A 64-year-old woman was referred to our endoscopic unit for investigation of abdominal
pain. At colonoscopy we found a sessile polyp, 15 mm in diameter, in the middle
part of the rectum (Figure [1]). Magnified chromoendoscopy using 0.2 % indigo carmine dye revealed a type IV
pit pattern according to Kudo’s classification, suggesting that the polyp was
a good candidate for endoscopic resection. However, this polyp seemed to be taller
than an ordinary sessile polyp, and a biopsy forceps was used to determine how
hard it was. This revealed that the polyp was elastically harder than an ordinary
adenomatous polyp. Eventually, excisional biopsy of the polyp was performed by
endoscopic mucosal resection rather than by snare polypectomy, and this procedure
was uneventful. Histologically, the tumor was found to consist of adenoma arising
from the mucosal layer, which showed transition to carcinoid tumor, mainly in
the submucosal layer (Figure [2]). Because there was evidence of both lymphatic and venous invasion of tumor
cells in the carcinoid component of the tumor, additional surgery was performed
as a curative measure. No local residual tumor or lymph node metastasis was
found.
Figure 1 Colonoscopy revealed a tall but sessile polyp, 15 mm in diameter, in the middle
part of the rectum. This polyp felt harder than an ordinary adenomatous polyp
when examined using biopsy forceps.
Figure 2 Histologically, the tumor consisted of an adenoma and a carcinoid tumor, with
a transitional zone between them.
The term “composite adenoma-carcinoid tumor” has been used for tumors consisting
of a glandular component (adenoma or adenocarcinoma) and a carcinoid component,
particularly if there is evidence of a transitional zone between the two components
[1]. It is extremely rare for the glandular component to be entirely benign [1]
[2]
[3]. The first such case was reported by Mori et al. in 1978 [2]. The presence of a transitional zone in this case supports the likely theory
that the adenomatous component and the carcinoid element were derived from a common
origin, and excluded the possibility of a “collision tumor”. The endoscopic
evidence of elastic hardness, as described above, provided a clue to the presence
of a submucosal mass beneath the adenomatous polyp. Although not available in
this case, endoscopic ultrasound is another option for evaluating this kind of
tumor.
Endoscopy_UCTN_Code_CCL_1AD_2AB
