Sonographic assessment of extent and aggressiveness of malignant breast disease

While contrast enhanced magnetic resonance imaging (MRI) is generally considered the modality of choice for staging malignant breast disease and PET/CT is considered the modality of choice for staging distant spread, ultrasound (US) can also be used to assess the local extent of malignant breast disease in many patients. Most patients will undergo breast sonography prior to breast MRI or PET/CT. Thus, US offers us our first chance to determine the local extent of disease in many cases. US is good enough at 'staging' that in any patient with a solid nodule characterized as BIRADS 4 or BIRADS 5 we routinely perform whole breast US and assess the axillary lymph nodes during the initial sonogram or immediately prior to performing US-guided biopsy of the index lesion.

US staging involves determining the maximum diameter of the index lesion, assessing for multifocal and multicentric disease, and looking for the presence of extensive intraductal components (EIC). Regional lymph nodes can also be assessed sonographically at the same time that the suspicious index solid nodule and ipsilateral breast are evaluated. US-detected secondary and tertiary lesions can, and should, be 'mapped out' with US-guided biopsies.

Accurate US staging leads to the appropriate type of extirpative surgery, minimizes the number of surgeries necessary to rid the patient of disease, and can minimize the risk of local recurrence. In fact, 'local recurrence' is almost always residual unresected disease that was not recognized preoperatively or intraoperatively by the surgeon. It can also obviate staging MRI and sentinel node procedures in some cases.

We then place nine individual suspicious findings into three categories: 'hard', 'soft', and 'mixed' suspicious findings. 'Hard' findings suggest the presence of invasion, and include angular margins, spiculation, and acoustic shadowing. 'Soft' findings suggest the presence of ductal carcinoma in situ (DCIS) components, and include duct extension, branch pattern, calcifications, and most cases of microlobulation. It is important to include soft findings in the sonographic algorithm because they improve the sensitivity for pure DCIS, but also because they help us to better assess the true extent of lesions that contain both invasive and intraductal components. Most invasive ductal carcinomas contain DCIS components, which frequently lie in the periphery and contribute to the surface characteristics and shape of the lesion. 'Mixed' findings are not specific and can be seen with either invasive or DCIS components of the lesion, and include taller-than-wide (antiparallel) shape, hypoechogenicity, and a minority of microlobulations.

The most basic prognostic feature of a malignant lesion is its maximum diameter. There are two different maximum diameters – the prognostic diameter used in determining the TNM stage and the surgical diameter necessary to completely remove the lesion. The prognostic diameter is the maximum diameter of the invasive component of the tumor, and is represented sonographically by the largest part of the lesion than manifests hard sonographic findings. The resection diameter includes both invasive and DCIS components of the tumor and is represented sonographically by the greatest length of combined hard and soft findings in the lesion.

Multifocal invasive carcinoma usually represents separate foci of invasion in a single malignant lesion that are connected by DCIS components of the lesion. By scanning parallel to the long axis of the mammary ducts in the region of a suspicious breast nodule, we are frequently able to show 'bridges' of DCIS connecting the foci of invasion.

EIC increase the likelihood of local recurrence in patients who undergo breast-conserving therapy. Prominent 'soft' findings suggest the presence of EIC.

Certain suspicious sonographic features correlate with the histologic grade of the lesion or with the nuclear grade of the DCIS components of invasive ductal carcinomas. The presence of enhanced through-transmission deep to a suspicious solid nodule more than doubles risks that the lesion is high grade. Shadowing favors the lesion being low or intermediate grade. The thicker the ill-defined echogenic halo relative to the size of the hypoechoic central nidus, the more likely the lesion is to be low grade. Circumscribed malignant nodules that are surrounded by a thin echogenic capsule are more likely to be high-grade invasive ductal carcinomas or special-type tumors such as colloid or medullary. Large microlobulations and branch pattern suggest a high-grade lesion, intermediate-sized microlobulations and branch pattern suggest an intermediate-grade lesion, and very small microlobulations suggest the presence of a low-grade lesion.

Once we have completely evaluated the breast to look for multifocal and multicentric disease and EIC, we proceed to evaluate the axillary lymph nodes. If abnormal lymph nodes are found, we perform US-guided biopsy of the lymph node. If the biopsy is positive for metastatic disease, the sentinel lymph node procedure becomes unnecessary and the patient proceeds straight to axillary dissection. If the biopsy is negative for metastatic disease, the patient undergoes the sentinel node procedure as originally planned. There is a distinct advantage to this pattern of sonographic evaluation. The sentinel node procedure is not perfect. False negative sentinel node procedures occur in a small percentage of patients. In such cases, the cause of failure is 'tumor damming'. Metastases to the sentinel node block the normal lymphatic drainage through the sentinel node, causing it to go through collaterals to a higher node that may still be histologically negative. Sentinel nodes that are so grossly filled with tumor that they alter the normal lymphatic drainage pattern are easily identified as being abnormal by sonography and can easily be targeted for US-guided biopsy.