This case possibly belongs to type 2b fatty infiltration.

Nevertheless, there is a massive lack of significant histopathological studies to prove or disprove that lipomatosis and fat replacement of the pancreas are (i) distinctive entities, (ii) associated entities in variable proportions in a definite case, or (iii) expressions of the same disease.

Lipomatous Pseudohypertrophy (LPH) of the pancreas, a rare, specific, and distinct entity was first described by Hantelmann in 1931 as a disproportionate replacement of the entire pancreas with increasing amounts of adipose tissue and subsequent enlargement of the entire gland [10].

Etiology

The exact etiopathogenesis behind fatty replacement is not known; however, several predisposing factors suggested including systemic and local causes and its association with various syndromes has been enumerated below:

1) Systemic

2) Local

3) Syndromic associations

Pancreatic lipomatosis has been found associated with several diseases comprising diabetes mellitus, metabolic syndrome, acquired or hereditary pancreatitis, alcoholic hepatitis, cystic fibrosis [12], and condition comprising increasing age, body mass index or more precisely visceral fat index and use of steroid therapy. Numerous cases are associated with condition compromising the permeability of the pancreas ductal system such as intraductal calculus, pancreatic tumors [13], and congenital or experimental stenosis [14].

Total fatty replacement of pancreas is important for radiologists as it results in malabsorption due to pancreatic exocrine insufficiency [9].

Role & limitations of imaging modalities

The role of ultrasound in the diagnosis of pancreatic steatosis is very limited; first, because the overlying bowel gas causes obscuration of the pancreas and second, the fatty infiltration results in increased echogenicity of the pancreatic tissue making its differentiation difficult from normal retroperitoneal fat.

Cross-sectional imaging, namely, CT and MRI has an important role in the evaluation of pancreatic disease. CT is particularly useful in detecting specific etiologies, for example, pancreatic duct obstruction by the calculus or tumor.

Unenhanced CT has negative attenuation value of pancreatic tissue replaced by the fat, therefore can reliably diagnose diffuse fatty change involving the pancreas. However, focal fatty change cannot be diagnosed confidently with CT alone, as on post contrast images, the normal pancreatic parenchyma entrapped between fatty replacement area shows contrast enhancement simulating a true mass [15].

Chemical shift MRI has advantage over CT in confirming the presence of focal fatty replacement of the pancreas due to its ability to distinguish fat from other tissues and because of fat suppression techniques [16]. A characteristic loss of signal intensity on opposedphase T1-weighted gradient-echo image as compared with corresponding in-phase image confirms the presence of microscopic lipid within the focal pancreatic mass [17]. This histologic condition is, in general, not present in pancreatic cancer [18]. MRI sequences with fat suppression are also useful for the diagnosis of FI.

MRCP/ERCP demonstrates the status of pancreatic duct and the biliary tree. Selective pancreatic angiography is especially useful in differentiating pancreatic lipomatosis from dorsal agenesis by showing the pancreatic circulation [13].

Sijens PE et al. determined fat content of human liver, pancreasand kidneys using MR spectroscopy and a previously validated gradient echo magnetic resonance imaging method with Dixon’s two point technique [19].

Lipotoxic damage to organs

It has been hypothesized that in obesity and metabolic syndrome, ectopic fat causes lipotoxic damage to organs e.g. Liver (steatohepatitis and cirhhosis), pancreas ( beta-cell dysfunction) and lipotoxicity of the kidney [20-24]. They concluded that the role of lipid accumulation in the pathogenesis of renal disease, diabetes and metabolic disease in human should be reconsidered.

A correlation has been demonstrated that obese nondiabetic subjects have increased fat in the pancreas and lipomatosis of the pancreas reflects early events in the pathogenesis of diabetes [25,26].

Marked pancreatic lipomatosis with atrophy has been observed in adult patients secondary to pancreatic duct obstruction by calculi or carcinoma [27]. Under these circumstances, the obstructed pancreatic duct is stenotic rather than dilated, and typically has a smooth wall. Important differentials in case of stenotic pancreatic duct include dorsal agenesis of pancreas, pancreatic carcinoma and chronic pancreatitis [27].

Haunz and Baggenstoss reported fat replacement in the body and tail of pancreas in a clinical study of 80 cases of carcinoma head of pancreas [28].

Pancreatic lipomatosis with stenotic pancreatic duct, secondary to pancreatic head adenocarcinoma after neoadjuvant chemoradiotherapy has been reported by Makay et al. [29].

Pancreatic lipomatosis following chronic pancreatitis/carcinoma is focal or diffuse associated with parenchymal atrophy that manifests as exocrine and endocrine or only exocrine deficiency. In normal individuals, only 10% of parenchyma is sufficient for the maintenance of normal exocrine function [30].

Differential diagnosis includes pancreatic agenesis: pancreatic duct is preserved in pancreatic lipomatosis.