Residual Cyst

Residual cyst is a radicular cyst that remains in the jaw after the causative tooth has been extracted, without removal of the cyst lining. It sits in an edentulous area, usually in older adults.

It is found by chance on radiographs in most cases. It makes up about 10% of odontogenic cysts and is more common in the posterior mandible and maxilla.

Pathophysiology. The inflamed epithelial lining of the original cyst persists in the extraction socket or adjacent bone, after the tooth that fed the inflammation has gone. Growth slows and may stop because the inflammatory stimulus is gone, but fluid pressure keeps the cyst slowly enlarging in some.

Cysts can become infected, and rarely undergo neoplastic change.

Usually asymptomatic. Some patients have a painless swelling, a sore denture, expansion of the alveolar ridge, or pain and discharge with infection. Large cysts in the mandible can cause a pathological fracture, and maxillary cysts can extend into the sinus.

Ask for a history of extraction or retained roots, and check denture fit over the area.

• Panoramic or periapical radiograph: a round or oval, well defined corticated radiolucency in an edentulous region at the site of a past extraction, with possible root fragments excluded.
• Cone beam CT for size, extent, relation to the sinus, nasal floor, inferior alveolar canal and mental foramen, and surgical planning.
• Aspiration before surgery for large lesions: straw coloured fluid with cholesterol crystals.
• Histology of all removed tissue is essential to exclude odontogenic keratocyst, ameloblastoma, mucoepidermoid carcinoma and other lesions that can look the same.

Differential diagnosis.

• Odontogenic keratocyst
• Unicystic ameloblastoma
• Central giant cell granuloma
• Simple bone cyst
• Stafne defect (lingual mandible)
• Retained root fragment with granuloma
• Maxillary sinus pseudocyst or mucous retention cyst
• Metastasis or other malignancy

• Enucleation with curettage under local or general anaesthesia, removing the whole lining, and primary closure. Send the whole specimen for histology.
• Large lesions, or those near the inferior alveolar nerve or sinus, and cysts in frail patients: decompression or marsupialisation with a tube or obturator for 6 to 12 months, with saline irrigation, followed by enucleation of any residual cavity.
• Protect the mandible after large cyst removal with a soft diet for 6 weeks, and consider plating when more than half the bone height is lost.
• 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 if suitable.
• Anticoagulated patients need peri-operative review, with continuation of warfarin when the INR is in range and the use of local haemostatic measures, and hold direct oral anticoagulants only after specialist advice.
• Patients on antiresorptive drugs (bisphosphonates, denosumab) need specialist planning to limit the osteonecrosis risk.

Monitoring. Radiographs at 6 and 12 months, then annually for 2 to 3 years. Recurrence is rare, but is more likely after incomplete removal or with an unrecognised keratocyst.

Referral and escalation. Refer to oral and maxillofacial surgery. Urgent referral for rapid growth, pain, paraesthesia of the lip, pathological fracture or histology showing keratocyst, ameloblastoma or malignancy.