Radiology

Breast MRI Findings: Post-Surgical Findings

by Josh Arnold, MD and Anne Hoyt, MD

Introduction

The detection of breast cancer recurrence following surgery may be challenging from both a clinical and imaging standpoint; breast MRI plays an increasing role in these cases. Most commonly, MRI is performed following breast conservation therapy (BCT). It is important to recognize expected MRI findings following lumpectomy and radiation, as well as suspicious findings which may prompt biopsy.

In some cases, MRI may be performed following mastectomy. Knowledge of the normal post-surgical appearance of mastectomy and various types of reconstruction is key in recognizing recurrent disease.

Imaging Following Breast Conservation Therapy

Post-Surgical Scar

Architectural distortion at the lumpectomy site is an expected finding, and represents a benign (BI-RADS 2) post-surgical scar (Figure 1). Surgical clips will appear as foci of metallic susceptibility artifact.

Breast MRI Findings: Post-surgical Findings
FIGURE 1: T1-weighted image without fat saturation. A post-surgical scar is seen in the left breast. T1 hypointense scar extends to the skin surface. Multiple foci of susceptibility artifact are seen secondary to surgical clips.

Seroma

A fluid- or blood-filled cavity following lumpectomy is a normal finding. Seromas are typically T2 hyperintense with smooth, thin rim enhancement (Figure 2a).1 Nodular enhancement greater than 5mm is concerning for residual disease (Figure 2b). A seroma with typical imaging features is a benign finding (BI-RADS 2).

Breast MRI Findings: Post-surgical Findings Seroma
FIGURE 2A: T2-weighted image with fat saturation image. A T2 hyperintense structure is seen in the medial right breast at the site of a lumpectomy. This represents a post-surgical seroma. FIGURE 2B: T1-weighted post contrast image with fat saturation. The seroma cavity demonstrates thin rim-enhancement, a normal finding.

Fat Necrosis

Fat necrosis has a variable imaging appearance, with many cases requiring follow-up imaging (BI-RADS 3) or biopsy (BI-RADS 4).2 Internal fat signal intensity is a classic imaging feature (Figure 3a). Enhancement is variable and may be rim, focal, or diffuse (Figure 3b).3 Calcifications may be seen as signal voids. Correlation with mammography is helpful in identifying central fat density as well as the typical calcifications seen in fat necrosis.

Breast MRI Findings: Post-surgical Findings Fat Necrosis
FIGURE 3A: T1-weighted image without fat saturation. Status-post lumpectomy with fat signal intensity within the surgical scar. FIGURE 3B: T1-weighted post contrast image with fat saturation. Enhancement at the margins of presumed fat necrosis. This enhancement was followed and remained stable.

Non-mass Enhancement

Minimal non-mass enhancement (NME) adjacent to the lumpectomy site can be a normal finding up to 18 months following surgery4. A small enhancing focus or minimal linear NME may be appropriate for 6-month imaging follow-up (BI-RADS 3).

Other than the above, NME within or adjacent to the lumpectomy site is generally suspicious (BI-RADS 4). This includes new or increasing NME, nodular NME measuring greater than 5 mm, mass like enhancement, and NME in suspicious distributions such as segmental, clumped, or regional (Figure 4a and 4b)5. Enhancement kinetics are an important component of the evaluation of NME. Rapid initial enhancement and washout are most concerning for malignancy.

Breast MRI Findings: Post-surgical Findings NME
FIGURE 4A: T1-weighted image without fat saturation. Status-post remote lumpectomy of the left breast for DCIS. FIGURE 4B: T1-weighted post contrast image with fat saturation. Non-mass enhancement within the lumpectomy site. Biopsy demonstrated DCIS.

Enhancing Masses

A new enhancing mass (Figure 5), especially those with irregular or spiculated margins, are highly suspicious (BI-RADS 4 or 5).

Breast MRI Findings: Post-surgical Findings Enhancing Masses
FIGURE 5: T1-weighted post contrast image with fat saturation. A new mass with irregular margins at a lumpectomy site. Biopsy demonstrated recurrent breast cancer.

Imaging Following Mastectomy:

The normal appearance following mastectomy is dependent on the type of reconstruction techniques include autologous tissue flaps and implant reconstruction. Autologous tissue flaps include the transverse abdominis myocutaneous (TRAM) and deep inferior epigastric perforator (DIEP) flaps, although numerous other techniques exist. In general, post-surgical changes such as seromas and fat necrosis will also be encountered following mastectomy as in breast conservation surgery. Recurrences are most common in the anterolateral breast and axilla, where residual breast tissue may remain (Figure 6)6,7. 

Breast MRI Findings: Post-surgical Findings
Figure 6: T1-weighted post contrast image with fat saturation. Previous mastectomy with implant reconstruction. Enhancing masses are seen in the axilla and in the anterior breast, the latter of which extends to the nipple-areolar complex. Biopsy demonstrated recurrent breast cancer.

Conclusion:

Breast MRI may be useful to assess for residual disease or recurrence following breast conservation therapy or in some cases following mastectomy. It is important to recognize benign findings such as a post-surgical scar and seroma. Fat necrosis has a variable imaging appearance and may require imaging follow-up, correlation with mammography, and/or biopsy. Suspicious findings following surgery include new NME, especially in a masslike or ductal pattern, and enhancing masses.

References

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