Obstetric anal sphincter injury (OASI) in the presence of an intact perineum

Abstract

Obstetric anal sphincter injury (OASI) in the absence of concurrent injury to the perineal skin is not a common diagnosis. A primiparous woman delivered a healthy male infant by spontaneous vertex delivery. At time of delivery, a compound presentation of the fetal hand with the head was noted. Initial examination revealed a presumed second-degree tear; however, a small laceration above the anal verge was noted, which on exploration revealed a perineal injury through the anal sphincter complex. In the operating theatre, the perineal skin was incised to reveal a 3c OASI, which was repaired appropriately. While atypical OASI has been reported previously, this specific injury has never been described in detail in the literature. Awareness of atypical perineal injuries is needed and while careful perineal examination is required in all cases, this is especially important where the perineal skin appears intact to ensure appropriate diagnosis of any concurrent OASI.

Background

At time of vaginal delivery, 65%–85% of women are expected to have some form of obstetric perineal injury.^{1 2} These obstetric injuries are classified from first degree to fourth degree (table 1).^1–3 Third-degree and fourth-degree tears involve the anal sphincter complex and collectively are known as obstetric anal sphincter injuries (OASI) and occur in 4%–9% of mothers delivering vaginally.^{4 5} The incidence of OASI injuries increases with certain risk factors including: nulliparity, maternal age, induction of labour, fetal macrosomia, fetal malposition, occipito-posterior position, compound presentations, a short perineum, Asian ethnicity, prolonged second stage of labour, operative vaginal deliveries (ventouse and forceps) and shoulder dystocia.^{1 2 6} OASI in the absence of laceration of the perineal skin is a rarely reported and clinically experienced perineal injury.^{3 7} Atypical OASI has been reported previously, though this specific injury identified has never been described before in detail in the literature. OASI results in significant consequences beyond the initial injury: increased recovery time, chronic pain, dyspareunia, sexual dysfunction and anal incontinence.^8–10 These sequelae can have significant physical, behavioural and psychological consequences, and identifying these injuries early, providing prompt treatment and appropriate follow-up is essential for holistic care of these women. We hope to increase awareness of this unusual presentation of an OASI with intact perineal skin to highlight the importance of careful perineal and rectal examination after any vaginal delivery.

Table 1.

Classification of obstetric perineal injuries

	Description of perineal injury
First degree	Injury to perineal skin and/or vaginal mucosa
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 the external anal sphincter (EAS) thickness is torn 3b: more than 50% of the EAS thickness is torn 3c: both the EAS and internal anal sphincter (IAS) are torn
Fourth degree	Injury to perineum involving the anal sphincter complex (EAS and IAS) and the anorectal mucosa

Case presentation

A gravida 1 para 0 woman in her early 40s was admitted for a scheduled induction of labour to the prenatal department in a large tertiary maternity unit at 39+4 weeks gestation. Her history was notable for irritable bowel syndrome and gestational anaemia for which she was taking oral iron supplementation. Her body mass index (BMI) was 23.4 kg/m² (weight 67 kg, height 168 cm). During her pregnancy, she had routine antenatal care including an early pregnancy ultrasound at 9 weeks gestation, a low-risk non-invasive prenatal test, a booking ultrasound at 12 weeks gestation, an anomaly scan at 20+6 weeks gestation and routine antenatal visits from 28 weeks gestation. During the early pregnancy ultrasound scan, the crown-rump-length (9+4 weeks gestation) was noted not to match the estimated gestation (11+4 weeks gestation), though it was acknowledged that her usual cycle length was 35 days. Close monitoring of fetal growth was commenced, and from 31 weeks gestation, she was followed in the fetal assessment unit for small for gestational age, which included weekly Doppler and fortnightly growth scans. The last estimated fetal weight at 38 weeks gestation was 2.356 kg, with good interval growth in the last 4 weeks.

The patient was scheduled for induction of labour for advanced maternal age and attended at 39+4. She had a routine admission, and induction of labour was commenced as per the local hospital protocol. Cervical ripening was commenced after examination revealed that the cervix was closed, posterior, 3 cm long and −3 station. A 2 mg dinoprostone gel was administered, and 6 hours later, a further 1 mg dinoprostone gel was administered, and the patient was allowed time to establish into labour overnight. Re-examination for pains was completed and her cervix was deemed to be 4 cm and fully effaced, and she was transferred to the labour ward 15 min later. On arriving to the labour ward 10 min later, she was re-examined and now her cervix was found to be fully dilated, with the fetal head at −1 station. At this point, there was a spontaneous rupture of membranes, with copious clear liquor and a small amount of blood stained liquor. An epidural was sited and an hour of passive descent was allowed. Following this, maternal effort was commenced and the patient had a spontaneous vertex delivery of a liveborn male infant at 04:37 hour. The latent first stage of labour lasted 14 hours 30 min. The second stage of labour lasted 2 hours and 12 min. The male infant weighed 2430 g with Apgar scores of 9 and 10 at 1 and 5 min. It was noted that there was a compound presentation at delivery, where the fetal hand and arm was covering the fetal face at delivery of the head. Postpartum perineal examination by the attending midwife revealed what was felt to be a second degree tear, and an estimated blood loss of 300 mL. Third stage of labour lasted 11 min.

Investigations

Following delivery, perineal examination and repair was commenced by a junior obstetrician. A per vagina and per rectal examination revealed an intact rectal mucosa and intact perineal skin. There was a deep second degree tear to the vaginal mucosa and perineal muscles, with active bleeding. The anal sphincter was palpated through the perineal skin and while the tone was deemed to be poor (though it was noted that there was a very effective epidural in situ) no OASI was diagnosed. This tear was initially classified as a second-degree tear; however, closer examination revealed a 6 mm horizontal laceration at 11 o’clock on the anal verge, completely separate to the vaginal mucosa, anus and rectum. Further examination of this laceration revealed a tract behind the perineal skin, through the anal sphincter muscles and in to the vaginal mucosa. Senior obstetric review was sought, and temporary haemostasis was achieved with sutures and vaginal packing. A consultant urogynaecologist attended and examined the patient. At this point, the patient was consented for repair of a suspected OASI in theatre, and was moved to the operating room with adequate lighting, sufficient analgesia and to ensure complete visualisation of the perineal injury.

Treatment

Once in theatre the patient was given an epidural top-up, positioned in lithotomy and cleaned and draped in the usual preoperative fashion. A single dose of intravenous co-amoxiclav was administered. The laceration above the anal verge was examined again confirming a tract up into the vaginal mucosa (figure 1A). The perineal skin was incised with a sterile size 11 scalpel (figure 1B) to reveal the anal sphincter complex, which was carefully dissected and examined. Following this examination, the rectal mucosa was deemed to be intact, though, both the internal anal sphincter (IAS) and external anal sphincter (EAS) were completely torn. A 3c OASI was the final diagnosis.

Figure 1.

Postpartum perineal injury. (A) Postspontaneous vertex delivery; intact perineal skin and a laceration at 10–12 o’clock above anal verge identified (white arrow). (B) Intraoperatively; having taken down the intact perineal skin it revealed a completed 3c degree perineal tear. (C) Intraoperatively; repair of the internal and external anal sphincters using the overlapping technique with mattress sutures using 2–0 polyglycolic acid suture material (Maxon). (D) Postoperatively; completed perineal repair.

The IAS was repaired by identifying each end with Allis forceps, and the muscle approximated using two interrupted sutures with 2–0 polyglycolic acid suture material (Maxon). The EAS was identified and was repaired using the overlapping technique with three mattress sutures using 2–0 polyglycolic acid suture material (Maxon) (figure 1C). Good muscle bulk of the anal sphincter complex was noted following the IAS and EAS repair. The vaginal mucosa and transverse perineal muscles were then repaired in continuous running (non-locking) fashion with 2–0 vicryl rapide, and a subcutaneous repair was made to the skin (figure 1D).

An examination of the rectum was completed following perineal repair, good muscle bulk to the repair, moderate anal tone on voluntary contraction, no breach to the rectal mucosa and no palpable sutures in the rectum. A 100 mg of diclofenac was administered per rectum for postnatal analgesia. Our institution’s postnatal care bundle for women following OASI was initiated, which includes three doses of intravenous antibiotics, lactulose to prevent constipation and straining, and physiotherapy input on the postnatal ward. The patient was debriefed by the obstetrician that identified the atypical perineal tear, as well as the two operating senior obstetricians.

Outcome and follow-up

On the first postoperative day, the patient was mobilising, eating, drinking and had passed flatus, and was on a regular diet. On day 2, she was reviewed by physiotherapy on the postnatal ward, and reported two episodes of loose stool following laxative use, and described absent anal sphincter control. A bowel regimen plan, pelvic floor exercise plan were discussed, and per rectum examination of the anal sphincter demonstrated a poor concentric squeeze effort.

Since discharge, the patient has been seen regularly, initially at 2 weeks postnatally, and then every 4 weeks in the outpatient physiotherapy department. She initially reported urinary, flatal and faecal incontinence. She had stress urinary incontinence on sudden movement (sneezing, standing, etc), and continued to have poor control of flatus, some faecal urgency and a sensation of incomplete emptying. She also reported reduced sensation to the right side, both internal and external to the anal sphincter.

She was seen in the specialist perineal clinic by a consultant obstetrician and gynaecologist 6 weeks following delivery. Her sphincter contraction was noted to be concentric, but poor, especially on the patient’s right. She was counselled on risk of recurrence in future pregnancies, the possibility of an elective caesarean section for perineal protection, and the latter in particular if voluntary squeeze effort remains poor.

Under guidance from the physiotherapists the patient began treatment with a pelvic floor stimulator to increase control and voluntary muscle contraction strength, with improvement in symptoms at both 4-week and 8-week interval follow-up.

The woman is now 9 months post partum. She has occasional stress urinary incontinence and has regained full sensation. She has minimal faecal incontinence—primarily linked to irritable bowel symptoms—and very intermittent flatal incontinence. Ongoing physiotherapy and obstetric follow-up are in place for this woman and she will be seen early in any future pregnancies to discuss potential mode of delivery.

Discussion

The Sultan classification system for obstetric perineal lacerations is used by both the Royal College of Obstetrician’s and Gynaecologists in the UK, and the American College of Obstetrician’s and Gynecologists in the USA^1–3 (figure 2). Atypical perineal obstetric lacerations have been described in the literature, in particular those not included in the current classification system such as buttonhole rectal lacerations, perineal hernias or bucket handle tears.^11–13

Figure 2.

Sultan classification of obstetric perineal injuries (left), and both a normal perineum (top right), and an illustration of the clinical case described, whereby there was an obscured third-degree obstetric anal sphincter injury behind intact perineal skin (bottom right). Figure created by APW.

Best practice recommends immediate diagnosis in the postnatal period, ideally while on a labour ward or delivery suite. Diagnosis requires careful digital rectal examination to ensure the anal sphincter complex is intact, to assess need for perineal injury and need for repair, and ideally this should be completed with adequate analgesia.

The incidence of OASI ranges between 4% and 9% of women delivering vaginally,^{1 2 4} with a higher rate in nulliparous women than in multiparous women. Our case describes an OASI obscured by intact perineal skin, which may represent a potential ‘missed’ or ‘occult’ tear. Our literature search found no detailed published case reports of this kind, though some textbooks make reference to the potential existence of OASI in the presence of intact perineal skin (figure 2).^{3 7} Missed obstetric lacerations or ‘occult’ obstetric injuries were historically thought to be rare findings, however, evidence suggests that most injuries can be detected given appropriate training.¹⁴ Some research groups report that OASI is likely much more prevalent and diagnosis of OASI using endoanal ultrasonography,^{9 14 15} transperineal ultrasonography^{16 17} and translabial ultasonography¹⁸ have demonstrated higher rates of OASI. Debate remains as to whether ‘missed’ OASI by clinical diagnosis at the bedside and those diagnosed by ultrasonographic methods have the greatest correlation to clinical impact on quality of life and incontinence post partum.¹⁵

Diagnosis of OASI has steadily increased in the last 10–20 years,¹⁹ though this is likely a combination of improved detection as well as a true increase in injuries. Detection of injuries can be optimised using even short-term training programmes²⁰ and this effect has been similarly shown in repair outcomes.²¹ Appropriate diagnosis is paramount, especially as involvement of the IAS (3c injuries) is underappreciated,²² and is linked to worse functional outcomes than 3a or 3b tears.^{22 23} Buttonhole tears which involve an injury through the vaginal mucosa into the anal mucosa, above the anal sphincter complex, have been a recent focus in obstetric injuries sustained during vaginal deliveries.^{12 24} These are another type of obstetric injury that might be missed without careful rectal examination at the time of postpartum perineal examination.²⁴

It is clear that OASI—indeed any obstetric injury—can result in significant sequelae for patients. Maternal morbidity after OASI is associated with both short-term and long-term morbidity including perineal discomfort and pain, dyspareunia, rectovaginal fistulae, abscess formation, flatal incontinence and faecal incontinence.^{3 25} The failure to recognise, accurately diagnose these obstetric injuries has severe consequences for women’s physical and psychological quality of life both in the postnatal period and in future years. A recommended algorithm for examination, diagnosis, repair and follow-up of these cases is described in table 2.

Table 2.

Summary of recommendations for examination, diagnosis, repair and follow-up of perineal injuries, in particular for obstetric anal sphincter injuries

Diagnosis	Delivering midwife or obstetrician examines perineum, identifying perineal injury. If complex or extensive injury, second opinion from senior obstetrician should be sought.
Examination	A thorough vaginal and perineal examination should be conducted, followed by careful rectovaginal examination of the anal sphincter complex and rectal mucosa.
Environment	Complex, atypical or extensive perineal injuries should be repaired in the operating theatre with adequate lighting and effective analgesia (regional).
Antibiotics	Prophylactic antibiotics should be administered as per local antimicrobial guidelines.
Suture type	Absorbable synthetic suture material is preferrable, such as polyglycolic acid suture or polyglactin suture material.
Visualisation	If there is clinical suspicion for an obscured perineal injury, the perineal skin and subcutaneous tissues should be dissected down to fully visualise the anal sphincter complex.
Rectal mucosa repair	The torn rectal mucosa should be repaired using continuous non-locking 3/0 or 4/0 braided polyglactin suture material.
IAS repair	The IAS should be carefully identified after dissection of the perirectal fascia and repaired with 3/0 polyglactin.
EAS repair	The EAS should be carefully identified and repaired with 3/0 polyglactin in either end-to-end or overlapping technique.
Follow-up	Follow-up includes adequate analgesia, antibiotics, regular laxatives, physiotherapy review and specialist perineal clinic review.

EAS, external anal sphincter; IAS, internal anal sphincter.

The clinical finding was one of great significance to the woman affected and has ensured that immediate treatment was provided, rather than missing such an injury and risking the severe morbidity associated with missed third-degree or fourth-degree tears. Our suspicion is that a combination of two factors led to this presentation; first the fetal compound presentation of a head and hand at time of spontaneous vertex delivery, and second maternal perineal skin quality that allowed for elasticity. This combination allowed for the described injury to occur hidden behind what had the appearance of an ‘intact perineum’ (ie, this case was in fact a third-degree tear (figure 2), but on initial review looked like a normal perineum). This case provided an excellent opportunity to remind and create awareness of obstetric perineal injuries that are rare, but should still be identified if careful perineal and rectal examination is completed after every vaginal delivery. We encourage obstetric providers to engage in refreshed learning and teaching sessions to keep staff up-skilled.

Patient’s perspective.

Before giving birth I was naturally fairly apprehensive about tearing during labour. Like so many others, I did a little reading and did my pelvic floor exercises to prepare for that eventuality. My memories of the birth are a little hazy. Some details I remember vividly and others are more of a blur. I think I remember an episiotomy briefly being on the cards but then that moment passed. I remember afterwards being enraptured by my new baby as well as still feeling the effects of an epidural so I wasn’t giving too much thought to the care I was receiving from the medical team around me. When I heard that I required stitches for a grade 2 tear, I seemed to take it in my stride. Possibly I felt a bit of relief that it wasn’t a more serious tear.

After the stitches were done, I remember my attending doctor discovering another tear, one that had not been obvious. I recall listening as she remarked how unusual it was and feeling grateful that she had discovered it. And then as more doctors came to assess, it became apparent that it might be a more serious tear and it would require further investigation in theatre. Going into theatre, I think the worst feeling I had was not wanting to be separated from my baby. I was still not worried about myself at all.

After surgery it was confirmed to me that an additional, grade 3 tear had been identified and repaired. Again, I remember not paying too much thought to what that really meant and remained unconcerned for the next day or so. There was a good deal of pain and discomfort once the anaesthesia wore off but I took this as par for the course and the painkillers I was given helped to manage it a little. There was just too much going on to distract me. Primarily the tiny baby I had just given birth to, who had all of my attention and energy.

It was two days later before reality started to sink in. This was despite the fact that a very sudden bowel movement had caught me unaware—this had just been put down to the medication I was taking for the pain. It was actually a visit from a member of the surgical team who had looked after me that started to put things in perspective. It is a visit that I am very grateful for now as this doctor explained with great compassion and sensitivity that this injury was more severe than many people in my life might recognise. He helped me to understand that I would be facing a longer recovery time than most, and also that I should be kind to myself in the process. It was particularly helpful that my partner was there to listen—not that he wouldn’t have been supportive anyway, but I think it helped him to really understand and to not compare our experiences to those of other new parents. I think so often injuries of this nature are downplayed as just part and parcel of motherhood, so to see it being taken so seriously was important for both of us.

Still, nothing could fully prepare me for how things would actually transpire. Caring for a new baby while dealing with an injury of this level was both physically and emotionally challenging.

I was lucky in terms of urinary control and had no big issues there. The biggest issue for me was with bowel movements. It would veer between a very sudden need to go and feeling like I had little or no control when this happened, to thinking I needed to go before I was ready, and consequently spending lots of time in the bathroom, away from my baby, feeling very confused and worried. I also felt no sense of completion upon passing a bowel movement so I didn’t know when I was done. Similar issues arose with anticipating and controlling wind, and with being able to distinguish what was what. Compounding all of this was the confusion I felt when trying to do my pelvic floor exercises. I felt like I had no idea what I was doing and started questioning if I had ever known.

What linked all of these problems was not just that I had lost muscle control but also that I had lost sensation. I don’t think I realised quite how important that part was until that really started to return. That is when I finally felt that I could regain control. It took some time to get to that stage, I can’t say exactly how long, but at least a couple of months. And there was still more work to do from there.

None of that even touches on the pain associated with healing from the injury, which was very significant in and of itself. But what I remember more distinctly is the stress and worry and confusion. I also remember how limited I felt in what I could do or where I could go and fearing how long that might last. I was very lucky that my partner was in a position to give me amazing support in those first two months as there were moments that I don’t know how I would have cared properly for our baby without his presence.

Thankfully I am now very much back to normal in my day to day life. I haven’t yet had the opportunity to return to physical exercise, so I can’t say yet that I have made a full recovery, but the difference between now and those early weeks and months is huge.

The extent of my recovery to date is due in large part to the excellent aftercare I have received and continue to receive from the physio team, and I am very grateful for their support. And I will of course be eternally grateful to the obstetrician for discovering the injury that would have been so easy for her to miss, and to the team who successfully repaired it. I don’t know what my life would be like today without their care and professionalism and I don’t want to imagine.

Learning points.

• Atypical perineal lacerations are rare and may occur without usual risk factors (eg, macrosomia, operative vaginal deliveries).

• Identifying these injuries early in the labour ward is essential, allowing for appropriate early repair and intervention, and helps prevent maternal morbidity.

• Increasing awareness and training of midwives and obstetricians to recognise and diagnose perineal tears ensures optimal outcome for women with anal sphincter injuries.

• Ensuring adequate senior obstetricians are present to review complex or atypical tears will allow for the best outcome for women.

• Appropriate diagnosis should be combined with existing best evidence including good lighting and surgical technique at repair in theatre, antibiotics, laxatives, pelvic floor exercises, physiotherapy and follow-up in a specialised perineal clinic.

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Patient consent for publication

Consent obtained directly from patient(s).