Odontogenic Myxoma

Odontogenic myxoma is a benign, locally aggressive tumour of the jaws made of stellate and spindle cells in an abundant myxoid stroma. It makes up about 3 to 20% of odontogenic tumours depending on the series.

It is most common in the second to fourth decades and in the posterior mandible, with a slight female predominance. It does not metastasise, but it infiltrates marrow spaces and recurs.

Pathophysiology. The tumour arises from the mesenchymal components of the tooth germ (dental papilla, follicle or periodontal ligament). Its gelatinous stroma contains hyaluronic acid and little collagen.

The lack of a capsule and the tendency to extend between trabeculae into apparently normal bone explain the high recurrence after curettage.

Slowly progressive painless swelling, with tooth mobility or displacement, delayed eruption, cortical thinning and perforation. Paraesthesia is uncommon. Maxillary lesions can extend into the sinus, nose and orbit.

Rapid growth, pain, numbness or extension into soft tissue suggests an aggressive tumour and needs urgent staging and planning.

• Panoramic radiograph: a multilocular radiolucency with a soap bubble, honeycomb or tennis racket pattern, with fine septa at right angles, and scalloped margins. Unilocular lesions occur, particularly in small tumours.
• CT: cortical expansion and perforation, and bony septa. MRI: T2 hyperintense signal with septal enhancement, to show soft tissue extension.
• Incisional biopsy, taken deep enough to include tumour, with histology: sparsely cellular, myxoid tissue with stellate cells, minimal collagen and occasional islands of odontogenic epithelium.
• Aspiration to exclude a vascular lesion before biopsy.

Differential diagnosis.

• Ameloblastoma
• Central giant cell granuloma
• Odontogenic keratocyst
• Aneurysmal bone cyst
• Central haemangioma
• Fibrous dysplasia and ossifying fibroma
• Myxoid chondrosarcoma and other sarcomas
• Ameloblastic fibroma

• Small, well defined lesions: enucleation with curettage and peripheral ostectomy.
• Large, multilocular or recurrent lesions: resection with a margin of 1 to 1.5 cm of normal bone, and reconstruction with grafts or plates. Resection has a lower recurrence rate than curettage.
• Reported recurrence is about 25% (range 10 to 35%) after conservative surgery, and about 5 to 10% after resection, with the figures of lower certainty.
• Recurrence can be late, so review is long term. Re-resection is the usual treatment.
• Antibiotics only for infection with spread: amoxicillin 500 mg orally three times daily for 5 days (reduce to 500 mg every 12 hours at eGFR 10 to 30), or clindamycin 300 mg four times daily in penicillin allergy.
• Analgesia: paracetamol 1 g every 6 hours (maximum 4 g daily) with ibuprofen 400 mg every 8 hours with food.

Monitoring. Clinical and radiographic review every 6 months for 2 years, then annually for at least 5 to 10 years. Use CT or MRI for suspected recurrence.

Referral and escalation. Refer to oral and maxillofacial surgery or head and neck surgery. Urgent referral for rapid growth, soft tissue extension, orbital or skull base involvement or recurrence.