Discussion
Evaluating the shape and size of the uterine cavity is helpful for us to
understand and make a correct judgement in our clinical work. For
instance, it has been reported that small uterine cavity size was
beneficial in LNG-IUS users, as they reported less bleeding and pain
compared with women with larger measurements (17) and transverse
dimensions of uterine cavity far less than the length the transverse arm
of IUD resulted in distortion, displacement, and expulsion of the IUD
(18). So, it is especially important and necessary to have a detailed
understanding of the shape of the uterus cavity of the patients. The
present study was original in that we presented data of uterine cavity
measurements of adult women on a 3D coronal view of uterine cavity.
The length and internal os width of uterine cavity do not seem to be
important Clinically, but the importance of the cavity width has been
studied a lot, especially in the field of application of intrauterine
device (18, 19, 20). In our study the measurements of uterine cavity
width (fundal transverse diameter) obtained using 3D-US ranged from 24
mm to 44 mm. This result was consistent with Jia-guang Wang’s results
(19), who measured 8217 transverse diameter of the uterine cavity of the
normal fertile women in Liao-Ning district of China and reported that
normal transverse diameter of the uterine cavity was 23-39mm. In another
research it was reported that the more usual transfundal endometrial
cavity width was 22–34 mm depending on parity (20). According to these
researches, we propose that if the width of the uterine cavity measured
on the coronal plane is less than 22mm it can be judged to be narrow.
One can now use three measurements with cut-offs (lateral indentation
depth ≥ 7 mm, lateral indentation angle ≤ 130° and T-angle ≤ 40°), which
have good accuracy and moderate reliability to confirm the diagnosis
when there is any suspicious of T-shape uterus by subjective assessment
of the uterine cavity on the coronal plane (16). Our research showed the
consistent results with this consensus. In our study an adult female
with normal uterus had lateral indentation depth ≤ 7mm (the maximum was
7mm), lateral indentation angle ≥130° (the minimum was 130° and the mean
was 151°) and cornual angle ≥40° (the minimum was 40° and the mean was
63 °). Our research shows that these three indexes and the thresholds we
currently apply can well distinguish between normal uterus and T-shape
uterus.
So far, we have not found any report on the uterine cavity area on the
coronal section by 3D ultrasound in adult women( only one publication
reported the uterine cavity area21 but used different
calculating method without comparability). We found the uterine cavity
surface area on the coronal section ranged from 3.4 to
10.5cm2, the mean was 5.5cm2, which
was a relatively large range of floats. We speculate that this is due to
many factors, such as the width, length, and angles of the uterus
cavity, can affect the area of uterine cavity. Further multivariate
analysis confirmed this point. We think that measuring the area of
uterine cavity is helpful to diagnose uterine adhesion. For uterine
adhesion, the commonly used diagnostic methods are hysterosalpingography
and hysteroscopy, but they are invasive procedures that cause pain and
have certain complications (22). With the development of ultrasonography
resolution, transvaginal three-dimensional ultrasonography (3D TVS) has
been more frequently used in the diagnosis of IUA (4). 3D ultrasound can
provide a more accurate depiction of adhesions and extent of cavity
damage than hysterosalpingography in patients with suspected Asherman’s
syndrome(23). In another article we have published, we found that using
uterine cavity area 4.23cm2 on the coronal section as
the diagnostic threshold to distinguish uterine adhesion, it could reach
86% sensitivity and 74% specificity, and for every 1
cm2 reduction in the area of the uterine cavity, the
risk of uterine adhesion increased by 18.9%(14). In the present data,
about 10% adult females had uterine cavity areas less than
4cm2 and about 2% less than 3.5cm2.
The mean uterine cavity area was 5.5cm2 and 95%
reference interval was 3-8cm2. Maybe uterine cavity
area less than 3cm2 can be considered “small uterine
cavity”. We believe Data from present study may be useful in screening
cases of uterine adhesion and other disorders that may need further
evaluation.
In conclusion, our research showed that a normal uterine cavity in adult
women of childbearing age had lateral indentation depth ≤7mm, lateral
indentation angle ≥130° and cornual angle ≥40°. The width of the uterine
cavity measured on the coronal plane less than 22mm and the uterine
cavity area less than 3cm2 can be considered smaller
than normal.
Our study is limited by the lack of data concerning gravity and parity
of the subjects in the study. So, we cannot analyze the relationship
between uterine cavity measurements and the number of pregnancies and
parturient. It was reported that nulligravid and nulliparous women have
smaller uterine dimensions than parous women(24,25). But considering
that our purpose of this study is to provide data for clinical work, the
results of this study are still of practical significance.