Water-Soluble Contrast Swallow

The water soluble contrast swallow is a fluoroscopic study of the pharynx, oesophagus, stomach and, in the postoperative setting, the anastomosis or conduit, after the patient drinks a water soluble iodinated contrast agent in place of barium.

A low osmolar or iso osmolar non-ionic agent (for example iohexol, iopamidol or iodixanol, 150 to 300 mg iodine in each mL, diluted if there is a risk of aspiration) is swallowed in volumes of 20 to 100 mL. Images are taken in the erect, oblique and prone positions in real time.

It is used when barium is unsuitable: suspected perforation, anastomotic leak, fistula, recent surgery, risk of aspiration, or before endoscopy or surgery in a patient with obstruction. The effective dose is about 1 to 3 mSv, depending on the length of fluoroscopy.

Barium in the mediastinum or pleura causes severe inflammation and fibrosis, and barium in the airway can cause pneumonitis, so water soluble contrast is the first agent for any suspected leak.

Oesophageal perforation has a high mortality (10 to 25% overall, up to 40% or more if treatment is delayed beyond 24 hours). Anastomotic leak after oesophagectomy occurs in 5 to 15%, after gastrectomy in 2 to 5%, and after gastric bypass or sleeve gastrectomy in 1 to 5%. A fast, accurate study affects survival.

Water soluble contrast is less dense than barium, so it is less sensitive for small leaks; CT with oral contrast adds sensitivity and shows collections.

Indications. Suspected oesophageal perforation (after vomiting, instrumentation, foreign body, trauma, caustic ingestion or surgery). Suspected anastomotic leak after oesophagectomy, gastrectomy, bariatric surgery, or fundoplication. Suspected fistula (tracheo oesophageal, bronchopleural). Assessment before starting oral feeding after oesophageal or gastric surgery.

Suspected high grade obstruction (food bolus impaction, tumour) before endoscopy. Dysphagia with a risk of aspiration or an incompetent swallow, when a first look at the swallow is needed. Foreign body ingestion with suspected perforation. Post-operative gastric band or sleeve complications.

Congenital oesophageal anomalies in the neonate (a small volume of non-ionic contrast through a tube for the H-type fistula, atresia). Small bowel obstruction in the post-operative or adhesive setting, as a diagnostic and therapeutic test (a water soluble follow through). Not for the routine investigation of reflux or motility, for which barium and manometry are better.

Contraindications and precautions. Aspiration risk: hypertonic ionic agents (such as diatrizoate, high osmolality) draw fluid into the lungs and cause severe pulmonary oedema, so only low osmolar non-ionic agents are used when aspiration is possible, and the volume is small.

Allergy to iodinated contrast (oral absorption is small, but a reaction is possible, and absorption increases through a leak or an inflamed mucosa). Hyperthyroidism or thyroid disease (iodine load). Renal impairment (small absorbed dose, but increases with leakage). Neonates and infants: hyperosmolar agents cause fluid shifts, so only non-ionic, low osmolar contrast is given.

Pregnancy: avoid unless essential. A patient who is hypotensive, septic or unstable needs resuscitation before the study, and a CT may be the preferred test.

Preparation and technique. Nil by mouth for 4 to 6 hours before an elective study (no wait in an emergency). A small amount of contrast (10 to 20 mL) is swallowed first in the oblique position to show the pharynx and cervical oesophagus, followed by larger volumes with the patient turned from left to right to show the whole oesophagus, stomach and anastomosis.

A feeding tube or a nasogastric tube is used to instil contrast in patients who cannot swallow. If the first study is negative and the suspicion remains high, a second study with barium (if the risk of aspiration is low) or a CT scan with oral contrast is performed.

Normal appearances. The contrast outlines the pharynx and cervical oesophagus in a smooth, uninterrupted column, passes through the cricopharyngeus without delay, and flows down the oesophagus in a peristaltic wave. The mucosal pattern is faint, because water soluble contrast is thin and coats the wall poorly.

The gastro oesophageal junction opens and contrast enters the stomach without delay and without leakage. After surgery, the anastomosis (a neck, chest or abdominal join) shows smooth contrast passage through a patent lumen with no extraluminal collection. The gastric conduit is smooth and empties by 5 to 10 minutes. No contrast enters the airway.

Interpretation.

• Oesophageal perforation: extraluminal contrast outside the oesophageal wall, in the mediastinum (a line or collection of contrast alongside the oesophagus, often at the site of the tear).
• Contrast may also be seen in the pleural space (hydropneumothorax or pleural effusion, usually left sided for a lower oesophageal tear), or the neck (tracking in the fascial planes).
• Boerhaave syndrome (spontaneous rupture at the lower left posterior oesophagus) shows leak into the left chest.
• Iatrogenic tears occur at the narrow points (cricopharyngeus, the level of the aortic arch, and the lower oesophagus just proximal to the diaphragm).
• Anastomotic leak: a jet or tract of contrast outside the lumen at the anastomosis, a contained collection near the join, a leak into the pleural space or the peritoneal cavity, or a fistula to skin or the airway. Size (contained or free) and drainage (into a drain or the mediastinum) are described.
• Fistula: contrast in the airway (tracheo oesophageal, bronchopleural), the pleural space, or a chest drain.
• Stricture: narrowing at an anastomosis or the lower oesophagus, with delayed passage of contrast and dilated proximal oesophagus; tumour recurrence at an anastomosis shows an irregular narrowing.
• Obstruction: failure of contrast to pass, a food bolus (a filling defect), a hold up proximal to an obstructing lesion, an impacted foreign body, and a dilated oesophagus proximal to it.
• Gastric complications of bariatric surgery: leak at the staple line or the gastrojejunal anastomosis, stricture, stomal ulcer, band slippage (an abnormal band angle, a dilated pouch), and a twisted sleeve.
• Aspiration: contrast enters the larynx or trachea before, during or after the swallow, with or without cough (silent aspiration has no cough).
• Neonatal anomalies: a blind ending upper pouch in oesophageal atresia.
• A fistula between the oesophagus and the trachea in an H-type tract is found at the level of the thoracic inlet, requiring a prone or lateral study with the contrast injected through a tube under pressure).
• Hiatus hernia and volvulus: contrast outlines a gastric pouch in the chest.
• Small bowel obstruction (water soluble follow through): contrast reaching the colon within 24 hours suggests that the obstruction will resolve without surgery.
• Failure to reach the colon in 24 hours predicts the need for surgery.
• The hyperosmolar agent may also draw fluid into the bowel and relieve obstruction.

Critical values and findings needing immediate action.

• Oesophageal perforation or anastomotic leak with mediastinitis or sepsis: nil by mouth, broad spectrum intravenous antibiotics and antifungal cover, fluids, proton pump inhibitor, drainage, and urgent thoracic surgical or endoscopic management (stent, clip, drain).
• Cervical perforation with deep neck infection: urgent surgical drainage and airway assessment.
• Aspiration of hyperosmolar contrast with respiratory failure: oxygen, suction, ventilation if required, and monitoring for pulmonary oedema.
• Free leak into the peritoneum or pleura with haemodynamic instability: resuscitation and emergency surgery.
• Impacted foreign body or food bolus with complete obstruction and pooling in the airway risk: urgent endoscopy.
• Tracheo oesophageal fistula in an infant: nil by mouth, upright positioning, suction of the pouch, and neonatal surgical referral.
• Anaphylaxis to contrast: stop, adrenaline, oxygen and fluids.

Limitations and artefacts.

• Water soluble contrast is less radio dense than barium and flows quickly, so small leaks, a thin tract, or a sealed perforation can be missed.
• Sensitivity for oesophageal leak is about 50 to 80%, and about 20 to 40% of leaks are missed.
• A negative study with a high clinical suspicion needs a repeat study with barium (if aspiration risk is low) or CT with oral contrast.
• Contrast is rapidly diluted in the stomach or a large conduit, and the mucosal detail is poor, so superficial lesions, early tumour, and ulcers are missed.
• A normal swallow at the time of the study does not exclude aspiration at other times.
• Hyperosmolar ionic agents cause severe pulmonary oedema if aspirated, and a hyperosmolar load can cause fluid shifts and dehydration in neonates, so non-ionic low osmolar contrast is used.
• Contrast bubbles and a collapsed oesophagus mimic collections, and normal anatomy (aortic arch, left bronchus, the diaphragmatic hiatus) can look like a narrowing or a leak.
• The study cannot assess the extent of mediastinal infection or collections; CT does this.
• The positioning may be limited in sick patients, and a supine film is insensitive for a leak.
• Radiation dose is moderate and repeated studies should be avoided if CT will answer the question.

Special groups.

• Post-operative patients: the study is done at day 5 to 7 after oesophagectomy or bariatric surgery in some units before restarting oral intake, and sooner when a leak is suspected; practice varies widely.
• Neonates and children: oesophageal atresia and fistula, caustic strictures; use only low osmolar non-ionic contrast in small volumes.
• Older adults: aspiration risk and dysphagia after stroke; videofluoroscopy with a speech therapist is the better test for swallowing.
• Patients with caustic ingestion: leak or necrosis suspected; endoscopy and CT first.
• Pregnancy: avoid.
• Regions: caustic strictures in children, oesophageal cancer, and delayed presentation of perforation with mediastinitis are common, and a water soluble swallow is often the first test where CT is unavailable.

Follow up tests.

• CT of the chest and abdomen with oral and intravenous contrast (the most sensitive test for leak and collection).
• Barium swallow in selected cases.
• Upper gastrointestinal endoscopy (to assess the defect and place clips or stents).
• Bronchoscopy for fistula.
• Videofluoroscopic swallow study.
• Ultrasound of the neck and chest.
• Blood cultures, C-reactive protein, white cell count, lactate.
• Pleural fluid analysis (amylase, pH, microscopy, culture, food particles).
• Referral to thoracic, upper gastrointestinal or paediatric surgery services.