Men I syndrome and islet cell lesions of the pancreas

Detection of small, functional islet cell tumors in the pancreas: selection of MR imaging sequences for optimal sensitivity

PURPOSE

To determine the sensitivity and specificity of magnetic resonance (MR) imaging for depicting pancreatic small, functional islet cell tumors and the minimum number of sequences for expedient diagnosis.

MATERIALS AND METHODS

Twenty-eight patients clinically suspected to have functional islet cell tumors underwent T1- and T2-weighted spin-echo (SE) MR imaging with and without fat suppression, T2-weighted fast SE imaging, and spoiled gradient-echo (GRE) imaging before and after injection of gadopentetate dimeglumine. Sensitivity, specificity, and the best and minimum number of sequences for definitive diagnosis were determined.

RESULTS

MR images depicted proved islet cell tumors in 17 of 20 patients (sensitivity, 85%). Images were true-negative in eight patients with negative follow-up examination results for more than 1 year. Specificity was 100%; positive predictive value, 100%; and negative predictive value, 73%. Among 20 patients with tumor, T1-weighted SE images with fat suppression and nonenhanced spoiled GRE images each showed lesions in 15 (75%); T2-weighted conventional SE with fat suppression, in 13 (65%); gadolinium-enhanced spoiled GRE, in 12 (60%); and T2-weighted fast SE, in seven of 10 patients (70%).

CONCLUSION

MR imaging accurately depicts small islet cell tumors. T2-weighted fast SE and spoiled GRE sequences usually suffice. Gadolinium-enhanced sequences are needed only if MR imaging results are equivocal or negative.

Imaging islet cell tumours

The localization of islet cell tumours presents a challenge to the radiologist and requires meticulous attention to detail in both technique and interpretation. As several imaging techniques are capable of demonstrating the tumour and none is absolutely accurate, a rational approach to the localization of these tumours requires a careful consideration of cost, sensitivity and the availability of special expertise. In almost all cases, initial imaging is performed with a combination of transabdominal ultrasound and CT. This will demonstrate the tumour and any hepatic metastases in about 40% of gastrinomas, 80% of insulinomas and almost all other functioning and non-functioning tumours. Where these tests are negative or equivocal, arteriography (which may be combined with ASVS) is the next line of investigation. If the tumour remains undetected, it is likely to be a small insulinoma or gastrinoma. Further investigation is dependent on local practice and the tumour type. Endoscopic ultrasound is rapidly emerging as a technique of high sensitivity in detecting small pancreatic tumours and may also demonstrate extrapancreatic gastrinomas. Transhepatic venous sampling and somatostatin receptor imaging have the advantage that they are not directly dependent on tumour size and they are particularly applicable to difficult cases where other imaging modalities are negative. TPVS is invasive and, while sensitive for insulinomas, is frequently unhelpful in gastrinomas. Somatostatin receptor scintigraphy, on the other hand, is more sensitive for gastrinomas. In future, MRI may prove to be at least as accurate as CT but as yet its exact role is uncertain. At the time of surgery, intraoperative ultrasound is a useful adjunct to palpation, and may avoid a standard distal pancreatectomy in patients with insulinoma.

Screening for multiple endocrine neoplasia type 1 in patients with recognized pituitary adenoma

A total of 79 consecutive patients with pituitary tumours were screened for multiple endocrine neoplasia type 1 (MEN-1). The 79 patients included 21 patients with acromegaly, nine with Cushing's disease, 18 with prolactinomas, three with mixed pituitary adenomas (GH and PRL), and 28 patients with no detectable hypersecretion of hormones. The screening consisted of: (1) a family history, (2) a uniform medical history of the patient using a standard questionnaire, and (3) hormonal evaluation including measurements of the serum levels of insulin, gastrin, glucagon, somatostatin, vasoactive intestinal polypeptide and pancreatic polypeptide. Ionized calcium and glucose concentration in serum were also measured. We found no patients with the MEN-1 syndrome. In one patient, we found a transient elevation of serum concentrations of pancreatic polypeptide for which we have no explanation. In another patient, the serum gastrin concentration was elevated secondary to achlorhydria. No other endocrine disorders were found, and no patients had relatives with recognized endocrine pancreatic tumours, primary hyperparathyroidism (HPT), or pituitary adenomas.