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Everything you need to know about Computed Tomography (CT) & CT Scanning

Ob Gyn: Pregnant Patient and CT Imaging Pearls - Educational Tools | CT Scanning | CT Imaging | CT Scan Protocols - CTisus
Imaging Pearls ❯ OB GYN ❯ Pregnant Patient and CT

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  • “Postpartum hemorrhage continues to be the leading preventable cause of maternal illness and death globally. Worldwide, postpartum hemorrhage accounts for 8% of maternal deaths in developed regions of the world and 20% of maternal deaths in developing regions. The United States has one of the highest maternal mortality rates among developed countries, with approximately 11% of all maternal deaths associated with postpartum hemorrhage.3 During the period from 1993 through 2014, the rate of postpartum hemorrhage (which was defined as blood loss >1000 ml after vaginal or cesarean delivery) requiring a blood transfusion4 increased from approximately 8 cases per 10,000 deliveries to 40 per 10,000 deliveries in the United States.”  
    Postpartum Hemorrhage  
    Jessica L. Bienstock et al.
    N Engl J Med 2021;384:1635-45
  • “The traditional definition of postpartum hemorrhage is blood loss of more than 500 ml after a vaginal delivery or more than 1000 ml after a cesarean delivery. More recently, postpartum hemorrhage has been redefined as a cumulative blood loss of 1000 ml or more or blood loss associated with signs or symptoms of hypovolemia, irrespective of the route of delivery. Typical clinical signs and symptoms of hypovolemia (e.g., hypotension and tachycardia) due to postpartum hemorrhage may not appear until blood loss exceeds 25% of total blood volume (>1500 ml during late pregnancy).”
    Postpartum Hemorrhage  
    Jessica L. Bienstock et al.
    N Engl J Med 2021;384:1635-45
  • “Postpartum hemorrhage is considered to be primary when it occurs within the first 24 hours after delivery and secondary when it occurs between 24 hours and up to 12 weeks after delivery. The causes of postpartum hemorrhage can be summarized by the four “T’s”: tone (uterine atony), trauma (lacerations or uterine rupture),  tissue (retained placenta or clots), and thrombin (clotting-factor deficiency).10 The most common cause is uterine atony (accounting for approximately 70% of cases), followed by obstetrical lacerations (approximately 20%), retained placental tissue (approximately 10%), and clotting-factor deficiencies (<1%).”
    Postpartum Hemorrhage  
    Jessica L. Bienstock et al.
    N Engl J Med 2021;384:1635-45
  • "The causes of postpartum hemorrhage can be summarized by the four “T’s”: tone (uterine atony), trauma (lacerations or uterine rupture), issue (retained placenta or clots), and thrombin (clotting-factor deficiency). The most common cause is uterine atony (accounting for approxi- mately 70% of cases), followed by obstetrical lac- erations (approximately 20%), retained placental tissue (approximately 10%), and clotting-factor deficiencies (<1%).”
    Postpartum Hemorrhage  
    Jessica L. Bienstock et al.
    N Engl J Med 2021;384:1635-45
  • "Other risk factors for postpartum hemorrhage are closely linked to the type of hemorrhage that develops. For example, obstetrical lacerations can be caused by operative vaginal delivery, precipitous delivery, or episiotomy, whereas retained placental tissue can be caused by placenta accreta spectrum (PAS; a spectrum of abnormal placentation disorders, including placenta accreta, placenta increta, and placenta percreta), which is associ- ated with prior uterine surgery. Retained placental tissue can also be the result of incomplete delivery of the placental tissue and membranes. Maternal coagulopathy that leads to postpartum hemorrhage can be a complication of severe pre- eclampsia and eclampsia, HELLP (hemolysis, elevated liver-enzyme level, and low platelet count) syndrome, intrauterine fetal death, placental abruption, or a coagulation disorder that is acquired (e.g., amniotic fluid embolism) or inherited.”
    Postpartum Hemorrhage  
    Jessica L. Bienstock et al.
    N Engl J Med 2021;384:1635-45
  • "Postpartum hemorrhage remains a clinically significant cause of maternal complications and death; worldwide, one woman dies from postpartum hemorrhage every 7 minutes. There- fore, prompt identification of patients who are at risk for postpartum hemorrhage, routine ac-  tive management of the third stage of labor, expeditious assessment of blood loss, appropriate patient monitoring, and management of postpartum hemorrhage are important.”
    Postpartum Hemorrhage  
    Jessica L. Bienstock et al.
    N Engl J Med 2021;384:1635-45
  • “Placenta percreta (PP) is a condition in which the placenta abnormally penetrates entirely through the myometrium and into the uterine serosa. This might be complicated by attachment of the placenta to surrounding structures or organs, such as the urinary  bladder or rectum. PP is a potentially fatal condition, and mortality rate is correlated to the extent of involvement of surrounding structures. When PP is complicated by bladder invasion, mortality  rates have been estimated as high as 9.5% and 24% for mother and child, respectively.”
    Placenta Percreta With Invasion into the Urinary Bladder  
    Zachary L. Smith et al.
    Urology Case Reports,Volume 2, Issue 1,2014,Pages 31-32
  • "The incidence of PP has increased 50-fold in the last half-century to a currently estimated 1 in 1000 pregnancies. This increased prevalence is attributed to the increased frequency of  Caesarean deliveries. The incidence of concomitant bladder invasion is much lower, occurring in approximately 1 in 10,000 births.  he diagnosis of PP might be made during prenatal screening ultrasound; however, bladder involvement is usually not identified  until the time of delivery.”
    Placenta Percreta With Invasion into the Urinary Bladder  
    Zachary L. Smith et al.
    Urology Case Reports,Volume 2, Issue 1,2014,Pages 31-32
  • "PP is a morbid condition of increasing incidence. It should be considered in any pregnant patient presenting with gross hematuria, although this is not a sensitive finding. A previous history of Caesarean section might be associated with PP; however, there has been no correlation between other pelvic procedures to this con- dition, making screening even more difficult. After review of our case and the current published data available, it is our opinion that early urologic consultation and a multidisciplinary approach to delivery and management are of utmost importance. If possible, preoperative ureteral catheter placement is recommended to aid in intraoperative identification of ureters.”
    Placenta Percreta With Invasion into the Urinary Bladder  
    Zachary L. Smith et al.
    Urology Case Reports,Volume 2, Issue 1,2014,Pages 31-32
  • Advanced abdominal pregnancy (AAP) is defined as a pregnancy of over 20 weeks’ gestation with a fetus living, or showing signs of having once lived and developed, in the mother’s abdominal cavity Abdominal pregnancy has an incidence of about 1 in 400 to 1 in 50,000 deliveries, and the variable incidence depends on the characteristics of a particular geographic region. It is associated with a high rate of maternal and fetal complications.
  • Ectopic pregnancy is estimated to occur in 1–2% of pregnancies. Over 90% are located in the fallopian tube, and the remainder implant in locations such as the abdomen, cesarean (hysterotomy) scar, cervix, and ovary. Abdominal pregnancy accounts for 1.4% of ectopic pregnancies . Most cases of abdominal pregnancies are secondary to aborted or ruptured tubal pregnancy.
  • “Abdominal pregnancies constitute approximately 1% of all ectopic pregnancies, occurring in 1/2200 to 1/10 200 pregnancies and 1/6000 to 1/9000 births. Mortality rates are 7.7 times higher than in tubal pregnancy, and 89.8 times higher than in intrauterine pregnancy. Because of the rarity and associated mortality of abdominal pregnancies, early diagnosis and early recourse to intervention is paramount.”
    Early abdominal ectopic pregnancy: challenges, update and review of current management
    Nilesh Agarwal et al.
    The Obstetrician & Gynaecologist 2014;16:193–8
  • • Early abdominal ectopic pregnancy (EAP), though rare, has a high mortality rate.
    • There are no pathognomic symptoms of abdominal pregnancy. Symptoms are akin as for other types of ectopic pregnancy, thus a high index of suspicion is necessary for diagnosis.
    • The tool of choice for diagnosis is ultrasound but it only gives 50% accuracy when used along with clinical evaluation. On occasion, magnetic resonance imaging may help to diagnose EAP.
    • Medical management is commonly used where potential life-threatening bleeding is anticipated. A number of women who are treated medically may need subsequent treatment with multiple therapies.
    • Surgical management requires a great deal of surgical expertise and in most cases a multidisciplinary approach in anticipation of possible life-threatening bleeding during the operation.
    Early abdominal ectopic pregnancy: challenges, update and review of current management
    Nilesh Agarwal et al.
    The Obstetrician & Gynaecologist 2014;16:193–8
  • “EAP is rare, and successful management depends on a high index of suspicion. While ultrasound and serial human chorionic gonadotrophin may help in the diagnosis, there is no single diagnostic tool available. At laparoscopy it is important that if an ectopic pregnancy is not visualised in the usual locations, then all of the abdominal cavity is inspected to include all abdominal organs. If the diagnosis is still not confirmed then MRI or intraoperative ultrasound may assist in diagnosis.”
    Early abdominal ectopic pregnancy: challenges, update and review of current management
    Nilesh Agarwal et al.
    The Obstetrician & Gynaecologist 2014;16:193–8
  • " In cases where CT is needed, protocols should be optimized for the individual with careful planning, with use of dose reduction techniques that allow adequate imaging without unnecessary radiation exposure. As in all cases, the benefit of an imaging diagnosis needs to be weighed against theoretical risks."
    Invited Commentary
    Levine D
    RadioGraphics 2010; 30:1230-1233
  • " The risk associated with a radiologic examination appears to be rather low compared with the natural risk. However, any added risk, no matter how small, is unacceptable if it does not benefit the patient."
    Radiation Risk: What You Should Know to Tell your Patient
    Verdun FR et al.
    RadioGraphics 2008:28:1807-1816
  • " The risk burden of radiation exposure to the fetus has to be carefully weighed against the benefits of obtaining a critical diagnosis quickly and using a single tailored imaging exam ."
    Imaging in Pregnant Patients: Examination Appropriateness
    Wieseler KM et al.
    RadioGraphics 2010; 30:1215-1233
  • "We aimed to combine previously described pregnancy specific CTPA technique alterations with a dose reduction strategy and a low kVp technique to yield a low dose CTPA protocol specifically tailored to pregnant patients, without a reduction in clinical image quality. The results demonstrate that by using a low kVp CTPA technique tailored to pregnancy, effective doses under 1 mSv are routinely achievable in a pregnant population."
    Low dose computed tomography pulmonary angiography protocol for imaging pregnant patients: Can dose reduction be achieved without reducing image quality?
    Halpenny D et al.
    Clinical Imaging: Volume 44, July–August 2017, Pages 101-105
  • "Pregnancy is a hypercoagulable state, and consequently pregnant patients are at high risk for PE. The diagnosis of PE can be challenging in pregnant patients, as the clinical signs and symptoms of PE can mimic the physiological effects of pregnancy. In the ATS/STR guidelines, CTPA is the recommended when a chest radiograph is abnormal and therefore maintains an important role in the evaluation of PE. While both V/Q scintigraphy and CTPA have high sensitivities and specificities, CTPA is quick to perform and interpret, and provides a higher rate of alternate diagnoses."
    Low dose computed tomography pulmonary angiography protocol for imaging pregnant patients: Can dose reduction be achieved without reducing image quality?
    Halpenny D et al.
    Clinical Imaging: Volume 44, July–August 2017, Pages 101-105
  • "CTPA image quality is potentially impacted by the hemodynamic changes of pregnancy. Increased plasma volume, cardiac output, total vascular resistance, and heart rate can lead to hemodilution of injected intravenous contrast with decreased peak arterial enhancement and shorter contrast material arrival time in the pulmonary arteries. Additionally, the gravid uterus increases IVC pressure and can accentuate transient contrast interruption."
    Low dose computed tomography pulmonary angiography protocol for imaging pregnant patients: Can dose reduction be achieved without reducing image quality?
    Halpenny D et al.
    Clinical Imaging: Volume 44, July–August 2017, Pages 101-105
  • “ In major trauma, when there is concern for maternal injury, CT is the mainstay of imaging. The risks of radiation to the pregnancy are small compared with the risk of missed or delayed diagnosis of trauma.”
    Imaging of Trauma: Part 2, Abdominal trauma and Pregnancy---A radiologists Guide to Doing What is Best for the Mother and Baby
    Sadro C et al.
    AJR 2012;199:1207-1219
  • “ Trauma is the leading cause of non-obstetric maternal mortality affecting up to 7% of pregnancies and is a significant cause of fetal loss. Approximately 2% of level-1 trauma patients have a positive pregnancy test.”
    Imaging of Trauma: Part 2, Abdominal trauma and Pregnancy---A radiologists Guide to Doing What is Best for the Mother and Baby
    Sadro C et al.
    AJR 2012;199:1207-1219
  • “ Causes of trauma in pregnancy include motor vehicle injury (49%), falls (25%), assaults and domestic violence( 18%), and gunshot wounds (4%).”
    Imaging of Trauma: Part 2, Abdominal trauma and Pregnancy---A radiologists Guide to Doing What is Best for the Mother and Baby
    Sadro C et al.
    AJR 2012;199:1207-1219
  • “Certain injuries in pregnancy are associated with an increased risk of fetal loss.Pelvic and acetabular fractures occurring in pregnancy are associated with a high maternal (9%) and higher fetal mortality (35%), increasing to 75% for severe fracture patterns.”
    Imaging of Trauma: Part 2, Abdominal trauma and Pregnancy---A radiologists Guide to Doing What is Best for the Mother and Baby
    Sadro C et al.
    AJR 2012;199:1207-1219
  • "Placental abruptions are often overlooked on CT scans. Sensitivity may be improved by systematic evaluation of the placenta and specificity by training on normal placental morphology."

    CT Evaluation of Placental Abruption in Pregnenet Trauma Patients
    Wei SH et al.
    Emerg Radiol (2009) 16:365-373

  • "True placental abruptions were characterized by large, contiguous, and retroplacental and/or full-thickness areas of low enhancement that form acute angles with myometrium."

    CT Evaluation of Placental Abruption in Pregnenet Trauma Patients
    Wei SH et al.
    Emerg Radiol (2009) 16:365-373

  • Placental Abruption: Complications
    - Pre-term labor
    - Fetal distress
    - Fetal death in 20-60%
    - Maternal shock
    - DIC
    - Maternal death
  • Conclusion

    "In cases where CT is needed, protocols should be optimized for the individual with careful planning, with use of dose reduction techniques that allow adequate imaging without unnecessary radiation exposure. As in all cases, the benefit of an imaging diagnosis needs to be weighed against theoretical risks."

    Invited Commentary
    Levine D
    RadioGraphics 2010; 30:1230-1233

  • Suspected Acute Abdomen
    - There are numerous causes for the acute abdomen
    - When a diagnosis can not be made CT is the study of choice
  • Urolithiasis (r/o)
    - Calculi in pregnancy are uncoomon
    - Ultrasound is done first but if not helpful CT is done to r/o stone and also look for other causes of flank pain.
    - If CT is done low dose non-contrast CT is fine
  • Trauma
    - The severity of the injury determines workup but priority is given to maternal survival
    - CT is used as needed in the chest and abdomen
    - Most common uterine injury is placental abruption which occurs in up to 40% of patients with severe injury. Uterine rupture is rare
  • Appendicitis (rule out)
    - Most common cause of surgical abdomen in pregnancy (50-70 per 1000 patients)
    - Ultrasound can be used first and in some institututions MR is done
    - If indeterminate a CT is done using oral and IV contrast material
  • Pulmonary Embolism
    - Leading cause of maternal morbidity
    - Pregnancy increases risk of PE by a factor of 5
    - Chest x-ray and ultrasound are often first test used to screen
    - If chest x-ray and ultrasound are negative and high suspicion CT is done
    - VQ scan is done if patients allergic to IV contrast
  • Common Clinical Scenarios in the Pregnant Patient
    - r/o pulmonary embolism
    - Trauma
    - r/o appendicits
    - Urolithiasis
    - Acute abdomen
  • 2008 ACR Practice Guidelines

    "To maintain a high standard of safety, particularly when imaging potentially pregnant patients, imaging radiation must be applied at levels as low as reasonably achieveable (ALARA), while the degree of medical benefit must counterbalance the well managed levels of risk."

    ACR Practice Guideline for imaging pregnant and potentially pregnant adolescents and woman with ionizing radiation (American College of Radiology)

     

  • At 150 mGy the risks will vary on stage of pregnancy but include
    - 3% chance of cancer development
    - 6% chance of mental retardation
    - Loss of 30 IQ points per 100 mGy
    - 15% chance of microcephaly
  • Nonstochastic Effects
    - Threshold effects or deterministic effects are caused by exposure to radiation at a high level
    - These effects are predictable and involve multicellular injury including chromosomal alterations
    - Threshold dose is usually 150 mGy and these patients need to be accessed for termination
  • "As shown in table 1, the ACR suggested that the theoretical risks are not likely at doses less than 100 mGy."

    Imaging in Pregnant Patients: Examination Appropriateness
    Wieseler KM et al.
    RadioGraphics 2010; 30:1215-1233

  • Stochastic effects
    - Are the results of cellular damage likely at the DNA level causing cancer or other germ cell mutations
    - They have no threshold dose and are theorized to any with exposure to any amount of radiation
    - The threshold for radiation induced Stochastic effects was established at 50mGy
  • Radiation Effects and Risk
    - Stochastic effects
    - Nonstochastic effects
  • Practical Points in Performing CT in the Pregnant Patients
    - Make sure that CT is the study of choice
    - Prepare the patient for the study as completely as possible (oral contrast etc. done early)
    - Design the optimal protocol for that patient (kVp, mAs, etc)
    - Scan only the area needed to be scanned
    - Monitor the scan to make sure you have a dx
  • Estimated Average Fetal Radiation Dose from a Single Acquisition with 64 MDCT

    Type of CT exam

    Dos
    mGy

    Section thickness (mm)

    Noise index

    mAs

    pitch

    CT  of the Chest

    0.02

    2.5

    30

    80

    1.375

    CT for PE

    0.02

    1.25

    30

    88

    0.984

    CT of the Abdomen

    1.3

    2.5

    36

    110

    1.375

    CT of the Kidney and bladder

    11

    2.5

    36

    110

    1.375

    CT of the Pelvis

    13

    2.5

    36

    130

    1.375

    CT of the Abdomen and Pelvis

    13

    2.5

    36

    130

    1.375

    CT Angiography

    13

    2.5

    30

    130

    1.375

  • Estimated Average Fetal Radiation Dose from a Single Acquisition with 64 MDCT

    Type of CT exam

    Dos
    mGy

    Section thickness (mm)

    Noise index

    mAs

    pitch

    CT  of the Chest

    0.02

    2.5

    30

    80

    1.375

  • Potential Radiation Effects on the Fetus by Gestational Age and Radiation Exposure
    Potential Effects by Radiation Exposure  

    Gestational age (weeks)

    <50 mDy

    50-100mGy

    >100 mGy

    0-2nonenonenone
    3-4noneprobably nonepossible spontaneous abortion
    5-10noneuncertain

    Possible malformations

    11-17noneuncertain

    Possible defects in IQ or mental retardation

    18-27nonenone

    IQ deficits not detectable at diagnostic doses

    >27nonenone

    None applicable to diagnostic radiology

  • Potential Radiation Effects on the Fetus by Gestational Age and Dose
    - Under 50 mGy there is none
    - With 50-100 mGy there is none at over 18 weeks and probably none under 4 weeks and uncertain at 5-17 weeks
    - Over 100 mGy there are typically no issues over 18 weeks and possible issues between 4 and 17 weeks Data from ACR practice guidelines
  • "However, no examination should be withheld when an important clinical diagnosis is under consideration. Exposure to ionizing radiation may be unavoidable, but there is no evidence to suggest that the risk to the fetus after a single imaging study and an interventional procedure is significant."

    Imaging in Pregnant Patients: Examination Appropriateness
    Wieseler KM et al.
    RadioGraphics 2010; 30:1215-1233

  • "The risk burden of radiation exposure to the fetus has to be carefully weighed against the benefits of obtaining a critical diagnosis quickly and using a single tailored imaging exam ."

    Imaging in Pregnant Patients: Examination Appropriateness
    Wieseler KM et al.
    RadioGraphics 2010; 30:1215-1233

     

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