The assessment of normal female urethral vascularity with Color Doppler endovaginal ultrasonography: preliminary report
Original article by
ANDRZEJ PAWEL WIECZOREK - MAGDALENA MARIA WOZNIAK
- ALEKSANDRA STANKIEWICZ (1)
MICHAL BOGUSIEWICZ - TOMASZ RECHBERGER (2) - GIULIO ANIELLO SANTORO (3) - JAKOB SCHOLBACH (4)
(1) Department of Pediatric Radiology, Children's Hospital, Skubiszewski Medical University of Lublin, ul. Chodzki 2, Lublin, Poland
(2) 2nd Department of Gynecology, Skubiszewski Medical University of Lublin, ul. Jaczewskiego 8, Lublin, Poland
(3) 3rd Division of Surgery, Pelvic Floor Unit, Regional Hospital, Treviso, Italy
(4) Chameleon Software, Kunzenweg 2b, Freiburg, Germany
Abstract: In this study we compared vascular intensity in female urethra in its midsagittal plane at 3 predefined parts (intramural, midurethral
and distal) and in its axial plane at the level of midurethra (rhabdosphincter vs. the inner part of urethra) in premenopausal, nulliparous,
continent patients. Eighteen nulliparous patients, mean age 32.67 years (range 18-53 years) with no pelvic floor disorders and no history of
incontinence were enrolled in the study. In the first part of their menstrual cycle, the subjects underwent endovaginal ultrasound with the use
of a biplane, high frequency (5-12 MHz) transducer. Vascular pattern of the urethra was obtained in color-doppler mode using both, the linear
and transverse arrays of the transducer and the data were registered as video files in a stable position of the probe. For each patient two video
acquisitions were taken, one in midsagittal plane, second in axial plane at the level of midurethra. For the quantitative assessment of the blood
flow, a PixelFlux software was applied. The comparison of intensity among three levels of vascularity observed in sagittal section as well
as the comparison of vascular intensity between outer (rhabdosphincter) and inner (circular smooth muscle, longitudinal smooth muscle and
submucosa) rings of the urethra were performed. The results of the analysis show that the midurethra has got the largest intensity of vascularity,
which is statistically significantly better that the latter part of urethra (intramural and distal parts). Statistical analysis showed the differences
of vascular intensity between intramural part of urethra and midurethra (0.47, p < 0.05) and between midurethra and distal urethra (0.43, p <
0.05). No statistically significant differences were found between the vascular intensity of in outer and inner part of the midurethra; but on
contrary the values were very similar (0.76, p < 0.05). High frequency transvaginal ultrasound with the use of Color Doppler mode is a very
reliable method enabling visualization of urethral vessels distribution. The data obtained from the scans may be further analyzed with the use
of dedicated software in order to define the intensity of urethral vascularity and different anatomical areas, which are responsible for various
functionalities.
Key Words: Urethral vascularization; Color-doppler; Endovaginal ultrasound.
INTRODUCTION
The female urethra has very complex anatomy and function
which are still not fully understood.1 Vascularity is one
of the major factors contributing to maintaining the normal
function of urethra. The usefulness of color-doppler as well
as of spectral analysis of blood flow within the urethral vessels
have been already described in the literature.2-4 From
these reports it is known that a number of various elements,
such as age, parity, body mass index, estrogen/gestagen profile,
menopause, hormone replacement therapy can influence
the appearance of Doppler flow spectrum in urethral vessels.
However, the research describing the number and the distribution
of urethral blood vessels is scarce. It is known from
anatomy that the female urethra is supplied by 3 different
vessel networks manifested by 3 major vascular levels - proximal
(intramural), middle (midurethra) and distal. The aim of
the study was a comparison of intensity of the vascularity of
urethra at 3 levels in its sagittal plane (intramural, midurethra
and distal part), and in its axial plane at the level of midurethra
(rhabdosphincter vs. the inner part of urethra) in premenopausal,
nulliparous, continent patients.
Eighteen nulliparous patients, mean age 32.67 years (range 18-53
years), consecutively referred for gynecologic ultrasound due to
symptoms other than SUI, voiding dysfunction, POP, cystocoele
or entero/rectocele were recruited from 2nd Department of Gynecology
of the Skubiszewski Medical University of Lublin.
All the
women gave written informed consent and underwent endovaginal
ultrasound using a biplane transducer (type 8848, B-K Medical,
Herlev, Denmark) 21 mm in diameter, frequency range from 5 to 12
MHz. The patients were scanned in the first part of their menstrual
cycle. Ultrasound scanning was performed at rest in the supine
position. Longitudinal images of the bladder neck and urethra were
displayed using the 12 MHz linear array of the transducer positioned
towards the symphysis pubis (SP). The transducer was placed
in the vagina in the neutral position. The position of the transducer
was assumed as symmetrical when the lumen of the urethra was
visualized along the entire length of the urethra, from the bladder
neck to external meatus of urethra.
The vascular pattern of the urethra was obtained in color-doppler
mode using both the linear and transverse arrays of the transducer
and the data were registered as video files in a stable position of the
probe (Fig. 1a, 1b)
.
For each patient, two video acquisitions were
taken: one in the sagittal plane at the level of urethral lumen, and
the second in the axial plane at the level of midurethra. For the
quantitative assessment of the blood flow, the Pixel Flux software
(Chameleon Software, Freiburg, Germany) was applied. With the
use of PixelFlux software, the vascular pattern was analyzed within
manually defined regions of interest (ROI).
At first, the video files
in the sagittal plane were used for the analysis. Regions of interest
were set at sequence at 3 levels (intramural, midurethra and distal
urethra) (Fig. 2a, 2b, 2c) for each patient.
Subsequently, video files
recorded in the axial plane at the level of midurethra were studied.
Two regions of interest were defined for each patient - one comprising
the rhabdosphincter (the outer ring of urethra), and the second
comprising the circular smooth muscle, the longitudinal smooth
muscle and the submucosa (the inner ring of the urethra) (Fig. 3a,
3b).
The intensity of vascularity defined as the ratio between the area
of the vessels detected in Color Doppler and the area of ROI was
calculated for each patient for all 3 regions of interests in sagittal
plane and 2 regions in axial plane. Two measurements of the intensity
were performed for all patients:
- A comparison of intensity among three levels of vascularity
based on the data obtained from files recorded in sagittal section ( table 1)
. - A comparison of intensity between two rings of vascularity
(the outer ring and the inner ring of the urethra) based on the data
obtained from files recorded in axial section ( table 2 ).
The descriptive statistics (SPSS 14.0 PL for Windows) for continuous
data was performed. The results were given as mean values with
standard deviation (SD). The Kolmogorov-Smirnov test (KS-test) was
used to define the distribution of data. Subsequently, the relationships among different variables were assessed with T test for dependent samples.
P < 0.05 was considered as statistically significant ( table 3 ) .
Statistical differences of intensity of vascularity were observed between intramural part of urethra and midurethra and also between midurethra and distal urethra. The results of the analysis show that the midurethra, which is the part of urethra comprising rhabdosphincter muscle, has got the largest intensity of vascularity, which is statistically significantly better that the latter part of urethra (intramural and distal parts). While performing the analysis of the urethra in its axial section at the level of midurethra, the authors did not find any statistically significant differences in the intensity of vascularity in vessel distribution between the outer ring of the urethra (rhabdosphincter) and the inner ring of the urethra (circular smooth muscle, longitudinal smooth muscle and submucosa). On the contrary, the intensity of vascularity in both anatomical areas was very similar (0.76, p < 0.05).
Up till now no reliable diagnostic tool existed that would
enable a quantitative analysis of urethral vascularization.
Different authors assessed urethral vascularity with the use
of color and spectral doppler techniques. 2-6 However, the
appearance of the Doppler flow spectrum can be impaired by
number of factors, among which the sexual hormones profile
is the most important one.7 Besides, spectral Doppler studies
are generally time consuming and relatively difficult to perform
from the technical point of view, particularly for the vessels
of a very small diameter, such as found in the urethra.
Moreover, this kind of examination is usually performed from
the transperineal approach, where the urethra is prone to be
pressed by the transducer, which results in artificial increasing
of resistance index (RI) giving false results. Additionally,
moving artifacts, breathing artifacts, the difficulty in obtaining
proper insonation angle, as well as placing the gate properly
in a little vessel greatly limit the usefulness of spectral
Doppler studies in the assessment of urethral vascularity.
Because of these limitations, it is important to find an easy
method which would allow assessment of the number of vessels
and their distribution. According to Ashton-Miller, the
lumen of the urethra is surrounded by a prominent vascular
plexus that is believed to contribute to the continence by
forming a watertight seal via coaptation of the mucosal surfaces.
6
Basing on this theory, the authors believe that the distribution
of vessels, their number and localization, as well as
the regions supplied by them, seem to play a very important
role. Thus, in order to acknowledge the normal vascularity
of the urethra, the study including premenopausal, nulliparous,
continent patients was performed. The authors believe
that, together with the urethral dysfunctions and morphological
disturbances, particularly urinary incontinence and pelvic
organ prolapse, a change in urethral vascularity may occur,
possibly prior to the appearance of clinical signs.8-10
In such
a situation the assessment of urethra vascularization could
become a predictive value which would give the opportunity
to implement the prophylaxis or early treatment for the
patients, before the symptoms become severe. The technique
used in the study appeared very useful in the assessment of
the vascular pattern of the urethra, being at the same time easy
and fast to perform, with the results obtained as an absolute
value. The literature review does not contain much information
about urethral vascularity. Siracusano et al.11 performed
transperineal ultrasound after intravenous application of ultrasound
contrast media in order to enhance Doppler signals
from the urethral vessels.
The method, although it might give
information about the vessels in the urethral complex, is invasive
and relatively expensive. The transperineal access with
a large array of the transducer, too deep a focus, and a large
distance to the urethra, also greatly limit the reliability of the
method. In another study, the same author (2) assessed urethral
vascularization in healthy young women using Color Doppler
and spectral Doppler scans, defining resistance index (RI) in
urethral vessels at three parts of urethra (proximal, middle and
distal). This study was also performed from the transperineal
access.
access. In the current study, the authors applied a transvaginal
high frequency ultrasound which, due to almost direct contact
of the urethra to the transducer and owing to the focus transverse
point placed on the right depth, creates the opportunity
of precise evaluation of the assessment of urethral vascularity.
High frequency 5-12 MHz biplane transducer, with perpendicular
and transverse ultrasound beam formation appeared
to be a very reliable diagnostic tool in the assessment of urethra
vascularity.
The results showed that the midurethra is
the most vascularized part of the urethra, with the latter parts
(intramural and distal) having less blood supply, comparable
to each other. While Siracusano's study 6 depicted similar
spectrum of blood flow within midurethra and distal urethra,
with increased RI in proximal (intramural) part. In conclusion,
high frequency transvaginal ultrasound with the use of
Color Doppler mode is a very reliable method enabling visualization
of urethral vessels distribution. The data obtained
from the scans may be further analyzed with the use of dedicated
software in order to define the intensity of urethral vascularity
and different anatomical areas, which are responsible
for various functionalities.
- De Lancey JOL, Ashton-Miller JA. Pathophysiology of Adult Urinary Incotinence. Gastroenterology 2004; 126: S23-S32.
- Siracusano S, Bertolotto M, D'Aloia G. et al. Colour Doppler ultrasonography of female urethral vascularization in normal young volunteers: a preliminary report. BJU International 2001; 88, 378-38.
- Yang JM, Yang SH, Huang WC. Functional correlates of Doppler flow study of the female urethral vasculature. Ultrasound Obstet Gynecol 2006; 28: 96-102.
- Kobata SA, Girão MJ, Baracat EC et al. Estrogen therapy influence on periurethral vessels in postmenopausal incontinent women using Doppler velocimetry analysis. Maturitas 2008; 20: 43-7.
- Jackson SR, Brookes S, Abrams P. Measuring urethral blood flow using Doppler ultrasonography. BJU Int 2000; 86: 910 (15-17).
- Siracusano S, Bertolotto M, Silvestre G, et al. The feasibility of urethral color ultrasound imaging in the diagnosis of female intrinsic sphincter deficiency: preliminary results. Spinal Cord 2002; 40: 192-5.
- Miodrag A, Castleden CE, Vallance TR. Sex hormones and the female urinary tract. Drugs 1988; 36: 491.
- Ashton-Miller JA, DeLancey JO. Functional anatomy of the female pelvic floor. Ann N Y Acad Sci 2007; 1101: 266-96.
- Rud T. Anderson KE, Asmussen M. et al. Factors maintaing the intraurethral pressure in women. Invest Urol 1980; 17: 343.
- Sorensen S. Urethral pressure variations in healthy and incontinence women: doctoral thesis. Neurourol Urodyn 1992; 141: 817-20.
- Siracusano S, Bertolotto M, Cucchi A, et al. Application of ultrasound contrast agents for the characterization of female urethral vascularization in healthy pre- and postmenopausal volunteers: preliminary report. Eur Urol, 2006;50:1316-2
Correspondence to:
WIECZOREK PAWEL
Department of Surgery, Clinica Chirurgica 2
University of Padova, Italy
email: wieczornyp@interia.pl