Anorectal malformations
Key points
1 in 4-5000 births
1.2:1 M:F
Males - 70% recto-urethral
Females - 70% rectovestibular, 18% perineal, 5% cloaca
Pathophysiology
Disorder of hindgut development
NO evidence that cloaca is because of persistent embryological cloaca
Week 7 - cloaca divided by urorectal (anorectal) septum into urogenital sinus and posterior rectum
Cloacal membrane on ectodermal surface - 2x ruptures
Anal canal recanalises 9th week
Development of urinary and genital tracts from urogenital sinus
Not known why anorectal malformation (ARM) happens
Possible risk factors: Maternal diabetes, thalidomide, In-vitro fertilisation
'Anterior anus'
Can only describe as anterior anus if partially surrounded by muscle. Otherwise is perineal fissure
Rintala paper shows conservative management has approximately equal continence to general population in females
Potential benefits of ASARP/anoplasty ?hygeine ?continence ?cosmetic
Constipation is unlikely improved. Need to counsel against vaginal delivery
Megarectums in ARM
1. Primary megarectum - since birth
2. Secondary - post op
High risk of developing megarectum if spinal abnormality
Funnel anus
Very rare - described by Nixon, then Rintala
Perianal skin extends in a funnel to an interior fibrotic ring - no transitional epithelium
Often constipation secondary to megarectum
Currarino association
Dilations unsuccessful
Can do pullthrough but may have incontinence secondary to lack of normal anoderm
Genetics
Risk of sibling having ARM 3-4%
Sonic hedgehog pathway
Autosomal dominant conditions:
Currarino, Townes-Broks, Palister-Hall
Antenatal features
More likely see associated abnormalities e.g sacrum, absent kidney, hydrocolpos, hydronephrosis
Severe abnormalities more likely to show
Dilated bowel
Echogenic bowel
Polyhydramnios (but this may be related to other abnormality)
Calcified meconium - as urine mixes with meconium
If intra-abdominal cyst seen in female foetus, could be hydrocolpos secondary to cloaca
Needs surveillance for:
Increasing cyst size
Ascites
Polyhydramnios
Hydronephrosis - Consider shunting or tapping cyst
Look for pulmonary hypoplasia
Get MRI
Associations
Trisomy 21 - if ARM, 95% chance of pure rectal atresia
No correlation of cardiac malformations with type of ARM
Safest to get echo in all patients no matter how minor the abnormality
VACTERL
Vertebral
Possible vertebrae abnormalities:
Hemi
Wedge
Absent
Butterfly
Bar
Full or partial sacral agenesis
Caudal regression syndrome (sacral agenesis) associated with maternal diabetes
Spinal - Tethered cord, lipomas, myelomeningocele
Genitourinary
Vesicoureteric reflux (VUR) is most common
Other causes of hydronephrosis
Renal agenesis (unilateral agenesis common with cloaca) in and dysplasia
Undescended testes
Hypospadias
Bicornate uterus, vaginal septum/atresia (Mullerian duplications in 50% of cloaca patients)
Limbs
Tibial malformation, can cause club foot
Radial abnormalities
Thumb hypoplasia/absence
Associated defects should be repaired top to bottom e.g OA/TOF, then DA, then colostomy
Currarino triad
Autosomal dominant - MNX1 gene
1. ARM - likely rectal atresia or anal stenosis
2. Pre-sacral mass - can be: Teratoma, meningocoele, dermoid cysts, enteric cyst, rectal duplication
3. Sacral abnormality: Agenesis, scimitar shaped
For anal stenosis/rectal atresia - may indicate Currarino triad - must always screen for presacral mass
Mass sometimes seen on AXR
Anterior displacement of rectum on contrast lateral view
Important examination points
Cloaca can have hypertrophied clitoris or phallic like structure
Can’t tell from examination alone whether low or high defect, but can speculate. Remember to lift scrotum
Correct position of anus: Line between ischial tuberosities.
Can be correct position but stenosed. Need to check that enough meconium is coming out. May need to do PR or tube insertion
On EUA - Check anus position AND that it is lined by mucosa with dentate line (i.e. make sure not a funnel anus) AND within sphincter complex
Females should have 0.5-1cm perineal body
Expected Heger sizes:
Neonates - 10-12mm
1 year - 14mm
3 year - 16mm
12 year - 17 mm
Histology
Do not send fistula specimen for histology - as can lead to incorrect diagnosis of HD due to a normal lack of ganglion cells. A subsequent rectal resection will lead to incontinence
Incidence of HD is low
Radiology
AXR - calcifications “balls” from meconium mixing with urine
Sacral ratio and ARM continence index - useful tool for predicting continence
Iliac crests to the posterior inferior iliac spines (AB)/posterior iliac spines to the tip of the coccyx (BC). The sacral ratio is BC/AB
Need high pressure distal loopogram WITH MCUG + antibiotic cover
Always do colostogram first - may not need MCUG if anterior, posterior urethra and bladder seen on colostogram
If no fistula seen - enquire about pressure - if high enough, then likely pure rectal atresia
Contrast enters bladder at right angle with recto-vesicular fistula
Complications of repair
Excessive bleeding during the anterior dissection indicates entry into the spongiosum tissue that surrounds the urethra
Rectal/vaginal/urethral injuries intra-op - repair with suture and if possible place a flap of fat over area
Acquired late fistula should be repaired in the same way
Skin level stricture - do not dilate - do stricturoplasty - incise longitudinal - close transverse
Constipation should be aggressively managed
Sacral malformation can have consequences for leg length
Remnant of original fistula (ROOF) - Think of urethral diverticulum (like a utricle) in patient with UTI
Needs MRI/cystoscopy for diagnosis
Prolapse repair - remove hemicircumference of rectum
Anorectal mislocation - redo unless not good potential for continence anyway
Presumed recto-vaginal fistula operated - actually cloaca and their urogenital sinus needs repair
If a patient with ARM has had a total colectomy for any reason do not do a PSARP as there is no possibility of forming solid stools AND there is a lack of anoderm and normal sphincter - therefore unlikley to achieve continence
Standard scenario
Neonate with ARM
NICU team to resuscitate
Check antenatal scans
Examine abnormality and for VACTERL features
Ensure NG passes and Echocardiogram performed
Describe abnormality and make diagnosis
Assess suitability for primary procedure if following criteria met:
1. Patient stable: not obstructed, no severe co-morbidities
2. Meconium seen
3. <48h of age
4. Not fed
5. Senior colorectal surgeon available
Male
If fresh meconium seen - can proceed to primary anoplasty
If not (or only pearls seen) can wait for up to 24 hours, probe fistula, then do cross prone lateral XR - if air past coccyx at 24 hours, likely low malformation without fistula. Use blunt drawing pin and tape. Use roll under hips, wait 20 mins before XR - if <1cm - can do primary PSARP
If not suitable for primary anoplasty:
Divided sigmoid colostomy
Near peritoneal reflection of descending colon to prevent prolapse
Ensure correct orientation
Washout of distal segment
Planning definitive procedure at age 3 months:
Complete VACTERL screen
High pressure MCUG + distal colostogram under antibiotic cover
Recto-urethral fistula
Posterior Saggital Anorectoplasty (PSARP)
Recto-prostatic fistula - PSARP approach
Difficult to reach recto-prostatic fistula from abdomen
At PSARP, a neoanus should be size 12
Should be size 14 at colostomy closure
Recto-vesical/bladder neck - Abdominal approach
laparoscopy - with urologist and ligate fistula
Do not leave long length of residual rectum on urinary tract - ROOF (remnant of original fistula)
For recto - urinary fistulas, leave catheter for 5-7 days
Female
Assess suitability for primary procedure as above if fistula (either recto-perineal or recto-vestibular) sufficient calibre
If not suitable - if decompressing with dilatations can do PSARP/ASARP at 3 months (Simultaneous colostomy + PSARP/ASARP if family able to do stoma training and care for the wound at the same time. Staged procedure if not)
If not decompressing - neonatal sigmoid colostomy
Follow up post PSARP
Dilatations starting at 2 weeks - train parents to do 1 or 2x per day
Increase size by 1mm every 2 weeks until expected size for age - bring in patient to check size increase is ok
Close stoma at around 6 weeks post PSARP
Follow up should focus on aggressive management of constipation
Perform renal USS when toilet trained to look for VUR
May need joint urology follow up depending on abnormality, urodynamics if bladder dysfunction
Special scenario - Cloaca
Describe abnormality and make diagnosis
NICU team to resuscitate - Treat for pulmonary hypoplasia
Check antenatal scans:
An intra-abdominal cyst may represent hydrocolpos
Hydronephrosis
Polyhydramnios ?due to OA/TOF
Have they had counselling?
Examine abnormality + abdomen for hydrocolpos
VACTERL screen + Echo
USS pelvis + renal
Decompress hydrocolpos if present - can use catheter via common channel
EUA + Colostomy + initial cystovaginoscopy
+/- Pigtail drain for hydrocolpos if not successful on ward (may need 2 if septate uterus)
+/- divide vaginal septum (present in 40-50%) ONLY if not long common channel requiring switch procedure - beware rectum can be found in septum
Monitor for hyperchloraemic metabolic acidosis due to absorption of urine refluxing from common channel
Workup during wait for definitive surgery 3-6 months:
Distal loopogram + MCUG
DMSA to document renal function (MAG 3 if upper tract dilatation)
Complete VACTERL screen - MRI spine if abnormal
Cross sectional imaging if unclear anatomy
Repeat EUA - Measure common channel with cystoscope (opening to urethra), then measure urethral length
At procedure:
1. Very short channel procedure
PSARP + Partial urogenital mobilisation (PUM)
The anterior dissection performed during PUM stops at the pubourethral ligament
2. Short channel procedure <3 cm
PSARP + Total urogenital mobilisation (TUM)
Identify and open rectum first posteriorly (should but may not be first structure encountered - importance of imaging)
Open common channel along length posteriorly - Urethral catheter
Separate rectum from vagina and urethra
Keep urethra and vagina together (urogenital sinus) perform TUM
Develop anterior plane 3mm away from clitoris and divide bladder + urethra suspensory ligaments
Bring urogenital sinus to perineum
Create perineal body
3. Channel >3cm
PSARP + extended TUM - abdominoperineal approach
4. Long channel procedure - >5cm
If common channel >3cm, likely urethra not adequate length
The common channel can be used as the urethra once the vagina and rectum are mobilised
PSARP approach for rectum + separate vagina from urethra
Continue mobilisation with laparotomy
If short vagina - can replace with colon
If hemivagina - vaginal switch procedure
Follow up points for cloaca
Dilatation and removal of catheter at ~2 weeks
Monitor renal function - repeat renal USS when toilet trained
Aggressive management of constipation
Needs joint urology follow up, urodynamics if bladder dysfunction
Gynaecology follow up - consider risk of haematocolpos at menarche - may need endometrial suppression if no channel for drainage
Psychology
Special scenario - Incontinence after PSARP
Do contrast enema to look for megarectum
If megarectum present - rectal irrigation only, no need for constipating diet or loperamide
If megarectum not present - may be unable to form stools, so needs constipating diet and loperamide
If previous failed PSARP + incontinence - start rectal irrigations before redo, as long as has good potential for continence
References
Shailinder Singh - Nottingham Children's hospital teaching series
Speck, K. Elizabeth, et al. "Anorectal Malformations." Pediatric Surgery NaT, American Pediatric Surgical Association, 2021. Pediatric Surgery Library, www.pedsurglibrary.com/apsa/view/Pediatric-Surgery-NaT/829049/all/Anorectal_Malformations.
Kyrklund K, Pakarinen MP, Taskinen S, Rintala RJ. Bowel function and lower urinary tract symptoms in females with anterior anus treated conservatively: Controlled outcomes into adulthood. J Pediatr Surg. 2015 Jul;50(7):1168-73. doi: 10.1016/j.jpedsurg.2014.09.074. Epub 2014 Dec 5. PMID: 25783328.
Rintala RJ, Järvinen HJ. Congenital funnel anus. J Pediatr Surg. 1996 Sep;31(9):1308-10. doi: 10.1016/s0022-3468(96)90261-4. PMID: 8887112.
Dworschak GC, Reutter HM, Ludwig M. Currarino syndrome: a comprehensive genetic review of a rare congenital disorder. Orphanet J Rare Dis. 2021 Apr 9;16(1):167. doi: 10.1186/s13023-021-01799-0. PMID: 33836786; PMCID: PMC8034116.
Weerakkody Y, Elfeky M, Bell D, et al. Currarino syndrome. Reference article, Radiopaedia.org (Accessed on 22 Jun 2024) https://doi.org/10.53347/rID-8308
Speck, K. Elizabeth, et al. "Cloaca." Pediatric Surgery NaT, American Pediatric Surgical Association, 2020. Pediatric Surgery Library, www.pedsurglibrary.com/apsa/view/Pediatric-Surgery-NaT/829050/all/Cloaca.