Odontogenic Cysts - Comprehensive Overview

Classification

Fig. 16.8 - Robbins Pathology: Diagrammatic comparison of anatomic location of common inflammatory and developmental odontogenic cysts

WHO Classification (Table 16.3 - Robbins; Table 25.3 - Scott-Brown's)

Epithelial Origins

1. Rests of Malassez - from fragmentation of Hertwig's root sheath at root completion → Radicular cysts
2. Reduced enamel epithelium - fusion of inner/outer enamel epithelia covering the unerupted crown → Dentigerous, eruption, and paradental cysts
3. Rests (glands) of Serres - remnants of the dental lamina → Lateral periodontal, gingival, and keratocystic odontogenic tumour (OKC)

Individual Cysts in Detail

1. Radicular Cyst (Periapical / Dental Cyst)

• Most common jaw cyst overall
• Pathogenesis: Pulpitis (usually from caries or trauma) → pulp necrosis → periapical inflammation → stimulation of Rests of Malassez → epithelial proliferation → cyst formation
• Location: Root apex of a non-vital tooth (or lateral root canal in lateral variant; residual cyst remains after tooth extraction)
• Radiology: Unilocular radiolucency at tooth apex, with a radiopaque rim
• Treatment: Root canal treatment (enucleation if residual cyst remains)
• Note: The term "periapical granuloma" is still used despite the fact that the lesion does not show true granulomatous inflammation - it is actually epithelialized in true radicular cysts (Robbins, p. 687)

2. Dentigerous (Follicular) Cyst

• Second most common jaw cyst (accounts for ~15-18% of jaw cysts)
• Pathogenesis: Expansion of the dental follicle around the crown of an unerupted tooth; attached at the cemento-enamel junction (CEJ)
• Commonly associated teeth (in decreasing frequency): mandibular third molars ("wisdom teeth"), maxillary canines, mandibular second premolars, maxillary third molars
• Peak age: 2nd-3rd decades
• Clinical features: Often asymptomatic, found incidentally on X-ray for a missing tooth; may cause swelling, tooth displacement, secondary infection. Can reach up to 5 cm diameter.
• Radiology: Unilocular radiolucency attached to/surrounding the CEJ of an unerupted tooth
• Histology: Thin non-keratinized squamous or cuboidal/columnar lining; focal keratinization and mucous/ciliated cells possible via metaplasia
• Complications: Root resorption of adjacent teeth; transformation to ameloblastoma is a recognized (though rare) complication - ameloblastomas can form in the cyst wall
• Differential diagnosis for larger lesions: OKC, unicystic ameloblastoma
• Eruption cyst variant: Superficially located dentigerous cyst; presents as a bluish gum swelling over an erupting tooth, especially in children; cyclosporin therapy is a predisposing factor

3. Odontogenic Keratocyst (OKC) / Keratocystic Odontogenic Tumour (KCOT)

• Derived from: Rests of Serres (dental lamina remnants)
• Important: Previously reclassified by the WHO (2005) as "Keratocystic Odontogenic Tumour (KCOT)" due to aggressive behavior; the 2017 WHO classification reverted to OKC terminology
• Location: Most often in the posterior mandible (angle/ramus region); can occur in a dentigerous relationship or independent of any tooth
• Clinical behavior: Locally aggressive; recurrence rates for inadequately removed lesions can be as high as 60%. About 80% of lesions are solitary.
• Gorlin syndrome (Nevoid Basal Cell Carcinoma Syndrome): Multiple OKCs = strong indicator; caused by germline loss-of-function mutations in PTCH (Patched tumor suppressor gene). Patients with multiple cysts must be evaluated for this syndrome.
• EGFR: Recent studies show EGFR signaling plays a role in OKC behavior and growth (PMID 37314601)
• Radiology: Unilocular or multilocular radiolucency; can mimic dentigerous cyst when associated with a tooth root; may expand along the medullary cavity with little cortical expansion (characteristic)
• Histology: Thin, uniform parakeratinized stratified squamous epithelium (typically 6-8 cell layers thick); flat epithelial-connective tissue interface; prominent palisaded basal cells with hyperchromatic nuclei ("tombstone" appearance); corrugated parakeratotic surface
• Treatment: Excision; curettage and partial excision result in high recurrence. Some advocate marsupialization followed by enucleation. Peripheral ostectomy and Carnoy's solution used adjunctively.

4. Lateral Periodontal Cyst

• Derived from Rests of Serres
• Located lateral to the root of a vital tooth (distinguishes it from lateral radicular cyst of non-vital tooth)
• Botryoid variant: Multilocular / polycystic form; higher recurrence rate

5. Glandular Odontogenic Cyst (Sialo-Odontogenic Cyst)

• Rare but locally aggressive developmental cyst
• Contains gland-like structures (mucous cells, ciliated cells) within its lining - hence "glandular"
• Higher recurrence rate; must be distinguished from central mucoepidermoid carcinoma

6. Calcifying Odontogenic Cyst (Gorlin Cyst / CCOT)

• Contains "ghost cells" - keratinized cells lacking nuclei
• May contain calcifications
• Some cases progress to "dentinogenic ghost cell tumor" (solid variant)
• Recent reviews support reclassification into cystic vs. solid forms (PMID 39217025)

7. Orthokeratinized Odontogenic Cyst

• Distinct from OKC; lining shows orthokeratin (not parakeratin)
• Less aggressive than OKC; lower recurrence
• Not associated with Gorlin syndrome
• Important to distinguish histologically from OKC due to different prognosis

Radiology Summary - Differential Approach

Key Distinguishing Features at a Glance

Recent Evidence

• A 2024 systematic review and meta-analysis (PMID 38530559) evaluated machine learning accuracy in diagnosing odontogenic cysts and tumors - showing promising diagnostic performance for AI-assisted radiographic classification.
• A 2023 review (PMID 37314601) highlights the significance of EGFR investigation in OKC, with EGFR overexpression contributing to the aggressive behavior and recurrence potential of OKC.
• A 2025 review (PMID 39217025) proposes a novel outlook on classification, diagnosis, and management of calcifying odontogenic cysts.