Medical Illustration - A Pictorial Essay Visual Illustration of Obstetric Anal Sphincter Injuries (OASIS) Degrees of Severity, a Picture is Worth a Thousand Words

Abstract

Obstetric anal sphincter injury affects about 5.7% of primiparous women who deliver vaginally. Perineal injury during childbirth is a common event with important morbidity associated with third-and-fourth degree perineal tears (also referred to as obstetric anal sphincter injuries—OASIS). As there was a lack of consistency in the classification of a partial anal sphincter injury, with up to 33% of consultant obstetricians classifying a complete or partial tear of the EAS as a second-degree tear. We have proposed simple, digital diagrammatic drawings to visually represent all degrees (grades) of OASIS based on the WHO OASIS classification.

Keywords
obstetric anal sphincter injuries (OASIS); anal sphincter; perineal tear; faecal incontinence; diagnostics; treatment

Introduction

Obstetric anal sphincter injury affects about 5.7% of primiparous women who deliver vaginally. Perineal injury during childbirth is a common event with important morbidity associated in particular with third-and-fourth degree perineal tears (also referred to as obstetric anal sphincter injuries—OASIS).

Early diagnosis of these damages is mandatory to define a prompt therapeutic strategy and avoid the development of faecal incontinence.¹

Post-delivery muscular damages are known as obstetric anal sphincter injuries (OASIS). OASIS are also referred to as third- and fourth-degree spontaneous perineal lacerations, according to the currently accepted classification.²

Traditionally, the severity of perineal tear was limited to 4 grades: grade 1 (superficial vaginal and/or perineal skin), grade 2 (vaginal muscles), grade 3 (in or through external anal sphincter muscle), and grade 4 (external and internal anal sphincters and anorectal lumen).³

As there was a lack of consistency in the classification of a partial anal sphincter, with up to 33% of consultant obstetricians classifying a complete or partial tear of the EAS as a second-degree tear⁴ Sultan.² devised a more specific classification, later adopted by the WHO⁵ and the International Consultation on Incontinence.⁶ In this classification, grade 3 is further refined as involving the anal sphincter complex and is divided into 3a, 3b, and 3c (Table 1).

Table 1
WHO Classification of OASIS

First degree	Injury to perineal skin only
Second degree	Injury to perineum involving perineal muscles but not involving the anal sphincter
Third degree	Injury to perineum involving the anal sphincter complex:
3a	Less than 50% of EAS thickness torn
3b	More than 50% of EAS thickness torn
3c	Both EAS and IAS torn
Fourth degree	Injury to perineum involving the anal sphincter complex (EAS and IAS) and anal epithelium

http://www.who.int/classifications/icd/en

The type of third-degree tear seems to have an impact on symptoms, with OASIS grades 3a and 3b having a better prognosis than 3c. In fact, those with a 3c OASIS had symptoms similar in severity to those with a fourth degree laceration⁷.

A button-hole injury, where only the vaginal and rectal mucosa are involved, should not be reported as a third- or fourth-degree tear if found in isolation. Documentation of the presence or absence of a tear, as evidenced on rectal examination, should be disclosed to the patient, and incorporated into the delivery note, and repair should be done to avoid fistulization.

The World Health Organization classification should be used to classify obstetrical anal sphincter injury. This distinguishes the degree of external sphincter tear (3a: < 50% or 3b: ≥ 50%) and the presence of internal sphincter defects (3c). A button-hole injury is distinct and should be classified separately as such. Table 1

Such a grading system considers the degree of tearing experienced by the external sphincter separately from that of the internal sphincter. Such distinction is meant to improve reporting, guide repair, and facilitate outcome research.⁸

Aim

For better simplified, objective understanding of The WHO obstetric anal sphincter injury (OASIS) classification by physicians who are involved in the care of patients with such anal sphincter injuries including obstetricians, general surgeons & even midwives, We have proposed simple, digital diagrammatic drawings Figure 1 (using Paint 3D program on Microsoft Windows10 then edited on Paint program on Windows 10) to visually represent all degrees (Grades) of based on the WHO OASIS classification table.1

Fig. 1
Visual illustration of obstetric anal sphincter injuries (OASIS) grading of severity.

Conclusion

We hope that providing such a simple, diagrammatic digital illustration of anal sphincter injuries might be very helpful to fully understand, appreciate, and differentiate between each grade of anal sphincter injury, especially in performing primary repairs of these injuries which will be eventually reflected in on the proper diagnosis, management, and better outcomes.

Abbreviations
• OASIS  obstetric anal sphincter injuries
• AI  anal incontinence
• EAS  external anal sphincter
• IAS  internal anal sphincter
• RTC  randomized control trial
• SVD  spontaneous vaginal delivery
• WHO  World Health Organization

Acknowledgments

None.

References

• ¹
  Spinelli A, Laurenti V, Carrano FM, Gonzalez-Díaz E, Borycka-Kiciak K. Diagnosis and Treatment of Obstetric Anal Sphincter Injuries: New Evidence and Perspectives. J Clin Med 2021;10(15):3261. Doi: 10.3390/jcm10153261
  » https://doi.org/10.3390/jcm10153261
• ²
  Sultan AH. Obstetric perineal injury and anal incontinence. Clin Risk 1999;5:193–196
• ³
  Cunningham F, Leveno KJ, Bloor S, Hauth J, Rouse DJ, Spong C. Normal labor and delivery. In: Cunningham F, Leveno KJ, Bloor S, Hauth J, Rouse DJ, Spong C, eds. William's Obstetrics. 23rd ed. New York (NY): McGraw-Hill; 2011
• ⁴
  Fernando RJ, Sultan AH, Radley S, Jones PW, Johanson RB. Management of obstetric anal sphincter injury: a systematic review & national practice survey. BMC Health Serv Res 2002;2 (01):9
• ⁵
  Thach T. Methods of repair for obstetric anal sphincter injury: RHL commentary. Geneva (CH): World Health Organization, The WHO Reproductive Health Library; 2006
• ⁶
  Koelbl H, Nitti V, Baessler K, Salvatore S, Sultan A, Yamaguchi O. Pathophysiology of urinary incontinence, faecal incontinence and pelvic organ prolapse. In: Abrams P, Cardozo L, Khoury S, Wein A, eds. Incontinence. 4th ed. St Hillier, (GB): Health Publication; 2009:255–330
• ⁷
  Roos AM, Thakar R, Sultan AH. Outcome of primary repair of obstetric anal sphincter injuries (OASIS): does the grade of tear matter? Ultrasound Obstet Gynecol 2010;36(03):368–374
• ⁸
  World Health Organization. International Classification of Diseases (ICD). Geneva (CG): WHO; 2015. Accessed on September 15, 2015 at: http://www.who.int/classifications/icd/en
  » http://www.who.int/classifications/icd/en

Publication Dates

• Publication in this collection
  05 July 2024
• Date of issue
  2024

History

• Received
  11 Jan 2024
• Accepted
  09 Apr 2024