British Journal of Radiology (2006) 79, 627-629
© 2006 British Institute of Radiology
doi: 10.1259/bjr/19356841
Focal pancreatic lesion: can a neoplasm be confidently excluded?
J Hague, FRCR and
Z Amin, FRCR
Department of Radiology, Middlesex Hospital, Mortimer Street, London W1T 3AA, UK
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Introduction
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A 56-year-old female patient was referred to our institution for further investigation of diarrhoea and weight loss over the previous 3–4 months. Extensive biochemical investigation had revealed no abnormality. The patient underwent a CT scan of the pancreas (pre-contrast, pancreatic phase and portal venous phase), which demonstrated a low density focus in the head of the pancreas. Selected images from this study are presented below (Figure 1
). What is the diagnosis? What further tests should be done?
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Figure 1. (a) Unenhanced axial image through the head and neck of the pancreas demonstrating a region of hypoattenuation in the pancreatic head. (b) 5 mm reconstructed contrast enhanced axial section through the head of pancreas. (c) 5 mm reconstructed contrast enhanced axial section through the body and tail of pancreas.
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The patient subsequently underwent MRI. The in and opposed phase axial images are presented (Figure 2).
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Figure 2. (a) In phase T1 weighted gradient-echo image through the head and neck of pancreas. (b) Opposed phase T1 weighted gradient-echo image through the head and neck of pancreas demonstrating signal drop in part of the head corresponding to the CT abnormality.
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This demonstrates uniformly high signal in the entire pancreas on the in phase T1, with signal drop in the anterior head/neck, body and tail on the opposed phase images. This is in keeping with uneven fatty infiltration in part of the head and uncinate process, which has been described as a normal variant.
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Discussion
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Fatty change in the pancreas can be diffuse, or may be uneven, sparing certain regions (focal fatty sparing, FFS). Alternatively, fat infiltration can be confined to one region of the pancreas (focal fatty infiltration, FFI) [1, 2].
Diffuse mild fatty infiltration of the pancreas frequently occurs in elderly and obese persons, and is of little clinical importance [1–3].
Focal areas of FFS in the pancreas are analogous to focal sparing in the liver [4]. FFS can mimic a mass, in a pancreas with diffuse fatty infiltration. Areas of FFS are usually within the head or uncinate [1, 2]. FFS has been associated with a pancreas divisum. FFS can appear as a hypoechoic mass on ultrasound, and appears as an enhancing mass relative to the normal pancreas on contrast enhanced CT [4].
FFI is associated with insulin-dependent diabetes mellitus (IDDM), chronic pancreatitis, hepatic disease, dietary deficiency, viral infection and steroid therapy. Distribution of FFI is variable, dominant in the body and tail. FFI of the head or uncinate or both have been described [3].
FFI can appear as a hypoechoic mass on ultrasound, and a hypoattenuating region on non-enhanced CT and contrast enhanced CT. A pancreatic neoplasm may be diagnosed on this basis. There will, however, be no dilatation of the pancreatic duct, and no contour deformation, but the appearances may be progressive on serial scans.
MRI using chemical shift can detect and characterize focal fatty infiltration of the pancreas and exclude a diagnosis of neoplasm [5]. The loss of signal intensity on an opposed phase T1 weighted gradient echo image compared with a corresponding in phase image establishes the lipid content of the focal abnormality and excludes a diagnosis of a pancreatic adenocarcinoma or a neuroendocrine tumour, both of which do not contain fat.
Focal lesions in the pancreas detected on CT (or ultrasound) that do not have any associated features of malignancy (for example, no venous attenuation, or duct dilatation) and do not deform the contour, may be caused by uneven pancreatic lipomatosis (FFI or FFS) and can be further evaluated with in and opposed phase MRI [5].
The patient's symptoms resolved without treatment and she remained well on follow up 1 year later.
Received for publication April 18, 2005.
Revision received July 11, 2005.
Accepted for publication July 25, 2005.
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References
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- Marchal G, Verbeken E, Van Steenbergen W, et al. Uneven lipomatosis; a pitfall in pancreatic sonography. Gastrointest Radiol 1989;14:233–7.[Medline]
- Donald JJ, Shorvon PJ, Lees WR. A hypo echoic area within the head of the pancreas; a normal variant. Clin Radiol 1990;41:337–8.[Medline]
- Matsumoto S, Mori H, Miyake H, Takaki H, Maeda T, Yamada Y, et al. Uneven fatty replacement of the pancreas: evaluation with CT. Radiology 1995;194:453–8.[Abstract/Free Full Text]
- Jacobs JE, Coleman BG, Arger PH, Langer JE. Pancreatic sparing of focal fatty infiltration. Radiology 1994;190:437–9.[Abstract/Free Full Text]
- Isserow JA, Siegelman ES, Mammone J. Focal fatty infiltration of the pancreas: MR characterization with chemical shift imaging. AJR Am J Roentgenol 1999;173:1263–5.[Free Full Text]
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Introduction
Discussion
