Videofluoroscopic Swallowing Study (VFSS): Patient Preparation and Result Interpretation

The videofluoroscopic swallowing study (VFSS) — also known as the modified barium swallow (MBS) study — is one of the two gold-standard instrumental assessments for dysphagia. It provides real-time, dynamic X-ray imaging of the entire swallowing sequence from oral cavity through oesophagus, using barium-opacified food and liquid boluses that show up clearly under fluoroscopy.

VFSS is the only instrumental assessment that visualises the oral preparatory phase, provides simultaneous view of all four swallowing phases, and allows precise measurement of swallowing timing and bolus movement. For these reasons it remains an indispensable part of the dysphagia assessment toolkit despite the advantages of bedside FEES.

This article follows ASHA Practice Portal guidance on adult dysphagia and NICE CG162.

What VFSS Reveals

VFSS produces a lateral-view (and often anteroposterior-view) fluoroscopic image of the head and neck during swallowing. It shows:

Oral Phase

• Lip closure and anterior bolus containment — presence of anterior spillage
• Tongue movement and bolus formation — bolus shape, cohesion, and tongue tip-to-alveolar ridge contact
• Oral transit time — time from posterior tongue movement onset to swallow trigger
• Premature posterior spillage — bolus falling into the pharynx before the swallow reflex triggers

Pharyngeal Phase

• Swallow initiation timing — when the swallow reflex triggers relative to bolus position
• Hyolaryngeal excursion — measured as anterior and superior displacement of the hyoid
• Epiglottic deflection — adequacy of posterior tilt
• Pharyngeal constrictor wave — completeness of superior-to-inferior peristalsis
• Upper oesophageal sphincter opening — diameter and duration
• Penetration — material entering the laryngeal vestibule above the vocal folds
• Aspiration — material passing below the vocal folds (below the white line of the glottis on fluoroscopy)
• Post-swallow residue — pyriform sinus, vallecular, or posterior pharyngeal wall residue

Oesophageal Phase

• Oesophageal transit — peristaltic progression of the bolus from UOS to LOS
• Oesophageal motility — identifies tertiary contractions, aperistalsis
• Structural lesions — strictures, pouches, rings visible on barium coating
• Gastro-oesophageal reflux — reflux of barium from stomach into oesophagus

Barium Bolus Preparation and IDDSI

VFSS must use barium-opacified boluses that match the IDDSI consistencies tested. The IDDSI framework provides standardised definitions of all seven food and liquid levels (0–7). When barium powder is mixed into food or liquid to create VFSS boluses, the final consistency must be verified using IDDSI testing methods (flow test, fork drip, spoon tilt) before use in assessment.

A standardised VFSS bolus protocol typically includes:

• IDDSI Level 0 thin liquid — 5 mL, 10 mL, 20 mL sequential single swallows; sequential multiple swallows; cup drinking
• IDDSI Level 2 (Mildly Thick) — 5 mL single swallows
• IDDSI Level 3 (Moderately Thick) — 5 mL single swallows
• IDDSI Level 4 (Puréed) — spoon-fed bolus
• IDDSI Level 6 or 7 solid — biscuit or cracker coated with barium paste

The SLT and radiographer work together during VFSS. The SLT administers boluses and directs the fluoroscopy study; the radiographer controls X-ray exposure.

Indications for VFSS

VFSS is preferred over FEES when:

1. Full four-phase assessment is needed — particularly when oral phase dysfunction needs detailed analysis alongside pharyngeal findings
2. Oesophageal assessment is indicated — VFSS provides oesophageal phase information that FEES cannot; useful in suspected peptic stricture, achalasia, or GORD evaluation concurrent with swallowing assessment
3. The patient cannot tolerate nasal scope passage — VFSS only requires the patient to swallow boluses in a lateral sitting position
4. Precise biomechanical measurements are required — hyolaryngeal excursion, timing of pharyngeal events, and bolus flow characteristics are more precisely measured from VFSS
5. Paediatric assessment — VFSS is more commonly used than FEES in paediatric dysphagia assessment in Hong Kong

Interpreting a VFSS Report: Key Findings

Penetration-Aspiration Scale (PAS)

The PAS (Rosenbek et al., 1996) is the most widely used standardised rating of aspiration severity on VFSS, with scores from 1 (no airway entry) to 8 (silent aspiration). PAS scores are reported for each bolus type and volume tested.

Modified Barium Swallow Impairment Profile (MBSImP)

The MBSImP is a validated, standardised scoring tool for VFSS that rates 17 specific components of swallowing physiology. It provides a detailed impairment profile beyond the PAS, identifying which specific physiological components are impaired (e.g., tongue base retraction score, laryngeal elevation score) and enabling targeted therapy planning.

Temporal Measures

Published normative data allow comparison of individual patient timing measures against age-matched norms:

• Stage Transition Duration (STD) — time from bolus crossing the posterior tongue border to swallow trigger; >0.5 seconds is abnormal
• Pharyngeal Transit Time (PTT) — time from swallow trigger to bolus clearing the UOS
• Laryngeal Vestibule Closure Duration — how long the glottis remains closed

Residue

Post-swallow residue is rated using the Yale Pharyngeal Residue Severity Rating Scale — separate ratings for valleculae and pyriform sinuses, with scores from 0 (none) to 4 (complete filling).

VFSS in Hong Kong

VFSS is performed in radiology departments of public and private hospitals in Hong Kong. In the public sector, it is typically available at major cluster hospitals. Scheduling may take several weeks for outpatients. For inpatients acutely post-stroke or post-surgical, FEES is often more rapidly accessible. Prof. Karen Chan’s HKU Swallowing Research Lab has contributed to standardised VFSS protocols for Chinese food boluses — including congee, tofu, and modified dim sum — adapted for Hong Kong clinical practice.

For referral guidance, see When to Refer to a Speech and Language Therapist.

References

1. American Speech-Language-Hearing Association. Adult Dysphagia Practice Portal. https://www.asha.org/practice-portal/clinical-topics/adult-dysphagia/
2. National Institute for Health and Care Excellence. Stroke Rehabilitation in Adults (CG162). https://www.nice.org.uk/guidance/cg162
3. IDDSI. The IDDSI Framework. https://www.iddsi.org/framework
4. Logemann JA, et al. (2015). Disorders of deglutition. Handbook of Clinical Neurology, 129, 465–487. PMID: 26315994