Purpose or Case Report: To describe the spectrum and incidence of alternative etiologies for lower abdominal and pelvic pain identified on magnetic resonance imaging (MRI) following indeterminate appendix ultrasound (US) in pediatric patients.
Methods & Materials: In this IRB-approved, HIPAA compliant retrospective study, we reviewed the radiology database for all pediatric patients who underwent appendix MRI after indeterminate appendix US between 1/1/2011 and 8/31/2014. When etiologies other than appendicitis were identified for acute lower abdominal and pelvic pain, they were categorized as follows: (1) gynecologic, (2) non-appendix gastrointestinal, (3) urinary tract, (4) hepatobiliary, and (5) musculoskeletal.
Results: We identified 276 patients (4-17 years of age) who underwent appendix MRI after indeterminate appendix US. 55 (19.9%) patients were diagnosed with appendicitis on MRI and were therefore excluded from the analysis. 221 (80.1%) patients’ MRI examinations were negative for appendicitis. 159 (71.9%) of these patients had no alternative etiology for abdominopelvic pain identified on MRI. 63 (28.5%) patients’ MRI examinations revealed alternative causes for their symptoms. Gynecologic etiologies were found in 27 (42.9%) cases: e.g., ovarian or paratubal cysts (n=19) and adnexal torsion (n=2). Non-appendix gastrointestinal abnormalities were seen in 26 (41.3%) cases: e.g., regional enteritis or colitis (n=18) and epiploic appendagitis (4). Urinary tract pathology was identified in 6 (9.5%) cases: e.g., pyelonephritis (n=2) and urolithiasis (n=2). Hepatobiliary abnormalities were found in 3 (4.8%) cases: e.g., cholelithiasis (n=1) and choledocholithiasis (n=1). Finally, a musculoskeletal cause of pain was identified in 1 (1.6%) patient: a rectus muscle strain.
Conclusions: MRI performed after indeterminate appendix US in children with acute lower abdominal pain provides an alternative diagnosis in approximately one-in-four patients. Pathologies evident on MRI involve multiple organ systems and are of varying clinical urgency from simple muscle strain to emergent adnexal torsion.