Diseases of the oral mucosa

Chapter 11 Diseases of the oral mucosa




















Introduction


Oral and maxillofacial pathology is the specialty of dentistry that is involved in the diagnosis and management of diseases of the oral mucosa and supporting bone and soft tissues, teeth, salivary glands, lip vermilion, and perioral skin. It would be impossible to discuss diseases affecting all of the above entities in one chapter. As such, this chapter is confined to common and uncommon mucosal lesions that are often seen and biopsied by the oral and maxillofacial surgeon, dermatologist or an otorhinolaryngologist. If a condition presents on the skin in addition to the mouth (such as pemphigus), only a brief mention of the oral manifestations is made since the topic will have been covered in detail elsewhere in this book.


From a histological perspective, the oral mucosa is divided into nonkeratinized and keratinized sites. The former include the labial mucosa (wet surface of the lip), buccal mucosa, maxillary and mandibular sulci (sometimes also called the ‘vestibule’), ventral tongue, floor of mouth, soft palate, nonattached gingiva and crevicular epithelium (Fig. 11.1). The crevicular epithelium is the continuation of marginal gingiva where it turns to face the tooth. Any keratin on these surfaces is considered abnormal and should be reported as such. The linea alba (‘bite line’) which is located on the buccal mucosa where the upper and lower teeth meet may be thinly parakeratinized and this is considered within the realm of normal (Fig. 11.2).




Keratinized sites include the hard palate mucosa, the attached gingiva (extending from the tooth for a band of 3–7 mm) and the tongue dorsum. The tongue is a specialized structure because of its role in taste sensation and has filiform, fungiform, and circumvallate papillae, the last two also containing taste buds (Fig. 11.3).



The oral mucosa consists of epithelium and underlying lamina propria that can be arbitrarily divided into superficial and deep portions, and underlying muscle or bone. Since there is no muscularis mucosa, there is no true submucosa. The epithelium of the oral mucosa is thickest on the tongue dorsum and thinnest on the floor of mouth and is generally two to four times thicker than the epidermis (Fig. 11.4). Pathologists not familiar with this feature tend to diagnose normal mucosa as acanthosis or psoriasiform hyperplasia. The attached gingiva and mucosa of the hard palate abut the periosteum so that the deep lamina propria appears densely fibrotic (Fig. 11.5). A diagnosis of ‘fibrosis’ is therefore inappropriate since this feature is normal for the site.




The tooth is composed of an outer highly calcified thin shell of enamel on the visible crown of the tooth; the non-visible portion within the bone is covered by cementum, which is similar in composition and appearance to bone. The bulk of the tooth consists of dentin and through the tooth runs the pulp containing fibrovascular and neural tissues (the source of most toothaches). Odontogenic epithelium is often seen within the gingival tissues and in odontogenic tumors in the gingiva. This consists of nests of squamous epithelium that may have clear cytoplasm and sometimes show palisading of the basal cell nuclei (Fig. 11.6).




Hereditary conditions



Macular lesions



White sponge nevus



Clinical features


White sponge nevus (Canon white sponge nevus, leukoedema exfoliativum mucosae oris, familial white folded dysplasia of mouth) is an autosomal dominant condition with high penetrance and variable expressivity. Onset is in early childhood with 50% of patients diagnosed before age 20.13 The buccal mucosa is almost invariably affected and other common sites are the labial mucosa, tongue, alveolar mucosa, and the floor of mouth. Nasal, esophageal, vaginal, anal, and penile mucosae may be involved, but not that of the conjunctiva, although there is one report of associated colobomas.4 Lesions appear as diffuse, white-to-gray, painless, spongy, folded plaques with a tendency to slough off (Fig. 11.7).2,5,6 There may be periods of exacerbation and remission.




Pathogenesis and histological features


White sponge nevus has been traced to a mutation in the helical domain of mucosal-specific keratins K4 (on chromosome 12q) and K13 (on chromosome 17q). The mutations are in the form of amino acid deletions, substitutions, and insertions resulting in keratin filament instability and abnormal aggregation of tonofilaments.79 Since some cases remit with antibiotic therapy, this suggests that infections and/or inflammation may play a role in the expression of disease.10,11


There is parakeratosis, acanthosis with the formation of large, blunt rete ridges, vacuolation of cells; anucleate keratinocytes are present superficially (Fig. 11.8). Dyskeratotic cells exhibit dense peri- and paranuclear eosinophilic condensations and there is insignificant inflammation (Fig. 11.9).5,12,13 Parakeratin plugs and streaks have been noted beneath the superficial keratinocytes. One case that exhibited foci of epidermolytic hyperkeratosis has been documented.14




The eosinophilic condensations correspond to tonofilament aggregates in a peri- and paranuclear location.1,12,13,15 Organelles tend to segregate and are absent in vacuolated cells. Odland bodies are abundant within keratinocytes but few are present in the intercellular spaces, suggesting a lack of acid phosphatase leading to retention, rather than normal shedding, of superficial cells.1



Hereditary benign intraepithelial dyskeratosis





Pachyonychia congenita



Clinical features


This rare genodermatosis is characterized by nail dystrophy, disorders of the palmoplantar skin and hair and leukoplakia; the larynx and eye may also be affected.1 The oral findings, usually noted within the first two decades of life, are characterized by focal or generalized white hyperkeratotic plaques on the dorsum and lateral borders of the tongue and buccal mucosa, and are present in 75–95% of cases.14 Natal teeth (teeth present at birth) are a common finding in the type 2 form of the disease.1,5,6





Darier’s disease



Clinical features


Oral findings occur in approximately 50% of patients with Darier’s disease (Darier-White disease, keratosis follicularis). Mild involvement comprises minute white or pink keratotic papules, while in more extensive disease coalescence results in larger plaques or a cobblestone surface. Lesions are generally asymptomatic.14 The palate is the most common site affected, perhaps because of its normally keratinized nature, followed by the gingiva, tongue, buccal mucosa, and floor of mouth. The lips are rarely involved.5 Recurrent parotid or submandibular swelling may be reported in up to approximately one-third of cases and is most likely the result of strictures in the main duct causing obstruction.4,5 In general, the degree of oral involvement parallels the extent of skin lesions.2,5





Warty dyskeratoma



Clinical features


This usually solitary lesion resembles Darier’s disease and may present as a papule or nodule (oral focal acantholytic dyskeratosis) in the oral cavity. It generally occurs in the fifth or sixth decade and almost always arises on the keratinized and attached mucosa of the palate or gingiva with a 2:1 female predominance.1 Most lesions measure less than 1 cm and rare cases develop on the buccal mucosa and tongue.24 Interestingly, the majority of cases occur on the left side of the mouth, raising the possibility that trauma plays an important role since most individuals are right-handed and may brush the left side of the mouth more vigorously. The papular variety appears as a white papule or plaque while the nodular variety has an umbilicated or crateriform appearance. There is an association with tobacco use.3,5



Histological features


Oral warty dyskeratoma is characterized by Darier’s disease-like features including suprabasilar clefting with lacunae formation, villous-like projections, corps ronds and grains.3 The papular lesions show multifocal involvement and sometimes papillary epithelial hyperplasia.6 There is no association with underlying sebaceous or salivary glands.




Tumor-like lesions



Choristomas





Sebaceous choristoma, hyperplasia and adenoma





Gastrointestinal choristoma



Clinical features

Almost all of these are cystic lesions that present as swellings of the tongue, usually on the ventral surface, or the floor of mouth.13 Sometimes they appear as sinuses.4 They are most often seen in infancy or early childhood and may be associated with orofacial malformations.3


Many theories of pathogenesis have been postulated including epithelial entrapment, incomplete coalescence of lacunae, and persistence of intestinal epithelial buds.4,5


The cystic lesions are lined by epithelium typical for the cardiac, fundic or pyloric regions of the stomach with parietal and Paneth cells.4 However, some are lined by colonic and/or ciliated epithelium.5 Smooth muscle is usually identified. The presence of pancreatic tissue has also been reported.6 If ectodermal and mesodermal elements are also present, the lesion should be considered a teratoma.





Epidermoid and dermoid cysts





Differential diagnosis


Gingival cyst of the adult is generally nonkeratinized and is lined by low cuboidal to columnar or stratified squamous epithelium, with occasional epithelial plaques and clear cells.8 Gingival cysts of the newborn, which are generally not biopsied because they exteriorize on their own, are filled with keratinaceous material.9 Both can be differentiated from epidermoid cysts by their location on the gingiva.



Dermoid tumor (dermoid), teratoma, and epignathus



Clinical features


These rare conditions generally present congenitally or in infancy as masses protruding from the mouth, causing respiratory distress and feeding difficulties. They have been classified as follows:





Of these, the dermoid is the most common.1


Dermoids tend to occur in females (six to seven times more often than in males) as pedunculated masses in the nasopharynx, oropharynx, and soft palate.2,3 The mass is covered by skin, hence its other name, ‘hairy polyp’. It may also grossly resemble an accessory auricle.4


Teratomas, teratoid tumors, and epignathi present as masses that may protrude from the mouth, and airway obstruction is a frequent presenting symptom; there is a female predilection and most are present at birth.5 Unlike dermoids, these tumors are often associated with other malformations and findings such as elevated alpha fetoprotein and polyhydramnios.6,7


Epignathi in particular may be associated with severe congenital malformations, and stillbirth is a common occurrence. They most often arise from the hard palate (hence its name), although the posterior nasopharynx and upper lip can be involved, and there may be palatal clefts and cranial extension.79 Grossly, the tumor sometimes contains rudimentary limbs, or even a head resembling an incomplete twin or fetus in fetu.10


Lingual (tongue) teratomas are generally not associated with such developmental defects.11




Oral lymphoepithelial cyst



Clinical features


Oral lymphoepithelial cysts generally occur in the fourth decade of life with an equal sex distribution.1,2 These also occur in the parotid gland in particular in HIV-positive individuals.3 They present as painless yellowish nodules, usually less than 1 cm in diameter, most commonly affecting the floor of mouth followed by the posterior ventral tongue, soft palate, and tonsillar fauces (Fig. 11.20).35 They are commonly filled with cheesy, keratinaceous material. Some authors consider lesions which present at sites where tonsillar tissue is normally found to be inflammatory/obstructive tonsillar reactions.4




Pathogenesis and histological features


Three theories of pathogenesis have been proposed:





The last theory pertains primarily to floor of mouth lesions, a site where tonsillar/lymphoid tissue is not normally found.


The cyst is lined by parakeratotic stratified squamous epithelium and the lumen is filled with desquamated keratinaceous material (Fig. 11.21).3,4,7 Rare cases may be lined by pseudostratified columnar epithelium with or without mucous cells.5 The epithelium usually demonstrates lymphocytic exocytosis (Fig. 11.22). The surrounding lymphoid tissue may encircle the cyst epithelium completely or partially, and germinal centers are usually well formed although not always present. Some cases demonstrate communication with the overlying surface epithelium, often through a narrow opening.




Salivary glands and ducts may be present in the vicinity, especially floor of mouth lesions.1,3




Lingual thyroid



Clinical features


Approximately 10% of cadaveric tongues contain nests of thyroid tissue, with no sex predilection.1,2 However, when thyroid tissue occurs as a mass in the tongue, the term ‘lingual thyroid choristoma’ or ‘ectopic lingual thyroid’ is used. Since approximately 86% of such tumors consist of the only thyroid tissue in the body, the terms ‘lingual thyroid ’or ‘ectopic lingual thyroid’ are more accurate.3


The lesion presents as a rounded, soft-to-firm mass within the base of the tongue between the foramen cecum and the epiglottis. It may cause dysphagia, dyspnea, dysphonia or hemorrhage.24 Females are three to seven times more likely to be affected than males and there are two peaks of presentation, i.e., the first and second decades and the fifth and sixth decades, probably related to hormonal influences;4,5 it is uncommon in children.6 One-quarter of patients may be hypothyroid.




Congenital granular cell tumor/epulis



Clinical features


The congenital granular cell tumor presents as a pink, pedunculated mass, usually on the anterior alveolar ridge with an intact surface (Fig. 11.23). There is a 10:1 female predilection and it is three times more common in the maxilla.1 It may cause problems with nursing. Approximately 9% of patients have multiple nodules and some may have concurrent tongue lesions.24



Jul 23, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Diseases of the oral mucosa
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