Ultrasound and Infrared-Based Imaging Modalities for Diagnosis and Management of Cutaneous Diseases

Abstract

Non-invasive bedside imaging tools are becoming more prevalent for assessing cutaneous lesions. Ultrasound used at specific frequencies allows us to assess margins of lesions to minimize the extent of the biopsy that is performed and improve cosmetic outcomes. Vascularity, seen on Doppler ultrasound and contrast-enhanced ultrasound, and stiffness, assessed on tissue elastography, can help differentiate between benign and malignant lesions for clinicians to be more judicious in deciding whether to biopsy. Moreover, research has shown the efficacy in using ultrasound in monitoring flares of hidradenitis suppurativa, a disease affecting apocrine gland-rich areas of the body, for which the current gold standard involves examining and scoring inflammatory lesions with the naked eye. Infrared-based modalities have also been on the uptrend to aid in clinical decision-making regarding suspiciousness of lesions. Reflectance confocal microscopy has lateral resolution that is comparable to histopathology and it has been shown to be an appropriate adjunctive tool to dermoscopy, specifically when evaluating melanomas. Optical coherence tomography has utility in determining lesion thickness because of its depth penetration, and spectrophotometric intracutaneous analysis is becoming more popular as a tool that can be used by general practitioners to know when to refer to dermatology regarding worrisome pigmented lesions. Strides have been made to incorporate electrical impedance spectroscopy alongside dermoscopy in decision-making regarding excision, although the evidence for its use in the clincial setting remains inconclusive. This paper reviews the efficacy and drawbacks of these techniques in the field of dermatology and suggests future directions.

Keywords: dermatology; electrical impedance spectroscopy; hidradenitis suppurativa; non-invasive imaging; optical coherence tomography; reflectance confocal microscopy; spectrophotometric intracutaneous analysis; ultrasound.

Figure 1

The most recent array-based ultrasound technologies for dermatology provide a choice of operating frequency, which enables the operator to “trade off” the field of view and resolution. For example, a deeper lesion (lipoma) is best imaged with a lower center frequency of 30 MHz (A) while a more superficial lesion and hair are better imaged at a center frequency of 50 MHz (B) with higher resolution but a smaller overall field of view. These images are courtesy of VisualSonics. Permissions obtained to reprint from Vevo MD for Dermatology (27), retrieved from https://www.visualsonics.com/product/imaging-systems/vevo-md Copyright 2017 Fujifilm VisualSonics Inc.

Figure 2

Using ultrasound to detect retained hair tracts (indicated by the arrows) within fistulae in hidradenitis suppurativa. This is indicative of regions that could flare with further inflammatory reactions and worsen extent of the disease. The mean length of hair tracts was 4.4 mm with a wide dispersion (SD of 6.9 mm) and a range of 2–31.7 mm. Images were taken with a General Electric Logic E9 with a maximum ultrasound bandwidth of 18 MHz. Permissions obtained to reprint from Wortsman and Wortsman (61).

Figure 3

Reflectance confocal microscopy has allowed for sub-classification of melanomas using morphological descriptions. Permissions obtained to reprint from Grazziotin et al. (70). In their study, it was found that dendritic cell melanomas (A) were linked to more sun exposure and round cell melanomas (B) occurred in patients with familial melanomas and fairer skin. Dermal nest (C) and combined (D) melanomas were associated with a lack of pigmented network on dermoscopy and thicker tumours on histology. The morphological expression can also be linked to tumor behavior, for example, the non-classifiable type (E) had less atypia on basal layer melanocytes and had lower asymmetry, border, color, dermoscopic structures (ABCD rule in dermoscopy) scores using dermoscopy.

Figure 4

Patient with previously treated lentigo maligna (LM) melanoma had a new brown pigmented areas (indicated with the arrows) on clinical examination (A) and dermoscopy (B). Reflectance confocal microscopy (RCM) of the pigmented area in the middle of the upper lip (blue arrow) showed round cells with dendritic processes in the epidermis (C). RCM-targeted biopsy of this was performed and histopathology confirmed recurrence of LM (D). Not shown in this figure: the pigmented area indicated by the green arrow showed features in keeping with solar lentigo on RCM. Permissions obtained to reprint from Maher et al. (71).

Figure 5

A demonstration of sclerosing basal cell carcinoma on the nose (circle) visualized with (A) clinical examination and (B) dermoscopy (“c” representing milia-like structures and the arrows pointing to erosions). Slide-mode optical coherence tomography is depicted in box (C) with nodules that are hyporeflective with hyporeflective rims (arrows) and hyperreflective peritumoral borders (asterisk) and a cyst marked “c.” In box (D), the en-face mode gives information on the peritumoural fibers (star-shaped dotted line), vessels (marked “v” with smaller dotted line), and hyporeflective nodules with bright centers (arrows). Histopathology in panel (E) demonstrates peritumoural fibers surrounding tumors (arrows) and cysts marked with “c.” Permissions obtained to reprint from von Braunmühl et al. (1).

Figure 6

A proposal of a novel approach for examination of cutaneous diseases. Spectrophotometric intracutaneous analysis may be useful for primary care physicians in considering lesions before referral. Clinical visualization and dermoscopy are always the first component of the examination of a lesion. Some literature suggests that electrical impedance spectroscopy can aid in the decision-making process regarding excision. Ultrasound can be incorporated next with modification of frequency parameters to obtain optimal penetration depth; ultrasound features such as color Doppler for assessment of lesion vascularity can be used as needed. Reflectance confocal microscopy and optical coherence tomography may be helpful in specific cases, and biopsy and histopathology remain the final step if further diagnostic clarification is needed.