MRI lexicon: Morphology of contrast enhanced breast lesions

 

This new MRI lexicon provides and evaluation of the breast MRI scans and integrates dynamic enhancment properties of the breast lesions. Generally speaking, the cost of MRI breast cancer screening is quite excessive and has not proven to be dramatically more beneficial thans screening mammograms and ultrasound. However, contrast enhanced breast MRI can determine whether a lesions is cancerous or benign with a very high degree of sensitivity. (The specificity of breast cancer screening MRIs is not as high, however). The image below shows an early phase contrast-enhanced T1 weighted breast MRI, with mild enhancement, which is suggestive of a benign lesion like fibroadenoma.

Morphology of enhancing breast lesions MR images

When a breast lesion is ‘enhancing’ there are various decriptive criteria that the radiologist will use in assessment. The first descriptive criteria describes the lesion either as a focus, a mass, or a non-mass, based on the type of enhancment being seen.

 

Morphology
Focus
Mass: margin, shape, pattern of enhancement
Non-mass:
linear smooth. irregular, crumpled
segmental homogenous,heterogeneous,clumped
regional homogenous,heterogeneous,clumped
diffuse homogenous,heterogeneous,clumped

 

Morphological description of a ‘focus’ contrast enhanced breast MRI

A focus is basically a tiny spot or ‘dot’ of enhancment, which is generally round and smooth and without ‘mass effect’. (Mass effect defines displacement of mass, which would likely be caused by a growth or nodule )

A ‘focus’ or ‘focal enhancment’ is generally something smaller than 5mm. Since it is so small it cannot really be classified morphologically. Foci (multiple dots) can also have a chaotic effect in the analysis of the ‘enhancment kinetic curve’ (on account of the volume averaging effect with the surrounding normal tissues) Usually, an enhancement focus will be the result of a benign bresat lesions such as papilloma, small fibroadenoma, or generic fibrocystic change. It could also be indicating an intramammary lymph node. However, enhancement foci due rarely show as the result of focal DCIS or even a very small invasive breast cancer.

The subsquent management of a ‘focal enhancement’ is a bit of a judgement call. Most radiologists would tend to consider a biopsy as uneccesary (breast lesions smaller than 5mm are caused by breast cancer only about 3% of the time.) But, if there are corresponding results from mammography and ultrasound and the patient is already considered ‘high risk’, a biopsy might be performed.

Morphological description of a ‘non mass’ with contrast enhanced breast MRI

 

A ‘Non-mass-like’ enhancement is will be mostly characterized by the distribution pattern of the enhancements, whether they are linear, focal, segmental, regional, in multiple regions, diffuse, or ductal. The distribution pattern of non-mass-like enhancement can also be further defined according to ‘internal’ characteristics. These internal characteristics would include observations as to whether the enhancement was homogeneous, heterogeneous, clumped, stippled/punctate, or reticular/dendritic. The radiologist will also note whether or not the enhancement is symmetric or asymmetric between both breasts. The distribution pattern, margins, shape, and internal enhancement patterns all help determine whether or not a non-mass breast lesion is benign or malignant.

 

To describe an image finding as a ‘non-mass’ seems a little bit ambiguous. What this means is that on the contrast enhanced image, there is an enhancment pattern which is distinct from the normal surrounding breast parenchyma, but ther is also no ‘space-occupying’ effect. Invasive ductal carcinoma will tend not to show as a ‘non-mass’ enhancement, but invasive lobular carcinoma and DCIS might. Other lesions that may present with a non-mass-like enhancement are focal adenosis, fibrocystic breast changes due to hormonal stimulation, and inflammatory breast conditions.

The images below are of a pre-contrast and post-contrast enhanced subtraction breast MRI. Note the ductal clumped ‘focal’ pattern.

This would be considered a ‘non-mass-like’ contrast enhancement morphology, and is probably suggestive of lobular carcinoma in situ.

Interestingly, no estrogen receptor positive breast cancers will present in a non-mass-like enhancement, and less than 20% of estrogen receptor negative invasive ductal cancers will show non-mass-like enhancement.

 

Morphological description of a ‘Mass’ on contrast enhanced breast MRI

A lesion found during MRI contrast enhancement is described as a ‘mass’ when it seems to occupy space in three dimensions. Breast masses are then characterized by shape (round, oval, lobulated, irregular), by margin (smooth, irregular, spiculated), and also by ‘internal mass enhancement’ characteristics. These are terms and indicators which describe the manner in which the contrast enhancement is obserbed, including whether it is homogeneous or heterogeneous, if there is rim enhancement, dark internal septations, enhancing internal septations, or central enhancements.

 

A “Homogenous enhancement” pattern will tend to show confluent uniform enhancement within the entire mass. A “heterogeneous” breast lesion enhancement tends to be non-uniform and with a variable signal intensity. The term “Rim enhancement” refers to a more pronounced enhancement towards the periphery of the breast lesion than the center. “Dark internal septations” are actually non-enhancing lines within a breast mass, while the term “enhancing internal septations” refers to enhancing lines within a breast mass. And, obviously, a “central enhancement pattern” will show a more pronounced enhancement at the center of the mass.

 

Amongst various breast lesion shapes observed with MRI contrast enhancement, the highest agreement among observers is that an ‘irregular shape’, tends to suggest breast cancer, while a lobulated shape, tends to suggests fibroadenoma. The two MRI scans shown below reveal invasive lobular breast carcinoma. In the first image, there is some indication of unusual growth in the right breast, but nothing dramatically different from the right breast.

However, the contrast enhanced ‘subtraction’ image clearly shows a spiculated mass, and additional linear enhancment extending all the way to the nipple.

 

Histopathological Association of enhancing masses

Among all the contrast-enhancing features visualized with MRI, margin assessment is probably the most important characterization of a breast mass and has a very high predictive value. Breast masses with smooth margins are almost always indicative of benign disease. (Between 97% and 100% of breast masses with smooth margins turn out to be benign according to some studies.) Lobulated masses with non-enhancing septations and poorly enhanced lobulated masses are also usually benign, and tend to represent fibrocystic changes or fibroadenoma.

Contrast enhanced MRI features typical of breast fibroadenomas

Fibroadenomas can actually exhibit a variety of enhancements, depending of whether there is hormonal stimulation of the breast and on the degree of fibrosis present. In ‘myxoid’ fibroadenomas, the contrast enhancement is actually quite strong but it lingers into the late phase, unlike breast cancer which tends to ‘wash-out’ in the late phase. Fibroadenomas also tend to have a homogeneous internal enhancement pattern, which also has a high predictive value for benign breast lesions. However, a homogeneous internal contrast enhancement pattern is occassionally associated with invasive breast cancer as well, so it will likely still be treated with some suspicion.

The images above and below show a pre-contrast T1-weighted breast MRI, and then a contrast-enhanced subtraction image. One notes an irregular shaped mass with spiculated margins and rim enhancement, which is highly suggestive of invasive breast cancer.

Phyllodes tumors also have a unique DCE MRI profile

In Phyllodes tumors, which constitute less than 1% of breast tumors, contrast enhancing breast MRI tends to reveal a lobulated mass with non-enhancing internal septations. Phyllodes tumors also tend to have more heterogeneous internal structures than true breast cancer lesions.

 

Morphological presentations of breast cancers based on hormone receptor status

The main morphological presentation of most ‘triple negative’ breast cancers ( negative for HER-2 receptor, progesterone receptor, and estrogen receptor) is a mass ( about 97% of the time) Her-2 positive breast cancers tend to have more multiple mass lesions than Her-2 negative (about 57% and 15% respectively). Breast cancers that are estrogen receptor positive tend to present slightly more frequently as a mass, as compared to estrogen receptor negative breast cancers (100% and 82% respectively), but there is little difference in lesion multiplicity based on positive or negative estrogen receptor status.

 

Additional MRI contrast enhancement features suggestive of breast cancer

Enhancing breast masses with septations, and also enhancing lobulated masses without septations, are both highly suggestive of malignant breast cancer. Breast masses with marked to moderate heterogenous enhancement with wash-out kinetics are also highly suggestive of malignant breast cancer, but not to specific types of breast cancer. The pre-contrast MRI scan below shows a suspicious lesions which likely indicates invasive lobular breast carcinoma.

The post-contrast ‘subraction’ image of the same lesion below clearly reveals a heterogenous pattern of enhancment, consistent with invasive lobular carcinoma.

Irregular, spiculated margins and rim enhancement are suggestive of breast cancer

Irregular masses, and those this spiculated margins or rim enhancement have a positive predictive value for malignant breast cancer in the 80%-100% range, with infiltrating ductal carcinoma being the most common breast cancer type found.

Rim enhancement is more frequently observed in larger tumors of a higher histological grade. Rim enhancement is essentially a clearly brighter or enhanced ‘ring’ around the periphery of the lesion, which suggests different tissues and blood demands on the in the center vs the rim of the lesion. When rim enhancement appears in a small breast tumor (occuring about 20% of the time), it is highly suggestive of breast cancer.

 

Contrast enhancing breast lesions with spiculated margins are most often, but not always, associated with malignant carcinoma. Most commonly they are found with invasive ductal carcinoma, but occur with tubular breast carcinoma as well.Invasive lobular breast carcinoma and DCIS can also manifest as irregular masses or masses with spiculated margins. However, benign lesions like radial scars can also show spiculated margins, so this is a situation in which the assessment of ‘enhancement kinetics’ (the realtime observation of the increases and decreases in contrast enhancement) can help determine a more conclusive diagnosis.

Distribution patterns of non-mass-like enhancements in breast MRI

The distribution pattern of a non-mass-like enhancement can take many forms. Non-mass-like breast MRI contrast enhancing patterns can be described as focal, linear, segmental, ductal, regional, diffuse, and with multiple regions.

A ‘focal’ area of a non-mass-like enhancement would typically be defined as a single, small and confined abnormal enhancing area occupying less than 25% of a given breast quadrant. (Note, this is a different finding than a ‘focus’, which by definition will measure less than 5mm.) An area of ‘focal’ non-mass-like contrast enhancement will quite often have fat or nomral glandular tissue interspersed between the abnormally enhacing components.
A ‘linear‘ enhancment pattern involves enhancement along a ‘line’, but one not conforming to a ductal pattern. A linear enhancement pattern when seen on a three dimentional image will appear as a ‘sheet’ and not a line, or may extend across the breast in a non-ductal distribution pattern.

The images below show a precontrast and post contrast enhanced subtraction breast MRI. The contrast enhanced image shows a non-mass-like linear enhancement.

The enhancement pattern, suggesting invasive breast cancer, does not conform to a ductal structure, and is therefore simply described as ‘linear’.

Contrast enhanced breast MRI may reveal multiple foci of dcis, hidden to mammography

The two MRI scans above and below reveal invasive ductal carcinoma and also multiple foci of ductal carcinoma in situ. There also appears to be some lymphatic invasion in the nipple areolar complex. One also notes a branching ductal pattern toward the nipple, with skin thickening.

Multiple foci of non-mass-like DCIS may be difficult to spot using conventional mammography and ultrasound.

‘Ductal non-mass-like enhancing breast lesions follow a breast duct system

A non-mass-like contrast enhanced distribution of a breast MRI is described as ‘ductal’ when it appears in a linear or linear branching which follows one or more ducts. Usually these patterns will radiate towards the nipple. There is not always a clear separation between linear enhancement and ‘ductal’ enhancement, and sometimes the terms are used to mean the same thing. However, a ductal enhanecment pattern of non-mass-like contrast enhanced MRI is more specific, and indicates the presence of a suspicious breast lesion following a breast duct. Ductal contrast enhancement is thought to have a positive predictive value for breast cancer ranging from about 26% to 59%. Most commonly, it represents ductal carcinoma in situ, but might also indicate atypical ductal hyperplasia, lobular carcinoma in situ, or other benign breast conditions. Approximately 50% of these MRI non-mass-like linear and ductal enhancement distributions turn out to be benign.

 

The segmental non-mass-like enhancment pattern apexes at the nipple

A non-mass-like contrast enhanced MRI breast lesion is described as ‘segmental’ when it appears in a cone or triangle shape, with an apex at the nipple. A segmentally enhanced non-mass-like lesion will usually represent the substantial involvement of a single braching duct system.

The positive predictive value for breast cancer of a segmental contrast enhanced breast lesion is quite high, ranging from about 68% to near 100%. Segmental contrast enhancement is one of the most frequent manifestations of ductal carcinoma in situ. Surprisingly, for around 17% women with ductal carcinoma in situ discovered as a segmentally enhancing MRI image, there was no abnormality noted on a breast cancer screening mammogram.

A segmental contrast enhanced breast lesion is occasionally found to be invasive lobular carcinoma, but most commonly it is associated with infiltrating ductal carcinoma. About 67% of non-mass-like lesions in a segmental distribution turn out to be breast carcinoma.

The two images below are of a pre and post contrast enhanced breast MRI. The second ‘subtraction’ image reveals a clumped segmental distribution pattern, likely indicative of infiltrating ductal carcinoma.

Internal Patterns of breast MRI contrast enhancement

There are additional descriptors for the enhancement patterns of MRI lesions, which focus on the overall appearance visually. These include homogenous, heterogeneous, stippled/punctuate, clumped and reticular/dendritic.

A ‘homogenenous’ contrast enhancement pattern is essentially a uniform and confluent enhancement, while a ‘heterogenous’ enhancement is more random and non-uniform. Areas of heterogenous enhancment will typically be separated by areas of breast parenchyma or fat. The likelihood of a homogeneous enhancement pattern as representing breast cancer would be about 67%, which is quite high. A heterogenous enhancement pattern will indicate breast cancer about 54%-68% of the time.

 

The ‘stippled‘ or ‘punctate‘ pattern of enhancement refers to multiple tiny dot-like lesion, 1-2 mm in size only. They will appear as similarly punctuate foci scattered throughout a given breast area. Stippled and punctate enhancements will usually not conform to a duct. Most of the time, a stippled or punctate enhancement pattern will indicate either normal breast tissue, or benign fibrocystic breast changes. The changes of a stipled enhancement patterns being malignant breast cancer is about 25%.

 

A “Clumped’ pattern of breast MRI contrast enhancement basically refers to an ‘aggregate of enhancing masses or foci more-or-less in a ‘cobblestone’ pattern. A clumped pattern is considered suspicious for DCIS or invasive ductal carcinoma. In fact the chances of a clumped breast MRI enhancement pattern representing DCIS or breast cancer ranges from about 41% up to 88%, however almost 90% of these cancers turn out to be DCIS. It is quite typical for the clumped or beaded enhancement pattern reviled by breast MRI to be caused to randomly ‘heaped-up’ tumor cells in a breast ducts which is expanding due to DCIS.
A ‘reticular’ or ‘dendritic‘ enhancement pattern is one in which some glandular breast tissue has undergone ‘involution’, leaving tissue strands among strands of fat.

Symmetric enhancment is self evident, referring to a ‘mirror image’ contrast enhancement pattern in both breasts, and will almost always be indicative of benign breast changes. An ‘asymmetric non-mass-like contrast enhancement pattern is simply more pronounced in one breast than the other.

Segmental contrast enhanced breast MR images often show a pattern growing towards the nipple

The images below show a pre and post-contrast subtraction MRI, which reveal a segmental enhancement pattern.Because the enhancement pattern appears to be moving towards the nipple, it would be consistently described as a segmental non-mass-like contrast enhanced pattern. This paritular legion is most likely invasive lobular breast carcinoma.

“Regional” pattern of contrast enhancement involves a broader area

When a contrast enhanced MRI of a breast lesion is described as ‘regional‘, this implies the involvement of a broader area, and typically not conforming to a ductal distribuation. Regional contrast enhancement tissues tend not to be as distinct from the surrounding tissues when compared to previous patterns. Usually, regional enhancment is patchy or ‘geographic’ ( almost like a map) in appearance, and will lack convex borders. Most of the time, regional enhancement represents a benign lesion such as fibrocystic change, but it can indicate a cancer growth as well. The likelihood of regional enhancement being breast cancer is in the order of 21%, and most often the cancer presents as DCIS or infiltrating lobular carcinoma, and rarerly as invasive ductal carcinoma.

The two images below are a pre and post-contrast-subtraction MR image demonstrating regional enhancement.

Though faint, the patchy enhancement in the left breast would likely indicate fibrocystic change.

Contrast enhanced breast MRIs are described as ‘multiple‘ if there are at least two or more large volumes of tissues not conforming to a ductal distribution pattern, and, which are separated by either normal breast tissues or fat. Similarly, an enhancement pattern may be described as ‘diffuse‘ if there are widely scattered yet more-or-less evenly distributed enhancements appearing through the breast fibroglandular tissue. Generally speaking, both diffuse and multiple regions of MRI contrast enhancement will tend to represent benign proliferative changes. However, it is not uncommon for multicentric breast carcinoma such as invasive ductal carcinoma or invasive lobular carcinoma, to also show a multiple of diffuse distribution.The contrast enhanced subtraction MRI below reveals a symmetrical diffuse enhancment in both breasts, likely indicative of benign breast fibrocystic changes.