In Vivo Reflectance Confocal Microscopy

In Vivo Margin Mapping as an Adjunct to Surgery

Oftentimes, tumor margins are poorly defined and can be difficult to map clinically and dermoscopically. Studies have demonstrated the use of RCM in delineation of surgical margins prior to surgery or excisional biopsies.^11,12 Alternatively, when complete removal at biopsy would be impractical (eg, for extremely large lesions or lesions located in cosmetically sensitive areas such as the face), RCM can be used to pick the best site for an appropriate biopsy, which decreases the chance of sampling error due to skip lesions and increases histologic accuracy.

Nonsurgical Treatment Monitoring

One advantage of RCM over conventional histology is that RCM imaging leaves the tissue intact, allowing dynamic changes to be studied over time, which is useful for monitoring nonmelanoma skin cancers and lentigo maligna being treated with noninvasive therapeutic modalities.¹³ If not as a definitive treatment, RCM can act as an adjunct for surgery by monitoring reduction in lesion size prior to Mohs micrographic surgery, thereby decreasing the resulting surgical defect.¹⁴

Limitations

Imaging Depth
Although RCM is a revolutionary device in the field of dermatology, it has several limitations. With a maximal imaging depth of 350 µm, the imaging resolution decreases substantially with depth, limiting accurate interpretation to 200 µm. Reflectance confocal microscopy can only image the superficial portion of a lesion; therefore, deep tumor margins cannot be assessed. Hypertrophic or hyperkeratotic lesions, including lesions on the palms and soles, also are unable to be imaged with RCM. This limitation in depth penetration makes treatment monitoring impossible for invasive lesions that extend into the dermal layer.

Difficult-to-Reach Areas
Another limitation is the difficulty imaging areas such as the ocular canthi, nasal alae, or helices of the ear due to the wide probe size on the VivaScope 1500. The advent of the smaller handheld VivaScope 3000 device allows for improved imaging of concave services and difficult lesions at the risk of less accurate imaging, low field of view, and no reimbursement at present.

False-Positive Results
Although RCM has been shown to be helpful in reducing unnecessary biopsies, there still is the issue of false-positives on imaging. False-positives most commonly occur in nevi with severe atypia or when Langerhans cells are present that cannot always be differentiated from melanocytic cells.^3,15,16 One prospective study found 7 false-positive results from 63 sites using RCM for the diagnosis of lentigo malignas.¹⁶ False-negatives can occur in the presence of inflammatory infiltrates and scar tissue that can hide cellular morphology or in sampling errors due to skip lesions.^3,16

Time Efficiency
The time required for acquisition of RCM mosaics and stacks followed by reading and interpretation can be substantial depending on the size and complexity of the lesion, which is a major limitation for use of RCM in busy dermatology practices; therefore, RCM should be reserved for lesions selected to undergo biopsy that are clinically equivocal for malignancy prior to RCM examination.¹⁷ It would not be cost-effective or time effective to evaluate lesions that either clinically or dermoscopically have a high probability of malignancy; however, patients and physicians may opt for increased specificity at the expense of time, particularly when a lesion is located on a cosmetically sensitive area, as patients can avoid initial histologic biopsy and gain the cosmetic benefit of going straight to surgery versus obtaining an initial diagnostic biopsy.

Cost
Lastly, the high cost involved in purchasing an RCM device and the training involved to use and interpret RCM images currently limits RCM to large academic centers. Reimbursement may make more widespread use feasible. In any event, RCM imaging should be part of the curriculum for both dermatology and pathology trainees.

Future Directions

In vivo RCM is a noninvasive imaging modality that allows for real-time evaluation of the skin. Used in conjunction with dermoscopy, RCM can substantially improve diagnostic accuracy and reduce the number of unnecessary biopsies. Now that RCM has finally gained foundational CPT codes and insurance reimbursement, there may be a growing demand for clinicians to incorporate this technology into their clinical practice.