Clinical Radiology (1994) 49, 808-813

Ultrasound Demonstration of Small Breast Cancers Detected by Mammographic Screening

A. J. POTTERTON, D. J. PEAKMAN and J. R. YOUNG

Breast Screening and Assessment Centre, Queen Elizabeth Hospital, Gateshead, Tyne and Wear

The visibility on ultrasound (US) of 79 screen-detected small breast cancers was studied retrospectively. Overall visibility on US was 61% (48/79). Cancers presenting as micro- calcification alone on mammography were rarely demonstrated (1 of 26 tumours). However, the US visibility of cancers with other mammographic appearances was 88.7% (47/53). The majority of cancers were impalpable but were demonstrated using free-hand ultrasound. All cancers visible on US appeared as bypoechoic masses with three quarters of these showing distal attenuation. US is useful in assessing and localizing small cancers detected by mammographic screening. Potterton, A.J., Peakman, D.J. & Young, J.R. (1994). Clinical Radiology 49, 808-813. Ultrasound Demonstration of Small Breast Cancers Detected by Mammographic Screening

Accepted for Publication 20 June 1994

It is generally accepted that ultrasound (US) has a useful role in breast imaging as a method of further character- izing mammographic abnormalities [1-4]. It is particu- larly useful for differentiating cystic from solid masses [3-5]. Although there is overlap in the US features of benign and malignant lesions, US may offer significant supportive evidence for either diagnosis [6-12]. US has also been advocated for imaging women with mammo- graphically dense breasts, symptomatic women with breast augmentations and young women with a palp- able mass [13,14].

The introduction of population screening mammo- graphy has led to increasing numbers of small breast lesions (10ram or less in diameter) being seen for assessment. Can US demonstrate these small lesions and therefore have a role in their assessment? Few papers in the current literature have addressed this question. Sickles et al. [15] using automated water-path sonography detected only one of 12 turnouts less than 1 cm in size despite prior knowledge of the mammo- graphic findings. Guyer et al. [8] demonstrated 48 small cancers in their study of symptomatic women using direct contact B-scan US, but other workers have failed to achieve similar results. A recent study of mammo- graphically screened women found US unreliable in demonstrating small cancers and unable to detect micro- calcification using hand-held real-time scanning [16].

In this unit free-hand US is used extensively and forms an integral part of the further assessment of screen- detected abnormalities. A mammographically-guided ultrasound technique has also been developed [17]. This technique enables precise correlation of US and mammographic appearances. Ultrasound-guided fine needle aspiration (FNA) and guide-wire insertion is used routinely. This extensive use of US led us to observe that even small lesions were regularly demon- strated. This prompted us to review the US appearances of small breast cancers and to assess the contribution

Correspondence to: Dr A. J. Potterton, Department of Radiology, Royal Victoria Infirmary, Queen Victoria Road, Newcastle upon Tyne NE1 4LP.

of the mammographically-guided technique to their demonstration.

PATIENTS AND METHODS

The patient records and hard copy images of 79 screen-detected cancers measuring 10ram or less on pathological examination were retrospectively analysed. The pathological diagnoses of malignancy were subject to the rigorous quality assurance process required by the National Health Service Breast Screening Programme (NHSBSP) [181.

In each case the mammographic appearance, visibility on US, US features, US techniques used, size, palpability and pathological type of the lesion were recorded. Imaging data combined the opinion of the radiologist assessing the case and independent review of the hard copy images by two radiologists. There was close agree- ment on the findings in 60 cases (76%). In 19 cases where there was some discrepancy, most commonly relating to the classification of the mammographic appearance, all information was reviewed and the appearances defined by consensus. A lesion was considered impalpable if guide-wire localization was required for excision biopsy.

Ultrasound was performed by consultant radiologists experienced in breast screening using a hand-held 7.5MHz linear array probe (Siemens Sonoline). All patients attending for assessment underwent US using a free-hand technique. In some cases, depending on clinical factors, the patients were also examined using the mammographically-guided technique, for further clarification of the US appearances, for fine needle aspiration or guide-wire insertion. There was no selec- tion of patients undergoing US on the basis of the mammographic appearances.

RESULTS

The mammographic appearance and pathological

ULTRASOUND OF SMALL BREAST CANCERS

Table 1 - Mammographic appearance by pathological type

809

Pathology Mammographic appearance

Microcalcification Stellate PDO STE + MIC PDO + MIC MIC + FO

Tota/

DCIS 24 0 0 0 0 2 26 Invasive ductal 2 20 17 3 i 1 44 Invasivetubular 0 7 0 0 0 0 7 Medullary 0 0 1 0 0 1 2

Total 26 27 18 3 1 4 79

STE, Stellate; PDO, poorly-defined opacity; STE + MIC, stellate + microcalcification; PDO + MIC, poorly-defined opacity + microcalcification; MIC + FO, microcalcification + faint opacity; DCIS, ductal carcinoma in situ.

Table 2 - Visibility of tumours on U S and their mammographic appearance

Visibility on ultrasound Mammographic appearances Total

MIC STE PDO STE + MIC PDO + MIC MIC + FO

Yes 1 26 16 3 1 1 48 No 25 1 1 0 0 2 29 Uncertain 0 0 1 0 0 1 2

Total 26 27 18 3 1 4 79

MIC, Microcalcification; STE, stellate; PDO, poorly-defined opacity; STE+MIC, stellate+microca|cification; PDO+MIC, poorly-defined opacity + microcalcification; MIC + FO, microcalcification + faint opacity.

types of the 79 cancers are shown in Table 1. For 71 cancers the mammograph ic appearances were classified simply as either a mass or microcalcification alone. The remainder were manifest as both a mass and microcalci- fication. Of these, three were considered to be predomi- nant ly stellate lesions and one a poorly defined opacity; four cancers were identified as p redominant ly microcal- cification with a faint under lying mass. The 79 cancers ranged in size from 3 to 10 m m on pathological exami- na t ion with a mean size of 8.2 rnm.

Forty-eight of the 79 cancers were visible on US (61%). The mammograph ic appearance of the cancers and their visibility on US are given in Table 2. In two cases the visibility on US was considered uncer ta in when the op in ion of the assessing radiologist and image review were combined; one case presented as a cluster of microcalcification with a faint under ly ing mass, and, a l though an area of a t tenua t ion was identified using the combined (mammographicaUy-guided u l t rasound) technique, this was no t considered reliable and guide- wire localization was performed using stereotaxis. The second uncer ta in case was a poorly defined opacity on m a m m o g r a p h y and a possible hypoechoic mass was described at assessment using the combined technique. However, this was no t identified on review of the images, a l though guide-wire localization was successfully per- formed using combined m a m m o g r a p h y and US. These two cancers have been considered no t visible in all the following data analyses.

C a n c e r s N o t V i s i b l e o n U S

Thir ty-one cancers were not demonst ra ted on US including the two 'uncer ta in ' cases already described. This group ranged in size from 3 to 10 ram, with a mean size of 7 .5mm. Twenty-five presented as microcalcifi-

Fig. 1 - Magnified compression view of a stellate mass representing a 9 mm invasive ductal carcinoma (arrow). This tumour was not visible on US.

810 CLINICAL RADIOLOGY

Table 3 - Size, palpability and pathological type of small tumours not visualized on U S

Table 5 - Ultrasound techniques used

Mammographie Size (ram) Palpable Pathological Comments appearance type

STE 9 No Invasive Large breast ductal

PDO 7 Yes Invas ive Retro-areolar ductal lesion

MIC + FO 10 No Invasive ? attenuation ductal on US

MIC + FO 7 No DCIS MIC + FO 7 No DCIS PDO 7 No Invasive ? hypoechoic

ductal mass on US

Palpability Ultrasound techniques used

Freehand only Combined only Both

STE, Stellate; PDO, poorly-defined opacity; MIC + 130, microcalci- fication + faint opacity; DCIS, ductal carcinoma in situ; Invasive ductal, invasive ductal carcinoma.

cation alone on mammography while six presented as a mass or more complex lesion. The two cases where visibility was considered 'uncertain' were in the latter group. One stellate mass was not demonstrated on US, but this 9 mm invasive ductal carcinoma lay in a large breast (Fig. 1). A further retro-areolar, poorly defined opacity on mammography was not demonstrated on US and proved to be a 7 mm invasive ductal carcinoma. Two more cancers were predominant microcalcification with an associated faint soft tissue density. Table 3 sum- marizes the features of the six cancers not demonstrated on US which had a mammographic appearance other than microcalcification alone.

C a n c e r s V i s i b l e o n U S

Forty-eight cancers were clearly demonstrated on US. These comprised 26 stellate lesions, 16 poorly defined opacities, three stellate lesions with microcalcification, one poorly defined opacity with microcalcification, one area of microcalcification with a faint associated mass and one area of microcalcification alone. The cancers visible on US had a mean size of 8.7ram (range 5- 10mm). Of the 26 cancers presenting solely as micro- calcification on mammography, only one was visible at assessment with US. This tumour was seen as an irregular area of attenuation using free-hand US and proved to be an 8 mm invasive ductal carcinoma.

Of the 48 cancers visualized on US, 34 (71%) were impalpable at clinical assessment. Table 4 compares palpability with visibility on US. It was not possible to define the palpability of one cancer visible on US as this lay in a breast containing several abnormalities. The impalpable cancers were demonstrated with both free- hand and mammographically-guided US in the majority

Palpable 12 0 1 Impalpable 8 2 24 Uncertain 1 0 0

of cases (24/34, 71%), providing confirmatory evidence that the US findings corresponded to the mammographic lesion. Two impalpable cancers were only demonstrated using the mammographically-guided US technique (Table 5). Figure 2 illustrates one of these cancers.

Appearances of the cancers on US were remarkably consistent. All were hypoechoic compared to the normal glandular tissue of the breast. The ultrasound beam was attenuated by 36 of the 48 cancers visualized (75%). The majority appeared ill-defined on US, with only six (13 %) having a well defined margin. Figure 3 shows the typical appearances.

Mammographically-guided US was used for localizing cancers for fine needle aspiration (FNA) and guide-wire insertion. Twenty impalpable cancers underwent FNA using mammographically-guided US; adequate cytology specimens were obtained in 75% and there was just one false negative cytology result. Ten of the cancers visible on US did not require localization for FNA as they were clinically palpable. The remaining 18 cancers visible on US did not undergo FNA. This reflects the lack of a cytology service early in the screening programme when suspicious findings on mammography and US were referred directly for excision biopsy. Guide-wire inser- tion was performed using mammographically-guided US in 20 cases.

Table 4 - Tumour palpability and visibility on US

Palpability Visibility on US Totals

Visible Not visible Uncertain

Palpable 13 1 0 14 Impalpable 34 28 2 64 Uncertain 1 0 0 1

Fig. 2 - A 7 mm invasive ductal carcinoma demonstrated by mammo- graphically-guided US. The size of the lesion and the depth below the skin surface are measured prior to fine needle aspiration.

ULTRASOUND OF SMALL BREAST CANCERS 811

(a)

(a)

@

Fig. 3 - (a) Mammograpl-fic appearance of a 10mm invasive ductal carcinoma. (b) The same tumour seen on US as a hypoechoic, ill- defined mass with distal attenuation.

D I S C U S S I O N

This study presents the US features of 79 clinically occult small breast cancers, 10mm or less in size,

(b)

Fig. 4 - (a) Free-hand US appearance of an impalpable 9 mm invasive tubular carcinoma. (b) A 6 mm medullary carcinoma also demonstrated using free-hand US and showing distal attenuation.

detected in a population breast screening programme. Overall visibility of the cancers on US was 61%. In common with previous studies, cancers presenting as microcalcification alone were unreliably demonstrated on US in this series. When cancers presenting as micro- calcification alone are excluded, the visibility of small cancers on US increased to 89% (47/53 lesions). On reviewing the six cancers not visualized from this group of 53, there were only two dominant masses on mammo- graphy. Two further lesions could not be confidently demonstrated on US, although an abnormal area was seen in both cases. Finally, two cancers presenting as microcalcification with only a faint associated mass were not seen on US. This compares favourably with the results published by Pamilo et al. [16], who failed to

812 CLINICAL RADIOLOGY

(a)

demonstrate 12 of a total o f 38 cancers 10ram or less in size, seven of these 12 being masses on mammography.

Guyer et al. [8] reported success in imaging small cancers, but the study consisted of symptomatic women presenting to the breast clinic with a palpable mass. The majority of cancers in our study were impalp- able but, with knowledge of the mammographic appear- ance, the majority of malignant masses were demon- strated on US.

A number of factors may contribute to this success in demonstrating small cancers on US. Technical improve- ments in US equipment and the use of higher frequency probes have led to improved contrast and spatial resolu- tion. In this centre, the development of the mammo- graphically-guided US technique has increased radiologists' confidence in interpreting US appearances and has encouraged use of US in all patients at assessment.

It is accepted that there is overlap in the features of benign and malignant lesions on US and that US appearances should always be interpreted together with mammographic and clinical features. Moreover, this study excludes small benign breast lesions and therefore contains no false positive diagnoses of malignancy. Nevertheless, the consistent appearance of cancers in this study as hypoechoic, ill-defined and attenuating lesions provides valuable information for the further assessment of mammographical ly indeterminate masses and for the use of US in the assessment of the mammo- graphically dense breast. Seventy-five per cent of the small cancers visualized exhibited distal attenuation of the US beam (Figs 4 and 5). This figure of 75% falls within the range described by other authors for malig- nant tumours of all sizes. Guyer and Dewbury found distal attenuation to be a feature of 72% of cancers in a very large series [19] and 93% of the cancers evaluated by Harper et al. attenuated the ultrasound beam [6].

There are insufficient numbers of more unusual patho- logical types of breast cancers in the series to allow separate analysis of their US appearance. However, the two medullary carcinomas were poorly defined on both mammography and US. Neither medullary carcinoma exhibited the enhanced through-transmission described in the six tumours examined with US by Meyer et al. [12].

(b)

Fig. 5 - (a) Screening mammogram demonstrating a small opacity. (b) The same lesion seen on US as a hypoechoic mass with distal attenuation. This was one of the smallest cancers in the group visible on US but has a prominent effect on through transmission. Patho- logical examination revealed a 5 mm invasive ductal carcinoma.

C O N C L U S I O N S

US can demonstrate the majority of small cancers presenting as a mass lesion on mammography, with 89% being visualized in this series. Cancers presenting as microcalcification alone are rarely demonstrable using US. The mammographically-guided US technique is not a major factor in the demonstration of small cancers, the vast majority being seen using free-hand US. These results should encourage the use of US in the assessment of mammographic abnormalities of all sizes. Knowledge of the consistent appearance of small cancers on US may influence decisions to biopsy small lesions demonstrating features of malignancy on US but producing a negative result on FNA. US can be used to locate small lesions for F N A and for guide-wire insertion, this being a major role for mammographically-guided US in this centre.

Acknowledgements. The authors thank the Women's Cancer Detec- tion Society for financial assistance and Mr W. Oakes for help with illustrations.

ULTRASOUND OF SMALL BREAST CANCERS 813

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