Purpose or Case Report: Postoperative abscess is the most common complication of perforated appendicitis in children with an incidence of 3-25%. Though the imaging algorithms for diagnosis of pediatric appendicitis have evolved to magnetic resonance imaging (MRI), the use of MRI for post-operative evaluation of these children remains in its infancy.
The purpose of our study was to evaluate our experience with a rapid non-contrast MR protocol for evaluation of post-appendectomy cases with concern for abscess.
Methods & Materials: This was a retrospective, IRB approved study. All patients underwent a clinically indicated non-contrast MRI abdomen/pelvis on a 1.5 or 3 Tesla scanner. All MR studies were reviewed by 2 blinded pediatric radiologists to identify presence of drainable fluid collection (diffusion restriction and minimum size 2cm). Each fluid collection was further characterized as accessible or not accessible for percutaneous (overlying bowel loops), or transrectal drainage (location in cul-de-sac). Imaging findings were compared to clinical outcome.
Results: There were 8 girls and 7 boys; age range 6-17 (median 12.6) years. 14/15 cases had perforated appendicitis, 1 had non-perforated appendicitis. Median time interval between initial intervention to MRI was 8 (range 5-31) days. Indications for MRI were: persistent leukocytosis (10), follow up abscess (4), fever (3), and abdominal pain (3).
13/15 patients had foci of diffusion restriction on MR. 3/13 had no corresponding T2 fluid signal and were categorized as phlegmons. 10/13 had corresponding T2 fluid signal and were classified as abscesses. Using a minimum diameter of 2 cm, 7/10 were considered to be clinically significant. 5/7 clinically significant abscesses were accessible for drainage by interventional radiology based on location (cul-de-sac) while 2 were be non-accessible (overlying bowel). Trans-rectal drainage of the cul-de-sac collections was performed in 4/5 cases, 1 was managed medically. All patients with no drainable abscess were discharged to home in <48 hours. Minimum ADC value in the abscesses was 299 - 549 (median 398) mm/s².
Conclusions: Rapid non-contrast MRI utilizing fluid sensitive and diffusion weighted sequences can be used to identify drainable fluid collections in post-appendectomy cases. This protocol can be used to triage patients between conservative management vs. abscess drainage without oral/intravenous contrast or exposure to ionizing radiation.