Micro-Computed Tomography Whole-Block Imaging Reveals Origin and Path of Rectal Cancer Tumor Deposits: A Pilot Study

In colorectal carcinoma (CRC), tumor deposits (TDs) are described as macroscopic/microscopic nests/nodules in the lymph drainage area discontinuous with the primary mass, without identifiable lymph node (LN) tissue, and not confined to vascular or perineural spaces. A TD is categorized as pN1C only when no bona fide LN metastasis exists. However, there has been an ongoing debate on whether TDs should be counted as LNs. The fact that the origin of TDs is not fully understood adds further uncertainty. This pilot study aims to evaluate whether whole-block imaging by micro-computed tomography (micro-CT WBI) that enables three-dimensional reconstruction of whole-mount (WM) blocks can serve as a tool to assess the origin and path of CRC TDs. We evaluated whole-slide imaging (WSI) and micro-CT WBI of 20 WM blocks from a rectal cancer resection that contained TDs. Each TD was tracked through the contiguous blocks to define their origin and path. Of eleven TDs identified on WSI, six were detected on WBI. Strikingly, six of six TDs trackable through the blocks on WBI revealed an origin from the main tumor. This pilot study provided evidence that micro-CT WBI can serve as an effective tool to evaluate the origin and path of CRC TDs.