Editing Perianal abscess


== '''Aetiology''' ==

* Primary perianal abscess     (obstructed crypt)
* Secondary
** Inflammatory
*** Crohn disease
*** TB
*** Actinomycosis
*** Lymphogranuloma venereum
** Trauma
*** Impalement
*** Foreign body
*** Anal fissure
*** Iatrogenic
*** Episiotomy
*** Haemorrhoidectomy
*** Prostatectomy
*** Radiation
** HIV
** Radiotherapy
** Malignancy
*** Rectal or anal cancer
*** Leukaemia
*** Lymphoma

== '''Pathophysiology''' ==

* Typically results from     infection of anal glands secondary to obstruction of the draining duct by     faecal debris. This leads to stasis, bacterial overgrowth, and ultimately     inter-sphincteric abscess.
* The abscess can then expand     caudally to the anoderm (perianal abscess) or across the external     sphincter into the ischiorectal fossa (ischiorectal abscess), or less     commonly, into the supralevator or submucosal spaces (see below).
* About 10% of abscesses occur     due to other processes

== '''Presentation''' ==

* Indolent onset of constant,     throbbing anal pain with localised swelling, erythema and fluctuance
* Even if no fluctuance is     palpable, most patients with erythema and pain have some sort of deeper     abscess
* If the diagnosis is uncertain     (pain and sepsis but no visible or palpable abscess), a pelvic CT or EUA     is best

== '''Classification''' ==

* Perianal (60%)
** '''small,      tender, red fluctuant swelling near anus'''
* Ischiorectal (20%) - larger,     deeper, diffuse, tender, indurated area within buttocks. Penetrate through     external anal sphincter. Can extend bilaterally to become a horseshoe     abscess - if untreated can spread to lower abdominal wall, scrotum, and     perineum. Deep post-anal space infections leading to horseshoe abscess     typically have a posterior midline internal opening.
** '''Gluteal      induration, tenderness and fluctuance without tenderness on DRE'''
* Intersphincteric (5%) - only     about 5% of perianal abscesses. No skin changes, just a fluctuant mass     penetrating into lumen.
** '''Exquisite      tenderness on DRE, but no external findings'''
* Supralevator (4%) - forms     EITHER BY an obstructed gland process tracking superiorly, OR spread from     pelvis (Crohn's?). Difficult to diagnose clinically - feel for induration     above anorectal ring, but may be a/w severe pain, fevers, urinary     retention. May require CT to diagnose.
** '''May have no      anorectal exam findings'''
** Often treated by IR or      abdominal drainage rather than EUA and I+D
* Submucosal/'gluteal' (1%)
** No anal/rectal involvement
* Postanal space
** '''Localised      tenderness posterior to the anal verge, often without induration or      fluctuance'''
** Can extend into bilateral      ischiorectal fossas to become a horseshoe abscess.


== '''Differential diagnosis:''' ==

* Anal fissure - usually     posterior tear below dentate line - this pain is more likely to be only     a/w passing stool
* Thrombosed haemorrhoid
* Anal fistula
* Prolapsed internal     haemorrhoid
* Pilonidal sinus
* Buttock skin abscess eg     carbuncle
* Bartholin cyst
* Hidradenitis suppuritiva
* Be concerned for Crohn's with     large, thick skin tags, fissures off the midline, or complex fistulae

== '''Management''' ==

* Promptly drain, even if no     fluctuance
* See separate topic under     'colorectal operations'

== '''Special populations''' ==

* Immunocompromised     neutropaenic - if they don't have enough neutrophils to mount a     suppurative response, there won't be a target for drainage. In this case,     long-term Abx is warranted. Imaging or EUA may help to identify a target. 
** Broad-spectrum      antibiotics
** Bone marrow      stimulating growth factors
** Sitz baths
** Stool      management
* Necrotising infections -     rapid onset of disproportionate pain, especially in obese smokers with     diabetes and renal impairment or neurologic conditions.

== '''Complications''' ==

* Recurrence - 44%
* Fistula - 15-38% after one     abscess

[[Category:Colorectal]]
[[Category:Intern education]]