Ultrasound above 14 MHz images epidermis, dermis, and subcutaneous tissues in real time. Tumor depth is ascertained with B-mode. Three-dimensional imaging depicts nonpalpable, in-transit, and satellite lesions. Doppler blood flow technologies measure tumor neovascularity and map vascular structures. Three-dimensional Doppler histogram reconstruction measures tumor aggression and metastatic potential proportional to the percentage of malignant vessels. Subcutaneous investigation reveals nonpalpable metastatic disease and nodal basin lymphadenopathy. Adjacent nerves may be studied. Preservation of the fat–fascia border refines surgical staging of deeper malignancies. Image-guided biopsy is facilitated. Treatment under image guidance is optimized with radiation and various photo and thermal technologies.
Key points
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Sonographic tumor depth evaluation has 99% histopathologic correlation.
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Melanoma metastatic potential is proportional to vessel density of neovascularity as measured by Doppler histogram analysis.
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Intransit and nonpalpable locoregional metastases can be detected with 3-dimensional image reconstruction.
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Three-dimensional mapping of nerves and arteries optimizes preoperative planning.
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Image-guided biopsy and treatments are cost effective and reduce morbidity.
Introduction
Today’s health conscious society means adults routinely seek reassurance about suspicious skin lesions. Diagnostic ultrasound examinations can accurately and rapidly differentiate between epidermal, subdermal, and subcutaneous tissues in real time. This procedure may help to identify lesions invisible to the spatially restricted human eye. The high resolution and low cost of today’s ultrasonographic equipment allow this modality to be used readily in an outpatient office setting.
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.
Introduction
Today’s health conscious society means adults routinely seek reassurance about suspicious skin lesions. Diagnostic ultrasound examinations can accurately and rapidly differentiate between epidermal, subdermal, and subcutaneous tissues in real time. This procedure may help to identify lesions invisible to the spatially restricted human eye. The high resolution and low cost of today’s ultrasonographic equipment allow this modality to be used readily in an outpatient office setting.
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 scans 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. 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 nonmelanoma 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. Identification of these foci is useful because neovascularity 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, which allows for better preoperative planning ( Fig. 3 ).
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Using Raman Spectroscopy to Detect and Diagnose Skin Cancer In Vivo
Smartphone-Based Applications for Skin Monitoring and Melanoma Detection
Teledermatology Applications in Skin Cancer Diagnosis
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