Odontogenic Keratocyst

Odontogenic keratocyst (keratocystic odontogenic tumour, now classified as a cyst) is a developmental cyst of the jaw lined by a thin, regular, parakeratinised stratified squamous epithelium with a palisaded basal layer. It accounts for 10 to 12 percent of odontogenic cysts. Peak incidence is in the second to fourth decades, with a male predominance. About 70 percent occur in the mandible, mainly the posterior body and ramus; a minority involve the maxillary canine and third molar region.

It arises from dental lamina remnants. PTCH1 gene mutations (sporadic, and germline in Gorlin-Goltz syndrome) are found in many cases. Gorlin syndrome (nevoid basal cell carcinoma syndrome) is characterised by multiple keratocysts, multiple basal cell carcinomas, palmar and plantar pits, bifid ribs, calcified falx cerebri, macrocephaly, and medulloblastoma in childhood.

The cyst grows along the marrow space without much bony expansion, so it can reach a large size before it is noticed. Recurrence is 10 to 30 percent after simple enucleation, because of thin friable lining, daughter cysts and satellite microcysts in the cyst wall. Rarely, malignant transformation occurs.

• Often asymptomatic and found on a routine radiograph.
• Painless swelling, buccal and lingual cortical expansion, displacement and mobility of teeth, delayed tooth eruption.
• Pain, discharge, and swelling when secondarily infected; paraesthesia of the lip if the inferior alveolar nerve is involved.
• Pathological fracture in large mandibular lesions.
• Multiple cysts in Gorlin syndrome, with basal cell carcinomas, jaw cysts appearing in teenage years.
• Red flags: rapid growth, cortical perforation, soft tissue mass, numbness, fracture, and multiple cysts at young age.

• Panoramic radiograph: well defined unilocular or multilocular radiolucency with scalloped corticated margins, growing anteroposteriorly along the jaw; root resorption is uncommon (unlike ameloblastoma).
• Cone beam CT: shows extent, cortical thinning, perforation, and relationship to the inferior alveolar canal, teeth, and sinus.
• Aspiration: yellowish, cheese like, keratin rich fluid (protein content below 4 g/dL).
• Incisional biopsy to confirm the diagnosis: corrugated parakeratotic surface, uniform 5 to 8 cell thick epithelium with palisaded basal cells, flat epithelium connective tissue interface, and no rete pegs.
• Screening for Gorlin syndrome in young or multiple lesions: skin examination, chest radiograph (bifid ribs), skull radiograph or CT (calcified falx), MRI brain in children, and PTCH1 genetic testing.
• Exclude dentigerous cyst, ameloblastoma, lateral periodontal cyst, radicular cyst, odontogenic myxoma, central giant cell granuloma, and traumatic bone cyst.

• Enucleation with peripheral ostectomy (removal of 1 to 2 mm of bone with a bur) and chemical cauterisation with Carnoy solution (ethanol, chloroform, glacial acetic acid and ferric chloride) applied for 3 minutes, with careful protection of the inferior alveolar nerve (the solution should not be used near exposed nerve or thin cortex); recurrence reduces to 2 to 8 percent.
• Marsupialisation or decompression for large cysts near vital structures (reduction in size over 6 to 12 months using an irrigating tube, with saline irrigation twice daily), followed by enucleation of the remaining cyst: preserves teeth and nerve.
• Resection (segmental or marginal) for recurrent, aggressive, or multiple recurrences, with reconstruction.
• Perioperative antibiotic: cefazolin 1 g intravenously at induction, single dose (amoxicillin 500 mg orally every 8 hours for 5 days if infected); analgesia with paracetamol 1 g every 6 hours and ibuprofen 400 mg every 8 hours.
• Gorlin syndrome: sun avoidance and sunscreen (SPF 50), avoid radiotherapy (increases basal cell carcinoma), dermatological surveillance every 6 months, topical imiquimod 5 percent or surgical excision for basal cell carcinomas, vismodegib 150 mg orally once daily for advanced basal cell carcinoma (monitor for muscle cramps, alopecia, taste loss; teratogenic); genetic counselling.
• Complications: fracture, nerve injury (inferior alveolar nerve paraesthesia), infection, recurrence.
• Follow up: clinical and panoramic radiograph every 6 months for 2 years, then yearly for at least 5 years, ideally 10 years or lifelong for Gorlin syndrome; CBCT for suspected recurrence.
• Counselling: recurrence is frequent; the need for long term review and genetic screening of the family in syndromic cases.