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Review of serrated lesions by JCP

Mention the term 'serrated lesions" (of the colorectum) and immediately I will get a brief panic attack.  Based on my limited knowledge, the lesions sound and look the same.  Even when a senior teacher made a nice diagram of how to differentiate all of these lesions, it still did not hit me how things work... until today.

There is a nice review article in Journal of Clinical Pathology regarding pathological diagnosis of serrated lesions by Bateman and Shepherd (J Clin Pathol 2015;68:585-591).  I think it very helpful in terms of clearing up the terminologies involved.

Basically, the recommended terminology of serrated lesions in the colorectum is as follows:

1. Hyperplastic polyp
2.  Sessile serrated lesion (SSL)
3.  SSL with dysplasia
4. Traditional serrated adenoma
5. Mixed polyp

Hyperplastic polyp is easy enough, but what about sessile serrated lesions?  They have listed the key histological features as follows:

▸ Irregular distribution of crypts
 ▸ Dilatation of crypt bases 
▸ Serration present at crypt bases 
▸ Branched crypts 
▸ Horizontal extension of crypt bases* 
▸ Dysmaturation of crypts† 
▸ Herniation of crypts through muscularis mucosa 
▸ WHO criteria: at least three crypts or at least two adjacent crypts must show one or more of these features to enable a diagnosis of SSL 
▸ American Gastroenterology Association criteria: one crypt showing the characteristic features is sufficient for the diagnosis of SSL Key: 
*Involved crypts often have an ‘L’ or inverted ‘T’ shape (may be boot-shaped as well - my addition). 
†Dysmaturation is disordered cellular maturation within crypts and is evidenced by subtle nuclear enlargement, crowding, pseudostratification and mitotic activity together with the presence of a disorganised mixture of non-mucus-containing epithelial cells and mature goblet cells within the deep aspects of crypts. In this context, assessment of proliferation index, for example, using MIB-1 may provide supporting evidence for a diagnosis of SSL by highlighting epithelial cell proliferation within the superficial half of crypts. However, such immunohistochemistry, while sometimes helpful, does not reveal features that are alone diagnostic of SSL.


                                                          SSL (Source: Wikimedia)

                                                       
                                                             TSA (Studyblue.com)

While SSL has a  sawtooth appearance, TSA has an undulating and softer appearance.  TSA also has classical adenomatous feature, which makes its management no different than classical adenomas. Another important point is that TSA has ectopic crypts forming perpendicular to the villi.

The review includes great images as well.  
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