Bedside Focused Ultrasound in Necrotizing Fasciitis: The “Black-hole Sign”

Introduction: Necrotizing fasciitis (NF) is a life-threatening infection of soft tissues, requiring prompt diagnosis and an aggressive management.
The role of ultrasonography (US) in emergency setting for early diagnosis of NF was reported in literature, its accuracy being estimated 92% both before and without gas production.
Presentation of the Case: A 65-year old man, with pulmonary metastasis from colon-rectal cancer, treated with chemotherapy, complained of dyspnoea, fever and a dull pain in his left calf for 3 days. Skin was spared and no evidence of tactile alterations or edema was found.
Bedside US focused on the painful zone revealed a small hypo-anechoic area in deep subcutaneous tissue with blurred contours and posterior shadowing (“black-hole sign”), referable to soft tissue necrosis. Thickness and hyperechogenicity of surrounding subcutaneous tissue, due to diffuse inflammatory infiltrate and edema, and thin distal fluid collection along the fascia, were also detected, without gas artifacts. Surgery debridement was performed, tissue cultures yielding Escherichia Coli, maybe due to the disruption of bowel mucosal wall.
Discussion and Conclusion: Bedside goal-directed US performed by emergency physician can exclude alternative aetiologies to NF in severe localized pain of the lower extremity. The depiction of blurred focal changes in the soft tissue, configuring an US “black-hole sign” and referable to fat necrosis and suppurative infiltration, may represent the main early finding of NF, especially in the idiopathic form. Its identification should alarm physicians, inducing further investigations and close monitoring. The employment of bedside goal-directed US should be stressed in Emergency Department.