1 Department of Obstetrics and Gynecology, McGill University, Royal Victoria Hospital, 687 Avenue des Pins Ouest, 2 Département d'obstetrique et gynécologie, Université de Montréal, Hôpital Ste Justine and 3 Department of Radiology, McGill University, Royal Victoria Hospital, Montréal, Québec, Canada H3A 1A1
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: echogenicity/ovary/polycystic ovary syndrome/stroma/ultrasound
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Swanson et al. (1981) were the first to describe the ultrasound findings associated with PCOS. The classical image is that of enlarged ovaries containing an increased number of small follicles (210 mm) encircling the ovarian cortex like a string of pearls, although this is sometimes incomplete, and the presence of an increased bright echogenic stroma (Adams et al., 1985). The presence of hypertrophic ovarian stroma has been used by many groups to distinguish between PCOS and normal ovaries (Conway et al., 1989
; Dewailly et al., 1993
).
The degree of echogenicity of the ovarian stroma is usually assessed subjectively but this is open to observer bias where other features of PCOS are already seen. Methods of quantitatively measuring ultrasound image data, often termed textural feature analysis, have been useful in identifying diffuse diseases of the liver (Raeth et al., 1985) and brain (Barr et al., 1995
). Using these recent advances in ultrasound software, the brightness, or echogenicity, of the ovarian stroma can be determined objectively by measuring the intensity level of the ultrasound pixels within the stroma displayed on an ultrasonic image. The mean echogenicity of a given area can then be calculated.
The objective of this study was to determine whether the ovarian stromal echogenicity measured objectively differed significantly between women with PCOS and those with normal ovaries.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
All ultrasound examinations were performed firstly using a 5 MHz endovaginal probe with colour and pulsed Doppler facilities (Acuson XP 128/10®; Acuson Corp., Mountain View, CA, USA), and then using a 7.5 MHz endovaginal probe with histogram measurement of echogenicity (Aloka SSD 2000®; Aloka Co., Tokyo, Japan). All ultrasound examinations were performed by one of the authors (W.B.).
A systematic examination of the morphology of the uterus and ovaries was performed using previously described criteria (Zaidi et al., 1995a; Tan et al., 1996
). An ultrasound diagnosis of PCOS was made when there were greater than 10 small cysts/follicles (28 mm diameter) around a dense core of stroma. These ultrasound findings were invariably accompanied with an increased ovarian volume. Any ovaries which contained ovarian cysts (over 12 mm mean diameter) or ultrasound evidence of endometriomas were excluded from the analysis.
Intra-ovarian blood flow was assessed by pulsed Doppler examination of blood vessels in the ovarian stroma, as previously described (Zaidi et al., 1995bZaidi et al., 1996).
The mean echogenicity was defined as the sum of the product of each intensity level (varying from 063) and the number of pixels for that intensity concentration divided by the total number of pixels in the measured area, as follows:
mean = (.xi.fi)/n
where n = total number of pixels in the measured area
x = intensity level (from 0 to 63)
f = number of pixels corresponding to that level.
The mean echogenicity of the entire ovary and of the ovarian stroma were separately calculated. The spread of intensities was also displayed by histogram, where the horizontal axis indicated the different intensity concentrations and the vertical axis the number of pixels at each intensity level (Figures 1 and 2).
|
|
The stromal index was then calculated by dividing the mean stromal echogenicity by the mean echogenicity of the entire ovary in order to correct for cases where the gain was adjusted to allow optimal image definition. The stromal index was therefore more than one if the mean stromal echogenicity was greater than the mean echogenicity of the entire ovary.
Serum follicle stimulating hormone (FSH), luteinizing hormone (LH), testosterone, and dihydroepiandrosterone sulphate (DHEAS) were also measured in the early follicular phase on the day of the baseline ultrasound scan.
Normally distributed data were expressed as means with 95% confidence limits and compared using Student's unpaired two-tailed t-test. Non-parametric data were expressed as medians with interquartile range and compared using the MannWhitney rank sum test.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The total ovarian volume, stromal volume, and peak stromal blood flow (as assessed by colour Doppler) were all significantly higher (P < 0.0001; P < 0.05; and P < 0.001 respectively) in the women with PCOS compared with those with normal ovaries (Table I).
|
|
The endocrine parameters of PCOS were all significantly raised in the PCOS group (Table III), although the serum FSH was lower than in the control group.
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Interestingly, the mean stromal echogenicity was no higher in women with PCOS compared with women with normal ovaries which suggests that there is no intrinsic difference in the nature of the stroma itself. This is an important finding as a highly echogenic stroma is a cardinal feature in the ultrasound diagnosis of PCOS (Conway et al., 1989; MacDougall et al., 1992
; Dewailly et al., 1993
). The significant difference in the stromal index would suggest that the impression of a highly echogenic stroma in PCOS is primarily due to a visual perception of the difference in echogenicities between the stroma and the ovary as a whole with its multiple small cysts. Clearly the greater the number and the larger the size of the cysts the greater the stromal index would be since the mean total ovarian echogenicity would be lower.
The greater total stromal echogenicity would also suggest that the subjective impression of highly echogenic stroma in women with PCOS may be partly due to the increased stromal volume. The reason that statistical significance was not reached is probably because of the small sample size.
Histological examination of ovaries from women with PCOS has shown a five-fold increase in the sub-cortical (medulla) stroma (Hugheson, 1982). The findings of the present study that the mean stromal echogenicity is comparable in the two groups of women are consistent with the histological evidence that although the stromal volume is increased, there is no other change which could account for an increased echogenicity per se.
It has been suggested that vascular endothelial growth factor (VEGF) has a role in the maintenance of perifollicular blood flow (Van Blerkom et al., 1997) and recent evidence shows a positive correlation between VEGF and ovarian stromal blood flow velocities in women with ultrasound diagnosed polycystic ovaries and PCOS (Agrawal et al., 1998
). This increased vascularity, possibly mediated by VEGF, is therefore probably responsible for the formation of increased stroma and the ultimate phenotype associated with PCOS.
In conclusion, the ultrasonic measurement of mean ovarian stromal echogenicity adds little to the ultrasound diagnosis of PCOS and cannot be recommended in the routine ultrasound assessment of the pelvis. Although the stromal echogenicity appears subjectively brighter, this is primarily a reflection of the difference between the echogenicity of the stroma compared with that of the entire ovary. There was an increased stromal index as well as an increased stromal volume in women with polycystic ovaries. Although the measurement of ovarian and stromal volume and intra-ovarian blood flow were not primary outcomes in this study, we recommend their routine measurement in women undergoing induction of ovulation because of their predictive value in the responsiveness of the ovary to hormonal stimulation (MacDougall et al., 1992; Zaidi et al., 1996b
).
![]() |
Notes |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Agrawal, R., Sladkevicius, P., Engmann, L. et al. (1998) Serum vascular endothelial growth factor concentrations and ovarian stromal blood flow are increased in women with polycystic ovaries. Hum. Reprod., 13, 651655.[Abstract]
Barr, L.L., McCullough, P.J., Ball, W.S. Jr et al. (1995) Quantitative sonographic feature analysis of clinical infant hypoxia: a pilot study. Am. J. Neuroradiol., 17, 10251031.[Abstract]
Battaglia, C., Artini, P.G., Ganazzi, A.D. et al. (1997) Color Doppler analysis in oligo- and amennorrheic women with polycystic ovary syndrome. Gynecol. Endocrinol., 11, 105110.[ISI][Medline]
Conway, G.S., Honour, J.W. and Jacobs, H.S. (1989) Heterogenicity of the polycystic ovary syndrome: clinical, endocrine, and ultrasound features in 556 patients. Clin. Endocrinol., 30, 459470.[ISI][Medline]
Dewailly, D., Duhamel, A., Rober, Y. et al. (1993) Interrelationship between ultrasonography and biology in the diagnosis of polycystic ovarian syndrome. Ann. N. Y. Acad. Sci., 687, 206216.[Abstract]
Franks, S. (1989) Polycystic ovary syndrome: a changing perspective. Clin. Endocrinol., 31, 87120.[ISI][Medline]
Hugheson, P.E. (1982) Morphology and morphogenesis of the SteinLeventhal ovary and of so-called `hyperthecosis'. Obstet. Gynecol. Surv., 37, 5977.[Medline]
MacDougall, M.J., Tan, S.L., Balen, A.H. and Jacobs, H.S. (1992) A controlled study comparing patients with and without polycystic ovaries undergoing in-vitro fertilization. Hum. Reprod., 8, 233237.[Abstract]
Polson, D.W., Wadsworth, J., Adams, J. and Franks, S. (1988) Polycystic ovaries: a common finding in normal women. Lancet, ii, 70.
Raeth, U., Schlaps, D., Limburg, B. et al. (1985) Diagnostic accuracy of computerized B-scan texture analysis and conventional ultrasonography in diffuse parenchymal and malignant liver disease. J. Clin. Ultrasound, 13, 8799.[ISI][Medline]
Swanson, M., Sauerbrie, E.E. and Cooperberg, P.L. (1981) Medical implications of ultrasonically detected polycystic ovaries. J. Clin. Ultrasound, 9, 219222.[ISI][Medline]
Tan, S.L., Zaidi, J., Campbell, S. et al. (1996) Blood flow changes in the ovarian and uterine arteries during the normal menstrual cycle. Am. J. Obstet. Gynecol., 175, 625631.[ISI][Medline]
Van Blerkom, J., Antczak, M. and Schrader, R. (1997) The development potential of the human oocyte is related to the dissolved oxygen content of follicular fluid: association with vascular endothelial growth factor concentrations and perifollicular blood flow characteristics. Hum. Reprod., 12, 10471055.[ISI][Medline]
Zaidi, J., Jurovic, D., Campbell, S. et al. (1995a) Description of circadian rhythm in uterine artery blood flow during the peri-ovulatory period. Hum. Reprod., 10, 16421646.[Abstract]
Zaidi, J., Campbell, S., Pitroff, R. et al. (1995b) Ovarian stromal blood flow in women with polycystic ovaries a possible new marker for diagnosis? Hum. Reprod., 10, 19921996.[Abstract]
Zaidi, J., Tan, S.L., Pitroff, R. et al. (1996a) Blood flow changes in the intra-ovarian arteries during the peri-ovulatory period relationship to the time of day. Ultrasound Obstet. Gynecol., 7, 135140.[ISI][Medline]
Zaidi, J., Barber, J., Kyei-Mensah, A. et al. (1996b) Relationship of ovarian stromal blood flow at the baseline ultrasound scan to subsequent follicular response in an in vitro fertilization program. Obstet. Gynecol., 88, 779784.
Submitted on June 18, 1998; accepted on December 2, 1998.