Table of Contents
Introduction:
Reflectance confocal microscopy is a US (United States) Food and Drug Administration-approved optical imaging technology that offers noninvasive visualization of skin lesions in vivo at nearly histologic resolution. However, the cost of purchasing the device has previously limited its use to large academic and research centers. The easing of the payment modalities will attract more practitioners to this technology. As a result, confocal reflectance microscopy is increased, and light passes through the beam, scanned and focused by the optical lens and the device that contacts the skin.
What Is Called Reflectance Confocal Microscopy?
Reflectance confocal microscopy (RCM) is a noninvasive imaging technique that enables in vivo visualization of the epidermis down to the papillary dermis in real time. Resolution is almost comparable to conventional histology, allowing the clinician to do a "virtual biopsy" on the skin, and these diagnostic clues are used while minimizing unnecessary skin biopsies.
How Does Reflectance Confocal Microscopy Work?
Reflectance confocal microscopy uses the diode laser as a monochromatic and coherent light source.
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The light passes through a beam splitter, scanning and focusing an optical lens and a skin contact device.
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It penetrates the skin and illuminates a small tissue spot.
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Light from the focal point reflects through the lens, focusing it into a tiny pinhole and forming an image on a photodetector.
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The pinhole only allows light from the focal point to pass through (that is, it is confocal) and prevents light from another tissue point or out of the focus plane from getting through.
Reflectance confocal microscopy relies on reflectance (back-scattering) of light from structures with different refractive indices, such as membranes, keratohyalin granules, and melanosomes.
This wavelength does not cause tissue injury for the patient or injury to the eyes of the operator.
How Is Reflectance Confocal Microscopy Used?
Reflectance confocal microscopy is a painless procedure. The steps of the procedure are listed below:
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A small amount of immersion oil is applied to the skin (the refractive index of oil is close to that of the stratum corneum).
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A glass window is attached to a metal ring and placed over the oil.
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The glass window is fixed to the skin using medical adhesive tape to prevent skin movement.
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A water-based immersion medium, for example, water-based gel, is placed inside the ring, which is magnetically attached to the optical lens housing of the microscope.
Reflectance confocal microscopy allows horizontal scanning of the imaged tissue at a pre-selected depth.
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Each basic image generated is 5 mm x 5 mm, with imaging entire lesions up to 8 x 8 mm.
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The primary images are stitched together by a computer forming a block or mosaic.
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Vertical series of images, called a stack, can be obtained at the same horizontal position.
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A cube is a stack of blocks or mosaics.
What Are the Potential Clinical Applications?
Reflectance confocal microscopy is used to diagnose benign and malignant skin lesions, such as:
Reflectance confocal microscopy is used to monitor treatment, such as the effectiveness of Imiquimod in actinic keratosis. Additionally, access appropriate surgical margins in Mohs surgery. Reflectance confocal microscopy can also diagnose inflammatory conditions, such as psoriasis, dermatitis/eczema, and infestations like scabies.
What Are the Features Seen in Normal Skin Using RCM?
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Stratum Corneum: It is the highly refractive (bright) surface that is surrounded by visible skin folds (these are dark). Corneocytes are large polygonal or seen even without a visible nucleus.
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Stratum Granulosum: Keratinocytes visualized in the granular cell layer have well-demarcated outlines forming a honeycombed pattern. The cytoplasm can be seen as white and grainy due to organelles and keratohyalin granules.
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Stratum Spinosum: Squamous cell layer keratinocytes are small and polygonal and have thin white cytoplasm and oval dark nuclei. They also form a honeycomb pattern.
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Stratum Basale: Melanocytes and pigmented keratinocytes appear as solitary round/oval structures and are indistinguishable.
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Dermo-Epidermal Junction (DEJ): Small basal cells and melanocytes form bright rings surrounding dark dermal papillae at the DEJ. Within these, the small blood capillary loops with blood vessels are seen. This arrangement is termed an ''edged papillae.
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Dermis: Dermal blood vessels appear as a dark tubular structure that contains weakly and brightly refractile cells. Collagen fibers appear as bright, elongated fibrillar structures.
RCM Features of the Skin Lesions:
1. Melanoma:
Early melanoma is characterized by:
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Alteration of the dermo-epidermal junction, which is flattened and disarranged.
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Ill-defined papillary contours ("non-edged "papilla).
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The dermal papilla is replaced by atypical cells.
Features of more advanced melanoma are:
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Malignant cells occupy the entire junction.
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Loose, large, bright cells within the epidermis.
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Large bright cells with dark, eccentric nuclei are seen in the superficial epidermis.
2. Inflammatory Diseases:
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Inflammatory skin diseases can be grouped into four main categories,
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Psoriasiform diseases.
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Diseases with interface changes.
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Pigmentary disorders are other than tumors.
3. Psoriasis:
Features of chronic plaque psoriasis are:
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Non-rimmed papilla at the dermo-epidermal junction. Faint rings surround the papillae.
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Epidermal thickening.
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Several vessels within the non-rimmed papillae.
Limitations:
In the commercially available confocal microscope, limitations include the following:
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It cannot differentiate benign lesions from melanoma, which is seen in most cases.
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Lesions on a large scale can impair visualization of the dermo-epidermal junction.
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Image interpretation requires extensive training.
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The instrument can be difficult to place in small concave sites such as the ear and inner canthus due to its bulkiness.
With new diagnostic codes for reflectance confocal microscopy imaging, physicians can now be reimbursed for the acquisition and interpretation of skin lesions. That may improve the diagnostic accuracy and early detection of equivocal skin lesions and reduce the number of unnecessary excision of benign tumors.
Conclusion:
The reflectance confocal microscope can scan the entire lesion non-invasively and determine the most diagnostically and prognostically significant area to biopsy. Thus it helps reduce the risk of sampling error and false negative rates due to heterogeneity within the lesions. A novel imaging technology, reflectance confocal microscopy, will continue to evolve and become more widespread in the upcoming years in the field of dermatology.
