Ultrasound imaging has played an integral role in medical diagnostics for many years. Recent advances in image quality and resolution have now made it possible to examine living tissue ultrasonically at a microscopic level. Indeed, the use of ultrasound biomicroscopy is of growing interest and great importance.1 Advances in computer technology have paved the way for currently available ultrasound units that are portable and cost-effective for office practice.
Indications for diagnostic ultrasound of the foot and ankle include the prevention and treatment of wounds, detecting tendon and ligament pathology, and detecting soft tissue lesions and foreign bodies. Many people believe ultrasound imaging will become an integral part of podiatric practice.
Identifying Skin Lesions
Images using 20 MHz ultrasound reveal detailed anatomical images of the skin. There have been studies that compared ultrasound imaging to histological sections, revealing that ultrasound provides accurate assessment of the skin structure. In fact, ultrasound measurement of skin thickness is likely to provide a more accurate indication of skin thickness than histological measurements since the latter are subject to dimensional changes due to fixation and processing.3
Reflective patterns of the skin enable you to visualize the stratum corneum and differentiate it from the deeper layers of the epidermis. You can also get a clear view of the epidermal-dermal juncture. You can see reflections from acoustic interfaces (e.g. between collagen and hydrated ground substance) in the papillary layer of dermis, and differentiate the denser reticular layer of the dermis. High-frequency ultrasound clearly demonstrates the juncture between the dermis and the adipose hypodermis.4 You can accurately measure variations in skin thickness and identify and quantify lesions within the skin.
You can use high-resolution ultrasound to image skin lesions and other common soft tissue masses within the foot and ankle. Skin cancers, such as basal cell and squamous cell carcinoma and melanoma, can be imaged. This technology allows you to reliably demonstrate the lesion margin and the overall architecture.5 While you cannot make a tissue diagnosis with ultrasound, you can determine valuable information such as depth, subcutaneous satellites and sub-surface size.
Can This Modality Make An Impact In Preventing And Treating Wounds?
Obviously, we see plenty of diabetic wounds, pressure ulcers and venous stasis wounds in our practices. High resolution ultrasound enables you to monitor the depth and width of these wounds, edematous regions, granulation tissue and developing scar tissue. Indeed, we can use this information to prevent and direct treatment of these conditions.6
Pressure ulcers are a very common problem in people with compromised mobility and fragile skin. Many pressure relieving devices are available, but it is not feasible to use them at all times. The heel is one of the most common sites for pressure ulcers and they can lead to amputation without proper care.
One of the great things about using ultrasound is it’s very sensitive in detecting fluid changes within the tissue.7 When we use a high resolution ultrasound, it enables us to detect a pressure ulcer before there are clinical signs. We have seen an increase in fluid 48 to 72 hours prior to clinical signs. This allows us to employ pressure relief measures before the ulcer breaks through the skin.
There are two common patterns that you will see. In superficial ulcers that are caused by friction on rubbing, you will see an area of inflammation (a hypoechoic band) directly beneath the epidermis. You will see this inflammation spread downward into the dermal tissue as the ulcer progresses. The lesion will also break through the epidermis and form a friction ulcer. You’ll see the other common pattern in ulcers caused by prolonged direct pressure. In these ulcers, you will see an area of inflammation beneath the dermis with strips of inflammation protruding upward into the dermis as the tissue damage progresses. As the dermis breaks down further, it will eventually break through the epidermis, forming an overt pressure ulcer. You can obtain ultrasonic images of the initial phases of both of these types of ulcers before seeing any clinical signs.