Oncocytoma in the Parotid Gland Presenting a Remarkable Increase in Fluorodeoxyglucose Uptake on Positron Emission Tomography

Positron emission tomography (PET) scanning has recently been introduced into the otolaryngologic field and has already been reported to be useful in the management of head and neck cancers, especially for early detection of lymph node metastasis, estimation of therapeutic effect, and early detection of tumor recurrence.1, 2 However, some benign lesions also present uptake of radiolabeled fluorodeoxyglucose (FDG), which can lead to diagnostic confusion.3, 4 We describe the first reported case of a parotid oncocytoma presenting a remarkably high uptake of FDG during PET scanning. A 49-year-old woman with a history of brain infarction underwent follow-up MRI, during which a round lesion was detected unexpectedly in her right parapharyngeal space. She was referred to another hospital for a PET scan. In January 2003, an FDG PET scan was performed and a remarkably high uptake of FGD (standard uptake value, 8) was observed on the right side of the head (Fig 1). She was referred to our department in February 2003. A, PET image of patient coronal frontal (left) and lateral (frontal) views. Arrow indicates high uptake on the right side of the head (standard uptake value, 8). B, Coronal MRI demonstrates round mass in the right parapharyngeal space corresponding to lesion demonstrated on PET scan. The patient had never complained of any symptoms. Physical examination identified no mass or swelling in her neck, oral cavity, or pharynx. No facial, lingual, palatine palsy, or other neurologic deficits were observed. She underwent MRI again, which detected a nodular mass approximately 2 cm in diameter. The mass was located in the right parapharyngeal space and was also in contact with the deep lobe of the parotid gland. The tumor showed a low signal intensity on both T1 and T2-weighted images and showed a slight enhancement on a T1-weighted Gd-DTPA enhanced image (Fig 1). The size of this tumor on these MRI images was nearly the same as seen on the first MRI. No lymphadenopathy was seen. Fine-needle aspiration biopsy was not performed due to technical difficulty. The PET findings were suggestive of a malignant lesion; however, clinical features and other images did not indicate any malignancy. Surgical removal of the tumor was performed in July 2003. After a superficial parotidectomy with facial nerve preservation, the deep lobe of the parotid was carefully removed from surrounding tissues, and a reddish-brown tumor was exposed. Part of the tumor was surrounded by the deep lobe, and the rest was situated in the parapharyngeal space. The tumor was removed together with the deep lobe of the parotid. No other tumor was observed in the parapharyngeal space. The tumor was multinodular and had a soft but solid consistency. A diagnosis of oncocytoma was made histologically. The patient has been followed for 9 months postoperatively without any signs of further disease. Follow-up MRI indicated no residual tumor and no tumor recurrence. Oncocytic neoplasms in the parotid gland are divided into 3 categories: oncocytosis, oncocytoma, and oncocytic carcinoma.5 These are all relatively rare tumors of the parotid gland; oncocytoma is the most commonly occurring. Oncocytoma is characterized by oxyphilic granules in the cytoplasm.5 These granules are known to be mitochondorial accumulations; however, it is uncertain whether these accumulations are related to the high uptake of FDG observed in the present report. Recommended treatment for oncocytoma is total removal of the tumor and adjacent parotid tissue. In contrast to the management of parotid malignancies, total parotidectomy is not necessary and the facial nerve should be preserved. Fine-needle aspiration is an important diagnostic tool for making a treatment decision. However, the diagnosis offered by fine-needle aspiration does not warrant being accurate for oncocytoma.5 Moreover, for tumors in the deep lobe of the parotid and in the parapharyngeal space that do not extend to the oral cavity or the pharyngeal wall, such as in the present case, traditional type of fine-needle aspiration is relatively difficult as compared with that for tumors in the superficial lobe of the parotid. CT-guided fine-needle aspiration biopsy of the parapharyngeal space is a well-established and safe technique. PET scanning is undoubtedly a useful modality for clinical management of head and neck lesions. However, some benign tumors, such as Warthin's tumor, have been reported to exhibit high FDG uptake during PET scanning, leading to a false-positive diagnosis.4 Special care is thus needed when using PET scanning for the preoperative evaluation of parotid lesions. We deeply acknowledge Professor Kensuke Watanabe (Department of Otolaryngology, Koshigaya Hospital, Dokkyo Medical University) for clinical advice.