Confocal Microscopy in Skin Cancer

Abstract

Purpose of review: Reflectance confocal microscopy (RCM) enables imaging of skin lesions at cellular level resolution at the bedside (in vivo) or in freshly excised tissue (ex vivo). This article provides an overview of strengths and limitations of non-invasive RCM in skin cancer diagnosis.

Recent findings: RCM features of common melanocytic and non-melanocytic skin neoplasms such as melanoma, actinic keratosis/squamous cell carcinoma, basal cell carcinoma, and nevi have been well defined and show good correlation with dermoscopic and histopathologic findings. Due to its technical properties, RCM is especially suitable for the examination of flat skin lesions.

Summary: In vivo RCM has been shown to increase the accuracy of non-invasive diagnosis of common skin neoplasms and is a valuable adjunct to dermoscopy, particularly in cosmetically and functionally sensitive areas such as the face or the genital area.

Keywords: Basal cell carcinoma; Dermoscopy; Facial macules; Histopathology; Lentigo maligna; Melanoma; Nevi; Non-melanoma skin cancer; Reflectance confocal microscopy; Skin tumors.

Fig. 1

Horizontal RCM sections (1 × 1 mm) of normal skin at various imaging depths, as indicated on the corresponding vertically cut histological image. (A) Polygonal skin islands are separated by dark furrows (arrow); the furrows correlate to skin surface folds (dermatoglyphics). The stratum corneum presents as a “wrinkled”-appearing bright sheets (circle). A refractile long cylindrical tube correlating to a hair shaft is observed (arrowhead). (B) Regular honeycomb pattern of the granular and spinous layers seen with RCM. Dark holes of regular size, correlating to nuclei of keratinocytes (arrow) and bright lines with uniform thickness and reflectivity, correlating to cytoplasm of keratinocytes and intercellular connections, are seen. (C) Dark, round to oval dermal papillae surrounded by a slightly brighter rim of pigmented basal keratinocytes and melanocytes (“edged papillae”) are observed at the DEJ (arrows). (D) Within the papillary dermis, a web-like pattern of bright collagen fibers is seen (circle). The bright, centrally hollow structure (arrow) is a sweat duct; spiraling of the epidermal portion of the sweat duct (acrosyringium) through the epidermis can be seen when sequential images are obtained along the z-axis (“Vivastack”)

Fig. 2

Clinical, dermoscopic, and RCM images of Bowen’s disease (SCC in situ). a Clinically, a red-brown scaly plaque measuring 15 mm in diameter is seen (inset). An ill-defined pink-brown structureless lesion with diffuse dotted vessels (arrow) is observed on dermoscopy. b On RCM at the level of the stratum corneum, irregularly shaped and heterogeneously bright sheets with loss of the normal skin folds are seen at low magnification (3.5 × 4 mm field-of-view). The brighter foci (arrows) correlate to the scale seen clinically. Hair shafts (arrowhead) are also seen. c An irregular honeycomb pattern is seen at the level of the spinous layer (1 × 1 mm field-of-view), with variability in the width and brightness of the lines (dashed arrows) and size and shape of the holes (arrows). In foci, large holes, representing abnormally large nuclei of keratinocytes are seen. d At the DEJ, increased density of dermal papillae having different sizes and shapes (dashed arrows) and harboring dilated blood vessels are visualized (1 × 1 mm field-of-view). In addition, a single large, round, bright-nucleated cell is seen (arrow) at the basal layer of the epidermis, probably correlating to a dyskeratotic keratinocyte

Fig. 3

RCM image (1 × 1 mm field-of-view) of bright tumor islands and dark silhouettes seen in basal cell carcinoma (BCC). a On RCM, the bright tumor islands of BCC harbor numerous bright dendritic structures (arrow). These are dendrites of melanocytes in pigmented basaloid aggregates of BCC. Dark cleft-like spaces are also observed surrounding the tumor islands (dashed arrow). b Hyporeflective tumor islands appear as “dark silhouettes” (arrows) within the bright collagen of the tumor stroma; these correlate with non-pigmented basaloid aggregates of BCC

Fig. 4

Dermoscopic and RCM images of a junctional nevus. a Dermoscopy shows a pigment network (dashed arrow) and focal small brown globules (arrow). b On RCM mosaic, a ringed pattern (arrows) composed of edged dermal papillae is observed at the DEJ (2 × 2 mm field-of-view). c At higher magnification (500 × 500 μm field-of-view), edged papillae are seen composed of dark round to oval dermal papillae (arrow) surrounded by a rim of monomorphous bright cells (basal keratinocytes and small melanocytes, dashed arrow). Round blood vessels traversing dermal papillae are detected during real-time imaging. d A deeper section of the DEJ displays small junctional dense nests (arrows) that protrude into the papillary dermis

Fig. 5

Dermoscopic and RCM images of a compound nevus. a Dermoscopy shows light to dark brown aggregated globules (arrow). b On RCM, a clod-and-meshed pattern is seen at the DEJ on low magnification (3 × 4 mm field-of-view); the clods being bright round structures (arrows) and the mesh being elongated, tubular structures (dashed arrow), both correlating to melanocytic nests. c At higher magnification (1 × 1 mm field-of-view), the tubular structures observed at the DEJ are junctional thickenings (dashed arrows) that widen and bridge the rete ridges. d Round to oval dense nests are seen within the dermal papillae on RCM (1 × 1 mm field-of-view); these are dermal nests

Fig. 6

Images of a biopsy-diagnosed compound Clark (dysplastic) nevus, which shows features raising concern for melanoma on both dermoscopy and RCM. a Clinically (inset), a 4 × 5 mm dark brown, flat topped papule is seen. With dermoscopy, a dark brown atypical pigment network (arrows) and focal pseudopods at the lesion’s periphery (dashed arrows) are observed. b On RCM mosaic (2 × 2.5 mm field-of-view), few bright large cells (arrows) are seen at the level of the spinous layer, corresponding to melanocytes in Pagetoid pattern. c On RCM mosaic (2 × 2.5 mm field-of-view) at the DEJ level, a meshed pattern (arrowheads) is seen, composed of edged as well as non-edged papillae and bright tubular structures (“junctional thickening,” arrows); these tubular structures correlate with confluent melanocytic nests on histopathology. d Non-edged papillae are visualized on higher magnification RCM (approximately 1 × 1 mm field-of-view) at the DEJ level. Widened interpapillary spaces harboring bright tubular structures of variable reflectivity (“junctional thickening,” thick arrows) are observed. Single large, bright, nucleated cells are detected (arrow); these cells represent solitary atypical melanocytes. According to Pellacani’s RCM method for melanoma diagnosis, the lesion will get a score of 5 (non-edged papillae—2, atypical melanocytes at DEJ—2, cells in pagetoid pattern—1), denoting suspicion for melanoma

Fig. 7

Clinical, dermoscopic, and RCM images of a melanoma in situ. a Clinically, a tan to dark brown patch with a diameter of 10 mm is seen. With dermoscopy, a dark brown atypical network (arrows) is observed. b With RCM mosaic (2.5 × 2.5 mm field-of-view), large, bright cells are seen within the upper epidermis (arrows). In addition, areas displaying bright dendritic processes are observed (dashed arrow). c Large, bright, nucleated cells of variable size and shape are seen at level of the spinous layer at higher magnification RCM (500 × 500 μm field-of-view), denoting melanocytes in Pagetoid pattern displaying pleomorphism. The normal honeycomb pattern is not seen (“disarranged pattern”). d On RCM mosaic (2.5 × 2.5 mm field-of-view) at the DEJ level, an irregular meshed pattern is seen (arrow) with some variability in the width and brightness of the lines of the meshwork. Focally, the meshed pattern is not seen (arrowhead); there is absence of dermal papillae in this focus, suggesting a flattened DEJ. Single bright cells (dashed arrows) stand out both within the meshwork and in the focus that lacks the meshed pattern, suggesting focal predominance of solitary melanocytes at the DEJ

Fig. 8

a RCM image (500 × 500 μm field-of-view) displaying pleomorphism of melanocytes in a melanoma. Round, triangular, dendritic, and spindle-shaped nucleated cells of variable size and reflectivity are seen at the suprabasal levels of the epidermis. There is a disarranged pattern, with loss of the normal honeycomb pattern. b RCM image (1 × 1 mm field-of-view) of a melanoma at the DEJ level displays junctional thickenings (arrowheads) with variable reflectivity and with widening of the interpapillary spaces. Multiple bright-nucleated and dendritic cells of variable size and shape (arrows), correlating to pleomorphism of melanocytes, are seen

Fig. 9

RCM images of a melanoma. a On RCM mosaic (2.5 × 2.5 mm field-of-view), multiple round, oval and tubular structures of variable reflectivity (arrowheads) are seen at the suprabasal epidermal levels; these correlate with nests of atypical melanocytes. The majority of the nests appear as “dense clusters” that are homogenous in brightness and in which individual melanocytes are mostly unapparent; however, “sparse nests,” which correspond to discohesive aggregates of atypical melanocytes, are also seen (arrow). b On high magnification RCM (500 × 500 μm field-of-view) of the upper epidermis, sparse nests appear as aggregates of nucleated cells of variable reflectivity, in which the individual cells are discernible. c High magnification RCM (500 × 500 μm field-of-view) at the level of the superficial dermis shows “cerebriform nests.” Cerebriform nests are confluent aggregates of low reflecting cells (melanocytes) in the dermis that are separated by a darker rim, resulting in a multilobate appearance

Fig. 10

Clinical, dermoscopic, histopathological, and RCM images of a facial melanoma in situ (lentigo maligna). a Clinically (inset), a 2 × 3 cm tan macule with focal dark brown areas is seen. With dermoscopy, asymmetrically pigmented follicular openings (arrow) and early rhomboidal structures (dashed arrow) are visualized. b On RCM (approximately 2 × 2 mm field-of-view), bright dendritic cells and dendritic processes (arrowheads) form sheets and tubular structures at the basal layer. Small melanocytic nests are focally detected (thin arrow). Some of the sheets and tubular structures of dendritic cells and dendritic processes are located around adnexal structures (thick arrows). c On histopathology, atypical melanocytes are seen as crowded single cells and small nests (arrows) along a flattened DEJ (H&E, magnification × 100). d At high magnification RCM (500 × 500 μm field-of-view), bright, pleomorphic nucleated, and dendritic cells infiltrate the adnexal epithelium (arrows); imaging deeper into the tissue can show the extension of atypical melanocytes down adnexal structures