Where Is the Filler? Magnetic Resonance Imaging Reveals Hidden Hyaluronic Acid in a Delayed Chin Complication.

Diagnosing late-onset complications after hyaluronic acid (HA) fillers can be challenging, particularly when clinical symptoms are mild. Although ultrasound (US) is widely regarded as the gold standard for evaluating facial fillers, it has limitations in certain scenarios. We report the case of a 30-year-old woman who developed a persistent sensation of pressure in the mental region 2 years after chin augmentation with a high-G-prime HA filler (brand unknown). Two high-frequency US examinations performed by experienced radiologists identified only a small supraperiosteal bolus, without significant deposits to explain the symptoms. High-resolution facial magnetic resonance imaging (MRI) unexpectedly revealed a substantial amount of HA diffusely dispersed within the subcutaneous fat of the chin, undetectable by US. A targeted injection of hyaluronidase (150 IU) was administered, resulting in complete symptom relief. Follow-up MRI confirmed the resolution of the HA deposits. This case highlighted a diagnostic blind spot of US when filler material was diffusely infiltrated into adipose tissue and lacked nodular morphology. MRI, although not routinely used due to cost and availability, may provide crucial complementary information in cases of clinical-radiological discordance. This case suggested that MRI may provide useful complementary information in selected scenarios of clinical-radiological discrepancy.