Fistula in ano - TMS

Question 1

What is a perianal fistula (or fistula in ano)

Answer 1

• Abnormal connection
• Between anal canal and perianal skin
• Majority associated with anorectal abscesses

Question 2

Classfication of fistula in ano

Answer 2

• Parks classification system
• 4 types

Question 3

Parks classification system

Answer 3

• Inter-sphincteric fistula (most common)
• Trans-sphincteric
• Supra-sphincteric (least common)
• Extra-sphincteric

Question 4

Formation of fistula - causes

Answer 4

• Anorectal abscess
• Inflammatory bowel disease - perianal Crohns
• Systemic - Diabetes mellitus
• Trauma to anal region
• Previous radiation to anal region

Question 5

Clinical features of fistula in ano

Answer 5

• Recurrent perianal abscesses
• Intermittent or continious discharge into perineum inc mucus, blood, pus or faeces

Question 6

Examination for fistula in ano

Answer 6

• External opening onto perineum may be seen
• Can be fully opened or covered by granulation tissue
• Fibrous tract may be felt underneath skin on DRE

Question 7

Rule to predict trajectory of a fistula tract

Answer 7

• Goodsall rule

Question 8

Goodsall rule

Answer 8

• External opening posterior to the transverse anal line - tract will follow a curved course to posterior midline
• External opening anterior to transverse anal lien - tract will follow straight radial course to the dentate line

HINT posterior is curved because bootays are curvy

Question 9

Investigations for fistula in ano

Answer 9

• MRI imaging - can visualise and then plan surgery

Question 10

Surgery for fistula in ano

Answer 10

• Depends on cause and site
• Eg for Crohns medical management initiated after drainage of abscess before further surgery

Question 11

Most common surgical methods for fistula in ano

Answer 11

• Fisulotomy
• Placement of seton

Question 12

Fistulotomy

Answer 12

• Suitable for superficial disease
• Laying tract open
• Done by cutting through skin and subcut tissue, allowing it to heal by secondary intention

Question 13

Placement of seton

Answer 13

• Suitable for high tract disease
• Goes through fistula tract, attempts to bring together and close the tract
• Passing out at opening of the perianal skin adjacent to external opening

Question 14

How is procedure chosen?

Answer 14

• Depends on course of tract
• If low track course, through less subcut tissue and muscle - faecal continence is rarely impaired post op
• However, if high tract course, higher change of incontinence impairement