Objective:To investigate the clinical characteristics and treatment of patients with perianal necrotizing fasciitis.Methods:This study was a retrospective cohort study. Twenty patients with perianal necrotizing fasciitis who met the inclusion criteria were admitted to the Department of Burn and Plastic Surgery of the First Affiliated Hospital of Guangxi Medical University (hereinafter referred to as our department) from August 2013 to September 2023, including 19 males and 1 female, aged 24-74 (56±11) years. Based on the spreading route of perianal infection to the lower abdomen, the patients were divided into perianal-inguinal-lower abdominal wall group (12 cases) and perianal-pelvic cavity-retroperitoneal group (8 cases). The following clinical data were compared between the two groups of patients: general data, including gender, age, combined underlying diseases, blood glucose level and acute physiology and chronic health evaluation Ⅱ (APACHE Ⅱ) score when admitted to our department, and laboratory risk indicator for necrotizing fasciitis (LRINEC) score when admitted to our department and at 14 d after admitted to our department; infection indicators when admitted to our department, including C-reactive protein level, white blood cell count, lymphocyte count, procalcitonin level, and lactic acid level; clinical outcome-related indicators, including time from onset to definite infection range, number of surgery, treatment in intensive care unit (ICU), length of hospital stay, treatment outcome, and recurrence of necrotizing fasciitis during follow-up; detection of pathogen and bacterial drug resistance in wound necrotic tissue specimen when admitted to our department.Results:Compared with those in perianal-inguinal-lower abdominal wall group, the APACHE Ⅱ score and lactic acid level when admitted to our department and LRINEC score at 14 d after admitted to our department (with t values of -5.98, -5.01, and -2.86, respectively, P<0.05) and ICU treatment ratio ( P<0.05) were significantly increased, the time from onset to definite infection range was significantly prolonged ( Z=-3.75, P<0.05), and the number of surgery was significantly increased ( Z=2.80, P<0.05) in patients in perianal-pelvic cavity-retroperitoneal group. There were no statistically significant differences in other data between the two groups of patients ( P>0.05). Eighteen patients were cured, and no recurrence of perianal necrotizing fasciitis was observed during follow-up of 6 months in 18 cured patients. The main bacteria were Escherichia coliand Klebsiella pneumoniae, and the fungui were Aspergillus and Candida albicans detected in wound necrotic tissue specimens in two groups of patients when admitted to our department. The ratio of multiple drug resistance of bacteria in wound necrotic tissue specimens in perianal-pelvic cavity-retroperitoneal group of patients was significantly higher than that in perianal-inguinal-lower abdominal wall group ( P<0.05). Conclusions:Perianal necrotizing fasciitis can spread to the lower abdomen through two routes: the perianal-inguinal-lower abdominal wall route and the perianal-pelvic cavity-retroperitoneal route. The latter is more insidious in disease progression and more challenging in treatment. Establishing a mechanism of multi-disciplinary team diagnosis and treatment can achieve the goal of early diagnosis and precise treatment of perianal necrotizing fasciitis.