Abstract
Introduction
Pure mucinous breast carcinomas (PMBC) are commonly lobulated, therefore appear relatively benign compared with the imaging features of invasive ductal carcinoma. The aim of this study was to determine mammographic and sonographic patterns of PMBC, in particular features that may result in misdiagnosis.
Methods
Retrospective review of available mammography and sonography in 90 patients diagnosed with PMBC within the Monash BreastScreen service, 1993–2011 inclusive.
Results
PMBC commonly have indistinct or lobulated mammographic and sonographic margins. Mammographic calcifications are absent in the majority (82%). On ultrasound, these neoplasms are commonly isoechoic (51%) with normal posterior acoustic appearances (80%). However, most (77%) of these lesions have suspicious or definite imaging features of malignancy.
Conclusion
PMBC are commonly lobulated with homogeneous, isoechoic and normal posterior acoustic sonographic appearances but rarely have benign imaging features.
Figure 4. Typical imaging appearances of pure mucinous
breast carcinomas. Contact (a) mediolateral oblique (MLO) and (b) craniocaudal
(CC) and spot (c) MLO and (d) CC mammographic views of the right breast
demonstrating a lobulated mass with microlobulations (arrows). (e) Ultrasound
demonstrates an isoechoic lobulated lesion with normal acoustic transmission.
Figure 6. Imaging of pure mucinous breast carcinomas (PMBC)
demonstrating interval growth. Contact mediolateral (MLO) mammography taken 2
years apart demonstrating a lobulated mass (arrows), which is difficult to
appreciate on (a) initial examination but is more conspicuous on (b) later
imaging. Further imaging work-up demonstrates typical appearance of PMBC on
spot MLO (c) mammography and (d) sonography.
Discussion
Published literature
regarding the imaging features of mucinous breast carcinomas are limited as it
is a relatively uncommon malignancy. This Australian study is the largest
contiguous series of screen-detected PMBC in an asymptomatic population to
date.
PMBC are commonly lobulated;[6, 9, 14, 15]
however, the lesions in our series often demonstrated additional mammographic
features that raise the suspicion for malignancy. These include multiple small
lobulations (≥4), incompletely smooth margins or interval growth particularly
in a postmenopausal population. None of the lesions in this large series
presented mammographically with completely smooth, sharply defined margins
typical of a simple breast cyst. Furthermore, none of the PMBC detected on
mammography in women under 60 years of age, at their first screening study,
could have been mistaken for benign lesions. Unlike IDC, spiculations are an
uncommon feature in PMBC.[4, 7]
There have been varying
reports in previous publications regarding the presence of calcifications,
ranging from rare[1, 4, 9, 15]
up to 62.5%,[9]
and are seen in the ductal rather than mucinous component of the tumour.[1]
We found mammographic suspicious or indeterminate calcifications in only 18% of
tumours, with associated DCIS found on pathology in one-third of these
patients, a similar rate to Cardenosa et al.[4]
Although 25% of tumours in this study could be identified retrospectively on an earlier mammogram, which is lower than the 38% described by Dhillon et al.,[16] delay in diagnosis did not affect prognosis, with no significant differences in tumour size (12.5 mm compared with 15 mm) or axillary nodal metastasis (5% compared with 9%). Furthermore, the imaging appearances in this subset of lesions were similar to the majority of PMBC diagnosed as a new lesion.
In a subset of younger women
(under 60 years) with no prior imaging, mucinous carcinomas were more likely to
be detected on the basis of DCIS on screening mammography, with lobulated
lesions being less common than in an older population. It has been suggested
that the relative lack of calcification makes differentiation between mucinous
carcinomas from benign lesions difficult; however, suspicious or definite
features of malignancy were identified in the majority of lesions, concordant
with previous studies.[6, 14]
Although 25% of tumours in this study could be identified retrospectively on an earlier mammogram, which is lower than the 38% described by Dhillon et al.,[16] delay in diagnosis did not affect prognosis, with no significant differences in tumour size (12.5 mm compared with 15 mm) or axillary nodal metastasis (5% compared with 9%). Furthermore, the imaging appearances in this subset of lesions were similar to the majority of PMBC diagnosed as a new lesion.
In this large series of
asymptomatic women with an average tumour size of 15 mm, 75% of lesions were
identified as a discrete mass on ultrasound. Non-palpable PMBC are less likely
to be seen sonographically,[6]
with only 39% identified in a recent screening study.[16]
Although a solid mass is seen on ultrasound in majority of lesions (92%),[6]
it has been suggested that cystic components in a mass in an older patient
should raise the suspicion of mucinous carcinoma.[15]
Spiculations and posterior acoustic shadowing, typical for IDC, are rarely
demonstrated. Enhanced sound transmission has been described in 71% mucinous
carcinomas,[11]
and in particular in 100% of those >1.5 cm.[11]
This is an uncommon finding in our study, attributed to advances in sonographic
equipment enabling compounding, which diminishes acoustic transmission
characteristics by steering the beam in at multiple different angles.[11]
Identification of mucinous carcinomas on ultrasound may be difficult as these
lesions are frequently homogeneous, isoechoic to normal breast tissue[7]
with normal posterior acoustic appearances and indistinct contours.
