Recognizing sessile serrated adenomas/polyps: a diagnostic challenge for pathologists

In the past 15 years, it has become increasingly clear that a significant proportion of colorectal cancers arise from a serrated precursor lesion rather than the conventional adenoma. These lesions are known as sessile serrated adenoma or polyps (SSA/P) and are mediated by a different molecular (serrated) pathway to the chromosomal instability pathway. Several researchers have suggested that the serrated pathway is an accelerated one leading to carcinogenesis. For these reasons, it is imperative that both gastroenterologists and pathologists are not only aware of the existence of SSA/P, but are able to make the correct diagnosis and, subsequently, to manage the patient appropriately. It must be acknowledged that pathologists have been slow to recognize SSA/P and this is largely due to lack of awareness. For those who are aware of the lesion, some confusion has prevailed about the diagnostic criteria and the association with dysplasia. Recently, the American College of Gastroenterology established diagnostic criteria for the diagnosis of SSA/P [ 1 ]. Despite this and other previous publications highlighting histologic criteria, there remains poor recognition of the entity [ 2 ] [ 3 ]. Over and above awareness (which is increasing), there are technical factors that often impede a pathologist’s ability to provide a confident diagnosis of SSA/P. As highlighted in the paper by Morales et al. in this issue of Endoscopy , orientation of the tissue section is an important rate-limiting step in making the diagnosis of SSA/P and distinguishing it from a hyperplastic polyp [ 4 ]. Due to obliquity of sectioning, the architectural features that are critical for the diagnosis of SSA/P are not readily apparent despite serial or stepwise sections through the tissue. The pathologist is then left with the unsatisfactory diagnosis of an “indeterminate or unclassifiable serrated” lesion, that may be an SSA/P or a hyperplastic polyp. The study by Morales et al. advocates and recommends an easy and inexpensive way to ensure that proper orientation can be achieved in a larger proportion of cases. They have assessed a significant number of SSA/P specimens using an orientation score and also showed an almost 35 % increased diagnosis rate of SSA/Ps using their modified “envelope” technique compared with routine practice [ 4 ]. Improved orientation will eliminate some of the equivocal or indeterminate diagnoses of SSA/P, thus ensuring a more accurate diagnosis on which the clinician can act to determine surveillance protocols.

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