Breast MRI

Indications and technical features

Contrast-enhanced MRI does not replace routine methods (ultrasound, mammography), but complements them due to its exceptionally high sensitivity.

Main indications:

• Local staging: determination of exact tumor dimensions, detection of multifocal disease (especially important in invasive lobular carcinoma, which is often occult on mammography).
• Screening: for women with a high genetic risk (e.g., BRCA mutations) or those who underwent mantle-field radiotherapy at a young age.
• NAC monitoring: the gold standard for assessing tumor response to neoadjuvant chemotherapy to plan breast-conserving surgery.

The procedure requires a scanner with a magnetic field strength of at least 1.5 Tesla. The patient is placed in the prone position, with the breasts positioned in a dedicated phased-array coil. A critical scanning requirement is fat suppression (using subtraction methods or spectrally selective pulses) so that bright fat on T1-weighted images does not obscure the contrast-enhancing tumor.

Evaluation of lesions: morphology and kinetics

Image interpretation is based on two pillars: how the lesion looks and how it is vascularized.

1. Contrast enhancement kinetics. A gadolinium-based contrast agent is administered (0.1 mmol/kg). Malignant tumors, possessing an abnormal vascular network, rapidly enhance within the first 2 minutes, followed by a washout or plateau phase. Benign tissues are characterized by slow and persistent contrast accumulation.
2. Morphology. Cancer often presents with irregular margins, spiculation, and causes parenchymal distortion.

Descriptions are standardized using the BI-RADS lexicon, which divides findings into three categories:

• Focus (Focus) — a tiny punctate spot measuring up to 5 mm.
• Mass (Mass) — a three-dimensional space-occupying lesion measuring greater than 5 mm.
• Non-mass enhancement (Non-mass enhancement) — an area of enhancement without a corresponding mass effect (often seen in ductal carcinoma in situ and lobular carcinoma).

Additional sequences: DWI and spectroscopy

To improve MRI specificity, non-contrast techniques reflecting tissue microstructure and metabolism are used.

• Diffusion-weighted imaging (DWI) evaluates the random motion of water molecules. Due to high cellularity in cancerous tumors, diffusion is restricted, manifesting as a decrease in the apparent diffusion coefficient (ADC typically <1.5 × 10⁻³ mm²/s).
• MR spectroscopy detects metabolic markers. The presence of a prominent choline peak indicates active cell membrane synthesis, which is typical for rapidly dividing malignant cells.

Changes in these parameters (increase in ADC and drop of the choline peak) occur before the tumor decreases in size, making them excellent early biomarkers of chemotherapy response.

Controversial issues and overdiagnosis

Despite high sensitivity, routine preoperative MRI staging remains a subject of debate. Clinical trials (e.g., COMICE and MONET) have not confirmed that MRI reduces re-cision rates or improves long-term outcomes.

Due to lower specificity (81–97%), MRI frequently identifies false-positive lesions, leading to the risk of unnecessary mastectomies. Golden rule: surgical management should not be altered until new lesions are histologically confirmed. Targeted second-look ultrasound (second-look ultrasound) is often used for biopsy navigation.

Breast implant MRI

MRI outperforms ultrasound and mammography in assessing implant integrity (sensitivity and specificity > 90%). The procedure is performed without contrast.

The primary objective is to detect filler leakage. In intracapsular rupture, silicone leaks from the implant shell but is contained by the fibrous capsule. On T2-weighted images, this yields characteristic signs: the "wave line" or "linguine" (linguini), "keyhole" (key-hole), and "salad oil" (salad oil sign) signs. Extracapsular rupture, in which silicone extends into tissues or lymph nodes, is also successfully diagnosed, although ultrasound is often sufficient in such cases.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Management tactics for patients with MRI findings: the role of second-look ultrasound and biopsy.
• Features of detecting lobular carcinoma on MRI compared to routine methods.
• Criteria for intracapsular breast implant ruptures: linguine and keyhole signs.
• Application of nuclear medicine methods (PET, scintimammography) in diagnostic breast imaging.

Other topics in the "Diagnostic Radiology in Oncology" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.