MRI of Fetal and Maternal Diseases in Pregnancy 1st ed.

25. Role of MRI in Trauma in the Pregnant Patient

Whitney Manlove1Kathryn J. Fowler2Vincent M. Mellnick2Christine O. Menias3 and Constantine A. Raptis 

(1)

Radiology, Mallinckrodt Institute of Radiology, St. Louis, MO, USA

(2)

Abdominal Imaging Section, Mallinckrodt Institute of Radiology, St. Louis, MO, USA

(3)

Radiology, Mayo Clinic - Scottsdale, Scottsdale, AZ, USA

(4)

Cardiothoracic Imaging Section, Mallinckrodt Institute of Radiology, St Louis, MO, USA

Constantine A. Raptis

Email: raptisc@mir.wustl.edu

Keywords

TraumaInjuryPregnancyMRIImagingHemoperitoneumPneumoperitoneum

25.1 Imaging of Pregnant Patients Involved in Trauma

Trauma is the leading cause of nonobstetric maternal mortality and affects between 5 and 8 % of pregnancies [14]. The majority of cases of trauma in pregnant patients are due to motor vehicle collisions, although falls, assaults, burns, and other wounds can contribute to maternal trauma [4]. Fetal loss is also an important problem in the setting of a pregnancy complicated by trauma, with fetal loss rates of approximately 40–50 % in life-threatening trauma. Although the rates of fetal loss in minor trauma are much lower (1–5 %), given the increased incidence of minor trauma, the majority of fetal losses occur after minor trauma [1].

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Fig. 25.1

Hemoperitoneum. (a) Axial T1-weighted gradient recalled echo image with fat saturation, (b) sagittal T2-weighted single shot turbo spin echo, and (c) axial T2-weighted turbo spin echo with fat saturation images through the pelvis demonstrate T1- and T2-hyperintense free fluid in the pelvis representing moderate-volume hemoperitoneum in a 33-year-old woman who presented with positive urine pregnancy test and acute pelvic pain due to a ruptured ectopic pregnancy. Note the large blood clot in the rectovaginal cul-de-sac (arrows)

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Fig. 25.2

(a) Axial T1-weighted gradient recalled echo image and (b) coronal T2-weighted single-shot turbo spin-echo image demonstrate pneumoperitoneum in a patient following abdominal surgery. Note the air outlining the falciform ligament on the axial image (arrow)

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Fig. 25.3

Solid organ injuries on CT and MR. Liver laceration and pancreatic transection in a teenage female following blunt abdominal trauma. (ab) Axial contrast-enhanced CT images demonstrate a complex liver laceration and transection through the pancreatic neck. Selected images from an MR examination performed 2 days later demonstrate the appearance of the same injuries on (cd) axial T1-weighted images with and without fat saturation, respectively, and (ef) axial T2-weighted images with fat saturation. The liver laceration is seen as an irregular linear T2-hyperintense and T1-hypointense defect in the left hemiliver (arrow). There is complete disruption of the pancreatic neck with T1-hypointense and T2-hyperintense fluid within the defect (arrow)

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Fig. 25.4

Diaphragmatic injury in a 24-year-old pregnant patient in a motor vehicle collision. (a) Initial chest radiograph and (b) follow-up chest radiograph obtained 4 days show development of a right hemidiaphragmatic contour abnormality, which raised concern for diaphragmatic injury. (c) Coronal and (d) sagittal T2-weighted images from a subsequent MR examination confirm herniation of the right hemiliver through a defect in the right hemidiaphragm (arrows). This was occult on the initial trauma CT examination

The primary goal in the management of pregnant trauma patients is to stabilize the mother, bearing in mind that maternal demise almost always leads to fetal demise [5]. Imaging examinations play an important role in this process as they allow for both the diagnosis and exclusion of suspected injuries. In the acute setting, injuries need to be diagnosed promptly, as maternal shock portends a poor prognosis with fetal loss rates approaching 80 % [6]. When exams are positive, they are pivotal in determining whether operative management is required and can guide surgical technique to ensure that all injuries are addressed as efficiently as possible. Negative examinations are also valuable, as they can help avoid an unnecessary laparotomy, which is beneficial given the incidence of preterm labor after nonobstetrical laparotomy is 26 % in the second trimester and 82 % in the third trimester [67].

Given the need for rapid assessment of pregnant trauma patients, the workhorse imaging modalities used in this setting are conventional radiography and computed tomography (CT). These examinations can be performed rapidly and either in or very near the trauma bay, making them excellent first-line choices for the evaluation of pregnant trauma patients. There is often some initial hesitation to the use of ionizing radiation in the pregnant patient, but it is important to recognize that the risks are often poorly understood and, in the setting of a trauma, the benefits outweigh the risks. While a detailed description of the effects of radiation on the fetus is beyond the scope of this chapter and has been described elsewhere, a key point is that virtually all diagnostic imaging studies utilizing ionizing radiation that would be used in the evaluation of a pregnant trauma patient result in a fetal radiation dose of less than 50 mGy. This is important to recognize, as there are no known risks of pregnancy loss or fetal anomalies below this 50 mGy threshold [5].

25.2 Role of MRI in Imaging Pregnant Patients Involved in Trauma

There is currently no literature to support the use of magnetic resonance imaging (MRI) in the initial evaluation of a critically injured trauma patient. There are a number of factors that preclude MRI from being a viable modality in the initial evaluation of a trauma patient. MRI scanners are often physically removed from the emergency department. Transport to and from the scanners consequently uses valuable time and removes the patient from the resuscitation area. Examination times are also on the order of at least 10–15 min, which adds an additional delay. From a practical standpoint, appropriate MRI screening may be difficult if not impossible for a trauma patient with altered mental status, and family may not be readily available to provide such information.

There are certain situations, however, where MRI may be of benefit in the evaluation of a pregnant trauma patient. The primary application is in the setting of suspected spine trauma. The ACR appropriateness criteria for suspected spine trauma (2012) recommend MRI for evaluating suspected spinal cord injury, cord compression, and ligamentous injury. In these cases, MRI is complementary to, but does not replace, the initial CT of the spine [8]. MRI can also be used in the evaluation of complex musculoskeletal injuries, typically after management of life-threatening injuries has been performed.

Another potential situation for the use of MRI in the pregnant trauma patient relates to repeat or delayed abdominal imaging. For example, MRI could be used for follow-up of injuries initially seen on CT that were managed conservatively in patients who had a negative initial exam but subsequently develop symptoms or in patients who were not thought to require imaging at initial presentation but who later develop symptoms. To this end, there have been few studies evaluating the use of MRI in the nonpregnant adult population with abdominal trauma. McGehee et al. compared noncontrast MRI and contrast-enhanced CT in a small group of seven patients and concluded that MRI offered no significant advantage over CT for the evaluation of acute abdominal trauma [9]. Case reports have been published regarding the use of MRI in splenic, renal, and pancreatic injuries [1012]. Dedicated magnetic resonance pancreatography (MRCP) protocol examinations may be useful in the evaluation of pancreatic duct injuries from blunt trauma [13]. Finally, MRI has been utilized to confirm or exclude diaphragmatic injury in patients with blunt trauma and suspicion for diaphragmatic injury [14].

25.3 Safety of MRI in Pregnancy

In the most recent American College of Radiology white paper for safe MR practices (2013), the use of MRI was deemed acceptable at any stage of pregnancy if the risk-benefit ratio to the patient warrants that the study be performed and if the required information cannot be obtained with another modality that does not use ionizing radiation [15]. Although there is no evidence of harmful effects to the fetus as a result of MRI, the main concerns are the potential effects of energy deposition and resultant tissue heating in the fetus as well as the potential effects of acoustic noise [1618]. To minimize these potential risks, MRI of pregnant patients should be performed at field strengths of 1.5 T or less. MRI protocols should be tailored to include the minimum number of sequences required to answer the particular clinical question. In regard to the use of intravenous contrast, gadolinium is considered a pregnancy category C drug by the FDA, indicating that animal studies have shown adverse effects but adequate data are not available in humans, and the potential benefits may warrant its use in pregnant women if it is considered critical for evaluation. Typically, gadolinium-based contrast agents are not required for imaging as the necessary clinical information can be obtained from nonenhanced MRI. In rare cases in which gadolinium-based contrast material is felt to be absolutely necessary for diagnosis in a pregnant trauma patient, it can be used, but consultation with the patient regarding the potential risks and benefits is advised, if possible [19].

25.4 MRI Protocol Design for Pregnant Patients in Trauma

Choosing an appropriate MRI protocol is essential when imaging the pregnant patient in trauma. For neuro and musculoskeletal applications, standard nonenhanced protocols performed on 1.5 T scanners can answer most relevant questions. When it comes to abdominal applications, given the lack of research and experience in imaging pregnant trauma patients, or even patients involved in trauma in general, there is no standard protocol which can be broadly recommended. The important considerations in the design of a protocol for imaging the pregnant trauma patient are to choose sequences that will allow for identification of potential pathology related to trauma, namely, solid and hollow viscera injuries, hemoperitoneum, free intraperitoneal fluid, and free intraperitoneal gas. In light of safety concerns, utilizing the fewest sequences possible is recommended.

Our MRI protocol for imaging the pregnant trauma patient with suspected abdominal trauma is similar to that which we use for pregnant appendicitis cases, but the entire abdomen and pelvis need to be included, typically requiring a 2-station exam. The exam begins with axial and coronal T2-weighted single-shot turbo spin-echo (TSE) sequences. These sequences are relatively motion insensitive allowing for a rapid assessment of organs, free fluid, and bowel. Axial fat-saturated T2-weighted single-shot TSE sequences are also obtained. The fat suppression in these images is helpful for identifying more subtle edema adjacent to organs and within the mesentery. We then perform axial and coronal balanced steady-state free precession imaging which allows for an additional interrogation of the organs as well as bright blood imaging of the vasculature without contrast. Finally, we conclude with axial T1-weighted fat-saturated spoiled gradient recalled echo sequences. The T1 weighting of these sequences allows for ready identification of blood products in the peritoneal space, within organs, and associated with the placenta and uterus. The T2-weighted and balanced steady-state images are mostly motion insensitive and can be performed during free breathing or as a navigated sequence for the fat-suppressed images. The T1 gradient echo images require breath holding for optimal image quality. A summary of our MRI protocol for abdominal trauma in the pregnant patient is shown in Table 25.1.

Table 25.1

Sample MRI protocol for abdominal trauma in the pregnant patient

MRI sequence

Axial T2-weighted single-shot turbo spin echo

Coronal T2-weighted single-shot turbo spin echo

Axial fat-saturated T2-weighted single-shot turbo spin echo

Axial balanced steady-state free precession

Coronal balanced steady-state free precession

Axial fat-saturated T1-weighted spoiled gradient echo

If specific musculoskeletal or neurologic trauma is suspected, dedicated commonly used sequences applied to the regions of interest can be performed.

25.5 MRI Findings of Injuries

Identification of injuries in pregnant trauma patients on MRI examinations relies on a careful and systematic approach to the study at hand. For neurologic and musculoskeletal injuries, the findings of traumatic injuries in pregnant patients do not differ from nonpregnant patients and the imaging protocols can be applied with minimal modification. The findings of musculoskeletal and neurologic injuries are well described in the literature and radiologists interpreting these examinations are familiar with their appearances. Abdominal injuries, on the other hand, present a different challenge given the lack of literature describing their appearance on MRI in both the pregnant and nonpregnant population. Consequently, identification of traumatic abdominal injuries on MRI requires a systematic search pattern as well as an understanding of the expected appearance of these injuries based on knowledge of their appearance on CT examinations.

Interpretation of an abdominal MRI for trauma should begin with an evaluation for free intraperitoneal fluid, blood, or gas. Fluid is best identified on T2-weighted sequences and will be seen in dependent portions of the abdomen and pelvis. Simple fluid can be physiologic in pregnant patients but is typically small in volume and localized to the pelvis or to the space adjacent to the adnexa. Larger volume fluid, or fluid outside these dependent locations, should raise the suspicion for potential bowel injury. Hemoperitoneum is best seen on T1-weighted sequences and will appear hyperintense or isointense to solid organs or muscle. In the setting of trauma, hemoperitoneum should raise the suspicion of solid organ or vascular injury. When hemoperitoneum is detected within a dependent portion of the abdomen or pelvis, a careful search of the solid organs and mesentery should be performed to evaluate for a source. Hemoperitoneum or a hematoma (also hyperintense) can also appear immediately adjacent to the injured organ – a so-called sentinel clot – thus a careful survey of nearby organs can be helpful. Free intraperitoneal gas will typically localize to nondependent portions of the abdomen and pelvis. Free intraperitoneal gas will be hypointense (a signal void or black) on both T1 and T2 sequences and will typically show characteristic blooming from T2* artifact on the T1-weighted gradient echo sequences. Careful evaluation of the bowel and anterior peritoneum on the T2-weighted images is essential as small foci of pneumoperitoneum can be masked if surrounded by bowel on the gradient echo images.

Diagnosis of specific abdominal injuries on MRI relies on identifying the same findings that would be expected on corresponding CT images. For injured solid organs such as the spleen and liver, parenchymal defects, hematoma adjacent to or within the organ, or subcapsular fluid collections are used to make the diagnosis. Injuries to the pancreas can be well demonstrated on T2-weighted MRI, with pancreatic edema, adjacent pancreatic inflammation, or pancreatic ductal disruption being the key imaging findings. Bowel injuries, which are also difficult to identify on CT, can manifest with free intraperitoneal fluid or gas with the affected segment demonstrating wall thickening or adjacent inflammation. Diaphragmatic injuries can also be depicted on MRI images, particularly coronal sequences, and manifest with defects in the diaphragmatic contour in addition to herniation of abdominal fat or organs above the diaphragm.

The pregnant patient can also suffer pregnancy-specific injuries which may be seen on MRI. Placental abruption is the most common cause of fetal death in cases in which the mother survives, with a 67—75 % rate of fetal mortality for placental abruption incurred by trauma [620]. Although the diagnosis of placental abruption is often made based on clinical findings, abruption can be seen on MRI. On T1-weighted sequences, hematoma from an abruption can be seen as hyperintense material in either a retroplacental or marginal (periplacental) location. T2-weighted sequences can help to identify the hematoma and determine the age of the blood products. Abruption from trauma can also demonstrate full or partial thickness defects filled with hematoma in the placenta itself. Blood products may be seen layering dependently within the amniotic fluid. While MRI is seldom used to diagnose placental abruption, Masselli et al. demonstrated that MRI performs favorably in comparison to ultrasound for this diagnosis [21]. Uterine rupture is another pregnancy-specific injury which can be seen on imaging studies, but it would be unlikely to be diagnosed on an MRI given that these patients are typically unstable at presentation. The typical constellation of findings for uterine rupture includes hemoperitoneum, a myometrial defect, and fetal parts outside the uterus [5].

It is important to remember that a negative abdominal MRI, one that demonstrates no free fluid, free gas, or evidence of solid organ injury, is valuable in the management of pregnant trauma patients. It can serve as a reassuring data point for clinicians managing a stable patient with abdominal pain or a patient with pain that develops after their initial presentation. In either case, allowing for conservative management is beneficial as nonobstetric laparotomies increase the risk of preterm labor [7].

25.6 Conclusion

Pregnant trauma patients present a unique challenge for the radiologist. While the workhorse modalities used in the imaging evaluation of the pregnant trauma patient remain CT and conventional radiography, MRI has the potential to play an important additional role. For musculoskeletal and neurologic injuries, MRI examinations at 1.5 T can be utilized in essentially the same manner as they would be for nonpregnant patients. MRI examinations can also be useful in the evaluation of pregnant patients with abdominal trauma who are stable at presentation and develop delayed symptoms or who require follow-up imaging examinations. For these indications, a short protocol that allows for identification of free fluid and free gas in addition to solid organ, bowel, and pregnancy-specific injuries is recommended.

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