Definition
A radicular (periapical) cyst is a cyst on the apex of a non-vital tooth. It is the most common type of cyst in the jaws and an inflammatory odontogenic cyst.
Etiology and Pathophysiology
- Inflammatory odontogenic cyst arising from a non-vital tooth (necrotic pulp, e.g. from dental caries or tooth fracture).
- Defined by its location at the apex of a non-vital tooth; results from periapical inflammation extending from the pulp.
- Pathogenesis (sequence):
- Initiation — cell rests of Malassez (remnants of Hertwig’s epithelial root sheath) are activated by products of necrotic pulp / inflammation in a periapical granuloma.
- Cyst formation (cavitation) — proliferating epithelial islands degenerate and die centrally, producing a cavity.
- Cyst enlargement — increased osmolality (breakdown products become smaller and more osmotically active); the cyst wall acts as a semi-permeable membrane → balloon-like expansion with pressure effects on bone and teeth.
- Bone-resorbing factors (prostaglandins, collagenase) released by cyst tissue facilitate bone destruction to accommodate growth.
- Cyst contents: cell breakdown products, serum proteins, water and electrolytes, and cholesterol crystals.
Contributory factors :
- Non-vital tooth (necrotic pulp) — required by definition.
- Periapical granuloma containing proliferating epithelial rests of Malassez.
- Secondary inflammation from the non-vital tooth (degenerating erythrocytes release cholesterol → foreign-body reaction).
- Rests of Malassez are more frequent around the apical third of the root and vary between individuals — may explain why some patients develop multiple radicular cysts.
Prevalence
- Most common cyst of the jaws — 60–75% of all jaw cysts (Cawson UK estimates: radicular ~45%, residual radicular ~7%).
- Odontogenic cysts make up ~90% of jaw cysts.
- Peak incidence in the 4th and 5th decades; wide age range (~20–60 years).
- More common in males than females (roughly 3:2).
- Rare in deciduous teeth / before age 10 (time required to form).
Histological Features
- Lined by irregular, non-keratinised stratified squamous epithelium of variable thickness.
- More inflamed cysts show hyperplastic epithelium with a net-like / “arcading” pattern and irregularly elongated rete ridges; polymorphs (neutrophils) may emigrate through the epithelium.
- Fibrous (connective tissue) wall with chronic inflammatory infiltrate — lymphocytes, plasma cells, foamy macrophages (foam cells).
- Cholesterol clefts (cholesterol dissolved out during preparation) with foreign-body giant cells, in wall and lumen; hemosiderin pigment.
- Approximately 10% contain hyaline (Rushton) bodies in the epithelium — confirm odontogenic origin.
- Mucous (and occasionally ciliated columnar) metaplasia may occur.
- Longstanding cysts: thinner, flattened, less-inflamed lining with a thick fibrous wall.
- Developmental sequence: early lesions are little more than a periapical granuloma with proliferating epithelial strands.
Clinical Features
Location
- At the apex of a non-vital tooth (apical); variants:
- Lateral — forms at the side of the root at the opening of a lateral/accessory root canal.
- Residual — persists in the jaw after extraction of the causative tooth.
- Maxilla affected more than three times as often as the mandible; the upper lateral incisor is the most commonly affected tooth.
Appearance
- Often asymptomatic, especially when small (~1–2 cm); frequently an incidental radiographic finding.
- Slowly progressive painless swelling — rounded and hard initially.
- As bone thins to eggshell thickness → “springy” sensation → egg-shell crackling → fluctuation (soft, bluish swelling beneath the mucosa once wall resorbs).
- Secondary infection → pain; acute exacerbation may produce a draining sinus/fistula.
- Radiographic features: monolocular, well-defined and well-corticated (sclerotic) outline, uniformly radiolucent area around the apex of the non-vital tooth. Corticated periphery is more prominent in longstanding/slow-growing cysts. Adjacent teeth may be tilted/displaced; root resorption can occur.
Differential Diagnoses
- Periapical granuloma / apical granuloma (no defined radiographic size cut-off distinguishes the two; sharp radiographic definition is a poor discriminator).
- Lateral periodontal cyst (forms beside a vital tooth root — must be distinguished from a lateral radicular cyst).
- Dentigerous cyst (tooth vitality is the key differentiating feature — the tooth involved by a dentigerous cyst is vital).
- For residual cysts: other odontogenic and non-odontogenic cysts and tumours may mimic the appearance.
- Rarely, squamous cell carcinoma can arise within the cyst lining (longstanding, untreated cysts).
Relevant Clinical Investigations
- Pulp vitality testing — the associated tooth is non-vital (primary diagnostic clue).
- Radiographs — assess shape (monolocular), outline (well-defined, corticated), radiodensity (radiolucent), relation to the apex of a non-vital tooth; CT for larger/expansile lesions.
- Diagnosis is by the combination of radiographic appearance, a non-vital tooth, and appropriate histology.
- Histopathology / biopsy — clinical and radiographic features are usually adequate; biopsy reserved for unusual features (root resorption, poorly defined margin) and to exclude unsuspected diagnoses. Excised tissue (especially for residual cysts) should be submitted for histopathological examination.
Patient Management
- Enucleation and primary closure is the usual treatment (radicular cysts do not recur after enucleation).
- The associated non-vital tooth is usually extracted, or it can be preserved by orthograde root filling before surgery plus apicectomy and retrograde filling (e.g. mineral trioxide aggregate) at enucleation.
- Endodontic (root canal) therapy alone may resolve small suspected cysts (lesions up to ~20 mm have been shown to resolve); worth attempting for small lesions if the patient accepts a risk of failure, though it carries risk of infection or missing an unsuspected lesion.
- Healing/bone fill may take several months; cortical expansion remodels slowly.
- Residual cysts are treated by enucleation, with histopathological examination of removed tissue.