11.2 Odontogenic Cysts
Key Takeaways
- A radicular (periapical) cyst is the most common odontogenic cyst, arising from rests of Malassez at the apex of a non-vital tooth; a residual cyst is the same lesion left in bone after extraction
- A dentigerous (follicular) cyst is the second most common, attaching at the cementoenamel junction around the crown of an unerupted tooth — classically the mandibular third molar or maxillary canine
- The odontogenic keratocyst (OKC) is classified by WHO 2017 and retained as a cyst in WHO 2022; it shows parakeratinised epithelium with basal palisading, behaves aggressively and recurs, and is associated with Gorlin-Goltz (naevoid basal cell carcinoma) syndrome via PTCH1 mutation
- A nasopalatine duct (incisive canal) cyst produces a midline anterior maxillary heart-shaped radiolucency between the vital upper central incisors
- Marsupialisation (decompression) is preferred for very large cysts or when preservation of an associated erupting tooth is desired; otherwise enucleation is definitive
Definition and Classification
An odontogenic cyst is a pathological cavity lined by epithelium derived from odontogenic epithelium. The jaws are uniquely susceptible because of the remnants of tooth development.
| Cyst | Epithelial origin | Relative frequency |
|---|---|---|
| Radicular (periapical) | Rests of Malassez | ~65% (most common) |
| Dentigerous (follicular) | Reduced enamel epithelium | ~20% (2nd most common) |
| Odontogenic keratocyst (OKC) | Dental lamina rests | ~10% |
| Nasopalatine duct (incisive canal) | Nasopalatine duct epithelium | ~5% |
| Lateral periodontal cyst | Dental lamina rests | uncommon |
| Calcifying odontogenic cyst (Gorlin) | Reduced enamel epithelium | uncommon |
Radicular (Periapical) Cyst
- Most common odontogenic cyst.
- Inflammatory in origin; sequel of periapical periodontitis in a non-vital tooth.
- Pathogenesis: necrotic pulp → periapical inflammation → rests of Malassez proliferate under inflammatory stimulus → cyst formation.
- Site: apex of any non-vital tooth (most often maxillary incisors).
- Radiology: well-defined periapical radiolucency with sclerotic margins; loss of lamina dura; may displace adjacent structures. A periapical granuloma is radiologically indistinguishable; size >2 cm and a cortical buccal plate suggests cyst rather than granuloma.
- Histology: non-keratinised stratified squamous epithelium, mixed inflammatory infiltrate, Rushton bodies (hyaline bodies), cholesterol clefts with foreign-body giant cells, haemosiderin.
- Management: endodontic treatment; extraction with apical curettage if the tooth is unsavable; apicectomy if the cyst persists after adequate root treatment.
Residual Cyst
A residual cyst is a radicular cyst left in the jaws after extraction of the causative non-vital tooth. Radiology: well-circumscribed radiolucency in an edentulous area. Management: enucleation if symptomatic, enlarging, or interfering with prosthesis/prosthetic planning.
Dentigerous (Follicular) Cyst
- Develops from the reduced enamel epithelium around the crown of an unerupted tooth after the crown has formed.
- 2nd most common odontogenic cyst.
- Classical sites: mandibular third molar > maxillary canine > maxillary third molar.
- Radiology: unilocular radiolucency attached at the cementoenamel junction (CEJ) enclosing the crown. Cortical expansion is buccal/lingual.
- Histology: thin non-keratinising stratified squamous epithelium.
- Management: enucleation with extraction of the associated tooth; marsupialisation if very large, or when eruption of the associated tooth is desired (e.g. young patient with an impacted canine that could be brought down orthodontically).
Odontogenic Keratocyst (OKC)
The WHO 3rd edition (2005) reclassified the OKC as a neoplasm (keratocystic odontogenic tumour, KCOT) on the basis of PTCH1 mutation, aggressive behaviour, and association with Gorlin-Goltz syndrome. The WHO 4th edition (2017) reverted it to the cyst category, and the WHO 5th edition (2022) continues to classify it as a cyst. The debate continues because of its neoplasm-like behaviour.
- Site: mandibular ramus / posterior mandible / third molar region (most common); may occur in the maxilla.
- Radiology: unilocular or multilocular radiolucency, often with scalloped margins; may mimic a dentigerous cyst around an unerupted third molar; cortical expansion less pronounced than dentigerous.
- Histology: parakeratinised stratified squamous epithelium, basal palisading of columnar cells, corrugated luminal surface; thin friable lining with daughter (satellite) cysts in the wall — the so-called 'swiss-cheese' quality.
- Behaviour: aggressive, locally infiltrative, high recurrence (reported 20–60% depending on technique and follow-up); recurrence is due to daughter cysts and friable lining left behind.
- Gorlin-Goltz (naevoid basal cell carcinoma) syndrome — autosomal dominant, PTCH1 mutation; multiple OKCs, multiple basal cell naevi/carcinomas, bifid ribs, calcified falx cerebri, palmar/plantar pits, broad nasal bridge, ovarian fibromas. Panoramic radiography from age 10 onwards is recommended.
- Management: enucleation with peripheral osteotomy ± decompression/marsupialisation first to reduce the size; long-term radiographic follow-up because of recurrence. Carnoy's solution (a chemical cautery) has historically been used to fix the friable lining — note its use has been restricted in some settings because of its methanol/chloroform content.
Nasopalatine Duct (Incisive Canal) Cyst
- From epithelial remnants of the nasopalatine duct in the anterior maxilla.
- Classically midline radiolucency between the upper central incisors, often heart-shaped.
- Patients typically 30–60 years; swelling of the anterior palate; sometimes palatal paraesthesia or pain.
- Histology: squamous and/or respiratory epithelium; neurovascular bundles of the nasopalatine nerve and vessels in the wall (diagnostic clue).
- Differential diagnosis: a large but normal incisive foramen — radiographic size threshold >6 mm is often used to suggest a cyst; the adjacent teeth must test vital (unlike a radicular cyst from a non-vital central incisor).
- Management: enucleation via a palatal approach; teeth are preserved.
Lateral Periodontal Cyst and Calcifying Odontogenic Cyst
- Lateral periodontal cyst — from dental lamina rests on the lateral root surface; the adjacent tooth is vital; classical site is the mandibular premolar region; the gingival cyst of the adult is the soft-tissue counterpart. Treat by enucleation.
- Calcifying odontogenic cyst (COC, Gorlin cyst) — variable radiolucent/radiopaque appearance; ghost cells and calcifications; can be associated with an odontome; the WHO 2022 5th edition moved 'ameloblastoma-like epithelium' from essential to desirable criteria. Treat by enucleation; malignant transformation is rare.
Principles of Cyst Management
| Technique | Description | Indication |
|---|---|---|
| Enucleation | Total removal of the cyst lining with primary closure | Definitive for most cysts; allows histopathology |
| Marsupialisation (Partsch I) | Cyst opened and sutured to mucosa; decompresses and shrinks | Very large cysts; when tooth preservation/eruption desired; OKC as first stage |
| Decompression | Small drain placed to reduce pressure; second-stage enucleation | Large OKC; large dentigerous cyst |
MFDS rule: Every cyst lining removed must be sent for histopathology — clinical appearance is not reliable, and unsuspected OKC, unicystic ameloblastoma, or early carcinoma may otherwise be missed.
A 45-year-old patient has a 2 cm well-defined periapical radiolucency at the apex of a non-vital maxillary lateral incisor. Histology shows non-keratinised squamous epithelium with cholesterol clefts and Rushton bodies. What is the most likely diagnosis?
A 22-year-old presents with an unerupted maxillary canine and a unilocular radiolucency that attaches at the cementoenamel junction and encloses the crown. What is the most likely diagnosis?
A 35-year-old man has a multilocular radiolucency in the mandibular ramus with a friable parakeratinised lining showing basal palisading and daughter cysts. He has had a similar cyst enucleated 4 years ago. According to the WHO 5th edition (2022) classification this lesion is best categorised as:
A 40-year-old presents with a swelling of the anterior palate and a heart-shaped radiolucency in the midline between the upper central incisors. Both central incisors test vital. What is the most likely diagnosis?
A 30-year-old man has a 6 cm radiolucent cyst in the posterior mandible associated with an impacted third molar. The team wishes to preserve the third molar to allow its later eruption. What is the most appropriate initial surgical management?