Salivary Gland Disease in Children

Introduction

Salivary gland disorders remain an uncommon entity in the pediatric population but are not infrequently seen in a pediatric otolaryngology practice. The differential diagnosis includes acute or chronic inflammatory and/or infectious conditions, congenital lesions, vascular malformations, benign or malignant tumors, traumatic injury, and many systemic diseases ( Box 24.1 ).

A good history and physical examination are extremely useful in diagnosing the specific salivary gland disorder. An algorithm for the evaluation of pathology in the parotid gland, the most common salivary gland affected in children, is illustrated in Figs. 24.1 and 24.2 . Ultrasound (US), computed tomography (CT), magnetic resonance imaging (MRI), and fine-needle aspiration biopsy (FNAB) have proved valuable for a more thorough evaluation of the nature and extent of salivary gland masses. Sialendoscopy has become an indispensable tool in the diagnosis of ductal pathology such as inflammation, stenosis, and stricture and is also valuable in the management of sialolithiasis and juvenile recurrent parotitis (JRP). A comprehensive understanding of salivary gland anatomy, physiology, and function remains essential for the diagnosis and treatment of salivary gland disorders.

Anatomy and Physiology

The three pairs of major salivary glands are the parotid, submandibular, and sublingual glands ( Fig. 24.3 ); there are also hundreds of minor salivary glands that are predominantly located in the palatine mucosa. All salivary glands are derivatives of ectoderm. During development, ectodermal rests pierce surrounding mesenchyme and arborize before terminating into multiple acini. Each salivary gland is an aggregate of multiple salivary secretory units composed of acini and ducts ( Fig. 24.4 ). Saliva produced by the secretory cells of the acini passes through intercalated, intralobular, and excretory ducts before collecting in the main excretory duct of the gland. The parotid gland consists mainly of serous acini that secrete a watery serous fluid. The submandibular gland is composed of a mixture of serous and mucinous acini, whereas the sublingual gland and minor salivary glands contain predominantly mucinous acini that secrete thick mucinous fluid. The primary saliva secreted is modified because it transits through the ductal system.

The parotid is the largest major salivary gland and is the first to develop in utero. Rarely, agenesis of the parotid and/or submandibular glands has been reported ( Fig. 24.5 ). ^, The parotid becomes encapsulated after development of the lymphatic system and is therefore the only salivary gland that contains lymph nodes. It lies between the external auditory canal, the ramus of the mandible, and the mastoid tip and is artificially divided by the facial nerve into a deep and a superficial lobe. It is separated by the stylomandibular ligament from the submandibular gland, and both glands are covered by the superficial portion of the deep cervical fascia. The parotid acinar units and ductal systems drain into a final secretory duct known as the Stensen duct. The latter arises from the anterior border of the parotid gland, courses superficial to the masseter muscle in a direction parallel and inferior to the zygoma, then turns sharply, pierces the buccinators, and enters the oral cavity opposite the second upper molar. Detached accessory parotid glands have been described, located at variable distances from the main gland along the Stensen duct in 21% of cadaver specimens. The Stensen duct is 4 to 7 cm in length and has a variable diameter along its length; histologic studies reveal a mean diameter ranging between 0.5 and 1.4 mm, a narrowing at the middle of the duct, and the smallest diameter at the ostium (0.5 mm).

Because the anatomic landmarks are not as well defined in infants and young children, the facial nerve is much more prone to injury during pediatric salivary gland surgery than that in adults. Before complete pneumatization of the mastoid air cells, the facial nerve takes a more abrupt and lateral course after exiting the stylomastoid foramen and can be found just deep to the subcutaneous tissue before entering the parotid gland. Because the parotid gland is not completely developed in children, the facial nerve may be more vulnerable to injury. Finally, the marginal mandibular branch of the facial nerve is located more superiorly in children compared with adults, often taking a superficial course over the mandible. It is only after the development of the mastoid tip and tympanic ring that the facial nerve takes a deeper and more protected position behind the mastoid bone and the tragal cartilage.

The submandibular and sublingual glands are small in young infants and are often anatomically contiguous. Rapid growth of these glands occurs during the first 2 years of life. The submandibular gland is located in the floor of the mouth and consists of a larger superficial part separated from a smaller deep part by the posterior free edge of the mylohyoid muscle. The superficial part rests between the anterior and posterior digastric muscles just below the body of the mandible and is bounded superomedially by the mylohyoid muscle and inferiorly by platysma and the investing layer of the deep cervical fascia. The deep part is located between the mylohyoid and the hyoglossus muscles. Acinar units and ductal systems drain into a single and final secretory duct known as the Wharton duct . The submandibular duct emerges from the medial deep part of the gland and runs anteriorly above the mylohyoid and on the lateral surface of the hyoglossus and genioglossus muscles. It is 5 cm long, has a mean diameter that ranges between 0.5 and 1.5 mm, and opens in the floor of the mouth through a papilla lateral to the tongue frenulum. Its minimum width (0.5 mm) is located at the ostium. The duct has an intricate relation with the lingual nerve (see Fig. 24.3 ). Posteriorly, the lingual nerve lies above the duct; then, as the nerve descends, it crosses the lateral side of the duct and passes below it, winding around its lower border before crossing it medially and ascending toward the genioglossus. The hypoglossal nerve is located anterior, deep, and medial to the submandibular gland. It also courses deep to the Wharton duct and to the digastric tendon.

The sublingual glands lack a capsule and are located in the floor of the mouth above the mylohyoid muscle in the space between the mandible and the genioglossus muscles, immediately below the oral mucosa. They drain directly via several small ducts (ducts of Rivinus) into the floor of the mouth; occasionally some of the ducts collect into a larger common duct known as the Bartholin duct, which empties into the Wharton duct. The sublingual glands are often the source of ranulas, which are mucus-filled swellings in the floor of the mouth.

The remaining upper aerodigestive tract is lined by hundreds of minor salivary glands that lie just deep to the mucosa. The highest concentration of minor glands is in the buccal, lingual, labial, and palatal regions. Each minor gland has a draining duct that opens directly into the mucosa. Occlusion of these ducts can lead to small mucoceles that are frequently found along the lower lip of young children.

Salivary flow is controlled via the autonomic nervous system. The parotid gland receives parasympathetic secretomotor innervation from preganglionic fibers that arise in the inferior salivatory nucleus of the medulla. These fibers travel with the ninth cranial nerve to exit the skull via the jugular foramen. They then leave the glossopharyngeal nerve as the Jacobson nerve and reenter the skull via the inferior tympanic canaliculus. The fibers pass through the middle ear space over the promontory of the cochlea (tympanic plexus) and exit the temporal bone as the lesser petrosal nerve. This nerve exits the middle cranial fossa through the foramen ovale, where the preganglionic fibers synapse in the otic ganglion. The postganglionic fibers travel with the auriculotemporal nerve to supply the parotid gland. The submandibular, sublingual, and minor salivary glands receive parasympathetic secretomotor innervation from preganglionic fibers, which originate in the superior salivatory nucleus in the pons. These fibers leave the brainstem as the nervus intermedius to join with the facial nerve. They then leave the facial nerve with the chorda tympani in the mastoid segment and travel through the middle ear and petrotympanic fissure to the infratemporal fossa. The presynaptic fibers are then carried by the lingual nerve, a branch of the mandibular division of the trigeminal nerve, to synapse in the submandibular ganglion. Postganglionic fibers innervate the submandibular and sublingual glands. Postganglionic sympathetic innervation of the major salivary glands is through the external carotid plexus, which originates from the superior cervical ganglion.

Frey syndrome, also known as gustatory flushing or auriculotemporal nerve syndrome, is characterized by facial skin flushing and sweating that classically occurs in response to gustatory or olfactory stimuli. Its postulated etiology is related to the abnormal regeneration of the parasympathetic fibers that normally innervate the parotid gland, because acetylcholine is the neurotransmitter for both sympathetic and parasympathetic fibers. The traumatized regenerated fibers aberrantly innervate the vessels and sweat glands of the overlying skin, which are normally supplied by sympathetic nerve fibers. In children, Frey syndrome can occur after any local trauma to the parotid area, such as vaginal delivery with forceps, postcondylar fracture or seizure, or parotid surgery or infection (herpes zoster). The latent time required for the development of this condition can vary from days to several years after the insult. Frey syndrome has also been described to occur in a familial pattern in the absence of a history of perinatal trauma. Most children do not require any treatment. In adolescents with severe symptoms, intradermal botulinum toxin injections are safe, effective, and well tolerated.

Saliva is a complex solution composed of mostly water (99%), electrolytes, proteins, and enzymes. The elements of saliva maintain moisture within the oral cavity, lubricate food, inhibit bacterial growth (lysozyme and immunoglobulin [Ig]), and begin the food digestion process (amylase). The amount of saliva secreted ranges between 0.5 and 1.5 L daily, depending on the size of the child. High bicarbonate ion content is responsible for its relatively alkaline pH of 7.4. Secretions from the parotid gland are mostly serous in nature, with a high water content and relatively lower mucin content. In contrast, the submandibular and sublingual gland secretions are mixed (mucous and serous), leading to a more viscous, mucin-rich saliva. Resting salivary secretions are produced predominantly by the submandibular glands (60% to 70% of total saliva). The parotid is the major contributor to stimulated saliva, and salivary flow increases with the sight and smell of food, with chewing and taste sensations, and with esophageal and gastric reflex–mediated responses. Parasympathetic postganglionic cholinergic nerve fibers stimulate the secretion of large amounts of a low-protein serous saliva. On the other hand, sympathetic stimulation of the salivary glands causes the secretion of a small and variable amount of thicker saliva, likely caused by contraction of the myoepithelial cells.

History and Physical Examination

A detailed history—including the onset, duration, severity, and frequency of symptoms—is crucial in the assessment of children with salivary gland disorders. Perinatal salivary gland swelling is more likely to be a congenital lesion, such as hemangioma or a lymphatic or vascular malformation. A gradual painless increase in size suggests a neoplasm, especially in older children. An acute onset of pain and swelling, especially with fever, indicates an inflammatory or infectious process. Ductal obstruction often presents with intermittent and recurrent postprandial swelling of the gland. Painless violaceous lesions of the skin are often seen with atypical mycobacterial infections, which typically affect the preauricular and submandibular areas. A history of cat exposure raises the possibility of cat-scratch disease (CSD), and exposure to sick contacts and vaccination history should be elicited to rule out mumps. The history should assess for the presence of other systemic conditions, and involvement of more than one gland may indicate systemic or autoimmune disease. A history of trauma suggests duct injury or disruption.

Physical examination should note the location, size, mobility, symmetry, tenderness, and consistency of the glands in addition to any overlying skin changes such as erythema, edema, dermal involvement, or presence of a fistula. A complete exam includes bimanual palpation performed with one hand externally and a gloved finger intraorally. The buccal mucosa, oral cavity, and floor of the mouth should be inspected, and the ducts should be palpated for the presence of stones. Signs of trauma related to oral appliances or cheek biting may point to the source of ductal obstruction. Massaging the gland while observing the saliva expressed from the ductal opening can be useful to rule out ductal blockage or to identify pus, therefore confirming the presence of an obstruction or an infection, respectively. Punctal edema with clear saliva is suggestive of viral sialadenitis.

Facial nerve function in all divisions, tongue mobility for hypoglossal nerve function, and general somatic sensation (fifth cranial nerve) should be documented. A salivary gland mass accompanied by facial nerve weakness is highly suspicious for a malignant process. In contrast to those in adults, solid lesions in children are more likely to be malignant; the larger the gland of origin in children, the more likely a tumor will be malignant. A good history and physical examination will guide the need for additional investigations such as laboratory studies and diagnostic imaging.

Evaluation