The use of Gamma Knife stereotactic radiosurgery in the treatment of ameloblastic carcinoma

Abstract

A case of recurrent maxillary ameloblastic carcinoma treated with Gamma Knife stereotactic radiosurgery is reported. This case demonstrates an alternative treatment modality that has not been described previously for this rare and often difficult to treat odontogenic malignancy.

Ameloblastic carcinoma is a rare malignant odontogenic tumour that combines the histological features of an ameloblastoma with features of cytological atypia. Histological diagnosis is difficult. There are two types, primary arising de novo, and less commonly, secondary arising from an existing ameloblastoma.

Fewer than 70 cases have been described in the literature, and there is no standard care protocol. The majority of cases are treated in a similar way to squamous cell carcinomas of the jaws with wide local resection plus selective neck dissection if indicated on staging. Conventional radiotherapy is frequently used, but only as an adjuvant therapy. Very few cases of conventional external beam radiotherapy or carbon ion radiotherapy as primary treatments have been reported.

Gamma Knife stereotactic radiosurgery has been used to treat vascular malformations and intracranial and skull base malignancies, but it has not been described for the treatment of ameloblastic carcinoma.

Case report

We present the case of a 35-year-old man, otherwise fit and well, with a 2-year history of a completely excised maxillary ameloblastoma. Primary surgery involved a left maxillectomy reconstructed with a radial forearm free flap. He had remained disease-free.

A surveillance magnetic resonance imaging (MRI) scan revealed a recurrence adjacent to the original site, extending into the nasal cavity, and a further separate nodule pushing up into the left orbital floor. He underwent an extended maxillectomy as part of an en-bloc resection, including the orbital floor superiorly, lateral wall of the nose medially, and pterygoid plates laterally.

Histopathology revealed ‘atypical’ ameloblastoma. As intraoperative frozen sections at the orbital apex were clear, the multidisciplinary team (MDT) decision was to keep the patient under close review.

Three months later, a further MRI surveillance scan showed an isolated dumb-bell mass passing through the foramen ovale, but no recurrence elsewhere. The histology was therefore reviewed and revised to a diagnosis of ameloblastic carcinoma with evidence of de-differentiation, spindle cells, and peri-neural involvement. A computed tomography (CT) scan of the chest and abdomen showed no signs of metastasis. The MDT advised surgical excision including orbital exenteration. The patient declined radical surgery and opted to preserve his vision for as long as was possible. As assessment for both conventional and stereotactic radiotherapy had been thought to be ineffective at this site, the decision to try Gamma Knife stereotactic radiosurgery using the Perfexion system was considered.

The patient underwent Gamma Knife radiosurgery using a dose of 16 gray (Gy) to the lesion; treatment was uneventful and he was discharged home the following day ( Fig. 1 ).

Fig. 1
Treatment 1. MRI scan showing a tumour volume of 10.9 ml, prescription volume of 11.8 ml, and dose of 16 Gy

Both the 3-month and 6-month MRI scans showed a good response to treatment with no recurrence. However, the 12-month MRI scan showed evidence of two out-of-field recurrences, in the left masseter and in the left nasal cavity extending into the pterygopalatine fossa and through the inferior orbital fissure into the orbital apex, towards the infratemporal fossa. A positron emission tomography (PET) scan confirmed high fluorodeoxyglucose (FDG) uptake in keeping with carcinoma at these sites, with standard uptake values (SUV) of 9.6 and 10.0, respectively. There was no increased uptake at the site of previous Gamma Knife surgery.

The patient was treated with a further course of radiosurgery using a dose of 12 Gy to the region of the left maxillary sinus, orbit, and infratemporal fossa ( Fig. 2 ). Despite the close association of the optic nerve to the tumour site, the maximum dose to the left optic nerve was only 7 Gy to a very small volume of 0.2 mm 3 . The side effects were minimal – mild peri-orbital swelling and conjunctival blushing, but these resolved overnight. The 3-month MRI and PET scans following this second course of Gamma Knife radiosurgery showed a marked reduction in tumour volume.

Fig. 2
Treatment 2. PET scan showing tumour volume of 83.9 ml, prescription volume of 88.4 ml, and dose of 12 Gy. Treatment 1 demarcated in blue (For interpretation of references to colour in this figure legend, the reader is referred to the web version of this article.).

Six months following the second treatment, an MRI showed a further tumour mass medial to the mandibular ramus, which was confirmed on PET scan showing a high FDG uptake (SUV 15.0). Again, there was no evidence of recurrence at either of the previously treated sites. The patient underwent a third course of Gamma Knife radiosurgery using a dose of 12 Gy ( Fig. 3 ), with obvious shrinkage of the tumour after 10 weeks ( Fig. 4 ). Minimal side effects of hair loss and mild erythema overlying the residual tumour volume were noted.

Jan 24, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on The use of Gamma Knife stereotactic radiosurgery in the treatment of ameloblastic carcinoma
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