Pancreatic lipoma- A multimodality imaging approach

Clinical History

90-year-old male patient referred to the radiology department complaining of upper abdominal pain lasting for 1 month.

Imaging Findings

Ultrasonography revealed a well-defined hypoechoic lesion in the neck-body junction of the pancreas suggestive of mass lesion. CT was advised for further characterisation of the lesion.
On CT, a hypodense fat attenuation mass lesion was seen in the neck-body junction of the pancreas. The HU of the mass lesion was ranging from -90 to -100.
On MRI, the lesion showed uniform hyperintense signal on both T1 and T2 weighted images (similar to that of adjacent omental and retroperitoneal fat) and drop out of signal on STIR images.

Discussion

Pancreatic lipoma is a rare benign tumour composed of homogenous adipose tissue which is identical to subcutaneous fat histologically and circumscribed by a thin collagenous capsule that may contain fibroreticular septae and scattered vessels [1, 2]. Bigard, in 1989, described the first case [3]. The majority of pancreatic neoplasms are epithelial ductal adenocarcinomas, however, 1% to 2% are mesenchymal tumours arising from connective, lymphatic, vascular or neuronal tissue [1]. These nonductal neoplasms may be benign or malignant and are usually identified only by histopathological examination [4].

Computed Tomography is the modality of choice for the detection of fat containing lesions of the pancreas. Hounsfield unit (HU) values ranging from - 80 to -120 indicate a lesion composed of fat. CT can readily detect these lesions and usually no further investigations are required [5, 6].
On MRI, pancreatic lipomas appear as homogeneous mass lesions which are isointense with both intraabdominal and subcutaneous fat on T1 and T2 weighted sequences. There is homogenous suppression of signal on fat suppressed sequences (STIR) [7].

Focal fatty infiltration of pancreas is one condition which has to be differentiated from lipoma of pancreas. Focal fatty infiltration also appears as a well circumscribed mass lesion composed of fat; however, it has direct contact or continuity with peripancreatic fat tissue which helps in making the differential diagnosis [8].
MR imaging is helpful in differentiating between fatty replacement of the pancreas and the lipoma of the pancreas [5]. Fatty replacement of pancreas is a more infiltrative process and grows along the fascial planes when compared to a lipoma which is an encapsulated, well circumscribed, septated, fatty mass surrounded by pancreatic parenchyma [3].
Liposarcoma of the pancreas is characterised by higher densitometric values (HU), greater size, areas of solid or fluid densities, and blurred outlines and should be differentiated from lipoma of pancreas [3].
Another differential diagnosis is lipomatous pseudohypertrophy which is characterised by an enlarged pancreas with massive replacement of pancreatic tissue by adipose tissue [3].

Since pancreatic lipomas are completely benign entities, conservative management is preferred with surgery indicated only in rare cases causing mass effect.

Differential Diagnosis List

Final Diagnosis

Pancreatic lipoma

URL:	https://www.eurorad.org/case/10028
DOI:	10.1594/EURORAD/CASE.10028
ISSN:	1563-4086