Radicular Cyst

• Odontogenic cyst of inflammatory origin
• Preceeded by pulp necrosis and chronic periapical granuloma
• Most common odontogenic cyst
• Also known as periapical cyst
• Described as a residual cyst if present following tooth extraction
• Lateral radicular cyst - occasionally form at the side of a non-vital tooth as a result of the opening of a lateral branch of the root canal

Epidemiology

• Commonest type of jaw cyst (~60% of all cases)
• Most common between ages of 20-60yrs old – rare <10yrs old
• ♂ > ♀ (3:2)
• Maxilla > Mandible (3:1)
• Incidence of different types of radicular/peripical cysts:
  1. Apical - 70%
  2. Lateral - 20%
  3. Residual - 10%

Clinical Features

• Slowly progressive painless swellings
• Usually cause no symptoms unless large enough to be conspicuous
• Can get infected → painful and rapid expansion (inflammatory oedema)
• If visible, swelling is usually round and hard
• If left to enlarge →
  • Bone can be reduced to egg shell thickness and a crackling sensation may be felt on gentle pressure
  • Finally if part of the wall is resorbed entirely the swelling is soft, fluctuant and bluish in colour
• A necrotic tooth from which the tooth has originated is (by definition) present (if not then the cyst is termed a residual cyst)

Differential Diagnosis

• Other cysts of the jaws

Aetiology and Pathogenesis

Aetiology

• Radicular cysts are cysts of inflammatory origin
• Preceded by necrotic tooth and periodical granuloma

Pathogenesis

• Major factors in the pathogenesis of cyst formation:
  1. Proliferation of epithelial lining and fibrous capsule
     • Apical periodontitis → resorption of alveolar bone via immune-inflammatory process
     • Inflammtory cytokines and growth factors released in apical periodontitis can stimulate epithelial cell rests of Malassez (remnants of Hertwig's epithelial root sheath)
       • Basal cells of the epithelial cell rests of Malassez are stimulated to proliferate and form the cyst
  2. Hydrostatic pressure of cyst fluid
     • Cyst fluid (inflammortary exudate and necrotic cellular debris) contains straw-coloured fluid containing cholesterol cystals with protein content >5g/dL
     • ∴ osmostic tension can cause cysts to expand in balloon like fashion
     • Expansion tends to occur in pathway of least resistance therefore tend to be less destructive
     • Hydrostatic pressure within cysts is ~70cm of water (higher than the capillary blood pressure)
  3. Resorption of surrounding bone
     • Cyst tissues have been shown to release bone-resorbing factors (prostaglandin E2 and E3) and collagenases
     • It is not fully clear what affect these have on cyst growth

Investigations

Orthopantogram of a radicular cyst in the mandible. Image from AboulHosn et al. 2019

Histopathology of a radicular cyst, with metaplastic changes of mucous secreting cells, and ciliated cells

Histopathology of cholesterol clefts of a radicular cyst

Imaging

Plain film

• Commonly an incidental finding on routine intra-oral or panoramic radiographs
• Cysts only make up ~15% of all periapical radiolucencies
  • Consider a cyst as opposed to periapical abscess when lesion is larger than 2cm²
• Common radiographic features:
  • Round radiolucent area
  • Unilocular
  • Sharply defined
  • Condensed radio-opaque periphery is present in long standing cysts
  • Associated with necrotic tooth
  • Large lesions can cause displacement/tilting of adjacent teeth
  • Large cysts in maxilla may extend in irregular shapes
  • Infected cyst may cause hazy outline and resorption of surrounding bone

Computed Tomography

• Can facilitate diagnosis, and 3D characterisation for surgical planning

Histopathology

• Common histopathological findings:
  1. Epithelial lining
     • Stratified squamous epithelium (non-keratinised) - except when near maxillary sinus where there is respiratory epithelium (pseudostratified ciliated columnar epithelium)
     • Varying thickness
     • Lacks well defined basal cell layer (may be missing)
     • Hyaline bodies and mucous cells may be present ∵ of metaplasia
     • Longstanding cysts = thin epithelial lining, thick fibrous wall and minimal inflammatory infiltrate
  2. Cyst capsule and wall
     • Collagenous fibrous connective tissue
     • Vascular during active growth
  3. Clefts
     • Clefts are present in cyst capsule
     • These occur ∵ breakdown of blood cells → cholesterol formation → cholesterol then dissolves out → clefts
  4. Cyst fluid
     • Usually watery and opalescent
     • Sometimes viscid and yellowish
     • Microscopy (after smear) shows cholesterol crystals
     • Histology shows protein (broken down leucocytes and cells distended within fat globules)

Management

• Cyst enucleation - usually treatment of choice along with one of the following:
  1. Orthograde endodontic treatment
  2. Apicectomy
  3. Extraction
• Orthograde endodontic treatment alone is suitable for small cysts (<1cm) as the cyst may subsequently heal
• Marsupialization may sometimes be needed for very large cysts

Prognosis and Complications

• Recurrence is uncommon if capsule is completely removed

Follow-up

• Routine follow-up not needed
• Suitable for results to be given to patient via remote consultation/mail