title: Acute appendicitis, inflammatory appendiceal mass and the risk of a hidden malignant tumor: a systematic review of the literature.
abstract: Acute appendicitis is significantly common. Despite the increased use of computed tomography, the number of perforated cases has been stable in the past three decades. Between 2% and 6% of patients with acute appendicitis present appendiceal mass, often described as inflammatory phlegmon or abscess. Malignant tumors are confirmed by pathological analysis in 0.9-1.4% of all appendectomies performed to treat acute appendicitis. However, recent series demonstrate an elevated incidence of malignancies, ranging from 5.9 to 12%, in patients with inflammatory appendiceal mass.
  
  
  
  The analysis was based on a systematic review of the literature. The articles were searched in PubMed for the period from 1987 to 2016. Articles presenting the incidence of the hidden malignancy among patients with appendiceal inflammatory mass were selected. Variables as age, interval appendectomy rate, the incidence of neoplasm, time to surgery, minimally invasive assessment, histology, right colectomy rate and morbidity were analyzed.
  
  
  
  A total of 13.244 patients were described as presenting acute appendicitis. Appendiceal tumor is present in approximately 1% of the appendectomies, while the rate of neoplasm varies from 10 to 29% in patients presenting appendiceal inflammatory mass. Interval appendectomies, despite been the minority of the procedures, disregard the higher morbidity associated with right sided colectomies. The review of literature also describes oncologic, histologic and clinical aspects of patients presenting appendiceal neoplasm, describing the most frequent histologic subtypes of this illness.
  
  
  
  Hidden appendiceal neoplasm in acute appendicitis are rare, fortunately. However, its incidence is much higher in patients presenting appendiceal inflammatory mass. Hence, interval appendectomy should be considered in this subgroup of patients.
authors.affiliation: Surgical Oncology Group from the III Surgical Clinic Division, Hospital das Clínicas of the University of São Paulo (USP), School of Medicine, Rua Dr. Ovídio Pires de Campos, 255, 8 th floor, room 8131, Cerqueira César, 05403-010 São Paulo Brazil.
authors.forename: Frederico José Ribeiro
authors.initials: FJR
authors.lastname: Teixeira
authors.affiliation: Surgical Oncology Group from the III Surgical Clinic Division, Hospital das Clínicas of the University of São Paulo (USP), School of Medicine, Rua Dr. Ovídio Pires de Campos, 255, 8 th floor, room 8131, Cerqueira César, 05403-010 São Paulo Brazil.|Emergency Surgical Service, Hospital das Clínicas of the University of São Paulo (USP), School of Medicine, Rua Dr. Ovídio Pires de Campos, 255, 8 th floor, room 8131, Cerqueira César, 05403-010 São Paulo Brazil.|850, Francisco Matarazzo Avenue, apt 181, Bloco 2, Zip Code 05001-200 Perdizes, São Paulo Brazil.
authors.forename: Sérgio Dias do
authors.initials: SDD
authors.lastname: Couto Netto
authors.affiliation: Sarcoma and Melanoma Surgery group - São Paulo Cancer Institute, University of São Paulo, School of Medicine, Cerqueira César, Brazil.
authors.forename: Eduardo Hiroshi
authors.initials: EH
authors.lastname: Akaishi
authors.affiliation: General and Trauma Surgery - III Surgical Clinic Division, Hospital das Clínicas of the University of São Paulo (USP), School of Medicine, Rua Dr. Ovídio Pires de Campos, 255, 8 th floor, room 8131, Cerqueira César, 05403-010 São Paulo Brazil.
authors.forename: Edivaldo Massazo
authors.initials: EM
authors.lastname: Utiyama
authors.affiliation: General Surgery Senior Resident - III Surgical Clinic Division, Hospital das Clínicas of the University of São Paulo, School of Medicine, São Paulo, Brazil.
authors.forename: Carlos Augusto Metidieri
authors.initials: CAM
authors.lastname: Menegozzo
authors.affiliation: Chief of Staff of the Emergency Surgical Service - III Surgical Clinic Division, Hospital das Clínicas of the University of São Paulo, School of Medicine, São Paulo, Brazil.
authors.forename: Marcelo Cristiano
authors.initials: MC
authors.lastname: Rocha
mesh_terms: D000038:Abscess / Q000209:etiology; D000328:Adult; D001063:Appendiceal Neoplasms / Q000150:complications / Q000175:diagnosis*; D001064:Appendicitis / Q000150:complications* / Q000175:diagnosis; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D018570:Risk Assessment
keywords: Acute appendicits; Appendiceal inflammatory mass; Appendiceal neoplasms; Appendiceal neuroendocrine tumors; Interval appendectomy; Pseudomixoma peritonei