Abbreviated MRI in patients with suspected acute appendicitis in emergency: a prospective study
Islam, G. M. N., Yadav, T., Khera, P. S., et al.
Abdominal Radiology (2021). doi:10.1007/s00261-021-03222-5
Acute appendicitis is one of the most common abdominal emergencies, with a lifetime risk of 7-8% (1). Nowadays, the requirement of appendectomy in patients without complicated appendicitis is being increasingly refuted, since in these selected cases the choice of antibiotic treatment-only avoids the risk postoperative morbidity. The most widely used imaging methods for the radiological diagnosis of acute appendicitis are transabdominal ultrasound (US) and computed tomography (CT).
US is more available than CT, but it has a lower accuracy: with US the visualization of the appendix is highly dependent on the skill of the sonographer, patient habitus, position of the appendix and presence of intestinal gas (sensitivity 44-100%, specificity 47-99%) (2-3).
Previous literature has demonstrated that magnetic resonance imaging (MRI) is superior to US in the diagnosis of appendicitis, and nearly equal to CT (4-5). The main limitations of MRI include its high cost, limited availability, and long examination times.
Therefore, the objective of this prospective study is to determine the feasibility and diagnostic performance of an abbreviated MRI protocol for the diagnosis of appendicitis.
A total of 152 consecutive patients with clinical suspicion of acute appendicitis were referred to the emergency department of radiology. The choice between surgical intervention and medical-only treatment was based on the specific institution’s protocol, based on a clinical-radiological assessment with ultrasound and CT in selected cases only. Of these 152 patients, 67 patients underwent MRI, based on the results of a severity score (Alvarado score ≥ 5) and were subsequently included in this study. The abbreviated MRI protocol was acquired on a 3T MR system (Discovery 750w, GE Healthcare) with patients in the supine position, with axial and coronal T2-Weighted (T2W) sequences and axial Diffusion-weighted Imaging (DWI). No oral or intravenous contrast agents or antiperistaltic agents were used in the study.
MRI images were analyzed by two radiologists, blinded to clinical and other imaging data, on consensus. Features analyzed were: maximum serosa-to-serosa diameter of the appendix, maximum wall thickness, T2 signal intensity in the wall and lumen, presence of diffusion restriction in the wall, fat stranding in the right lower fossa (RIF), presence of appendiculitis, free fluid in the abdomen, and presence of loco-regional mesenteric lymphadenopathy. For the diagnosis of appendicitis, an appendix greater than 6 mm in diameter with signs of inflammation was considered positive (6). T2 hyperintensity and diffusion restriction in the wall of the appendix were used to determine positivity in suspect cases.
Histopathological examinations (HPE) were used as reference standard in surgical cases (n= 39); in non-surgically treated cases, the clinical diagnosis at discharge and 3-months follow-up were used instead (n= 28).
The mean and median duration of acquisition with the abbreviated MRI protocol was 14 and 12.5 min, respectively. The appendix was visualized at MRI in 62/67 patients (92.5%) and a diagnosis of appendicitis obtained in 45/67. Of the remaining 22 cases, an alternative diagnosis was found in 6, and the remaining 16 were considered negative MRI examinations. Of the 39 patients who underwent surgery, HPE determined that 34 had appendicitis, 3 normal appendix, 1 cecal perforation, and 1 appendiceal diverticulum.
The abbreviated MRI protocol had a sensitivity, specificity, PPV, NPV and accuracy of 93.3%, 86.4%, 93.3%, 86.4%, and 91.0%, respectively. The two parameters with best diagnostic accuracy were fat stranding in RIF and diffusion restriction in the wall of the appendix, 86.6% and 83.7%, respectively. The median diameter of the appendix in patients with acute appendicitis was 9.7 mm and 5.9 mm in those without appendicitis. The ROC curve of appendix diameter for the diagnosis of appendicitis had an AUC of 0.843: a cut-off of 8 mm had a sensitivity of 81.8% and specificity of 83.3%. The median appendix wall thickness in patients with acute appendicitis was 3.3 mm and 2.3 mm in those without appendicitis: the ROC curve had an AUC of 0.737. The ADC values in the appendix wall could only be satisfactorily measured in 49 subjects, and no significant difference was found between those with and without appendicitis.
In conclusion, the authors have defined an abbreviated MRI protocol consisting only of T2W and DWI sequences, without contrast or antiperistaltic agents, able to reduce the duration of the examination while maintaining an excellent diagnostic accuracy.
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Dr. Alessandro Calabrese is a fourth-year radiology resident at Sapienza University of Rome, Italy. He graduated from Sapienza University in 2017 with a thesis on the role of Intravoxel Incoherent Motion (IVIM) in the evaluation of breast lesions. His main interests include breast and abdominal radiology, with several papers as author/co-author published on these topics in international journals.
Comments may be sent to: alessandro.calabrese@uniroma1.it