Sessile serrated adenoma/polyps (SSA/Ps) are early precursor lesions in the serrated
neoplasia pathway. Some of these lesions can rapidly become dysplastic or invasive
carcinomas that exhibit high lymphatic invasion and lymph node metastasis potentials.
Detecting serrated lesions, including SSA/Ps with and without dysplasia/carcinoma,
is challenging. Unlike hyperplastic polyps, SSA/Ps are more frequently larger than
5 mm, and the question raised here is whether diminutive Serrated lesions (< 5 mm)
really exist?
Of course, detection of these SSAP despite virtual chromoendoscopy is much more difficult
than detection of adenomas. This may be partly explained by the minimum size requirement
of 5 mm for detection of discrete mucosal and vascular changes. On the other hand,
our endoscopes have improved considerably [1], our capacities to detect small lesions have also improved, indigo carmine makes
it easier to detect very small abnormal areas and yet, it must be said that we do
not often find diminutive SSAP, including in sessile serrated polyposis. How can this
inconsistency be explained?
Is the development of SSAP so rapid initially with intense cell multiplication that
the period during which the lesions are <5mm is too short for us to detect them lesions?
When several colonoscopies are performed successively in patients, there is no major
increase in the size of the lesions in a few months, and very rapid extension initially
followed by a slow-down in growth is not supported by histological findings.
Is there initial lateral development of the deep lesion of the crypts before the anomaly
appears on the surface of the glands? For this second hypothesis, we would then have
to find histologically larger lesions at depth than at the mucosal surface, resembling
an iceberg. However, cell division in SSAPs occurs at the bottom of the crypt, lesion
size at the deep part of the mucosa is identical to the surface area ([Fig. 1c], [Fig. 1d]).
Fig. 1 Diminutive SSAP with thin aspect. a White light imaging with subtle color and texture anomalies. b NBI imaging with thin aspect. c, d Histological confirmation of the serrated component.
Finally, there do not seem to be any histological arguments to support deep initial
development of the lesion, therefore, it must be recognized that these lesions exist
but our ability to detect them is compromised. First, at an early stage, a diminutive
SSAP appears thin and therefore translucent, allowing the vasculature of the underlying
colonic wall [2] to be seen through that transparency ([Fig. 1]). In such cases, interruption of the background vascular relief, with its subtle
color and texture anomalies, cannot be relied upon as a way for the eye to detect
a lesion. The lesion presented here is barely visible because it is so thin ([Fig. 1]). Indigo carmine dye could improve detection of such small lesions, as previously
demonstrated in sessile serrated polyposis, and virtual chromoendoscopy can help characterize
tiny lesions ( [Fig.2]) [3].
Fig. 2 Diminutive SSAP in BLI and Indigo carmine dye.
In addition, the small amount of serrated glands in a diminutive lesion with a small
surface area is most likely correlated with low mucus secretion ([Fig. 3]), even though the mucus cap has become a criterion for detecting these lesions when
deposits adhering to the wall against gravity are identified. Finally, these tiny
lesions pose characterization problems because presence of the diagnostic criteria
of the WASP classification [4] (indistinct edges, cloudy appearance, black spot at the bottom of the crypts) are
less likely to be present than in large lesions.
Fig. 3 Different examples of diminutive SSAP. a,b White light and NBI imaging of a 5-mm SSAP with low mucus production. c, d SSAP of 3 mm without any mucus cap.
In conclusion, because we were entrusted with writing of this editorial, we have detected
multiple diminutive SSAP that we didn't believe we were finding before. They therefore
exist but represent a huge detection challenge and could become a quality criterion
for defining super-detecting endoscopists in the future.
