A 53-year-old male was admitted to hospital due to "repeated perianal exudation and dull pain and discomfort during defecation for more than 1 year". Physical examination: Anal diagnosis: The external opening of the anal fistula can be seen at 8 o'clock in the knee-chest position, 6 cm away from the anal margin (Figure 1), with a cord leading to the anus. At 11 o'clock, 2 cm away from the anal margin, palpation of the local texture is tough, which is considered to be the internal opening of the anal fistula. The rectal mucosa is smooth, and the finger cuff is withdrawn without blood staining. MRI examination was performed, 20 ml of meglumine gadoterate injection was injected from the external port of anal fistula, and then MRI scan was performed. Tubular, patchy and other non-uniform long T2 signals were seen in the soft tissue from the inner side of the left gluteus maximus muscle to the left and posterior side of the anal canal, and the DWI sequence showed a high signal. The patchy long T1 long T2 signals were seen around it, and T2 lipid pressure showed a high signal. Contrast medium filling was seen in the soft tissue of the canal and the left and posterior side of the anal canal (Figure 2). If the diagnosis of anal fistula is clear, considering the long fistula distance (about 7 cm), it is a huge anal fistula. If the anal fistula resection is performed, the local wound is huge, the healing cycle is long, and the quality of life is poor. Autologous platelet-rich plasma (PRP) was performed. The treatment has been reviewed and approved by the hospital ethics committee.
