Management of Pregnant Patients with Indeterminate CT Scan for Pulmonary Embolism

Initial Approach to Indeterminate CT Results

The American College of Chest Physicians recommends that pregnant patients with suspected pulmonary embolism and an indeterminate CT scan should receive empiric anticoagulation therapy while awaiting further diagnostic testing to prevent potentially fatal outcomes 1
For pregnant patients with suspected PE and an indeterminate CT pulmonary angiography, further diagnostic testing rather than clinical management alone is recommended by the American Thoracic Society 2, 3
If the patient has a high clinical suspicion of PE and a low risk of bleeding, anticoagulant therapy should be initiated immediately while awaiting additional diagnostic test results, as recommended by the American College of Cardiology 1

The American College of Radiology recommends assessing for signs and symptoms of deep vein thrombosis (DVT) in pregnant patients with indeterminate CT scans, and performing bilateral compression ultrasound of lower extremities if DVT symptoms are present 2, 4
The American Thoracic Society recommends considering lung scintigraphy (V/Q scan) in pregnant women with a normal chest X-ray and an indeterminate CT scan 5, 3
V/Q scanning has a similar false-negative rate to CTPA in pregnancy, according to the American College of Nuclear Medicine (0.5% vs 0.4%) 6

The American College of Chest Physicians recommends standard therapeutic dosing of low-molecular-weight heparin (LMWH) should be initiated promptly when PE is suspected with an indeterminate scan and high clinical suspicion 1

Pregnancy physiological changes affect contrast dynamics during CTPA, which may contribute to indeterminate results, as noted by the American College of Radiology 1
Protocol optimization for pregnant patients includes automated bolus triggering, high iodine flux, and high iodine concentration, according to the American College of Radiology 7, 1

Pulmonary embolism is a leading cause of pregnancy-related mortality, accounting for 20% of maternal deaths in the United States, according to the Centers for Disease Control and Prevention 3
The risk-benefit ratio strongly favors treatment when diagnostic uncertainty exists, as untreated PE has significantly higher mortality than the bleeding risks of anticoagulation, as recommended by the American College of Cardiology 1

The American College of Chest Physicians recommends avoiding reliance solely on clinical assessment for diagnosis, as signs and symptoms of PE overlap with normal physiologic changes of pregnancy 3
The American College of Radiology recommends avoiding repeated radiation exposure through multiple imaging studies and optimizing the first CTPA study with pregnancy-specific protocols 7
The American College of Cardiology recommends not withholding anticoagulation while awaiting additional testing if clinical suspicion is high and bleeding risk is low 1

The American College of Radiology suggests that both V/Q scanning and CT pulmonary angiography have similar and low false-negative rates when used to evaluate suspected pulmonary embolism during pregnancy (0.5% vs 0.4% respectively) 8, 9
For every 1000 pregnant women scanned, approximately 5 pulmonary emboli would be incorrectly ruled out with V/Q scanning and 4 with CT pulmonary angiography 8
Unlike in non-pregnant populations, the rate of inconclusive or non-diagnostic scans is not appreciably higher with V/Q scanning compared to CT pulmonary angiography in pregnant women 8, 9

V/Q scanning exposes the mother to significantly lower breast-absorbed radiation dose compared to CT pulmonary angiography 8, 9
While fetal radiation dose may be slightly greater with V/Q scanning than with CT pulmonary angiography (depending on protocol and gestational age), both are far below the accepted maximal threshold for fetal radiation exposure 8, 9
The potential absolute increase in risk of childhood cancer from either imaging modality is likely to be very small 8, 10

CT pulmonary angiography might be preferred in patients with abnormal chest radiographs, as V/Q scans are less accurate in this scenario 8, 11
If V/Q scanning is not readily available, CT pulmonary angiography is an acceptable alternative 8

The American College of Radiology recommends obtaining a chest radiograph first when pulmonary embolism is suspected in pregnancy, as this informs the choice between CTPA and VQ scanning, and may reveal alternative diagnoses 12
The American College of Radiology suggests that if chest X-ray is normal and VQ scanning is available, proceeding with VQ scan is appropriate, while if chest X-ray is abnormal, CTPA is preferred, and alternative diagnoses need to be excluded 12