Case 3 -
Colonic Muco-Submucosal Elongated Polyp
Ian S. Brown, Envoi Pathology, Herston, Queensland, Australia
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Male 60 years. Colonoscopy performed for investigation of a positive fecal occult blood test. Solitary 25 mm long filiform polyp removed from the sigmoid colon. No history of previous colorectal disease.
Case 3 - Slide 1
Pathological/Microscopic Findings and any Immunohistochemical or Other Studies:
The scanned image
displays a colorectal polyp with 3 key features: 1) An elongate, cylindrical shape with a narrow base.
2) A lining of non-neoplastic large intestinal mucosa displaying minimal architectural disturbance but no
inflammation. 3) The presence of an expanded submucosa in the stalk, devoid of inflammation.
Lymphangiectasia, venous congestion and mild stromal edema are evident.
1) Polypoid prolapsing mucosal fold.
2) Filiform polyposis - related to inflammatory bowel disease or occuring without an identifiable
3) Inverted colonic diverticulum.
4) Residual stalk of a pedunculated polyp.
5) Other forms of colorectal mucosal prolapse eg inflammatory myoglandular polyp.
6) filiform neoplasm eg filiform traditional serrated adenoma and inflammatory fibroid polyp.
Colonic Muco-Submucosal Elongated Polyp
This case illustrates an incidentally discovered endocopically filiform/cylindrical polyp. The key
histological findings are: 1) an elongate, cylindrical shape with a narrow base ; 2 ) a lining of
non-neoplastic large intestinal mucosa displaying minimal architectural disturbance but no inflammation;
and 3) The presence in the stalk of an expanded submucosa devoid of inflammation. These features are
typical of what has been termed Colonic Muco-Submucosal Elongated Polyp (CMSEP).
The differential diagnosis includes the following lesions:
1) Polypoid prolapsing mucosal fold (PMF) - also known as the 'Kelly polyp' is a form of
mucosal prolapse polyp that has a strong association with sigmoid diverticular disease
likely arises due to traction prolapse of the concertinaed haustral folds found in this condition. The
main clinical differences from CMSEP are the more frequent association with diverticular disease and
frequent multiplicity of PMF polyps, while CMSEP is usually single. Macroscopically, PMF is broad based
and 'leaf like' appearance and is often red or dark brown in appearance due to haemorrhage and haemosiderin
while CMSEP is slender based, cylindrical and exhibits no evidence of previous haemorrhage.
Microscopically, PMF polyps demonstrate evidence of mucosal prolapse with crypt architectural abnormality,
fibromuscular obliteration of the lamina propria and thickening, reduplication and splaying into the lamina
propria by muscularis mucosae. This is often accompanied by active chronic inflammation and hemorrhage and
hemosiderin deposition . Not infrequently mucosal glands become inverted into the submucosa at the tip of
the polyp. By contrast, CMSEP lack mucosal prolapse features and inflammation
Despite clinicopathological differences, it is probable a kinship exists between PMF polyps and CMSEP based on a common traction prolapse etiology. Additionally, we have encountered polyps with hybrid feature in being elongate and cylindrical but exhibiting mucosal prolapse features and mucosal inversion at the tip. Furthermore, we have seen concurrence of typical examples of both forms of polyp in resections for severe diverticular disease.
2) Other mucosal prolapse related polyps – these
include inflammatory 'cap' polyps, inflammatory cloacogenic polyp and inflammatory myoglandular polyps.
Inflammatory 'cap' polyps differ from CMSEP in being broad based, usually multiple, localised to the rectosigmoid
region and covered by a cap of granulation tissue and fibrin . Inflammatory cloacogenic polyp is restricted to
the anal transition zone  and this characteristic site, in association with ulceration and inflammation, allows
distinction from CMSEP. Inflammatory myoglandular polyps differ from CMSEPs by the prominence of smooth muscle
proliferation and inflammation with granulation tissue in the mucosal lamina propria .
3) Filiform polyposis (FP) - is believed to represent a non-specific
mucosal/submucosal reaction to previous injury, in particular, inflammatory bowel disease (IBD), although examples do
occur outside this condition
In contrast to CMSEP, filiform polyposis presents as numerous polyps that generally
display an irregular fibrovascular proliferation in the stalk, sometimes including entrapped nerves and reduplicated
Mucosal inflammation is typical in inflammatory bowel disease associated cases.
4) Inflammatory pseudopolyp – typically seen in the setting of inflammatory bowel disease and pathologically distinct from CMSEP by the presence of chronic inflammion and fibrosis.
5) Filiform patterns associated with neoplasms – These may include
mucosal based lesions such as serrated adenoma
or submucosal based lesions such as perineurioma or inflammatory
fibroid polyp. The associated neoplasm allows separation from CMSEP.
6) Inverted colonic diverticulum (ICD) - is a (probably) under
recognised lesion, which if biopsied or resected, will reveal a normal mucosa and congested submucosa, . ICD is
seldom >10mm and lacks the abundant submucosal tissue typical of CMSEP. Sometimes adipose tissue (derived from the
mesentery) comprises the bulk of this lesion.
7) Residual stalk from a previous pedunculated polyp presents
as a polyp with normal mucosa and expanded submucosa . The history of previous polypectomy and changes related to
this such as diathermy artefact, stromal hemosiderin and fibrosis allow distinction of this lesion from CMSEP.
8) Other – Hamartomatous polyps, particularly those occurring in Peutz -Jeghers syndrome, might be a diagnostic consideration. An arborizing muscle proliferation and other syndromic features allow easy distinction from CMSEP.
Summary table – differential diagnosis non neoplastic colorectal polyps comprised of mucosa and submucosa
|Diagnosis ||Clinical setting ||Macroscopic/endoscopic ||Microscopic|
|CMSEP ||Usually no pre-existing disease ||Solitary, filiform/cylindrical ||Normal/minimally abnormal mucosa covering an expanded submucosa.|
|Prolapsing mucosal fold ||Sigmoid diverticular disease ||broad based/‘leaf like’; dark due to hemorrhage ||Mucosal prolapse change in mucosa; hemosiderin; mucosal inversion into submucosa|
|Mucosal prolapse syndrome ||Often rectum or recto-sigmoid colon region ||typically broad based and often with ulceration ||Prominent fibromuscular obliteration of lamina propria with thickened, reduplicated muscularis mucosae.|
|Filiform polyposis ||Inflammatory bowel disease (sometimes other association) ||Multiple, filiform + branching polyps ||Active chronic inflammation in mucosa/submucosa in|
|Inflammatory pseudopolyp ||Inflammatory bowel disease; other inflammatory process ||Often multiple ||Inflammation and fibrosis in mucosa/submucosa|
|Inverted colonic diverticulum ||Diverticular disease (may be right sided) ||Usually single, small (<10mm) and dome shaped ||Minimal submucosa|
|Stalk of pedunculated polyp ||Previous polypectomy at site ||Solitary, filiform/cylindrical ||Fibrosis + hemosiderin and cautery artefact|
|Hamartomatous polyp ||Clinical syndrome ||Multiple, lobulated ||Arborizing smooth muscle, other|
Review of the Literature:
Colonic muco-submucosal elongated polyp (CMSEP) was the descriptive name given by Matake et al to
series of colorectal polyps characterised by a pedunculated, elongated shape and composed mainly of
expanded submucosa with an essentially normal mucosal lining . Since their initial description in
1994, CMSEP have been infrequently reported and until recently this has been exclusively by Japanese
CMSEPs are usually an incidental discovery at the time of screening colonoscopy for adenomatous
polyps or as a result of positive faecal occult blood test. In one series, the prevalence of CMSEP was
reported to be 0.39% of all colorectal polyps .
A review of 50 Japanese cases, including meeting abstracts, 
revealed a mean age of polyp presentation of 62 years and slight male predominance 58% to that
encountered in our series. Just over half of the polyps (52%) were discovered at either routine
screening colonoscopy or on investigation of faecal occult blood loss. Altered bowel habit and abdominal
pain were also frequent presenting complaints. Co-existent diverticular disease has been noted in
approximately 15% of patients  . Most polyps
were located in the transverse colon (28%) and sigmoid colon (26%)
Recently, Alizart et al reported a series of 13 CMSEP in a Western cohort .
While the basis for discovery, male predominance and average age were similar to the Japanese experience,
there was a greater preponderance for the sigmoid colon location, although diverticular disease was noted
in only 1 case.
In the reported cases, the mean polyp size is 35mm (range of 5-240mm). Clearly, CMSEP can reach
impressive size, but it is important to realise that the vast majority are in the range 10-30mm
Occasionally, surface ulceration and capillary congestion may encountered in otherwise typical
and might account for fecal occult blood loss.
The etiology of CMSEP is unknown. Traction of these surface layers during peristalsis may be
This is implicated in pathogenesis of giant fibrovascular polyp of the
oesophagus, which shows analogous pathological features to CMSEP. What might initiate the traction is
unknown as an underlying mucosal lesion is consistently not identified in CMSEP. The prominent central
submucosal venous plexus in CMSEP could potentially elevate the mucosa sufficiently to initiate the
process; however, prominent submucosal veins are a common finding in all forms of pedunculated polyps so
a local vascular abnormality is speculative. A focal functional abnormality could be also be
CMSEP does not appear to portend any clinical significance and is usually an incidental finding. It
could be responsible for occult blood loss in some patients. Recurrence of these lesions is not
The differential diagnosis of non neoplastic colorectal polyps composed of mucosa and submucosa is
broad. Colonic muco-submucosal elongated polyp is a pedunculated, elongated shape and composed mainly of
expanded submucosa with an essentially normal mucosal lining. This lesion has no great clinical
significance; however, it may attain impressive size and is likely to become more frequently encountered
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