Pediatric surgery topics One of the commonest neonatal malformations requiring a complex system of management. Important for Surgical trainees.

1. Pathology of Anorectal
Malformations
Dr. I Aniebo and Dr. Rachel Odoks
Surgery Residents. University of Calabar Teaching Hospital. Calabar.
Cross River State. Nigeria

2. Outline
• Introduction
• Historical perspective
• Epidemiology
• Classification
• Pathology
1. Embryogenesis
2. Pathophysiology
3. Associated malformations
• Complications
• Prognosis
• Conclusion
• Sources

3. Introduction
• Anorectal malformation is a widespread disorder of the distal
gastrointestinal tract affecting both sexes
• Anorectal malformations (ARMs) occur commonly throughout all
continents and even under the best circumstances, children
undergoing operative treatment for ARMs may have lifelong bowel
management problems
• Few surgeons have the expertise to manage such diseases and most
operations are undertaken out of desperation by doctors with
inadequate training and poor equipment.

4. Introduction Cont’d
• The term ‘imperforate anus’ has been used to describe all anorectal
abnormalities in females and males. Although imperforate anus
implies that the anus never opened anywhere, a purely blind anal
pouch is actually rare
• The spectrum of abnormalities is quite broad, thus the term
‘anorectal malformations’ is used for all these abnormalities with
further clarification to describe the specific malformation
• Imperforate anus then refers to the specific portion of any anomaly
where the rectum does not open properly through the anal
musculature

5. Historical perspective
• Throughout history, surgeons have attempted to treat infants and children
with anorectal malformations
• Attempts have ranged from rupturing an obstructing membrane with a finger
or the point of a knife to Posterior Sagittal Anorectoplasty (PSARP)
• The first inguinal colostomy was performed in 1783 but was largely
unsuccessful
• In 1835, Amussat mobilized the bowel through a perineal incision, thus
performing the first anoplasty
• In the mid 1900’s Stephens described a procedure that emphasised the
passage of the rectum within the puborectalis sling
• In the 1980’s, this procedure was modified to include a longer perineal
incision to gain more exposure which eventually led to the PSARP a procedure
made popular by Alberto Pena.

6. Epidemiology
• ARMs in children are among the most common and most complex
problems affecting children worldwide.
• They occur in an estimated 1 in 4-5000 births worldwide
• In some instances, particularly in rural areas, neonates identified with
ARMs at birth are abandoned or euthaniszed because they are
considered non-viable due to their abnormality
• ARMs are the most common cause of intestinal obstruction in neonates
and the commonest congenital anomaly causing intestinal obstruction in
the older children
• Males are more affected than females

7. Epidemiology Cont’d
• A study carried out in Ibadan on 88 children managed for ARMs
revealed that a 69% of patients with anorectal were male and about
80% of patients managed had a high or intermediate malformation
and the urogenital system was the most common system whose
anomalies were associated with anorectal malformations
• Associated Congenital malformations were also noted in 20% of
patients.

8. Epidemiology Cont’d
• The most common defect in females is the imperforate anus with
recto vestibular fistula whilst in males the most common defect is the
imperforate anus with rectourethral fistula.
• Imperforate anus without fistula occur in 5% of patients. Half of
whom also have Down’s syndrome. Patients with Down’s syndrome
have this type of defect 95% of the time

9. Classification
• Wingspread Conference classification (1984)

10. Classification cont'd
• Pena Classification (1995)

11. Cross table lateral x-ray
• Picture

12. Classification cont'd
• Krickenberg Classification (2005)

13. Pathology
• Embryogenesis
• The cause of ARMs is unknown
• No known factor predisposes a person to have a child with
imperforate anus
• These defects are probably due to misexpression of genes during
epithelial-mesenchymal signalling

14. Embryogenesis Cont’d
• The cloaca, formed at around 21days gestation, is a cavity which
opens up into the hindgut, tailgut, allantois and later, the
mesonephric ducts
• The terminal portion of the hindgut enters into the posterior region
of the cloaca, the primitive anorectal canal; the allantois enters into
the anterior portion, the primitive urogenital sinus.
• A layer of mesoderm, the urorectal septum, separates the region
between the allantois and hindgut

15. Embryogenesis Cont'd
• At the end of the 7th week, the cloacal membrane ruptures creating the
anal opening for the hindgut and a ventral opening for the urogenital
sinus. Failure of the urorectal septum to reach the cloacal membrane
creates the cloacal anomaly
• The upper part of the anal canal is derived from endoderm and the
lower part from ectoderm and degeneration of the cloacal membrane (
anal membrane ) between these two establishes continuity between
them.
• By the 9th week, all relevant structures are in place including the
musculature

16. Embryogenesis Cont'd
• Interference with anorectal structure development at varying stages
leads to various anomalies, ranging from anal stenosis, incomplete
rupture of the anal membrane, or anal agenesis to complete failure of
the upper portion of the cloaca to descend and failure of the
proctodeum to invaginate.
• Continued communication between the urogenital tract and rectal
portions of the cloacal plate causes rectourethral fistulas or
rectovestibular fistulas.

17. Pathology Cont'd
Pathophysiology
• Bowel control implies the ability to detect and retain flatus and stool
until the appropriate time for evacuation.
• It is the result of a complex interplay among sphincter function,
anorectal sensation, and colonic motility.
• All these factors are affected in children with anorectal malformations

18. Pathology Cont'd
Sphincter Mechanism
• Children with anorectal malformations have varying degrees of
striated muscle development from almost normal appearing muscle
to complete absence
• The muscle groups of the sphincter mechanism form a funnel-like
structure in the pelvis.
• These muscles are innervated by the pudendal nerve S2-S4 as well as
by the autonomic nervous system via the nervi enigentes from S2-S4
• Patients with improperly developed sphincter mechanism develop
diarrhea and incontinence even following surgical anatomic
correction

19. Pathology Cont'd
Sensation and Proprioception
• Under normal circumstances, the anal canal is an exquisitely sensitive
area, allowing the individual to discriminate between solids, liquids
and gases.
• The overwhelming majority of children with anorectal malformations
are born without an anal canal and lack this ability. Proprioception is
intact in most patients.
• These patients loose control over their defecation when they suffer
diarrhoea but have the ability to be toilet trained when they form
solid stool and learn to perceive it.

20. Pathology Cont'd
Colonic and Rectosigmoid motility
• The rectosigmoid acts as a reservoir and holds back material for a
variable period of time. The anal canal (below the pectinate line) is
usually empty due to the action of the surroinding sphincter
mechanism.
• Occassionally, however, there are peristaltic waves in the colon that
push fecal material toward the anus. The rectal contents touch the
anal canal thereby providing valuable information as to the nature of
the rectal contents.
• Depending on the surrounding social circumstances, the individual
may contract the sphincter mechanism to push stool or gas back into
the rectum and then voluntarily relax at the appropriate time.

21. Pathology Cont'd
• Little is known about the mechanism that triggers peristalsis of the
rectosigmoid to defecate but it is clear that the degree of rectal
fullness plays an important role.
• Children with anorectal malformations have a spectrum of
rectosigmoid motility disorders
• These patients, subjected to surgical procedures that preserve the
recrosigmoid usually suffer from constipation which is self
perpetuating and self aggravating
• Fecal impaction could result with encoperesis

22. Pathology cont'd
• The clinician, therefore, is to avoid the cycle of hypomotility,
constipation and megasigmoid with aggresive follow-up plus dietary,
mechanical and pharmacologic treatment
• Patients who have their rectosigmoid removed, on the other hand,
suffer from diarrhoea. They have no reservoir capacity and are highly
sensitive to certain foods and suffer incontinence.

23. Pathology Cont’d
• Associated malformations
1. Vertebral anomalies: Hemivertebrae, scoliosis, tethered cord
2. Gastrointestinal anomalies (13%): Tracheoesophageal
abnormalities, duodenal atresia
3. Cardiovascular anomalies (33%): Atrial septal defect, Patent ductus
arteriosus, Tetralogy of Fallot
4. Genitourinary anomalies (33% to 50%): Vesicoureteric reflux, renal
agenesis,Posterior ureteric valve.
5. Gynaecologic anomalies: Hydrocolpos, Mullerian anomalies

24. Complications
• Recurrent UTI
• Intestinal obstruction

25. Prognosis
• Prognosis is good but largely dependent upon the extent and severity
of associated anomalies some of which can be life threatening or
complicate recovery

26. Conclusion
• Anorectal malformations are fairly common ( 1 in 4-5,000 life births)
• Early diagnosis and treatment with a proper bowel management plan
can make a significant positive change in a child’s life.

27. Sources
• Paediatric Surgery: A Comprehensive Text For Africa
• Paediatric Surgery 7th Edition
• Experience with the management of anorectal malformations in
Ibadan Nigeria; Ogundoyin O O, Olulana D I and Lawal T A.
• Langman’s Medical Embryology
• Medacape: Paediatric Imperforate anus