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Original Research |
1 All authors: Department of Radiology, Duke University Medical Center, Erwin Rd., Box 3808, Durham, NC 27710.
Received March 19, 2007;
accepted after revision June 7, 2007.
Address correspondence to T. A. Jaffe
(jaffe002{at}mc.duke.edu).
Abstract
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MATERIALS AND METHODS. A survey was sent to the abdominal imaging division of 183 radiology residency programs in the United States. The survey asked for information regarding CT and MRI of abdominal complaints in pregnant patients.
RESULTS. Eighty-five surveys (46%) were returned. Sixty-three (74%) of 85 of respondents have a written departmental policy regarding imaging pregnant women. Eighty-two (96%) of 85 perform CT in pregnant women when benefits outweigh risks, with 58 (68%) obtaining written informed consent before CT examination. Eighty (94%) of 85 perform MRI in pregnant women, and 43 (51%) obtain written consent before MRI. Fifty-seven (67%) of 85 respondents do not administer gadolinium in pregnancy. In the setting of trauma, respondents choose CT over MRI for imaging in all three trimesters (75% vs 5%, 85% vs 5%, and 88% vs 4%). In the second and third trimesters, respondents prefer CT to MRI to evaluate for maternal renal calculus (35% vs 20% and 48% vs 18%, respectively), appendicitis (48% vs 38% and 58% vs 29%), and abscess (49% vs 41% and 58% vs 35%). However, MRI is preferred for imaging of appendicitis and abscesses in the first trimester (39% vs 32% and 46% vs 32%).
CONCLUSION. Most academic radiology departments have written policies regarding imaging of pregnant women. Academic radiologists prefer CT to MRI for imaging abdominal complaints in pregnant women, especially in the second and third trimesters.
Keywords: abdominal pain • CT • MRI • pregnancy
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CT has traditionally been avoided during pregnancy because of its ionizing radiation and its risk of teratogenesis and carcinogenesis [5, 6]. Although the safety of MRI in pregnancy has not been conclusively proven [3, 7–13], the American College of Radiology (ACR) White Paper on MR Safety states that pregnant patients may undergo MRI at any stage of pregnancy if it has been determined the benefits outweigh the risks [14]. This recommendation was based on prior safety guidelines issued earlier [15–17]. The decision to administer contrast material for MRI in pregnancy is even more controversial [4, 11, 12, 14, 17–19]. Although gadolinium in a chelated form is harmless from a toxicologic perspective, its free form is severely toxic. Although it is administered in a chelated form, small amounts of free gadolinium may appear during the repetitive fetal circulation, as shown in an animal study [18, 20]. To our knowledge, the effects of free gadolinium on the developing human fetus have not been well documented.
No consensus exists regarding an algorithm for imaging abdominal complaints in pregnant patients. To our knowledge, no studies have evaluated the current practice patterns of U.S. academic radiologists in imaging for acute abdominal complaints in obstetric patients. Our aim was to identify national trends in the radiology departments of academic medical centers for imaging in these complex clinical cases.
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Respondent Demographics
Recipients of the questionnaire were asked about hospital and department
demographics, including number of hospital beds, number of radiologists,
number of radiologists interpreting abdominal CT and MRI examinations, and the
number of radiologists with fellowship training in abdominal imaging.
Respondents were also asked whether MRI is performed after 11:00 pm and on
weekends and whether there is a high-risk obstetrics division in their
hospital.
Pregnancy Workup
Respondents were asked if they queried all woman of reproductive age as to
whether they were pregnant before an imaging procedure with ionizing
radiation, and whether a ß-hCG level (urine or serum) is obtained before
the procedure. The remainder of the questionnaire pertained to imaging for
abdominal complaints in the pregnant woman when sonography was negative or
inconclusive. Respondents were asked about departmental policies on imaging
the pregnant patient, including whether the radiologist counsels the patient
before CT or MRI, whether a policy exists on imaging the pregnant woman, and
whether written informed consent is obtained before CT or MRI.
CT and MRI in the Pregnant Woman
Respondents were asked if they ever perform CT in the pregnant woman:
Options included whenever asked, when benefit outweighs risk, only in dire
circumstances, and never. Respondents were asked whether, before CT, there is
a discussion between radiology resident and attending radiologist, whether a
physician speaks to the patient before this procedure, and whether written
consent is obtained. Respondents were asked if CT protocols were modified to
decrease radiation dose. They were also asked to select indications for CT,
with questions stratified by trimester of pregnancy. Choices included trauma,
appendicitis, abscess search, malignancy staging, kidney stone, bowel
obstruction, and "other." A similar question was posed regarding
the administration of IV iodinated contrast material.
These questions were also asked in reference to MRI. In addition, respondents were asked to choose from a variety of MR sequences used in imaging the pregnant patient. Respondents were queried about the use of IV gadolinium-containing contrast agents in this patient population.
Department Policy
Respondents were asked whether an agreement exists in the abdominal imaging
division on the management of imaging for acute abdominal complaints in the
pregnant patient and whether there is agreement between the abdominal imaging
division and the obstetrics department on this issue.
Hypothetic Scenarios
Respondents were given multiple clinical scenarios, including suspected
appendicitis, renal colic, abscess search, and trauma, with a query of imaging
technique of choice for each situation. For each of these questions,
respondents were told to choose from CT, MRI, or "none of the
above." Each question was stratified by trimester. Respondents were also
questioned on the choice of management for an incidental liver lesion found on
sonography in a pregnant woman. Response choices were no workup until after
delivery, CT without IV contrast material, CT with IV contrast material, MRI
without IV contrast material, and MRI with IV contrast material. Respondents
were asked whether the stage of pregnancy influenced their choice in workup of
the liver lesion.
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Abdominal MRI is performed after 11:00 pm in 73 (86%) of 85 of the responding centers and on the weekend in 81 (95%) of 85. There are high-risk obstetric departments in 70 (82%) of 85 responding centers. Four of the 85 respondents did not know whether their obstetric department includes a high-risk obstetrics subspecialty division.
Pregnancy Workup
Eighty-four (99%) of the 85 responding medical centers query women of
reproductive age about their pregnancy status before CT or MRI; however, only
12 (14%) of the 85 obtain either urine or serum ß-hCG. Fifty-seven (67%)
of the 85 respondents counsel women before CT or MRI. Sixty-three (74%)
departments have a policy about imaging with ionizing radiation during
pregnancy, and 62 (73%) obtain written consent before imaging these women with
ionizing radiation.
CT and MRI in the Pregnant Woman
Eighty-two (96%) medical centers image a pregnant woman with CT, mostly
when benefits outweigh the risks (80/82, 98%). Forty-seven (55%) respondents
consult with the resident on call before performing CT of a pregnant woman,
and 65 (76%) responding institutions have a physician counsel women on the
risks of radiation with CT. Fifty-eight (68%) respondents obtain written
consent before CT in the pregnant woman, and 20 (24%) add a note in the
pregnant woman's hospital chart before CT.
Only 27 (32%) responding physicians have a dedicated CT protocol for pregnant women. Twenty-six (31%) of the respondents always lower the CT dose, 40 (47%) sometimes lower the dose depending on the clinical question, and 19 (22%) respondents never alter the CT dose in pregnant women.
When given multiple clinical queries for abdominopelvic CT in pregnant women, respondents are more likely to choose CT for trauma in all three trimesters than for other acute abdominal indications such as appendicitis, abscess, kidney stone, or small-bowel obstruction. Respondents are more likely to use CT for imaging the latter indications in the second and third trimesters (Table 1). The administration of IV iodinated contrast material varies greatly among respondents (Table 2).
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Eighty (94%) respondents perform MRI in pregnant women with abdominal complaints, with 57 (81%) qualifying the answer by noting "only when benefits outweigh risks." Residents consult an attending physician on call before beginning MRI in pregnant women in 53 (62%) responding medical centers. Fifty-one (60%) respondents ensure a physician speaks with the woman before the MRI and 43 (51%) obtain written informed consent before MRI.
A range of sequences is used in MRI of the pregnant abdomen, with emphasis on motion-robust techniques (Table 3). Fifty-seven (67%) of the respondents do not administer gadopentetate dimegluminein pregnancy. The most common indication for the administration of gadolinium is malignancy staging.
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Respondents' application of MRI for acute abdominal pain in the pregnant woman varies little across the three trimesters (Table 4). Respondents are less likely to use MRI in the setting of trauma than they are in the setting of appendicitis, small-bowel obstruction, or abscess.
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Department Policy
When asked about controversies in imaging acute abdominal complaints in the
pregnant woman, 53 (62%) of the responding physicians noted complete agreement
with their partners in the management of these patients. Twenty-three (27%) of
the respondents noted that an agreement exists despite a lack of policy in
this setting, and 27 respondents (32%) leave the imaging management (including
choice of technique) to the person responsible for interpreting the study.
Forty-five (53%) respondents note some disagreements between the abdominal
imaging and high-risk obstetric divisions in the imaging management of these
patients.
Hypothetic Scenarios
Respondents' selections of imaging technique in acute abdominal complaints
in pregnancy are shown in Figure
1A,
1B,
1C. Respondents overwhelmingly
prefer CT to MRI in the evaluation of trauma in a pregnant woman, regardless
of trimester. In the evaluation of suspected renal calculus, respondents
choose CT over MRI in both the second (35% vs 20%) and third (48% vs 18%)
trimesters. Respondents were not asked about imaging choice for renal colic in
the first trimester because physiologic hydronephrosis of pregnancy is usually
not an issue this early in pregnancy. In the evaluation of suspected abscess
or appendicitis, respondents prefer imaging with CT over MRI in the second and
third trimesters. Forty-two (49%) of the respondents choose CT over MRI for
imaging abscesses in the second trimester, and 49 (58%) for imaging in the
third trimester, whereas 35 (41%) and 30 (35%) of the respondents prefer MRI
for the same indications during the second and third trimesters, respectively.
Forty-one (48%) and 49 (58%) of the respondents select CT for imaging
appendicitis in the second and third trimesters, respectively, in contrast to
the 32 (38%) and 25 (29%) respondents who choose MRI. In the first trimester,
however, MRI is vastly preferred over CT for abscess and appendicitis (46% vs
32% and 39% vs 32%, respectively).
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Our questionnaire was sent to 183 U.S. academic radiology departments that have an accredited radiology residency program. The response rate of 46% (85/183) was within our expectation and is similar to the rates for other questionnaire-based studies documented in the radiology literature [21–24].
In general, most divisions have a similar approach to screening pregnant women before imaging. Although most groups ask all women of reproductive age about the possibility of pregnancy, only a small number obtain laboratory data to exclude this possibility before imaging. This additional effort is likely thought to be time-consuming and costly. Two thirds of the academic radiologists counsel pregnant patients and obtain written informed consent before CT. Three quarters of the responding departments have a written policy covering the use of ionizing radiation in pregnancy.
Few departments have a dedicated abdominal CT protocol for imaging pregnant women, and whether the radiation dose is altered for this patient population varies. This inconsistency might be explained by the infrequent, and often "after hours," occurrence of this clinical situation, when protocol decisions are made by residents. With respect to determining a radiation dose, pregnant women vary significantly in size during the three trimesters, so a standard protocol may not fit all women.
Radiologists are more likely to choose CT for maternal trauma, regardless of the trimester. This follows trends found in the radiology literature because most studies concerning CT in pregnancy focus on trauma [25–27]. MDCT is fast, is readily available, and allows immediate surgical intervention if needed. Concern about radiation to the fetus in this setting is outweighed by the necessity to intervene for the preservation of both maternal and fetal health. Studies from the nuclear explosion in Japan and nuclear accident in Chernobyl have shown no increase in intrauterine demise from radiation exposure [28, 29]. The radiology literature suggests that for most radiologic procedures, the risk of fetal demise in the first 2 weeks after conception is less than 1% [27]. Estimation of fetal demise as a consequence of CT is difficult to assess because women are often unaware of the pregnancy at this stage, and the overall rate of miscarriage during the first 2 weeks in the general population is believed to be high (25–50% of conceptions). Fetuses between 2 and 15 weeks' gestation are most sensitive to radiation effects, most notably CNS defects and growth retardation [30]. The estimated level of radiation below which no adverse developmental effects can be seen is believed to range between 5 and 15 rad (0.05 and 0.15 Gy) [31, 32]. New data on radiation doses to the first-trimester fetus undergoing abdominopelvic 16-MDCT are lower than threshold levels thought to induce these teratogenic effects [6].
The positive statistical relationship between prenatal radiation and childhood malignancies was first reported in the 1950s from the results of the Oxford Survey of Childhood Cancers (OSCC) [33, 34]. The OSCC was a longitudinal, case-control study of cancer deaths occurring in children younger than 16 years in Britain. As noted by Wakeford [35], the interpretation of this association has been under debate since the study results were published [36, 37]; a discussion of the argument is beyond the scope of this article. Additional studies of prenatal radiation and childhood cancers have followed [38–41], and after similar findings were reported by MacMahon [38] in a study of children in the northeastern United States in 1962, the association between prenatal radiation and childhood cancers became widely accepted [40]. On the basis of evidence collected to date, Doll and Wakeford [40] conclude that "radiation of a fetus in utero increases the risk of a childhood cancer, that an increase in risk is produced by doses on the order of 10 mGy, and that in these circumstances the excess risk is approximately 6% per Gy." Estimates from the International Commission on Radiological Protection publication 90 [32] suggest that the overall risk of a childhood cancer for a fetus receiving 3.0 cGy (the fetal dose reported by Hurwitz et al.[6] for an appendicitis MDCT protocol) is double that of the general population, approximately 2 in 600, increased from 1 in 600. The relative risk of carcinogenesis secondary to ionizing radiation decreases later in pregnancy [42]. The excess relative risk of developing childhood cancer has been estimated to be approximately 0.28 at 1.0 mGy in the first trimester; 0.03 at 1.0 mGy in the third trimester; and overall during pregnancy, 0.037 at 1.0 mGy [43]. Given these statistics, health care professionals involved in the management of the pregnant woman should take into account these potential risks before undertaking CT.
Only a small number of academic abdominal imagers avoid CT in the first trimester; however, fewer than half of the practices surveyed administer iodinated contrast material in this patient population. As would be expected, most administer contrast material in the setting of trauma, when early diagnosis of organ injury is critical to both maternal and fetal survival. Fewer academic radiologists administer IV contrast material for the other clinical entities. Of note, IV iodinated contrast material is a U.S. Food and Drug Administration (FDA) pregnancy classification B drug, defined as a drug in which either animal reproduction studies have not shown a fetal risk but there are no controlled studies in pregnant women, or animal reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the first trimester and there is no evidence of a risk in later trimesters [44]. Iodinated contrast material potentially decreases thyroid hormone production in the fetus, and newborns who received IV iodinated contrast material in utero should have thyroid screening at 1 week of life [45].
Most of the respondents perform MRI in pregnant women with abdominal complaints. This follows recommendations in the literature [18, 46–48], specifically as noted by Shellock and Crues [48]: "In cases where the referring physician and attending radiologist can defend that the findings of the MR procedure have the potential to affect the care of the mother or fetus...the MR procedure may be performed with oral and written informed consent, regardless of the trimester." Although early animal research has raised the question of possible teratogenic effects of MRI and spontaneous abortions in early pregnancy [49–51], further animal data did not support these findings, and there are no human data to corroborate these findings [48, 52–57]. Nor have data substantiated any evidence of acoustic injury in utero [58, 59]. Although respondents were not queried specifically about field strength, these studies are presumably performed on a 1.5-T system, because abdominal imaging in pregnancy is still performed at this field strength. To our knowledge, no research has been performed of safety or efficacy of fetal MRI at 3 T, although a proposal exists stating that increased artifacts and safety concerns make 3 T inappropriate in this clinical setting [60, 61].
More than half of the institutions responding to our survey will consult with the resident on call before undertaking MRI in a pregnant woman, and approximately half will obtain informed written consent before beginning the study. Most academic abdominal radiologists use a variation of a fast, motion-robust T2-weighted MR sequence. This trend is in direct correlation with suggested protocols in the literature [2, 7, 9, 62]. These sequences limit bowel peristaltic artifacts with a short imaging time and increase resolution of the mucosal surfaces seen adjacent to high T2 signal luminal contents [2]. These characteristics increase conspicuity of many bowel abnormalities such as appendicitis and obstruction.
Few institutions are using MRI for imaging of maternal trauma. More than half of academic abdominal imagers do not administer gadolinium in pregnancy, and if they do it is typically for malignancy staging. This trend follows the ACR suggestions with respect to gadolinium administration because in this setting, the benefits would markedly outweigh the risks [18]. As noted before, gadopentetate dimeglumine is a pregnancy category C drug, the FDA classification for drugs in which there are no well-controlled studies in pregnant women and animal studies have shown an adverse effect [44]. Studies have shown that maternally administered gadolinium crosses the placenta and enters the fetal circulation; from there it is filtered by the fetal kidneys and excreted into the amniotic fluid [11, 13, 16–19, 45]. This fluid is swallowed by the fetus and reabsorbed from the gastrointestinal tract. Although gadolinium in a chelate form is harmless from a toxicologic perspective, its free form is severely toxic. And although it is administered in a chelated form, small amounts of free gadolinium may appear during the repetitive fetal circulation, as shown in an animal study [20]. The effects of gadolinium on the developing fetus have not been well documented, and several authors of MR studies in pregnancy advise against its administration [11, 12].
Almost two thirds of respondents note complete agreement among their partners in the management of imaging of the pregnant patient, with fewer leaving the choice of the imaging technique to the person interpreting the study. Just more than half experience conflict with their high-risk obstetric colleagues in the imaging management of women with abdominal complaints. The obstetrics literature contains little on the preferred algorithm for imaging pregnant women. The American College of Obstetricians and Gynecologists (ACOG) recommends that "concern about possible effects of ionizing radiation exposure should not prevent medically indicated diagnostic X-ray procedures from being performed on a pregnant woman" [63]. The ACOG Committee on Obstetric Practice further suggests that both CT and MRI contrast agents are unlikely to cause harm but should be used only if the benefit outweighs potential risk to the fetus [63]. These guidelines are similar to those of the ACR and leave determination of "benefit" and "risk" to the physicians involved.
When faced with a hypothetic clinical scenario and choice of imaging technique, imagers overwhelmingly prefer CT to MRI for imaging of trauma, regardless of trimester. Radiologists are also more likely to image for suspected renal calculus with CT than with MRI in both the second and third trimesters, despite an emerging interest in MR urography. Interpretation of the latter requires identification of either the signal void of a renal calculus or a ureteral transition point at an unusual site (outside the expected narrowing at the sacral promontory seen in physiologic hydronephrosis of pregnancy) [11–13, 64].
Given the scenario of imaging appendicitis or abscess in pregnancy, radiologists again choose CT over MRI; however, in patients in the first trimester of pregnancy, the same radiologists are more likely to image with MRI. This is thought to represent their concern about the potential teratogenic effects of ionizing radiation in the first trimester.
More than half of radiologists delay workup of an incidentally discovered liver lesion until after delivery, regardless of when the lesion is discovered. Those who choose to pursue further evaluation select MRI without gadolinium as the technique of choice. This sentiment suggests a belief among radiologists that pregnancy is a time-limited event and that the potential risk to the fetus outweighs any benefit to the mother. It is important to remember that the clinical suspicion of the obstetrician will likely affect the decision to further work up this lesion.
The structure of our survey had several limitations, and, ultimately, so did the study results. First, the questionnaire may not evaluate the experience of the entire staff at each practice but reflect only one staff member's opinion. We attempted to contact the division chief in the hopes that this person would have a global perspective. It is inappropriate to assume, however, that this one respondent's opinion reflects the general consensus of his or her own group. Indeed, even in our own group there is a wide range of opinions on the appropriate imaging management of these patients. For this reason, adoption of one universal guideline or standard is difficult. Second, this questionnaire was directed toward the imaging practice patterns and opinions of academic radiologists, neglecting private practice, and thus this study reflects the opinions of only a small subset of practicing radiologists. Finally, obstetricians were not surveyed. Their judgment in the clinical examination and their level of concern are vital when making decisions about how to image the pregnant woman.
In summary, 74% of academic abdominal radiology departments have policies regarding imaging and pregnancy. Most academic abdominal radiologists prefer CT to MRI for imaging maternal trauma in all three trimesters, and they prefer CT to MRI for the evaluation of abdominal complaints in the second and third trimester but choose MRI in the first trimester.
Given the lack of consensus in approach to imaging pregnant women, radiologists are faced with majority decisions in selecting the procedure with this patient population. Although the ACR suggests that potential radiation risks and clinical benefits should be considered in imaging pregnant women [5], there are only unofficial guidelines in the literature for radiologists to follow when considering this imaging algorithm. These guidelines include appropriate screening of women of reproductive age, avoidance of ionization radiation in pregnant women if possible, clinical consultation between the ordering physician and the radiologist before undertaking nonsonographic imaging studies in pregnant women, and documentation of this discussion in the radiology report [8, 15, 18, 19, 31, 48, 63]. As written, these principles should be applied uniformly throughout the radiology department, regardless of time of day or imaging technique used. Further investigation regarding imaging of pregnant women is warranted as new technologies are introduced. Additional debate is expected as radiologists and referring clinicians continue to be challenged by this imaging conundrum.
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