The National Comprehensive Cancer Network has developed a series of criteria based on which tumors can be classified as resectable, borderline resectable or unresectable, relating to the degree of tumor extension to the neighboring structures and the degree of their involvement (fig. 2, fig.3).

The extent of circumferential vascular involvement is assessed in 90-degree increments. Contact involving less than 180 degrees is referred to as abutment, while contact exceeding 180 degrees is called encasement (fig.4).

Changes in vessel morphology that may indicate vascular invasion include: teardrop sign – this describes a shape change of the portal vein (PV) or superior mesenteric vein (SMV) from oval or round to a teardrop form, often resulting from tumor encasement or fixation by surrounding fibrotic tissue; irregular vessel contour – an irregular vessel outline suggests possible vascular invasion, especially in arteries, as their walls are thicker compared to veins; thrombosis – the presence of a thrombus within an artery can be an indicator of vascular invasion.

The imaging report should also note any anatomical variations in the adjacent vascular structures (fig.5).

Along with the above criteria, there are a few additional findings that the surgeon needs to consider, including: perineural spread, spread to the transverse mesocolon, and spread to the root of the mesentery (fig.6).