The Tongue
Library of Congress Cataloging-in-Publication Data
Names: Filippi, Andreas, editor. I Lindenmuller, Irene Hitz, editor.
Title: The tongue / [edited by] Andreas Filippi, Irene Hitz Lindenmuller.
Other titles: Zunge. English
Description: Batavia, IL : Quintessence Publishing Co, Inc, [2018] | Includes bibliographical references.
Identifiers: LCCN 2018033055 | ISBN 9780867157765 (hardcover) | eISBN 9780867159028
Subjects: | MESH: Tongue | Tongue Diseases | Atlases
Classification: LCC QL946 | NLM WI 17 | DDC 612.8/7--dc23
LC record available at https://lccn.loc.gov/2018033055
© 2019 Quintessence Publishing Co, Inc
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Editor: Marieke Zaffron
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Printed in the USA
CONTENTS
Foreword
Contributors
1.INTRODUCTION
Andreas Filippi
2.ANATOMY AND PHYSIOLOGY OF THE TONGUE
Ralf J. Radlanski
Parts of the tongue
Development of the tongue
Internal structure of the tongue
Lingual mucosa
Filiform papillae
Fungiform papillae
Foliate papillae
Circumvallate papillae
Innervation of the tongue
Clinically relevant relationships
3.NORMAL VARIATIONS
Andreas Filippi
4.DIAGNOSTICS
Inga Mollen, Irène Hitz Lindenmüller
History taking and clinical examination
Glass spatula test (diascopy)
Fungal diagnostics
Blood tests
Iron deficiency
Vitamin B12 deficiency
Folic acid (vitamin B9) deficiency
Zinc deficiency
Hba1c (long-term blood sugar level)
Antinuclear autoantibodies and rheumatoid factors
Anti-desmoglein 1 and 3 autoantibodies
Bullous pemphigoid 180 and 230
Cytodiagnostics (brush biopsy)
Autofluorescence
Toluidine blue
Conventional biopsy
Direct immunofluorescence
Conclusion
5.CHANGES TO THE TONGUE
Michael M. Bornstein, Andreas Filippi, Jörg Halter, Irène Hitz Lindenmüller, Peter Itin, Sebastian Kühl, J. Thomas Lambrecht, Inga Mollen, Adrian Ramseier, Andrea Maria Schmidt-Westhausen, Richard Steffen, Valérie G. A. Suter, Branka Tomljenovic, Astrid Truschnegg, Tuomas Waltimo, Brigitte Zimmerli
Addison disease
Anemia
Ankyloglossia
Aphthae
Betel consumption
Black hairy tongue
Caviar tongue
Cheilitis granulomatosa
Cowden syndrome
Crohn disease
Ehlers-Danlos syndrome
Erythroplakia
Fibroma and fibrous hyperplasia
Fissured tongue
Focal epithelial hyperplasia
Foreign body in the tongue
Geographic tongue
Graft-versus-host disease
Hand, foot, and mouth disease
Hemangioma/vascular malformation
Hereditary hemorrhagic telangiectasia
Herpes zoster
Herpetic gingivostomatitis
Hyperkeratosis
Impressions caused by orthodontic appliance
Infectious mononucleosis
Leukoplakia
Lichenoid reaction
Lingual tonsil hypertrophy
Lipoma
Lymphangioma
Macroglossia
Median rhomboid glossitis
Melkersson-Rosenthal syndrome
Morsicatio linguarum
Multiple endocrine neoplasia
Neuroma
Neutropenia
Oral candidiasis
Oral hairy leukoplakia
Oral lichen planus
Oral verruca vulgaris
Papilloma
Pemphigus vulgaris (PV) and bullous pemphigoid (BP)
Piercing scars
Pyogenic granuloma
Salivary gland cysts
Scarlet fever
Sjögren syndrome
Split tongue
Syphilis
Systemic amyloidosis
Systemic lupus erythematosus
Tongue carcinoma
Tongue piercing
Tongue pigmentation
Tongue tattoo
Ulcer
Varicella (chicken pox)
6.TREATMENT
Irène Hitz Lindenmüller, Inga Mollen
Choice of oral care products
Avoidance of habits
Protective splint
Dietary guidance
Tobacco and alcohol
Diagnosing metallurgic reactions
Splinter test
Intraoral corrosion measurement with EC-pen
Retinoids
Immunosuppressants
Corticosteroids
Calcineurin inhibitors (tacrolimus)
Antifungals
Dental adhesive paste
Laser
CO2 laser
Diode laser
FOREWORD
Dental practitioners, pediatricians, otorhinolaryngology specialists, general practitioners, and dermatologists as well as dental hygienists, dental nurses, and dental assistants regularly look into the oral cavity or throat of their patients. The largest organ within this field of vision is the tongue, about which all of these specialties have relatively little detailed knowledge. Dentists in particular see their patients’ tongues regularly during the course of routine dental check-ups, whereas an ear, nose, and throat specialist or general practitioner only gets to see the tongue when examination of their patient requires it. The tongue not only exhibits a multitude of normal variations and pathologic changes, but it tends to reflect the general medical, internist, diet-related, and mental state of our patients.
In training as well as in continuing professional development, relatively little attention has so far been paid to the tongue. This is evident in everyday clinical practice from uncertainties about visible or sometimes invisible changes to the tongue (eg, burning tongue) that occasionally crop up. The aim of this book is to shed light on the tongue from the perspective of current academic literature. It was written by several authors with experience in the diagnosis and treatment of changes to the tongue. This volume is not designed as a textbook but as an illustrated atlas and reference work that aims to give all the relevant professional groups greater certainty when diagnosing and treating tongue changes. A further aim is to communicate the latest knowledge to students of dentistry and medicine for the benefit of their eventual patients.
The first four chapters deal with the importance of the tongue in dentistry, the anatomy and morphology of the tongue, the normal variations of the tongue, and diagnosis of changes to the tongue. In the fifth chapter, numerous possible changes to the tongue are presented in the form of brief, standardized, easy-to-read tables containing the most important information and illustrated with a number of clinical photographs. Treatment is first summarized in the tables and then described in more detail in chapter 6. Of course, there are different schools of thought and approaches, especially in the treatment of oral pathologic changes.
Many tongue lesions or changes appear in several chapters either because there are smooth transitions between normal variations and pathology or because individual diseases involve increased diagnostic and therapeutic efforts and complexity. The literature citations in all chapters have generally been kept to a minimum.
Acknowledgments
We express our special thanks to everyone involved in producing this book: our coauthors Michael M. Bornstein, Jörg Halter, Peter Itin, Sebastian Kühl, J. Thomas Lambrecht, Inga Mollen, Ralf J. Radlanski, Adrian Ramseier, Andrea Maria Schmidt-Westhausen, Richard Steffen, Valérie G. A. Suter, Branka Tomljenovic, Astrid Truschnegg, Tuomas Waltimo and Brigitte Zimmerli, Nicolas Lienert and Nicola Feola (as ever, for the excellent cover illustration), Inga Mollen for her outstanding commitment to the compilation of this book, Christoph Langerweder, Chantal Pfammatter, Fabio Saccardin, Silvio Schütz, Caroline Signorelli-Moret, Angela Stillhard, Paco Weiss, Christian Zedler, Melanie Zimmerli, and Marco Züger for providing their photographs, Anita Hattenbach from Quintessenz-Verlag for her kind and highly professional editing work, Johannes Wolters from Quintessenz-Verlag for years of trusting and always pleasant cooperation (even though we rather exceeded the deadline this time), and last but not least our families, without whose patience it would not have been possible to produce this book alongside all our professional commitments.
CONTRIBUTORS
Michael M. Bornstein, Prof Dr med dent
Associate Professor
Department of Oral Surgery and Stomatology
Bern University
Bern, Switzerland
Clinical Professor
Oral and Maxillofacial Radiology Department
University of Hong Kong
Pokfulam, Hong Kong
Andreas Filippi, Prof Dr med dent
Department of Oral Surgery, Oral Radiology, and Oral Medicine
University Center for Dentistry
University of Basel
Basel, Switzerland
Jörg Halter, Dr med
Assistant Professor
Department of Hematology
University Hospital Basel
Basel, Switzerland
Irène Hitz Lindenmüller, Dr med dent
Department of Oral Surgery, Oral Radiology, and Oral Medicine
University Center for Dentistry
University of Basel
Basel, Switzerland
Peter Itin, Prof Dr Med
Professor and Chair
Department of Dermatology
University Hospital Basel
Basel, Switzerland
Sebastian Kühl, Prof Dr med dent
Assistant Professor
Department of Oral Surgery, Oral Radiology, and Oral Medicine
University Center for Dentistry
University of Basel
Basel, Switzerland
J. Thomas Lambrecht, Dr med, Prof Dr med dent
Professor and Chairman
Department of Oral Surgery, Oral Radiology, and Oral Medicine
University Center for Dentistry
University of Basel
Basel, Switzerland
Inga Mollen, Dr med dent
Center of Dental Traumatology
Department of Oral Surgery, Oral Radiology, and Oral Medicine
University Center for Dentistry
University of Basel
Basel, Switzerland
Ralf J. Radlanski, Dr med dent
Director
Department of Craniofacial Developmental Biology
Charité University Hospital Berlin
Berlin, Germany
Adrian Ramseier, Dr med, Dr med dent
Research Associate
Clinic for Preventive Dentistry and Oral Microbiology
University Center for Dentistry
University of Basel
Basel, Switzerland
Andrea Maria Schmidt-Westhausen, Dr med dent
Professor
Section of Oral Medicine, Dental Radiology, and Surgery
Charité University Hospital Berlin
Berlin, Germany
Richard Steffen, Dr med dent
Chief Physician
Department of Orthodontics and Pediatric Dentistry
Center for Dentistry
Zurich University
Zurich, Switzerland
Founder, Co-Owner, and Scientific Director
Medcem GmbH
Weinfelden, Switzerland
Valérie G. A. Suter, Dr med dent
Head of Dental Radiology and Stomatology
Department of Oral Surgery and Stomatology
Bern University
Bern, Switzerland
Branka Tomljenovic, Dr med dent
Department of Oral Surgery, Oral Radiology, and Oral Medicine
University Center for Dentistry Basel
Basel, Switzerland
Private Practice Brugg, Switzerland
Astrid Truschnegg, Dr med
Assistant Professor
Department of Dentistry and Oral Health
Medical University Graz
Graz, Austria
Tuomas Waltimo, Prof Dr odont
Head of Clinic for Preventive Dentistry and Oral Microbiology
University Center for Dentistry Basel
Basel, Switzerland
Brigitte Zimmerli, Dr med dent
Private Practice
Burgdorf, Switzerland
1
INTRODUCTION
Andreas Filippi
The tongue is by far the largest organ in the oral cavity. With its excellent innervation and mobility, it performs important functions for humans, such as touching, tasting, speaking, whistling, sucking, and cleaning the mouth. The tongue also fulfills an important role in mastication: It moves the food around in the mouth so that it can easily be chewed and lubricated with saliva. If one or more of these functions is restricted, quality of life is often greatly impaired. Many people suffering from advanced dysfunction or even complete loss of individual functions can also suffer from depression as a result. Articulation as well as the sense of touch and taste are so important to quality of life that patients who undergo radiotherapy to the head and neck area repeatedly report complaints. In addition to mucositis, they suffer severe impairment of their sense of taste (eg, things taste differently or blander than usual). In some cases, people develop aversions to particular foods and stop enjoying things that they used to like eating. Fortunately, these sensory disturbances usually go away after oncology treatment is finished.
The dorsal surface (ie, top) of the tongue is the only oral mucosa to have a microrough surface. This harbors more than half of all oral microorganisms, which live there in a highly organized biofilm that protects them against chemical and mechanical influences. Aerobes are more likely to be found on the surface and anaerobes in the depth of the tongue. The latter reside in the fissures of the strikingly rugged filiform papillae, which are only present on the dorsal surface of the tongue (Figs 1-1 and 1-2).
Fig 1-1 (a) The tongue surface is covered with filiform papillae. (b and c) As magnification increases, it becomes clear that the papillae are very rugged.
Fig 1-2 Difference between upper and lower surfaces of the tongue.
Treatment of the consequences of microbiologic diseases in the oral cavity (eg, caries, marginal periodontitis, apical periodontitis) is the most common type of work done in dental practices. Some causal microorganisms may reside on the teeth or in the sulcus or periodontal pockets, but a great many reside on the tongue. Even if great skill and effort is put into cleaning individual periodontal areas, this may not actually have a sustained impact on reinfection of the periodontium. Consider the current debate about the benefits of dental floss or the fact that the market introduces new toothbrushes each year that supposedly clean better than past toothbrushes. When it comes to caries prevention, clean teeth are only one consideration. In light of this growth of knowledge in prevention and therapy, modern medicine is fortunately focusing more and more on the largest site of oral microorganisms: the tongue. This is illustrated by examples such as full-mouth disinfection, modern halitosis treatment, and the idea of caries prevention by means of tongue cleaning. Furthermore, attempts are repeatedly being made to alter the oral biofilm (the largest of
which is located on the dorsal surface of the tongue) with the aid of probiotic medicines or probiotic foods to benefit oral health (Fig 1-3). There has been some success in relation to gut flora with certain changes or diseases, although attempts have not yet been successful in the oral cavity. However, in recent years there has been growing awareness of diagnostics of the tongue among dental practitioners and especially dental hygienists. This started with the extensive professional tongue diagnostics performed on halitosis patients, which is beyond the scope of this book but covered in other textbooks.3 Fundamentally, dentistry should not concentrate solely on the teeth. It is not without reason that universities in many countries have departments such as Oral Medicine, Oral Diagnostic Sciences, or Oral Health—a trend that should spread across the globe.
Fig 1-3 The largest oral biofilm is found on the tongue.
During a thorough dental examination, the borders, underside, and base of the tongue as well as the floor of the mouth should be inspected as a basic principle. If there are any visible or merely palpable changes, further diagnostic investigation should be discussed and—depending on the results—suitable treatment initiated. As well as visible and/or palpable changes, subjective complaints are playing a growing role in the aging population, who often require drug treatment in the general medical practice. The decrease in the saliva flow rate is a common problem that can lead to redness, inflammation, fungal infections, and a burning sensation of the tongue. This frequently demands an interdisciplinary approach to provide satisfactory help to patients whose quality of life is often impaired.
2
ANATOMY AND PHYSIOLOGY OF THE TONGUE
Ralf J. Radlanski
In its resting state when the mouth is closed, the tongue completely fills the oral cavity palatal to the rows of teeth (ie, the oral cavity proper). Because of its muscular core, the tongue is so variably mobile that the tip of the tongue is able to reach nearly every point in the mouth (Fig 2-1).1 Only a shortened lingual frenulum (ie, ankyloglossia) would limit this mobility.
Fig 2-1 The tongue in lateral view (a) and ventral view (b). (Reprinted with permission from Radlanski.1)
PARTS OF THE TONGUE
The median sulcus (ie, midline groove) divides the left and right half of the body of the tongue in the sagittal direction. The terminal sulcus runs in the transverse direction as a slightly V-shaped line (Fig 2-2) and divides the tongue into two parts. One part is the root or base, which lies in the pharynx. The second part comprises the body and tip, which lie within the oral cavity (Fig 2-3). The root accounts for roughly one-third of tongue volume, while the two anterior parts make up two thirds. The circumvallate papillae are on the body of the tongue, and the foramen cecum is located dorsally to the terminal sulcus (ie, on the root of the tongue).2–4
Fig 2-2 Macroscopic anatomy of the tongue in schematic diagram, cranial view.
Fig 2-3 Schematic diagram of the tongue in sagittal section.
DEVELOPMENT OF THE TONGUE
The pharyngeal arches have a major influence on the development of the face, including the tongue. The apex and body of the tongue develop from the first pharyngeal arch, and the root of the tongue develops from the third and fourth pharyngeal arches. The foramen cecum marks the endpoint of the thyroglossal duct and is evidence of the descent of the thyroid gland during the embryonic period of development.5
INTERNAL STRUCTURE OF THE TONGUE
The body of the tongue is permeated by intrinsic muscles that run in the sagittal, transverse, and vertical directions, partly interwoven with each other (Figs 2-4 to 2-6). The superior longitudinal muscle, the inferior longitudinal muscle, the genioglossus, and the geniohyoid muscles run sagittally; the transverse muscle runs transversally; and the vertical muscle runs vertically. Fasciae running in these directions appropriately compartmentalize the muscles. The lingual septum runs sagittally-vertically in the middle, and the lingual aponeurosis covers the dorsum of the tongue.3,4
Fig 2-4 Schematic diagram of the tongue in frontal section.
Fig 2-5 (a) Sagittal section through the tongue. Hematoxylin-eosin stain. (b) Tongue musculature cut longitudinally and transversally. (Reprinted with permission from Radlanski.1)
Fig 2-6 Sagittal section through the floor of the mouth region of the tongue and its intrinsic musculature. The epithelium on the underside of the tongue is free of papillae, smooth and thin, like the epithelium on the floor of the mouth. In the submucosa of the floor of the mouth, the sublingual gland and the excretory duct of the submandibular gland are cut. Hematoxylin-eosin stain. (Reprinted with permission from Radlanski.1)
The genioglossus, hyoglossus, palatoglossus, and styloglossus muscles radiate from outside into the tongue. Mediated by insertions of individual muscles onto the hyoid bone, these muscles afford support for tongue mobility. The lingual aponeurosis lies under the mucosa of the dorsum of the tongue (see Fig 2-3). The individual deforming movements of the body of the tongue that come from its intrinsic musculature are transmitted to the mucosa by the lingual aponeurosis.
LINGUAL MUCOSA
The epithelium on the dorsum of the tongue is keratinized. Underneath it is a relatively tough lamina propria that is rich in nerves and vessels. The high number of papillae (up to roughly 9,000) is characteristic of the dorsum of the tongue.2 These papillae are prominent in the connective tissue lamina propria and covered by the epithelium of the tongue. They are found in various different forms (Fig 2-7). Threadlike (ie, filiform) papillae are spread over the entire dorsum of the tongue. Mushroom-shaped (ie, fungiform) papillae are distributed at the apex and the border of the tongue, where they are interspersed with filiform papillae. Foliate papillae, whose leaves stand vertical, can be found at the posterior margin of the tongue in front of the terminal sulcus. On the dorsum shortly before the terminal sulcus, there are usually 8 to 10 wall-like circumvallate papillae that are arranged in a slight V-shape.
Fig 2-7 Schematic diagram of the regions of the tongue. Left: distribution of the types of papilla. Right: Although every taste bud can perceive all tastes, there are peak distributions of the different taste regions5 (Adapted with permission from Radlanski.1)
The filiform papillae enable sensations for the sense of touch, while sensations for temperature and taste are conveyed by the other papillae. For this purpose, the epithelium of the papillae contains taste buds, and each taste bud can have receptors for all of the taste sensations.6 Peak distributions of taste perception are concentrated on certain regions of the tongue and can also overlap (see Fig 2-7). Dorsally to the terminal sulcus, in the base of the tongue region, the mucosa is extremely rugged because lymphatic tissue dominates in the form of the lingual tonsil. The underside of the tongue (ventral surface) bears a smooth, thin, three-layered epithelium that lacks a stratum corneum. The mucosa resembles that on the floor of the mouth. The lamina propria is wider than on the dorsum and loosely connected to the fasciae of the musculature via connective tissue; there is no submucosa.
Filiform papillae
Filiform papillae are spread over the entire dorsal surface (see Fig 2-7). They follow the rims of connective tissue of the tongue that are lined up close together parallel to the terminal sulcus.7–10 These rims are often visible, running obliquely from the posterior to the border of the tongue; at the apex, they also run in the anterior direction.
The primary papilla bulges outward in the lamina propria, measuring 0.3 to 0.5 mm wide and 0.5 mm high (Fig 2-8). At its cranial edge, it may be divided into 10 to 30 secondary papillae.9,11 Per 1 square centimeter of dorsal surface, there are an average of 20 primary papillae with about 400 to 500 secondary papillae; their distribution is denser at the apex of the tongue.8,12 The papillae of the lamina propria are covered by an epithelium that is keratinized and contains numerous Langerhans cells and melanocytes. It is 0.8 to 0.9 mm thick at the apex, while epithelial thickness decreases to 0.2 to 0.3 mm toward the terminal sulcus.8,12 The thickness can diminish by another 30% in old age.1,13
Fig 2-8 Filiform papillae. Hematoxylin-eosin stain. Several secondary papillae emerge from one primary papilla. At the tips of the papillae, the keratinized oral epithelium projects as a fine-pointed cone.
The epithelium at the tip of the papilla mainly tapers threadlike to form a fine-pointed cone (see Fig 2-8). The tips of the papillae are often inclined toward the pharynx.8,12 The regrowth of epithelial cells pushes the epithelium further to the surface so the concentric shells appear to slide inside each other. A correspondingly high rate of division is found in the stratum basale, given a mitotic index of 2.2 (ie, the ratio of the dividing cells and the total number of cells observed). Therefore, more than half of the cells here are in the process of dividing.
Connective tissue contains ample collagenous and elastic fiber bundles, which are arranged primarily around vessel and nerve endings. The blood supply comes from the lingual artery, from which arterial capillary loops (15 µm) ultimately ascend in the secondary papillae and descend again as venous capillaries (25 µm).
The connective tissue is innervated from multiple sources. One source is complex-structured terminal organs, which are present as complex-structured terminal clusters of unmyelinated fibers. The connective tissue can also be innervated via lamellar-differentiated or minimally differentiated corpuscles or via tactile corpuscles (ie, Meissner corpuscles). In addition, there are free nerve endings that extend into the secondary papilla and terminate in the subepithelial tissue. They originate from unmyelinated branches and nerve fibers. From the side branches of these complex-structured terminal organs, epithelial nerve endings run into the region of the basement membrane or into the epithelium. These complex-structured sensory nerve endings are likely mechanosensors. Minute movements of the fine-pointed cones are mechanically conveyed as tension and compression into the connective tissue, where they are transmitted to nerve conduction. Minute particles or areas of roughness can be perceived when magnified by a factor of 1.6.14,15
Fungiform papillae
The fungiform papillae are visible macroscopically as round red spots on the tongue (Fig 2-9). They are less numerous than the filiform papillae, among which they are scattered. Per 1 square centimeter, there are about 90 papillae at the apex and roughly 45 in the middle of the tongue. The primary papilla can be up to 1 mm long and 0.5 to 0.9 mm wide. A few short secondary papillae project, mainly at the periphery of the fungiform dome.11,16 The papillae are covered by a keratinized epithelium, while the stem of the papillae and the epithelium between the papillae are nonkeratinized.11 The papillae contain a variable number of taste buds: Roughly half of them have no taste buds, a quarter exhibit one to three taste buds, and many have four or more.1,7 The taste buds are able to perceive the qualities of sweet, sour, salty, and bitter as well as water, fat, and umami (ie, meaty or savory).6,17 If several different taste buds are located on one papilla, as is usually the case, different taste sensations can be perceived on a single papilla. In addition to taste sensations, fungiform papillae can also perceive temperature and pressure because they also contain numerous lamellate mechanoreceptors and thermoreceptors as well as free nerve endings.16
Fig 2-9 Fungiform papillae. Mallory trichrome stain. Connective tissue primary papillae can be divided into secondary papillae, which are covered by oral epithelium. It is keratinized on the papilla and nonkeratinized between the papillae. Taste buds are located at the tip.
Foliate papillae
At the posterior margin of the tongue, 8 to 15 leaf-like folds of mucosa run vertically on either side roughly level with the palatoglossal arch. They are known as the foliate papillae (Fig 2-10). Their morphology is variable, which is why rather broad rims or nipple-like structures may be present instead of the leaf form. They may be entirely absent in old age.18,19 The excretory ducts of serous von Ebner’s (ie, gustatory) glands are located in the depth of the epithelial infoldings. The epithelium is parakeratinized or orthokeratinized; usually three upward connective tissue folds run within the epithelial folds.
Fig 2-10 Foliate papillae. (a) Overview. Hematoxylin-eosin stain. (b) Detail. The connective tissue papillae extend into the epithelial papillae. (Reprinted with permission from Radlanski.1)
Circumvallate papillae
There are 8 to 10 circumvallate papillae arranged in a slightly V-shaped line at the anterior edge of the terminal sulcus (Fig 2-11). They are the largest lingual papillae with a diameter of 2 to 3 mm and a height of approximately 1 mm. They are mostly round and surrounded by a deep trench or trough. The nature of the epithelium is orthokeratinized.20 Mainly abundant, short secondary papillae are to be found on the primary papillae under the smooth epithelial surface. Several taste buds, which are able to perceive the bitter taste sensation, are located in the lateral epithelial wall of the papilla. Numerous serous von Ebner’s glands are embedded in the lamina propria with excretory ducts at the base of the trenches.21
Fig 2-11 Circumvallate papillae. (a) Overview. (b) Detail. Hematoxylin-eosin stain. (Reprinted with permission from Radlanski.1)
INNERVATION OF THE TONGUE
Innervation of the tongue by various nerves is a consequence of combined development from the different pharyngeal arches. Motor innervation is provided by the hypoglossal nerve (CN XII). Sensory innervation of the lingual mucosa in the anterior two thirds is provided by the lingual and mandibular nerves (V3). The dorsal third (dorsal to the terminal sulcus) receives sensory innervation from the glossopharyngeal nerve (CN IX). Sensory innervation of the lingual mucosa comes from the lingual nerve for the anterior two thirds; taste sensation is conducted to the facial and intermediate nerves (CN VII) via the chorda tympani. The circumvallate and foliate papillae are supplied by CN IX. Parasympathetic innervation (eg, for the secretomotor function of salivary glands) is conducted in the anterior two thirds via the lingual nerve and the chorda tympani to CN VII. CN IX is responsible for the posterior third. Innervation seems to be significant to the development of the papillae if it follows a structurally correct course.22
CLINICALLY RELEVANT RELATIONSHIPS
In view of such a complex structure of the lingual mucosa, variations from normal anatomy and microanatomy can be expected. These variations may not have any pathologic relevance. There can be diseases that are confined to the tongue, and the tongue may also serve as an indicator of general medical conditions. Possible morphologic changes to the fine structure of the lingual mucosa—such as fluid content, firmness of the tissue, swelling, atrophy, and blood flow—are macroscopically visible and enable conclusions to be drawn about the general condition of the body.
The proximity of the tongue to the teeth can have macroscopically visible repercussions on the tongue. For instance, tooth impressions may become visible on the edges of the tongue if the tongue is habitually pressed against the dentition. These changes are usually rapidly compensated for by contraction of the lingual muscles; however, if the tongue is interocclusally interposed, rather permanent bite traumas may remain visible.
The dorsum of the tongue has a relatively rugged surface. The threads of papillae, the edges around the papillae (especially the circumvallate papillae), and the lingual tonsil located in the dorsal third of the tongue offer surfaces onto which a coating can be deposited; this coating consists of food remnants, epithelial rests, and saliva, which can be colonized by bacteria and fungi. Halitosis (ie, bad breath) may develop as a result of the metabolic products formed in the tongue coating. This is why regular tongue cleaning is a preventive measure for avoiding halitosis.
The filiform papillae can also undergo hypertrophy, in which case it is called hairy tongue (lingua villosa). A dark green, brown, or black coloring may be present, depending on the color absorbed as a result of diet or the metabolism of local bacteria. Antibiotics, corticosteroids, and tobacco smoking are potential causes. The use of mouthwashes can also lead to a hairy tongue. Administration of antibiotics encourages colonization of the tongue by Candida spp because of changes to the ecological equilibrium in the oral cavity. The mucosa on the dorsal surface can exhibit map-like changes that are known as geographic tongue. These are chronic inflammatory changes to the tongue that are visible in the form of locally variable, migrating desquamation of filiform papillae. In the region of the foramen cecum, an oval to mesiodistally elongated papilla-free region is noticeable that is known as median rhomboid glossitis. Lingual fissures can occur increasingly in old age but in themselves should not be seen as pathologic. However, they can cause an unpleasant feeling such as burning of the tongue in the fissured area.
There may be clearly visible changes to the lingual papillae due to nutritional deficiencies. In the case of B vitamin deficiency (pernicious anemia due to vitamin B12 deficiency), there is initially edematous enlargement of the fungiform papillae, and the tongue looks as if it is coated with fine pebbles. If the edematous swelling is more severe, the dentition creates impressions on the border of the tongue. Subsequently, after hypertrophy of the papillae, flattening, coalescence, and finally atrophy of the papillae are observed. If the filiform papillae atrophy, a purple-magenta-colored tongue predominates. A tongue without papillae is known as mirror tongue. In autoimmune dermatoses such as pemphigus vulgaris, destruction of the stock of papillae in the ulcerated region is observed. Endocrine influences such as menopause lead to the sensation of a dry tongue, often combined with glossitis. Scarlet fever, an infectious disease caused by streptococci, initially results in a whitish-grey, furry coating on the tongue through which the fungiform papillae emerge bright red, giving the impression of strawberry tongue. In angioneurotic edema, which can occur as an allergic reaction or as a side effect of pharmaceuticals, the tongue swells up until it causes life-threatening blockage of the pharynx.
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