PATHOLOGY
Carcinomas of the colon and rectum occur in the
various regions
of
the large gut in the
following propoertions :
Cecum-8%,
ascending colon-6%, hepatic flexure-2%
Seventy percent colorectal cancers are
found in the distal colon
and rectum
and 30% of
all cancers can
be felt on
P.R.
examination.
*
Polypoidal
*
Nodular
*
Ulcerating or
*
Scirrhus
Fig. 19.3 shows three of these
varieties.
MICROSCOPICALLY
Carcinomas resemble
the parent tissue
in varying degree,
depending on the
degree of differentiation of the
neoplastic
cells.
In
well-differentiated tumors, the cells are grouped in
acinar
clusters and look like normal glands.
In
poorly differentitated or anaplastic tumours, the cells with
little or no resemblance to colonic
mucosa cells are distributed
in irregular sheets or cords.
The
cells show malignant
characteristics of "pleomorphism",
hyperchromatism, large vesicular
nuclei and frequent mitoses.
Carcinoma spreades
by direct extension,
by lymphatic or
bloodstream dissemination, by
gravitational seeding and
by
implantation at operation.
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