Rectal NET Tumors
Unclear smaller polyps in the rectum may represent a pitfall — if they do not look like perfectly typical hyperplasia or small adenomas, then carcinoids should always be considered. These are usually yellowish or glassy, but they may also be reddish or have reddish components. If they are simply excised with forceps or a snare without an injection underneath them, histology will show a neuroendocrine tumor (NET; formerly called carcinoid), and the grading is usually also G1, but the completeness of the excision will be doubtful. A more aggressive type of resection should therefore be used (at least a cap-assisted EMR) in order to ensure R0 resection in the first step – see the video ‘Resection of rectal NET tumors’ by Endo Club North (2014). The state of the evidence here (EMR / cap-assisted EMR / ESD / full-thickness wall resection) is not yet conclusive. Otherwise, there is a risk of a prolonged follow-up period with biopsies; the scar is often no longer visible, and it is not uncommon for usually pointless but elaborate and costly sectional imaging procedures or scintigrams to be undertaken.
It is therefore important to consider NET with this type of lesion, take a biopsy and then either carry out the resection immediately or electively with one of the above-mentioned procedures.
A small, yellowish submucosal tumor, with a superficial scar following a biopsy (Fig. 1a without and Fig. 1b with narrow-band imaging).
A small, yellowish submucosal tumor with reddish components.
A large, glassy polyp, just under 1 cm in size, with a structure resembling a hyperplastic lesion (Fig. 3a). On closer examination, however, the superficial mucosa is normal (Fig. 3b), even on narrow-band imaging (Fig. 3c).
A relatively large (15 mm) rectal polyp with a villous-appearing surface pattern (Fig. 4a). On closer examination, a normal mucosal pattern with swollen mucosa appears (Fig. 4b). The risk of mistaking this for an adenoma is particularly great here. Possible full-thickness wall resection makes subsequent endoscopic resection easier here if the polyp, with suspected adenoma, is removed with a snare.
A NET, a good 1 cm in size, in the rectum, with a central cicatricial, reddish depression (Fig. 5a; biopsies from this area are often positive); after full-thickness wall resection (Fig. 5b).
And don’t forget — NETs may also be found incidentally in the ileum as well, in this case again as a submucosal tumor with a hint of a central depression (Fig. 6a), as becomes clearer with more air insufflation and closer examination (Fig. 6b).