Dr. Bailey is a Radiology Resident, Dr. Twickler
is a Professor of Radiology and Obstetrics/Gynecology, Vice Chair for
Academic Affairs, and Holder of the Fred Bonte Professorship in
Radiology, and Dr. Rofsky is a Professor and Chairman of the
Department of Radiology, at the University of Texas Southwestern Medical
Center at Dallas, Dallas, TX. Dr. Pedrosa is Associate Professor
of Radiology, Harvard Medical School, and Director of Body
MRI, Department of Radiology, Beth Israel Deaconess Medical Center,
Boston, MA. Dr. Rofsky also serves as a Consultant to Bioclinica.
frequently guides patient management in the evaluation of pelvic pain.
When the patient is also pregnant, the source of the patient’s pain is
often clinically confounded. An accurate imaging diagnosis is important,
since surgical and medical management decisions often rely on those
findings. However, the anatomic and physiologic changes associated with
pregnancy pose substantial challenges to the interpreting radiologist.
Ultrasound should be used as initial evaluation given its lack of
ionizing radiation and wide availability. When ultrasound evaluation is
equivocal or limited, cross-sectional imaging is often requested
typically with computed tomography (CT).
With a heightened
awareness of radiation exposure and faster, motion immune sequences,
magnetic resonance (MR) imaging is being used with increased frequency.1-5 MR
of the abdomen with a gravid uterus displacing familiar anatomy can be
challenging for the otherwise seasoned radiologist well versed in
cross-sectional imaging.1 In this review, we will present
practical applications of MR in the pregnant patient with pelvic pain,
knowing that rapid diagnosis and prompt treatment is of the utmost
importance in this population.6
the lack of ionizing radiation characteristic of MR imaging represents
an obvious safety advantage for imaging pregnant patients, it is
important to consider exposure to the electromagnetic fields that are
encountered. Numerous tissue, cell culture, and animal experiments have
failed to reveal adverse impacts resulting from such exposure.7-14 Concerns
for heat deposition are most relevant at the skin, and even then,
whenMR imaging is performed within the FDA guidelines for specific
absorption rate (SAR) the risk is minimal and negligible at the body
core.15 A study using volunteers with fluid-filled stomachs
suggests sound intensity levels are attenuated to a safe level by the
amniotic fluid.9 Fetal heart rate and fetal movement patterns during MR procedures are unchanged with comparison to baseline.10 Studies following children imaged in utero have also demonstrated no increased rate of disease or disability.11,12
American College of Radiology considers MRI safe during pregnancy and
acceptable to use when the imaging results will affect clinical
management of the fetus or mother during the pregnancy.8,13,16 During
the first trimester, more judicious use of MR is recommended because of
organogenesis; early research suggested disorders of embryogenesis and
teratogenic effects in animal studies.11,16,17 However, to
date there are no known negative effects in the human population.
Current recommendations are to explain the risks and benefits of the
exam to the mother prior to imaging and to obtain written consent.
MR contrast agents
widely used extracellularly distributed, gadolinium-based intravenous
contrast agents cross the placenta in primate studies and
gadolinium-chelate molecules remain for an indeterminate time within the
amniotic fluid.16,18 During that time, there is potential
for dissociation and release of toxic, free gadolinium ions, which the
fetus is repeatedly exposed to as it swallows and excretes.8 Intravenous
MR contrast should not be routinely used in pregnancy, as
gadolinium-based contrast agents are considered category C drugs by the
Oral contrast preparations containing barium sulfate are not systemically absorbed in animal models.19 Gastrointestinal
absorption of iron from oral MR contrast agents containing iron oxide
(such as Ferumoxil) is variable, but animal studies have not
demonstrated detrimental effects at doses multiplicatively exceeding the
expected concentrations achieved with specified dosing for human use.
According to package information of oral contrast agents, studies have
not been done on pregnant humans and iron oxide MR contrast agents are
considered category B drugs by the FDA.
MR sequences that we use for pregnant patients with abdominal pain
include motion insensitive T2-weighted images, single shot fast spin
echo (SSFSE or HASTE) in three planes as well as fat-saturated SSFSE
images in the axial plane. Also, axial 2D TOF (to identify thromboses
and for anatomical differentiation) and axial T1-weighted GRE (in- and
out-of-phase to assist in characterization of hemorrhage) are included.2 The
use of diffusion-weighted imaging is gaining popularity in the
diagnosis of inflammatory conditions, such as appendicitis, in the
Given the often urgent condition of many
patients, there has been interest in and success using MR evaluation
without oral contrast agents.21,22 Several studies, however, consider negative oral contrast agents helpful in anatomic differentiation during pregnancy3 and diagnostically advantageous when used as a problem-solving tool.23-26 For
the majority of our studies, an oral preparation using 300 mL
Gastromark (Mallinckrodt Medical, St Louis, MO) and 300 mL Readi-cat 2
(Bracco Diagnostics, Princeton, NJ) given 1.5 hours prior to examination
was used to provide negative contrast within the bowel lumen without
substantial susceptibility effect.2 While outcomes assessments have been reported for series with oral contrast,1 at the time of this writing, studies without oral contrast with similar rigor have not been reported.
is the most common cause of abdominal pain in pregnant patients
requiring surgical intervention, and it occurs at a frequency comparable
to that of the general population (0.02% - 0.07%).1 The risk
of perforated appendicitis is greater in pregnant patients, possibly
due to delay in diagnosis. Efficient, accurate diagnosis is paramount as
complications of appendicitis include increasing rates of maternofetal
morbidity and mortality. Because surgical intervention alone imparts
increased fetal mortality (3%), every effort should be made to prevent
The criteria for
diagnosing appendicitis with MR are similar to that for using CT,
including a fluid-filled appendix of >6 mm to 7 mm indiameter and
ancillary findings of inflammation.1,13 However, identifying
the appendix can be challenging on MR, as well as in the gravid abdomen.
It is important to recognize that, as the uterus enlarges with
pregnancy, the appendix tends to migrate cephalad and medially.2 When
identifying the appendix, verify its location using all 3 imaging
planes and a localizing or “cross referencing” tool where
Oral contrast or air will fill
the normal appendix and appear dark on T2-weighted images.
Fat-saturation pulses are invaluable when differentiating
peri-appendiceal inflammation (high signal fluid) from fat (high signal
on T2-weighted images without fat saturation). Furthermore, the
demonstration of peri-appendiceal fluid can be helpful in suggesting
appendicitis in otherwise equivocal cases, whereas th eabsence of
peri-appendiceal fluid can be helpful in ruling out appendicitis when
the appendix cannot be visualized.1,3 Detection of
inflammation is particularly important when the appendix is not well
seen, borderline dilated (early appendicitis) or in cases of
perforation.2 Restricted diffusion is seen as high signal intensity in inflamed appendices on diffusion-weighted imaging (Figure 2).20 Since
dilated gonadal vessels can mimic the appearance of the appendix on T1-
and T2-weighted images, time-of-flight (TOF) images are recommended to
distinguish between the high signal of vessels and low signal intensity
of the appendix (Figure 3).2
can be used to evaluate the intestinal tract and is sensitive for
detecting the early inflammation seen in active flares of inflammatory
bowel disease (IBD). Bowel-wall edema is readily identified on MR using
single shot, T2, fat-suppressed images and balanced steady-state,
free-precession (bSSFP) images. However, this finding is not specific to
IBD; it can also be seen in various enteritidies/colitidies,
enteropathies, and ischemic insults (Figure 4). As in other modalities,
MR often cannot completely differentiate infectious from inflammatory
conditions of the bowel;however, the distribution and affected segments
(eg, the terminal ileum is a typical target of inflammatory bowel, skip
lesions versus continuous involvement from the rectum) and signs, such
as mesenteric inflammation related to dilated vasa rectae, may aid in
diagnosis. The sequelae ofIBD, such as inner-loop abscesses (very high
T2 signal, more easily seen if negative oral contrast agents are used to
differentiate from fluid filled bowel26), fluid- or gas-filled fistulae, and luminal strictures, can also be identified with MR.
the etiology of bowel obstruction may not be readily apparent on MR
imaging, the diagnosis can be reliably made. Small bowel is considered
dilated at 3-cm transverse diameter and colon is considered dilated
beyond 6 cm (cecum >9 cm) as with other modalities (Figure 5). A keen
search is advised when assessing for the signal void of gas, as can be
seen in the setting of pneumatosis or free air; extraluminal gas is more
difficult to identify on MR compared to CT. Adhesions and hernias are
the most frequent causes of bowel obstruction.2 Excellent
soft-tissue differentiation is possible using single-shot, echo-train,
spin-echo, T2-weighted images when oral contrast is given and motion
artifact is minimized by otherwise fasting the patient prior to
examination (to decrease peristalsis).
thickening and diverticular abscesses can be identified using similar
sequences and methods as described above and do not strictly require
intravenous contrast. On non-fat suppressed, T1-weighted images,
inflammatory fluid will be of low signal intensity and standout in
comparison to pericolonic fat (Figure 6). Diverticula are more common in
the sigmoid and descending colon. It is also worth emphasizing that
focal thickening from diverticulitis may, at times, be difficult to
differentiate from colonic neoplasm; in those instances a follow-up
assessment for resolution is advised. However, for women of childbearing
age colonic neoplasms are rare.
is excellent for visualization of the biliary tree by using MR
cholangiopancreatography (MRCP) to accurately diagnose a wide range of
abnormalities and to facilitate surgical planning. The SSFSE sequence
used in evaluating the pregnant patient is a common staple of MRCP
examinations and an assessment of the biliary tract is inherent to the
protocol, almost always captured with the large, coronal field-of-view.
MRCP is of particular value when the anatomy is unfavorable for adequate
sonographic visualization (as is frequently encountered in pregnancy)
(Figure 7). Biliary stones and biliary gas both produce signal void on
MR; however, nondependent positioning suggests biliary gas. Inflammation
of the biliary system appears as wall thickening and edema, and can be
associated with luminal dilation, adjacent fat stranding and fluid
collections. The full extent of biliary neoplasm, stricture or
malformation can be readily identified using MR. Oral contrast helps to
delineate anatomy near the pancreatic head,30,31 but if prior
sphincterotomy of the major or minor papillae has been performed, the
negative contrast can reflux into the biliary system and obscure
visualization of the biliary tree.32
(fibroids) are benign, smooth muscle neoplasms extending from or
involving the myometrium of the uterus. Fibroids that rapidly grow
during pregnancy may cause pain. Pain can also be associated with
torsion of pedunculated fibroids and degeneration if the fibroids
outgrow their blood supply. Hemorrhagic infarction or “red” degeneration
is specifically associated with pregnancy and demonstrates high
T1signal due to hemorrhagic components that may be diffuse or
peripheral. Signal on T2-weighted imaging is often variable; however,
high T2signal located centrally in the fibroid is consistent with
necrosis.2,33 Diffusion-weighted imaging can be performed to
evaluate for the restricted diffusion of acute degeneration in the
fibroid (Figures 8-10).
pelvic mass is identified during sonographic examination, compression
can determine if the mass is associated with or separate from the ovary.
However, in pregnancy, the actual location and characterization of
ovarian masses may be problematic. MR is particularly helpful in
defining the relationship of masses to the uterus and ovary and can
offer tissue characteristics based on the T1- and T2-weighted signal
Acutely, ovarian torsion may cause enlargement and
edema of the affected ovary, which may be more easily detected on
fat-saturated,T2-weighted images. An ovarian mass or cyst is often
associated with cases of ovarian torsion. Hemorrhage within the ovarian
stroma itself is a later finding of torsion and demonstrates variable
signal on T1- and T2-weighted images, depending on the age of the
contained blood products.2
endometriosis is a common cause of infertility, pain related to
endometriomas can be encountered during pregnancy. Endometriomas will
demonstrate high signal on T1-weighted images and typical “shading” (low
signal on T2-weighted images), as seen in nonpregnant patients.
Multifocal involvement, adhesion, and tethering of adjacent structures
also support a diagnosis of endometriosis (Figure 12).2
Atypical ectopic pregnancy
percent of ectopic pregnancies are tubal and can be diagnosed with
ultrasound. In the setting of atypical locations and large ectopics, the
large field of view afforded by MR is helpful in defining the anatomic
origin and effect on other structures in the pelvis (Figure13). One
example is the case of a cesarean ectopic in which the relation to the
cesarean scar can clearly be seen (Figure 14).34
Cystitis and pyelonephritis
with urologic conditions, ultrasound is the primary imaging modality
for diagnosis in pregnant patients. However, thickening of the urinary
bladder wall can be detected on MR as well as on CT and may suggest
inflammation related to infection. Nondependent signal voids in the
urinary bladder suggest air, which is only normal if iatrogenic (eg,
recent Foley catheter placement or cystoscopy). Pyelonephritis is
usually a complication of lower urinary tract infections. The affected
kidney may be enlarged or have perinephric fluid, which is nonspecific.
The prototypical “striated nephrogram” will not be detected without
intravenous contrast, but diffusion-weighted imaging may identify
restricted diffusion (Figure 15). Proteinaceous material in the
collecting system will be of higher signal intensity than urine on
unenhanced T1-weighted images. Renal abscesses may complicate
pyelonephritis; they are difficult to confidently identify on MR without
intravenous contrast. A focal area of perinephric stranding (versus
perinephric stranding surrounding the whole kidney) is a clue to a
possible underlying abscess.33
half-Fourier single-shot fast SE for evaluation of the urinary tract,
collecting system, and ureteral stones will be detected as focal areas
of signal void. Similarly, blood clots and fungus balls are also of low
signal intensity. Collecting system air should layer nondependently.
When there is laminar flow in the ureter, a central, poorly defined
filling defect may be seen on the SSFSE sequence (Figure 2). Perirenal
fluid can be seen in obstruction, but is nonspecific, as in other
radiographic modalities.2 Urothelial tumors are less common
causes of urinary obstruction and may be eccentrically located within
the collecting system and have associated wall thickening. The full
extent of tumor involvement may be difficult to delineate without
Hydronephrosis is a common
finding late in pregnancy. If the degree of hydronephrosis is moderate
to severe, or the patient is symptomatic, MR can further evaluate the
ureters. Typically, pregnancy-related hydronephrosis will show tapering
of the ureter to the point where it is extrinsically compressed by the
gravid uterus and posterior structures, often at the sacral promontory
(Figure 16). Ureteral calculi are typically symptomatic, will cause a
more abrupt caliber change of the ureter, and may have associated
periureteral inflammatory changes (Figure 17). If ureteral dilation is
distal to the pelvic inlet, there is an increased likelihood of an
obstructing calculus being the cause of hydronephrosis.2
the source of abdominal and pelvic pain in the pregnant patient
necessitates an accurate and timely diagnosis. Imaging will continue to
provide vital diagnostic information; the utilization of MR technology
is growing in cases where sonographic evaluation alone is not sufficient
to guide management.13 An awareness of the utility of MR
imaging for the pregnant patient with abdominal and pelvic pain and an
appreciation for the appearances of a variety of pathologies can be
useful for enabling a broader implantation of this technology, thereby
minimizing exposure to ionizing radiation.
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