[Pancreatic insulinoma (uncinate progress)] [Radiology for the surgeon]

A 43-year-old schoolteacher had a 2-year history of personality change with episodes of unusual behaviour, confusion, amnesia, agitation and double vision. Depression was the initial diagnosis. However, treatment with anti-depressants did not alleviate her symptoms. She was referred to a neurologist who suspected an endocrine cause for her condition. A selected image from an infused computed tomography scan is shown (Fig. 1). Can you make a diagnosis? What other imaging study may be helpful?

PANCREATIC INSULINOMA (UNCINATE PROCESS)

This condition is seen in more detail on magnetic resonance imaging (Fig.1, arrow).

Although many different modalities are available for preoperative localization of functional islet cell tumours, the accuracy of these techniques remains controversial. Traditionally a combination of computed tomography and angiography has been used. More recently, newer imaging techniques, including ultrasonography (transabdominal, endoscopic and intraoperative), MRI and radionuclide scanning with a stomatostation analogue have come into use.

Detection of functional islet cell tumours is challenging because the small size (less than 2 cm) of these lesions necessitates imaging techniques with both high resolution and high inherent tissue contrast. Recent studies have shown that a combination of introperative ultrasonography and palpation has a sensitivity of 100%.(f.1) Many pancreatic surgeons may, however, wish to have the tumour localized preoperatively.

Although recent application of 2-phase dynamic helical CT has been reported to have a sensitivity as high as 82%,(f.2) this technique relies on the administration of an exogenous contrast agent precisely timed to attain adequate tissue contrast and on appropriate collimation to achieve adequate resolution. Even with these parameters optimized, CT sensitivity decreases with tumours smaller than 1 cm in dimension. MRI, a modality that has superior inherent tissue contrast discrimination, has been limited in the past by motion artifacts and decreased spatial resolution. The development of new software and hardware has helped to reduce these problems, improve resolution and enhance existing tissue conspicuity through fat suppression techniques. MRI is now considered particularly good at detecting tumours less than 1 cm in dimension. For this reason the current literature suggests that MRI alone(f.1,3) or in combination with ultrasonography,(f.4) be used as the initial radiologic approach to detect clinically suspected small endocrine pancreatic tumours.

References

(f.1) Moore NR, Togers CE, Britton BJ. Magnetic resonance imaging of endocrine tumours of the pancreas. Br J Radiol 1995;68:341-7.

(f.2) Van Hoe L, Gryspeerdt S, Marchal G, Baert AL, Mertens. Helical CT for the preoperative localization of islet cell tumours of the pancreas: value of arterial and parenchymal phase images. AJR 1995;165:1437-9.

(f.3) Mori M, Fukuda T, Nagayoshi K, Kohzaki S, Matsunaga N, Hayashi K, et al. Insulinoma: correlation of short-T1 inversion-recovery (STIR) imaging and histopathologic findings. Abdom Imaging 1996;21:337-41.

(f.4) Angeli E, Vanzulli A, Castrucci M, Venturini M, Sironi S, Zerbi A, et al. Value of abdominal sonography and MR imaging at 0.5 T in preoperative detection of pancreatic insulinoma: a comparison with dynamic CT and angiography. Abdom Imaging 1997;22:295-303.