E2009. Diagnostic Yield of Ultrasound First with MR as a Problem-solving Tool in Evaluation of Pregnant Patients Presenting with Acute Appendicitis
  1. Javeria Munir; The University of Ottawa
  2. Shauna Duigenan; The University of Ottawa
This study assesses the accuracy of ultrasound, as the primary modality, and MR, as an adjunct modality in each trimester, for diagnosing appendicitis in pregnant patients.

Materials and Methods:
Pregnant patients (females aged >= 18 years) who presented with acute right lower abdominal pain between 2015 and 2019 were retrospectively assessed via review of reports through the search feature of a McKesson PACS system. Information was collected on gestational age, patient management, BMI, Multiparity, prior abdominal surgery and other causes of lower abdominal pain. All patients having prior appendectomy were excluded. Data was collated by trimester and statistical assessment was performed for accuracy.

493 pregnant patients underwent US assessment for clinical suspicion of acute appendicitis and were grouped into gestational age (trimester) and US findings. Of the 493 patients who had US, 461 (93.5%) had a negative or equivocal US. 32 out of 493 (6.4%) had a diagnosis of acute appendicitis. 290 patients (58.8%) had no cause of pain. 271 patients (54.9%) were diagnosed with another cause of acute abdominal pain including ectopic pregnancy, renal colic, cholelithiasis/cholecystitis, corpus luteal cyst, fetal loss, Crohn's exacerbation, rectus sheath hematoma, and fibroid. Calculated US sensitivity for detection acute appendicitis is as follows: sensitivity of 81.3% [63.6% - 92.8%], specificity of 98.7% [97.2% - 99.5%] with PPV of 81.3% [63.6% - 92.8%] and NPV of 98.7% [97.2% - 99.5%]. Of the 493 pregnant patients who had initial ultrasound, 85 (17.2%) went on to have MR. The most common indication for the MR was equivocal or non-diagnostic findings on US due to raised BMI, multiparity or previous abdominal surgeries. 67 out of 85 patients who underwent MR exam had an initial equivocal US. 12 out of 85 patients had an US that was negative for acute appendicitis. 6 out of 85 patients had an US positive for acute appendicitis. 4 patients who had an equivocal or non-diagnostic study on US had MR that was positive for acute appendicitis. 3 patients who had a positive US had a positive MR. 59 patients having an equivocal or non-diagnostic study on US had an MR that was read as negative for appendicitis. Sensitivity and Specificity for MR performed as adjunct to US was 100% [59% - 100%] and 100% [95.3% - 100%] respectively.

Although ultrasound is the primary diagnostic modality for diagnosing the etiology of right lower quadrant pain in pregnancy, MR is a useful adjunct imaging test to problem solve.