Comparison of techniques for the non-invasive assessment of skin tumours

High-frequency ultrasound for diagnosing skin cancer in adults

BACKGROUND

Early, accurate detection of all skin cancer types is essential to guide appropriate management and to improve morbidity and survival. Melanoma and squamous cell carcinoma (SCC) are high-risk skin cancers with the potential to metastasise and ultimately lead to death, whereas basal cell carcinoma (BCC) is usually localised, with potential to infiltrate and damage surrounding tissue. Anxiety around missing early curable cases needs to be balanced against inappropriate referral and unnecessary excision of benign lesions. Ultrasound is a non-invasive imaging technique that relies on the measurement of sound wave reflections from the tissues of the body. At lower frequencies, the deeper structures of the body such as the internal organs can be visualised, while high-frequency ultrasound (HFUS) with transducer frequencies of 20 MHz or more has a much lower depth of tissue penetration but produces a higher resolution image of tissues and structures closer to the skin surface. Used in conjunction with clinical and/or dermoscopic examination of suspected skin cancer, HFUS may offer additional diagnostic information compared to other technologies.

OBJECTIVES

To assess the diagnostic accuracy of HFUS to assist in the diagnosis of a) cutaneous invasive melanoma and atypical intraepidermal melanocytic variants, b) cutaneous squamous cell carcinoma (cSCC), and c) basal cell carcinoma (BCC) in adults.

SEARCH METHODS

We undertook a comprehensive search of the following databases from inception up to August 2016: Cochrane Central Register of Controlled Trials; MEDLINE; Embase; CINAHL; CPCI; Zetoc; Science Citation Index; US National Institutes of Health Ongoing Trials Register; NIHR Clinical Research Network Portfolio Database; and the World Health Organization International Clinical Trials Registry Platform. We studied reference lists as well as published systematic review articles.

SELECTION CRITERIA

Studies evaluating HFUS (20 MHz or more) in adults with lesions suspicious for melanoma, cSCC or BCC versus a reference standard of histological confirmation or clinical follow-up.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted all data using a standardised data extraction and quality assessment form (based on QUADAS-2). Due to scarcity of data and the poor quality of studies, we did not undertake a meta-analysis for this review. For illustrative purposes, we plot estimates of sensitivity and specificity on coupled forest plots.

MAIN RESULTS

We included six studies, providing 29 datasets: 20 for diagnosis of melanoma (1125 lesions and 242 melanomas) and 9 for diagnosis of BCC (993 lesions and 119 BCCs). We did not identify any data relating to the diagnosis of cSCC.Studies were generally poorly reported, limiting judgements of methodological quality. Half the studies did not set out to establish test accuracy, and all should be considered preliminary evaluations of the potential usefulness of HFUS. There were particularly high concerns for applicability of findings due to selective study populations and data-driven thresholds for test positivity. Studies reporting qualitative assessments of HFUS images excluded up to 22% of lesions (including some melanomas) due to lack of visualisation in the test.Derived sensitivities for qualitative HFUS characteristics were at least 83% (95% CI 75% to 90%) for the detection of melanoma; the combination of three features (lesions appearing hypoechoic, homogenous and well defined) demonstrating 100% sensitivity in two studies (lower limits of the 95% CIs were 94% and 82%), with variable corresponding specificities of 33% (95% CI 20% to 48%) and 73% (95% CI 57% to 85%), respectively. Quantitative measurement of HFUS outputs in two studies enabled decision thresholds to be set to achieve 100% sensitivity; specificities were 93% (95% CI 77% to 99%) and 65% (95% CI 51% to 76%). It was not possible to make summary statements regarding HFUS accuracy for the diagnosis of BCC due to highly variable sensitivities and specificities.

AUTHORS' CONCLUSIONS

Insufficient data are available on the potential value of HFUS in the diagnosis of melanoma or BCC. Given the between-study heterogeneity, unclear to low methodological quality and limited volume of evidence, we cannot draw any implications for practice. The main value of the preliminary studies included may be in providing guidance on the possible components of new diagnostic rules for diagnosis of melanoma or BCC using HFUS that will require future evaluation. A prospective evaluation of HFUS added to visual inspection and dermoscopy alone in a standard healthcare setting, with a clearly defined and representative population of participants, would be required for a full and proper evaluation of accuracy.

Melanoma versus dysplastic naevi: microtopographic skin study with noninvasive method

Malignant melanoma (MM) is a cutaneous tumour that originates from the epidermal melanocytes, and whose prognosis is strongly determined by tumour vertical thickness. ABCDE system is currently used for the clinical diagnosis of MM: lesion asymmetry, border irregularity, change or variegation in colour, diameter > 6mm and rapid evolution. Different methods have been used to improve the diagnosis of MM, but the results have not been convincing. Our work investigates the differences between MM and atypical naevi through skin surface analysis, using scanning electron microscopy (SEM): in fact ABCDE classical criteria are often insufficient for differential diagnosis of melanoma. In our study, we analysed 15 malignant melanomas surfaces from 15 patients and of 15 atypical naevi from 10 patients. On histological examination five superficial spreading melanoma (SSM) and 10 nodular melanoma (NMM) were found. Inclusion criteria used for selection were clinical diagnosis of SSM or clinical doubt between MM and atypical naevi (dysplastic naevi). Superficial skin texture was analysed using the silicone replica technique. The replica material is a polyvinylsiloxane derivative for dental application. Our results show that the melanoma has a very irregular surface, with a marked reduction or disappearance of cutaneous furrows, and formation of new lines with varying direction. In conclusion, the method above based on skin surface analysis, may be of help in diagnosis of early stage MM and in differentiating from atypical naevi.

Non-invasive preoperative assessment of basal cell carcinoma of nodular and superficial types

BACKGROUND/AIMS

Although various biophysical properties can be used to distinguish basal cell carcinoma (BCC) tissue from normal skin, none permits typing of the tumour. In this study, we assessed nodular (NBCC) and superficial (SBCC) types of BCC using three different non-invasive instruments and placed special emphasis on their clinical value as diagnostic tools.

METHODS

We included 35 patients with 35 tumours (15 NBCC and 20 SBCC), which had been diagnosed clinically. All lesions were evaluated preoperatively with an instrument measuring electrical impedance (IMP). Methods for determining transepidermal water loss (TEWL) and laser Doppler (LD) were also used. Measurements were also made in healthy skin on the contralateral side as reference. The diagnosis was confirmed by histological examination.

RESULTS

We found clear differences between the lesions and their reference values, using all three bioengineering techniques for NBCC and SBCC. The biophysical parameters of all types vary with anatomical location. Since most of the NBCC were located on the face and most SBCC on the trunk, their baseline impedance characteristics (i.e., impedance indices magnitude index (MIX) and imaginary part index (IMIX)) differed significantly. We therefore compared delta (a difference between the reference and tumour) MIX and IMIX of NBCC and SBCC instead of the absolute figures. We found no significant differences in TEWL, blood flow and IMP between the two types of BCC and attribute this to biological variation and electromagnetic noise.

CONCLUSIONS

As with LD and TEWL, definite differences in IMP were detected between healthy skin and BCC lesions. However, at this stage of development of the bioimpedance technique, we were unable to distinguish between the two types of BCC. An improved IMP device with semi- invasive probes or a more sophisticated type of data analysis may increase the diagnostic usefulness of the IMP method.

Ultrasound in dermatology - basic principles and applications

Ultrasound is widely used in general clinical medicine for non-invasive internal imaging. Over the last twenty years, technological advances have enabled the application of high-resolution ultrasonic imaging to the skin. Equipment and hardware is now available to produce cross-section images and three-dimensional reconstructions of selected skin segments. Resolution in vivo is not comparable to light microscopy but continues to improve with superior transducer designs. Skin ultrasonography has been reliably employed as an imaging modality in experimental designs, its quantifiable parameters being a distinct advantage. In particular, increased water content of the upper dermis, as occurs in inflammatory conditions or as a result of photodamage, can be demonstrated clearly as an echo-poor zone. Thus, the future of high-resolution ultrasound (HRU) may reside in its experimental role in monitoring inflammatory or photodamage processes in response to novel treatments. With regard to skin tumours, HRU reliably measures tumour thickness and also holds promise as a differentiator between seborrhoeic keratoses vs. melanoma and benign naevi vs. melanoma. While largely an experimental tool, the potential as an accurate, quantitative and reliable diagnostic and monitoring aid, merits further attention with an emphasis on clinical outcome measures.

Angiogenesis in cutaneous melanoma: pathogenesis and clinical implications

Neovacularization is an essential step in the multistage progression of malignant melanoma. The onset of new blood vessel formation is ushered in by the release of VEGF and numerous other angiogenic molecules by the tumor cells. Human melanoma is unique among neoplasms that both avascular (early horizontal growth phase characterized by very slow progression and 99%, 10-year survival) and vascular (late radial and vertical growth phase associated with rapid growth, metastasis and death in many cases), phases are discernible by the naked eye. Although cell biologists have made great strides in unraveling the mechanisms involved in the laying down of tumor vasculature and the factors that inhibit it, clinicians treating melanoma have been rather slow to realize and utilize the full potential of suppressing the tumor blood flow to the best advantage of the patient. We suggest a consorted endeavor by all the melanoma experts across the globe to establish an "angiogenesis database" wherein they pool the blood flow and vascularity information along with Breslow's thickness, Clark's level of invasion, lymphatic and vascular invasion, regression, and outcome of their patients.

Tumor vascularization in experimental melanomas: correlation between unenhanced and contrast enhanced power Doppler imaging and histological grading

The purpose of this study was to evaluate the reliability of unenhanced and enhanced power Doppler sonography in visualization of intratumoral angioneogenesis. Thirty-seven malignant melanomas, which had been implanted intra- or subcutaneously in 22 mice, were examined. Various B-mode criteria, power Doppler criteria and spectral Doppler parameters were evaluated before and after IV-application of the d-galactose-based contrast agent Levovist. After sonographic examination, all tumors were analyzed histologically with semiquantitative grading of tumoral vascularization. Unenhanced, in 70% of the tumors, no intratumoral vessels were visible using power Doppler, but only in 11% of the intracutaneous and in 0% of the subcutaneous after injection of the contrast agent. The enhanced mode was definitely superior to unenhanced Doppler in showing the intratumoral vascularity. The intratumoral vascular structure could be sufficiently analyzed in 30% of all tumors by unenhanced Doppler, but in 92% enhanced. The mean percentage vessel area increased about 433% after application of Levovist (intracutaneous: 485%, subcutaneous: 280%). Despite the missing direct correlation between the sonographically and histologically determined grade of tumor vascularization (Pearson's correlation unenhanced 0,356, p <.05/enhanced 0.395, p <.05), the correlation between the percentage vessel area and the histologic grade of vascularization was improved after application of the contrast agent (Pearson's correlation unenhanced 0.347, p <.05/enhanced 0.686, p <.01). We did not find a significant direct correlation between histologically and sonographically determined degree of vascularization. However, the correlation was improved using a d-galactose-based signal-enhancing agent in power Doppler sonography.

Differentiation of common benign pigmented skin lesions from melanoma by high-resolution ultrasound

BACKGROUND

There are potential clinical benefits if non-invasive methods can be used to diagnose or exclude melanoma.

OBJECTIVES

We investigated high-resolution ultrasound (HRU) as a potential non-invasive diagnostic aid for pigmented skin lesions.

METHODS

Using a 20-MHz ultrasound B-scan imaging system interfaced to a computer, we assessed acoustic shadowing and entry echo line enhancement (EEE) for 29 basal cell papillomas (BCPs) and 25 melanomas. Acoustic shadowing was estimated by the dermal echogenicity ratio (DER), comparing mean echogenicity below the lesion with that of adjacent dermis. Histological features were scored independently.

RESULTS

DER < 3 correctly distinguished melanoma from BCP with 100% sensitivity and 79% specificity. Specificity increased to 93% if the presence of EEE was included as a discriminator. Shadowing correlated most significantly with histological extent of hyperkeratosis (P < 0.0001). Consequently, this method falsely identified non-keratotic acanthotic BCP (n = 3) as melanoma. Highly significant differences between benign naevi (n = 15) and melanomas (n = 24) were found. The SD of retrolesional echogenicity was higher for naevi than melanomas (P < 0.0001), but such an analysis was poorly specific for the diagnosis of melanoma (30%).

CONCLUSIONS

Overall, HRU has considerable potential as a high-performance screening tool to assist in the discrimination between BCP, but not benign naevi, and melanoma. In particular, it may be possible to exclude melanoma with 100% certainty in the differentiation of BCP from melanoma.

Failure of gadopentetate dimeglumine-enhanced, high-resolution magnetic resonance imaging to differentiate among melanin-containing skin tumors

RATIONALE AND OBJECTIVES

We evaluated the diagnostic potential of gadopentetate dimeglumine-enhanced, high-resolution magnetic resonance (MR) imaging to differentiate benign from malignant melanin-containing skin tumors.

METHODS

Forty-five patients were prospectively examined using high-resolution MR imaging at 1.5 T using a 2.5-cm surface coil. For tumor assessment, T1-weighted and T2-weighted transverse spin-echo sequences were acquired. After intravenous administration of gadopentetate dimeglumine (0.1 mmol/kg), the T1-weighted transverse sequence was repeated. Contrast enhancement was quantitatively determined as the percentage increase of signal intensity. Histologic findings were correlated using the Wilcoxon signed-ranks test. The quality of contrast enhancement was assessed by three independent investigators who were unaware of the patients' history and histologic data. The signal-to-noise ratio (SNR) was calculated in the T2-weighted sequence. Significance was tested using the Wilcoxon signed-ranks test.

RESULTS

In all tumors, contrast enhancement was visually discernible. Half of the cases were enhanced inhomogeneously. The percentage of contrast enhancement did not correlate with histologic findings. Malignant melanomas could not be differentiated from benign melanocytic nevi with the use of gadopentetate dimeglumine. Determination of the SNR in T2-weighted sequences revealed no significant difference for histologic subgroups or tumor type.

CONCLUSION

Gadopentetate dimeglumine-enhanced MR imaging does not differentiate malignant melanomas from benign melanocytic nevi. Determination of the SNR in the T2-weighted sequences revealed no significant difference for histologic subgroups.

Influence of skin tension and formalin fixation on sonographic measurement of tumor thickness

BACKGROUND

High-resolution sonographic measurement of skin tumors, especially of malignant melanomas, allows presurgical assessment of the most important prognostic factor--tumor thickness. A good correlation between ultrasonographic and histopathologic thickness measurement has been reported. Procedures for preparing tissue for histopathologic examination, such as excision, fixation in formalin, dehydration in alcohol, and embedding in paraffin, may cause the tissue to retract and shrink and may therefore affect thickness measurement results.

OBJECTIVE

Our purpose was to evaluate the influence of skin preparation procedures on ultrasound measurement results and to compare tumor thickness values obtained sonographically versus those obtained histopathologically.

METHODS

Sixty-three epithelial (n = 37) and melanocytic (n = 26) tumors, benign as well as malignant, were measured by ultrasound before and immediately after excision and after overnight fixation. Sonographically and histopathologically determined tumor thicknesses were compared.

RESULTS

Loss of skin tension after excision led to an increase in measured tumor thickness because of spherical retraction of the specimen. Subsequent fixation, dehydration, and embedding reversed this effect, so that altogether, histopathologically assessed tumor thickness was only slightly lower than ultrasound-derived thickness before excision. This was true for melanocytic as well as epithelial lesions.

CONCLUSION

Loss of skin tension after excision and tissue preparation procedures seem to offset each other and lead to a good overall correlation between ultrasonographic and histopathologic measurements.

Computer screening for early detection of melanoma--is there a future?

Computer image analysis in the study of pigmented lesions is critically examined and discussed in the light of the current published data. The potential for objective analysis by computers as a possible screening aid for the inexperienced clinician is discussed. The future for this technology is exciting if handled with care.

Clinical relevance of sonometry-derived tumour thickness in malignant melanoma--a statistical analysis

High-frequency sonography has been shown to be a useful tool in planning operative strategy in the surgery of malignant melanoma (MM). The purpose of the present study was to compare sonometric and histometric data of tumour thickness in primary cutaneous MM, applying statistical methods in order to evaluate the pre-operative relevance of sonometry. The thickness of 259 melanomas was measured preoperatively by a 20-MHz B scan, and postoperatively by histometry. Statistical analysis was performed using Pearson's correlation coefficient and absolute and relative differences. Although the correlation between sonometry and histometry was good (r = 0.88), there was a mean difference of 0.39 mm (relative difference 28%). Overall, sonometry was in agreement with the corresponding histological classes in 75% of cases. However, tumours assessed by ultrasound as between 0.55 and 0.95 mm thick were incorrectly classified according to histology in 34%, and those between 1.30 and 1.70 mm were incorrectly classified in 50% of cases. Our data reveal greater differences between sonometry and histometry using appropriate statistical methods. A concept to assess differences between sonometry and histometry is recommended.

Three-dimensional imaging and reconstruction of skin lesions

An optical instrument called a "nevoscope" is used to image skin lesions by transillumination with visible light. The lesion is transilluminated by a fiber-optic annular ring light source that directs light into the skin area surrounding the lesion, forming a virtual source just beneath the lesion. Mirrors uniformly spaced around the lesion and tilted at various angles provide orthographic projections of the skin lesion. Additional views are obtained by rotating the mirror assembly. These multiple views are used in a direct three-dimensional (3D) reconstruction of the lesion using a filtered backprojection method. In this paper, we discuss the methodology of direct 3D reconstruction from 2D views of a transilluminated skin lesion as obtained using the new prototype nevoscope. We present the results of direct 3D reconstruction of a simulated phantom and a test object imaged using the nevoscope. In addition, a skin lesion was scanned in situ using the new prototype nevoscope. Results of the reconstruction of this lesion are also presented.

What dermatologists should know about digital imaging

The digital imaging revolution that swept other medical specialties in the late 1970s and early 1980s is beginning to find new and important roles in dermatology. This technology has a wide range of educational, clinical, and research applications. Dermatologists should understand certain basic concepts about images and imaging techniques to take advantage of progress in this field and eventually apply it to their own research and/or clinical practice.

The use of A-scan ultrasound in the assessment of small skin tumours

This study describes the use of A-scan ultrasound for the measurement and characterization of tumour tissue in small skin tumours--basal cell carcinoma, melanocytic naevus, hypertrophic scars and intraepidermal epithelioma. Assessment of the A-scan traces by measurement of: (i) the amplitude of echoes within the area of interest; (ii) the density (number per unit depth) of these echoes; (iii) the regularity of spacing and amplitude of the echoes, and (iv) the amplitude of echoes beneath the area of interest, was used to assist in the differential diagnosis. The results show significant differences in echo amplitude between all the tumours and normal skin. When the tumour A-scan traces were analysed the results indicated that the best discriminating feature between tumours was that of amplitude, followed by regularity, density, non-normalized thickness and finally amplitude of echoes from beneath the tumour. Ultrasound-derived skin thickness measurements were compared to histological measurements for the lesions, and an excellent correlation was found (r = 0.96). It was considered that the A-scan ultrasound investigation of small tumours of the skin was able to provide information on the nature of the tissues contained and may assist in their differential diagnosis.

Magnetic resonance imaging of cutaneous melanocytic lesions

This is the first literature report on magnetic resonance imaging (MRI) examination of cutaneous melanocytic or any other type of skin lesions. Good resolution, clinically useful MRI scans of a congenital nevus and a metastatic melanoma to the skin are presented. The potential usefulness of MRI technique to physicians dealing with cutaneous disease is discussed.