Orofacial cysts


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


(I) Odontogenic cysts

1. Inflammatory (dental cysts)

2. Developmental

(II) Non odontogenic cysts

1. Fissural cysts

2. Bone cysts/pseudocysts

3. Soft tissue cysts

4. Maxillary antral cyst

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


Source of epithelium

TypeEpithelium sourceRests originCyst
Odontogenic restsRests of MalassezEpithelial root sheath– Radicular cyst
Odontogenic restsReduced enamel epithelium (REE)Enamel organ– Paradental cyst
– Dentigerous cyst
– Eruption cyst
Odontogenic restsRests of dental lamina (Serres)Epithelial connection between mucosa and enamel organ– Lateral periodontal cyst
– Gingival cyst
– Odontogenic keratocyte
– Glandular cyst
Non odontogenic restsNasopalatine canal duct remnantsVestigial 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 source of epithelium

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


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

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