Tracheo-Oesophageal Fistula (TOF) - MD Exam Answer

Definition

Embryology

• Failure of complete division of the cranial foregut results in a defective tracheo-oesophageal septum, producing a TOF.
• Incomplete separation of the developing oesophagus and trachea by the lateral mesodermal ridges results in an isolated TOF.
• The embryologic origin of OA + TOF combined is less clearly understood.

Classification (Gross Classification)

Associated Anomalies - VACTERL Association

• V - Vertebral anomalies
• A - Anorectal malformations
• C - Cardiac defects (most common associated anomaly)
• TE - Tracheo-Oesophageal fistula
• E - Oesophageal atresia
• R - Renal anomalies
• L - Limb defects (especially radial ray)

Clinical Features

Antenatal

• Polyhydramnios (in ~50% of OA cases) - due to inability of amniotic fluid to pass through the GI tract for absorption
• Absent stomach bubble on antenatal ultrasound after 20 weeks
• Dilated and blind-ending upper oesophageal pouch on fetal MRI

Postnatal (OA/TOF - the common type)

1. Frothing/drooling at the mouth (excess saliva, unable to swallow)
2. Choking and cyanosis - especially on feeding
3. Respiratory distress and aspiration

• Feeds precipitate severe choking and aspiration
• Gas in the abdomen due to air passing through the distal fistula into the stomach
• Gastric contents may reflux back through the fistula causing aspiration pneumonitis

H-type TOF (late presentation)

• Recurrent chest infections, chronic respiratory disease, bronchospasm
• Often investigated for cystic fibrosis before diagnosis
• May present in the ENT clinic

Diagnosis

Bedside Test

• Inability to pass an orogastric/nasogastric tube - virtually diagnostic of OA. A 10Fr or larger tube must be used (thin tubes may coil in the upper pouch giving a false negative appearance)

Radiological Investigations

1. Chest X-ray (with the NG tube in situ):
   • Tube coiled in the upper oesophageal pouch confirms OA
   • Gas in the abdomen = associated distal TOF present
   • Gasless abdomen = isolated OA (no fistula) or rare proximal fistula only
   • Associated vertebral and rib anomalies visible
2. Contrast oesophagogram (tube/pull-back oesophagogram):
   • Method of choice for H-type fistula
   • Patient prone/left lateral; contrast injected under pressure while NG tube withdrawn under fluoroscopy in lateral view
   • Risk of aspiration; resuscitation must be available
   • Negative result does not exclude H-type TOF
3. Tracheobronchoscopy:
   • Gold standard for identifying fistula position before surgery
   • Identifies upper pouch fistulae
   • Allows the anaesthetist to position the ETT distal to the fistula
   • Mandatory if tube oesophagogram is negative but clinical suspicion remains high
4. Echocardiography - essential preoperatively to exclude congenital heart disease and locate the aortic arch (right-sided in 2% - makes surgery more challenging)
5. Renal ultrasound - to exclude renal anomalies

Pre-operative Management

1. Nil by mouth immediately
2. Replogle (Sump) tube in the upper oesophageal pouch on continuous suction - prevents aspiration of secretions (must be flushed regularly with air to prevent blockage)
3. Prone head-up positioning - reduces aspiration risk
4. Avoid endotracheal intubation and positive pressure ventilation (PPV) if possible - PPV forces air through the fistula into the stomach, causing gaseous distension, impaired ventilation, hypoxia, hypercapnia, and risk of GI perforation
5. Broad-spectrum antibiotics if aspiration pneumonia present
6. Correct metabolic/electrolyte abnormalities
7. Full VACTERL workup before surgery

Anaesthetic Considerations

• Inhalational induction preferred; spontaneous ventilation maintained until fistula is ligated
• Bronchoscopy performed after induction to assess fistula size and location
• ETT placed distal to the fistula (may require intentional right main bronchus intubation then careful pullback until equal air entry)
• A balloon embolectomy catheter can be placed in the fistula to occlude it
• Invasive arterial BP monitoring recommended
• Pre-ductal and post-ductal SpO2 monitoring for intracardiac shunts

Surgical Management

Timing

• Surgery is urgent but not an emergency in most cases; performed within the first few days of life
• Pre-operative stabilisation is essential

Approach

• Open extrapleural right posterolateral thoracotomy (standard approach)
• Thoracoscopic (minimally invasive) repair is now widely performed

Procedure

1. Fistula identified and dissected from surrounding structures
2. Fistula divided and sutured closed flush with the trachea
3. End-to-end oesophageal anastomosis (single-layer all-coats) over a trans-anastomotic feeding tube
4. Bronchoscopy beforehand guides ETT placement and confirms fistula position

Long-Gap OA (when primary repair is impossible)

• Ligation of TOF + feeding gastrostomy created first
• Upper pouch kept on continuous sump suction
• Delayed primary anastomosis after allowing growth/stretching (weeks to months)
• Open oesophagostomy (spit fistula) may be created as a last resort - but almost always precludes later primary repair
• Oesophageal substitution using gastric pull-up, colonic or jejunal interposition if primary repair is impossible

Post-operative Complications

Early (Days to Weeks)

• Anastomotic leak - occurs in 5-20%; higher in long-gap OA; tension pneumothorax may be the presentation
• Recurrent TOF - due to incomplete ligation or breakdown
• Anastomotic stricture - most common long-term complication; requires oesophageal dilatation
• Pneumonia/respiratory complications

Medium to Long-Term

• Gastro-oesophageal reflux (GERD) - very common; may require Nissen fundoplication
• Tracheomalacia - causes "TOF cough" (barking cough); severe cases may need aortopexy
• Oesophageal dysmotility - lifelong, leads to dysphagia
• Recurrent chest infections
• Barrett's oesophagus (long term)

Prognosis

• Birth weight
• Presence of pneumonia
• Severity of associated congenital anomalies

• Group I (birth weight >1500g, no major cardiac defect): survival >97%
• Group II (birth weight <1500g OR major cardiac defect): survival ~59%
• Group III (birth weight <1500g AND major cardiac defect): survival ~22%

Key Points for MD Exams

1. Most common type is OA with distal TOF (Type A/Gross C) - ~85%
2. H-type (N-type) TOF has no atresia - presents late with recurrent chest infections
3. Polyhydramnios antenatally + inability to pass NG tube postnatally = cardinal diagnostic features
4. Gas in abdomen on CXR = distal TOF present; gasless abdomen = isolated OA
5. VACTERL association - always screen
6. Avoid positive pressure ventilation before fistula ligation
7. Surgery: fistula ligation + end-to-end oesophageal anastomosis via right extrapleural thoracotomy
8. Most common long-term complication = anastomotic stricture + GERD + tracheomalacia