Odontogenic Cysts

Definition

• Rests of Malassez in the periodontal ligament
• Reduced enamel epithelium
• Dental lamina remnants (rests of Serres)
• Occasionally remnants of the enamel organ

Flowchart 1: Origin of odontogenic cysts

Odontogenic epithelial remnants
            │
            ├── Rests of Malassez
            │       └── Radicular cyst
            │
            ├── Reduced enamel epithelium
            │       └── Dentigerous cyst
            │
            ├── Dental lamina remnants (rests of Serres)
            │       ├── Odontogenic keratocyst
            │       ├── Lateral periodontal cyst
            │       ├── Gingival cyst
            │       └── Glandular odontogenic cyst
            │
            └── Odontogenic epithelium with ghost cells
                    └── Calcifying odontogenic cyst

Classification

A. Inflammatory odontogenic cysts

Inflammatory odontogenic cysts
          │
          ├── Radicular cyst
          │       ├── Apical radicular cyst
          │       ├── Lateral radicular cyst
          │       └── Residual cyst
          │
          └── Inflammatory collateral cyst
                  ├── Paradental cyst
                  └── Mandibular buccal bifurcation cyst

B. Developmental odontogenic cysts

Developmental odontogenic cysts
          │
          ├── Dentigerous cyst
          │       └── Eruption cyst
          ├── Odontogenic keratocyst (OKC)
          ├── Orthokeratinized odontogenic cyst
          ├── Lateral periodontal cyst
          │       └── Botryoid odontogenic cyst
          ├── Gingival cyst
          │       ├── Gingival cyst of adult
          │       └── Gingival cyst of newborn
          ├── Glandular odontogenic cyst
          └── Calcifying odontogenic cyst

Important Odontogenic Cysts

1. Radicular cyst

Definition

Etiopathogenesis

Dental caries / trauma
        ↓
Pulpal necrosis
        ↓
Periapical inflammation or granuloma
        ↓
Stimulation of rests of Malassez
        ↓
Epithelial proliferation and central degeneration
        ↓
Formation of radicular cyst

Clinical features

• Usually occurs in the third to fifth decades
• More frequent in the maxillary anterior region
• Associated with a non-vital carious, traumatized, or previously treated tooth
• Usually asymptomatic initially
• Large lesions may cause swelling, cortical expansion, pain due to secondary infection, tooth mobility, and root resorption

Radiographic features

• Well-defined, round or ovoid unilocular radiolucency
• Located at the apex of a non-vital tooth
• Often surrounded by a thin corticated margin
• May cause displacement or resorption of roots

Histopathology

• Non-keratinized stratified squamous epithelial lining
• Lining thickness is variable, usually 6-20 cell layers
• Fibrous connective tissue wall with chronic inflammatory infiltrate
• May show:
  • Cholesterol clefts with foreign-body giant cells
  • Rushton bodies
  • Mucous cells or ciliated cells in maxillary lesions

Treatment

• Endodontic treatment or extraction of the causative tooth
• Enucleation and curettage for most lesions
• Marsupialization/decompression for very large cysts
• Residual cyst requires enucleation

2. Dentigerous cyst

Definition

Pathogenesis

Unerupted tooth
       ↓
Fluid accumulation between
reduced enamel epithelium and crown
       ↓
Expansion of dental follicle
       ↓
Dentigerous cyst

Clinical features

• Second most common odontogenic cyst
• Commonly found in the second and third decades
• Common sites:
  • Mandibular third molar
  • Maxillary canine
  • Maxillary third molar
  • Mandibular second premolar
• Usually painless and detected on routine radiograph
• May delay eruption of a tooth and produce jaw expansion when large

Radiographic features

• Well-circumscribed unilocular radiolucency around crown of an unerupted tooth
• Radiolucency is attached at the cementoenamel junction
• Three radiographic patterns:
  1. Central type
  2. Lateral type
  3. Circumferential type

Histopathology

• Thin non-keratinized epithelial lining, typically 2-4 cell layers
• Fibrous connective tissue wall resembling dental follicle
• In inflamed lesions, epithelial hyperplasia and rete ridges may occur

Treatment

• Enucleation with removal of the associated tooth
• Marsupialization may be preferred in children or for large lesions to permit eruption of a potentially useful tooth
• Histopathology is essential because a dentigerous cyst-like radiolucency can conceal unicystic ameloblastoma or other lesions

3. Odontogenic keratocyst (OKC)

Definition

Clinical features

• Common in second to fourth decades
• Most common site: posterior mandible and ramus
• May grow extensively in the medullary bone with minimal buccolingual expansion
• May be associated with an unerupted tooth, mimicking a dentigerous cyst
• Multiple OKCs suggest nevoid basal cell carcinoma syndrome (Gorlin syndrome)

Radiographic features

• Well-defined unilocular or multilocular radiolucency
• Often has a smooth, corticated border
• Tends to extend anteroposteriorly within the medullary bone
• Root resorption is less common than in ameloblastoma

Histopathology

• Thin, uniform epithelial lining, about 6-10 cells thick
• Corrugated parakeratin surface
• Palisaded, hyperchromatic basal cells
• Flat epithelial-connective tissue interface
• Satellite or daughter cysts may occur in the fibrous wall

Treatment

• Enucleation with peripheral ostectomy, with or without adjunctive therapy
• Decompression followed by enucleation for large lesions
• Long-term clinical and radiographic follow-up is required because recurrence may occur

4. Lateral periodontal cyst and botryoid odontogenic cyst

Lateral periodontal cyst

• Developmental cyst found on the lateral root surface of a vital tooth
• Usually occurs in mandibular canine-premolar region
• Most patients are middle-aged adults
• Radiograph: small, well-circumscribed lateral periodontal radiolucency
• Histology: thin non-keratinized epithelium with focal plaque-like thickenings and clear glycogen-rich cells
• Treatment: simple enucleation

Botryoid odontogenic cyst

• Multicystic, grape-like variant of lateral periodontal cyst
• Usually larger and has greater recurrence tendency
• May present as a multilocular radiolucency

5. Gingival cyst

Gingival cyst of adult

• Soft-tissue counterpart of lateral periodontal cyst
• Occurs in mandibular canine-premolar gingiva
• Appears as a small, painless bluish swelling
• Treated by excision

Gingival cyst of newborn

• Small white or yellow keratin-filled nodules on the alveolar ridge
• Derived from dental lamina remnants
• Usually disappear spontaneously and need no treatment

6. Glandular odontogenic cyst

Features

• Rare developmental cyst
• Usually occurs in the anterior mandible
• Can cross the midline
• Often occurs in middle-aged adults
• May be large, multilocular, and locally aggressive

Histopathology

• Non-keratinized squamous lining of variable thickness
• Cuboidal eosinophilic surface cells
• Mucous or goblet cells
• Intraepithelial duct-like spaces and microcysts
• Plaque-like epithelial thickenings

Treatment

• Small lesions: enucleation with curettage
• Large or recurrent lesions: more aggressive surgery may be required
• Long-term follow-up is needed due to recurrence risk. A recent systematic review specifically evaluated recurrence in this cyst. Systematic review

7. Calcifying odontogenic cyst

Features

• Also called Gorlin cyst
• May occur in intraosseous or extraosseous form
• Usually affects anterior jaws
• Can be associated with impacted teeth or odontoma

Radiographic features

• Unilocular or multilocular radiolucency
• Variable radiopaque calcified foci may be present

Histopathology

• Ameloblastoma-like epithelial lining
• Characteristic ghost cells
• Calcification of ghost cells may occur
• May be associated with odontoma-like hard tissue

Treatment

• Enucleation and curettage
• Prognosis is usually good

General Clinical and Diagnostic Approach

Flowchart 2: Diagnosis of a suspected odontogenic cyst

Jaw swelling / incidental radiolucency
                ↓
History and clinical examination
                ↓
Assess tooth vitality and relation to teeth
                ↓
Radiographs: IOPA, occlusal radiograph, OPG
                ↓
CBCT if lesion is large, multilocular, or near vital structures
                ↓
Aspiration where indicated
                ↓
Incisional biopsy for large, atypical, or aggressive lesions
                ↓
Definitive diagnosis by histopathology
                ↓
Enucleation / marsupialization / decompression / resection
                ↓
Clinical and radiographic follow-up

General Principles of Treatment

Small, accessible cyst
        ↓
Enucleation + curettage

Large cyst with risk to teeth, nerve, or fracture
        ↓
Marsupialization / decompression
        ↓
Later enucleation if needed

Aggressive or recurrent lesion
(e.g., some OKCs or glandular odontogenic cysts)
        ↓
Enucleation with peripheral ostectomy
or selected resection
        ↓
Long-term follow-up

Key Differential Diagnosis

Conclusion

Odontogenic Tumours

Definition

Flowchart 1: Histogenesis

Tooth-forming apparatus
        │
        ├── Odontogenic epithelium
        │       └── Epithelial odontogenic tumours
        │
        ├── Odontogenic ectomesenchyme
        │       └── Mesenchymal odontogenic tumours
        │
        ├── Epithelium + ectomesenchyme
        │       └── Mixed odontogenic tumours
        │
        └── Malignant transformation / malignant counterpart
                └── Malignant odontogenic tumours

Classification of Odontogenic Tumours

A. Benign epithelial odontogenic tumours

Benign epithelial odontogenic tumours
        │
        ├── Ameloblastoma
        │       ├── Conventional ameloblastoma
        │       ├── Unicystic ameloblastoma
        │       ├── Peripheral/extraosseous ameloblastoma
        │       └── Metastasizing ameloblastoma
        │
        ├── Adenomatoid odontogenic tumour
        ├── Adenoid ameloblastoma
        ├── Calcifying epithelial odontogenic tumour
        └── Squamous odontogenic tumour

B. Benign mesenchymal odontogenic tumours

Benign mesenchymal odontogenic tumours
        │
        ├── Odontogenic myxoma / myxofibroma
        ├── Central odontogenic fibroma
        ├── Cementoblastoma
        └── Cemento-ossifying fibroma

C. Benign mixed epithelial and mesenchymal odontogenic tumours

Benign mixed odontogenic tumours
        │
        ├── Odontoma
        │       ├── Compound odontoma
        │       └── Complex odontoma
        │
        ├── Ameloblastic fibroma
        ├── Dentinogenic ghost cell tumour
        └── Primordial odontogenic tumour

D. Malignant odontogenic tumours

Malignant odontogenic tumours
        │
        ├── Ameloblastic carcinoma
        ├── Primary intraosseous carcinoma, NOS
        ├── Clear cell odontogenic carcinoma
        ├── Ghost cell odontogenic carcinoma
        ├── Sclerosing odontogenic carcinoma
        └── Odontogenic carcinosarcoma

Clinical Features of Odontogenic Tumours

• Slow-growing, painless swelling of jaw
• Facial asymmetry and cortical expansion
• Delayed eruption or impaction of teeth
• Displacement, mobility, or resorption of teeth
• Paraesthesia, pain, ulceration, or rapid enlargement may suggest infection, cortical perforation, or malignancy
• Often discovered incidentally on radiographs

General Diagnostic Approach

Flowchart 2: Diagnostic work-up

Jaw swelling / unerupted tooth / radiolucency
                  ↓
History and clinical examination
                  ↓
Assess tooth vitality, mobility, cortical expansion,
mucosal lesion, lymph nodes and sensory deficit
                  ↓
Radiographic examination
(IOPA + OPG ± CBCT)
                  ↓
Aspiration if cystic or vascular lesion is suspected
                  ↓
Incisional biopsy for large, aggressive,
multilocular or suspicious lesions
                  ↓
Histopathological diagnosis
                  ↓
Plan treatment according to:
type + size + site + extent + recurrence risk
                  ↓
Definitive surgery and long-term follow-up

Important Benign Odontogenic Tumours

1. Ameloblastoma

Definition

Types

1. Conventional ameloblastoma
2. Unicystic ameloblastoma
3. Peripheral or extraosseous ameloblastoma
4. Metastasizing ameloblastoma

Clinical features

• Usually occurs after 20 years of age
• About 80-85% occur in the mandible
• Common site: posterior mandible, angle, and ramus
• Slow, painless expansion of jaw
• May cause facial deformity, tooth displacement, root resorption, and cortical perforation

Radiographic features

• Well-defined unilocular or multilocular radiolucency
• “Soap-bubble” or “honeycomb” appearance in multilocular lesions
• Root resorption and expansion of cortical plates may be present
• Unicystic type may mimic a dentigerous cyst around an impacted mandibular third molar

Histopathology

• Islands and cords of odontogenic epithelium in fibrous stroma
• Peripheral columnar or cuboidal ameloblast-like cells
• Reverse nuclear polarity
• Central stellate-reticulum-like cells
• Follicular and plexiform patterns are common

Surgical management

Ameloblastoma diagnosed
          ↓
Assess type, site, extent, cortical breach and recurrence
          ↓
 ┌───────────────────────────────────────────────────┐
 │ Small unicystic lesion, luminal/intraluminal type │
 └───────────────────────────────────────────────────┘
          ↓
Enucleation + curettage
± peripheral ostectomy
          ↓
Long-term follow-up

 ┌───────────────────────────────────────────────────┐
 │ Conventional, mural unicystic, recurrent, large   │
 │ lesion or cortical perforation                     │
 └───────────────────────────────────────────────────┘
          ↓
Marginal or segmental resection
with an adequate bony margin
          ↓
Immediate or delayed reconstruction
          ↓
Long-term clinical and radiographic surveillance

Principles

• Conventional ameloblastoma usually needs resection because tumour cells can extend beyond the apparent radiographic boundary.
• A margin of approximately 1 cm beyond the radiographic limit is often used for conventional intraosseous lesions, subject to site and anatomic constraints. K J Lee’s Essential Otolaryngology, p. 757.
• Unicystic ameloblastoma may be treated conservatively if it is luminal or intraluminal. Mural invasion carries a higher recurrence risk and may require more extensive surgery.
• Peripheral ameloblastoma is treated by local excision with a cuff of normal soft tissue and superficial bone if involved.
• Reconstruction of segmental mandibular defects may require reconstruction plates, non-vascularized grafts in selected small defects, or vascularized free flap reconstruction for large defects.

2. Adenomatoid Odontogenic Tumour

Features

• Benign, encapsulated epithelial tumour
• Occurs mainly in adolescents and young adults
• More common in females
• Usually affects anterior maxilla
• Commonly associated with unerupted maxillary canine
• Often called the “two-thirds tumour”:
  • About two-thirds occur in maxilla
  • About two-thirds occur in females
  • About two-thirds are associated with unerupted canine

Radiographic features

• Well-circumscribed unilocular radiolucency
• Surrounds crown and often part of root of unerupted tooth
• Fine “snowflake” calcifications may be visible

Histopathology

• Duct-like or rosette-like epithelial structures
• Spindle-shaped epithelial cells
• Calcified material may be present

Treatment

• Conservative enucleation and removal of associated tooth if required
• It is usually well encapsulated
• Recurrence is rare

3. Calcifying Epithelial Odontogenic Tumour

Features

• Also called Pindborg tumour
• Rare benign epithelial tumour
• Usually occurs in posterior mandible
• Often associated with impacted tooth
• May show slow painless swelling

Radiographic features

• Unilocular or multilocular radiolucency
• “Driven snow” calcific opacities may be seen
• Can cause root resorption and cortical expansion

Histopathology

• Polyhedral epithelial cells
• Amyloid-like extracellular material
• Calcifications forming Liesegang rings

Treatment

• Enucleation with curettage for small lesions
• Marginal or segmental resection for large, recurrent, or infiltrative lesions
• Long-term follow-up is required

4. Squamous Odontogenic Tumour

Features

• Rare benign epithelial tumour
• Often associated with roots of teeth
• Usually presents as painless swelling, tooth mobility, or periodontal pocket
• Radiograph may show triangular radiolucency between roots

Treatment

• Local excision and curettage
• More extensive surgery if lesion is large or recurrent

5. Odontoma

Definition

Types

Odontoma
   │
   ├── Compound odontoma
   │       └── Multiple small tooth-like structures
   │
   └── Complex odontoma
           └── Irregular calcified mass of enamel,
               dentin and cementum

Clinical features

• Usually diagnosed in first two decades
• Commonly causes delayed eruption of a permanent tooth
• Often asymptomatic and discovered on radiograph

Treatment

• Conservative surgical removal
• Removal of obstruction may permit eruption of associated tooth
• Orthodontic traction may be needed if eruption does not occur

6. Ameloblastic Fibroma

Features

• Benign mixed odontogenic tumour
• Usually occurs in children and adolescents
• More common in posterior mandible
• Frequently associated with unerupted tooth
• Radiographically presents as well-defined unilocular or multilocular radiolucency

Treatment

• Enucleation and curettage
• Preserve involved tooth where feasible, depending on tumour relationship and eruption potential
• Follow-up is advised because recurrence can occur

7. Odontogenic Myxoma

Features

• Benign mesenchymal tumour but locally infiltrative
• Common in second and third decades
• More frequent in mandible, particularly posterior region
• Causes slow expansion of jaw

Radiographic features

• Unilocular or multilocular radiolucency
• May show “tennis-racket,” “step-ladder,” or soap-bubble trabecular pattern
• Margins may be poorly defined

Treatment

Small, well-defined odontogenic myxoma
                ↓
Enucleation + vigorous curettage
                ↓
Close follow-up

Large, multilocular or recurrent lesion
                ↓
Marginal / segmental resection
                ↓
Reconstruction if required
                ↓
Long-term surveillance

8. Cementoblastoma

Features

• Benign mesenchymal odontogenic tumour of cementoblasts
• Usually attached to root of mandibular first permanent molar
• Common in young patients
• May produce pain and jaw expansion

Radiographic features

• Well-defined radiopaque mass fused to tooth root
• Surrounded by a thin radiolucent rim
• Root outline may be obscured due to fusion with tumour

Treatment

• Complete excision of tumour along with extraction of involved tooth or root resection where feasible
• Curettage of surrounding bone
• Recurrence is uncommon after complete removal

Surgical Management: General Principles

Flowchart 3: Selection of surgery

Histopathological diagnosis
          ↓
Assess biological behaviour
          ↓
┌────────────────┬───────────────────────────┬─────────────────────┐
│ Encapsulated / │ Locally aggressive benign │ Malignant tumour    │
│ hamartomatous  │ tumour                    │                     │
└────────────────┴───────────────────────────┴─────────────────────┘
          ↓                    ↓                       ↓
Enucleation or          Wide local bony          Wide resection
local excision           excision / resection    with clear margins
          ↓                    ↓                       ↓
Curettage if needed     Reconstruction as needed Neck assessment
          ↓                    ↓                       ↓
Short to moderate       Long-term surveillance   Adjuvant therapy
follow-up               for recurrence           when indicated

Surgical options

1. Enucleation

• Small, well-encapsulated lesions
• Adenomatoid odontogenic tumour
• Odontoma
• Small ameloblastic fibroma
• Selected unicystic ameloblastoma

2. Curettage

• Often combined with enucleation
• Helps remove residual tissue in small benign lesions
• Not sufficient alone for infiltrative lesions

3. Peripheral ostectomy

• Selected ameloblastomas
• Recurrent lesions
• Tumours with limited cortical involvement

4. Marginal resection

• Selected benign but locally aggressive lesions
• Tumours without extensive inferior border involvement
• Some ameloblastomas and odontogenic myxomas

5. Segmental resection

• Large conventional ameloblastoma
• Recurrent ameloblastoma
• Cortical perforation or soft-tissue extension
• Large odontogenic myxoma
• Malignant odontogenic tumour

6. Maxillary resection

7. Reconstruction

Jaw defect after resection
          ↓
Small defect
          └── Plate fixation ± non-vascularized bone graft

Large mandibular defect
          └── Vascularized osseous free flap
              - Fibula free flap
              - Iliac crest flap
              - Scapular flap

Soft-tissue defect
          └── Local, regional or free soft-tissue flap

Management of Malignant Odontogenic Tumours

Suspected malignant odontogenic tumour
                  ↓
Incisional biopsy + CT/MRI staging
                  ↓
Assess cervical nodes and distant metastasis
                  ↓
Wide surgical resection with negative margins
                  ↓
Neck dissection if clinically/radiologically positive nodes
or high risk of nodal spread
                  ↓
Reconstruction of jaw and soft tissues
                  ↓
Postoperative radiotherapy ± systemic therapy
when indicated by histology, margins, nodal disease,
perineural invasion or unresectable disease
                  ↓
Long-term surveillance

Principles

• Surgery with clear margins is the main treatment.
• Neck dissection is not routine for every lesion, but is indicated for clinically involved cervical nodes and considered according to tumour type and risk.
• Radiotherapy may be used for positive/close margins, unresectable disease, nodal disease, or selected high-risk malignancies.
• Ameloblastic carcinoma and clear cell odontogenic carcinoma require aggressive oncologic treatment and long-term follow-up.

Follow-up

• Conventional ameloblastoma
• Mural unicystic ameloblastoma
• Odontogenic myxoma
• Calcifying epithelial odontogenic tumour
• Malignant odontogenic tumours

Postoperative review
       ↓
Clinical examination:
swelling, mucosa, occlusion, sensation, lymph nodes
       ↓
Radiographic surveillance:
OPG / CBCT when indicated
       ↓
Early detection of recurrence
       ↓
Further definitive surgery if required

Conclusion