Introduction
Post-surgical breast imaging is radiographic imaging done after the surgical procedure treating benign breast lesions or breast cancer. This scan is usually performed to detect normal postoperative changes in the breast or recurrent breast tumors. The recurrence rate of breast tumors after surgery is around one to two percent per year.
What Are the Different Surgical Procedures Performed for Breast Lesions?
Percutaneous Breast Biopsy:
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A percutaneous breast biopsy is the most common surgical procedure for breast masses and calcifications. This procedure includes core needle biopsy, cyst aspiration, and fine-needle aspiration. A percutaneous breast biopsy is performed by introducing a needle into the suspicious site under the guidance of ultrasonography. Then a tissue sample is removed and later viewed on a microscope.
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Mammographic findings after percutaneous biopsy are increased density, hematoma, and edema in mammography, healing after biopsy is less evident than reduced calcification or the presence of a marking clip.
Excisional Breast Biopsy:
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An excisional breast biopsy is a surgical procedure in which breast tissue is removed through the skin incision. The amount of breast tissue to be removed is determined by the surgical technique and the cancer treatment, such as radiation. The immediate post-surgical changes (one to two weeks) after excisional breast biopsy are hematoma, tissue destruction, and edema. In mammography, the changes after excisional breast biopsy appear as a poorly defined mass, area of distortion, increased density, and skin thickening.
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When the lesion heals, there might be fibrosis which results in scarring. The delayed healing changes in mammography appear as areas of dystrophic calcifications, irregular mass, and architectural distortion. Sometimes healing after an excisional biopsy may not show any mammographic findings. Usually, a follow-up mammogram is recommended after six months of an excisional breast biopsy.
Breast Conservation Treatment:
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Breast conservation treatment is performed by removing breast cancer along with the surrounding rim of non-cancerous tissue. This procedure involves complete lymph node removal or sentinel lymph node biopsy. In addition to this procedure, adjuvant radiation therapy is also performed to kill occult cancer cells.
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In mammography, the immediate post-treatment changes such as edema, skin thickening, post-operating fluid collection, fat necrosis, dystrophic calcification, and scarring are markedly visible up to six months after the treatment.
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Tumor recurrence on mammography is seen as increased breast density, skin thickening, microcalcifications, and axillary nodal recurrence.
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Chronic mammographic findings are poorly defined lesion architectural distortion and change in the breast appearance. In addition, the breast cancer recurrence rate after surgery is about 1 to 2 percent annually.
Breast Augmentation or Reconstruction Surgery:
Augmentation breast surgery is performed through a keyhole incision made around the areola and extended to the inferior mammary fold in the 6 o'clock position. Mammographic findings of breast augmentation are distorted architecture and displacement of the nipple due to breast tissue removal.
What Are the Imaging Techniques Used in Post-surgical Breast Imaging?
Mammography:
Mammography shows acute post-surgical changes such as hematoma, seroma, and edema. Chronic changes include scar formation, retraction, dystrophic calcification formation, fat necrosis, tissue asymmetry, and architectural distortion. These changes are usually associated with the type of surgical procedures.
Magnetic Resonance Imaging (MRI):
Magnetic resonance imaging cannot visualize the early postoperative surgical changes as the resection margins are highly enhanced due to the inflammatory reactions after the surgery.
Acute Changes
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In non-enhanced T1-weighted images, hemorrhage is seen as variable signal intensity.
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Early or intense enhancement, or sometimes both, may be seen.
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Hematomas and seromas appear as a cavity with high to low signal intensity. The signal intensity varies in acute and chronic changes.
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Hematomas and seromas have smooth and thin capsules, but the recurrent tumor appears irregular and nodular.
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Granulation tissue often shows slow or moderate enhancement. Faster enhancement leads to false-positive diagnoses.
Chronic Changes
After 9 to 18 months of lumpectomy, the enhancement may not be seen.
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Scar tissue is not seen as an enhanced structure after 18 months of surgery. However, if the tissues appear enhanced, a biopsy might be advised.
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On MRI, the appearance of fat necrosis varies based on the stage of the lesion. Non-fat-saturated images appear as high signal intensity on T1-weighted images and hyperintense on T2-weighted images. Fat, saturated images appear as hypointense on T2-weighted images. T1 fat-suppressed images help differentiate fat from the blood because the blood appears as high signal intensity images on T1-weighted images. Fat-containing lesions are rare in tumors so that fat necrosis can be easily differentiated from tumors. Tissue sampling is recommended when there is a suspension of the diagnosis.
Ultrasonography:
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Postoperative ultrasonography is performed using a linear array transducer with a high frequency of about 110 MHz or greater. Ultrasonography may show skin thickening, architectural distortion, or calcification. In addition, they appear as hypoechoic or hyperechoic masses with acoustic shadowing.
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In the acute stage, the hematomas appear as a poorly defined structure that produces complex echoes with distal acoustic shadowing. Later, hematoma organizes to form a mass-like structure, and fluid content becomes hypoechoic and appears like a cyst.
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In the chronic stage (after a few months to years), scar formation appears as an area of architectural distortion with acoustic shadowing and hypoechoic structures. These findings sometimes mimic breast tumors.
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In ultrasonography, fat necrosis and dystrophic calcification is seen as hypoechoic or irregular lesions with acoustic shadowing. These findings should be compared with mammography, clinical examination, and surgical history before the diagnosis.
Nuclear Imaging:
Scintimammography is a nuclear imaging test to diagnose breast lesions' postoperative changes. This is performed using technetium 99m sestamibi (MIBI). Sestamibi can penetrate the cell membranes of cancer cells as it is lipophilic. SPECT can increase sensitivity by 83 to 97 percent and shows less than 50 percent sensitivity for smaller lesions. (smaller than 1 cm). The radiotracer uptake depends on the size of the tumor. A dedicated small field of view (FOV) breast-specific gamma imaging (BSGI) is a recent advancement, and it is a substitute for contrast-enhanced MRI. BSGI can provide a better view of the size and location of the images.
Conclusion
Breast radiologists should have a keen knowledge of regular and atypical appearances of post-surgical breast lesions on imaging. Sometimes, the postoperative imaging findings may resemble cancer tissues; hence biopsy is recommended to exclude the tumor. Digital breast tomosynthesis is an emerging imaging technique used to detect the postoperative changes of breast lesions at various angles. This technique reduces the false positives by the overlap of parenchymal tissues.
