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lithotomy position.
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We could find abscess discharge from the fistula, and around a quarter area was influenced (Fig. 1, Fig. 2).
Colonoscopy examination.
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No inner-bowel damage was displayed during the colonoscopy examination (Fig. 3).
Perianal ultrasonography examination.
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According to this appearance, perianorectal abscess was found (Fig. 4).
T1 screenage.
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The deeper side was not contacted to muscles, while the shallow side broke through skin (Fig. 5).
Coronal  T2 screenage.
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This appearance clearly presented subcutaneous the relationship between abscess and ambient tissue. T2 coronary screenage showed up the precious ducts and abnormal tissue location (Fig. 6).
Coronal T2 screenage.
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T2 pressure lipid coronal position screenage removed the influence of fat, and the brightness part was diseased region that was more extensive than the general type (Fig. 7).
Sagittal plane T2 screenage.
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T2 sagittal position screenage displayed that the ducts did not connect with rectum, but the boundary between sphincter and diseased was indistinct (Fig. 8).
Using finger to explore.
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Fusiform incision was adopted at 10 o'clock direction to separate subskin tissue bluntly and excise hyperplastic inflammatory tissue, we discovered a fibrous strip fistula (Fig. 9).
Separating tissue to display the duct. the fistula.
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After separating the fistula, the inner end of fistula was displayed on the inside of external sphincter (Fig. 10).
Finishing operation.
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After stemming the bleeding well and performing local blockade on tissue around excision with methylene blue and lignocaine mixed liquid to alleviate postoperation pain, the surgery finished (Fig. 11).
The excised tissue.
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Pathology examination informed that the excised tissue was granulation tissue and fibrous tissue (Fig. 12).