Definition

• Pathological cavity containing pus and fluid/ semi-fluid/ gas ± lined with epithelium

Classification

(I) Odontogenic cysts

1. Inflammatory (dental cysts)

• Radicular and residual cysts – apical & lateral
• Paradental cyst
• Buccal bifurcation cyst

2. Developmental

• Follicular/ dentigerous cyst
• Eruption cyst
• Developmental lateral periodontal cyst – between canine and premolar
• Gingival cyst:
  • of new born
    • Mandible – Bohn’s nodule
    • Maxillary – Epstein pearl
  • of adult
• Odontogenic keratocyte (KCOT)
• Glandular/ sialo-odontogenic cyst

(II) Non odontogenic cysts

1. Fissural cysts

• Nasopalatine cyst/ incisive canal cyst
• Nasolabial cyst
• Globulomaxillary cyst
• Median palatine cyst

2. Bone cysts/pseudocysts

• Solitary bone cyst
• Aneurysmal bone cyst
• Static bone cyst (Stafne’s)

3. Soft tissue cysts

• Salivary: mucous extravasation & mucous retention cyst
• Dermoid cyst
• Epidermoid cyst
• Branchial (lymphoepithelial cyst)
• Thyroglossal duct cyst
• Cystic hygroma/ lymphangioma
• Thymic cyst

4. Maxillary antral cyst

• Mucous retention cyst, extravasation cyst, pseudocyst
• Mucosal lining of sinus, respiratory epithelium
• Radiology: opaque dome shape
• Picture

Pathogenesis

Source of epithelium

Type	Epithelium source	Rests origin	Cyst
Odontogenic rests	Rests of Malassez	Epithelial root sheath	– Radicular cyst
Odontogenic rests	Reduced enamel epithelium (REE)	Enamel organ	– Paradental cyst – Dentigerous cyst – Eruption cyst
Odontogenic rests	Rests of dental lamina (Serres)	Epithelial connection between mucosa and enamel organ	– Lateral periodontal cyst – Gingival cyst – Odontogenic keratocyte – Glandular cyst
Non odontogenic rests	Nasopalatine canal duct remnants	Vestigial nasopalatine ducts	– Nasopalatine cyst
Non odontogenic rests	– Salivary duct epithelium – Ductal epithelium in lymphoid tissue – Thyroglossal duct epithelium		– Mucous retention cyst – Branchial cyst – Thyroglossal cyst

Cyst initiation

Stimuli for cavitation and epithelial cell proliferation

Periapical abscess: Pus at root apex. Inflammation, pain, lymphadenitis, fever. Complication is acute osteomyelitis

Periapical granuloma: Chronic inflammation at apex of non vital tooth. Dull percussion sound, mild pain on chewing, feels elongated in socket. Well circumscribed ovoid radiolucency at apex <1cm

Inflammation

1. Necrotic/ infected pulp – periapical granuloma – inflammatory cells release cytokines – inflammatory cyst develops from rests of Malassez – Radicular cyst

2. Inflammation at base of periodontal pocket – lateral granuloma – lateral periodontal cyst in lateral root canals

• Inflammatory cells secrete cytokines – IL-6, IL-1, TNF, growth factors (EGF, TGFβ, KGF) – stimulate epithelial cell proliferation

• Plasma cell activity in inflammatory cysts – accumulation of gamma globulin – Russell bodies

• Breakdown of hemorrhagic products – hyalin aggregates – Rushton bodies

(EGF – Epidermal GF, TGFβ – Transforming GFβ, KGF – Keratinocyte GF)

Developmental factors

• Produce anti-apoptotic factors eg. Bcl2
• High proliferative index of epithelium (+ve Ki67 staining)

Cyst expansion

Continued cyst growth and bone resorption

Hydrostatic mechanism – Process of dialysis

• Cyst wall acts as semipermeable membrane
• Proteins accumulate in cyst
• Fluid accumulates due to osmotic gradient
• Fluid accumulates as inflammatory exudate in cyst lumen
• Creates +ve pressure in cyst + osmotic gradient for more fluid to accumulate
• Expansion of inflammatory cysts and dentigerous cyst

Cytokines and PGE2 mediated bone resorption

• Cyst produce proinflammatory cytokines – IL-1, TNF, PGE2 – potent inducers of bone resorption

Epithelial growth factors and mural growth

• EGF, TGFβ – Proliferation of cyst epithelium

Mechanism of bone resorption: Radicular cyst

• Bacterial antigens + irritants from necrotic pulp
• Inflammation of cyst capsule
• Chronic inflammatory cell infiltration
• Cytokines release Eg. IL-6
• Fibroblast activation
• Collagenase, prostaglandins, osteoclast stimulation
• Bone resorption

Investigations of cystic lesions of the jaws

1. Signs common to all cysts:

• Dull sound on tooth percussion
• Displaced teeth
• Swelling
• Eggshell crackling on pressure
• Loosened teeth (late stage)
• Fluctuation

2. Other signs:

• Non vital tooth – inflammatory dental cyst
• Unerupted tooth – dentigerous cyst

Specific histological features

Odontogenic inflammatory

1. Cholesterol clefts – Cholesterol crystals lost during tissue processing – slit like spaces in decalcified tissue sections

2. Rushton (hyalin) bodies – Common in inflammatory cysts

Odontogenic developmental

1. Cyst epithelium – Flat basement membrane

2. Mucous metaplasia – Most common in dentigerous cyst

Diagnosis for cystic lesions

1. Radiography:

• Morphology of lesion
• Relationship with teeth and other structures
• Soft tissue cyst – inject contrast media

2. Incisional biopsy:

• Extensive lesion that may not be a simple lesion
• Cyst at angle of ramus of mandible – KCOT and ameloblastoma commonly occur

3. Aspiration biopsy:

Following observations made:

1. Appearance:

• White sludgy material – Keratin of KCOT
• Cannot withdraw any fluid – solid tumor mass/ viscous keratin content
• Pus – infected cyst
• Air – needle in maxillary antrum
• Blood:
  • Contamination from needle wound
  • Central hemangioma
  • Aneurysmal bone cyst

2. Smell: Foul – infected

3. Culture: If infection suspected

4. Bilirubin content: Fluid from solitary bone cyst – clots on standing – high bilirubin content

5. Electrophoresis: Use normal serum as control

• KCOT – no soluble protein band (most protein is insoluble keratin)
• Inflammatory and dentigerous cyst – similar to serum
• Infected/blood contaminated – similar to serum

6. Total soluble protein content:

• KCOT < 4g/100ml
• Others > 5g/100ml

7. Smear, fix and stain for keratin:

• If keratinized squames seen – KCOT