Radiological impact of the use of calcium hydroxylapatite dermal fillers

Aim

To report a case series in which the radiological features of the subcutaneous use of calcium hydroxylapatite (CaHa) dermal fillers are described for the first time.

Materials and methods

Five patients with facial hyperattenuating hypermetabolic subcutaneous lesions were identified on 2- [¹⁸F]-fluoro-2-deoxy-d-glucose (FDG) positron-emission tomography/computed tomography (PET/CT), who gave a history of facial injections to augment physical appearance. Correlation with additional imaging studies was performed.

Results

All cases had subcutaneous high attenuation material on CT (range 280–700 HU), which was FDG avid on PET, with a standardized uptake value (SUV) range of 2.9–13.4. Magnetic resonance imaging (MRI) demonstrated a heterogeneous intermediate signal intensity subcutaneous lesion with enhancement post-gadolinium in one case.

Conclusions

CaHa dermal filler is hyperattenuating on CT, hypermetabolic on FDG-PET imaging, of intermediate signal intensity on MRI, and is a potential cause of a false-positive imaging study.

Introduction

Calcium hydroxylapatite dermal filler (CaHa; Radiesse^®, Bioform Medical, San Mateo, CA, USA) is a US Food and Drug Administration (FDA)-approved injectable material for the correction of certain soft-tissue defects and deformities. It was originally licensed in 2006 for the treatment of facial lipoatrophy associated with human immunodeficiency virus (HIV) infection; however, its use has become increasingly widespread. The soft-tissue augmentation achieved with CaHa can obliterate certain facial lines and wrinkles, and thus is seen as an effective non-surgical method of facial rejuvenation, with a durable result and low side effect profile.¹ Non-cosmetic indications include maxillofacial augmentation, vocal cord insufficiency, treatment of urinary stress incontinence, and radiographic soft-tissue marking. It is favoured as a soft-tissue filler because it does not migrate from the injection site, and the lack of an exuberant inflammatory response, which frequently complicated the use of Teflon for vocal fold injections (“Teflon granuloma”).

The administered agent consists of CaHa microspheres of 25–45 μm diameter suspended in an aqueous gel carrier. Following injection the gel is resorbed and the CaHa particles remain at the site of injection, acting as a matrix for fibroblast proliferation and collagen deposition. The three-dimensional conformation of the CaHa molecules allows pore formation. The CaHa molecules are macroporous, i.e., pore size 10–500 μm, which permits fibrovascular ingrowth and collagen deposition.² The duration of clinical response is long lasting (approximately 8 months), but not permanent, as the CaHa molecules eventually undergo enzymatic degradation in to calcium and phosphate ions. Repeat treatments may be administered as desired.

CaHa is known to be radio-opaque on conventional radiographic imaging. In a previous study, 58 patients were imaged immediately following facial injection of this material, a calcified mass was visible in 100% of cases on computed tomography (CT) and calcific material was seen in 56% of cases on conventional radiography.³ Two case reports have been published describing false-positive 2- [¹⁸F]-fluoro-2-deoxy-d-glucose positron-emission tomography (FDG PET) following the use of CaHa for vocal cord paralysis4, 5; however, the imaging characteristics associated with the dermal use of the agent have not been reported previously. The present study describes the imaging features associated with CaHa injection in a series of five patients.