Dr. Nelson is a Resident in Radiology and Dr. Harris is an
Associate Professor of Radiology at Dartmouth Medical School
and Dartmouth-Hitchcock Medical Center in Lebanon, NH.
regnancy is predominantly an uncomplicated physiologic state;
however, difficulties may arise at any time. These are mostly due
to problems with the placenta or fetus throughout gestation, but
extrauterine problems also may arise, usually in the second or
third trimester. Imaging of these complications is a crucial part
of the diagnostic work-up.
This article will concentrate on pregnancy complicated by
pathologic processes of the genitourinary tract: uterine fibroids,
adnexal masses, and renal calculi.
Fibroids are the most common pelvic mass in women of
child-bearing age, though they are more frequently seen in older
These benign tumors are composed histologically of smooth muscle
cells and fibrous tissue, the latter related to degeneration.
The incidence of fibroids within the general population is 20 to
while the incidence during pregnancy is 0.3 to 2.6%,
with 0.3 to 7% of these being symptomatic. In our society, as the
average age of child-bearing increases so does the percentage of
pregnant women with myomas, occurring more commonly in women in
their third to fourth decades of life.
Most fibroids are asymptomatic and present no threat to the
health of the mother or fetus. Large fibroids that are present at
the onset of pregnancy or during the first or second trimester may
result in spontaneous abortions or ectopic pregnancies (figure 1).
During the second half of gestation, the patient may experience
premature delivery, premature rupture of membranes, hemoperitoneum,
Additionally, fibroids greater than 6 cm in size and/or multiple in
number may cause pain, placental abruption, abnormal presentation,
prolonged labor, or retained products of conception.
Lower uterine fibroids may prevent vaginal delivery (figure 2). An
increased incidence of cesarean deliveries has been observed in
patients with myomas greater than 10 cm.
Fibroids' effect on fetal growth and development is
controversial; one series related a two-fold increase in caudal
dysplasia in fibroid pregnancies;
others have not found an association.
Fibroids that come in contact with the placenta are associated with
a higher incidence of complications, including placental abruption,
premature delivery, and post-partum hemorrhage.
Winer-Muram et al reported a 71% complication rate in pregnancies
with a placental-fibroid relationship. They also reported bleeding
within the first 18 weeks in 60% of patients (in comparison to a
general population rate of approximately 25% within the first half
of pregnancy), post-partum hemorrhage in 14% (vs 5% of the general
population), and premature delivery in 14% (vs 8%).
Rice et al observed abruption in 57% of patients with
retroplacental fibroids, in comparison to a 2.5% incidence in
patients with fibroids unrelated to the placenta. These researchers
also observed a correlation between premature delivery and fibroid
size, noting a prevalence in 21% of patients with fibroids of 3 to
5 cm, and in 28% of those with fibroids greater than 5 cm.
Smooth muscle cells in myomas have an abundance of estrogen
receptors, presumably accounting for the often rapid growth of
fibroids during the hyperestrogenic state of pregnancy.
In one study, Aharoni and coworkers measured the volume of fibroids
and reported no change in the size (±10% of initial volume) in 60%,
an increase in 21% (greater than 25% change), and a decrease in
size in 19% (maximum reduction of less than 20%); the lack of
increase in size is in accordance with three other retrospective
Ultrasound evaluation of uterine fibroids during pregnancy
should record the number and location of fibroids (including the
layer of uterus involved), the visualization of adnexa, and the
examination of the kidneys to exclude nonphysiologic
hydronephrosis, a rare complication of uterine fibroids in
On ultrasound, a fibroid is usually a solid-appearing mass with
acoustic attenuation. As connective tissue composition increases,
so does the echogenicity, as will acoustic shadowing if
calcification is present. CT will reveal solid masses that are
similar in density to normal myometrial tissue. With degeneration,
a low-attenuation mass (with or without calcification) may be seen.
Many authorities highly regard magnetic resonance imaging of
fibroids and find it superior in diagnosing and locating the
MRI allows imaging in multiple planes, is impervious to bone and
gas artifact, may distinguish uterine from ovarian tissue, and
provides better visualization of the lateral and posterior pelvis,
locating ovaries that may not be identified on ultrasound. An MRI
protocol may include a T1-weighted image, T2-weighted images, and a
STIR sequence to view possible degenerative changes.
MRI demonstrates well-demarcated round or oval lesions, often
appearing homogeneous and with low to intermediate signal with
myometrium on T1-weighted images and low signal on T2-weighted
Some such lesions may be surrounded by a high signal intensity rim
on T2-weighted images; these are believed to be secondary to
vascular congestion, although one study found a histologic
correlation with dilated lymphatics, veins, edema, or a combination
of the above.
After secondary changes occur in the fibroids, the typical
sonographic appearance becomes more complex (figures 3A,B). As
these tumors enlarge and outgrow their blood supply, smooth muscle
cells degenerate into myxomatous components, increasing the fibrous
Puerperal fibroids, often of the carneous or fleshy type,
demonstrate edema, necrosis, hyalinization, and hypertrophy of the
Edematous fibroids may resemble hydatiform moles sonographically,
with multiple cystic regions within a heterogeneous echogenic area.
On MRI, focal or patchy areas of high signal on T2-weighted images
are present in degenerated fibroids (figure 3C), and on occasion
may be mistaken for a molar pregnancy.
These areas also may mimic duplicated or retroverted uteri,
adenomyomas, calcified fetal parts, or an adnexal mass.
We have found ultrasound, especially color Doppler, to be
helpful in differentiating fibroids from uterine contractions and
subchorionic or retroplacental hematomas. Fibroids tend to be
hypoechoic, rounded, and to have one or two large feeding vessels
at the periphery, whereas contractions are isoechoic to myometrium
and often have hypervascular color Doppler flow, as befits
contracting musculature. Hematomas have variable echogenicity and
usually are completely avascular.
Several studies have investigated fibroid growth with pregnancy.
Strobelt and coworkers noted that most fibroids of less than 5 cm
tended to disappear with pregnancy, whereas fibroids that were
greater than 5 cm tended to remain stable or decrease in size.
Multiple myomas disappeared less often than single myomas.
Rosati et al noted that approximately one-third of fibroids
increased in volume with advancing gestation, but myoma volume was
not predictive of growth patterns. However, they found a higher
rate of complications in fibroids of greater than 200 cm
compared to those of less than 100 cm
A recent study suggests that color Doppler may provide clues
indicating growth potential of fibroids in non-pregnant patients
Fibroids with a detectable leiomyoma artery, defined as a prominent
artery identified at the periphery of the fibroid, were more likely
to increase in volume during pregnancy by at least 30%, in
comparison to those fibroids without a leiomyomatous artery which
demonstrated little growth. Color Doppler of fibroids may be
indicated to evaluate potential for growth and possible
complications in pregnancy, although this requires further
Gadolinium contrast is relatively contraindicated for use in
pregnant women, as little is known regarding its effects on the
human fetus. It has been used to differentiate bowel from fibroids,
but this is generally not a clinical problem; fibroids markedly
enhance, whereas the bowel wall enhances mildly.
Rofsky and coworkers studied the effects of intraperitoneal
gadopentetate administered to pregnant mice at 9.5 days of
gestation. At 18 days of gestation, one statistically significant
discrepancy was noted; the intraperitoneal saline-injected group
had a fetal weight below the mean, versus controls.
Gadolinium has been shown to increase the incidence of skeletal
malformations in rabbit fetuses given the contrast agent at 0.5
mmol/kg/day for 13 days (Omniscan package insert, Nycomed,
Princeton, NJ). No human fetal studies are available.
It is estimated that 0.5 to 1.2% of pregnant women will have an
Most of these are pregnancy related, corpus luteum or theca lutein
cysts and will resolve by 14- to 16-weeks of gestation. A complex
or persistent adnexal mass continues to be a significant clinical
problem, as the chance of ovarian malignancy is a small but
potentially traumatic risk to both patient and physician. The risk
of ovarian malignancy in pregnancy is quite low, occurring in 0.1
to 0.4% of pregnancies.
However, malignancy has been detected in 2 to 5% of adnexal masses
persisting after the first trimester, and 2.4 to 5% persisting
after the third trimester.
Complications of an adnexal mass include rupture, obstruction to
labor, and ovarian torsion. These occur with an incidence of less
than 1 to 2.3%, and often occur in the mid to late first trimester.
Fortunately, the diagnosis is often made at an early stage and the
carcinoma is of a low grade.
Ovarian torsion and/or rupture may be the presenting signs of
Similar to the non-pregnant state, surgical staging is essential
for determination of therapeutic options, and CT is the most useful
imaging modality for this task.
Historically, surgery was advocated for all masses persisting
into the second trimester, the point at which fetal demise
However, with the advent of transvaginal ultrasound and MRI,
operative rates are now lower, and in many situations patients may
be managed conservatively. The majority of adnexal masses are
identified at 13 to 20 weeks by ultrasound, and if the adnexal mass
is simple or characteristic for a benign lesion, it can be safely
monitored with ultrasound.
Some authors advocate sonographic appearance as a predictor of
benignity or malignancy and the need for surgical intervention. In
a series of 131 adnexal masses in 125 pregnancies, 89.3% of
patients were characterized with benign-appearing adnexal masses
Complex characteristics considered suspicious for malignancy were
noted in 10.7%. The features included a mass with both solid and
cystic constituents, or a uniformly but irregularly filled solid
lesion lacking through transmission. In this series, 95% of
dermoids, 80% of endometriomas, and 71% of simple cysts were
diagnosed correctly. Only one of the 14 (7%) suspicious lesions
proved to be an ovarian carcinoma, an overall incidence of 0.8%. No
loss of pregnancy occurred in the 24 (19%) patients that underwent
However, the above statistics are in contrast to those of more
surgically-oriented reports. In a surgical series of 31 patients, a
17-weeks pregnant patient experienced a miscarriage 24 hours
Neiswender and Toub advise surgical intervention if an adnexal mass
enlarges, contains solid components, or measures greater than 6 cm
during the second trimester of pregnancy.
They report a series of two patients who successfully underwent
laparoscopic excision in the second trimester. These authors
favored laparoscopic surgery over laparotomy due to its less
invasive nature. They also advocate performing surgery during the
second trimester; premature labor and delivery is less likely to
occur at this time compared to the third trimester. If delivery
occurs during this period of pregnancy, the fetus generally is
Several benign adnexal lesions have a characteristic sonographic
appearance. Simple cysts are anechoic, with well-defined thin
posterior walls and increased through transmission. Endo-metriomas
are characteristically homo-genous, with low-level echoes and
increased through transmission (figure 6). Teratomas have a typical
appearance of a highly echogenic or calcified solid portion with
acoustic shadowing, often with cystic components.
Complex masses are more difficult to assess noninvasively and
physicians may now refer patients with these types of lesions to
MRI before resorting to surgery. Endometriomas often demonstrate
foci of high signal intensity on T1-weighted images (T1WI), and are
variable on T2WI, with a characteristic fluid-fluid level;
dependent fluid may be very low signal on T2WI due to hemosiderin.
Serous cystadenomas demonstrate low signal on T1WI and markedly
high signal intensity on T2WI, with or without septations.
Pedunculated leiomyomas may mimic solid malignant ovarian tumors,
but MRI usually can differentiate between these entities.
Spectral Doppler ultrasound remains controversial in its role in
the diagnosis of ovarian malignancy. While conventional sonography
combined with color Doppler may increase the accuracy, sensitivity,
and specificity of ultrasound diagnosis, most studies show
significant overlap and limited value in the use of spectral
characteristics of resistive index, pulsatility index, and peak
systolic velocity for differentiating malignant from benign lesions
Urolithiasis is an uncommon but perplexing diagnostic problem in
pregnancy, affecting about 1 in 1,500 patients.
The gravid state confers no predisposition for renal stones; the
incidence is the same for non-pregnant females.
By 9 to 11 weeks of gestation, pregnancy is a hypercalciuric and
uric acid state as a result of increased renal plasma flow and
glomerular filtration rate.
Changes in urine composition, including alkalinization, elevated
levels of magnesium, citrate, and nephrocalcin, and the presence of
stone formation inhibitors oppose this stone-forming state during
In particular, increased urinary citrate and magnesium excretion
inhibits calcium stone formation, glycosaminoglycans and acidic
glycoproteins (nephrocalcin) inhibit oxalate stones, and urine
alkalinity from the respiratory alkalosis of pregnancy inhibits
uric acid stones.
Struvite stones are seen with infection and in association with
The vast majority of renal calculi during pregnancy are
asymptomatic and are incidentally found, although they are
responsible for the majority of chief complaints of abdominal pain
unrelated to the fetus or placenta (figure 8).
Acute pyelonephritis and obstruction by stones are the most
frequent urinary tract problems in pregnancy.
Most patients with stones present in their second or third
trimester with a combination of pain, sepsis, and/or obstruction.
Flank pain is the most common symptom, usually associated with
macroscopic or microscopic hematuria.
Haddad and coworkers describe three states of urinary tract
pregnancy: 1) physiological, 2) "over-distension syndrome," and 3)
"acute hydronephrosis in pregnancy." Physiologic dilatation is
asymptomatic (occurring in 80% of pregnancies, more often found on
the right side than the left).
The overdistension syndrome, resulting from obstruction by the
gravid uterus, is characterized by pain which may mimic renal
colic; treatment for this syndrome is conservative. Acute
hydronephrosis in pregnancy may result from a change in the
position of the fetus, diuresis, or passage of a stone into the
ureter. Constant pain, with occasional nausea and vomiting, that is
unresponsive to conservative therapy defines this entity.
Interventional treatment may be required for relief of
Urolithiasis should be considered in any pregnant patient with
fever that persists after 24 hours of antibiotics.
Differential diagnosis includes pyelonephritis, appendicitis,
cholecystitis, and pregnancy-related diseases such as ovarian vein
thrombosis, labor, placental abruption, or pregnancy-induced liver
disease. Complications of urolithiasis include urinary tract
infections, occurring in 10 to 20% of patients, precipitation of
premature labor by renal colic, or permanent renal failure when
diagnosis or intervention is significantly delayed.
Differentiation of the physiological pelvicaliectasis from
obstruction, particularly on the right side, is difficult.
Physiologic pelvicaliectasis may occur as early as at 6 to 10 weeks
of gestation and is present in up to 90% of pregnancies by the
It is the result of both hormonal and mechanical factors, the
latter more often involving the right ureter (85% vs 15%).
The gravid uterus compresses the ureter at the pelvic brim near the
crossing of the iliac vessels. The right ureter has been noted to
take a more acute angle at this position, thus causing the higher
incidence of right-sided physiological hydronephrosis. On a
hormonal basis, ureteral dilatation likely results from relaxation
of smooth muscle in response to progesterone.
In imaging of non-pathologic ureterohydronephrosis, the dilated
ureter tapers to a normal caliber pelvic ureter; the smooth
transition characteristically takes place at the crossing of the
common iliac vessels adjacent to the sacrum.
Therefore, pathologic urinary tract dilatation is suggested by
dilatation of the pelvic ureter (figure 9), a severe left-sided
delayed nephrogram or hydronephrosis (figure 10), or the presence
of a demonstrable stone (figure 11). Renal enlargement also may be
seen as a result of elevated renal vascular volume and interstitial
fluid in response to renal hemodynamic alterations.
Ultrasound, especially with the wide-spread use of spectral and
color Doppler, has assumed primary importance in diagnosis of
hydronephrosis in pregnancy. Excretory urography has an important
but secondary role in diagnosis, due to the increased risk of
ionizing radiation to the fetus.
Renal and bladder sonographic imaging in pregnancy should
include the renal size, echogenicity, presence or absence of
perinephric fluid, calculi, or ureteral jets, and at least three
measurements of resistive indices of interlobar or arcuate arteries
for each kidney. For Doppler waveforms, the lowest pulse repetition
frequency should be used to maximize the Doppler spectrum and
Transvaginal, transperineal, or transrectal ultrasound may be
necessary for detection of lower ureter calculi and dilatation.
Doppler may help identify the common iliac vessels and thus locate
tapering of the physiological dilated ureters.
Absence of marked asymmetry of ureteral jets in the bladder with
color Doppler over a 5- to 20-minute interval in well-hydrated
patients (600 to 1000 ml of fluid p.o. or IV) is strong evidence of
a moderate to high grade obstructive process (figure 12).
In 1993, Platt and coworkers reported that a mean resistive
index (RI) of greater than or equal to 0.70 and/or an inter-renal
difference (delta) of greater than or equal to 0.1 is indicative of
acute renal obstruction.
However, an intra-renal resistive index (RI=peak systolic
velocity-peak diastolic velocity/peak systolic velocity ) greater
than 0.70 is not typically seen in physiological dilatation of
pregnancy. Hertzberg et al demonstrated the lack of RI elevation in
pregnancy, even in the presence of physiologic pelvicaliectasis
With ureteral obstruction, renal vascular resistance increases,
diastolic blood flow decreases, and the RI increases. Resistive
index in the unaffected kidney also should be obtained for
comparison of inter-renal differences.
Spectral Doppler is not without controversy for diagnosis of
renal obstruction. In their study, Tublin et al were unable to
reproduce the high sensitivity or specificity of Doppler US for
obstruction using Platt's method and parameters.
They found duplex sonography to be 82% specific but only 44%
sensitive for the detection of acute renal colic in an experimental
According to a review by Ellenbogen et al, ultrasound detection
of symptomatic calculi is 98% sensitive and 74% specific in the
non-pregnant patient, but it drops off to 34% and 86%,
respectively, in the pregnant patient.
A KUB and limited excretory urogram (4 to 5 films) during pregnancy
has been reported to be 94% sensitive and 100% specific,
but has associated radiation risks. Although the risk of
radiation-associated anomalies and cancers is relatively low with
diagnostic studies, spontaneous abortion, teratogenicity, CNS
malformations, and childhood cancers are potential concerns.
In some cases, magnetic resonance urography may be useful for
differentiating physiologic from pathologic pelvicaliectasis.
It offers no ionizing radiation exposure and may be more accurate
than ultrasound. Roy and coworkers assessed the utility of rapid
acquisition with relaxation enhancement (RARE) MR-urography (RMU)
in pregnant patients with clinically suspected
ureterohydronephrosis. The researchers were able to differentiate
physiological from calculi-related hydronephrosis in the majority
of cases. Again, detection of physiologic dilatation presented as
tapering of the lower lumbar ureter, whereas obstructive
ureterohydronephrosis was evident by a ureteral filling defect on
heavily weighted T2 images with ureteral dilatation proximally. The
level of obstruction was determined in all cases by RMU, as opposed
to ultrasound, in which visualization of the blocked ureter is
often not possible.
Radiological imaging is paramount in the diagnosis of
genitourinary complications during pregnancy. Ultrasound is still
the first modality of choice, obviating the use of ionizing
radiation, although the risks associated with limited radiation
after organogenesis (first trimester of pregnancy) are minimal. MRI
is evolving as a very useful tool, especially in the imaging of
fibroids and adnexal masses in pregnant patients, and will probably
expand its use to the diagnosis of ureteral stones in the second
and third trimesters.
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