Friday, October 20, 2017
HIGH-FREQUENCY ULTRASOUND EXAMINATION IN THE DIAGNOSIS OF SKIN CANCER
The accuracy of ultrasonography in the epidermis, dermis, and subcutaneous tissues is both operator and equipment dependent. Standard 2-dimensional linear sonograms at 40 to 100 MHz image the epidermis. Probes using 15-to 22-MHz image the epidermis and dermis, including the adjacent tissues 1 to 2 cm deep to the basal dermal layer. Real time 3-dimensional (3D/4D) probes at 16 to 20 MHz using broadband technologies provide high resolution of these structures to a 4- to 7-cm depth in seconds. Today’s high-resolution equipment is widely available as imaging technology.
EVOLUTION OF DIAGNOSTIC ULTRASOUND IMAGING: Diagnostic ultrasound examination has been used on the skin and subcutaneous tissues for more than 25 years in Europe and Japan. The technology has evolved from its original use in cyst detection with B scans1 to its present use for cancer detection using 3D imaging to detect in-transit metastases. Additionally, in vivo flow velocity analysis can now be used to detect melanoma vessel density and analyze tumor microvascularity at 10 micron imaging.2 Experimental photo and laser acoustic technologies are also currently being studied in animal research. This article provides a basic overview of skin imaging applications. A more in-depth review of dermal ultrasonography may be found elsewhere in the literature.
HOW THE EXAMINATION IS PERFORMED: The application of ultrasonography depends on the area examined and equipment needed for specific diagnosis. All probes require gel contact with the skin and scan duration is typically proportional to the type of probe and examiner’s experience. Real-time imaging by a trained physician allows simultaneous picture generation and interpretation to occur within minutes. Routine B scan units require operator-dependent probe motion in 2 planes to obtain orthogonal images. The 3D imaging systems are operator independent because the probe is held steady over the area of interest and electronics scan a 4 4-cm area in 6 seconds. Patient motion rarely degrades the images owing to the rapid scan rate. Transducer size is matched to scan areas or can be focused to limited facial regions such as the nose. Three-dimensional imaging of ear and nose cartilage is also available with specialized probes. Lesions can be echogenic or hyperechoic (many internal echoes), such as hemorrhagic areas, echo poor or hypoechoic (few internal echoes), and echo free (no internal echoes), which are usually found in fluid, such as cysts.
ULTRASOUND EVALUATION OF DERMAL LESIONS: The incidence of melanoma and nonmelanoma skin cancer are both increasing. Earlier detection discovers smaller lesions where focal nonsurgical treatment may be preferred to standard operative techniques, which may limit potential long-term and postoperative side effects. Ultrasound examination permits rapid measurement of skin thickness, fat tissue depth, and fascial integrity. Medical imaging maps arteries, veins, and nerves, which provides preoperative landmarks that can reduce the risk of postoperative bleeding and nerve damage (Fig. 1). Image-guided treatment may also decrease the risk of postoperative disfigurement. Interval scans may also be used to track and assess lesions with low aggressive potential.
DIAGNOSTIC APPLICATIONS FOR NON-MELANOMA SKIN CANCER: Clinical diagnosis is the primary modality used to identify nonmelanoma skin cancer; however, visual diagnosis alone cannot determine tumor depth. Imaging allows preoperative mapping of a lesion, which may alert the surgeon to the depth or subclinical extent of a lesion. This information allows surgical planning, which can help to limit the number of stages required and allow for preoperative planning to identify optimal techniques for surgical closure. The presence of coexisting benign disease, such as seborrheic hyperplasia or peritumor inflammatory reaction, may falsely lead to a wider excision or inaccurate biopsy conclusions. Of basal cell carcinomas, 85% develop in the head and neck, showing a predilection for thin skin, such as the nose, lips, or eyelids. The various shaped probe constructions allow diagnostic evaluation of nearly all locations including external ear compartments (Fig. 2). Although most basal cell carcinomas lesions appear as well-defined, oval, echo-poor masses, lesions that may have a higher aggressive potential may also appear as hyperechoic spots.
Fig. 1. Basal cell carcinoma echo-poor lesion (circle) 2.1 mm deep located 5 mm from the facial nerve (arrows) and 7 mm from temporal vein (blue).
Fig. 2. Basal cell carcinoma (red circle) echo-poor mass in nasolabial groove imaged with small transducer to improve contact depth measurement of 1.5 mm.
Identification of these foci is useful because ovascularity is less than that in other cancers. Indeed, the appearance of tortuous vessels suggests squamous cell carcinoma, Merkel cell carcinoma, or metastatic tumor. The depth correlation between ultrasonography and histology is excellent, 5 which allows for better preoperative planning. (figure 3)
Fig. 3. Basal cell carcinoma echo-poor mass with involvement of the orbicularis oculus muscle (m). Tumor (asterisk) echogenic foci signifies increased aggression and invades the dermis (d) and muscle layer (m) into the fat (arrow).
Squamous cell carcinoma presents as a hypoechoic lesion with irregular borders. Because the thickness or depth of invasion is an important predictor of metastases, the lesion should be followed along its entire course. Extra care is taken to find locoregional metastases and ultrasound examination of the liver and regional nodes may be performed simultaneously. The vascular pattern is increased diffusely throughout the entire mass as opposed to basal cell carcinomas, where the neovascularity is less prominent and often at the bottom of the lesion. Vascular mapping for major feeders with 3D ultrasonography is useful owing to the possibility of widespread penetration of the lesion.
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About the Author:
As of Jan '18, Dr. Robert Bard spearheaded a partnership with a host of cancer educators, medical practitioners and non-profit foundations (allied under AwarenessforaCure.org) to form a public resource program to aid in the advancement of the public's understanding about self-preservation from cancer and other chronic diseases. EARLY DETECTION & PREVENTION is a global health movement that promotes a higher regard for "clean living" - from toxins and a toxic lifestyle. Our program consists of four main efforts: EDUCATION, COMMUNITY CONNECTION, CURRENT NEWS & CLINICAL RESOURCES. EARLY DETECTION & PREVENTION brings the empowerment of wellness through group seminars, videos and the distribution of current articles & newsletters published/shared to all the major cancer charities and their members.
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