Discussion

Positron emission tomography provides physiological and biochemical data regarding the patient's disease. Eighteen F fluorodeoxyglucose is distributed throughout the body on the basis of intracellular intake via glucose transporters or transport proteins. The degree of 18F-fluorodeoxyglucose uptake has been shown to be strongly related to neoplastic growth, due to the overexpression of glucose transport proteins and certain key enzymes.Reference Rosenbaum, Lind, Antoch and Bockisch¹ A traditional PET scan lacks the anatomical detail needed for operative planning, but an integrated PET and CT scan allows the surgeon to localise the disease more precisely. Recently, 18F-fluorodeoxyglucose PET–CT scanning has become a useful adjunct in surveillance for thyroid cancer, detecting disease that can no longer concentrate radioiodine.Reference Schluter, Bohuslavizki, Beyer, Plotkin, Buchert and Clausen^2–Reference Nahas, Goldenberg, Fakhry, Ewertz, Zeiger and Ladenson⁴ A recent study by Shammas et al. examined the utility of 18F-fluorodeoxyglucose PET–CT scanning for detecting and localising recurrent or metastatic differentiated thyroid cancer in a cohort of 61 patients (59 of whom had negative radioiodine scans); they found an overall sensitivity and specificity in predicting histological disease of 68.4 and 82.4 per cent, respectively.Reference Shammas, Degirmenci, Mountz, McCook, Branstetter and Bencherif⁵

While 18F-fluorodeoxyglucose PET–CT scanning can be extremely useful for imaging head and neck cancer, the radiographic findings for some disease processes can be confusing even with fused imaging techniques. There are several sources of false positive results. Infectious, autoimmune or granulomatous disease may show increased uptake owing to the high glucose turnover seen in activated granulocytes, lymphocytes and macrophages.Reference Rosenbaum, Lind, Antoch and Bockisch¹ In a recent review, Rosenbaum summarised the many reports of false positive findings of 18F-fluorodeoxyglucose PET, which included cases of laryngeal uptake associated with vocalisation during the uptake period (generally this uptake is symmetrical), autoimmune thyroiditis, supraclavicular brown fat, physiological and post-chemotherapy hyperplasia uptake, post-operative inflammation, and some granulomatous disorders such as sarcoidosis, tuberculosis and fungal infections.Reference Rosenbaum, Lind, Antoch and Bockisch^1, Reference Shammas, Degirmenci, Mountz, McCook, Branstetter and Bencherif⁵ Reports have also described PET-positive osteoradionecrosis in patients with a past history of nasopharyngeal carcinoma.Reference Liu, Chang, Ng, Chan and Yen⁶

One of the recognised non-neoplastic causes of 18F-fluorodeoxyglucose uptake is a granulomatous reaction to Teflon (i.e. teflonoma). Teflon (polytetrafluoroethylene) was used in the past to facilitate medialisation of the paralysed vocal fold. Teflon granulomas of the larynx are a known complication of vocal fold medialisation, occurring in approximately 2–3 per cent of patients.Reference Loehrl and Smith⁷ The development of Teflon granulomas, even long after a technically successful injection, was one of the problems that led to the virtual abandonment of this procedure for vocal fold medialisation in the late 1980s. Teflon granulomas have previously been reported in a number of the head and neck sites. Beginning as early as 1980, Teflon granulomas have been described as mimicking thyroid nodules and neoplasms,Reference Sanfilippo, Shelburne and Ingram^8, Reference Wassef, Achouche, Guichard and Tran Ba Huy⁹ posterior fossa masses (following microvascular decompression with Teflon),Reference Megerian, Busaba, McKenna and Ojemann¹⁰ and laryngeal and neck lesions.Reference Wenig, Heffner, Oertel and Johnson^11, Reference Moukarbel, Youssef, Shab and Hamdan¹²

Microscopically, Teflon appears as a translucent, amorphous aggregate. As described in many major surgical pathology textbooks, when macrophages encounter a foreign object too large to be phagocytosed (such as Teflon), they fuse to form larger foreign body giant cells composed of up to several dozen individual macrophages. This fusion is a hallmark of the foreign body giant cell reaction. Macrophages and foreign body giant cells tend to remain at the surface of an implant for the duration of its residence. Encapsulation can also occur, involving a generally avascular collagen shell being deposited around a foreign body, effectively isolating the foreign body from the host tissues.

Radiographically, Teflon granulomas are characterised by hyperattenuated, poorly defined masses on unenhanced CT scans, intermediate signal intensity on T2-weighted magnetic resonance images (less signal intensity than expected for a tumour) and avid 18F-fluorodeoxyglucose PET uptake. Eighteen F fluorodeoxyglucose avidity is not directly related to the Teflon, but is believed to be a by-product of the inflammatory reaction in response to the foreign body.

Unfortunately, these lesions can easily mimic neoplasms. Perhaps the best differentiator between benign disease and neoplasm in this situation is a careful patient history. One reason that Teflon was abandoned was its propensity to induce granulomas. Fortunately, newer injectable materials used for vocal fold medialisation are more biocompatible and less likely to cause long-standing inflammation.

Teflon granulomas have been reported in several head and neck sites. Positron emission tomography positive Teflon granulomas have previously been reported in the nasopharynx (secondary to Teflon injections for repair of velopharyngeal insufficiency),Reference Harrigal, Branstetter, Snyderman and Maroon¹³ and two reports have described teflonomas located in or adjacent to the vocal folds.Reference Hewitt, Singh and Wareing^14, Reference Yeretsian, Blodgett, Branstetter, Roberts and Meltzer¹⁵ In one case report, the diagnosis was confirmed histologically after biopsy, and in the other a Teflon granuloma was presumed on the basis of the patient's history and the relative stability of the lesion over time, seen on PET–CT imaging.