Breast Tomosynthesis: Comprehensive Breast Imaging Cases

Introduction

This course provides a case-driven, practical overview of digital breast tomosynthesis (DBT) with a focus on workflow, interpretation strategies, and multimodality correlation. Using representative cases, we examine hallmark imaging findings (especially architectural distortion), common benign mimics such as fat necrosis, and the imaging phenotypes of invasive ductal and lobular carcinomas. Additional modules address synthesized 2D images, implants and implant-displaced views, preoperative localization, second-opinion value, and the role of MRI in high-risk screening and extent-of-disease assessment.

Principles of Digital Breast Tomosynthesis (DBT)

DBT uses conventional x-rays with a digital detector to generate tomographic, cross-sectional images of the breast. Systems acquire multiple low-dose projections over an arc and reconstruct thin slices, improving conspicuity of masses and architectural distortion by reducing tissue overlap.

Key Points

• FDA approval: Hologic 2011; GE 2014 (with 2017 Senographe iteration); Siemens MAMMOMAT 2015; Fujifilm 2017
• Typical acquisition: ~15 low-dose projections during a ~5-second sweep; slice thickness as small as 0.5 mm
• Dose: DBT plus 2D approximates roughly double a single 2D exposure, yet remains below historic FDA film mammography limits

Clinical Performance and Outcomes

Large population studies demonstrate DBT’s clinical advantages compared with full-field digital mammography (FFDM), with both improved detection and reduced recalls.

Key Points

• ~450,000-patient study (2014): decreased recalls by ~16/1000 and increased cancer detection (notably invasive cancers) by ~1/1000
• Comparable performance to diagnostic spot compression views in many scenarios
• Potential to reduce additional mammographic views in diagnostic workups, streamlining throughput

Reading Workflow and Hanging Protocol

A disciplined, reproducible approach improves sensitivity and efficiency when reading DBT with synthesized 2D images and priors.

Key Points

• Initial survey: current CC/MLO on bottom, priors on top; scan current images first, then compare up–down with priors
• Systematic comparisons: side-to-side (left vs right) for CC and MLO; scroll back through multiple prior years to detect developing asymmetries
• Dedicated calcification search: zoomed halves on CC and MLO for microcalcifications
• Tomosynthesis interrogation: start with synthesized 2D (e.g., Hologic C-View), then scroll DBT slices, examining the breast in thirds; review navigator thumbnails for dense foci and extra views (e.g., exaggerated CC)

Synthesized 2D Images (C-View, V-Preview)

Synthesized 2D images are algorithmically generated from the DBT dataset to emulate a conventional projection while emphasizing features such as architectural distortion.

Key Points

• FDA approved (2013) as a replacement for standard 2D when DBT is acquired
• Clinical performance non-inferior to FFDM; phantom work shows relative microcalcification limitations
• Vendor naming: Hologic C-View; GE V-Preview; resolution is improving in newer iterations
• Practical pearl: C-View can accentuate architectural distortion visibility

Recognizing Architectural Distortion on DBT

Architectural distortion is a premier strength of DBT and a high-yield sign of malignancy when unexplained.

Key Points

• Look for radiating thin lines converging on a focal point across DBT slices
• Confirm reality by scrolling into and out of plane across both CC and MLO to localize
• Malignancy rates for isolated distortion: >60% with ultrasound correlate; ~20–30% without sonographic correlate
• Unexplained architectural distortion warrants biopsy

Fat Necrosis and Postoperative Breast Changes

Fat necrosis is a benign process that can mimic malignancy, especially after surgery, trauma, reduction, or radiation. DBT helps separate oil cysts and scar from primary lesions.

Key Points

• Mammography: oil cysts appear as radiolucent circumscribed lesions; fibrosis may cause spiculation
• Ultrasound: hypoechoic masses with indistinct/angular margins and hyperechoic halo are possible
• MRI: T1-bright foci that suppress on fat-sat; enhancement may reflect surrounding inflammation
• Correlate with surgical history (lumpectomy clips, reduction scars); DBT depicts scar-related distortion conspicuously

Ultrasound Correlation and BI-RADS Assessment

Accurate multimodality correlation underpins appropriate BI-RADS categorization and biopsy selection.

Key Points

• Define target features on mammography/DBT (e.g., spiculation) and seek matching margins/shape on ultrasound
• Do not accept a discordant benign-appearing cyst as a correlate for a spiculated mammographic target
• Radial/antiradial planes improve ductal and architectural assessment
• BI-RADS 4 for suspicious features; escalate to 4C/5 for highly suspicious mass/distortion
• Doppler: presence of flow supports vascularity; absence does not exclude malignancy

Invasive Ductal Carcinoma (IDC): Imaging and Biology

IDC is the most common invasive breast cancer, often presenting as an irregular, spiculated mass on DBT and ultrasound.

Key Points

• Imaging: irregular mass, often with or without associated calcifications; higher-grade cancers more often calcified
• Pathophysiology: invasion through the ductal basement membrane
• Phenotypes and typical biology:

- Luminal A: ER/PR+, HER2−, low Ki-67 (most common; favorable)

- Luminal B: ER/PR+, HER2−, high Ki-67

- HER2-enriched: HER2+, ER/PR− (targetable)

- Triple-negative: ER−/PR−/HER2− (basal-like; more aggressive)

• MRI: irregular enhancing mass; useful for extent and contralateral assessment in select scenarios

Male Breast: Gynecomastia and Malignancy

Male patients may harbor both gynecomastia and carcinoma; thorough evaluation is required, especially with focal palpable findings.

Key Points

• Do not dismiss focal masses as gynecomastia; evaluate with diagnostic mammography/DBT and targeted ultrasound
• Prior cross-sectional imaging may show enhancing spiculated masses
• IDC is the predominant male breast cancer; management often includes mastectomy, radiation, endocrine therapy (e.g., tamoxifen)
• Prostate cancer therapy can promote gynecomastia; estrogen therapy is now rarely used

Using Navigator Thumbnails and Tomo Spot Views

Small thumbnail images and targeted spot reconstructions can improve lesion detection and definition.

Key Points

• Navigator thumbnails highlight the densest foci; use them to prioritize areas for close DBT scrutiny
• Tomo spot compression can sharpen margins and accentuate subtle spiculations
• Avoid overcalling well-circumscribed, low-density masses that remain benign-appearing across DBT slices; prioritize those with angular margins or spiculation

Preoperative Localization: SAVI Reflector

Wire-free localization tools improve surgical workflow and patient experience.

Key Points

• SAVI Scout/Reflector: ~12 mm reflector placed percutaneously; detects signals from a handheld probe to guide excision
• Deployment: sheath retraction at the hub unsheathes the reflector in situ
• Approved for long-term placement (2017); supports bracketing (lesions ~2.5–2.6 cm apart in reported series)
• Limitations: deep targets and hematomas can attenuate signal; outcomes (positive margins, retrieval rates) comparable to wires

Second-Opinion Interpretations

Expert reinterpretation at tertiary centers can alter management and detect additional disease.

Key Points

• Frequently results in additional imaging and changed recommendations (high discrepancy rate)
• Added cancer detection is clinically meaningful (reported yields ~13–50% when recommended biopsies are performed)
• Can both upgrade to malignancy/high-risk lesions and appropriately downgrade benign findings

Invasive Lobular Carcinoma (ILC): Imaging Patterns and MRI

ILC can be more subtle on mammography due to its growth pattern, with MRI often used to define extent.

Key Points

• Imaging: often presents as spiculated masses but may be mammographically subtle; ultrasound may show hypoechoic lesions with shadowing
• Biology: up to ~15% of breast cancers; typically ER/PR+, low grade, low proliferation
• Pathology: loss of E-cadherin in ~90% facilitates cell migration and single-file infiltration
• Clinical: higher rates of bilaterality, multifocality, and multicentricity; consider preoperative MRI for extent and contralateral evaluation

Imaging the Augmented Breast

Specialized techniques and careful targeting are essential with implants.

Key Points

• Silicone implants are radiopaque on mammography; saline implants are radiolucent
• Identify implant position (retropectoral vs prepectoral) and use implant-displaced views to better visualize anterior breast tissue
• DBT can reveal subtle architectural distortion adjacent to implants
• Biopsy near implants: use shallow approaches; hydrodissection with lidocaine to lift lesion off implant; avoid capsule puncture

Ductal Carcinoma In Situ (DCIS): Imaging Spectrum and MRI

DCIS is noninvasive carcinoma confined to ducts; while commonly detected via calcifications, it can also appear as distortion or mass.

Key Points

• Mammography: ~90% present as microcalcifications

- Suspicious descriptors: fine linear/branching, pleomorphic

- Intermediate: amorphous, coarse heterogeneous (still biopsy)

• Upstaging: ~15% harbor invasive components at surgery; consider sentinel node sampling in appropriate surgical candidates
• MRI: most sensitive modality (~92%); commonly non-mass enhancement with clumped/heterogeneous pattern; clustered ring (less common) is highly specific
• Mammography may underestimate extent if portions of DCIS lack calcifications

MRI-Detected Lesions and Multimodality Correlation

High-risk screening MRI detects lesions occult on 2D mammography that DBT and ultrasound can localize.

Key Points

• Use nearby benign landmarks (e.g., T2-bright cysts) to guide targeted mammography/ultrasound
• DBT often reveals corresponding architectural distortion not visible on 2D
• Ultrasound may identify small hypoechoic, angular, taller-than-wide masses adjacent to cysts
• Pathology can reveal small IDC correlates; integrate findings across modalities for biopsy planning

Skin Findings and Artifacts: Antiperspirant and Markers

DBT slice navigation helps distinguish skin-based objects from parenchymal calcifications.

Key Points

• Skin-based objects are visible on the first 1–2 tomographic slices and fade rapidly with depth
• Antiperspirant (aluminum salts) can mimic calcifications in the axilla and along skin
• Skin markers (e.g., scar markers) confirm superficial location; instruct patients to avoid antiperspirant on the day of imaging

Practical Biopsy and Intervention Pearls

Careful technique reduces complications and improves diagnostic yield.

Key Points

• Target the most suspicious lesion/margin (spiculation/architectural distortion) for tissue sampling
• Confirm imaging-pathology concordance; do not allow negative Doppler to dissuade biopsy of suspicious targets
• In scars, compare meticulously to prior imaging for interval change; new palpable abnormalities warrant targeted ultrasound despite scar complexity
• Post-biopsy localization clips facilitate future correlation and surgical planning

Conclusion

Digital breast tomosynthesis enhances detection of architectural distortion and improves cancer detection while reducing recalls. A structured interpretation protocol leveraging synthesized 2D images, DBT scrolling, and targeted ultrasound improves accuracy. Case-based patterns—fat necrosis, scarring, IDC, ILC, DCIS, male breast cancer, and implant-related considerations—highlight common pitfalls and best practices. MRI complements mammography/DBT in high-risk screening and extent-of-disease assessment, while modern localization techniques such as SAVI reflectors streamline surgery. Integrating multimodality findings with clinical context and rigorous correlation remains central to high-quality breast imaging.