title: Occult anal sphincter injuries--myth or reality?
abstract: OBJECTIVE
  To establish the true prevalence of clinically recognisable and occult obstetric anal sphincter injuries (OASIS).
  
  
  METHODS
  Prospective interventional study.
  
  
  METHODS
  Busy district general hospital.
  
  
  METHODS
  Two hundred and fifty-four women having their first vaginal delivery over a 12-month period were invited. Two hundred and forty-one (95%) participated and 208 (86%) attended follow up.
  
  
  METHODS
  Women had a clinical examination at delivery by the accoucheur and repeated by an experienced research fellow immediately after delivery. All identified OASIS were verified and repaired by the duty specialist registrar or consultant. Endoanal ultrasound was performed immediately postpartum prior to suturing and repeated seven weeks later.
  
  
  METHODS
  Prevalence of recognised and occult anal sphincter injuries.
  
  
  RESULTS
  Fifty-nine (24.5%) women sustained OASIS. The prevalence of OASIS increased significantly from 11% to 24.5% when women were re-examined. Of these, 30 occurred in deliveries by midwives who missed 26 (87%) and 29 following deliveries by doctors who missed 8 (28%) injuries. All clinically apparent OASIS were also identified on endoanal ultrasound. In addition, three (1.2%) women had an occult anal sphincter injury. Two of these occult sphincter injuries were isolated to the internal anal sphincter (IAS) and would not usually be clinically detectable.
  
  
  CONCLUSIONS
  OASIS occur more frequently than previously reported. Many remain undiagnosed and are subsequently classified as occult when identified on anal endosonography. Genuine occult injuries are rare. Training in perineal anatomy and recognition of OASIS needs to be enhanced in order to increase detection of OASIS and minimise the risk of consequent anal incontinence.
authors.affiliation: Mayday University Hospital, Croydon, Surrey, UK.
authors.forename: Vasanth
authors.initials: V
authors.lastname: Andrews
authors.forename: Abdul H
authors.initials: AH
authors.lastname: Sultan
authors.forename: Ranee
authors.initials: R
authors.lastname: Thakar
authors.forename: Peter W
authors.initials: PW
authors.lastname: Jones
mesh_terms: D001003:Anal Canal / Q000000981:diagnostic imaging / Q000293:injuries*; D003951:Diagnostic Errors; D019160:Endosonography / Q000379:methods; D005260:Female; D006801:Humans; D033162:Incidental Findings; D007744:Obstetric Labor Complications / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000209:etiology*; D011247:Pregnancy; D015995:Prevalence; D011446:Prospective Studies; D014620:Vacuum Extraction, Obstetrical / Q000379:methods