Sex & Gender in Acute Care Medicine

Sex & Gender in Acute Care Medicine Chapter 12: Imaging

Chapter 12: Gender and Diagnostic Imaging Christopher L. Moore

Case • A 28-year-old woman who is otherwise healthy and taking no medications presents to the Emergency Department with right-sided chest pain • The pain is worse when she moves or takes a deep breath • The pain started this morning and is sharp • She feels it is making her short of breath

Case, continued • Review of systems otherwise negative • On exam, her rate is 74, blood pressure 125/70, respiratory rate 12, O2 saturation 100% on room air • Clear breath sounds bilaterally and some reproducible tenderness over the right rib cage • No lower extremity pain or swelling

Case, continued • Urine hCG is negative for pregnancy • EKG shows normal sinus rhythm • The resident caring for the patient is concerned about pulmonary embolism and suggests that a d-dimer be obtained to determine whether the CT pulmonary angiogram should be obtained

Introduction • Diagnostic imaging is an integral part of evaluation of the Emergency Department (ED) patient • Numerous imaging modalities are now routinely available in the ED setting: • Plain radiography (X-ray) • Ultrasound • Computed tomography (CT) • Often MRI and nuclear studies

Introduction • Overall, nearly half (46.6% in 2008) of ED visits in the US involve an imaging study • Plain X-rays are the most common imaging test obtain in the ED setting • CT is the second most common • Challenges are to determine what (if any) imaging is appropriate and what the value of imaging is in a given situation

Introduction • Women account for more than half of all ED visits and sex should have a role in determining appropriate imaging • Much attention has been focused on advanced medical imaging (CT, MRI, and nuclear studies), which now results in nearly $100 billion in annual expenditures in the US • This growth may be justifiable if advanced imaging improves patient outcomes

Introduction • However, imaging does not always change rates of diagnosis, intervention, or hospitalization • It adds time to the ED visit, which may contribute to ED crowding • Imaging may also lead to incidental findings, which are occasionally helpful but much more commonly lead to further imaging, anxiety, and unnecessary intervention

Introduction • CT is second only to X-ray in frequency of use in the ED • Yet it is more expensive and exposes patients to substantially more ionizing radiation • It is estimated that radiation from medical sources – primarily CT – has doubled the average yearly radiation dose received by individuals in the US over the past several decades

Introduction • CT use in the US peaked in 2011 • CT use has declined about 5% per year since then • Some of this may be due to efforts to curb overutilization • As well as broader understanding of the risks of radiation from CT scans • However, this still represents nearly one CT performed per year for every 4 US residents • A rate nearly twice that of Canada

Introduction • An estimated 20% to 40% of CT scans may be “medically unnecessary” • Women face a greater risk of malignancy from CT scanning • In addition to radiation risks, contrast-induced nephropathy and anaphylactoid reactions to contrast media are also more prevalent in women

Introduction • Prevalence and type of disease will vary by sex as will diagnostic yield and risk from radiation • Cost, time, and radiation should not be an impediment to an appropriate imaging study • However, sex differences can help guide the appropriate use of diagnostic imaging

“Appropriate” Imaging • Diagnostic imaging saves lives every day • What constitutes “appropriate” imaging, however, is elusive and depends on the imaging procedures, the patient, and the setting • Appropriateness criteria have been published by organizations such as the American College of Radiology and the American Society of Echocardiography

“Appropriate” Imaging • While there are some differences in suggested appropriate imaging based on patient characteristics, in general the guidelines do not factor in patient sex • Despite increased imaging, it is debatable whether patient-centered outcomes have improved

“Appropriate” Imaging • A study of ED visits for abdominal pain found in increase in CT use from 10.1% of visits in 2001 to 22.5% of visits in 2005 • No difference was found in detection of surgical disease and no decrease in hospital admissions • Understanding the role of patient sex may help clinicians make more informed decisions about appropriate imaging

Risks of Radiation from CT • A 2004 study suggested that physicians largely misunderstood and misestimated the risk of radiation from CT • Quantifying the risk has remained difficult because of debates about the evidence as well as confusion about units of measurement • Ionizing radiation is the type used by CT scans, plain radiographs (X-rays), and nuclear studies

Measuring Radiation from CT • Generally acknowledged that there is a small increased risk of cancer when ionizing radiation is applied to radiosensitive organs • The magnitude of this risk for an individual and a population is incompletely understood • May be quite variable based on age, size, and sex • Remains controversial

Measuring Radiation from CT • The best way to get a working understanding of how radiation is measured to is to look at the metrics displayed with each scan • Most modern CT scanners include an image at the end of a CT series that includes to measures: • CT dose index (CTDI or CDTIvol, in mGy) • Dose-length-product (CLP, in mGy-cm)

Measuring Radiation from CT • The CTDIvol can be considered the output of the scanner • DLP is related more to overall absorbed radiation and is equal to the CTDIvol x the length of the body scanned • While DLP is the more frequently reported dose metric, it is important to understand that DLP is calculated based on a simulated patient

Measuring Radiation from CT • DLP does not take patient size into account in terms of actual effective organ dose • For a given CTDIvol or DLP, a larger patient will have relatively lower actual dose delivered to radiosensitive organs due to absorption by non-radiosensitive tissue • Regarding actual radiation dose delivered to a patient, several metrics are in use

Measuring Radiation from CT • Ongoing controversy about the best reporting methods can make comparison and estimation of risk confusing • Both rad and gray refer to the amount of radiation absorbed • Rem and sievert refer to the effective organ dose that should be most directly related to risk of malignancy

Measuring Radiation from CT • For CT, the most commonly used units will be milligray (mGy) and millisieverts(mSv) • Converting to effective dose can be estimated based on the body part is being scanned • For example, the conversion factor for a CT abdomen and pelvis is ~15-17 microsieverts per milligray-centimenters • So a CT scan with a DLP of 622mGy-cm would be estimated to deliver an effective dose of approximately 10.6 mSv

Measuring Radiation from CT • To put this in perspective, the average yearly background radiation in the US approximately 2-3 mSv • ~6 mSv per year including medical radiation • A 2009 paper estimated that there could be as many as 29,000 future malignancies resulting from CT performed in the US in 2007 alone

Risk of Radiation from CT • Population-based risks of malignancy from CT depend on age, sex, and type of scan • Estimates range from approx. 1 in 150 for a 20-year-old female undergoing a CT angiogram to about 1 in 15,000 for a 60-year-old man undergoing a routine head CT • These estimates of risk were derived by extrapolating the rates of malignancy in survivors of the atomic bomb attacks on Japan during World War II

Risk of Radiation from CT • The current generally accepted model is called the “no threshold linear model” • Each increased radiation dose is directly related to increased risk of malignancy; there no single threshold amount that becomes more dangerous • However, the number of people in these cohorts developing cancer after receiving smaller doses of radiation is small • A recent study has called this model into question

Dose Variability from CT • Given the potential harms of ionizing radiation, radiological societies have endorsed the use of a dose that is “as low as reasonably achievable” (ALARA) • While this is good in theory, in practice dosing may vary considerably for similar protocols between centers • The American College of Radiology founded the Dose Imaging Registry (DIR) in 2011

Risk of Radiation from CT • However, there is no actual requirement to lower dosing for a given protocol • These protocols are typically set by manufacturers but may be modified by radiologists and CT technicians • A recent report form the DIR found that dosing for CTs looking for kidney stones could vary by a factor of 10, with less than 2% done using the low-dose protocols (<3 mSv)

Sex Considerations: Chest Pain • Chest pain is the most common presenting ED chief complaint in adult males • The second leading complaint in adult females • It is estimated that 40% of all medical radiation is related to cardiovascular imaging and intervention • Almost all chest pain evaluated in the ED will receive a plain chest X-ray

Imaging in Chest Pain • While the utility of this as a routine test has been questioned for more than 30 years, it is inexpensive and without much radiation • It typically functions as a screen for pneumonia, heart failure, pneumothorax, and aortic pathology • Whether imaging beyond chest X-ray is obtained depends on the suspicion for serious pathology

Imaging in Chest Pain • Echocardiography offers an attractive modality with no ionizing radiation that can be helpful in evaluation of the ED patient with chest pain and/or dyspnea • While access to formal echocardiography is often restricted in the ED setting, point-of-care ultrasound of the heart and lungs involves no radiation and is easily performed at the bedside

Imaging in Chest Pain • Bedside echocardiography can exclude pericardial effusion, provide information about left ventricular function, right ventricular strain, and aortic root size • Accuracy for these conditions will vary based on the experience of clinician performing it

Imaging in Chest Pain • Definitive diagnosis in coronary disease, PE, or thoracic aortic dissection (TAD) is typically obtained using modalities with ionizing radiation • For PE and TAD, the test of choice is contrast-enhanced CT of the chest • For coronary disease, cardiac catheterization with coronary angiography is the reference standard

Imaging in Chest Pain • However, in both PE and ACS evidence-based approaches allow effective exclusion of disease in many patients without using ionizing radiation • Data suggest that testing occurs more than is warranted by the evidence • When ionizing radiation of the chest is overused, women are disproportionately at risk due to the exposure of breast tissue to potentially carcinogenic radiation

Chest Pain Concerning for CAD • Heart disease is the leading cause of death in the US for both men and women • Efforts to minimize missed diagnoses have led to extensive diagnostic testing • The majority of chest pain seen in the ED can be considered “low-risk chest pain,” with a normal or nonspecific EKG and negative cardiac biomarkers

Chest Pain Concerning for CAD • About 2-4% of people presenting with low-risk chest pain will ultimately be found to have significant coronary disease • If the history is concerning, it is often standard care in the US to evaluate the coronary arteries with a CT angiogram or stress test • Nuclear stress tests account for about 20% of the medical radiation received by the population

Chest Pain Concerning for CAD • While nuclear stress tests are an effective tool for risk stratification, other options such as exercise echocardiography may be as effective and do not involve radiation • A recent survey of practitioners using nuclear stress tests found that only 7% were using a stress-first approach (i.e., only moving to a nuclear study if stress EKG or stress echo were inconclusive)

Chest Pain Concerning for CAD • Increasingly, coronary CT angiogram (CCTA) is an option for detecting coronary disease • However, the radiation involved is higher than that of a typical CT abdomen and pelvis and includes irradiation of the breasts in female patients • Our recommendation is that in younger, lower risk patients, stress EKG, stress echo, or CT/nuclear strategies be considered first

Chest Pain Concerning for PE • Pulmonary embolism (PE) is estimated to occur in 600,000 patients annually in the US • CT pulmonary angiogram is now considered the diagnostic gold standard • Since its introduction, the diagnosis of PE has nearly doubled in the US • However, with increased diagnosis, mortality from PE has only been minimally affected

Chest Pain Concerning for PE • Complications from anticoagulation have risen, suggesting that we are treatment more and potentially less clinically significant PEs • Several clinical decision rules can stratify patients with symptoms of PE below the testing threshold for CT • The Wells score indicates whether patients have a low enough pretest probability that if a d-dimer is negative, further imaging is not needed

Chest Pain Concerning for CAD • Women are more likely to have a positive d-dimer, which is more likely to be falsely elevated • This may contribute to the higher rate of imaging even if decision rules are followed • However, it is estimated that as many as 1/3 of CTPAs (in both sexes) could be avoided by using evidence-based rules

Imaging in Abdominal Pain • Abdominal pain is the leading reason that adult females visit the ED • A substantial number of patients with abdominal pain will not have a definitive diagnosis established during their ED visit • Like chest pain, evaluation of abdominal pain in the ED setting has seen a marked rise in advanced medical imaging

Imaging in Abdominal Pain • Despite the rise in CT imaging, there has been no change in the diagnosis of appendicitis, diverticulitis, or gallbladder disease • Admission rates for patients with abdominal pain have not changed • This suggests that utilization of CT may not be adding value to patient-centered outcomes

Imaging in Abdominal Pain • Ultrasound is a safe and effective alternative to CT for most common diagnosable causes of abdominal pain • The benefit:risk ratio may be higher for women • Biliary disease represents a disorder that is more common in women and is most effectively diagnosed with ultrasound

Imaging in Abdominal Pain • Biliary disease accounts for as many as 9% of admissions for abdominal pain • Ultrasound is the initial test of choice if biliary disease is suspected • May be performed at the bedside by experienced practitioners

Imaging in Abdominal Pain • While appendicitis occurs more commonly in males, the diagnosis may be more challenging in women due to other etiologies of right lower quadrant pain • CT is often considered the test of choice and is highly accurate • Ultrasound is typically the first-line approach for pediatric and pregnant patients

Imaging in Abdominal Pain • A recent analysis of an ultrasound-first approach for appendicitis estimated that such an approach could avoid ~180 excess cancer deaths per year • As well as substantial cost savings • Such an approach would again be most effective in younger female patients

Imaging in Abdominal Pain • The elderly with abdominal pain represent a special population as they are more likely to harbor a serious diagnosis, particular a vascular etiology • Abdominal aortic aneurysm (AAA) causes about 15,000 deaths annually in the US with twice as many deaths occurring in men • While AAA is more common in men, women face increased risk of rupture at smaller sizes

Imaging in Abdominal Pain • Ultrasound screening for AAA is currently recommended by the USPSTF for asymptomatic men between age 65 and 75 who have never smoked • Routine screening is not recommended for women • Identification of AAA may be accomplished at the bedside in the ED • A non-diagnostic ultrasound should generally be followed by a CT

Imaging in Abdominal Pain • Sex-specific causes of lower abdominal pain must also be considered • In men with lower abdominal pain, a testicular etiology should be considered and a testicular exam should be performed • If there are concerning findings on exam, scrotal ultrasound is typically the test of choice

Sex & Gender in Acute Care Medicine