Clinical Indications

Indications for the test to be performed depend on the clinical conditions and the symptoms. Manometry, often performed after a barium swallow or endoscopy, is the gold standard for diagnosis of primary esophageal motility disorders in patients with dysphagia; these can include achalasia, scleroderma, diffuse esophageal spasm, hypertensive LES, and nonspecific esophageal motility disorders. Transit studies are indicated in conditions in which the use of manometry is prevented by its intrinsic limitations (i.e. it measures peristalsis only indirectly and the procedure itself can affect normal physiology), for instance in patients with dysphagia following surgery, with mechanical obstruction (neoplasia, scar), after radiotherapy, and in all those patients with poor or no compliance to manometry

Radiologic Evaluation of Esophageal Transit by Barium Swallow Videofluoroscopy

The examination does not require any specific preparation, except fasting over the prior 4–6 hours, and is performed via ingestion of a single or double radiologic contrast agent. Although barium sulfate contrast is the primary agent used, in patients at risk for aspiration or those who have undergone recent neck or esophageal surgery (in whom the examination is needed to rule out anastomotic leaks), barium is contraindicated and must be replaced with an iodinated contrast agent. Barium contrast can be prepared in different concentrations to obtain different consistencies and radiopacity.

The examination begins with the patient standing up in the lateral oblique position and taking three consecutive swallows of barium suspension for evaluation of the proximal, mid, and distal portions of the thoracic esophagus, respectively. Further projections can be acquired with additional swallows and different decubitus positions to obtain a panoramic depiction of the esophageal morphology and function. In particular, the presence and degree of gastroesophageal reflux can be assessed by acquiring radiographs with the patient in the semiprone decubitus with Trendelenburg position, followed by a Valsalva maneuver to increase abdominal pressure. Fluoroscopic images are acquired in real time at a high frame rate (e.g. 30 frames per second) [2–5].

Main Motility Disorders Investigated with Barium Swallow Videofluoroscopy

Patients with esophageal motility abnormalities often present with slowly progressing dysphagia for fluids and solids, sometimes associated with weight loss. The main causes of this condition are achalasia, diffuse esophageal spasm, and scleroderma.

Achalasia is the most frequent primary motility disorder of the esophagus. Its etiology is unknown and its basic pathophysiologic mechanism is the inability of the LES to relax upon swallowing, associated with a complete loss of peristaltic coordination along the esophageal body. At the barium study, the esophagus is dilated (ranging from mild dilatation to megaesophagus in severe cases) with a tapered appearance of its distal tract (Figure 13.2). In the initial stages, the only sign may be stasis of contrast medium in the esophageal lumen with an air‐fluid level inside it, followed by rapid emptying by gravity when the hydrostatic pressure of the ingested barium column exceeds that of the LES, thus forcing its release and passage of the meal into the stomach. The main differential diagnosis is against pseudo‐achalasia, in which the esophagus is dilated with narrowing of its distal portion and of the gastroesophageal junction due to the presence of a tumor.

Diffuse esophageal spasm is a motility disorder characterized by multiple, spontaneous, and intermittent contractions of the distal two thirds of the esophagus. Usually such contractions give rise to a segmented (“corkscrew”) appearance of the affected esophagus (Figure 13.3).

Scleroderma is a connective tissue disorder characterized by atrophy of the esophageal smooth muscle, leading to reduced or absent peristalsis of the distal two‐thirds of the esophagus, to incompetent LES, and dilation of the upper esophagus [3–5].

Patient Preparation and Scintigraphic Acquisition

After fasting for at least 3 hours, the acquisition procedure starts with the patient standing in front of a gamma camera (equipped with a low‐energy, high‐resolution, parallel‐hole collimator, energy window 140 keV ± 10%), with the face tilted 80° to the left to include the entire region from the mouth to the epigastric area in the field of view. The patient keeps in the mouth a 10‐mL bolus of water labeled with 37 MBq (1 mCi) of ^99mTc‐colloid, and is asked to swallow it 2 seconds after starting a dynamic acquisition for 60 seconds (0.125 s/frame, matrix 64 × 64, zoom 1). At the end of the dynamic scan, with the patient still in the same position, a 60‐second static image is acquired to detect any retention in the esophagus and/or tracheobronchial aspirate. The same test is repeated 30 minutes later, using a semisolid bolus (10 mL of a jelly‐based drink labeled with 37 MBq of ^99mTc‐colloid), followed by 60 seconds of static acquisition, with the same protocol employed for the liquid bolus.

Scintigraphy with a single swallow has poor sensitivity (44%) and specificity (71%), mainly due to aberrant swallows (which can also occur in healthy subjects) and intrasubject variability. This issue can be overcome by summing the images of six independent liquid bolus swallows at 30‐second intervals, and calculating both time parameters (mean time, mean transit time, and transit time) and retention parameters at particular time points (Figure 13.4).

In adults this examination can be integrated with a high‐temporal‐resolution dynamic sequence with four or five Valsalva maneuvers (to increase intra‐abdominal pressure) performed over 120 seconds to detect the presence of gastroesophageal reflux [1].

Qualitative and Quantitative Image Processing

Acquired images can be reviewed over time to detect aberrant swallowing patterns and quantitatively by drawing at least three regions of interests (ROIs) around the oral cavity, pharynx, and whole esophagus (Figure 13.5), to measure the rate of the oropharyngo‐esophageal transit and to identify retention. In turn, the esophagus can be further subdivided by drawing three ROIs around its upper, middle, and lower thirds, respectively.

Quantitative indices can be defined as follows:

• Oral transit time (OTT) is the time required for the bolus to exit the oral cavity after the subject has been asked to swallow (<1 second in normal controls). The oral curve shows a rapidly decreasing pattern with <5% residual activity.
  
• Pharyngeal transit time (PTT) is the time between the radioactive bolus entrance into and exit from the pharynx (<1.2 seconds in normal controls). The pharyngeal curve shows a rapid increase in radioactivity (from 0% to 100%), followed by a relatively slower decline with <5% residual activity.
  
• Esophageal transit time (ETT) is the time between the bolus entrance into and exit from the (whole) esophagus (<10 seconds in normal controls, mean time = 5.6 ± 4 seconds). The esophageal curve shows a rapid increase in radioactivity, followed by a slower decrease, with less than 20% residual activity.
  
• Retention index (RI) is the fraction of the radioactive bolus remaining in each tract 10 seconds after swallowing. This value is less than 5% in normal subjects for the oropharyngeal area, while it is less than 20% in the esophagus.
  
• Esophageal emptying rate (EER) is the fraction of radioactivity cleared from the esophagus 10 seconds after maximum peak. This is achieved through the formula [(E_max – E_10s)/E_max] × 100, where E_max is the maximum radioactivity counts detected in the esophagus and E_10s is the activity present in the esophagus 10 seconds after maximum peak. This value is greater than 80% in normal controls.

The aspiration percentage (PA) can be calculated to quantify radioactivity in the larynx or in the tracheobronchial tract [11] by dividing the counts obtained in the aspiration area (RA) by the initial activity detected in the oral cavity before swallowing (activity time 1, AT1), subtracted from the residual activity after swallowing (activity time 2, AT2), by means of the following formula:

An OPES study provides particularly helpful information in all the clinical conditions linked to mechanical and muscular disorders. For instance, nutcracker esophagus is associated with noncardiac chest pain or dysphagia and high‐amplitude peristaltic waves in the distal esophagus, caused by hypertensive LES that can show abnormally elevated tone at rest, exaggerated LES contraction, or incomplete LES relaxation. Diffuse esophageal spasm, described as simultaneous contractions induced by liquid swallows, can be scarcely detected by manometry, but it is always identified by multiple liquid‐bolus OPES. Classic achalasia, caused by degeneration of intramural neurons of the esophagus, causes a rise of the basal LES pressure, resulting in impaired esophageal clearance and delayed transit times, which can be detected during diagnosis (with a sensitivity close to 100%) and monitored after treatment (myotomy, pneumatic dilation, or botulinum toxin injections) using OPES. In scleroderma, impaired esophageal motility can be detected by OPES in otherwise asymptomatic patients as patients show a typical pattern of retention of radioactivity in the lower esophagus, which has a higher sensitivity compared to manometry and barium swallows. Neurogenic dysphagia is secondary to diseases of different parts of the central (e.g. supranuclear, motor and sensory nuclei) or peripheral nervous system (e.g. nerves, muscle cells and spindles) involved in the swallowing process as a result of conditions such as stroke, brain tumors, brain injury, bulbar and pseudobulbar paralysis, and neurodegenerative diseases (e.g. amyotrophic lateral sclerosis, multiple sclerosis, Parkinson’s disease, Huntington’s disease, myasthenia, myopathies) (Figure 13.6) [12, 13]. OPES, with its lack of invasiveness and excellent tolerability, allows for the functional, objective, and qualitative–quantitative study of swallowing in patients with neurogenic dysphagia, with sensitivity and overall validity values (97.9% and 86.7%, respectively) akin to videoendoscopy in oropharyngeal dysphagia [14].

As most recently summarized by Maurer et al. [15], there are some clinical scenarios where the use of esophageal transit scintigraphy (often associated with the evaluation of gastroesophageal reflux) is most appropriate. These scenarios include dysphagia and quantification of response to therapy (the latter following treatment for achalasia); in turn, the underlying causes of dysphagia include achalasia, scleroderma, diffuse esophageal spasm, hypertensive LES, nonspecific motility disorder, and esophageal outflow obstruction. On the other hand, esophageal transit scintigraphy may be appropriate in cases of suspected aspiration, rumination, gastroesophageal reflux, and evaluation of patients pre‐ and postfundoplication.