Radicular Cyst

§ overviewOverview

An inflammatory odontogenic cyst arising from the epithelial cell rests of Malassez in the periodontal ligament, triggered by pulpal necrosis and periapical inflammation.

§ icdICD Classification

ICD-10 K04.8

§ etiologyEtiology

• 01Pulp necrosis from dental caries
• 02Traumatic pulp injury
• 03Failed root canal treatment
• 04Deep restorations reaching pulp

§ riskRisk Factors

• 01Untreated deep caries
• 02Chronic periapical granuloma > 3 months
• 03Cracked tooth
• 04Prior trauma to anterior teeth

§ geneticsGenetics & Molecular Biology

• 01No germ-line predisposition
• 02Upregulation of IL-1, IL-6, TNF-α, RANKL, MMP-9 drives epithelial proliferation and bone resorption

§ epidemiologyEpidemiology

Accounts for 52–68% of all jaw cysts. Peak incidence: 3rd–5th decade. M > F (~1.5:1). Maxilla > mandible (~3:1); most common at maxillary anteriors.

§ pathogenesisPathogenesis

Pulp necrosis → periapical inflammatory infiltrate → cytokine-mediated activation of epithelial cell rests of Malassez → three-phase development: (1) initiation of epithelial proliferation, (2) cyst formation by central necrosis of epithelial mass or coalescence of microcysts, (3) enlargement by osmotic pressure gradient and bone resorption via RANKL/OPG imbalance.

§ clinicalClinical Features

• 01Usually asymptomatic — incidental radiographic finding
• 02Non-vital associated tooth (negative to EPT and cold)
• 03Slow painless bony swelling as cyst enlarges
• 04Egg-shell crackling when cortex thins
• 05Occasional discharging sinus

§ signsSigns & Symptoms

• 01Discoloured non-vital tooth
• 02Tenderness on percussion when acutely infected
• 03Fluctuant swelling in vestibule
• 04Rarely paraesthesia (excludes malignancy)

§ differentialDifferential Diagnosis

• 01Periapical granuloma
• 02Periapical cemento-osseous dysplasia (early stage)
• 03Lateral periodontal cyst
• 04Traumatic bone cyst
• 05Central giant cell granuloma
• 06Ameloblastoma (in molars)

§ criteriaDiagnostic Criteria

• 01Radiolucency (usually > 1 cm) associated with a non-vital tooth
• 02Well-defined corticated margin
• 03Histologic confirmation of non-keratinised stratified squamous epithelial lining with inflammatory infiltrate

§ histopathHistopathology

• 01Non-keratinised stratified squamous epithelium (6–20 cell layers, arcading pattern)
• 02Fibrous connective tissue capsule densely infiltrated by lymphocytes, plasma cells and neutrophils
• 03Rushton hyaline bodies (~10%) — eosinophilic, hairpin-shaped intra-epithelial structures
• 04Cholesterol clefts with foreign-body giant cells
• 05Haemosiderin pigment; occasional dystrophic calcification

§ radiographicRadiographic Features

• 01Round to oval well-circumscribed radiolucency at root apex
• 02Corticated margin (lost when acutely infected)
• 03Continuous with lamina dura of offending tooth
• 04Root resorption in long-standing cysts (~30%)

§ opgOPG Findings

• 01Best initial screening; assess extent, cortical integrity, relation to sinus/IAN canal
• 02Loss of lamina dura is the earliest sign

§ cbctCBCT Findings

• 013D delineation of buccolingual expansion
• 02Relation to maxillary sinus floor or inferior alveolar canal
• 03Small-FOV CBCT preferred to limit dose

§ ctCT Findings

• 01Reserved for large lesions or infected cysts extending into deep spaces; assess cortical perforation

§ mriMRI Findings

• 01Hypointense on T1, hyperintense on T2, no enhancement of contents; peripheral rim enhancement of lining

§ investigationsInvestigations

• 01Vitality testing (EPT + thermal) — pathognomonic negative response of causative tooth
• 02Percussion & palpation
• 03Aspiration — straw-coloured fluid, cholesterol crystals shimmer
• 04Biopsy for histopathologic confirmation after enucleation

§ labsLaboratory Findings

• 01Aspirate protein > 5 g/dL (< 4 g/dL suggests OKC)
• 02Cholesterol crystals on microscopy

§ ihcIHC / Special Stains

• 01Cytokeratin 13/14 positive lining
• 02Ki-67 low (< 5%) — distinguishes from OKC (10–35%)
• 03p53 low

§ whoWHO Classification

WHO 2022 Classification of Head & Neck Tumours: Inflammatory odontogenic cyst — Radicular cyst (apical, lateral, residual variants).

§ classificationClassification

• 01Apical radicular cyst — at root apex
• 02Lateral radicular cyst — from lateral accessory canal
• 03Residual cyst — persists after tooth extraction

§ planTreatment Planning

• 01Confirm non-vitality of associated tooth
• 02Small (< 2 cm) cysts amenable to endodontic therapy alone
• 03Large cysts or failed RCT → surgical management
• 04Assess relation to vital structures on CBCT before surgery

§ treatmentTreatment

• 01Non-surgical root canal treatment for small lesions — up to 85% heal without surgery
• 02Apicoectomy + retrograde MTA seal for persistent apical pathosis
• 03Enucleation ± peripheral ostectomy for lesions > 2 cm
• 04Marsupialisation (Partsch I) for very large cysts adjacent to vital structures, followed by staged enucleation
• 05Extraction of hopeless tooth with enucleation of cyst

§ medicalMedical Management

• 01Antibiotics only if secondary infection (amoxicillin 500 mg TID × 5 d ± metronidazole)
• 02Analgesics as required

§ surgicalSurgical Management

• 01Enucleation (Partsch II) — cyst removed en bloc with lining
• 02Marsupialisation (Partsch I) — decompression via window
• 03Apicoectomy with retrograde filling
• 04Guided bone regeneration with membrane + graft for large defects

§ reconstructionReconstruction Options

• 01Small defects: heal by secondary intention with clot
• 02Medium: xenograft (Bio-Oss) or autogenous chin/ramus graft
• 03Large: iliac crest graft; rarely microvascular flap

§ complicationsComplications

• 01Secondary infection → cellulitis
• 02Pathologic fracture of atrophic mandible
• 03Displacement into maxillary sinus or IAN canal injury
• 04Recurrence if lining incompletely removed
• 05Very rare: SCC or mucoepidermoid carcinoma arising in cyst lining

§ recurrenceRecurrence Rate

< 2% after complete enucleation; residual cyst if incomplete removal.

§ followupFollow-up Protocol

• 01Clinical + radiographic review at 3, 6, 12 months post-op
• 02Annual OPG until complete bony infill (usually 12–24 months)
• 03Long-term follow-up for large lesions or those adjacent to vital structures

§ prognosisPrognosis

Excellent. Endodontic success rate 85–90%; surgical enucleation > 95% cure.

§ preventionPrevention

• 01Early caries management
• 02Prompt endodontic treatment of pulpal disease
• 03Regular dental review
• 04Trauma prevention (mouthguards)

§ examKey Examination Points

• 01Always test pulp vitality of adjacent teeth
• 02Radiolucency + non-vital tooth = radicular cyst until proven otherwise
• 03Aspiration protein content > 5 g/dL supports diagnosis

§ revisionQuick Revision Summary

• 01Most common odontogenic cyst
• 02From cell rests of Malassez
• 03Always non-vital tooth
• 04Non-keratinised stratified squamous lining
• 05Rushton bodies pathognomonic when present
• 06Enucleation is curative

§ vivaBDS Viva Questions

• 01Define radicular cyst.
• 02Which cells give rise to a radicular cyst?
• 03Describe the three phases of cyst development.
• 04How do you differentiate a radicular cyst from a periapical granuloma?
• 05What is a Rushton body?
• 06List the contents of aspirated cyst fluid.
• 07Describe Partsch I vs Partsch II operations.
• 08What is a residual cyst?
• 09Complications of an untreated radicular cyst?
• 10Recurrence rate after enucleation?
• 11When would you choose marsupialisation?
• 12How does cholesterol accumulate in a radicular cyst?
• 13Role of RANKL/OPG in cyst enlargement?
• 14Radiographic differential diagnosis for a periapical radiolucency?
• 15How is the maxillary sinus involvement managed?
• 16Antibiotic regimen if infected?

§ bdsBDS Professional Examination

• 01Long essay: Classify odontogenic cysts. Describe aetiopathogenesis, clinical & radiographic features, and management of radicular cyst.
• 02Short essay: Rushton bodies.
• 03Short note: Residual cyst.
• 04Short note: Marsupialisation vs enucleation.

§ fcpsFCPS Residency Questions

• 01Discuss the molecular pathogenesis of inflammatory odontogenic cyst enlargement and evidence-based rationale for surgical vs non-surgical management.
• 02Compare radicular cyst with OKC in terms of biology, imaging, histology, treatment and recurrence.
• 03Discuss reconstruction of a large mandibular cystic defect following enucleation.

§ pearlsClinical Pearls

• 01Not every periapical radiolucency is a cyst — histology is the arbiter.
• 02Failed RCT + persistent radiolucency at 6 months → surgical exploration.

§ mnemonicsMnemonics

• 01Radicular = Rest of Malassez, Rushton bodies, Root apex, Rotten (non-vital) tooth

§ readingSuggested Reading

• 01Shear M, Speight PM. Cysts of the Oral and Maxillofacial Regions, 4e — Wiley-Blackwell
• 02Nair PNR. On the causes of persistent apical periodontitis: a review. Int Endod J 2006.
• 03Lin LM et al. Periapical bone regeneration after endodontic microsurgery. J Endod 2020.

§ differentialDifferential Comparison

§ mcqsMCQs — Assessment (20)

§ relatedRelated Diseases

References

1. WHO Classification of Head and Neck Tumours, 5e (2022)
2. Neville BW et al. Oral and Maxillofacial Pathology, 4e
3. Shafer WG et al. Textbook of Oral Pathology, 9e
4. Peterson LJ. Contemporary Oral & Maxillofacial Surgery, 7e
5. Nair PNR. Non-microbial etiology: periapical cysts sustain post-treatment apical periodontitis. Endod Topics 2003.