Perineal abscesses and fistulae Flashcards
Define anal fistula.
A track that communicates between the sin and anal canal/rectum.
What is the aetiology of anal fistula?
Thought to be caused by blockage of deep intramuscular gland ducts which then predispose to abscess formation, which when drained forms a fistula.
Causes:
- Perianal sepsis
- Abscsses
- Crohn’s
- TB
- Diverticular disease
- Rectal carcinoma
- Immunocompromise
What is Goodsall’s rule for anal fistula?
Determines the path of the fistula track
- It asks you to imagine a transverse line through the anus in the lithotomy position.
- If antierior external opening then the track is in a straight line (radial)
- If posterior then the internal opening is always at the 6 o’clock position, taking a tortuous course
What investigations are done for anal fistula/anorectal abscesses?
- Endoanal US
- MRI
- Examination under anaesthetic
Then exclude sepsis/associated disease e.g. Crohn’s and TB
How do you manage anal fistula?
Fistulotomy and excision
High fistulae (involving continenece muscles of the anus) require “seton suture” tighetened over time to maintain continence;
Low fistulae are “laid open” to heal by secondary intention (division of sphincters poses no risk to continence)
Name 4 types of perianal fistulae.
- Transsphincteric
- Intersphincteric
- Extrasphincteric
- Suprasphincteric
Parks’ classification states that 70% will be intersphincteric, 25% transsphincteric and 5% suprasphincteric.
What is an anorectal abscess?
An infection in the cryptoglandular epithelium lining the anal canal spreads to the surrounding soft tissues, with subsequent abscess formation.
How common are ano-rectal abscesses?
- Develop in a third of Crohn’s patients
- x2-3 more common in men than women
- occur between age 20-40
- Usually in spring and summer
What are the symptoms of anorectal abscess?
- Hx of Crohn’s and anal fistula
- Anal/perianal pain - 1-2 days before presentation and becoming more severe
- Swelling and warmth of perianal tissues
- No rectal bleeding unless abscess burst
- Fever common <38.6oC
What are the signs of anorectal abscess on physical examination?
Inter-sphincteric and supra-levator abscesses may require anaesthesia for full examination
- Anal fistula - key risk factor
- Perianal pain
- Low grade fever
- Mild tachycardia
- Tender, indurated area immediately adjacent to anus above anorectal ring - the further it is from the anal verge the less likely it is to be an anorectal abscess. If >3cm from anal verge then infected epidermal inclusion cyst more likely. In if inter-gluteal area then pilonidal disease more likely
- In anal fistulae associated with anorectal abscess - may be hard, cord-like structure
What investigations would you do for an anorectal abscess?
Rarely helpful in diagnosis
Bloods:
- FBC - WBC elevated, Hb normal
- Glucose - hyperglycaemia if associated with diabetes
- Culture of aspirate
Imaging:
- US/CT/MRI - for complicated cases e.g. atypical presentation or supralevator/horseshoe abscess
What is a horseshoe abscess?
When the infection of an anorectal abscess spreads to involve both the ischo-rectal fossae and the post-anal space - may appear to be bilater abscesses
What are the risk factors for anal abscess?
- Anal fistula - impaction of food mattter in the fistula tract
- Crohn’s disease - in one third
- Male - 2-3:1
- Other: hard stools, aged 20-40yrs
How do you manage an ano-rectal abscess?
Surgical drainage +/- fistulotomy
Postoperative care - baths x2-3 daily, absorbent dressings, diet containint 25-30g fibre
If elderly and immunocompromised/co-morbid:
Broad spectrum antibiotics +/- aminoglycosides - ampicillin + ciprofloxacin AND/OR gentamicin
What are the complications of anorectal abscess?
Necrotising soft tissue infection - of the perineum (Fournier’s gangrene) with life threatening sepsis may occur if there is diagnosis of management. More likely with co-morbidities.
Anal fistula - develops in 37%of patients
