Quantitative Analysis of Frozen Section Histology in Mohs Micrographic Surgery

Piston-based specimen holder for rapid surgical and biopsy specimen imaging

Advanced fluorescence imaging modalities such as confocal microscopy and two photon fluorescence microscopy can provide rapid, real-time histology images, but the mounting of fresh tissue specimens in standard orientations required for diagnosis without embedding and sectioning remains an unsolved problem. Here, we introduce a piston-based specimen holder designed for consistent, even pressure distribution. We improve upon previous designs by incorporating an air piston system with a flexible membrane and wick that extracts fluid during compression. We combine this with support fixtures to aid in the distribution of pressure, enabling imaging of specimens with small surface areas relative to their thickness, such as bisected shave skin biopsies in standard orientation without embedding or sectioning. We image both fresh biopsy specimens and diagnostic Mohs first stage specimens during clinical procedures, demonstrating improved visualization of the tissue surface in real time. Finally, we show that conventional cryosectioning can exaggerate the extent of margin positivity, which can be avoided using the piston-based holder.

Intraoperative margin assessment for basal cell carcinoma with deep learning and histologic tumor mapping to surgical site

Successful treatment of solid cancers relies on complete surgical excision of the tumor either for definitive treatment or before adjuvant therapy. Intraoperative and postoperative radial sectioning, the most common form of margin assessment, can lead to incomplete excision and increase the risk of recurrence and repeat procedures. Mohs Micrographic Surgery is associated with complete removal of basal cell and squamous cell carcinoma through real-time margin assessment of 100% of the peripheral and deep margins. Real-time assessment in many tumor types is constrained by tissue size, complexity, and specimen processing / assessment time during general anesthesia. We developed an artificial intelligence platform to reduce the tissue preprocessing and histological assessment time through automated grossing recommendations, mapping and orientation of tumor to the surgical specimen. Using basal cell carcinoma as a model system, results demonstrate that this approach can address surgical laboratory efficiency bottlenecks for rapid and complete intraoperative margin assessment.

An international survey characterizing Mohs tissue processing techniques and Mohs margin thresholds: how close is too close?

BACKGROUND

From practice, we identified heterogeneity in Mohs micrographic surgery (MMS) specimen tissue processing techniques and specifications, and in the Mohs surgeons' assessment of MMS specimen histological tumour clearance.

AIM

By surveying an international cohort of Mohs surgeons, we determined to characterize variation in margin threshold assessment (number of wafers/sections free of tumour to declare tumour clearance).

METHODS

An online questionnaire was distributed to Mohs surgeons in the UK, European countries, Australia and New Zealand, assessing the background demographics of the surgeons and the technical factors involved in MMS tissue processing and posing three MMS scenarios to define margin thresholds.

RESULTS

In total, 114 consultant/attending-level Mohs surgeons responded, giving a response rate of 33.5% from 20 countries (including UK nations). The first scenario posed was a 20-mm cheek basal cell carcinoma (BCC) excised by MMS with a fully complete first wafer (7 μm) clear of tumour and the second wafer (after trimming interval of 50 μm) demonstrating a small dermal focus of nodular BCC; of the 58 surgeons, 16 (27.6%) would not take another stage. With a follow-up question, 16 of the 58 (27.6%) surgeons specified wanting three clear sections to declare tumour clearance. When the same scenario had a change to a 20-mm infiltrative BCC, 84.2% (48 of 57 surgeons) required a second MMS stage, with a follow-up question clarifying that a third (19 of 57) wanted three clear sections to determine clearance. For a well-differentiated 15-mm squamous cell carcinoma with the same factors there was no majority consensus, with the same proportion of surgeons (22.6%; 12 of 53) calling tumour clearance after one, two and three clear section(s) respectively. For MMS specimen processing specifications, routine sections/wafers of 5-10 μm were reported by 77.4% of respondents (48 of 62) and for trimming interval values, 78.6% (48 of 61) specified a range between 20 and 200 μm.

CONCLUSION

By surveying international Mohs surgeons, we highlight surgeon background characteristics, peer-compare assessment of margin thresholds for tumour clearance across three scenarios, and delineate tissue processing and intraoperative approaches.