Dermal fillers on PET-CT

A 71-year-old female, with a history of lacunar stroke and unilateral internal carotid artery stenosis, had an F18-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) for further characterisation of a 9 mm left upper lobe ground-glass nodule. She is an ex-smoker.

On the PET-CT, in addition to the ground-glass nodule, illustrated in Figure 1, there was the incidental finding of bilateral FDG-avid calcifications present within the subcutaneous tissues of the face and jaw (Figures 2 and 3). These demonstrated a maximal standardised uptake value (SUV) of 13.0.

Given the PET-CT findings, supplementary examination revealed no visual abnormality however these calcifications were palpable. The patient provided an added history that she had silicone dermal injections for facial rejuvenation six months prior.

Besides their use for facial rejuvenation, injectable dermal fillers are used for HIV-associated facial lipoatrophy, Romberg disease, and post-surgical/traumatic facial disfigurement [1]. Dermal fillers demonstrate an increased FDG uptake which is non-specific.  Complications from dermal fillers include cellulitis, non-inflammatory nodules, foreign body granulomas, non-granulomatous inflammation, and abscess. These are all hypermetabolic on PET-CT and are of similar appearance to uncomplicated injectable dermal fillers.  This FDG uptake is due to increased glycolysis in macrophages.

Acutely, a mild degree of inflammation occurs with most types of fillers and is usually transient [3]. This increased FDG uptake may decrease and even disappear with time, leaving evidence of permanent microcalcifications on CT scans [2].

This subcutaneous increased FDG uptake poses a diagnostic challenge in head and neck cancer patients as it can be misinterpreted for a new primary or recurrence.  It should also be differentiated from Merkel cell carcinoma, a highly aggressive primary neuroendocrine skin carcinoma that typically involves the sun-exposed areas of the head, face, and neck [2].  Another potential misinterpretation of these injectable dermal fillers is for skin metastases in patients with malignant melanoma. The challenge is even greater if the dermal injections were performed between two follow-up scans [1].

Careful correlation with patient history, the CT component, and the anatomical context of FDG uptake helps in avoiding unnecessary biopsy. The CT component helps to identify subcutaneous tissue calcifications at the injection sites, a hallmark of certain fillers and related complications, as illustrated in Figure 4.

Mundada et al (2017) recommend high-resolution thin-slice MRI (512 x 512 matrix for a field of view of 16-20 cm; 1-3 mm slices) as the ideal modality for evaluation of injectable facial fillers [1]. If the injection filler is silicone or is an unknown type of filler, a “silicone only” sequence with simultaneous water and fat saturation (axial) before gadolinium injection should be obtained [1].  MRI is also excellent at demonstrating soft tissue inflammation, abscess and foreign material in the soft tissues.

Take-Home Message: MRI rather than PET-CT is the recommended modality for the assessment of injectable facial fillers or their associated complications as these fillers demonstrate non-specific FDG uptake on PET-CT.

Written informed patient consent for publication has been obtained.