Anorectal Atresia

Overview

Epidemiology

• 1 in 5,000 births in the United States
• Boys have a higher incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency than girls.
• Most cases are sporadic Sporadic Selective IgA Deficiency (no family history Family History Adult Health Maintenance).
• Parental risk factors:
  • Paternal: smoking Smoking Willful or deliberate act of inhaling and exhaling smoke from burning substances or agents held by hand. Interstitial Lung Diseases
  • Maternal: obesity Obesity Obesity is a condition associated with excess body weight, specifically with the deposition of excessive adipose tissue. Obesity is considered a global epidemic. Major influences come from the western diet and sedentary lifestyles, but the exact mechanisms likely include a mixture of genetic and environmental factors. Obesity and diabetes Diabetes Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. Diabetes Mellitus
• Associated anomalies occur frequently and are easily remembered using the acronym VACTERL:
  • Vertebral anomalies
  • Anal artesia
  • Cardiac defects
  • TracheoEsophageal fistula Fistula Abnormal communication most commonly seen between two internal organs, or between an internal organ and the surface of the body. Anal Fistula/ atresia Atresia Hypoplastic Left Heart Syndrome (HLHS)
  • Renal anomalies and Radial aplasia Aplasia Cranial Nerve Palsies
  • Limb anomalies
• There is an association between anorectal atresia Atresia Hypoplastic Left Heart Syndrome (HLHS) and trisomy 21 Trisomy 21 Down syndrome, or trisomy 21, is the most common chromosomal aberration and the most frequent genetic cause of developmental delay. Both boys and girls are affected and have characteristic craniofacial and musculoskeletal features, as well as multiple medical anomalies involving the cardiac, gastrointestinal, ocular, and auditory systems. Down syndrome (Trisomy 21) and 18.

Etiology

Anorectal atresia Atresia Hypoplastic Left Heart Syndrome (HLHS) arises out of deviations from the normal embryological development of abdominal organs to create the adult rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal: Anatomy and anal canal.

• At 7–8 weeks’ gestation, the hindgut Hindgut Development of the Abdominal Organs and allantois Allantois An extra-embryonic membranous sac derived from the yolk sac of reptiles; birds; and mammals. It lies between two other extra-embryonic membranes, the amnion and the chorion. The allantois serves to store urinary wastes and mediate exchange of gas and nutrients for the developing embryo. Development of the Abdominal Organs open into a common cloaca Cloaca A dilated cavity extended caudally from the hindgut. In adult birds, reptiles, amphibians, and many fishes but few mammals, cloaca is a common chamber into which the digestive, urinary and reproductive tracts discharge their contents. In most mammals, cloaca gives rise to large intestine; urinary bladder; and genitalia. Development of the Abdominal Organs.
• The cloaca Cloaca A dilated cavity extended caudally from the hindgut. In adult birds, reptiles, amphibians, and many fishes but few mammals, cloaca is a common chamber into which the digestive, urinary and reproductive tracts discharge their contents. In most mammals, cloaca gives rise to large intestine; urinary bladder; and genitalia. Development of the Abdominal Organs is endoderm Endoderm The inner of the three germ layers of an embryo. Gastrulation and Neurulation lined and separated from the surface ectoderm Ectoderm The outer of the three germ layers of an embryo. Gastrulation and Neurulation by the cloacal membrane Cloacal membrane Development of the Abdominal Organs.
• By 7 weeks’ gestation, the cloaca Cloaca A dilated cavity extended caudally from the hindgut. In adult birds, reptiles, amphibians, and many fishes but few mammals, cloaca is a common chamber into which the digestive, urinary and reproductive tracts discharge their contents. In most mammals, cloaca gives rise to large intestine; urinary bladder; and genitalia. Development of the Abdominal Organs is divided by a urorectal septum Urorectal septum Development of the Abdominal Organs into the urogenital sinus Urogenital Sinus Congenital Malformations of the Female Reproductive System and rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal: Anatomy/anal tubercle.
• Following a ventral urogenital opening, the cloacal membrane Cloacal membrane Development of the Abdominal Organs dorsal to the urorectal septum Urorectal septum Development of the Abdominal Organs (i.e., anal membrane) gradually resorbs, connecting the ectoderm Ectoderm The outer of the three germ layers of an embryo. Gastrulation and Neurulation to endoderm Endoderm The inner of the three germ layers of an embryo. Gastrulation and Neurulation and creating the anal opening.
• Developmental arrest anywhere during these stages results in anorectal malformation.

Classification

Anorectal malformations may be divided into high and low lesions based on the level of the pelvic floor Pelvic floor Soft tissue formed mainly by the pelvic diaphragm, which is composed of the two levator ani and two coccygeus muscles. The pelvic diaphragm lies just below the pelvic aperture (outlet) and separates the pelvic cavity from the perineum. It extends between the pubic bone anteriorly and the coccyx posteriorly. Vagina, Vulva, and Pelvic Floor: Anatomy (levator ani muscle):

• High/ supralevator Supralevator Perianal and Perirectal Abscess lesions
  • More difficult to correct and prone to fecal incontinence Fecal incontinence Failure of voluntary control of the anal sphincters, with involuntary passage of feces and flatus. Pediatric Constipation
  • Boys:
    • Rectobulbar fistula Fistula Abnormal communication most commonly seen between two internal organs, or between an internal organ and the surface of the body. Anal Fistula (most common type)
    • Rectoprostatic fistula Fistula Abnormal communication most commonly seen between two internal organs, or between an internal organ and the surface of the body. Anal Fistula
    • Rectovesical fistula Fistula Abnormal communication most commonly seen between two internal organs, or between an internal organ and the surface of the body. Anal Fistula
  • Girls: 
    • Rectovestibular fistula Fistula Abnormal communication most commonly seen between two internal organs, or between an internal organ and the surface of the body. Anal Fistula
    • Rectovaginal fistula Fistula Abnormal communication most commonly seen between two internal organs, or between an internal organ and the surface of the body. Anal Fistula
    • Cloacal malformation has the worst prognosis Prognosis A prediction of the probable outcome of a disease based on a individual’s condition and the usual course of the disease as seen in similar situations. Non-Hodgkin Lymphomas.
• Low/infralevator lesions
  • Relatively easy to correct, but prone to constipation Constipation Constipation is common and may be due to a variety of causes. Constipation is generally defined as bowel movement frequency < 3 times per week. Patients who are constipated often strain to pass hard stools. The condition is classified as primary (also known as idiopathic or functional constipation) or secondary, and as acute or chronic. Constipation
    • Rectoperineal fistula Fistula Abnormal communication most commonly seen between two internal organs, or between an internal organ and the surface of the body. Anal Fistula in both sexes
    • The rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal: Anatomy communicates with the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions but the canal is not protected by a sphincter. 
  • The anus may also end in a blind pouch.

Diagnosis

Defects are often identified during the newborn Newborn An infant during the first 28 days after birth. Physical Examination of the Newborn physical examination. Missed cases are usually identified within 24 hours following failure to pass meconium Meconium The thick green-to-black mucilaginous material found in the intestines of a full-term fetus. It consists of secretions of the intestinal glands; bile pigments; fatty acids; amniotic fluid; and intrauterine debris. It constitutes the first stools passed by a newborn. Prenatal and Postnatal Physiology of the Neonate and abdominal distension.

Physical examination

• Clues about the neonate Neonate An infant during the first 28 days after birth. Physical Examination of the Newborn’s type of malformation:
  • Perineal opening: indicates a low defect 
  • Urine sampling for meconium Meconium The thick green-to-black mucilaginous material found in the intestines of a full-term fetus. It consists of secretions of the intestinal glands; bile pigments; fatty acids; amniotic fluid; and intrauterine debris. It constitutes the first stools passed by a newborn. Prenatal and Postnatal Physiology of the Neonate:
    • In boys without a perineal opening and girls without a perineal or vestibular opening
    • Positive sample indicates urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract: Anatomy fistula Fistula Abnormal communication most commonly seen between two internal organs, or between an internal organ and the surface of the body. Anal Fistula.
  • Palpation Palpation Application of fingers with light pressure to the surface of the body to determine consistency of parts beneath in physical diagnosis; includes palpation for determining the outlines of organs. Dermatologic Examination for abdominal masses: may indicate hydronephrosis Hydronephrosis Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients. Hydronephrosis or hydrocolpos
• Discovery of anorectal atresia Atresia Hypoplastic Left Heart Syndrome (HLHS) should prompt a close examination for associated congenital Congenital Chorioretinitis anomalies:
  • Umbilical stump Umbilical Stump Staphylococcal Scalded Skin Syndrome (SSSS) exam
    • Absence of an umbilical artery Umbilical artery Specialized arterial vessels in the umbilical cord. They carry waste and deoxygenated blood from the fetus to the mother via the placenta. In humans, there are usually two umbilical arteries but sometimes one. Prenatal and Postnatal Physiology of the Neonate often associated with anal atresia Atresia Hypoplastic Left Heart Syndrome (HLHS)
    • Potentially associated absent kidney
    • Boys: verify presence of descended testes Testes Gonadal Hormones
    • Girls: check vaginal patency
  • Cardiac exam: Auscultation of the heart may reveal the murmurs of Tetralogy of Fallot Tetralogy of Fallot Tetralogy of Fallot is the most common cyanotic congenital heart disease. The disease is the confluence of 4 pathologic cardiac features: overriding aorta, ventricular septal defect, right ventricular outflow obstruction, and right ventricular hypertrophy. Tetralogy of Fallot or a ventricular septum defect.

Imaging

• Prenatal ultrasound may identify suggestive features such as
  • Polyhydramnios Polyhydramnios Polyhydramnios is a pathological excess of amniotic fluid. Common causes of polyhydramnios include fetal anomalies, gestational diabetes, multiple gestations, and congenital infections. Patients are often asymptomatic but may present with dyspnea, extremity swelling, or abdominal distention. Polyhydramnios
  • Intra-abdominal cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change
  • Hydrocolpos
  • Hydronephrosis Hydronephrosis Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients. Hydronephrosis  
• By 24 hours of age, if the infant has not passed stool:
  • Lateral prone radiograph should be obtained.
  • Ultrasound may also identify associated genitourinary and gastrointestinal anomalies.
  • Other radiographic studies such as urethrogram, cologram, and fistulagraphy may be used.
  • Spinal magnetic resonance imaging (MRI) may be indicated in patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with abnormal pelvic radiography.

Management

Medical

• Once defects are identified, the infant should not be fed orally.
• Individualize intravenous fluids Intravenous Fluids Intravenous fluids are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids and electrolytes Electrolytes Electrolytes are mineral salts that dissolve in water and dissociate into charged particles called ions, which can be either be positively (cations) or negatively (anions) charged. Electrolytes are distributed in the extracellular and intracellular compartments in different concentrations. Electrolytes are essential for various basic life-sustaining functions. Electrolytes to meet nutritional needs for the infant.
• If urinary fistula Fistula Abnormal communication most commonly seen between two internal organs, or between an internal organ and the surface of the body. Anal Fistula is suspected: broad-spectrum Broad-Spectrum Fluoroquinolones antibiotics
• Treatment of life-threatening anomalies should take precedence.

Surgical

• Primary repair: often performed on rectal pouches
  • < 1 cm identified on imaging
  • With or without perineal/vestibular fistulas
  • Without associated urogenital anomalies
• Colostomy + staged repair: performed in children who do not qualify for primary repair
  • Within or after 24 hours: early colostomy 
  • Several weeks later: posterior sagittal Sagittal Computed Tomography (CT) anorectoplasty (most common procedure)
  • When wounds have healed: colostomy closure