Gastrointestinal
stromal tumours (GIST) are mesenchymal tumours arising in the GI tract
and sometimes within the abdomen without gastro-intestinal
connection.
Recent studies indicate that the tumour shows differentiation towards
interstitial cells of Cajal.
( Interstitial
cells of Cajal link the autonomic innervation of the gut with smooth
muscle cells and regulate GI motility ).
3.
Macroscopic features:
Single or
multiple tumours.
Size vary between 1 to more than 20cm.
Submucosal, intramuscular or subserosal mass.
Usually well circumscribed but lack a true capsule.
Cut surface gray to pink in colour .
Areas of cystic degeneration, infarction and hemorrhage and necrosis
.
Prone to surface ulceration and bleeding.
An hourglass defect may occur at the pylorus or cardia if the tumour
encircles the stomach.
5. GANT
(Gastrointestinal autonomic nerve tumours):
- Diagnosed by
presence of neuronal differentiation
on electron microscopy (dense core granules).
- Epithelioid cell component more prominent.
- Arborizing blood vessels and hemorrhagic spaces.
- Skeinoid fibres- (small eosinophilic, globular aggregates of filamentous material)
- Lymphocytic infiltrate in the stroma.
- Greater malignant potential and risk of metastasis.
7.
Guidelines for predicting behaviour of tumour using size of
tumour and mitotic count / 50HPF (Berman 2001 ; Fletcher et
al 2002) Size cm
Mitotic count
In a case of
stromal tumour the report should include the following
points;
- Tumour
cell type: Spindle/ epithelioid
- Nuclear pleomorphism and its severity
- Number of mitotic figures / 50hpf
- Tumour to be categorized according to relative risk.
of malignant behaviour.
- Presence of absence of necrosis
- Extent of tumour involvement (depth of involvement,
distance from resection margins and serosal margins and
lymphnode metastases).
May be associated with von Recklinghausen's disease and Carney's
triad ( epitheliod gastric stromal
tumour ,
extra-adrenal
paraganglioma
and
pulmonary chondroma)
Esophagus- 5%
Stomach- 50-70%
Small intestine- 25-40%
Colorectal- Less than 10%
Omentum,peritoneum,retroperitoneum- about 7%
4.
Microscopic
features:
2 main cell
types: Spindle
and
Epithelioid.
Spindle
cells:
Short.
uniform, blunt ended, eosinophilic cytoplasm. Paranuclear vacuole
may be present.
Arranged in sheets, fascicles whorled, storiform or palisaded
patterns.
Most gastric GISTs (corpus) and some small and large intestinal GISTs are spindle cell type.
Epithelioid
cells:
Epithelioid GISTs were previously were known as epithelioid
leiomyoblastoma.
Usually noted in gastric antrum.
Cell have abundant cytoplasm, round nuclei, cytoplasmic vacuoles
and are arranged in sheets or nests. Clear cell, signet ring,
oncocytic and plasmacytoid variants may be noted.
MICROSCOPIC
IMAGES
Spindle cell GIST:
Epithelioid cell GIST :
6.
GIST divided
into four major groups:
-
Differentiation towards smooth muscle cells.
- Differentiation towards neural elements.
- Dual differentiation (neural and smooth muscle).
- Lacking differentiation of either cell type.
