GI Surgical Aspects of Cystic Fibrosis Flashcards
Discuss cystic fibrosis.
Cystic fibrosis is an autosomal recessive disorder caused by mutations to the CFTR chloride channel protein that results in increased viscosity of epithelial secretions throughout multiple organ systems.
While the effects on the lung are most detrimental, there are a multitude of manifestations throughout the gastrointestinal tract of particular interest to the pediatric surgeon, including meconium ileus, distal intestinal obstruction, biliary disease, pancreatic insufficiency and rectal prolapse.
Although there is currently no cure for cystic fibrosis, there are many effective medical and surgical treatments for combating the complications of the disease.
What is cystic fibrosis?
Cystic Fibrosis (CF) is an autosomal recessive disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene resulting in an abnormal cell membrane chloride channel.
This manifests as an inability to properly regulate electrolyte content with thickening of secretions along secretory epithelium.
Poor clearance of desiccated secretions is the primary cause of morbidity across multiple organ systems.
How is CF diagnosed?
The two most common newborn screening tests are the serum immunoreactive trypsinogen (IRT), which is elevated in the first weeks of life, and DNA analysis for CFTR mutations.
In patients with a positive screen, sweat chloride testing should subsequently be performed as the gold standard diagnostic test.
A value of >60 mmol/L on two occasions is diagnostic [1, 2].
What organ systems are affected?
The most affected organ systems include the respiratory tract with chronic obstruction and infection, the gastrointestinal tract with obstruction and dysfunction of the biliary tract, pancreas, and alimentary canal, the sinus tracts with obstruction, infection and nasal polyposis, as well as the testes with defective sperm transport mechanisms resulting in infertility in males.
What is the earliest clinical manifestation of CF?
Meconium ileus is caused by obstruction of the small intestine by inspisssated meconium usually at the level of the terminal ileum.
It presents as abdominal distention and inability to pass meconium in the first few days of life.
It occurs in approximately 10–20% of neonates with CF, and 80–90% of all meconium ileus cases occur in infants with CF [2].
What causes meconium ileus?
Abnormally functioning CFTR ion channels within the pancreas and small intestine cause intraluminal dehydration and hyperviscous meconium that obstructs the mid to distal ileum.
What prenatal findings may be seen in meconium ileus?
Meconium ileus may be identified on prenatal ultrasound by visualization of dilated small intestine associated with hyperechoic intraluminal masses, representing the inspissated meconium.
Non-visualization of the gallbladder on prenatal ultrasound is another non-specific finding.
How does meconium ileus appear on plain film radiography?
The classic radiographic appearance includes dilated loops of small bowel without air-fluid levels and a soap bubble appearance as air mixes with inspissated meconium.
How is meconium ileus classified?
Meconium ileus is termed complicated if intestinal atresia, volvulus, bowel necrosis, perforation or meconium peritonitis are present.
Meconium peritonitis may be seen on prenatal ultrasound or plain radiographs as scattered calcifications.
Approximately 40% of patients will present with complicated disease.
Simple meconium ileus includes obstruction without any of the complications listed above [2].
How is simple meconium ileus diagnosed?
The gold standard diagnostic test is a hyperosmotic contrast enema with gastrografin, which will typically reveal a small caliber colon, meconium pellets in the distal ileum, and dilated, proximal small intestine.
What is the initial treatment for simple meconium ileus?
Following a confirmatory diagnostic enema, therapeutic gastrografin enemas are performed under close fluoroscopic guidance.
The hyperosmotic solution draws water into the lumen to soften and clear the obstructing meconium.
Complications of this procedure can include massive fluid shifts and subsequent hypovolemic shock, as well as bowel perforation.
IV access should be obtained prior to the procedure to allow adequate fluid resuscitation.
N-acetylcysteine solution may also be added to the enema to aid in breaking up the obstructing meconium.
If necessary, repeated gastrografin enemas may be performed [2].
When is surgery indicated for meconium ileus?
Surgery is the mainstay of treatment for all cases of complicated meconium ileus, but it is also indicated in patients with simple disease who have failed non-operative management.
What are the surgical options for meconium ileus?
For uncomplicated disease, an enterotomy is performed to allow intraoperative irrigation of the bowel to flush out the obstructing meconium, with either primary closure or creation of an enterostomy for continued irrigation post-operatively.
For complicated disease, the necrotic bowel is resected.
Primary anastomosis is generally not recommended, because it does not allow for postoperative irrigation and carries a risk of anastomotic leak.
Temporary diverting stomas (ileostomy and mucous fistula) have the benefits of not requiring complete evacuation of meconium at the time of operation resulting in a shorter operative time and elimination of the risk of anastomotic leak.
Ostomy-in-continuity operations, such as the Bishop-Koop or Santulli enterostomies, allow access for irrigation and maintenance of intestinal continuity via an end-to-side anastomosis of the proximal and distal ends (or vice versa, respectively).
These procedures reduce fluid losses, preserve the distal bowel as a site of nutrient absorption and protect the anastomosis with adequate decompression via the “chimney” limb which is brought up as a stoma [2].
What is distal intestinal obstruction syndrome (DIOS)?
DIOS can occur at any age outside the newborn period and results from inspissation of thickened intestinal contents causing impaction and obstruction typically at the terminal ileum or ileocecal valve.
The mechanism isn’t fully understood, but it is likely multifactorial, including pancreatic insufficiency, resulting in increased intraluminal fat content and increased intestinal transit time, as well as altered water and electrolyte content of ileal mucus, and global dehydration [3].
How is DIOS diagnosed?
A careful history typically reveals colicky abdominal pain, abdominal distention, constipation, nausea, and emesis when it progresses to full obstruction. A mass in the right lower quadrant can sometimes be palpated.
Plain radiographs may show a stool bulk in the right lower quadrant with a “bubbly” appearance, along with dilated loops of proximal bowel with air fluid levels.
Computed tomography (CT) may be useful to delineate the location of the obstruction and exclude other pathology.
A water-soluble contrast enema may reveal non-filling of the terminal ileum [3].
