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| Discussion |
A 32-year-old lady presented with repeated attacks of sweating, palpitation,
giddiness and weakness. She was found to have fasting hypoglycemia. On clinical
examination, no abnormality was detected. An insulinoma was suspected.
 | |
| Fig.1
. |
On the arterial
phase of the post contrast axial CT, the lesion demonstrated "hyperenhancement".
 | |
| Fig.
2 . |
On axial Trufisp
images, the lesion was hypointense. Also on e T2WI and gradient T1WI (Vibe), sequences,
the lesion was hypointense.
 |
 | |
Fig.
3 | Fig.
4 | |
 | ||
Fig.
5 | ||
Surgical
excision of the pancreatic tumor was performed. The histopathology confirmed the
diagnosis of insulinoma. The patient's symptoms dramatically improved following
surgery.
DISCUSSION:
Pancreatic endocrine tumors
are divided into functioning and non-functioning tumors depending on the production
of hormonally active peptides. Insulinomas and gastrinomas are the most common
functioning islet-cell tumors. Other tumors include glucagonomas, somatostatinomas,
VIPomas, and GRFomas which are frequently large at diagnosis and are often malignant.
Insulinomas
account for nearly 60% of all islet-cell tumors- the incidence being 1 per 250,000
people. They are usually solitary, benign and small tumors, but the hyperinsulinism
and hypoglycemia that they produce may be disabling or life threatening. 10% are
multiple, 10% are malignant and 10% will have either islet cell hyperplasia or
no tumor at all. Calcification is present in 20% of cases and may signify malignancy.
The tumor occurs in all age groups - the peak incidence being between 40 to 60
years of age. These tumors may be sporadic or occur as part of multiple endocrine
neoplasia I syndrome when they are associated with tumors of the pituitary, parathyroid,
thyroid and adrenal glands.
Curative treatment of insulinomas can be achieved
only with surgical resection and it is imperative to localize the tumor pre-operatively.
However the preoperative diagnosis of insulinomas remains a challenge because
of the small size of these tumors. There is continuing debate on the optimal strategy
of imaging for localization. In the past, percutaneous transhepatic portal venous
sampling, angiography or arterial stimulation venous sampling were used to localize
functional insulin-secreting tumors in patients suspected to have an insulinoma.
However these are invasive techniques and cannot provide accurate topographic
localization of the tumor.
Various techniques used to localize insulinomas
include ultrasound, CT, MRI and selective pancreatic arteriography. Ultrasound
has been reported to be capable of detecting more than 60% of islet-cell tumors.
Most of these tumors are hypoechoic, homogenous and have distinct margins. Endoscopic
ultrasound can demonstrate the size, shape and their relationship with pancreatic
duct, bile duct and great vessels and can display small pancreatic lesions undetectable
by CT and MRI. Intra-operative ultrasound can delineate small tumors, but is operator
dependent.
MDCT - Thin slice acquisitions of the pancreas and liver with
dual phase imaging in the arterial and portal phase is used to evaluate suspected
pancreatic neoplasms as these tumors are hypervascular. This also depicts peritumoral
and peripancreatic vascular anatomy. The involvement of vessels and local extension
can be well demonstrated. Instead of oral contrast media, water provides optimum
visualization of the duodenal ampulla and duodenal-pancreatic interface and local
invasion. PET is a valuable complement to CT and allows detection of unsuspected
distant metastasis. MRI - Most optimal sequences for pancreatic neuroendocrine
tumors are T2W fast spin echo, fat suppressed T1W spin echo, gradient echo and
dynamic contrast enhanced FLASH sequences on which these tumors show early enhancement.
MRCP is helpful in planning percutaneous biliary drainage and radiation therapy,
if required. Arteriography remains an important tool in localizing neuroendocrine
tumors. These tumors typically appear as a well circumscribed blush in capillary
and early venous phase.