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Invited Commentary |
1 Department of Radiology, University of Alabama at Birmingham, Birmingham, Alabama
It has been stated that "The general attitude of our society is that lifestyle during pregnancy should be as near normal as possible...leading to work, travel, and recreation in a mostly unaltered manner...This lifestyle puts pregnant females at risk for injury" (1). Seven percent of pregnant women suffer trauma (2). Most injuries are minor, so that only about 1% of hospital trauma patients are pregnant women (2). Consequently, most care givers, especially radiologists, do not often deal with severe trauma in a woman who is pregnant. When they are faced with such a patient, diagnosis and treatment may be delayed as a result of their unfamiliarity with the nuances of care and because of the emotional overlay inherent in the situation (3).
In the preceding article , Lowdermilk et al discussed the use of CT for the evaluation of pregnant trauma patients (4). This topic has received little attention, as shown by the authors' bibliography: only 10 references, with seven articles being from peer-reviewed journals and one from a major radiologic journal. Thus, their article, which illustrates both normal and abnormal CT appearances of the gravid uterus, adds significantly to the radiology literature.
Lowdermilk et al reported the combined experience of two trauma centers, at which 605 pregnant trauma patients were seen over 42 months out of a total of 27,500 trauma victims. Forty-eight of those women underwent CT, and the highly select nature of this group is reflected by the fact that only 35% of the patients (n = 17) had negative findings, whereas 31% (n = 15) had nonuterine injuries and 27% (n = 13) had both uterine and nonuterine injuries at CT. These results underscore the need for a CT imaging protocol designed to evaluate both uterine and nonuterine organs in pregnant trauma patients. In the series of 48 patients, CT demonstrated abnormal placental enhancement in 11 cases and uterine rupture in one; 10 of the 11 fetal deaths occurred in this group, indicating the importance of the CT findings. Five of the fetal deaths were a result of maternal demise.
Several prior reports of trauma during pregnancy have shown that although up to 7% of pregnant women suffer trauma during pregnancy, only 0.4% of these women are admitted to a hospital (5). The majority of their injuries result from motor vehicle collisions, with falls being the second most common cause and intentional assaults (including suicide) surprisingly common (2,3). Unsurprisingly, this patient population is young, with a mean age of about 25 years. Overall, the mortality in this group has been reported to be about 10%, which is similar to the death rate among general trauma patients, and there is no difference in morbidity between pregnant trauma patients and nonpregnant trauma victims (2). In cases of maternal trauma, the death rate for fetuses is about 33%, and, although fetal death is most closely correlated with severity of injury, abruptio placentae can occur with even minor maternal injury (2,6). Evaluating the seriousness of injury in a pregnant patient is made more difficult by the physiologic changes of pregnancy. Increases in plasma volume, cardiac output, shunting of blood away from the uterine circulation, and pH changes make measurements of blood pressure, pulse, and partial pressure of oxygen unreliable indicators of significant blood loss (2,3).
CT has become the standard method for investigating serious trauma, since it is accurate, is cost-effective for both blunt and penetrating trauma, and helps predict outcome to some degree (7–10). CT depicts hemoperitoneum, retroperitoneal hemorrhage, and orthopedic and solid organ injuries with high sensitivity and frequently demonstrates bowel and mesenteric injuries although with less sensitivity.
US may be proposed as an alternative to CT for evaluating the pregnant trauma patient, partly to avoid exposing the fetus to x rays. Although US has an important role, particularly for the assessment of fetal viability and age, it has significant shortcomings, one of which is its limited ability to depict placental abnormalities. In the report of Pearlman et al (6), the results of US examination were false negative in three of the five cases of abruptio placentae. Although Lowdermilk et al did not perform a prospective comparison of CT and US, their data suggest that CT may be more accurate for detection of placental lesions.
Several recent articles have discussed the utility of US for evaluating trauma victims (11–14). In general, these reports state that US can be a very useful, expeditious screening tool in the emergency department, particularly because it is highly sensitive for detection of intraperitoneal fluid, which is a strong indicator of significant injury. However, US is much less sensitive for detection of specific organ injuries and retroperitoneal injuries. In one report, US showed parenchymal abnormality in only 22% of renal injuries (15). In a report of three pregnant trauma victims, US did accurately reveal hemoperitoneum, although two patients underwent CT for further evaluation (16). The authors believed that the intraperitoneal fluid may be from either the uterus or elsewhere and concluded that US is not reliable for detecting uterine rupture or for ruling out fetal-placental injury (16).
Although a care giver may be hesitant about imaging pregnant patients with CT for fear of exposing the fetus to radiation, two basic tenets for guiding evaluation and treatment of the pregnant trauma patient should be followed:
1. What is good for the mother is good for the baby; if the mother does not survive, it is extremely unlikely the baby will.
2. "The secondary diagnosis of pregnancy should not generally alter the routine diagnostic, pharmacologic, or resuscitative procedures or interventions" (2). In other words, one should use the best imaging tools for diagnosis based on substantiated experience.
The radiologist should, however, be aware of and prepared to handle the anxiety of the patient or family members about exposure of the fetus to radiation. The general population believes that radiation is harmful, and they often do not separate the effects of low-dose ionizing radiation from the physical, psychologic, and radiation effects of the atomic bomb. The potential adverse effects of fetal radiation exposure are the induction of fetal anomalies, growth retardation, and increased risk of malignancies. However, all of these have a dose-response relationship and a threshold below which it is not possible to demonstrate a difference in prevalence between the general population and the irradiated population (17). The embryo is sensitive during early organogenesis (especially during the 2nd to 4th weeks of gestation) to growth retarding, teratogenic, and lethal effects of x rays (17). In the early fetal period (ie, after 8 weeks gestational age), there is less likelihood that radiation will induce teratogenic effects, but the central nervous system remains sensitive. In later fetal stages, radiation will not cause deformity, but there may be cell depletion if the dose has been high enough (17,18). It is estimated that an exposure of 0.1–0.2 cGy increases the risk of developing leukemia about 1.5 times. Some perspective is in order. First, even in the general population, 27.5 anomalies occur per 1,000 live births (17). No malformation or growth retardation has been reported in fetuses exposed to less than 0.5 cGy. The actual risk of developing leukemia is one in 2,000 in the irradiated population compared with one in 3,000 in the general population (17,18). It can be quite difficult to estimate the exact exposure to the fetus. With CT, fetal exposure depends not only on milliampere seconds, peak kilovoltage, section thickness and intervals, pitch for helical CT, and whether the same anatomic area is imaged more than once, but also on the size of the mother and the position of the fetus. It is unlikely that the radiation dose from any diagnostic x-ray study would exceed 0.5 cGy; most estimates of radiation dose incurred in a CT examination are less than 0.1 cGy, which is well below the level at which severe adverse effects could be expected (2,18). Actual follow-up reports are few, but Drost et al (1) indicated that no deleterious effects were observed in 23 babies whose mothers had undergone multiple x-ray procedures for evaluation of injuries while pregnant.
In summary, there is no reason to avoid use of CT to evaluate a pregnant woman with evidence that she has a life-threatening injury. CT most likely will provide more accurate diagnostic information than any other procedure and will allow the mother the best chance for survival and completion of the pregnancy.
In the future, other imaging options may be viable. There has been minimal experience with magnetic resonance (MR) imaging in the evaluation of trauma. A single comparison study showed that in a small number of patients, MR imaging had no distinct advantage over CT, but in fact MR imaging with standard spin-echo T2-weighted sequences performed as well as CT did (19). Several studies have shown that MR imaging with fast, heavily T2-weighted sequences (such as RARE or HASTE) can be used for fetal evaluation (20). The utility of such sequences for evaluating trauma patients in general or pregnant trauma patients has not been determined. Although MR imaging has not been fully proved to be safe, children imaged in utero have not shown abnormalities at follow-up (21). Currently, use of MR imaging to evaluate trauma patients is limited not only by lack of experience and documented diagnostic criteria but also by logistics. Most MR imaging facilities are not physically near the trauma center, and many have not been well designed to allow the level of monitoring required for trauma patients. Perhaps years from now, MR imaging will be considered the preferred method for evaluating pregnant trauma victims. Only future investigation will tell.
References
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