Discussion:
US-guided CNB of breast masses has been performed with automated needle devices using 14-gauge cutting needles to ensure that the specimens have a sufficient size to yield a reliable pathological diagnosis,
and it has been assumed that smaller-gauge cutting needles would yield lower quality and possibly inadequate samples.
Development of US-guided CNB
In 1990,
Parker et al performed a study of stereotactically guided CNB with 18-gauge,
16-gauge,
and 14-gauge automated cutting needles (Biopty gun,
Bard) and concluded that the 14-gauge needles yielded better quality and larger cores with a higher rate of agreement with surgical-pathological results than did 18-gauge and 16-gauge needles [3]. However,
this study did not indicate a level of statistical significance. In 1993,
Parker et al reported their preliminary experience with US-guided CNB using 14-gauge automated cutting needles (Biopty gun) and concluded that US-guided CNB has high diagnostic accuracy and can replace surgical biopsy [4].
However,
the authors did not compare the performance of 14-gauge needles with that of smaller-gauge cutting needles,
presumably assuming that what worked best for stereotactically guided CNB would also work best for US-guided CNB.
In 1995,
an in vitro study performed by pathologists on 57 surgically excised masses measuring ≥1 cm without imaging guidance and using a short-throw (12-mm) biopsy device (Biopty gun) concluded that 14-gauge cutting needles provided a more accurate diagnosis of malignancy than 16-gauge and 18-gauge needles. In that study,
the biopsies were guided only by palpation of the excised specimen.
Surprisingly,
smaller-gauge needles,
which were less accurate in the diagnosis of malignancy,
performed well with benign lesions [5]. In 1998,
Helbich et al reported that in a series of 66 radiologist-performed stereotactically guided CNBs of masses,
architectural distortions,
and microcalcifications,
14-gauge cutting needles performed better than 16-gauge and 18-gauge needles. However,
the difference was statistically significant only for lesions associated with microcalcifications [6]. It is important to note that neither of the latter two studies was performed under US guidance.
In 2001,
Margolin et al reported their experience with US-guided CNB done with 18-gauge,
16-gauge,
and 14-gauge cutting needles and a 22-mm-excursion automated device (Pro-Mag [Manan Medical Products,
Wheeling,
IL]).
They did not report a difference in performance depending on the needle’s gauge,
although the performances of the three types of cutting needles were not compared [7].
In 2007,
Uematsu et al reported that US-guided CNB using 18-gauge needles (Magnum,
Bard) with 22-mm or 15-mm throws and often a single pass was an accurate biopsy technique for US-visible discrete masses,
yielding a sensitivity in the diagnosis of cancer of 96% [8]. In 2013,
Lai et al reported that,
compared to surgical-pathology results,
there was no statistically significant difference in sensitivity and specificity of US-guided CNBs performed with 14-gauge or 16-gauge needles,
although 14-gauge CNBs showed better overall accuracy and lower false-negative rates [9].
In 2014,
Zhou et al reported that US-guided CNBs done with 16-gauge and 18-gauge needles (with 15- or 22-mm throw) for breast masses and non-mass lesions >10 mm yielded similar false-negative rates and rates of agreement with surgical-pathology findings [10].
Why use 18-gauge instead of 14-gauge cutting needles for US-guided CNB of breast masses?
Stereotactically guided needle biopsies are aimed at clusters of microcalcifications and areas of architectural distortions.
The expected pathological diagnoses include lesions ranging from various atypias and other high-risk lesions to invasive cancer,
with most lesions being DCIS.
These diagnoses require a large specimen,
hence the replacement of 14-gauge CNB with 11-gauge and now 9-gauge vacuum-assisted biopsy when stereotactic guidance is used.
In contrast,
US-guided biopsies are aimed at discrete solid masses with the goal of differentiating benign lesions from invasive cancers.
The diagnosis of an invasive cancer does not require the largest possible volume of the lesion,
but instead it requires a specimen (core) that is representative of the lesion,
i.e.,
that is known with certainty to come from within the lesion.
US guidance with verification of the position of the needle inside the target in two orthogonal planes,
as initially described [1],
provides that certainty.
The major advantage of the 18-gauge cutting needle over the 14-gauge one is that it is much sharper and penetrates more easily through firm,
dense breast tissue.
Another advantage is that there is no need to make a skin incision.
Although our study did not evaluate rates of complications,
it has also been our observation over the past 2 decades that 18-gauge cutting needles cause fewer traumatic complications than do larger-gauge cutting needles.
Conclusion:
Our study showed no statistically significant differences in specimen adequacy or diagnostic accuracy between 14-gauge,
16-gauge,
and 18-gauge automated cutting needles in US-guided CNB of breast masses.
Eighteen-gauge cutting needles have several notable advantages over 14-gauge needles and can therefore be used routinely for US-guided CNB of breast masses.