Artifacts and Pitfalls in Sonographic Imaging of the Breast

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1 Downloaded from by on 02/26/18 from IP address Copyright RRS. For personal use only; all rights reserved rtifacts and Pitfalls in Sonographic Imaging of the reast Fig. 1. Cartilaginous rib mimics solid breast mass on sonography of normal breast in 46-year-old woman., Sonogram obtained transverse to rib reveals apparent oval, circumscribed, markedly hypoechoic mass (M) with posterior acoustic shadowing. Position of this finding posterior to pectoralis muscle (arrows) confirms actual identity as rib., Sonogram obtained after transducer was rotated perpendicular to its location in shows long axis of structure (r), confirming its identity as rib. S onography is an increasingly important tool to the breast imager both for evaluation of breast lesions and for guidance of percutaneous interventions. lthough sonography has historically been used for differentiating cystic from solid breast masses, there has been growing interest in using sonography to differentiate benign from malignant solid masses [1, 2] and for screening the breasts of women with dense tissue [3]. Sonographic image quality has improved dramatically since its early use for breast imaging during the 1970s because of advances in technology such as the use of all-digital high-frequency transducers of up to 13 MHz, color and power Doppler imaging, and harmonic imaging. Despite these advances, the potential remains for encountering artifacts or unexpected, spurious findings during breast sonography. The artifacts and pitfalls associated with breast sonography are important to recognize because they may result in the failure to recognize a breast cancer or prompt unnecessary biopsy of a benign finding. Common sources of error include the failure to recognize the sonographic appearance of normal breast anatomy, the improper setting of instrumentation controls, peculiarities of sonography physics, and the presence of iatrogenic air and foreign bodies in the breast. To minimize confusion and misdiagnosis, we Pictorial Essay Jay. aker 1, Mary Scott Soo, Eric L. Rosen review and illustrate characteristic artifacts and pitfalls encountered during sonographic imaging of the breast. Normal natomy Rib Novice breast imagers may mistake a rib for a solid breast mass. In cross section, the cartilaginous portion of a rib has the appearance of a suspicious breast mass (Fig. 1). This portion of rib can be recognized by its position posterior to pectoralis muscle and, when imaged longitudinally, by its elongated shape (Fig. 1). Received ugust 22, 2000; accepted after revision September 19, ll authors: Department of Radiology, Division of reast Imaging, ox 3808, Duke University Medical Center, Durham, NC ddress correspondence to J.. aker. JR 2001;176: X/01/ merican Roentgen Ray Society JR:176, May

2 aker et al. Downloaded from by on 02/26/18 from IP address Copyright RRS. For personal use only; all rights reserved Nipple lthough the normal nipple is easily recognized at real-time sonography, on static images an inverted nipple may project beneath the skin of the areola giving the false appearance of a markedly hypoechoic, solid parenchymal breast mass with extensive acoustic attenuation (Fig. 2). wareness of the precise location of the transducer relative to the nipple is sufficient to identify this normal structure. Sonographic imaging of submamillary tissue should be performed from an angled or coronal projection because of the intense posterior acoustic shadow produced by the whirled smooth muscle bundles of the nipple. Fig. 2. Inverted nipple mimics suspicious solid breast mass at sonography of 69-year-old woman. Sonogram shows that inverted nipple projects beneath skin surface with appearance of ill-defined markedly hypoechoic mass. Striking posterior acoustic attenuation is present because of dense connective tissue and smooth muscle bundles comprising nipple. Fat Lobule The normal breast is composed of numerous fat lobules mixed with dense fibroglandular tissue. t sonography, cross section of a fat lobule can be mistaken for a solid mass that is isoechoic to surrounding adipose tissue (Figs. 3 and 4). The normal appearance of the structure can be revealed by rotating the transducer until the apparent mass is observed merging with surrounding normal fat tissue (Fig. 3). On occasion, a small lobule of normal fat tissue may be completely isolated from surrounding adipose tissue by echogenic fibroglandular tissue (Fig. 4). This configuration can be particularly confusing and may infrequently require biopsy to confirm its benign etiology. Lactiferous Duct etween 15 and 20 lactiferous ducts converge at the nipple of the normal breast. Normal ducts measure up to 3 mm in diameter, whereas ectatic ducts can dilate significantly. Even with the excellent resolution and contrast available with modern high-resolution sonography equipment, normal-caliber ducts imaged in cross section may mimic a small cyst. To avoid misidentification of tubular or elongated structures, imaging should always be performed in both radial and antiradial planes. coustic Shadowing lthough invasive breast cancer is usually identified at sonography as a visible mass, a focus of acoustic attenuation or shadowing without a definable mass may be the only feature identified (Fig. 5). This finding is an important one to recognize and distinguish from several other causes of isolated acoustic shadowing. coustic shadowing without a mass may be seen as an incidental finding in the normal breast. column of shadowing often identifies Cooper s suspensory ligament normal suspensory fibrous strands of the breast [4]. Shadowing due to Cooper s suspensory ligament is often faint and narrow but can be markedly hypoechoic and wide enough to simulate a malignant tumor (Fig. 6). When Cooper s suspensory ligament are the cause, the shadowing often resolves with mild increased pressure on the transducer or small changes in the angle of insonation. Poor contact between the transducer and skin can also cause acoustic shadowing without an underlying mass (Fig. 7). Short echogenic parallel lines at fixed intervals starting at the skin and leading to the acoustic shadowing are pathognomonic for poor skin contact. Postsurgical scar may also cause substantial acoustic shadowing without an underlying mass (Fig. 8). Significant shadowing at the site of prior lumpectomy may be impossible to differentiate from residual or recurrent tumor, limiting the usefulness of sonography in this setting. Sonography Physics and Instrumentation Edge Shadowing lthough acoustic shadowing identified behind a mass is suggestive of malignancy [5], a thin line of shadowing seen only be- Fig. 3. Normal fat lobule mimics isoechoic solid mass on breast sonogram of 44-year-old woman., Sonogram obtained in radial plane reveals circumscribed isoechoic mass (m) separated from surrounding adipose tissue., Sonogram obtained after transducer was rotated 90 into antiradial plane shows mass apparent in merged with surrounding fat tissue, confirming identity of structure as fat lobule JR:176, May 2001

3 Sonographic Imaging of the reast Downloaded from by on 02/26/18 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 4. Isolated fat lobule that was mistaken for solid mass on breast sonogram of 36-year-old woman. Radial projection reveals apparent mass is isoechoic to nearby fat tissue. pparent mass failed to merge with surrounding fat despite rotating transducer. Sonographically guided percutaneous needle core biopsy confirmed pseudomass as normal breast tissue. Subsequent follow-up examinations showed no change over 35 months. Fig year-old woman with invasive breast carcinoma. bnormality is denoted at sonography by intense acoustic attenuation without evident mass. Diagnosis was confirmed at surgery. Fig. 6. coustic shadowing from Cooper s suspensory ligament mimics breast neoplasm at sonography of normal breast in 43-year-old woman., reast sonogram reveals focus of intense acoustic attenuation without mass lesion. coustic shadowing originates from Cooper s ligament between normal fat lobules., Sonogram obtained after mild additional pressure was applied to sonography transducer shows acoustic attenuation has resolved. Cooper s ligament that is causing attenuation is visible (arrows). hind the peripheral edge of a mass should not be mistaken for a suspicious feature. This edge shadowing caused by the complex combination of absorption and refraction along the mass border [6] can be seen with cysts and benign or malignant solid masses and has no diagnostic significance. Reverberation rtifact Parallel echogenic lines caused by reflection of the ultrasound beam back and forth between the transducer and tissue interface can give the artifactual appearance of solid or complex material along the nondependent wall of a cyst (Fig. 9). When characteristic, this artifact is easily recognized. Less characteristic reverberation can be confirmed by changing the angle of insonation. Reverberation is always perpendicular to the direction of the ultrasound beam and will appear to shift position within the cyst as the angle of insonation is changed. 4 Gray-Scale Gain The gray-scale gain setting determines the amplitude of the returning sonographic signal. If the gain is set inappropriately high, spurious echoes may be displayed in a simple cyst resulting in the appearance of a complex cyst or solid mass (Fig. 10). The surrounding tissue also appears inappropriately echogenic. The appropriate gray-scale gain setting measured in decibels varies depending on the tissue type and sonography equipment. This parameter should be set so that fluid in a sonography cyst phantom appears black, whereas fat lobules in the breast parenchyma vary from dark gray to light gray. Dynamic Range Dynamic range settings determine the range of echo amplitudes detected by the sonography system; echo amplitudes are displayed using the available number of gray levels of the video monitor [7]. Dynamic range settings directly affect contrast resolution and function similarly to the window portion of window level settings on CT scans. Setting the dynamic range too low increases image contrast but may cause the low-level echoes in a solid mass to be displayed as black pixels so that the appearance of the mass mimics that of a simple cyst (Fig. 11). Setting the dynamic range too high re- 5 JR:176, May

4 aker et al. Downloaded from by on 02/26/18 from IP address Copyright RRS. For personal use only; all rights reserved Fig year-old woman with benign breast scar. Sonogram reveals extensive acoustic attenuation (arrows) at site of prior lumpectomy, indicating scar formation. sults in an image with little contrast, which hinders differentiation of fat lobules from subtle masses. Focal Zone The width of the ultrasound beam is narrowest and resolution greatest in a narrow range the focal zone that can be set to a particular depth by the user. The focal zone should be set to match the depth of the object being imaged. ecause resolution and beam width deteriorate outside the focal zone, imaging with an inappropriately positioned focal zone may cause a subtle mass to be less visible, sharp edges to appear ill-defined, and an anechoic simple cyst to appear to have internal echoes due to increased partial volume effects (Fig. 12). ir and Foreign odies Foreign odies Foreign bodies in the breast may have a variety of appearances at breast sonography. Solid foreign bodies such as a retained Dacron (DuPont, Wilmington, DE) cuff from a central Fig. 7. Poor transducer skin contact mimics suspicious acoustic shadowing at sonography in normal breast of 39-year-old woman., Sonogram reveals marked acoustic shadowing (sh) that appears similar to invasive carcinomas shown in Figure 5. Parallel echogenic lines between skin and superficial aspect of shadowing (arrows) indicate poor contact between transducer and skin as cause of apparent lesion., Sonogram obtained after additional acoustic gel was applied to skin reveals that apparent lesion and parallel echogenic lines have resolved. Fig. 9. Reverberation artifact in simple cyst on sonography of normal breast in 63-year-old woman., Sonogram reveals curvilinear echogenic lines parallel anterior wall of simple cyst (arrows). Lines result from multiple reflections of acoustic beam caused by impedance mismatch between breast tissue and cyst. Simple cyst may be mistaken for complex cyst because of apparent internal echoes., Sonogram obtained after angle of insonation was changed confirms finding is reverberation artifact. Curvilinear lines are now absent at position (arrowhead) where they are visible in. venous catheter may look like a solid mass with remarkably intense and sharp posterior acoustic shadowing (Fig. 13). The presence of a foreign body at sonography is easily confirmed by correlation with mammograms. small amount of extracapsular silicone due to implant rupture may initially be mistaken for a cyst or hypoechoic solid mass with posterior acoustic enhancement (Fig. 14). However, recognition of short echogenic lines paralleling the back wall of the structure allow a confident diagnosis of extracapsular silicone and, therefore, implant rupture JR:176, May 2001

5 Sonographic Imaging of the reast Downloaded from by on 02/26/18 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 10. rtifactual echoes in simple cyst caused by improper setting of gray-scale gain on sonography of normal breast in 38-year-old woman., Sonogram shows breast cyst appears complex with extensive internal echoes. Surrounding normal tissue is inappropriately echogenic. Gray-scale gain setting is 42 db., Sonographic image of same cyst as that shown in obtained with gray-scale gain set at 14 db shows that, with appropriate gain setting, cyst is anechoic with well-circumscribed margins and increased throughtransmission. Surrounding normal tissue varies from light to dark gray. Fig. 11. Fibroadenoma mimics simple cyst as result of inappropriate setting of dynamic range in 41-yearold woman., Sonogram obtained with dynamic range set at 40 db shows solid breast mass. Mass appears anechoic with questionable increased posterior acoustic sound transmission and appears similar to simple cyst. Surrounding tissue is conspicuously high contrast., Sonogram obtained with dynamic range set at 55 db of same breast mass as shown in clearly reveals solid nature of mass. Surrounding tissue has appropriate contrast. Fig. 12. Sonograms of simple breast cyst in 59-year-old woman were degraded by inappropriate placement of focal zone., Sonogram obtained with focal zone inappropriately placed at bottom of field of view (arrow) reveals small ill-defined hypoechoic mass with normal through-transmission suggestive of small complex cyst or, less likely, solid mass. Definite echoes are visible within mass., Sonogram obtained with appropriate positioning of focal zone at depth of mass (arrow) reveals characteristic simple cyst. Mass is completely anechoic with sharp margins and increased through-transmission of acoustic beam. ir ir introduced into the breast parenchyma during percutaneous needle procedures can cause several pitfalls during sonography. Considerable air may be introduced along the path of the needle, particularly during sonographically guided needle core biopsy. This air may substantially obscure visualization of the needle. In fact, the needle may be so severely obscured that it must be withdrawn and reinserted at a second site away from the obscuring air to allow simultaneous visualization of the mass and needle during tissue sampling. The introduction of air can be limited by purging air from all syringes and needles before local anesthesia is administered. ir persisting along a biopsy tract after removal of the biopsy needle may look like a thin JR:176, May

6 aker et al. Downloaded from by on 02/26/18 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 13. Central venous catheter Dacron (DuPont, Wilmington, DE) retention cuff mimics solid breast mass at sonography of 59-year-old woman., Sonogram shows focus of intense posterior acoustic attenuation similar to that of invasive carcinoma shown in Figure 5. Echogenic focus anterior to acoustic shadow (arrows) represents fibrosis adjacent to cuff. Hard palpable mass corresponded to sonographic abnormality., Mediolateral oblique mammogram confirms that sonographic and palpable abnormality correspond to retained Dacron retention cuff overlying pectoralis muscle (arrow). echogenic line. This echogenic line may closely mimic the appearance of a needle remaining in the mass (Fig. 15). When the needle is reinserted for subsequent sampling, it may be difficult to differentiate a prior needle tract from an actual needle. Rapid back-and-forth motion of the needle tip may allow differentiation of the two. Conclusion To avoid overlooking signs of breast cancer while preventing unnecessary biopsies, it Fig. 15. ir tract mimics in situ needle during sonographically guided needle core breast biopsy. Sonographic image shows needle traversing breast mass (M) has appearance of linear echogenic focus (arrows). However, needle was removed from breast before image was obtained as indicated by needle out notation at bottom of image. Echogenic line results from residual air in needle tract. Fig. 14. Extracapsular silicone deposit in 44-year-old woman. Sonogram reveals small solid circumscribed mass near silicone breast implant. Curvilinear echogenic lines paralleling posterior margin (arrow) confirm identity as extracapsular silicone. is important to recognize the artifacts and pitfalls commonly encountered at breast sonography. Knowledge of normal breast anatomy, an understanding of the appropriate setting of instrument controls, and the performance of routine imaging in two orthogonal planes are essential for accurate interpretation of breast sonograms. ecause the true cause of pseudolesions is often more evident at real-time imaging than on static films, it is often important for the breast imaging radiologist to actually perform the examination in real time or, at least, to recognize the sometimes subtle clues that identify a finding as an artifact. Finally, evaluating available mammograms in association with the sonographic images is essential to accurate breast sonography. References 1. Stavros T, Thickman D, Rapp CL, et al. Solid breast nodules: use of sonography to distinguish between benign and malignant lesions. Radiology 1995;196: Rahbar G, Sie C, Hansen GC, et al. enign versus malignant solid breast masses: US differentiation. Radiology 1999;213: Kohl TM, Lichy J, Newhouse JH. Occult cancer in women with dense breasts: detection with screening US diagnostic yield and tumor characteristics. Radiology 1998;207: Lanfranchi ME. reast ultrasound. Madrid: Marban ooks, 2000: Kopans D. reast imaging, 2nd ed. Philadelphia: Lippincott-Raven, 1998: Hedrick WR, Hykes DL, Starchman DE. Ultrasound physics and instrumentation, 3rd ed. St. Louis: Mosby, 1995: Hedrick WR, Hykes DL, Starchman DE. Ultrasound physics and instrumentation, 3rd ed. St. Louis: Mosby, 1995: JR:176, May 2001