, the outline of the enhancement is hardly analysable. (b) On the T₂ weighted image, the stellar outline of the mass is obvious.

Figure 4

Rim of enhancement around a fat necrosis. (a) Axial subtracted image from the dynamic T₁ weighted series: non-mass enhancement corresponding to an invasive breast cancer. 1 year after conservative treatment, (b) subtracted and (c) T₂ weighted axial images. A rim enhancement is seen around the fat necrosis. Note also that the retraction of skin is clearly seen on the T₂ weighted sequence.

Figure 5

Hypersignal on a T₂ weighted sequence in invasive ductal carcinoma. (a) Axial T₂ weighted image showing a circumscribed tumour with a central region of high signal intensity. (b) Axial subtraction image showing thick and irregular enhancement surrounding a hypointense area corresponding to necrosis within the tumour.

Figure 6

Thick enhanced rim around a cyst. (a) Axial subtraction image showing a thick and regular enhanced rim around a hyposignal area. (b) On the axial T₂ weighted image and (c) on the axial fat-saturated T₁ weighted image, the non-enhanced area has a high signal intensity suggesting a cyst, which was confirmed by ultrasound.

Figure 7

Regional non-mass-like enhancement in fibrocystic change of the breast. (a) Axial subtraction shows a non-mass enhancement on the outer part of the right breast. (b) Axial T₂ weighted image showing numerous cysts within the enhanced area. Note also cysts in the inner part of the breast close to the pectoralis muscle.

Figure 8

Clinically palpable breast cancer in the left axillary area with no enhancement on MRI. (a) Axial subtraction image does not show any enhanced mass in the axillary area. (b) Axial T₂ weighted image clearly shows a high signal intensity mass with irregular margins, corresponding to the palpable breast cancer (arrow). (c) On CT examination performed for breast cancer staging, the mass is paradoxically enhanced and clearly seen in the outer part of the breast (arrow).

Figure 9

True linear enhancement due to a ductal carcinoma in situ (DCIS) close to a pseudo-enhancement due to an artefact. (a) Axial subtraction showing two enhancements: a rim enhancement (arrow) and a linear enhancement (double arrows). Note a dark nodule behind the rim enhancement suggestive of an artefact (arrowhead). The comparison between axial native T₁ weighted images (b) before and (c) after contrast showing that only the linear enhancement is true, the nodule in hyposignal is not truly enhanced and the pseudo-enhancement is due to a subtraction artefact. Biopsy of the linear enhancement under MRI guidance showed a DCIS.

Figure 10

Missed breast cancer in a female with risk factors. (a) Axial subtraction showing an enhanced mass (arrow) close to a vessel (arrowhead). (b) The hypointense mass is clearly seen (arrow) on the axial T₂ weighted image. However, this mass was missed. 1 year later, the mass had grown and was well individualised on both (c) axial subtraction and (d) axial T₂ weighted images.

Figure 11

Breast cancer with non-enhancing septa. Axial subtraction showing an enhanced mass with non-enhancing septa. Note that the mass margins are irregular. The mass was biopsied under ultrasound guidance with a diagnosis of invasive breast cancer.