The following case was slightly unusual in the sense that cellulitis is more often seen in the acute setting rather than in primary care. However as an Extended Scope Physiotherapist using musculoskeletal ultrasound, you are likely to come across it at some point so it is important to know what cellulitis can look like on ultrasound. So I hope you find this case helpful.
This was a case of a man in his thirties who was very physically active and involved in martial arts. I saw him a few weeks after he first noticed a small lesion on the dorsum of his fore-arm, this was secondary to an insect bite. Initially he explained It had looked very benign, and he therefore more or less ignored it. However after a few sessions of martial arts training where the arm inevitably took some direct hits he did notice some swelling of the area and a mild erythema. He hoped it would go away of its own accord but unfortunately it seemed to progress.By the time I saw him in clinic it was a few weeks post insect bite he had started feeling slightly unwell in he past day or so . He looked rather pale and felt felt as if he was coming down with a cold. I performed the scan and it was clear that there was an extensive area of approximately at least 10cm long and 5 cm wide of a subcutaneous cobble stone appearance.
Chau et al (2005) in their article Musculoskeletal infections: ultrasound appearances, indicate that the ultrasound appearances of cellulitis vary according to the site and severity of infection. Ultrasound appearances range from diffuse swelling and increased echogenicity of the skin and subcutaneous tissues, to a variable cobblestone appearance depending on the amount of perifascial fluid, the degree of subcutaneous oedema and the orientation of the interlobular fat septa.
Colour or power Doppler imaging showed concurrent hyperaemia within the subcutaneous tissues. This is helpful in establishing an inflammatory element. Hyperaemia as Chau et al (2005) highlight, is not a feature of non-infective forms of oedema. Based on the clinical findings, informed by my ultrasound findings which indicated the large extent of peri-fascial fluid, I referred him immediately to A&E where he received IV antibiotics. He recovered fully within 1 week.A further useful resource is this article by Adihikari (2012)