Sessile serrated adenoma (SSA) and sessile serrated polyp (SSP) are equivalent terms
SSP appeals to those who note that the lesion lacks neoplastic cytologic features
SSA appeals to those who note the genetic abnormalities and association with carcinoma
Although not generally used as diagnostic criteria, characteristic location and genotypic abnormalities linking SSA/P to sporadic MSI high colorectal carcinoma (serrated carcinoma pathway) are the main justifications for defining this as a separate lesion from usual hyperplastic polyp
Serration is variably present throughout gland length
Usually exaggerated serration
Apical cytoplasm typically filled with microvesicular mucin
Goblet cells not conspicuous
Bases of crypts show architectural disturbances
Dilation of crypts with flattened bases
Horizontal glands at base
“L, inverted T, hockey stick or boot” shaped
Mature mucinous cells at base of crypts
May form serrations at base
How many abnormal crypts are required for the diagnosis is currently in a state of flux
The WHO requires at least three adjacent abnormal crypts to make the diagnosis
A recent consensus conference recommends that a single abnormal crypt be sufficient for the diagnosis of SSA (Rex 2012)
Lacks significant architectural complexity
Most crypts extend from lumen to muscularis mucosae
Proliferative zone frequently displaced from base
Patchy proliferative zones can be seen at all levels
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