Parks classification is a widespread classification system for fistula in ano proposed by Parks in 1976. Parks described four different types of perianal fistula considering the fistulous tract with respect to the anal sphincter complex. Crucial landmarks for this classification are represented by the external anal sphincter and by the levator ani muscle. Four types of fistulas are described by Parks: intersphincteric, transphincteric, extrasphincteric, and suprasphincteric. Parks classification is very useful since different types of fistulas categorized using Parks methods require different surgical approach. Basically the intersphincteric fistula (i.e., the more easy and common fistula) can be treated with surgical fistulectomy, whereas other types of fistulas in whom the fistulous tract involves the external anal sphincter or the levator ani muscle should be treated with surgical drainage by means of seton positioning in order to avoid iatrogenic damage to sphincter complex and possible fecal incontinence.

Gastrointestinal perforation is a cause of acute abdomen.

Gastrointestinal perforation is defined as a complete penetration of the wall of the stomach, small intestine, or large bowel resulting in intestinal contents flowing into the abdominal cavity. Perforation of the intestines results in the potential for bacterial contamination of the abdominal cavity with peritonitis. Perforation of the stomach can lead to a chemical peritonitis due to leaked gastric acid. Perforation anywhere along the gastrointestinal tract is a surgical emergency. Underlying causes include gastric ulcer, diverticulitis, appendicitis, gastrointestinal cancer, acute mesenteric ischemia, trauma, nonsteroidal anti-inflammatory drugs, and ingestion of corrosives. Perforation may also be iatrogenic during endoscopic procedures (ERCP, colonoscopy) or during abdominal surgery.