Case report: Histological findings of peri-appendicitis in three children with SARS-CoV-2 – related multisystem inflammatory syndrome: A mark for systemic inflammation?

Background: Multisystem inflammatory syndrome in children (MIS-C) is a rare but serious condition that can potentially develop after SARS-CoV-2 infection in children. Gastrointestinal manifestation in MIS-C can mimic acute abdomen, potentially leading to unnecessary surgical treatment. Immune-mediated mechanisms seem to be a determining factor in its pathogenesis, and histological studies can help to shed light on this aspect. We describe three cases of children diagnosed with MIS-C that underwent appendectomy. Methods: We retrospectively collected the clinical features and histological findings of three previously healthy children who underwent appendectomy for clinical suspicion of acute appendicitis but were later diagnosed with MIS-C. Findings: The three children presentedwith prominent abdominalmanifestations andfever leading tothe suspicion of acute abdomen.Histological findings showed transmural and perivascular inflammation. Notably, CD68+ macrophages were predominant in the child with milder abdominal symptoms without cardiac injury, while CD3+ lymphocytes in the patient presented with more severe abdominal pain and cardiovascular involvement at admission. Interpretation: Gastrointestinal symptoms of children with MIS-C improve after proper immunomodulatory therapy, conversely showing inadequate response to surgical appendectomy. Histological findings revealed different inflammatory cell infiltration that primarily involved perivisceral fat and vessels, and subsequently mucosal tissue, in contrast to other forms of acute appendicitis. Our findings suggest that this kind of peri-appendicitis in MIS-C could represent a focal sign of systemic inflammation, with different histological patterns compared to other forms of acute appendicitis.