ESSAY 4: Odontogenic Cysts - Calcifying Epithelial Odontogenic Cyst (CEOC / Gorlin Cyst)

Classification of Odontogenic Cysts

• Dentigerous (follicular) cyst
• Eruption cyst
• Odontogenic keratocyst (OKC / KCOT)
• Lateral periodontal cyst
• Glandular odontogenic cyst
• Calcifying odontogenic cyst (COC / Gorlin cyst)
• Orthokeratinized odontogenic cyst

• Periapical (radicular) cyst
• Residual cyst
• Paradental cyst
• Buccal bifurcation cyst

Calcifying Epithelial Odontogenic Cyst (CEOC / Gorlin Cyst / COC / CCOT)

Definition

Etiology and Pathogenesis

Clinical Features

• Age: Variable - occurs across a wide age range from infancy to elderly. Mean age at occurrence is in the fourth decade, with a peak incidence in the second and third decades. Lesions in younger patients are more commonly associated with odontomas.
• Sex: Essentially equal distribution between males and females overall.
• Location: The anterior jaw is more commonly involved than posterior regions. There is a slight maxillary predominance over the mandible.
• Presentation: COC occurs both intraosseously (central - within bone) and peripherally/extraosseously (in attached gingiva). Clinical behavior is variable; some lesions behave as simple cysts while others exhibit more aggressive neoplastic behavior. Intraosseous lesions may cause painless jaw expansion; peripheral lesions appear as gingival masses.
• The ratio of COC to dentinogenic ghost cell tumor (solid variant) is approximately 40:1.

Radiographic Features

• Radiographic appearance is highly variable.
• Lesions are most commonly unilocular radiolucencies; multilocular lesions also occur.
• COC is classically described as a mixed radiolucent-radiopaque lesion; however, the majority of lesions are purely radiolucent in the absence of an associated odontoma.
• When mineralization does occur without an odontoma, the radiopacities are peripherally located, giving a characteristic "snowdrift" pattern.
• An associated odontoma (compound or complex) may be present within the radiolucency, producing focal radiopaque foci.
• Well-demarcated borders, with root resorption of adjacent teeth in some cases.

Histopathological Features

• The lining epithelium resembles ameloblastoma, with a palisaded basilar layer of hyperchromatic columnar/cuboidal cells exhibiting reversed nuclear polarization, overlying a loosely arranged stellate reticulum-like layer.
• The hallmark feature is the presence of ghost cells - these are large, pale eosinophilic cells with a distinct cell outline but absent nuclei (anucleate squamous cells that have undergone abnormal keratinization). Ghost cells may coalesce to form large masses.
• Ghost cells may undergo dystrophic calcification (calcified ghost cells), accounting for the radiopaque foci.
• The cystic wall may contain odontogenic hard tissue (dentinoid or dysplastic dentin).
• Ghost cells are NOT pathognomonic of COC alone - they can appear in odontomas, ameloblastic fibro-odontomas, and even ameloblastomas. Thus, careful analysis is required.
• Subclassification based on histology (Praetorius et al.) exists, but is more of academic than therapeutic importance.

Treatment

• Intraosseous (central) COC: Enucleation and curettage (conservative approach). Some large or recurrent lesions may require wider excision.
• Peripheral (extraosseous) COC: Local surgical excision.
• Simple enucleation is generally curative for the cystic form.
• The solid dentinogenic ghost cell tumor requires wider resection due to more aggressive behavior.

Prognosis

• Generally excellent for the cystic (COC) form after conservative enucleation.
• Recurrence is uncommon for the cystic variant but reported for the neoplastic (solid) variant.
• Malignant transformation is very rare but has been reported (malignant dentinogenic ghost cell tumor).
• Regular clinical and radiographic follow-up is recommended.

ESSAYS 5, 6, 7 & 10: Ameloblastoma - Classification, Clinical, Radiographic, Histopathologic Features, Histologic Variants, Treatment, and Malignant Ameloblastoma

Classification of Odontogenic Tumors (WHO 2017)

• Ameloblastoma (conventional, unicystic, peripheral, metastasizing)
• Squamous odontogenic tumor
• Calcifying epithelial odontogenic tumor (Pindborg tumor)
• Adenomatoid odontogenic tumor (AOT)

• Ameloblastic fibroma
• Ameloblastic fibro-odontoma
• Odontoma (compound, complex)
• Primordial odontogenic tumor
• Dentinogenic ghost cell tumor

• Odontogenic fibroma
• Odontogenic myxoma
• Cementoblastoma
• Cemento-ossifying fibroma

• Malignant ameloblastoma (metastasizing ameloblastoma)
• Ameloblastic carcinoma
• Clear cell odontogenic carcinoma
• Malignant dentinogenic ghost cell tumor
• Malignant calcifying epithelial odontogenic tumor

• Squamous cell carcinoma (keratinizing/non-keratinizing)
• Mucoepidermoid carcinoma

Ameloblastoma

Definition

1. Ameloblastoma (conventional/solid/multicystic)
2. Unicystic ameloblastoma
3. Peripheral (extraosseous) ameloblastoma
4. Metastasizing (malignant) ameloblastoma

A. Conventional (Solid/Multicystic) Ameloblastoma

Clinical Features

• Age: Generally occurs after 20 years of age; peak in 3rd-4th decades.
• Site: Approximately 85% occur in the mandible, most commonly in the molar-ramus region (posterior mandible). Maxillary involvement is less frequent but carries a worse prognosis.
• Presentation: Slow, painless expansion of the jaw. As the tumor enlarges, facial deformity, displacement of teeth, cortical perforation, and rarely paresthesia may occur. Pain is uncommon unless secondarily infected.
• Molecular pathology: Mutations in genes of the mitogen-activated protein kinase (MAPK) pathway are observed in approximately 90% of all lesions. The most significant is a BRAF V600E mutation, particularly in the follicular histologic subtype.

Radiographic Features

• Radiolucent, well-demarcated lesion.
• May be unilocular (especially unicystic variant) or multilocular - the classic "soap bubble" or "honeycomb" multilocular appearance is characteristic of the conventional type.
• Cortical bone expansion and thinning ("egg-shell crackling").
• Resorption of tooth roots (a hallmark of ameloblastoma's aggressive nature).
• No calcification within the lesion (unlike Pindborg tumor or AOT).
• Borders are scalloped between tooth roots in multilocular pattern.

Histopathological Features

• The epithelium demonstrates peripheral columnar cells with reversed polarization (hyperchromatic nuclei polarized away from the basement membrane - the "reverse polarity" sign).
• "Piano key" appearance - the palisaded peripheral tall columnar cells lined up like piano keys.
• Central stellate reticulum-like cells within the epithelial islands - resembling the enamel organ.
• Subnuclear vacuolization is another classic feature.

Treatment

• Treatment is controversial but most authorities favor resection with a surgical margin of at least 1 cm past the radiographic extent of the tumor in bone (wide local excision/resection).
• Conservative approaches (enucleation, curettage, marsupialization) have high recurrence rates (up to 50-90%) for conventional ameloblastoma.
• Reconstruction is required after resection (bone grafting, plates, microvascular free flaps for large defects).
• Recurrent ameloblastoma with confirmed BRAF V600E mutation may be treated with BRAF-targeted therapy (e.g., dabrafenib/vemurafenib) - an emerging targeted molecular approach.

Prognosis

• Good with appropriate resection and regular clinical and radiographic surveillance.
• Recurrence rates with conservative surgery can be 50-90%; with resection, approximately 15-20%.
• Maxillary lesions carry worse prognosis due to proximity to skull base.

B. Unicystic Ameloblastoma

Clinical Features

• Majority in the mandible, molar-ramus region.
• Painless swelling of the jaw.
• Often associated with an unerupted third molar (similar presentation to dentigerous cyst).
• Younger age group than conventional ameloblastoma (second decade most common).

Radiographic Features

• Unilocular radiolucent, well-demarcated lesion - mimics a dentigerous cyst around an impacted molar.
• May be multilocular.

Histopathological Features (3 subtypes by Vickers and Gorlin):

1. Luminal unicystic - ameloblastomatous epithelium lining the cyst lumen only (no invasion of cyst wall). Lowest recurrence risk.
2. Intraluminal unicystic - nodular projections of ameloblastoma into the cyst lumen (luminal plexiform ameloblastoma). Treated conservatively.
3. Mural unicystic - ameloblastoma invades the fibrous cyst wall. Highest recurrence risk - requires resection with clear margins.

Treatment

• Luminal and intraluminal: enucleation/curettage with clear margins.
• Mural: resection with clear margins (same as conventional ameloblastoma).

Prognosis

• Good overall, but 10-20% recurrence rate even with surgery.

C. Peripheral (Extraosseous) Ameloblastoma

Clinical Features

• Occurs in middle-aged adults.
• Presents as a sessile or pedunculated, painless gingival mass over tooth-bearing areas.
• Does NOT involve underlying bone radiographically (by definition).
• Most common on the mandibular gingiva.

Treatment

• Conservative local excision with clear margins.
• Prognosis: excellent; recurrence is uncommon.

D. Metastasizing (Malignant) Ameloblastoma

Definition

Key Features

• Histologically, the metastatic lesion shows "normal" (non-malignant) ameloblastoma morphology.
• Most common site of metastasis: lungs (pulmonary metastases predominate in most series).
• Other sites: lymph nodes, liver, brain, bone.
• Malignant ameloblastoma is the most common of the malignant odontogenic tumors (59.7% in one series).
• Latency period between primary tumor and metastasis can be decades (average 9-18 years).
• Long history of inadequate/conservative treatment of the primary is a common feature.

Distinguishing from Ameloblastic Carcinoma

Treatment of Malignant Ameloblastoma

• Wide surgical resection of the primary tumor.
• Surgical resection of accessible metastases.
• Chemotherapy: Paclitaxel and carboplatin - reported responses in pulmonary metastatic disease.
• BRAF-targeted therapy (if BRAF V600E confirmed) in recurrent/metastatic disease.

Prognosis

• 5-year survival is variable; lung metastases can remain indolent for years.
• Prognosis is better than for ameloblastic carcinoma overall.

ESSAYS 8 & 9: Adenomatoid Odontogenic Tumor (AOT)

Definition

Classification

1. Follicular AOT (most common, ~73%) - intraosseous, associated with an unerupted tooth (resembles a dentigerous cyst)
2. Extrafollicular AOT (~24%) - intraosseous, NOT associated with an unerupted tooth (resembles a lateral periodontal or residual cyst)
3. Peripheral AOT (~3%) - extraosseous, in the gingiva

Etiology and Pathogenesis

• Arises from odontogenic epithelial remnants (dental lamina, enamel organ).
• Some evidence suggests it may arise from the reduced enamel epithelium surrounding the crown of the unerupted tooth (explaining the follicular variant).
• No viral or carcinogen etiology is established.
• KRAS gene mutations have been reported in some AOTs, suggesting a hamartoma-to-neoplasm spectrum in a subset.

Clinical Features

• Age: Most commonly in patients below 20 years of age (second decade, mean ~15-16 years); occasionally in third decade.
• Sex: Marked female predominance (female:male ratio approximately 2:1).
• Site: Majority occur in the anterior maxilla (most frequent site is the canine/incisor region). The "two-thirds rule" is a common memory aid.
• Presentation: Slow growing, relatively asymptomatic lesion. Patients typically present with painless swelling of the jaw or delayed tooth eruption. It may be discovered incidentally on routine radiographs.
• The associated unerupted tooth is most frequently the maxillary canine.

Radiographic Features

• Unilocular, well-demarcated radiolucency with a sclerotic (corticated) border.
• Follicular variant: radiolucency surrounds the crown AND extends below the CEJ (cemento-enamel junction) of the unerupted tooth - this extension below the CEJ helps differentiate from a dentigerous cyst (which only envelops the crown).
• Small radiopaque foci (calcifications) may be present within the radiolucency, which is an important differentiating feature from dentigerous cyst.
• The radiolucency may extend between the roots of erupted adjacent teeth.
• Root resorption is uncommon (another differentiating feature from ameloblastoma).

Histopathological Features

• Encapsulated tumor with a well-defined fibrous capsule.
• Duct-like (adenomatoid) structures are the hallmark - these are rosette-like or gland-like arrangements of columnar or cuboidal epithelial cells surrounding a central amorphous eosinophilic material (pseudo-lumen). These are NOT true glands.
• Whorled/nodular epithelial masses of spindled or polygonal cells forming sheets and strands.
• Tumor droplets - small eosinophilic amorphous droplets (known as "Liesegang ring"-like structures or "tumor droplets") in the stroma - representing amyloid-like or calcific material.
• Calcifications: varying degrees of mineralization may be present - dystrophic calcification within the duct-like structures or within the stromal component.
• Stroma is sparse fibrous connective tissue (paucicellular stroma).
• There is NO stellate reticulum, NO peripheral palisading with reversed polarization (which distinguishes it from ameloblastoma).

Treatment

• Enucleation (simple enucleation with preservation of associated tooth) is the standard and sufficient treatment.
• Due to its thick fibrous capsule, the tumor "shells out" easily from the surrounding bone.
• No need for wide excision or resection.

Prognosis

• Excellent.
• Recurrence is virtually unknown - this is one of the most important differentiating features from ameloblastoma.
• The associated unerupted tooth can generally be preserved and may erupt normally after tumor removal.
• Malignant transformation has never been documented.

ESSAY 11: Oral Potentially Malignant Disorders (OPMDs) - Oral Lichen Planus

Classification of Oral Potentially Malignant Disorders (OPMDs)

• Oral leukoplakia
• Oral erythroplakia (highest malignant potential - ~50%)
• Oral submucous fibrosis (OSF)
• Actinic keratosis (solar cheilitis)
• Oral lichen planus (OLP) - especially erosive/atrophic form
• Palatal lesions in reverse smokers
• Discoid lupus erythematosus
• Inherited conditions: Dyskeratosis congenita, Fanconi anemia, xeroderma pigmentosum

Oral Lichen Planus (OLP)

Definition

Etiology and Pathogenesis

1. Antigen-specific mechanisms:

• Antigen processing by resident dendritic cells in the epithelium.
• MHC class I-restricted antigen presentation to CD8+ cytotoxic T cells.
• MHC class II-restricted antigen presentation to CD4+ helper T cells by lesional keratinocytes.
• Clonal expansion of antigen-specific T cells at the site.
• Keratinocyte apoptosis triggered by antigen-specific CD8+ cytotoxic T cells (the key destructive event).

1. Non-specific mechanisms:

• Activation of matrix metalloproteinases (contributes to basement membrane destruction).
• Mast cell degranulation (releases inflammatory mediators).
• Basement membrane alterations with deposition of fibrinogen (key to direct immunofluorescence findings).
• Upregulation of laminin, fibronectin, and collagen types IV and VII due to basement membrane damage.
• Elaboration of proinflammatory cytokines including RANTES (Regulated on Activation, Normal T-cell Expressed and Secreted) - recruits inflammatory cells.

1. T-cell profile: Mixed CD4+ and CD8+ T cells expressing alpha-1 integrin molecules. The majority of lesional T cells are activated CD8+ cytotoxic T cells. More recent studies demonstrate the monoclonal nature of lesional T cells.
2. Triggering factors: Dental materials (mercury amalgam, gold), certain medications (lichenoid drug reactions - NSAIDs, antihypertensives, antimalarials), stress (psychological trigger), and possibly hepatitis C virus (especially in populations in Italy and Japan).

Clinical Features

• Age: Middle-aged population most commonly affected.
• Sex: Women more frequently than men - up to 75% of cases are in females.
• Distribution: Characteristically bilateral and symmetric over the buccal mucosa (pathognomonic distribution). Also involves the tongue (lateral and dorsal surfaces), gingiva, lips, and palate.

• Reticular striae may precede keratotic papules, which fuse to form the characteristic stria pattern.
• Wickham's striae on the skin (seen in cutaneous lichen planus) appear as fine white lines on the surface of violaceous papules.

• Primary biliary cirrhosis
• Primary sclerosing cholangitis
• Sjögren syndrome
• Lupus erythematosus
• Hepatitis B and C (particularly in Italian and Japanese populations)
• Possible genetic susceptibility/predisposition has been suggested.

Clinical Differential Diagnosis

• Leukoplakia / erythroleukoplakia
• Lupus erythematosus (DLE)
• Lichenoid drug reactions
• Graft-versus-host disease
• Candidiasis (chronic hyperplastic)
• Oral hairy leukoplakia
• Pemphigus vulgaris, mucous membrane pemphigoid (for erosive/gingival form)
• Erythema multiforme

Histopathological Features

1. Hyperkeratosis and/or parakeratosis of the surface epithelium (orthokeratosis in reticular OLP, parakeratosis in erosive form).
2. Degeneration of the basal cell layer - "liquefaction degeneration" or "vacuolar degeneration" of basal and parabasal keratinocytes; basal cells become vacuolated; the epithelium may assume a sawtooth rete ridge pattern.
3. Dense, band-like subepithelial lymphocytic infiltrate confined to the superficial lamina propria, closely apposed to ("hugging") the basal layer - the most distinctive feature.

• Civatte bodies (colloid/hyaline bodies) - eosinophilic, globular apoptotic bodies formed by degenerated basal keratinocytes; a hallmark of the lichenoid reaction.
• Lymphocytes migrate ("track") into the overlying epithelium (exocytosis), especially in lower spinous layers.
• Intercellular edema (spongiosis) in the lower spinous layer.
• Fibrinogen deposition along the basement membrane region (detected on direct immunofluorescence - DIF as shaggy fibrin along the BMZ - helpful in establishing diagnosis).
• In erosive OLP: the surface epithelium is absent (ulcerated) with a fibrinopurulent pseudomembrane overlying granulation tissue beneath.
• In atrophic OLP: the epithelium is thin (atrophic), and the rete ridges are flattened or absent.

Diagnosis

• Clinical diagnosis is usually adequate for classic reticular bilateral OLP.
• Biopsy with routine H&E for atypical, erosive, or uncertain presentations.
• Direct Immunofluorescence (DIF): Shaggy fibrin deposition along the BMZ is the characteristic pattern; Civatte bodies may fluoresce with IgM (cytoid body fluorescence).
• Rule out lichenoid drug reaction by careful medication history.

Treatment

• No cure - treatment is directed at symptom control and monitoring for malignant transformation.
• Asymptomatic reticular OLP: No active treatment required; periodic monitoring.
• Symptomatic (erosive/atrophic) OLP:
• First-line: Topical corticosteroids (fluocinonide, clobetasol propionate gel/ointment)
• Second-line: Systemic corticosteroids for severe or widespread disease (short courses)
• Topical tacrolimus (FK-506) and pimecrolimus (calcineurin inhibitors) - effective alternatives, especially for steroid-refractory cases
• Topical retinoids (isotretinoin)
• Elimination of identified trigger factors (replace amalgam restorations if amalgam contact reaction suspected, discontinue offending drugs)
• Antifungal treatment for secondary candidal superinfection (common with topical steroid use)

Prognosis and Malignant Transformation

• Overall prognosis is good for symptom control; complete remission is unusual.
• Malignant transformation rate: 0.5-2% (some sources quote up to 3%) over 5-10 years, particularly in the erosive and atrophic variants.
• Areas of transformation develop within long-standing erosive/atrophic OLP.
• The risk of oral squamous cell carcinoma (OSCC) developing from OLP - especially on the lateral tongue and buccal mucosa - warrants lifelong surveillance with regular follow-up biopsy of suspicious areas.

Summary of All 4 Essays

Essay 4 - Calcifying Epithelial Odontogenic Cyst (Gorlin Cyst / COC)

Essays 5/6/7/10 - Ameloblastoma

Essays 8/9 - Adenomatoid Odontogenic Tumor (AOT)

Essay 11 - Oral Lichen Planus