Recently, improved endoscopic imaging and advancements in diagnostic
technology, such as magnifying colonoscopy and image-enhanced endoscopy (IEE),
including narrow-band imaging (NBI) systems, have provided a higher rate of
detection of superficial and small colorectal tumors. Even a depressed colon
cancer as small as 5 mm in size can be correctly diagnosed as submucosal
deeply invasive carcinoma with magnifying chromoendoscopy and then
appropriately treated surgically without endoscopic resection
[1]. Furthermore, magnifying chromoendoscopy can
differentiate between colorectal neoplastic and non-neoplastic polyps
[2]. We report a case of a depressed lesion, about
8 mm in diameter, which was diagnosed as an inverted sessile serrated
polyp (SSP) by magnifying image-enhanced colonoscopy before removal.
A 63-year-old man underwent surveillance colonoscopy at our
department. Colonoscopy revealed a flat elevated polyp with a central
depression, about 8 mm in diameter, in the ascending colon (Paris
classification IIa and IIc) ([Fig. 1]).
Fig. 1 Colonoscopy revealed a
flat elevated polyp with a central depression, about 8 mm in diameter,
in the ascending colon.
No meshed capillary vessel (type I capillary pattern according to
Sano’s classification) was detected on the surface of the polyp by NBI
with magnification ([Fig. 2]) [3].
Fig. 2 Narrow-band imaging with
magnification did not show meshed capillary vessels (type-I capillary pattern
according to Sano’s classification).
After the dye-spraying of 0.4 % indigo carmine, a
depressed area was clearly defined in the polyp. However, the pit pattern of
the depressed area was not clearly observed because of the overlying dense
mucus ([Fig. 3]).
Fig. 3 After the dye-spraying
of 0.4 % indigo carmine, a depressed area was clearly defined in
the polyp. However, the pit pattern of the depressed area was not clearly
observed because of the overlying dense mucus.
Magnification with chromoendoscopy using 0.05 %
crystal violet staining after water washing showed a “dilated”
type-II pit pattern in the depressed area ([Fig. 4]) [4].
Fig. 4 Magnification with
chromoendoscopy using 0.05 % crystal violet staining after water
washing showed a “dilated” type-II pit pattern in the depressed
area.
Based on the above endoscopic findings, an inverted SSP was
suspected. Endoscopic resection was performed for histological evaluation. The
polyp was completely removed en bloc with endoscopic mucosal resection (the
lift and cut technique) without complication. A histological diagnosis of
inverted SSP was finally established ([Fig. 5]).
Fig. 5 Histological examination
revealed serrated tubular features in the depressed portion, some of which
showed the elements of extension and divergence. The muscularis mucosa was
rising at the both ends of the lesion and it was unclear in the depressed
portion. A histological diagnosis of inverted sessile serrated polyp was
finally established.
Inverted growth of a hyperplastic polyp is characterized by
epithelial misplacement or inversion of the epithelium into the submucosa,
which is a variant form of an exophytic hyperplastic polyp [5]. Owing to the inverted growth pattern, a depressed area
is present in such lesions, which could be misdiagnosed as an early colorectal
neoplasm on conventional view. Our case, however, was correctly diagnosed as an
inverted SSP before removal, because we applied magnifying IEE for histological
prediction. A “dilated” type-II pit pattern could be an endoscopic
hallmark of an SSP, which is different from a hyperplastic polyp with normal
type-II pit pattern.
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