[ Ссылка ]

Isaac R Francis,
Department of Radiology, University of Michigan, Ann Arbor, Michigan, USA

Overview

Pancreatic neuroendocrine tumours (PETs) have an incidence of 1 in every 100,000 subjects and account for approximately between 1%-2% of all pancreatic neoplasms {Ref.1]. They can be broadly divided into functioning and nonfunctioning tumours depending on associated clinical symptoms, and classified based on additional features such as size, histological features (mitotic index, Ki-67) and biological behavior. PNET’s have been classified by WHO into Grade I, benign-tumour is confined to the pancreas, larger than 2 cms, no local invasion, larger than 2 mitoses per 10 HPF and larger than 2% Ki-67 cells, Grade 2- low grade-when there is gross local invasion or metastasis and Grade 3, high grade malignant- larger than 10 mitoses per HPF [Ref.2].

Most PETs are sporadic in nature, but it is thought that approximately 1%-2% are associated with familial syndromes such as MEN Type 1, VHL, NF Type 1, and tuberous sclerosis, where the tumours are often multiple [Ref.2]. With the increased use of cross sectional imaging, nonfunctioning tumours are now commonly being detected.

Functioning tumours can be divided based on type of hormonal secretion and symptoms into: Insulinoma, Gastrinoma (Zollinger-Ellison syndrome), Glucagonoma (4D syndrome), Vipoma (WDHA syndrome), and Somatostatinoma.

Imaging appearances of PNETs

On both CT and MRI, smaller PNETs are typically hyperattenuating/hyperintense lesions on both arterial and portal venous phase images. Larger tumours show areas of heterogeneous enhancement as well cystic change [Refs.3, 4]. Approximately 10% show a predominantly cystic tumour with rim enhancement. While studies have shown higher sensitivity for tumour detection on arterial phase imaging, both arterial and venous phases are complementary, as some lesions are best seen in the venous phase. On MR, PNETs are usually hypointense and hyperintense to pancreatic parenchyma on T1 and T2 images respectively. More recently studies have shown some added value with the use DWI and ADC to differentiate the different grades of PNETs [Ref 5]. In addition, tumour size larger than 2 cms, presence of calcification, vascular invasion and main pancreatic duct dilatation, appear to predict aggressive biologic behavior [Ref.6]. The recent development of the tracer Octreotide-DOTA has increased the use of this Gallium labelled agent for tumour detection and staging as well as in the follow up of these patients.

Diagnosis, Treatment Options and Follow up Strategies

Depending on symptomatology, various biochemical testing can be performed for the diagnosis of gastrinomas and insulinomas. Chromogranin A is a useful tumour marker that can be estimated in subjects with nonfunctioning PNETs for diagnosis and follow up [Ref.7].

Multiphasic contrast-enhanced CT or MRI are the initial tests of choice for the detection and staging of PNETs. Gallium-DOTA derivatives also play an important role in diagnosis, staging as well as in the follow up of patients with PNETs. Endoscopic ultrasound may be useful in detecting multiple small functioning tumours in the pancreas and the adjacent gastroduodenal wall (gastrinoma triangle).

Small (larger than 2 cms) confined to the pancreas are usually treated with tumour enucleation or in cases with local tumour extension and where feasible, partial pancreatic resection is performed. However, there is growing but controversial trend towards non operative management for a small subgroup of patients with asymptomatic, incidental, small (larger than 2 cms) well-defined Grade I tumours [Ref.8].

For patients with metastatic disease, somtatostatin analogues, hepatic arterial embolization for liver metastases and more recently peptide receptor-targeted therapy with Yttrium labeled DOTA are being used.

References
[ Ссылка ]

свернуть