Dr. Mercado-Deane is an Assistant Professor in the Department of Radiology, University of Texas Houston Medical School, Houston, TX.

Abnormalities of swallowing are a surprisingly common occurrence in infants and young children. Swallowing dysfunction can be defined as interference with adequate nutrition, with the transport of food from the mouth to the stomach, or with the enjoyment of the feeding process. Such dysfunction can be clinically occult until serious complications occur, such as aspiration pneumonia, chronic sinusitis, apnea, or acute life-threatening events.

During the process of evaluating swallowing dysfunction, the videofluoroscopy or modified barium swallow study is an integral part of the armamentarium used for a complete evaluation. This study is performed by a radiologist, in conjunction with a speech pathologist. Knowledge of the physiologic and anatomical differences of swallowing of pediatric patients, as well as the radiological manifestations of swallowing dysfunction during the different phases of swallowing, allows the radiologist to tailor the study and take an active role in patient management.

This article will provide an overview of the anatomy, physical development, and normal oral-motor function, as well as radiological and clinical manifestations of swallowing dysfunction in infants and children.

Anatomy and development

Swallowing is a complex process that involves 5 cranial nerves (V, VII, IX, X, XII), 5 cervical nerves, cortical and subcortical pathways, as well as midbrain and brainstem involvement. Associated integration of 32 groups of muscles is necessary to achieve effective swallowing. ^1-3 Also, there are anatomical differences between infants, children, and adults that are associated with the stages of development, resulting in more efficient feeding as the patient matures. The infant has a small oral cavity, with a relatively large tongue that occupies most of the cavity. Lateral sucking fat pads aid the tongue in maintaining the milk bolus in a central canal. The structures in the pharynx are also in close proximity, allowing easy nasal breathing. The soft palate and arytenoids are prominent. The larynx is located anterior and superior, under the tongue base. The location of the larynx allows maximum airway protection during swallowing, with minimal effort of laryngeal elevation. ⁴ As growth and maturation occur, there is a change in the anatomic relationship of structures. The fat pads disappear and tooth eruption occurs as the child prepares for solid meals and cup drinking. The head and neck grow and elongate, the larynx starts to descend, and mouth breathing becomes possible (figure 1). ⁵

In neonates and infants, there are two types of sucking patterns: nutritive and non-nutritive. The non-nutritive pattern is more rapid, with no cessation of breathing occurring. It is as important as nutritive sucking in helping to preserve feeding skills during episodes of interruption of the feeding experience because of therapy or illness. ^6,7 In nutritive sucking, a breath precedes sucking and swallowing. Multiple sucks and swallows are possible with a single breath. In older infants and children, once they arrive at a more adult eating pattern that includes solids and liquids, their swallowing/breathing pattern becomes irregular, and then swallowing is restricted to expiration. ⁴

Swallowing is identified as early as 11 weeks gestational age (GA). True suckling is seen from 18 to 24 weeks GA. Non-nutritive sucking is seen at 27 to 28 weeks. A pattern 1:1:1 ratio of breathe, suck, and swallow is seen at 34 weeks, which allows sufficient oral feeding to meet nutritional needs. Episodes of several sucks and swallows occurring with a single breath are seen by 35 to 36 weeks GA. ^4,8,9

For the purpose of imaging evaluation, the swallowing process can be divided into 4 phases: 1) the oral preparatory phase, where the food is chewed and mixed with saliva; 2) the oral phase, with the bolus propelled posteriorly by the tongue; 3) the pharyngeal phase, with elevation of the soft palate and vallecula to seal the nasopharynx, elevation of the larynx to close the vestibule, relaxation of the cricopharyngeal muscle, and contraction of the lateral walls of the pharynx; and 4) the esophageal phase, during which the cricopharyngeal muscle contracts and the bolus is transferred through the esophagus. ⁴ In neonates and infants <6 months old, the first two phases are one. All this occurs in a fraction of a second (figure 2).

Clinical manifestation of swallowing dysfunction

Swallowing dysfunction is recognized in patients with neurological deficits and chronic illnesses. Awareness of different symptoms and presentations allows diagnosis of swallowing difficulties in the general population.

The clinical manifestations that prompt referrals for evaluation are not specific responses to an underlying cause. These include pulmonary signs and symptoms including recurrent pneumonias, difficult-to-control asthma, congestion and cough with feedings, apparent life-threatening episode, apnea, bradycardia, cyanosis with feedings, and persistent oxygen requirements. Gastrointestinal symptoms include poor weight gain and growth. Generalized manifestations of oral dysfunction include drooling and gagging, refusal to feed, messy eating, and tongue thrusting. ^4,9,10

Radiological evaluation of swallowing

Usually patients that present with respiratory and gastrointestinal symptoms will be referred initially for an upper gastrointestinal (UGI) study. This study evaluates the esophagus, stomach, and proximal duodenum, including assessing any evidence of reflux or its consequences, such as esophagitis or strictures. It is not designed for close evaluation of the swallowing phase. However, it can be used as a screening tool, looking for nasopharyngeal reflux (NPR), laryngeal penetration, and tracheal aspiration. In a recent article, Friedman et al ¹¹ suggest that deep laryngeal penetration, into the lower third of the laryngeal vestibule, during swallowing is a predictor of aspiration later into the feedings and warrants full evaluation.

The modified barium swallow study (MBSS) is the radiological method of choice for the evaluation of swallowing. ⁸ The MBSS is a diagnostic tool, concentrating on the oral and pharyngeal phases of swallowing. It provides a dynamic assessment of the phases of swallowing in real time. ¹² The handling of the bolus is visualized from the time it enters the oral cavity through its transit through the pharynx and its entrance into the esophagus. Other procedures, such as direct nasopharyngoscopy and cervical real-time ultrasound, have been advocated, due to the lack of ionizing radiation, but both have their limitations. The most important limitation is the inability to identify episodes of tracheal aspiration, which occur with swallowing. ^2,13 Traditionally, the MBSS is performed in conjunction with a speech pathologist and is videotaped with the patient in a semi-recumbent, lateral position for fluoroscopy of the airway. Videotaping permits additional review of the study and facilitates therapy recommendations. Pulsed fluoroscopy (<30 frames/sec) is not recommended because the episodes of laryngeal penetration and aspiration occur in a fraction of a second ¹⁴ and can be missed. ¹⁵ Different age-appropriate consistencies are given to ascertain the degree of dysfunction and evaluate therapeutic options.

Different consistencies of food and liquids, mixed with barium, are offered to the patient. This includes thin liquids with the consistency of nectar and honey, pureed food, and soft and hard solid food. A minimum of 3 swallows per type of liquid and solid food is observed, and the swallowing mechanism is recorded.

Radiological manifestations of swallowing dysfunction

In the oral phase, the radiological manifestations are similar to those seen clinically: spillage of contrast outside of the mouth due to poor lip seal, spillage of the bolus under the tongue, tongue tremors, and small bolus formation requiring multiple sucks per swallow due to tongue weakness and incomplete tongue elevation. Early spillage of contrast into the vallecula, prior to initiating swallow, reflects poor bolus control (figure 3). ²

The manifestations of pharyngeal dysfunction include nasopharyngeal reflux, laryngeal penetration, and aspiration. Reflux of the bolus into the nasopharynx (figure 4) is due to incomplete closure of the nasopharynx by the soft palate. Laryngeal penetration (figure 5) refers to penetration of the bolus into the vestibule of the larynx without aspiration, caused by delayed elevation of the larynx. Tracheal aspiration with penetration of contrast into the airway below the level of the vocal cords (figure 6) can result from delayed elevation of the larynx, delayed pharyngeal transit time of the bolus, decreased clearance of bolus (with residual noted in the vallecula and pyriform sinuses [figure 7]), and spillage of this residual into the larynx and trachea (figure 8). ² Cricopharyngeal muscle achalasia/dysfunction represents failure of relaxation or incoordinated relaxation of the cricopharyngeal muscle with swallowing. This dysfunction will cause either reflux of the bolus into the oropharynx or pooling of bolus in the pyriform sinuses, allowing spillage into the trachea and aspiration. ¹⁶

The handling of each consistency given should be documented, as well as the behavior of the patients. Documentation of any episode of refusal, associated cough or silent aspirations with swallowing, apneas, and bradycardias, if the patient is on a monitor, should be made. This will provide real-time information to the clinicians. Review of the recorded videofluoroscopic study with the speech pathologist is recommended.

Conclusion

Swallowing is a complex process, divided into three phases: the oral-preparatory, oral pharyngeal, and esophageal phase. Swallowing dysfunction can occur at different levels, due to immaturity, underlying central nervous system abnormalities, prolonged illness, or as a complication of gastroesoph-ageal reflux. It can occur in children with no underlying chronic illness or neurological disease. Swallowing dysfunction should be considered as one of the causes of exacerbation of respiratory illnesses. An upper gastrointestinal study can be used as a screening tool for identification of swallowing dysfunction, and the MBSS evaluates and provides therapeutic alternatives. AR