Architectural Distortion




A radiologist friend from another city called one day and asked for a review of his wife’s mammogram. She had been recalled from screening, told that the findings were probably benign, and asked to return in 6 months for a follow-up mammogram. He thought that there might be some architectural distortion present and wanted a second opinion. After review and a few additional images, architectural distortion was indeed identified. Biopsy showed invasive lobular carcinoma. She was stage I. They send a case of champagne every year on the anniversary of her diagnosis. Joie de vivre!


Architectural distortion (AD) is often a subtle sign of malignancy with a high positive predictive value of approximately 60% on diagnostic mammography. Detection of AD is challenging because it is often similar in density to the surrounding parenchyma and it may contain fat. It is often changeable in appearance in different projections or visible on only a single view. For these reasons, AD is a common cause of false-negative screening mammograms and is also frequently missed by computer-aided detection (CAD).


How to Recognize Architectural Distortion


AD can appear as radiating lines, alteration of the normal tissue contours, or both. It is described in the BI-RADS Atlas as follows:



The normal architecture is distorted with no definite mass visible. This includes thin lines or spiculations radiating from a point and focal retraction or distortion of the edge of the parenchyma. AD can also be associated with a mass, asymmetry, or calcifications.


AD can be the primary finding or an associated finding (e.g., a mass or calcifications with associated AD).


Radiating Lines


The classic appearance of AD is radiating lines without a visible central mass ( Fig. 9-1 ). If a central mass is visible, the finding is more accurately described as a mass with spiculated margins rather than AD. Imagine you are looking at the flight map in an airline magazine: looking for AD is like looking for hub cities. Normal overlapping structures (fibrous bands, ducts, and blood vessels) create patterns resembling intersecting flight paths.




FIGURE 9-1


Architectural Distortion.

A, Screening mammogram shows retraction of the interface between the fibroglandular tissue and subcutaneous fat ( arrow ) on the mediolateral oblique (MLO) view. B, Spot compression MLO and craniocaudal (CC) views more clearly demonstrate AD with radiating lines and no central mass. Diagnosis: multifocal infiltrating carcinoma with ductal and lobular features and ductal carcinoma in situ.


The lines of AD may not radiate in all directions or be symmetric about a central point. Only a portion of the distorted area may be visible. Think of these as a coastal hub such as LaGuardia airport in New York City. Most of the incoming flights arrive from the West, with many fewer arriving from the East ( Fig. 9-2 ). Detection of even a few lines that appear to radiate from a central point or are associated with tissue retraction warrants careful examination and often diagnostic evaluation.




FIGURE 9-2


Asymmetric AD.

CC spot compression view showing AD with asymmetric radiating lines. The spicules extend mainly anteriorly, into the fibroglandular tissue. Biopsy revealed infiltrating ductal carcinoma.


Abnormal Tissue Contours


Another presentation of AD results from tethering or retraction of tissue, causing abnormal tissue contours (see Fig. 9-1 ). These findings can appear mammographically as straightening of the Cooper ligaments, focal retraction, or angulation of tissue contours. It is as though a crochet hook had been dragged through the tissue at that spot.


Distorted tissue contours are often detected at the interface between the parenchymal tissue and the subcutaneous or retroglandular fat (see Fig. 9-1 ). During mammographic interpretation, it is important to evaluate these borders and to compare the tissue contours with previous studies.


Differentiating Architectural Distortion from Summation Artifact


Overlapping Cooper ligaments, ducts, and vessels may mimic the pattern of AD. However, these overlapping structures never actually radiate from a central point. What may appear at first glance to be AD on screening mammography may often be dismissed after close inspection without the need for additional imaging.


Normal lines extend through and beyond the center of the questioned finding, rather than ending at the central point, as occurs with true AD ( Fig. 9-3 ). If we use our airline route map analogy, normal structures represent overlapping flight paths rather than the hub city.




FIGURE 9-3


Schematic Representation of AD.

Intersecting pattern of AD ( A ) and common patterns of overlapping normal structures ( B and C ). With normal structures, note the off-center intersections and continuous visualization of individual lines as they extend through the questioned finding.


One technique that can be used to analyze questioned AD is to deconstruct the finding by visually subtracting the definitely normal structures, then imagining what it would look like without those structures. If the resulting appearance would no longer be suspicious, it is consistent with summation artifact ( Fig. 9-4 ). If you believe normal structures cannot fully account for the suspected distortion, additional evaluation is needed.




FIGURE 9-4


Summation Artifact.

Screening MLO ( A, full image and B, enlargement) views showing a finding marked by CAD ( arrow ) that at first glance appears to represent AD. However, on close inspection the lines extend through the finding, rather than radiating from its center. Subtracting these normal tissue lines, there would be no residual finding, and the appearance is therefore summation artifact rather than true AD.




Diagnostic Evaluation of Suspected Architectural Distortion


When AD is suspected on screening mammography, it should be evaluated in greater detail on diagnostic views ( Fig. 9-5 ). True AD will usually persist and appear more pronounced on spot compression views. Associated masses, asymmetries, or calcifications may also become apparent on these views.




FIGURE 9-5


AD with Abnormal Finding on US.

Screening mammogram ( A ) shows extremely dense tissue with subtle radiating lines of AD ( arrow ) in the subareolar region that is visualized on the CC view only. This finding is confirmed on a CC spot view ( B ). On US, there is an irregular hypoechoic shadowing mass in the 6 o’clock position ( C ). Biopsy revealed infiltrating ductal carcinoma.


Ultrasonography (US) is often useful in confirming, characterizing, and localizing lesions presenting as AD (see Fig. 9-5 ) and in detecting associated masses that may be mammographically occult. Harmonic tissue imaging improves conspicuity of some lesions presenting as AD. However, the use of compound imaging can eliminate the posterior acoustic shadowing often seen with AD—particularly when due to invasive lobular carcinoma (ILC)—and may make these lesions more difficult to detect ( Fig. 9-6 ). The lack of a US correlate should not eliminate the consideration of biopsy if distortion is present on the mammogram.




FIGURE 9-6


Reduction of Acoustic Shadow with Compound Imaging.

A, Screening detected subtle AD ( circles ) in a woman with a history of lumpectomy. B, On US, there is a corresponding hypoechoic solid mass ( arrow ) with irregular margins, echogenic halo, and posterior acoustic shadowing ( open arrow ). C, With compound imaging, the shadowing is much less obvious, making the lesion less conspicuous. This is most problematic with smaller lesions. Biopsy showed mixed IDC and ILC.


Magnetic resonance imaging (MRI) can be useful in a problem-solving role for occasional cases of questioned AD that are not resolved by diagnostic mammography or US ( Fig. 9-7 ). Keep in mind that even MRI does not have sufficiently high negative predictive value to avoid biopsy of AD that is mammographically suspicious.




FIGURE 9-7


MRI in Evaluation of AD.

A, AD with slight retraction and spiculation were questioned on a screening MLO view ( arrow ). This finding was suspicious on MLO spot ( B ) and mediolateral (ML) ( C ) views, but no abnormalities were seen on the CC view or by US. D, Sagittal postcontrast fat-suppressed MRI shows intense linear enhancement in the area of mammographic suspicion. Diagnosis: high-grade DCIS.


Differential Diagnosis of Architectural Distortion


Malignancies presenting as AD usually represent either infiltrating ductal or infiltrating lobular carcinoma. Ductal carcinoma in situ (DCIS) uncommonly presents with this appearance ( Box 9-1 ).


Aug 25, 2019 | Posted by in BREAST IMAGING | Comments Off on Architectural Distortion
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