Ultrasound
Sonographic Morphology of the Normal Menstrual Cycle 1 Deborah A. Hall, M.D., lucy E. Hann, M.D., Joseph T. Ferrucci, Jr., M.D., Edward B. Black, M.D., Barbara S. Braitman, M.D., William F. Crowley, M.D., Najmosama Nikrui, M.D., and Jane A. Kelley, R.D.M.S.
Sequential gray-scale sonograms were obtained during 20 menstrual cycles in 16 normal female volunteers. Hormonal and physical parameters of an ovulatory cycle were correlated with morphological changes in the ovaries, uterus, and cul-de-sac as seen on the sonogram. Ovarian cysts of two sizes were observed, corresponding chronologically and morphologically to Graafian follicles and corpora lutea. Small amounts of free pelvic fluid were demonstrated in many women at ovulation. A characteristic uterine appearance is seen prior to menstruation and is related to hormonal influences on the uterus. These findings emphasize the importance of recognizing normal physiological changes when interpreting gynecologic sonograms. (Female genitalia, normal variation, 8151,130; Female genitalia, ultrasonography, 8[51.1298) • Ovary, cysts. Ovary, ultrasound studies, 8[521.1298 • Uterus, ultrasound studies, 8[541.1298
INDEX TERMS:
Radiology 133:185-188. October 1979
technical advances in gray-scale ultrasound make recognition of changes in the normal menstrual cycle even more important. Although the female pelvic anatomy has been studied with both bistable and gray-scale imaging (1), we know of no in-depth sonographic correlations between pelvic morphology and physiological events during the menstrual cycle, This paper documents sequential structural changes in the ovaries, uterus, and cul-de-sac during the ovulatory cycle, These normal responses to hormonal flux must be appreciated to prevent potential confusion with pathological processes.
DAYS
HE RECENT
T
14
I
21
28
1 ESTROGEN
rORMONES
LH......... :......
PROGESTERONE
1
_
r##,.w-'##$$##$#/0'"##,.w-'###/0'";###/$/#$~$,.J;;; TEMPERATURE
.
.
.
98.6
98
97
US STUDY
MATERIAL AND METHODS
Fig, 1, Schematic diagram indicating the timing of the sequential sonograms in relation to basal body temperature and hormonal levels.
The protocol provided for volunteer participation of nulliparous women who had not had gynecologic disease or surgery and were not currently using intrauterine devices or oral contraceptives, To exclude occult pathology, all subjects underwent a pelvic examination by one gynecologist (N,N,), Sixteen women met the above criteria. and a total of 20 cycles were monitored, Four subjects were studied over 2 complete cycles, We recognized that diagnostic ultrasound has not been shown to have demonstrable hazards in humans when employed at levels of conventional clinical exposure (2), Ultrasound examinations were performed at three sequential points in the menstrual cycle; ovulation, midluteal phase, and menses (Fig. 1). Ovulation was estimated by currently accepted methods, using both cervical mucus changes and basal body temperature (3). The first sonogram was obtained within 48 hours of ovulation, the second 7-10 days later during the midluteal phase, and the third
during the subsequent menses, On the same day as the second study, a blood progesterone level was determined to confirm an ovulatory cycle. All sonograms were obtained with Searle Pho-Sonic gray-scale unit using a 2.25or 3,5-MHz medium-focus transducer, and images were recorded on Polaroid film. One technologist (J,A,K,) performed all examinations. RESULTS Fifteen volunteers had normal pelvic examinations. One had a minimally enlarged and irregular uterus, consistent with small leiornyornas which were also evident on ultra-
1 From the Departments of Radiology (D.A.H., L.E.H.. J,T.F.. E.B.B., B.S.B.. J.A.K.) and Gynecology (W.F.C.. N,N,), Massachusetts General Hospital and Harvard Medical School, Boston, Mass. Presented at the Sixty-fourth Scientific Assembly and Annual Meeting of the Radiological Society
of North America, Chicago, III., Nov. 26 Dec. 1, 1978. Received Jan. 5,1979; accepted and revision requested April 27; revision received May ~h
29,
185
186
DEBORAH
A.
HALL AND OTHERS
Ovulation
Luteal
MATURE FO LLiCLE
CORPUS LUTEUM
October 1979
Menses
INVOLUTING CORPUS LUTEUM AND DEVELOPING FOLLICLES
Fig. 2. Sagittal sonograms and sketches demonstrating cyclic changes in ovarian morphology. Ovulation: Graafian follicle (arrow) 0.8 cm in diameter in the upper pole of the ovary. Midluteal: Corpus luteum 2 cm in diameter (arrow) in the inferior pole of the ovary. Menses: Solid ovarian structure.
TABLE
3a,b
I:
SIZE AND TI::MPORAl OCCURRENCE
OF CYSTIC OVARIAN
FocI' Small Cysts (Follicles) (mean. 1.0 cm in diameter)
Large Cysts (Corpora Lutea) (mean, 2.0 ern in diameter)
No Ovulation Midluteal Menses
Unilateral
Bilateral
9
6
7
5
3
Unilateral
12 2
Bilateral
Cysts
5 4 10
• Data from 20 menstrual cycles
Fig. 3. Evolution of Graafian follicle to corpus luteum. a. Sagittal sonogram through the right ovary at ovulation reveals a small cyst (arrow) in the inferior pole. b. One week later, during the midluteal phase, a larger cyst. 2.4 em in diameter (arrow). is evident.
sound. In all 20 cycles, progesterone levels were within the normal range for the midluteal phase. Values ranged from 2.5 to 59.1 ng/ml, which is above the minimallaboratory standard of 2.0 ng/ml. Ovaries: The ovaries showed the most variation during the three sequential examinations (Fig. 2). Ovarian cysts
were readily identified throughout the cycle. The cysts were of two different sizes (TABLE I). Smaller cysts measuring 0.6-1.5 cm in diameter (mean, 1.0 ern) were evident at each of the three examination times. Larger cysts ranging from 1.6 to 2.4 cm in diameter (mean, 2.2 cm) were identified in the midluteal phase and rarely persisting into menses. At ovulation, small cysts were seen in 16 patients; 9 were unilateral and 6 were bilateral. In the other 5, no cysts were identified. Significantly, no cysts greater than 1.5 ern in diameter were demonstrated at this stage. Seven midluteal studies revealed small cysts and 12 showed larger cysts. Three patients had cysts of both sizes. The remaining midluteal examinations did not demonstrate cysts. Studies obtained at menses showed persistent large cysts in 2 and the smaller variety in 8 (5 unilateral, 3 bilateral). The other ten examinations demonstrated solid
187
SONOGRAPHIC MORPHOLOGY OF THE NORMAL MENSTRUAL CYCLE
Vol. 133
E~DOMETRIAL
CAVITY \
Ultrasound
----
Fig. 4. Transverse sonogram and sketch of the uterus in the midluteal phase, showing the "bull's-eye" appearance presumed to represent vascular and glandular engorgement of the endometrium surrounding the central echo from the uterine cavity.
ovaries bilaterally. Eleven of the 15 patients with small cysts at ovulation demonstrated a single large cyst one week later (Fig. 3). Ten of these cysts had regressed by the onset of menses. In the 4 subjects examined over more than one cycle, the patterns observed in a given ovary were not repetitive, and in 2 instances the contralateral ovary was active during the second cycle. No detectable changes in ovarian size or volume were evident during a single cycle or successive cycles in the same subject. Uterus: In contrast to the complex ovarian changes. uterine ultrasonic morphology remained relatively constant except for a characteristic hypoechoic transformation during the midluteal stage (Fig. 4). Eight of the 20 midluteal studies disclosed a "bull's-eye" uterine configuration of the uterus on the transverse images. characterized by an outer echogenic area (myometrium) with a more hypoechoic inner region (endometrium) and a high-amplitude central-echo complex (mucus and secretions within the uterine cavity). No observable changes in uterine size were recorded during an individual cycle. Cul-de-sac: A small amount of fluid (estimated mean value. 5-10 ml) was demonstrated in the cul-de-sac in 8 of 20 studies at ovulation. Four of these 8 women experienced mittelschmerz (Fig. 5). DISCUSSION
Interpretation of pelvic sonograms requires appreciation of the complex endocrine interactions which affect the female reproductive system. Since pelvic morphology changes in accordance with phases of the menstrual cycle. radiologists must become familiar with these phased al-
l~ \
W\
~ __ ~JiJJI'
fig. 5. Sagittal sonogram at ovulation associated with mittelschmerz. The arrow indicates a small amount of free fluid in the cul-de-sac. IReprinted from Hann et al. (5) with permission of the publisher I
LH
~•.. FSH
PITUITARY
,~~R:' 'C..~"J
o ()
\-)"
ESTROGEN
. / ,
~ ""\
-I'••
~
INHIBITION BY ESTROGEN AND PROGESTERONE
PROGESTERONE
------
WI -:;./,
\ \
1\
UTERUS
Fig. 6. Hormonal circuits of the ovulatory cycle. The negative feedback of estrogen and progesterone causes a decline in pituitary FSH and LH.
terations and the physiological environment of the ovaries and uterus they reflect (4). The ovaries respond to two key hormones produced by the adenohypophysis: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Both hormones promote maturation of the primordial Graafian follicle. FSH causes growth of the ovum and its surrounding layers of granulosa and theca cells. LH. secreted by the pituitary at midcycle, completes follicle maturation. resulting in extrusion of the ovum. The other developing follicles then become atretic. After the mature follicle has ruptured, the cells making up its rim become saturated with lipids, resulting in the characteristic yellow color; hence the name corpus luteum. During the luteal phase, these cells. which are re-
188
DEBORAH
A.
HALL AND OTHERS
sponsible for preovulation estrogen production, secrete increasing amounts of both estrogen and progesterone, which act as a negative feedback circuit on the pituitary, depressing FSH and LH production. The resulting decline in gonadotropin levels causes eventual involution of the corpus luteum, lowering blood progesterone and estrogen levels just prior to the onset of menses. These ovarian hormones are also responsible for the uterine endometrial cycle. The two interconnected hormonal circuits are diagrammed in Figure 6. The rising estrogen levels in the first two weeks of the cycle cause stromal, glandular, and vascular proliferation. With the addition of progesterone in the latter part of the cycle, both hormones work synergistically to prepare the uterus for implantation. This results in the secretory endometrial phase, in which the mucosal glands swell with secretions and the blood vessels become engorged. Without implantation, estrogen and progesterone levels fall, causing shedding of the endometrium and resulting in menstruation. This study discloses that normal hormonal influences on the female reproductive system may be associated with ultrasonographically observable effects. The ovaries display cystic elements which vary according to the stage of the menstrual cycle (Fig. 2). At ovulation, the time of peak LH and FSH activity, ripening Graafian follicles are abundant. Ovarian cysts measuring approximately 1 cm in diameter were demonstrated most frequently at ovulation and were visible on 75% of ovulatory sonograms. For this reason, we feel that these small cysts represent the Graafian follicles. An additional ultrasonic manifestation of ovulation was small quantities of free peritoneal fluid in the cul-de-sac. Forty per cent of ovulations were accompanied by transient pelvic fluid, most likely representing a small hemoperitoneum secondary to follicular rupture (Fig. 5). The concurrence of fluid and pain in 4 women at ovulation suggests an etiology for the long-disputed mechanism of mittelschmerz (5). After ovulation, the corpus luteum develops and its hormonal functions dictate morphological changes in the ovaries and uterus. During the midluteal stage, larger ovarian cysts, approximately 2.0 cm in diameter, could be seen in 60 % of cycles. These were considered corpora lutea, since they were not present at ovulation. All but two of the larger cysts regressed by the onset of menses. Four studies showed only small cysts in the midluteal phase. It is conceivable that these represented smaller corpora lutea, although by our size criteria they were indistinguishable from Graafian follicles. Under the influence of the ovarian hormones of the luteal
October 1979
phase, the uterus displays a unique sonographic appearance resembling a "bull's-eye" on transverse images (Fig. 4). The dense central echo from the uterine cavity is surrounded by a rim of relatively hypoechoic tissue. This may reflect vascular engorgement and glandular fluid in the thickened secretory endometrium. The cyclic normal variations in the uterus and ovary should not be contused with gynecologic pathology (6). Physiological ovarian cysts may mimic small neoplasms or endometriosis. When free peritoneal fluid is present, minimal ascites, inflammatory disease, and ectopic gestation enter the differential diagnosis. If the diagnosis is in doubt and the clinical condition permits, re-examination at a later date may help differentiate between pathological and physiological conditions. Pathological processes may persist, while physiological cysts and ovulatory fluid are transient phenomena which should not be seen if reexamination is performed at a subsequent phase of the menstrual cycle. Similarly, with awareness of these sonographic phenomena, scheduling Of clinical pelvic sonograms need not be temporally appointed to a selected phase of the menstrual cycle, since the normal functional sequences will be familiar morphological variations. CONCLUSION
The normal ovaries and uterus change dynamically in response to hormonal flux. Sonographic morphology of the female pelvis discloses a characteristic appearance at each phase of the menstrual cycle. Physiological and anatomical correlates now permit greater understanding of gynecologic ultrasonograms. Joseph T. Ferrucci, Jr., M.D. Department of Radiology Massachusetts General Hospital Boston, Mass. 02114
REFERENCES 1. Sample WF, Lippe BM. GyepesMT: Gray-scale ultrasonography of the normal female pelvis. Radiology 125:477-483, Nov 1977 2. Sanders RC, James AE Jr, ed: Ultrasonography in Obstetrics and Gynecology. New York. Appleton-Century-Crofts. 1977, Chapt 3, pp 29-38 3. Billings EL, Billings JJ, Brown JB, et al: Symptoms and hormonal changes accompanying ovulation. Lancet 1:282-284. 5 Feb 1972 4. Novak ER, Jones H Jr. Jones GS. ed: Novak's Textbook of Gynecology. Baltimore, Williams & Wilkins, 9th Ed, 1975. Chapt 2, pp 17-58 5. Hann LE. Hall DA, Black EB, et al: Mittelschmerz. Sonographic demonstration. JAMA 241:2731-2732, 22 Jun 1979 6. Lawson T, Albarelli IN: Diagnosisof gynecologic pelvic masses by gray scale ultrasonography: analysis of specificity and accuracy. Am J Roentgenol128: 1003-1006, Jun 1977
Sonographic Morphology of the Normal Menstrual Cycle 1 Deborah A. Hall, M.D., lucy E. Hann, M.D., Joseph T. Ferrucci, Jr., M.D., Edward B. Black, M.D., Barbara S. Braitman, M.D., William F. Crowley, M.D., Najmosama Nikrui, M.D., and Jane A. Kelley, R.D.M.S.
Sequential gray-scale sonograms were obtained during 20 menstrual cycles in 16 normal female volunteers. Hormonal and physical parameters of an ovulatory cycle were correlated with morphological changes in the ovaries, uterus, and cul-de-sac as seen on the sonogram. Ovarian cysts of two sizes were observed, corresponding chronologically and morphologically to Graafian follicles and corpora lutea. Small amounts of free pelvic fluid were demonstrated in many women at ovulation. A characteristic uterine appearance is seen prior to menstruation and is related to hormonal influences on the uterus. These findings emphasize the importance of recognizing normal physiological changes when interpreting gynecologic sonograms. (Female genitalia, normal variation, 8151,130; Female genitalia, ultrasonography, 8[51.1298) • Ovary, cysts. Ovary, ultrasound studies, 8[521.1298 • Uterus, ultrasound studies, 8[541.1298
INDEX TERMS:
Radiology 133:185-188. October 1979
technical advances in gray-scale ultrasound make recognition of changes in the normal menstrual cycle even more important. Although the female pelvic anatomy has been studied with both bistable and gray-scale imaging (1), we know of no in-depth sonographic correlations between pelvic morphology and physiological events during the menstrual cycle, This paper documents sequential structural changes in the ovaries, uterus, and cul-de-sac during the ovulatory cycle, These normal responses to hormonal flux must be appreciated to prevent potential confusion with pathological processes.
DAYS
HE RECENT
T
14
I
21
28
1 ESTROGEN
rORMONES
LH......... :......
PROGESTERONE
1
_
r##,.w-'##$$##$#/0'"##,.w-'###/0'";###/$/#$~$,.J;;; TEMPERATURE
.
.
.
98.6
98
97
US STUDY
MATERIAL AND METHODS
Fig, 1, Schematic diagram indicating the timing of the sequential sonograms in relation to basal body temperature and hormonal levels.
The protocol provided for volunteer participation of nulliparous women who had not had gynecologic disease or surgery and were not currently using intrauterine devices or oral contraceptives, To exclude occult pathology, all subjects underwent a pelvic examination by one gynecologist (N,N,), Sixteen women met the above criteria. and a total of 20 cycles were monitored, Four subjects were studied over 2 complete cycles, We recognized that diagnostic ultrasound has not been shown to have demonstrable hazards in humans when employed at levels of conventional clinical exposure (2), Ultrasound examinations were performed at three sequential points in the menstrual cycle; ovulation, midluteal phase, and menses (Fig. 1). Ovulation was estimated by currently accepted methods, using both cervical mucus changes and basal body temperature (3). The first sonogram was obtained within 48 hours of ovulation, the second 7-10 days later during the midluteal phase, and the third
during the subsequent menses, On the same day as the second study, a blood progesterone level was determined to confirm an ovulatory cycle. All sonograms were obtained with Searle Pho-Sonic gray-scale unit using a 2.25or 3,5-MHz medium-focus transducer, and images were recorded on Polaroid film. One technologist (J,A,K,) performed all examinations. RESULTS Fifteen volunteers had normal pelvic examinations. One had a minimally enlarged and irregular uterus, consistent with small leiornyornas which were also evident on ultra-
1 From the Departments of Radiology (D.A.H., L.E.H.. J,T.F.. E.B.B., B.S.B.. J.A.K.) and Gynecology (W.F.C.. N,N,), Massachusetts General Hospital and Harvard Medical School, Boston, Mass. Presented at the Sixty-fourth Scientific Assembly and Annual Meeting of the Radiological Society
of North America, Chicago, III., Nov. 26 Dec. 1, 1978. Received Jan. 5,1979; accepted and revision requested April 27; revision received May ~h
29,
185
186
DEBORAH
A.
HALL AND OTHERS
Ovulation
Luteal
MATURE FO LLiCLE
CORPUS LUTEUM
October 1979
Menses
INVOLUTING CORPUS LUTEUM AND DEVELOPING FOLLICLES
Fig. 2. Sagittal sonograms and sketches demonstrating cyclic changes in ovarian morphology. Ovulation: Graafian follicle (arrow) 0.8 cm in diameter in the upper pole of the ovary. Midluteal: Corpus luteum 2 cm in diameter (arrow) in the inferior pole of the ovary. Menses: Solid ovarian structure.
TABLE
3a,b
I:
SIZE AND TI::MPORAl OCCURRENCE
OF CYSTIC OVARIAN
FocI' Small Cysts (Follicles) (mean. 1.0 cm in diameter)
Large Cysts (Corpora Lutea) (mean, 2.0 ern in diameter)
No Ovulation Midluteal Menses
Unilateral
Bilateral
9
6
7
5
3
Unilateral
12 2
Bilateral
Cysts
5 4 10
• Data from 20 menstrual cycles
Fig. 3. Evolution of Graafian follicle to corpus luteum. a. Sagittal sonogram through the right ovary at ovulation reveals a small cyst (arrow) in the inferior pole. b. One week later, during the midluteal phase, a larger cyst. 2.4 em in diameter (arrow). is evident.
sound. In all 20 cycles, progesterone levels were within the normal range for the midluteal phase. Values ranged from 2.5 to 59.1 ng/ml, which is above the minimallaboratory standard of 2.0 ng/ml. Ovaries: The ovaries showed the most variation during the three sequential examinations (Fig. 2). Ovarian cysts
were readily identified throughout the cycle. The cysts were of two different sizes (TABLE I). Smaller cysts measuring 0.6-1.5 cm in diameter (mean, 1.0 ern) were evident at each of the three examination times. Larger cysts ranging from 1.6 to 2.4 cm in diameter (mean, 2.2 cm) were identified in the midluteal phase and rarely persisting into menses. At ovulation, small cysts were seen in 16 patients; 9 were unilateral and 6 were bilateral. In the other 5, no cysts were identified. Significantly, no cysts greater than 1.5 ern in diameter were demonstrated at this stage. Seven midluteal studies revealed small cysts and 12 showed larger cysts. Three patients had cysts of both sizes. The remaining midluteal examinations did not demonstrate cysts. Studies obtained at menses showed persistent large cysts in 2 and the smaller variety in 8 (5 unilateral, 3 bilateral). The other ten examinations demonstrated solid
187
SONOGRAPHIC MORPHOLOGY OF THE NORMAL MENSTRUAL CYCLE
Vol. 133
E~DOMETRIAL
CAVITY \
Ultrasound
----
Fig. 4. Transverse sonogram and sketch of the uterus in the midluteal phase, showing the "bull's-eye" appearance presumed to represent vascular and glandular engorgement of the endometrium surrounding the central echo from the uterine cavity.
ovaries bilaterally. Eleven of the 15 patients with small cysts at ovulation demonstrated a single large cyst one week later (Fig. 3). Ten of these cysts had regressed by the onset of menses. In the 4 subjects examined over more than one cycle, the patterns observed in a given ovary were not repetitive, and in 2 instances the contralateral ovary was active during the second cycle. No detectable changes in ovarian size or volume were evident during a single cycle or successive cycles in the same subject. Uterus: In contrast to the complex ovarian changes. uterine ultrasonic morphology remained relatively constant except for a characteristic hypoechoic transformation during the midluteal stage (Fig. 4). Eight of the 20 midluteal studies disclosed a "bull's-eye" uterine configuration of the uterus on the transverse images. characterized by an outer echogenic area (myometrium) with a more hypoechoic inner region (endometrium) and a high-amplitude central-echo complex (mucus and secretions within the uterine cavity). No observable changes in uterine size were recorded during an individual cycle. Cul-de-sac: A small amount of fluid (estimated mean value. 5-10 ml) was demonstrated in the cul-de-sac in 8 of 20 studies at ovulation. Four of these 8 women experienced mittelschmerz (Fig. 5). DISCUSSION
Interpretation of pelvic sonograms requires appreciation of the complex endocrine interactions which affect the female reproductive system. Since pelvic morphology changes in accordance with phases of the menstrual cycle. radiologists must become familiar with these phased al-
l~ \
W\
~ __ ~JiJJI'
fig. 5. Sagittal sonogram at ovulation associated with mittelschmerz. The arrow indicates a small amount of free fluid in the cul-de-sac. IReprinted from Hann et al. (5) with permission of the publisher I
LH
~•.. FSH
PITUITARY
,~~R:' 'C..~"J
o ()
\-)"
ESTROGEN
. / ,
~ ""\
-I'••
~
INHIBITION BY ESTROGEN AND PROGESTERONE
PROGESTERONE
------
WI -:;./,
\ \
1\
UTERUS
Fig. 6. Hormonal circuits of the ovulatory cycle. The negative feedback of estrogen and progesterone causes a decline in pituitary FSH and LH.
terations and the physiological environment of the ovaries and uterus they reflect (4). The ovaries respond to two key hormones produced by the adenohypophysis: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Both hormones promote maturation of the primordial Graafian follicle. FSH causes growth of the ovum and its surrounding layers of granulosa and theca cells. LH. secreted by the pituitary at midcycle, completes follicle maturation. resulting in extrusion of the ovum. The other developing follicles then become atretic. After the mature follicle has ruptured, the cells making up its rim become saturated with lipids, resulting in the characteristic yellow color; hence the name corpus luteum. During the luteal phase, these cells. which are re-
188
DEBORAH
A.
HALL AND OTHERS
sponsible for preovulation estrogen production, secrete increasing amounts of both estrogen and progesterone, which act as a negative feedback circuit on the pituitary, depressing FSH and LH production. The resulting decline in gonadotropin levels causes eventual involution of the corpus luteum, lowering blood progesterone and estrogen levels just prior to the onset of menses. These ovarian hormones are also responsible for the uterine endometrial cycle. The two interconnected hormonal circuits are diagrammed in Figure 6. The rising estrogen levels in the first two weeks of the cycle cause stromal, glandular, and vascular proliferation. With the addition of progesterone in the latter part of the cycle, both hormones work synergistically to prepare the uterus for implantation. This results in the secretory endometrial phase, in which the mucosal glands swell with secretions and the blood vessels become engorged. Without implantation, estrogen and progesterone levels fall, causing shedding of the endometrium and resulting in menstruation. This study discloses that normal hormonal influences on the female reproductive system may be associated with ultrasonographically observable effects. The ovaries display cystic elements which vary according to the stage of the menstrual cycle (Fig. 2). At ovulation, the time of peak LH and FSH activity, ripening Graafian follicles are abundant. Ovarian cysts measuring approximately 1 cm in diameter were demonstrated most frequently at ovulation and were visible on 75% of ovulatory sonograms. For this reason, we feel that these small cysts represent the Graafian follicles. An additional ultrasonic manifestation of ovulation was small quantities of free peritoneal fluid in the cul-de-sac. Forty per cent of ovulations were accompanied by transient pelvic fluid, most likely representing a small hemoperitoneum secondary to follicular rupture (Fig. 5). The concurrence of fluid and pain in 4 women at ovulation suggests an etiology for the long-disputed mechanism of mittelschmerz (5). After ovulation, the corpus luteum develops and its hormonal functions dictate morphological changes in the ovaries and uterus. During the midluteal stage, larger ovarian cysts, approximately 2.0 cm in diameter, could be seen in 60 % of cycles. These were considered corpora lutea, since they were not present at ovulation. All but two of the larger cysts regressed by the onset of menses. Four studies showed only small cysts in the midluteal phase. It is conceivable that these represented smaller corpora lutea, although by our size criteria they were indistinguishable from Graafian follicles. Under the influence of the ovarian hormones of the luteal
October 1979
phase, the uterus displays a unique sonographic appearance resembling a "bull's-eye" on transverse images (Fig. 4). The dense central echo from the uterine cavity is surrounded by a rim of relatively hypoechoic tissue. This may reflect vascular engorgement and glandular fluid in the thickened secretory endometrium. The cyclic normal variations in the uterus and ovary should not be contused with gynecologic pathology (6). Physiological ovarian cysts may mimic small neoplasms or endometriosis. When free peritoneal fluid is present, minimal ascites, inflammatory disease, and ectopic gestation enter the differential diagnosis. If the diagnosis is in doubt and the clinical condition permits, re-examination at a later date may help differentiate between pathological and physiological conditions. Pathological processes may persist, while physiological cysts and ovulatory fluid are transient phenomena which should not be seen if reexamination is performed at a subsequent phase of the menstrual cycle. Similarly, with awareness of these sonographic phenomena, scheduling Of clinical pelvic sonograms need not be temporally appointed to a selected phase of the menstrual cycle, since the normal functional sequences will be familiar morphological variations. CONCLUSION
The normal ovaries and uterus change dynamically in response to hormonal flux. Sonographic morphology of the female pelvis discloses a characteristic appearance at each phase of the menstrual cycle. Physiological and anatomical correlates now permit greater understanding of gynecologic ultrasonograms. Joseph T. Ferrucci, Jr., M.D. Department of Radiology Massachusetts General Hospital Boston, Mass. 02114
REFERENCES 1. Sample WF, Lippe BM. GyepesMT: Gray-scale ultrasonography of the normal female pelvis. Radiology 125:477-483, Nov 1977 2. Sanders RC, James AE Jr, ed: Ultrasonography in Obstetrics and Gynecology. New York. Appleton-Century-Crofts. 1977, Chapt 3, pp 29-38 3. Billings EL, Billings JJ, Brown JB, et al: Symptoms and hormonal changes accompanying ovulation. Lancet 1:282-284. 5 Feb 1972 4. Novak ER, Jones H Jr. Jones GS. ed: Novak's Textbook of Gynecology. Baltimore, Williams & Wilkins, 9th Ed, 1975. Chapt 2, pp 17-58 5. Hann LE. Hall DA, Black EB, et al: Mittelschmerz. Sonographic demonstration. JAMA 241:2731-2732, 22 Jun 1979 6. Lawson T, Albarelli IN: Diagnosisof gynecologic pelvic masses by gray scale ultrasonography: analysis of specificity and accuracy. Am J Roentgenol128: 1003-1006, Jun 1977
