Overview
Definition:
Posterior Sagittal Anorectoplasty (PSARP) is a surgical procedure designed to correct various types of anorectal malformations (ARMs), including imperforate anus, by creating an anal canal in the correct anatomical position via a posterior sagittal incision.
Epidemiology:
Anorectal malformations occur in approximately 1 in 4,000 to 5,000 live births
The prevalence varies slightly by geographic region and population
Males are more commonly affected than females, with a male-to-female ratio of approximately 1.5:1
Associated anomalies, particularly genitourinary and vertebral defects, are common.
Clinical Significance:
PSARP is the gold standard surgical repair for most types of ARMs, aiming to restore bowel continuity and achieve fecal continence
Successful surgical correction is crucial for long-term patient quality of life, preventing severe complications like fecal impaction, obstruction, and social/psychological distress
Understanding the nuances of PSARP is vital for pediatric surgeons and residents preparing for DNB and NEET SS examinations.
Clinical Presentation
Symptoms:
Failure to pass meconium within the first 24-48 hours of life
Abdominal distension
Vomiting
Visible anomaly of the anus or perineum
Passage of stool from an abnormal location (e.g., urethra, vagina)
Constipation
Poor weight gain in infants.
Signs:
Absence of a normal anal dimple
Perineal fistula (observed visually or with gentle probe)
Abdominal distension with tympany
Palpable distended bowel loops
Signs of intestinal obstruction
Abnormalities of the genitourinary tract (e.g., hypospadias, bifid scrotum, vaginal anomalies)
Sacral and spinal abnormalities (e.g., sacral dimple, tuft of hair, vertebral defects).
Diagnostic Criteria:
Diagnosis is primarily clinical, based on the physical examination of the newborn
The presence of a normal anal canal with a patent anus confirms a low-type ARM
otherwise, it is considered a high-type ARM
Associated anomalies, particularly those from the VACTERL association (Vertebral, Anal, Cardiac, Tracheoesophageal, Renal, Limb anomalies), are often present and require thorough evaluation.
Diagnostic Approach
History Taking:
Detailed antenatal history (ultrasound findings, maternal infections/medications)
Gestational age at birth
Birth weight
Presence of any other congenital anomalies noted at birth
Family history of ARMs or other congenital defects
Initial feeding pattern and stool output
Any episodes of vomiting or abdominal distension.
Physical Examination:
Thorough general examination to assess for other congenital anomalies, especially VACTERL association
Detailed assessment of the perineum: location of the anal dimple, presence of any fistulas, and patency of the observed opening
Digital rectal examination (if feasible and deemed safe) to assess rectal tone and presence of distal rectal pouch
Careful examination of the genitourinary system (penis, scrotum, urethra, labia, vagina) and spine.
Investigations:
Plain abdominal radiography (supine and cross-table lateral views) can help visualize the distal extent of the colon and the position of the sacrum, aiding in classifying the level of the malformation
A Foley catheter insertion into the suspected fistula can help delineate its course
Ultrasound of the abdomen and pelvis to evaluate kidneys and bladder
MRI of the spine to assess for spinal cord abnormalities (e.g., tethered cord)
Voiding cystourethrogram (VCUG) may be indicated for specific genitourinary concerns
Chromosomal analysis if multiple anomalies are present.
Differential Diagnosis:
Low ARM (anteriorly displaced anus, anal stenosis, membranous anus) requires different surgical approaches compared to high ARM
Cloacal malformations (a single common channel for rectum, vagina, and urethra) are complex and require specialized reconstructive surgery
Other causes of neonatal intestinal obstruction like intestinal atresias or malrotation.
Management
Initial Management:
In newborns with suspected ARM and signs of obstruction, immediate nasogastric decompression and intravenous fluids are administered
A colostomy (usually a loop colostomy) is often performed proximal to the malformation to decompress the bowel and allow the infant to grow, especially for high-type ARMs, before definitive repair
This also allows for bowel preparation prior to PSARP.
Surgical Management:
PSARP is the primary surgical intervention
The goal is to mobilize the distal rectum from the surrounding structures (vagina or urethra) and bring it down through the posterior sagittal incision to create a new anal canal in the correct anatomical position, typically with an external sphincter sling
The extent of the dissection depends on the specific type of ARM and the distance of the rectal pouch from the perineum
The procedure is usually performed between 3-6 months of age
In selected cases of low-type ARMs without a fistula, a simple cutback anoplasty may be sufficient, but PSARP is more commonly employed
The success of PSARP is significantly influenced by the surgeon's experience and the quality of the sphincter complex identified.
Postoperative Care:
Postoperative care includes pain management, intravenous antibiotics, and monitoring for wound healing and signs of infection
Stool softeners and regular anal dilations are crucial to maintain the patency of the newly created anal canal and prevent strictures
These dilations are typically initiated a few weeks after surgery and continue for several months
Diet is advanced as tolerated
A temporary diverting colostomy, if present, is usually closed after several weeks to months once the primary repair has healed well and bowel function is established.
Supportive Care:
Nutritional support is essential, especially for premature infants or those with associated anomalies
Close monitoring of fluid and electrolyte balance
Genetic counseling may be offered if significant associated anomalies are present
Psychosocial support for the family is important throughout the treatment course.
Complications
Early Complications:
Wound infection or dehiscence
Anal stenosis or stricture formation
Rectal prolapse
Bleeding from the surgical site
Injury to adjacent structures (e.g., urethra, vagina)
Fistula recurrence or formation of new fistulas.
Late Complications:
Fecal incontinence (soiling, urgency, constipation-predominant incontinence)
Poor anal tone
Recurrent anal strictures
Stool withholding
Sensory deficits
Sexual dysfunction (rare but possible)..
Prevention Strategies:
Meticulous surgical technique during PSARP, including precise identification and mobilization of the rectal pouch and sphincter complex
Careful handling of tissues to minimize injury
Appropriate wound closure and care
Prompt initiation of postoperative anal dilations to prevent stenosis
Regular follow-up to monitor for and manage complications like soiling or constipation.
Prognosis
Factors Affecting Prognosis:
The level of the malformation (lower anomalies generally have a better prognosis for continence)
The presence and integrity of the external anal sphincter muscle complex
Associated neurological or spinal cord anomalies
Quality of surgical repair and adherence to postoperative care, particularly anal dilations
Presence of other significant congenital anomalies.
Outcomes:
With appropriate surgical correction and diligent follow-up, a significant majority of patients achieve some degree of fecal continence
However, long-term fecal incontinence remains a common issue, ranging from mild soiling to severe, debilitating problems
Achieving social continence (i.e., ability to control bowel movements sufficiently for social participation) is the primary goal.
Follow Up:
Long-term follow-up is essential, typically involving pediatric surgeons and pediatric gastroenterologists
This includes regular clinical assessment of bowel function, assessment of continence using standardized questionnaires or objective measures, and periodic physical examinations
Anal dilations are continued as needed
Bowel management programs may be instituted for patients with persistent constipation or incontinence issues
Monitoring for potential late complications like sexual dysfunction is also important.
Key Points
Exam Focus:
PSARP is the surgical repair for most ARMs, focusing on creating a functional anal canal
High vs
low ARMs and their classification (e.g., by Pena classification or visual assessment of fistula)
The importance of the posterior sagittal incision
The critical role of the external anal sphincter complex
Common complications include stenosis, prolapse, and incontinence
Postoperative dilations are crucial for preventing strictures.
Clinical Pearls:
Always perform a thorough perineal and genitourinary examination in any newborn failing to pass meconium
Consider the VACTERL association in all infants with ARM
The "sacro-anal distance" on lateral X-ray with a colostomy catheter can be a guide, but intraoperative assessment is paramount
Adequate mobilization of the rectal pouch is key to avoid tension on the suture line
Aggressive postoperative dilation is often necessary, even if the patient appears well
Refer patients with significant continence issues to specialized centers.
Common Mistakes:
Inadequate assessment of the anal anatomy leading to incorrect classification or surgical approach
Insufficient rectal pouch mobilization, resulting in a high-riding anus or tension on the anastomosis
Failure to identify and preserve the sphincter complex
Inadequate or absent postoperative anal dilations leading to severe stenosis
Overly aggressive dilation causing injury
Neglecting to investigate for associated anomalies, especially spinal defects.