Abstract
Clear cell odontogenic carcinoma (CCOC) is a rare neoplasm; only 75 cases have been reported in the English language literature. They have a tendency for recurrence and a capacity to metastasize. There is very little known regarding the metabolic features of this tumour or the utility of fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) scans in the staging and follow-up of these tumours. We present two cases of CCOC with their relevant FDG-PET/CT scan findings. The first patient had primary CCOC of the mandible that was FDG-avid, and the other had recurrence of CCOC of the anterior mandible and superomedial orbit that was not FDG-avid. FDG uptake in CCOC appears to be variable. Although FDG-PET/CT is useful in other head and neck cancers and has benefits compared to other imaging modalities, further studies are needed to investigate the sensitivity of FDG-PET/CT in CCOC.
Positron emission tomography (PET) using 18 F-fluoro-2-deoxy- d -glucose (FDG) is well established as a useful imaging tool for the staging of squamous cell carcinoma of the head and neck. PET-only scanners have also largely been replaced by hybrid PET/computed tomography (PET/CT) scanners. FDG is a marker of glucose metabolism and is the most widely used radiotracer in oncological PET/CT. PET scanning has been shown to add incremental diagnostic and prognostic information in a wide range of malignancies. There is a broad correlation between the degree of FDG avidity and tumour aggressiveness and clinical prognosis. Many (but not all) types of head and neck cancer also demonstrate increased glucose metabolism, and FDG-PET/CT scanning has proven clinical value in squamous cell carcinomas and thyroid carcinomas in particular. However there are no cases in the literature exploring its use in clear cell odontogenic carcinoma (CCOC).
CCOC is a rare neoplasm; only 75 cases have been reported in the English language literature. It commonly presents in the fifth to seventh decades of life and disproportionately affects women. The anterior regions of the jaws are more frequently affected, and it is more common in the mandible than the maxilla. CCOC was first described by Hansen et al. as a benign separate entity. However, as a result of evidence of a marked tendency for local recurrence, regional lymph node and pulmonary metastases, and tumour-related deaths, it was formally reclassified as malignant by the World Health Organization in 2005.
CCOC has a loco-regional recurrence rate of 34% for resected tumours, and a distant metastatic spread rate of 14%. Sites of distant metastasis are most commonly the lungs, but there have been reports of metastasis to distant bone. Despite their tendency for recurrence and capacity to metastasize, a review of the literature revealed little information regarding the glucose metabolism of these lesions or the role of FDG-PET/CT in the staging and follow-up of these aggressive tumours.
We present two cases of CCOC with their relevant FDG-PET/CT findings; the first patient had primary CCOC of the mandible with FDG-avid disease, and the other had recurrence of CCOC of the anterior mandible and superomedial orbit with disease that was not FDG-avid.
Case reports
Case 1
A 59-year-old woman was referred by her dentist after an incidental finding of a painless lesion of the left body of the mandible. On presentation, she also complained of paraesthesia of the left lip and chin for 2 months and a 3-kg unintentional weight loss. Physical examination revealed a firm left mandible swelling with intact mucosa and left chin and lip numbness. Cervicofacial lymph nodes were not palpable. An orthopantomogram of the mandible showed a large lytic lesion in the left hemimandible with poor margination. CT and magnetic resonance imaging (MRI) showed a left mandibular lesion that involved extensive areas of the body and anterior mandible. An incisional biopsy and immunoperoxidase stain supported the diagnosis of CCOC. The patient was referred to a tertiary hospital for further investigation and treatment.
The staging FDG-PET/CT scan showed a left mandibular mass exhibiting markedly increased, slightly irregular FDG uptake ( Fig. 1 a) . There was mild FDG uptake crossing the midline into the anterior aspect of the right body of the mandible, which raised the possibility of infiltration across the midline. There was mild to moderate FDG uptake in bilateral level IIA neck lymph nodes possibly indicating low volume nodal metastatic disease or inflammatory changes ( Fig. 1 b). No evidence of distant metastasis was found.
The patient underwent a left hemimandibulectomy with bilateral neck dissection and left fibula free flap reconstruction. Postoperative histopathological evaluation confirmed the diagnosis of intraosseous CCOC of the mandible. The tumour was found to have extensive involvement of soft tissues with a 39-mm depth of invasion. Surgical margins were involved and numerous perineural invasions were identified. On microscopic examination, one left level 1 neck lymph node was found to have a 5-mm tumour deposit and all other dissected lymph nodes were negative. Immunohistochemistry results further supported the diagnosis of CCOC. Currently 2 months post-procedure, the patient has commenced a 4-week course of adjuvant radiotherapy given the positive surgical margins.
Case 2
The patient was a 68-year-old woman with a history of a midline anterior maxillary CCOC arising in March 2009. She underwent a maxillectomy at that stage and the defect was restored with an obturator. She was found to have a close surgical margin and underwent a subsequent procedure with no residual tumour. She had been well for 4 years postoperatively.
In 2013 she presented to her local doctor with a 6-week history of paraesthesia in the left infraorbital nerve and zygomaticotemporal nerve. On examination, she was found to have watering of the left eye with normal extraocular movements and visual acuity. She had an obvious swelling over the left maxilla, lateral nasal bones, and zygoma. There was also swelling intraorally over the left maxillary alveolus with no mucosal defects found. Cervicofacial lymph nodes were not palpable.
A CT scan of the head and neck showed an obvious mass in the left anterior maxilla, with local extension and bony destruction that was suspicious for recurrence. There were two other areas noted in the left posterior maxilla and a superomedial orbit lesion invading through the skull base. CT of the chest and upper abdomen showed no evidence of metastatic disease.
The FDG-PET/CT scan showed markedly increased FDG uptake of the left posterior maxillary lesion ( Fig. 2 a) . However, there was only mild FDG uptake by the left anterior maxillary lesion and superomedial orbit, which was non-specific ( Fig. 2 b).
