Cysts of the Oral and Para-oral Region PDF

Chapter 3 Cysts of the Oral and Para-oral Region Chapter ILOs: 1. Define cyst and pseudocyst. 2. Identify pathogenesis and histogenesis of cysts. 3. Classify different types of cysts. 4. Recognize clinical features, histopathology, radiographic picture and behavior...

Chapter 3 Cysts of the Oral and Para-oral Region Chapter ILOs: 1. Define cyst and pseudocyst. 2. Identify pathogenesis and histogenesis of cysts. 3. Classify different types of cysts. 4. Recognize clinical features, histopathology, radiographic picture and behavior of odontogenic cysts. 5. Recognize clinical features, histopathology, radiographic picture and behavior of non-odontogenic cysts. 0  Cysts of the Oral and Paraoral Region Cysts of the Oral and Para-oral Region Definition: A cyst is a pathological cavity lined with epithelium and having fluid or semi-solid contents occurring in either hard or soft tissues. Some cysts may not be epithelial-lined and therefore are not true cysts and termed: Pseudocysts. Cysts are more common in the jaws than in any other bone because of the many epithelial rests remaining in the tissues after dental development. Classification: I- Odontogenic cysts: These arise from odontogenic epithelial remnants associated with the development of teeth. A. Periodontal cysts 1- Inflammatory: i. Apical (radicular), lateral and residual cysts ii. Inflammatory Collateral Cysts: Paradental and Mandibular buccal bifurcation cysts 2- Developmental: i. Lateral developmental cyst ii. Botryoid odontogenic cyst iii. Gingival cyst of adults iv. Gingival cyst of newborn (Dental lamina cyst of Newborn/Bohn's nodules) B. Dentigerous cyst: (Central, lateral, circumferential); cysts of eruption. C. Odontogenic keratocyst D. Orthokeratinized Odontogenic cyst 1  Cysts of the Oral and Paraoral Region E. Calcifying odontogenic cyst (COC, Gorlin's cyst). II- Non-Odontogenic cysts: A- Cysts of vestigial ducts Nasopalatine tract Cysts: i.Incisive Canal Cyst ii.Cyst of palatine papilla B- Fissural Cysts: 1- Median Cysts: In the maxilla: Median palatal cyst In the mandible: Median mandibular cyst 2- Globulomaxillary cyst 3- Nasolabial cyst III- Pseudocysts: A. Simple bone cyst B. Aneurysmal bone cyst C. Static bone cyst IV- Soft tissue cysts of the floor of mouth and neck: A. Dermoid and epidermoid cysts. B. Thyroglossal tract cyst. C. Cervical lymphoepithelial cyst (Branchial cleft cyst). D. Mucous retention, mucous extravasation cysts and Ranula I- Odontogenic Cysts Odontogenic cysts affect the tooth-bearing region of the jaws. The epithelium associated with odontogenic cysts is derived from one of the following sources: 1. Enamel organ. 2. Reduced enamel epithelium. 3. Epithelial rests of Malassez. 2  Cysts of the Oral and Paraoral Region 4. Remnants of the dental lamina (epithelial rests of Serre’s). A- Periodontal cysts I- Inflammatory periodontal cyst Etiology: This cyst is the most common odontogenic cyst and represents 65% of all cysts. It results from inflammatory hyperplasia of the epithelial rests of Malassez in the periodontal ligament following death of the pulp. Periapical cysts usually develop from a preexisting periapical granuloma. Stimulation is caused by the inflammatory process within the granuloma. Classification: It is classified as follows: a) Apical or Periapical cyst: These are the cysts which are present at root apex. b) Lateral radicular cyst: These are the cysts which are present at the opening of lateral accessory root canals of offending a tooth. c) Residual cyst: These are the radicular cysts that remain even after extraction of the offending tooth. Pathogenesis: Pathogenesis of radicular cyst can be summarized into three phases: 1- Phase of initiation: It is generally agreed that the epithelial lining of these cysts is derived from epithelial cell rests of Malassez in periodontal ligaments. The mechanism of stimulation of epithelial cells may be due to inflammation in periapical granuloma or some products of dead pulp, which may initiate the process and at the same time it evokes an inflammatory reaction. 2- Phase of Cyst Formation It is a process by which a cavity becomes lined by proliferating epithelium. The most widely accepted theory suggests that the initial 3  Cysts of the Oral and Paraoral Region reaction leading to cyst formation is a proliferation of epithelial rests in periapical area involved by granuloma. This proliferation continues and the epithelial mass increases in size. The dividing cells are that of the periphery, corresponding to the basal layer of surface epithelium. The cells of the central portion of mass become separated further and further from nutrition so they fail to obtain sufficient nutrition. The central cells eventually degenerate, becoming necrotic and liquify. This creates an epithelium-lined cavity filled with fluid. 3- Phase of Cyst Enlargement Experimental work provided evidence that osmosis contributes in increasing the cyst’s size. Remnants of cellular debris are found within the cyst lumen, producing an increase in osmotic pressure of the cystic fluid, as a result of the breakdown of complex tissue proteins into a larger number of molecules of more simple proteins. The result is fluid transport across the epithelial lining and connective tissue, that act as a semi-permeable membrane, in an attempt to equalize the osmotic pressure; and so, enlargement occurs. This growth stimulates osteoclastic bone resorption thus enlarging the bony cavity and allowing further expansion of the cyst. Osteoclastic bone resorption is also stimulated by bone resorbing factors from the inflammatory cells and cellular elements within the peripheral portion of the lesion. a- Apical (periapical, radicular) Clinical Features: Age: Adult life (third to the sixth decades). Sex: More frequent in men. Site: Maxilla especially the anterior region. Most radicular cysts are asymptomatic and are discovered during routine dental radiographic examination. As they enlarge they cause slowly 4  Cysts of the Oral and Paraoral Region progressive painless swellings often on the labial or buccal side. If infection occurs, the swelling becomes painful and may rapidly increase in size secondary to inflammatory edema. The swelling is rounded and at first hard. Later, when bone has been reduced to eggshell thickness, a crackling sensation may be felt on pressure. Finally, part of the overlying bone is resorbed entirely, leaving a soft fluctuant swelling, bluish in color, beneath the mucosa. The tooth related to the periapical cyst is usually a non-vital tooth. Radiographically: Round or ovoid well-defined radiolucency surrounded by a narrow radio-opaque margin. The radio-opaque margin may not be apparent if the cyst is actively enlarging. The cyst ranges from 5mm to several centimeters in diameter. The dead tooth, from which the cyst has arisen, often has a large carious cavity or a filling. Root resorption of the offending tooth or adjacent teeth may be noted. Infection of a cyst causes the outline to become hazy. Distinction between a small radicular cyst and a periapical granuloma radio-graphically is difficult. 5  Cysts of the Oral and Paraoral Region Periapical Cyst. Well- Periapical Cyst. circumscribed radiolucency Radiolucency associated associated with the apex of with the maxillary central the mandibular central incisor, with significant root incisor. (1) resorption. (1) Histopathologic Features: Epithelial lining: The epithelial lining of apical periodontal cysts is usually a stratified squamous epithelium. In a newly formed cyst, the epithelium is hyperplastic, showing acanthosis (20 cell layers) with over vascularized connective tissue and many inflammatory cells are seen in the connective tissue. In fully formed, old cysts, the epithelial lining becomes more regular and flattened as inflammation decreases and the connective tissue contains few inflammatory cells. In case of intense inflammation, the epithelial lining of the cyst may be discontinuous and is frequently missing over these areas. 6  Cysts of the Oral and Paraoral Region Connective tissue: The underlying connective tissue is composed of parallel bundles of collagen fibers with variable numbers of fibroblasts and capillaries. Inflammatory cell infiltration is also present. Towards the epithelium, polymorphonuclear leucocytes predominate. Deeper within the connective tissue lymphocytes are more common. In the connective tissue wall of the cyst, foci of dystrophic calcification, cholesterol clefts and enlarged blood vessels may be found. Degenerated plasma cells may be present and are known as Russel bodies. Multinucleated foreign-body giant cells may frequently be seen close to cholesterol clefts and hemosiderin within the connective tissue wall. Occasionally a mass of cholesterol erodes through the lining epithelium and is extruded into the cyst lumen. The source of cholesterol seems to be due to local tissue damage. Collection of lipid-filled macrophages (foam cells) are present. Cyst Lumen The lumen of the cyst usually contains fluid, which stains eosinophilic. Sometimes the lumen may contain cholesterol in great amounts. Chemically, cystic fluid contains serum albumin, globulin, cholesterol and nucleoproteins. 7  Cysts of the Oral and Paraoral Region Periapical Cyst. Cyst lined by stratified squamous epithelium. Note connective tissue wall, which contains a chronic inflammatory infiltrate and numerous cholesterol clefts. (1) Differential Diagnosis: Periapical granuloma if the radiolucency is small. Periapical scar or surgical defect in areas of previously treated. Early phase of periapical cemental dysplasia in anterior mandibular area, but related teeth are usually vital. Microscopic Variations in Cyst Walls: Pseudo-stratified ciliated columnar epithelium. This may be seen in periapical cysts of maxillary teeth, which involve the maxillary sinus. Dystrophic calcification as haematoxyphilic-calcified deposits may be found in the epithelium and connective tissue. Keratinized lining (para-or orthokeratin). Hyaline bodies or Rushton bodies may be found within the epithelial lining; (Thin, linear, curved bodies, amorphous in structure, eosinophilic in reaction). The origin of such bodies is controversial. Some believe that they are of haematogenous origin 8  Cysts of the Oral and Paraoral Region arising from thrombus formation in small capillaries, being formed chiefly from their red blood cells as a rouleaux phenomenon. Others believe that they have an odontogenic origin. Periapical Cyst. Squamous epithelial cyst lining exhibiting numerous irregular and curvilinear Rushton bodies. (1) Treatment: If the cyst is small, enucleation of the cyst and apicectomy of the involved tooth. If the cyst is medium size, remove the tooth and enucleate the cyst. Large cysts need marsupialization to avoid the antrum or important structures as the inferior dental nerve. Larger cysts need enucleation and bone chips to fill the cavity. b- Inflammatory Lateral Periodontal Cysts Inflammatory lateral periodontal cysts are less common than periapical ones. They form along the lateral aspect of the root of a pulpless tooth as a result of opening of a lateral root canal and irritation of periodontal tissue. 9  Cysts of the Oral and Paraoral Region Lateral Inflammatory Cyst. Inverted pear-shaped radiolucency between the maxillary lateral incisor and cuspid (arrow). The lateral incisor ultimately proved to be nonvital. (1) Lateral Inflammatory Cyst. A rounded radiolucency between bicuspid and first molar extending laterally from the mesial root of the first molar (Courtesy of Dr. Carroll Gallagher). (1) c- Residual Cyst The pulpless tooth from which a periapical cyst has arisen may be extracted and the cyst may persist in the jawbone. It's one of the most common causes of swelling of the edentulous jaw. Residual cysts may cause trouble by interfering with the fitness of dentures, and sometimes enlarge to the extent of weakening the jaw with possible risk of jaw fracture. 10  Cysts of the Oral and Paraoral Region Residual Periapical Cyst. Well-circumscribed radiolucency of the maxilla at the site of previous tooth extraction. (1) II-Inflammatory Collateral Cysts: Odontogenic cysts located on the buccal or distal aspect of a tooth, usually a mandibular molar. It has two main types: a) A paradental cyst arises on the distal surface of a partially erupted lower third molar. Usually associated with a history of long standing pericoronitis, with associated symptoms of pain, swelling, trismus. The associated tooth is vital. Radiographic Features: Well-circumscribed radiolucent area on the distal side of a partially erupted lower third molar. b) Mandibular buccal bifurcation cyst arises subgingivally on the buccal aspect of lower first or second molars. Presents as a painless swelling, but infection can result in pain and suppuration. The tooth is usually tilted buccally, with deep periodontal pockets. Cyst formation may be exacerbated by a down-growth of enamel on the buccal aspect of the involved tooth or by food impaction. 11  Cysts of the Oral and Paraoral Region Radiographic Features: Well-demarcated buccal radiolucency, which may extend to the lower border of the mandible. A periosteal reaction with laminated new bone formation may be visible. Buccal Bifurcation Cyst: Axial computed tomography (CT) image showing a circumscribed radiolucency buccal to the roots of the mandibular first molar (Courtesy of Dr. Robert Clark). (1) Histopathologic Features: Not specific and is indistinguishable from that of a radicular cyst. The Inflammatory collateral cyst is lined by a hyperplastic layer of nonkeratinized stratified squamous epithelium. Cholesterol clefts and foamy macrophages may be seen in the cyst wall. The lining may be attached at the cementoenamel junction or be continuous with the epithelium of the peri-coronal tissues, forming an invagination or pocket protruding down the root of the tooth. 12  Cysts of the Oral and Paraoral Region 2- Developmental Periodontal Cysts: i. Developmental lateral Periodontal Cyst: Definition: A non-inflammatory developmental cyst that occurs adjacent or lateral to the root of a vital tooth. Etiology: The origin is related to proliferation of rests of odontogenic epithelium at the lateral side of the root of adjacent vital tooth (the cause of the epithelial proliferation is unknown and not due to an inflammatory process). Clinical features: Age: Any age, most common age from 40 to 60 years. Sex: Male to female ratio 2:1. Site: In the mandibular premolar and canine region. In the maxilla the lateral incisor region is a common site. Appearance: It often presents no signs or symptoms and may be discovered during routine radiographic examination of the related tooth. Occasionally, when the cyst is located on the labial surface of the root, there may be a slight bulge, although the overlying mucosa is normal. The related tooth is vital. If the cyst becomes infected, its signs and symptoms may resemble those of a lateral periodontal abscess. Radiographic features: Lateral developmental periodontal cyst appears as a radiolucent area. Small, seldom over 1cm in diameter. May or may not be well circumscribed with an opaque margin. 13  Cysts of the Oral and Paraoral Region Lateral developmental Cyst. Radiolucent lesion between the roots of the vital mandibular canine and first premolar. (1) Histopathologic Features: The cystic cavity is lined by stratified squamous epithelium which is thin and composed of one or two layers of cells. Some cysts show focal nodular thickenings of the lining epithelium. These often have a whorled appearance and the cells may have clear cytoplasm and small deeply staining nuclei due to accumulation of glycogen. Parakeratin or orthokeratin formation by the epithelial lining. Inflammatory cells may be present in the connective tissue wall but this is a secondary reaction when the cyst becomes infected. 14  Cysts of the Oral and Paraoral Region A A: This photomicrograph shows a thin epithelial lining with focal nodular thickenings. (1) B B: These thickenings often show a swirling appearance of the cells. (1) iii. Botryoid odontogenic cyst Definition: A developmental odontogenic cyst lined by non-keratinized epithelium, occurring on the lateral aspect or between the roots of erupted teeth. It is the multicystic variant of the developmental lateral periodontal cyst. The word Botryoid comes from Greek botruoeidēs, meaning ‘bunch of grapes. Gross specimen of a botryoid odontogenic cyst. Microscopically, this grapelike cluster revealed three separate cavities. (1) Etiology: It is believed to arise from rests of the dental lamina, reduced enamel epithelium, or rests of Malassez. 15  Cysts of the Oral and Paraoral Region Clinical Features: Age: Any age, commonly 50-60 years. Sex: Slight male predilection. Appearance: Well-circumscribed painless swelling of the bone. It occurs mostly in the mandibular premolar area. Radiographic features: Appears as a multilocular radiolucent area, lateral to the root surface of a tooth. Well-demarcated and often exhibits a corticated margin. Histopathology: It is lobulated, each lobule is lined by thin stratified squamous epithelium, which contains areas of thickenings “plaques”. The lining may contain cells with clear cytoplasm due to accumulation of glycogen. The lobulations are separated by thin fibrous septa. Botryoid odontogenic cyst showing multiple cystic spaces lined with thin epithelium with nodular thickenings. (2) Treatment: Enucleation. Due to the high potential of incomplete removal, it has a high recurrence rate. 16  Cysts of the Oral and Paraoral Region iii. Developmental Gingival Cyst of Adulthood Def.: A non-inflammatory developmental cyst occurring adjacent to a vital tooth, at the gingiva. It is considered to be the soft tissue counterpart of the lateral developmental cyst. Etiology: Gingival cyst arises from remnants of dental lamina in the soft tissue (epithelial rests of Serre’s). Clinical Features: Age: Any age, commonly 40-60 years. Sex: Males and females are almost equally affected. Appearance: The gingival cyst appears as a small, well-circumscribed painless swelling of the gingiva, less than 1cm in diameter. It may involve the free or attached gingiva and sometimes the gingival papilla itself. The lesion has the same color as the adjacent normal mucosa but sometimes larger lesions erode the underlying bone and assume a slightly bluish discoloration. Radiographic Features: Gingival cyst of the adult is a soft tissue lesion and does not manifest itself on dental x-ray films (negative). Histopathologic Features: Gingival cysts show epithelial lined cavity; the epithelium is very thin, flattened stratified squamous epithelium. In most cases, it has a non- keratinized epithelium, but occasionally, some keratin formation may be seen. 17  Cysts of the Oral and Paraoral Region Gingival Cyst of the Adult. Low-power photomicrograph showing a thin-walled cyst in the gingival soft tissue. (1) v. Gingival Cyst of the Newborn Bohn’s nodules The preferred name for that cyst is “Dental Lamina Cyst of Newborn” because gingiva is a structure related to teeth, which are not present in newborns. These are multiple white nodules of not more than a few millimeters in diameter on the alveolar ridge of a newly born infant. They originate from remnants of the dental lamina which proliferate to form small cysts. These lesions appear to be asymptomatic. In most cases these cysts degenerate, rupture and resolve spontaneously. Histopathologic Features: Thin epithelial lining usually two or three layers thick and the lumen is usually filled with desquamated keratin. 18  Cysts of the Oral and Paraoral Region Treatment: No treatment, cysts will usually fuse with the overlying oral epithelium and discharge their contents in the oral cavity during the neonatal period. B-Dentigerous Cyst (Follicular cysts) The term "dentigerous" means containing tooth. The term follicular was given as the cyst surrounds the crown of the unerupted tooth. The cyst is attached to the neck of the tooth. It represents 15-17% of all cysts of the jaws. Etiology: It originates through cystic change of the reduced enamel epithelium, after complete formation of enamel of the tooth, with accumulation of fluid between the reduced enamel epithelium and the tooth crown. The cyst appears to form between the layers of the reduced enamel epithelium; the layer which remains attached to the surface of the enamel is usually of negligible thickness and may partially degenerate. The attachment of the cyst lining at the amelocemental junction suggests this origin. The cause of the development of dentigerous cyst is not known. However, there is a strong association between failure of eruption of teeth and formation of dentigerous cysts. It is not merely that a dentigerous cyst may prevent a tooth from erupting. Expansion of the dentigerous cyst is related to a secondary increase in cystic fluid osmolarity as a result of degeneration of desquamated epithelial cells into the cyst lumen. The mitotic index for dentigerous cyst is low in comparison with Odontogenic keratocyst. 19  Cysts of the Oral and Paraoral Region Clinical Features: Age: Highest incidence second and third decades. Sex: More common in males. Site: More in mandibular third molar and maxillary canine areas, it may involve a supernumerary tooth or an odontome. Uncomplicated dentigerous cysts cause no symptoms and may be discovered accidentally. As the cyst grows within bone, it causes both resorption and expansion of bone with subsequent facial asymmetry. Displacement of teeth and resorption of roots of adjacent teeth is usually seen. If a dentigerous cyst becomes infected, there is pain and increased swelling. Radiographic Features: Well defined, unilocular radiolucency in association with the crown of an unerupted tooth, sometimes the radiolucent area is surrounded by a thin sclerotic line. An affected lower molar may be displaced to the lower border of the mandible or higher up into the ascending ramus. Root resorption of adjacent erupted teeth can occur. The cyst-crown relationship shows several radiographic variations: 1- In the central variant, which is the most common, the cyst surrounds the crown of the tooth and the crown projects into the cyst. 2- The lateral variant is usually associated with the mesioangular impacted mandibular third molars that are partially erupted. The cyst grows laterally along the root surface and partially surrounds the crown. 3- In the circumferential variant, the cyst surrounds the crown and extends for some distance along the root so that a significant portion of the root appears to lie within the cyst. 20  Cysts of the Oral and Paraoral Region Dentigerous Cyst. Central type showing the crown projecting into the cystic cavity (Courtesy of Dr. Stephen E. Irwin.). (1) Histopathologic Features: The cyst is lined by a thin regular non- keratinized stratified squamous epithelium attached to the tooth at the cementoenamel junction, in an uninflamed cyst the epithelial lining is about 2-4 cell layers thick. The epithelium-connective tissue junction is flat, and when inflammation or secondary infection occurs epithelial hyperplasia with rete pegs formation may be noted. Focal areas of mucous cells may be found in the epithelial lining of dentigerous cyst. In maxillary cysts, ciliated epithelium and hyaline bodies may be seen. The epithelium may sometimes be keratinized. The connective tissue wall of the cyst is rich in glycopoteins and mucoploysaccharides. Inflammatory cells are absent. Clefts from cholesterol may be occasionally found in the connective tissue capsule. Foreign body giant cells may be seen in close relation to the cholesterol clefts. 21  Cysts of the Oral and Paraoral Region Dentigerous Cyst. Central type showing the crown projecting into the cystic cavity (Courtesy of Dr. Stephen E. Irwin). (1) Dentigerous Cyst. Scattered mucous cells can be seen within the epithelial lining. (1) Cyst Contents: Yellowish fluid cholesterol crystals if the cyst is acutely infected the fluid may be purulent. Differential Diagnosis: 1- Unilocular ameloblastoma. 2- Odontogenic keratocyst. 3- Adenomatoid odontogenic tumor. 4- Ameloblastic fibroma. Treatment: 1- Removal of the associated tooth and enucleation of the cyst. 22  Cysts of the Oral and Paraoral Region 2- Very large cysts of the mandible may need marsupialization to allow for decompression and shrinkage of the bony defect. Complications: 1- Neoplastic transformation into an ameloblastoma. 2- Squamous cell carcinoma may arise in the lining of a dentigerous cyst. 3- Intraosseous mucoepidermoid carcinoma may develop from mucous cells in the lining of a dentigerous cyst. 4- Destruction of a large area of the jaw with possible fracture. Eruption Cyst It is an uncommon superficial dentigerous cyst. It occurs in the soft tissue of the gum over a tooth about to erupt. It is a dilatation of the normal follicular space above the crown of an erupting tooth caused by accumulation of tissue fluid or blood. Clinically: Age: Children, deciduous teeth or permanent molars i.e. with no predecessors. Site: Gum overlying the unerupted tooth. Shape: Soft rounded swelling if blood is present in the cystic space, the swelling appears deep blue & hence the term "Eruption haematoma". Eruption Cyst. This soft tissue swelling contains considerable blood and can also be designated as an eruption hematoma. (1) 23  Cysts of the Oral and Paraoral Region Treatment: Not needed because during tooth eruption, the cyst will disappear spontaneously. If the tooth cannot erupt the tissue overlying the crown may be removed to allow the tooth to erupt. C- Odontogenic Keratocyst The odontogenic keratocyst is an odontogenic cyst characterized by a thin regular lining of parakeratinized stratified squamous epithelium with palisading hyperchromatic basal cells. Therefore, although keratinization may be present in many other types of cysts; like: dentigerous, developmental lateral periodontal, radicular and residual cysts, the specific histological pattern of the odontogenic keratocyst separates it from all others. Etiology: Cysts which arise in an area without any missing teeth develop from supernumerary tooth germs or rests of the dental lamina. Clinical Features: Least common type of odontogenic cysts (7%). Age: Second and third decades. Sex: No sex predilection. Site: Common in the mandible posterior portion. Usually remains symptomless unless it becomes infected; it may produce paraesthesia of the lower lip, pain and swelling of the jaws, displacement of teeth of the involved area. Odontogenic Keratocysts tend to grow in an anteroposterior direction within the medullary cavity of the bone without causing obvious bone expansion. 24  Cysts of the Oral and Paraoral Region Radiographic Features: Unilocular or multilocular radiolucency: The unilocular lesions are well circumscribed radiolucency with smooth margins and thin radiopaque borders it may be situated below the roots of teeth, between the roots of adjacent teeth or near the crest of the ridge in place of a missing tooth. Multilocular radiolucency odontogenic keratocyst cannot be distinguished from ameloblastoma. Odontogenic Keratocyst (OKC). Large, multilocular cyst involving most of the ascending ramus (Courtesy of Dr. S.C. Roddy). (1) Cyst Contents: Keratocysts contain keratin seen during operation as dirty white or yellowish material which has an appearance similar to pus but without an offensive smell. The cystic fluids contain plasma protein. Histopathologic Features: Epithelial lining is a thin, regular, continuous layer of stratified squamous epithelium 6-8 cells thick, arises from a flat basement membrane (no rete pegs). The basal cells are columnar palisaded with prominent polarized and intensely stained nuclei, and the cells of the stratum spinosum show intercellular oedema. 25  Cysts of the Oral and Paraoral Region The surface is characteristically corrugated with a parakeratotic surface layer. The lumen may contain large amounts of keratin debris or clear fluid. The mitotic index of the epithelial lining is more than that of radicular cysts but similar to that found in ameloblastoma. Odontogenic Keratocyst (OKC). The epithelial lining is 6 to 8 cells thick, with a hyperchromatic and palisaded basal cell layer. Note the corrugated parakeratotic surface. (1) Histologic Variations of the odontogenic Keratocyst: 1) Budding of the basal layer into the underlying connective tissue. 2) Daughter/ satellite cysts may form within the connective tissue wall of the cyst (small or large islands of epithelial cells exhibiting central keratinization or micro-cyst formation). Recurrence of Keratocysts: high recurrence rate of about 40%. Reasons of recurrence are: 1- Thin epithelial lining may fragment and may be partially retained; as a weak attachment exists between epithelium and underlying connective tissue, leading to seeding of viable epithelial cells into the tissues. 2- Satellite cysts may be left behind in the bone after the cyst removal operation. 3- High mitotic index of the epithelium. 26  Cysts of the Oral and Paraoral Region D-Orthokeratinzed Odontogenic cyst It is an odontogenic cyst that is entirely or predominantly lined by orthokeratinized stratified squamous epithelium. It was originally referred to as an orthokeratinized variant of Odontogenic Keratocyst. However, it is now generally accepted that it is clinicopathologically different from the more common parakeratinized odontogenic keratocyst (OKC) and should be placed into a different category. Clinical Features: Age: Third and fourth decades. Sex: More common in males. Site: Most frequently found in mandible, posterior regions. Usually presents as a painless swelling or is symptomless and discovered accidentally during routine X-ray. Radiographic features: Well-demarcated unilocular radiolucent lesion, often with a corticated margin. Occasional cases are multilocular. Half of the lesions are related to an impacted tooth, often resulting in an appearance similar to that of a dentigerous cyst. Histopathologic Features: Thin, regular epithelial lining (5-8 cell layers thick), but without rete ridges. The surface exhibits orthokeratinization with a prominent granular cell layer. Unlike odontogenic keratocyst, the keratin surface is not corrugated, but is thick and lamellated. The basal cells do not show palisading or hyperchromatic nuclei. 27  Cysts of the Oral and Paraoral Region Orthokeratinized Odontogenic Cyst. Microscopic features show a thin epithelial lining. The basal epithelial layer does not demonstrate palisading, and a thick layer of orthokeratin is seen on the luminal surface. (1) Treatment and Prognosis: Treatment is by enucleation. Recurrence is rare. E- Calcifying Odontogenic Cyst This is a developmental odontogenic lesion that has some features of a cyst, however, some investigators used to classify it as a neoplasm. Etiology and Pathogenesis: It is believed to be derived from odontogenic epithelial remnants within the gingiva or within the mandible or maxilla. Clinical Features: Age: 40 years of age. Sex: Common in females. Site: More in maxilla and anterior part of the mandible. 75% of the cysts are intraosseous, 25% of cases present in soft tissue in the gingiva or retromolar area. Appearance: Painless swelling in the gingiva or in the alveolar bone. As the cyst enlarges it displaces roots of adjacent teeth. If the cyst becomes infected, the swelling becomes painful. 28  Cysts of the Oral and Paraoral Region Radiographic Features: Intraosseous COC present as a unilocular or multilocular radiolucency with well demarcated irregular margins. Within the radiolucency, scattered calcifications of variable densities are present. Sometimes the calcifications have an equal and diffuse distribution giving a "salt and pepper" appearance. In some cases, mineralization may develop to such an extent that the radiographic margins of the lesion are difficult to determine. The size of the cyst varies from 1 to 8 cm in diameter. Histopathologic Features: Lumen lined by stratified squamous epithelium having columnar or cuboidal layer of cells with their darkly stained nuclei polarized away from the basement membrane (ameloblast-like cells). In the more solid lesions, significant intraluminal epithelial proliferation will fill the cyst lumen. Above the basal layer, there are more loosely arranged epithelial cells that resemble the stellate reticulum of enamel organ (stellate reticulum- like cells). The most characteristic histopathological feature of the calcifying odontogenic cyst is the presence of variable numbers of ghost cells within the epithelium. These eosinophilic ghost cells are altered epithelial cells that are characterized by the loss of nuclei with preservation of the basic cell outline. The nature of the ghost cells is controversial. Some believe that this change represents coagulative necrosis or accumulation of enamel protein; others contend it as a form of normal or aberrant keratinization of odontogenic epithelium. The clusters of ghost cells may undergo dystrophic calcification and become basophilic. 29  Cysts of the Oral and Paraoral Region Areas of an eosinophilic matrix material that are considered by some authors to represent dysplastic dentin (dentinoid) also may be present adjacent to the epithelial component. This is believed to be the result of an inductive effect by the odontogenic epithelium on the adjacent mesenchymal tissue. Calcifying Odontogenic Cyst. Eosinophilic dentinoid material is present adjacent to a sheet of ghost cells. (1) Differential diagnosis: Early lesions with no calcification show a cystic radiolucency that must be differentiated from ameloblastoma. Later when a mixed radiolucent- radiopaque appearance is present, the lesion must be differentiated from adenomatoid odontogenic tumor. Treatment: Simple enucleation. 30  Cysts of the Oral and Paraoral Region II- NON-ODONTOGENIC CYSTS Cysts of Vestigial Ducts A- Nasopalatine tract cysts 1- Incisive Canal Cyst: That may be located within the nasopalatine canal (intra-bony). 2- Cyst of the Palatine Papilla: This lies within the palatal soft tissue at the point of opening of the canal. 1- Incisive Canal Cyst Etiology: The nasopalatine tract cyst is the most common non-odontogenic cyst of the oral cavity, occurring in about 1% of the population. The cyst is believed to arise from remnants of the nasopalatine duct, which is an embryologic structure connecting the oral and nasal cavities in the area of the incisive canal. This canal contains the nasopalatine ducts (which degenerate in humans but leave epithelial remnants behind the incisive canals). It also contains the nasopalatine nerve and anastomosing branches of the descending palatine and sphenopalatine arteries. Bacterial infection or trauma have been mentioned as possible etiologic factors. Clinical Features: Age: Any age, most commonly between fourth and the sixth decades. Sex: Males are affected more commonly. Site: Any point along the canal up to its nasal orifice. Size: The increase in size of the nasopalatine duct cyst is slow and it may remain static for many years. The majority of cysts are between 0.6 and 1.5 cm and do not exceed 2 cm in diameter. 31  Cysts of the Oral and Paraoral Region Rarely, the cyst penetrates the labial plate of bone and causes a swelling of the anterior palate. If the cyst becomes infected, it may cause a rapid swelling and radiating pain due to pressure transmitted by the cyst to the nasopalatine nerves. A salty taste due to drainage, numbness of the anterior aspect of the palate and a sensation of pressure or fullness may also be felt. The adjacent incisors are usually vital and not sensitive to percussion, and they may be tilted. Radiographic Features: It is usually symptomless and discovered during routine x-ray examination. There may be a round ovoid or heart-shaped radiolucency due to the superimposition of the nasal spine. It appears to lie in the midline between or above the roots of the maxillary central incisors. To distinguish a small cyst from the incisive foramen: The size of the incisive foramen, however, does not exceed 6 mm in diameter. Incisive Canal Cyst. Well-circumscribed radiolucency between and apical to the roots of the maxillary central incisors. (1) Histopathologic Features: The cyst is lined by stratified squamous epithelium, pseudostratified ciliated columnar epithelium or cuboidal epithelium or any combination of them. 32  Cysts of the Oral and Paraoral Region The epithelium may be respiratory in its nasal portion changing to squamous in its oral portion. The connective tissue wall of the cyst may show inflammatory cell infiltration and often contains mucous glands and several large thick-walled blood vessels. Nerve trunks may also be seen within the connective tissue wall and are well demonstrated by silver stain. Cholesterol clefts are uncommonly seen. Viscous fluid content, which may be mucoid material or even pus, exists if the cyst has been infected. Incisive Canal Cyst. Cyst wall showing thick-walled blood vessel (black arrow), nerve bundles (green arrow) and minor salivary glands (red arrow). (1) 2- Cyst of the Incisive Papilla It is the extraosseous counterpart of incisive canal cyst. The mucosal covering of the papilla is normal, superficial fluctuant bluish swelling appears just behind it, ruptures spontaneously with a discharge of salty fluid. And its x-ray picture is negative. 33  Cysts of the Oral and Paraoral Region B- Fissural Cysts (Inclusion Cysts) Arise from epithelium entrapped in the lines of fusion of embryonic processes: 1- Globulomaxillary cyst 2- Nasolabial cyst 3- Median palatal cyst 1- Globulomaxillary cyst This is a cyst found between the maxillary lateral incisor and canine teeth arising from non-odontogenic epithelium entrapped at the site of fusion of the globular process of the fronto-nasal process and the maxillary process. Currently, this theory is debatable, and most of them are considered as odontogenic developmental lateral periodontal cyst. B- Nasolabial Cyst It is a rare developmental, soft tissue cyst that occurs in the upper lip lateral to the midline. Etiology: Its pathogenesis is uncertain, where two main theories are suggested: It may be a fissural cyst arising from is epithelial remnants entrapped along the line of fusion of the maxillary, medial nasal and lateral nasal and processes. The second theory suggests that it may develop from misplaced epithelium of the nasolacrimal duct because of their similar location and histology. Clinical Features: Age: Mostly in fourth and fifth decades. Sex: More in females 4:1. 34  Cysts of the Oral and Paraoral Region Appearance: Soft tissue swelling of the upper lip in the canine region that obliterates the nasolabial fold, may result in mild nasal obstruction. The cyst may extend intraorally in the mucolabial fold. It grows at a slow rate. Nasolabial Cyst. Enlargement of the left upper lip with elevation of the ala of the nose. Intraoral swelling fills the maxillary labial fold (Courtesy of Dr. Jim Weir). (1) Radiographic Features: Negative in x-ray but bone resorption may result from pressure along the labial aspect of the anterior maxilla. Histopathologic Features: It is lined by pseudostratified columnar epithelium, with goblet cells and cilia. Inflammatory cells are absent in the connective tissue unless the cyst in infected. Nasolabial Cyst. Pseudostratified columnar epithelial lining. (1) 35  Cysts of the Oral and Paraoral Region 3- Median Palatal Cyst It is a rare fissural, intrabony, cyst that develops from epithelial remnants at the line of fusion of the palatal processes. It is a non-inflammatory developmental cyst. It occurs in the midline of the palate, posterior to incisive canal. Clinical Features: Age: Between third & sixth decades. Sex: Males are affected more than females. It is present as a firm or fluctuant swelling of the midline of the hard palate, posterior to the palatine papilla. It is painless unless it becomes infected. Radiographic Features: It is symptomless, discovered by routine x-ray examination. It appears as a round or ovoid radiolucency at the midline of the palate. Median Palatal Cyst. A well- circumscribed midline radiolucent defect can be seen, which is separate from the incisive canal (Courtesy of Dr. Craig Fowler). (1) Histopathologic Features: Epithelial lining is a thin, regular, continuous layer of stratified squamous epithelium. No or very few inflammatory cells can be seen in the connective tissue wall. Treatment: Simple enucleation. Similar epithelial inclusion cysts may occur along the midline of the palate; it is median palatine cyst of newborn or (Epstein pearls). These are of 36  Cysts of the Oral and Paraoral Region developmental origin but are not derived from odontogenic epithelium. Their epithelium originates as inclusions at the line of fusion between the two palatal shelves and the nasal septum. These cysts also contain keratin and show a thin epithelial lining. III- PSEUDOCYSTS A- Simple bone cyst The simple bone cyst lacks an epithelial lining and cannot be classified as a true cyst. It is a bony cavity with no epithelial lining and often no or very few fluid content. Pathogenesis: The pathogenesis of this cyst is not clear although most believe that it is associated with mild trauma to the jaw insufficient to cause fracture but causes bleeding and hematoma formation within bone. Rather than the clot becoming organized, it breaks down leaving an empty cavity within the bone. This is called “the trauma-hemorrhage” theory. Steady expansion of the lesion occurs until cortical bone is reached. About 80% of patients gave history of prior trauma to the area of involvement. Clinical Features: Age: Below 40 years of age. Site: Mandible body and ramus. The molar premolar region is the most common site. Generally, it occurs in long bones more commonly than in jaws. Most cases (75%) are symptomless and may be discovered accidentally on routine radiography. The lesion does not cause expansion of the cortical bone in most cases; swelling of the jaws is seen in only 25% of cases. Pain is uncommon. Teeth associated with the cyst retain their vitality and are often not loosened. 37  Cysts of the Oral and Paraoral Region Radiographic Features: The cyst varies in size and may extend from the body of the mandible into the ramus. It produces a well-defined radiolucent area. It is located above the inferior alveolar canal and appears as a well demarcated unilocular cavity. The cyst may project upwards into the interradicular septa and produce a scalloped contour between the roots of the teeth. In the anterior region, the outline is usually regular, round or oval in shape with no indentations between the teeth. Roots of adjacent teeth may be displaced but they are not resorbed nor do they become devitalized or mobile. The lamina dura of roots involved in the cyst is intact or partially lost in some cases. Histopathology: The lesion may contain remnants of blood or blood-stained fluid; the lining is thin fibrous or granulation tissue with no epithelial component. Red cells and hemosiderin may be seen within the cyst cavity or it may be empty.. Simple bone cyst consisting of connective tissue fragments lining surrounding bone (bottom). (3) 38  Cysts of the Oral and Paraoral Region Treatment: The cavity is opened surgically, irrigated with saline, the walls are then scratched to establish bleeding into the lesion prior to closure, bone repair will occur with no recurrence. B- Aneurysmal Bone Cyst It is classified as a pseudocyst because it appears radiographically as a cyst- like lesion but microscopically exhibits no epithelial lining. The lesion may arise in the mandible, maxilla or other bones. It is an intraosseous accumulation of variable-sized, blood-filled spaces surrounded by cellular fibrous connective tissue that is often mixed with trabeculae of reactive woven bone. Etiology and Pathogenesis: Although the pathogenesis of aneurysmal bone cyst is unclear. An aneurysmal bone cyst (ABC) is of two types: primary and secondary. Etiologic factors for ABC include trauma, vascular malformations and pre- existing neoplastic lesions such as giant cell granuloma and fibrous dysplasia. Primary ABC does not have any pre-existing lesion, while secondary ABC may be preceded by any primary tumor. The development of aneurysmal bone cysts typically involves an anomaly in venous blood circulation. This anomaly subsequently results in elevated venous pressure and vasodilation, causing expansion of the vascular bed. This expanded vascular bed also contributes to the bone's resorption and cortex erosion. 39  Cysts of the Oral and Paraoral Region Clinically: Age: Under 30 years of age (second decade). Sex: Slight female predilection. Site: Long bones, and jaws. In the jaws it chiefly affects the molar areas. Appearance: Firm swelling. The lesion is often painful and tender. At operation, upon entering the lesion, excessive bleeding is encountered resembling a blood-soaked sponge. Radiographic Features: There is multilocular radiolucency with a honeycomb or soap-bubble appearance. Ridges on the walls of the cavity and septa of new bone are the cause of the soap-bubble appearance. Teeth may be displaced with or without root resorption. Histopathologic Features: Fibrous connective tissue containing many blood-filled spaces. The spaces are not lined by endothelial cells. The cystic cavity is lined by cellular fibroblastic tissue containing histiocytes, extravasated red blood cells and haemosiderin and large multinucleated giant cells. New osteoid tissue and bone spicules are formed in varying amounts. Treatment: Curettage or excision. References 1. Biesecker J.L., Marcove R.C., Huvos A.G. and Mike V. (1970) Aneurysmal bone cysts. A clinicopathological study of 66 cases. Cancer 26, 615–625. 2. Channawar, R. A., Deshpande, S. V., Shrivastav, S., Date, S. V., & Wamborikar, H. (2022). Aneurysmal Bone Cyst of the Head of the Fibula: An Unusual Presentation. Cureus, 14(10), e30376. 3. Kransdorf M.J. and Sweet D.E. (1995) Aneurysmal bone cyst: Controversy, clinical presentation, imaging. American Journal of Roentgenology 164, 573– 580. 4. Shear M and Speight P :Cyst of the oral and maxillofacial regions. 4th edition (2007). Blackwell Munksgaard. Blackwell Publishing Ltd. Oxford , UK. 40  Cysts of the Oral and Paraoral Region Aneurysmal bone cyst of the mandible. Wide sinusoidal spaces are not lined with endothelial cells. (3) Low-power view of an aneurysmal bone cyst with macroscopic vascular spaces. (5) C- Static Bone Cyst (Developmental lingual mandibular salivary gland depression) This is not a true cyst as it has no epithelial lining but appears as a cystic or radiolucent area on radiographic examination. It is caused by a developmental inclusion of sub-mandibular salivary tissue within or adjacent to the lingual surface of the body of the mandible. Defects may be noted bilaterally and rarely anterior to the lower first molar. 41  Cysts of the Oral and Paraoral Region The lesion is entirely asymptomatic and may be discovered accidentally upon x-ray examination. Radiographically: It appears round to ovoid, sharply circumscribed radiolucency with a radiopaque margin. Radiolucency is situated beneath the level of the inferior dental canal. The lesion is constant in size and shape in the same patient and hence the name “static”. Static Bone Cyst. A circumscribed radiolucency beneath the level of the inferior alveolar canal. (1) To confirm diagnosis, a sialogram is made where a radiopaque material is injected into the duct of the sub-mandibular gland of the affected side, the presence of salivary tissue in the cyst can be detected. Histopathologic Features: Normal salivary gland is seen. Treatment: Once diagnosed, no treatment is required. 42  Cysts of the Oral and Paraoral Region IV- Soft Tissue Cysts of Floor of Mouth and Neck A- Dermoid and Epidermoid Cysts They are common cysts of the skin that are lined by epidermis-like epithelium. Pathogenesis: This developmental cyst is derived from epithelial debris in the midline during closure of mandibular arches. Clinical Features: Age: Young adults. Sex: No sex predilection. Site: Anterior part of the floor of the mouth, sub-mandibular and sub lingual areas. Appearance: When located above the mylohyoid muscle it produces a bulge in the floor of the mouth, causing elevation of the tongue causing difficulty in eating and drinking. When the cyst is deeper, between the geniohyoid and mylohyoid muscles it causes bulging in the submental area. The cyst is painless, slowly growing and varies in size from less than 2 cm in diameter to several centimeters. The consistency of the cyst varies from soft to fluctuant, or it may have a doughy consistency on palpation. A pale yellowish pink color is noted beneath thinned and intact epithelium. Histopathologic Features: Connective tissue wall lined by a thin layer of keratinized stratified squamous epithelium. The lumen is filled with keratin; therefore, these cysts are called "Epidermoid cysts". Similar histological picture to that of orthokeratinized 43  Cysts of the Oral and Paraoral Region odontogenic cyst, differentiated clinically with the latter being a central lesion. In other cases, numerous sebaceous glands, hair follicles and teeth may be found, therefore, these lesions are called “Dermoid cysts” as the epithelial cells causing these cysts are totipotent. Dermoid cyst lined by keratinized epithelium with sebaceous glands and rudimentary hair in the supporting connective tissue. (3) Treatment: Surgical removal. B- Thyroglossal Tract Cyst It is the most common developmental cyst of the neck (75% of neck cysts). Etiology and Pathogenesis: In the fourth week of I.U. life at the foramen caecum, the thyroid starts to develop by downward growth of epithelium (tract) through the base of the tongue to midline of the neck. By the tenth week of I.U. life, the tract breaks up but residual epithelial elements may persist and proliferate to form a cyst. The cause of proliferation of the remnants is not known. Clinical Features: Age: In young people but can develop at any age. Appearance: Slowly growing asymptomatic fluctuant, movable midline mass that varies in size from a few millimeters to several centimeters. 44  Cysts of the Oral and Paraoral Region Site: Anywhere along the thyroglossal tract. It may occur in the floor of the mouth. Only 2% of the lesions occur within the tongue near the foramen ceacum, if large, may cause dysphasia or interfere with eating and speech. When they are attached to the hyoid bone and tongue, they may move on swallowing. If the cyst becomes infected, sinus tract may occur (small opening on the skin or mucosal surface may be seen). Histopathologic Features: The cyst lining varies depending upon its location. If above the level of the hyoid bone, it is usually stratified squamous epithelial lining, and if below the level of the hyoid, it is usually a ciliated or columnar type epithelium. The connective tissue wall of the cyst may contain small areas of thyroid tissue and lymphoid tissue. Thyroglossal Tract Cyst showing thyroid acini in the submucosa. (2) Treatment: Complete surgical excision is recommended. 45  Cysts of the Oral and Paraoral Region LYMPHO-EPITHELIAL CYSTS Cervical Lympho-epithelial Cyst (Branchial Cleft Cyst, Benign Cystic Lymph Node) It is a developmental cyst, located on the lateral aspect of the neck, anterior to the sternomastoid muscle. Etiology: The origin of this cyst is from remnants of epithelial cells of branchial clefts. An alternative theory of origin is that it arises from cystic changes in parotid gland epithelium that becomes entrapped in the upper cervical lymph nodes during embryonic life. Clinical Features: Age: Childhood and young adults. Appearance: It is asymptomatic, soft and fluctuant, movable mass on the lateral aspect of the neck close to the anterior border of sternomastoid muscle. Slowly growing, but, if the cyst becomes infected, abscess and draining sinuses may occur. This cyst may occur at the angle of mandible, sub-mandibular and parotid area. Histopathologic Features: The cyst is usually lined by stratified squamous epithelium. The wall of the cyst is generally lymphoid tissue with a typical lymph node pattern showing well-formed germinal centers. The cyst contains a thin watery fluid or a thick gelatinous, mucoid material. 46  Cysts of the Oral and Paraoral Region Cervical Lympho-epithelial Cyst. The cyst lining is stratified squamous epithelium, which is surrounded almost completely by a dense lymphoid infiltrate containing several reactive lymphoid follicles. (2) Treatment: Surgical excision. D- Mucous Extravasation Cyst (Mucocele) It is a common lesion of the oral mucosa that results from rupture of the salivary gland duct and spillage of mucin into the surrounding soft tissues. It is considered a pseudocyst as it lacks an epithelial lining. It is a soft tissue pseudocyst. Etiology: It might be caused by mechanical trauma to the minor salivary gland excretory duct as biting the lip or check resulting in injury. This results in pooling of mucus into the surrounding connective tissue stroma. The pool of extravasated mucus induces an inflammatory reaction in the surrounding connective tissue, with polymorphnuclear leucocytes, macrophages, and granulation tissue response resulting in the formation of a wall around the mucin pool, giving a pseudocyst appearance. Clinical Features: Age: Children and young adults. Site: The lower lip is the most frequent site followed by buccal mucosa, ventral surface of the tongue, and floor of the mouth. 47  Cysts of the Oral and Paraoral Region Appearance: Superficial lesions are painless, dome shaped mucosal swellings with smooth surface showing bluish hue or translucency. A deep lesion appears as a diffuse swelling with no translucent or blue hue. They range from a few millimeters to a few centimeters, and if aspiration is attempted, they decrease in size. Fluctuation in the size of the cyst occurs due to engulfing the pool of the mucin and further production of mucin. If it ruptures, it will release its fluid content. When the mucocele occurs in the floor of the mouth, it is termed “ranula”. Histopathologic Features: The cavity contains pooled mucin, the overlying epithelium is often thinned and is separated from the mucin pool by compressed granulation tissue. The mucin pool is surrounded by compressed fibrous and granulation tissue infiltrated by large numbers of neutrophils, macrophages, lymphocytes and occasionally plasma cells. The adjacent salivary elements show acinic degeneration and ductal dilatation. Mucus extravasation cyst showing free mucin (top) surrounded by inflamed granulation and connective tissue and salivary gland tissue. (3) Treatment: Surgical excision. 48  Cysts of the Oral and Paraoral Region E- Mucous retention cyst (Salivary duct cyst) It is an epithelium lined cavity that arises from salivary gland tissue. It is considered a true cyst as it is lined by epithelium. Etiology: It may be caused by ductal dilatation secondary to ductal obstruction, which creates intraluminal pressure. It may also be a true developmental salivary duct cyst that is separate from the adjacent normal salivary ducts. Clinical features: Age: Mostly in adults Site: Can occur in either major or minor salivary gland, the parotid gland is the most common major salivary gland involved; while the floor of mouth, buccal mucosa and lips are the most common sites for minor salivary gland involvement. Appearance: It is a slowly growing, asymptomatic swelling. It is a soft, fluctuant swelling that may appear bluish, depending on the depth of the cyst below the surface. Histological features: The lining of the cyst is variable and may consist of cuboidal, columnar or atrophic squamous epithelium surrounding thin or mucoid secretions in the lumen. A mucus retention cyst with an epithelial lining. The inflammatory features that accompany a mucocele. (4) 49  Cysts of the Oral and Paraoral Region Salivary gland stone (top) in a minor salivary gland (bottom) excretory duct of the upper lip. (4) Mucus extravasation cyst (left) showing free mucin in the submucosa and a mucus retention cyst (right) showing mucin retained in the salivary excretory duct because of blockage by a sialolith (salivary gland stone). (4) References 1. Neville, B. W., Allen, C. M., & Damm, D. D. C., Angela C. (2016). Oral and Maxillofacial Pathology (Fourth Edition ed.). Canada: ELSEVIER. 2. R. Gnepp., D. (2009). Diagnostic Surgical Pathology of the Head and Neck (Second ed.): SAUNDERS 3. Range, D. E. S. J., Xiaoyin. (2019). Practical Head and Neck Pathology: Springer. 4. Regezi, J. A., Sciubba, J. J., & Jordan, R. C. K. (2003). Oral Pathology (fourth ed.). United States of America: SAUNDERS. 5. Marx, R. E., & Stern, D. (2012). Oral and Maxillofacial Pathology (Second ed.): Quintessence Publishing Co, Inc. 50