Shape Descriptors

An oval mass is elliptical or egg-shaped and includes lobulation, with two or three undulations (Fig. 8‑8; Fig. 8‑9; Fig. 8‑10). A round mass is spherical, ball-shaped, circular, or globular in shape (Fig. 8‑11) and an irregular lesion’s shape is neither round nor oval and usually implies a suspicious finding (Fig. 8‑12).

Margin Descriptors

The margin is the edge or border of a lesion. The descriptors of margin, in addition to the descriptors of shape, are important predictors of benignity or malignancy. A circumscribed margin (changed from smooth in the prior lexicon) is sharply demarcated with an abrupt transition between the lesion and surrounding tissue (Fig. 8‑13). The entire margin must be well defined in its entirety to be qualified as “circumscribed.” A not circumscribed margin may be categorized as irregular, edges that are either uneven or jagged (Fig. 8‑14), or spiculated, lines radiating from a mass implying a suspicious finding (Fig. 8‑15; Fig. 8‑16; Fig. 8‑17; Fig. 8‑18). When reporting a mass with both irregular shape and margin, the MRI report should indicate that there is “a mass of irregular shape and margin.” In general, circumscribed masses are indicative of benign lesions in all imaging methods in contradistinction to noncircumscribed masses, which are suspicious for carcinoma. Margin analysis is highly dependent on optimal spatial and temporal resolution for accurate diagnosis at MRI.

Internal Enhancement Characteristics

Internal enhancement describes the enhancement pattern within an abnormally enhancing structure, and is an important reflection of lesion biology. ⁸ Enhancement patterns are characterized as homogeneous, a confluent uniform enhancement of a mass, and heterogeneous, a nonuniform enhancement of a mass with variable signal intensity. Homogeneous enhancement is suggestive of a benign process; however, some small cancers can exhibit homogeneous enhancement, and careful margin assessment with high spatial and temporal resolution is essential for an accurate diagnosis of benignity (Fig. 8‑19). Heterogeneous enhancement is generally more characteristic of malignant lesions (Fig. 8‑20). ⁸ Rim enhancement is more pronounced at the periphery of a mass, and is commonly seen in high-grade malignancies. Cysts can become inflamed and enhance peripherally, but are usually bright on T2-weighted (T2w) sequences confirming internal fluid, unless they are very small or contain proteinaceous material (Fig. 8‑21). Fat necrosis (oil cysts) and normal postoperative seromata may exhibit smooth peripheral enhancement. Rim enhancement of a solid mass is a suspicious finding (Fig. 8‑22; Fig. 8‑23). The MRI features with the highest predictive value for malignancy are lesion mass types with irregular shape, irregular or spiculated margins, and marked enhancement. ⁹ Dark internal septations are seen as nonenhancing lines within an enhancing mass. These dark septations are seen more frequently at higher spatial resolution (3.0 Tesla) on either T2w precontrast or T1-weighted (T1w) postcontrast series and are suggestive of a fibroadenoma if other morphologic and kinetic characteristics support benignity (Fig. 8‑24; Fig. 8‑25). Myxoid fibroadenomata are highly cellular with moderate internal mucoid material exhibiting hyperintense signal on T2 in some cases. These circumscribed masses usually show dark internal septations and heterogeneous enhancement on T1w series (Fig. 8‑26, Fig. 8‑27). Fibroadenomata are frequently seen on breast MR studies, often occult at mammography, and must be confidently recognized as benign lesions whenever possible. Nonenhancing masses with benign morphology are benign.

Fat-Containing Lesions

These masses are generally benign and include lesions such as lipomata, fibroadenolipomata (hamartoma) (Fig. 8‑28, Fig. 8‑29), and lymph nodes (Fig. 8‑30; Fig. 8‑31). The key to accurate diagnosis is identification of fat signal within the lesion on a non–fat-suppressed high-resolution T2w or T1w series. Fat necrosis may present as a rim-enhancing mass exhibiting varying enhancement (Fig. 8‑32). History of prior trauma or surgery may explain the enhancing finding, and verified central fat content on non–fat-suppressed images may confirm the diagnosis (Table 8‑3).

T2w Precontrast Mass Findings

High-resolution T2w sequences provide important information and, when evaluating breast masses, can improve specificity of diagnosis. Comparing the morphology and signal intensity on T2w and T1w images can be helpful. High T2w signal may signify extensive necrosis seen most frequently in high-grade lesions, or in mucinous/loose myxoid stroma seen in mucinous carcinoma. Cystic or microcystic tumor components are rare and can be found most frequently in papillary cancers. Intratumoral fat-containing tissue usually indicates a benign diagnosis. The presence of peritumoral, stromal, subcutaneous, or prepectoral edema augurs an aggressive malignancy type.

Kinetic Curve Assessment

In general, benign lesions exhibit persistent curves, and malignant lesions exhibit washout curves, although there is considerable overlap between the kinetic curves that depict malignant and benign lesions. Diagnosis should only be made after consideration of both the morphologic and kinetic features of an enhancing lesion. Kinetic features reflect underlying lesion biology and the efficacy of advanced computerized analytic methods, using both morphologic and kinetic data, will be discussed in Chapters 12 and 13.

Histology

The heterogeneous nature of ILC is well established, and histologic subtypes of ILC lesions have been described. In 1982, Dixon and colleagues categorized 103 ILC lesions as classical, solid variant, alveolar variant, or mixed histologic subtypes, the classic and mixed types being the most common. ¹⁴ The classic type of ILC is described as a single filing growth pattern, with “peri-parenchymal” distribution and diffuse multifocal invasion. The solid variant consists of a “sheet-like” pattern or irregular-shape nests of cells, whereas the alveolar type is described as globular aggregates of 20 or more cells. These three subgroups exhibit small noncohesive regular cells with round or oval nuclei, whereas the fourth mixed type demonstrates cohesive cells with nuclear pleomorphism. Recently, subclassification has been reported using histological features and IHC ¹⁵ ; however, no clear differences in long-term patient outcome between the different histologic subtypes was found in either study. ^{14 , 15}

Two studies have reported on the mammographic imaging appearance of ILC subtypes and histopathology. ^{16 , 17} In 2014, Tabar and colleagues ¹⁶ reported on 428 consecutive cases of ILC, diagnosed in the screening era, from 1996 through 2010, and compared patient outcome of these cases with a cohort of ILC cases diagnosed and treated in the prescreening era 25 to 30 years earlier. ⁷ A classification of the mammographic features of ILC lesions was made with an approximate correlation to the earlier histologic classification of Dixon and colleagues ¹⁴ (Table 8‑4). ILC subtypes vary in their imaging characteristics and lesion size at diagnosis. The alveolar subtype is often extremely difficult to detect at mammography even though it is often palpable and multifocal, because it consists of many individual, tiny, scattered 2- to 3-mm cancer foci, often involving an entire quadrant but without a discrete tumor mass. Tumor sizes differed significantly in this study according to their mammographic subtypes (p < 0.001). Large tumor sizes (≥30 mm) were overwhelmingly more likely to be found in architectural distortion cases (76%) than in spiculated masses (21%), round masses (25%), and equivocal asymmetric densities (34%). Patient outcome was shown to be related to mammographic appearance when long-term survival of women with ILC lesions was compared in the two groups (1960–1970 vs. 1996–2010). Outcome for women with spiculated and circular/oval-shape lesions diagnosed during the screening era was dramatically improved; however, no change in survival was found in women with the classical architectural distortion subtype, despite the advent of screening mammography in the latter group and the introduction of new therapeutic regimens.

Magnetic Resonance Imaging

The MRI findings of ILC reflect the morphologic findings seen on mammography and ultrasound; however, determination of disease extent is more accurate at MRI, and ILC lesions, found to be occult on mammography and ultrasound, are almost always visible on MRI. An irregular or spiculated-shape mass, with heterogenous internal enhancement, is a common presentation of ILC, although focal and “sheet-like” regional nonmass enhancement may also be found. ^{12 , 18 , 19 , 20} ILC rarely presents as a round mass, an important distinction compared to IDC lesions, which may often present as round masses with not circumscribed margins, and are generally grade 2 lesions. Mann and colleagues reported that a round-shape mass was identified in only 1 of 143 ILC lesions. ¹⁸ ILC has been described as a “stranding” pattern of tumor enhancement, associated with multiple, small, enhancing foci, by some investigators, possibly reflecting the single-file pattern of tumor growth. ^{14 , 21} Reports on the kinetic features of ILC generally conclude that in the initial phase of enhancement, ILC enhances more slowly than IDC, although peak enhancement measures may be similar. In the delayed phase of enhancement, ILC exhibits washout curves less frequently and a larger proportion of the tumor shows persistent delayed-phase curves than are seen in IDC. ²²

Multimodal images of the four main presentations of ILC are shown.

1. 
   

   The classical subgroup of ILC: architectural distortion (Fig. 8‑34).

   
   
2. 
   

   The solid variant pattern subgroup of ILC: round/oval mass (Fig. 8‑35; Fig. 8‑36).

   
   
3. 
   

   The alveolar subtype of ILC: asymmetric density/NME (Fig. 8‑37, Fig. 8‑38; Fig. 8‑39; Fig. 8‑40; Fig. 8‑41).

   
   
4. 
   

   The mixed pattern of ILC: spiculated mass(s): (Fig. 8‑42; Fig. 8‑43; Fig. 8‑44).

Additional ipsilateral malignant lesions detected only on MRI were found in 32% of patients, in a study of preoperative assessment of ILC extent, resulting in changed management in 28% of cases. ¹⁸ Another study of preoperative assessment of ILC showed management change in 49% women, 40% needing more extensive surgery and 9% needing less extensive surgery (Fig. 8‑43, Fig. 8‑44). ²³ Patients with an ILC diagnosis are more likely to have positive surgical margins after lumpectomy than patients with IDC lesions. Reduction in reexcision rates of ILC lesions by use of preoperative MRI has been shown in a study of 267 patients undergoing breast conserving surgery (BCS). Investigators reported a 9% reexcision rate in the MRI group compared to a 27% reexcision rate in the group without preoperative MRI. ²⁴ MRI has been shown to be an essential imaging method in the preoperative assessment of women with a new diagnosis of ILC.

Tubular Subtype

Tubular carcinoma is an uncommon, low-grade subtype of invasive carcinoma accounting for fewer than 2% of all invasive breast cancers, its incidence increasing with the use of screening mammography. These cancers are generally small and node negative with a favorable prognosis, the overall 10-year disease-free survival rate for tubular cancer being greater than 90%. Tubular carcinoma contains a central fibroelastotic core that entraps glandular proliferating elements, exhibiting round, ovoid, or angulated tubules formed by a single layer of small, regular cells with little nuclear pleomorphism. A tubular component greater than 90% is a requirement for a histologic diagnosis of tubular carcinoma. ^{25 , 26}

Imaging Findings

The hallmark finding, on all modalities, is that of spiculation, which corresponds to reactive stroma surrounding the tumoral mass, seen on ultrasound as an echogenic “halo.” Small tubular cancers usually present on MRI as spiculated or irregular masses, with heterogeneous enhancement and persistent kinetics (Fig. 8‑45; Fig. 8‑46, Fig. 8‑47). Minimal enhancement or initial enhancement rates less than 100% are commonly found. This enhancement pattern can be explained by the slow progression of the contrast material within the dense fibrous and elastotic stromal components. The morphologic features of radial scar (complex sclerosing lesion) often mimic those of tubular carcinoma and their kinetic behavior is often variable. Although visible on MRI, the distinction between these two lesions is usually not possible if lesion enhancement is present, and pathologic examination of the surgically excised tumor is generally needed.

Related posts:

2 Screening MRI: Who Should Be Screened? 4 Screening MRI: Clinical Implementation 6 Diagnostic MRI Interpretation 9 Management of Findings Initially Detected at MRI 11 Advanced Breast MRI Techniques 10 Diagnostic MRI: Breast Cancer Applications

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