Facing the Danger Zone: The Use of Ultrasound to Distinguish Cellulitis from Abscess in Facial Infections

Physical exam alone is often insufficient to determine whether or not cellulitis is accompanied by an abscess. Bedside ultrasound can be a valuable tool in ruling out suspected abscess by allowing direct visualization of a fluid collection. The proximity of the infection to adjacent structures can also be determined, thus aiding clinical decision making. Patients with cellulitis near the eye and nose are of particular concern due to the adjacent facial structures and the anatomy of the venous drainage. Accurately determining the presence or absence of an associated abscess in these patients is a crucial step in treatment planning. The purpose of this report is to (1) emphasize the benefits of bedside ultrasound when used in conjunction with the physical exam to rule out abscess; (2) demonstrate the utility of bedside ultrasound in planning a treatment strategy for soft tissue infection; (3) depict an instance where ultrasound detected an abscess when computed tomography (CT) scan did not. 1. Background The physical exam findings of cellulitis include skin erythema, edema, and warmth. An abscess is suspected on physical exam when a tender, fluctuant area is palpated within this area of cellulitis [1]. If an abscess is diagnosed, incision and drainage must be performed. Cellulitis, however, can be medically managed with antibiotics. Distinguishing the two conditions is of utmost importance in order to properly treat the patient and to spare patients with cellulitis an invasive, uncomfortable procedure. 1.1. Soft Tissue Ultrasound Basics Ultrasound uses sound waves generated by the ultrasound probe. The sound waves strike objects in the body and bounce back stronger or weaker depending on the composition of the tissue the wave strikes. The ultrasound machine then displays the image as black (hypoechoic) to represent fluid, white (hyperechoic) to represent dense hard structures, and shades of gray to represent tissue compositions between these two extremes. 1.2. Soft Tissue Examination by Ultrasound When there is diagnostic uncertainty regarding the presence of an abscess, imaging is indicated to assist in the diagnosis. Imaging options may include CT scan (usually with IV contrast) or ultrasound. CT scan is considered by many to be the diagnostic “gold standard” for diagnosing abscesses. However, CT scans are not always available, expose patient to ionizing radiation and IV contrast, and are expensive [3]. Ultrasound, although user dependent, is usually readily available in the emergency department (ED) and can be rapidly performed, providing real-time