- Gastrointestinal carcinoid tumors most commonly occur in the small bowel and appendix. They arise from enterochromaffin cells and can produce symptoms if they secrete excess serotonin. - Diagnosis is usually achieved through complementary imaging techniques such as somatostatin receptor scintigraphy, CT, MRI, and ultrasound. Somatostatin receptor scintigraphy is particularly useful for detecting primary tumors and metastases. - Imaging findings include well-defined bowel masses that can invade the mesentery, associated lymphadenopathy, and liver metastases appearing as hypoechoic lesions that enhance with contrast.

1. Gastrointestinal carcinoids
Dr.R.Rengarajan

2. • Gastrointestinal carcinoid, also called carcinoid tumor, is the most
common primary tumor of the small bowel and appendix.
• Gastrointestinal carcinoid accounts for more than 95% of all
carcinoids.
• The tumors arise from enterochromaffin cells of Kulchitsky, which
are considered neural crest cells situated at the base of the crypts
of Lieberkühn.
• Gastrointestinal carcinoids account for 1.5% of all gastrointestinal
tumors.
• The tumors elaborate serotonin and other histamine like substances
that normally are transported to the liver, where they are
metabolized.

3. • Most tumors are clinically silent, but they may cause pain or
intestinal obstruction, weight loss, a palpable mass, or, rarely, bowel
perforation.
• Carcinoid syndrome occurs when the humoral load exceeds the
capacity of monoamine oxidase (MAO) present in the liver and lung
to metabolize serotonin.
• Most patients with carcinoid syndrome have liver metastases from
a bowel carcinoid, although in rare cases, the humoral load from a
primary tumor may overwhelm the liver and the capacity of the
lungs to metabolize serotonin.
• Rarer still is carcinoid syndrome that develops in patients with
noncarcinoid malignant tumors and dermatomyositis.

4. • Diagnosis is usually achieved by using several complementary
imaging techniques.
• The most promising imaging technique is somatostatin receptor
scintigraphy.The technique can aid diagnosis by localizing primary
and metastatic sites of gastro-enteropancreatic endocrine tumors.
The degree of radionuclide uptake is related to somatostatin
receptor density. In gastrointestinal carcinoids, the concentration at
the receptor sites is high (90%).
• Plain radiographic findings (eg, soft-tissue mass, punctate
calcification within a mass, signs of intestinal obstruction) are not
specific for carcinoids. Plain radiographs are usually obtained in an
acute setting, being taken, for example, in patients presenting with
intestinal obstruction or perforation.

5. • Plain abdominal radiographs may reveal curvilinear calcification within the
abdomen. These are usually smaller than 15 mm in diameter and result
from calcification within the tumor.
• On barium studies, findings consist of fairly well-defined, round,
intraluminal bowel-filling defects. These may be associated with
thickening of the valvulae conniventes resulting from interference of the
bowel blood supply by the tumor.
• With invasion of the mesentery, the mesenteric mass causes rigidity,
displacement/stretching, and fixation of small-bowel loops. Desmoplastic
reaction from mesenteric invasion causes sharp angulation of a bowel
loop or a stellate or spokelike wheel arrangement of adjacent bowel loops.
• The tumor often infiltrates the mesentery, provoking an intense fibrotic
reaction that results in kinking of the bowel segments; such kinking may in
turn cause intestinal obstruction.
• On a small-bowel barium series, kinking of the small-bowel loops is
considered the hallmark of a small-bowel carcinoid tumor.

7. • Ultrasonography of the bowel can depict bowel tumors, with a
pseudokidney sign. Associated lymphadenopathy and liver
metastases may be demonstrated on ultrasonograms.
• On ultrasonography, liver metastases vary from hypoechoic to
hyperechoic and show strong enhancement with intravenous
contrast media.
• Tumors demonstrate peripheral hypervascularity on color and
power Doppler images.

9. • CT scanning reveals a mass with soft-tissue attenuation and variable
size, with spiculated borders and radiating surrounding strands.
• Calcification may be noted in the tumor.
• Linear strands within the mesenteric fat probably are thickened and
retracted vascular bundles and represent peritumoral desmoplastic
reaction.
• Lymphadenopathy and liver metastases may be visualized on CT
scans.
• Helical CT enteroclysis has been used to detect small-bowel
carcinoids and has been found to be more sensitive than are
conventional barium studies.

13. • Liver metastases are demonstrated well on MRIs and usually have low
signal intensity on T1-weighted images and high signal intensity on T2-
weighted images.
• After the administration of a gadolinium-based contrast agent, liver
metastases enhance peripherally in the hepatic arterial phase and appear
as hypo-intense defects against the enhancing normal liver in the portal
venous phase.
• Somatostatin-receptor scintigraphy performed with indium-111 (111 In)
octreotide and111 In pentetreotide is used to image many neuro-endocrine
tumors, including carcinoids with somatostatin-binding sites.
• Several studies have shown that somatostatin-receptor scintigraphy is a
sensitive and noninvasive technique for imaging primary carcinoid tumors
and carcinoid metastatic spread.
• A refinement of the technique that increases sensitivity is the addition of
single photon emission CT (SPECT) scanning

15. • Scintigraphy performed with iodine-123 (123 I) meta-
iodobenzylguanidine demonstrates a 44-63% uptake in
gastrointestinal carcinoids.
• A higher frequency of radionuclide uptake is found in midgut
carcinoids and tumors with elevated serotonin levels.
• [Fluorine-18]fluorodopa positron emission tomography (18 F-dopa–
PET) scanning has been used to image primary gastrointestinal
carcinoid tumors and lymph node and organ metastases with
promising results.
• In general, FDG-PET scanning is useful in poorly differentiated
carcinoids and other neuro-endocrine tumors, but it should not be
used as a first-line imaging agent. FDG-PET scanning is primarily
useful when the results of somatostatin-receptor scintigraphy are
negative.

16. • Before the advent of cross-sectional imaging, mesenteric
angiography provided useful information regarding characterization
of small-bowel carcinoids.
• The angiographic appearances of small-bowel carcinoids
encountered on angiograms produced for other indications, such as
gastrointestinal bleeding, are worth noting.
• Foreshortening of the bowel occurring with desmoplastic reaction
makes mesenteric arteries tortuous and frequently narrowed; it
also draws the arteries into a stellate pattern.
• The areas involved appear hypervascular, but in reality, the number
of arteries in the area does not increase. Instead, the arteries
contract into a smaller area as a result of fibrosis.

17. • An additional arterial change associated with carcinoids is smooth,
multifocal stenosis of the mesenteric arteries distant from the
tumor.
• Tumors seldom show capillary blush or demonstrate early or dense
venous drainage.
• Venous occlusion and mesenteric varices also have been reported.
• These findings are nonspecific and have been reported with
sclerosing peritonitis and with a carcinoma of the pancreas invading
the mesentery.
• Selective hepatic angiography can demonstrate hypervascular liver
metastases by demonstrating capillary blush in involved areas,
highlighting the potential response of tumors to embolization.

18. Thank you