Pancreatic lipomatosis

Pancreatic lipomatosis refers to fat accumulation in the pancreatic parenchyma. This finding is most often associated with obesity and aging. It tends to be the most common pathological condition involving the pancreas. The condition may occasionally simulate a mass-like lesion particularly when fatty replacement is uneven ¹. 

Terminology

Many terms have been used in the literature to refer to similar conditions. Recognizing these differences, one nomenclature proposes that the general terms for pancreatic fat accumulation include pancreatic lipomatosis, fatty pancreas, and pancreatic steatosis ^8,9. The most extreme variant is lipomatous pseudohypertrophy, characterized by pancreatic enlargement, but some consider this a distinct entity ⁸.

The entity can be divided by etiology ⁸:

• fatty replacement: death of acinar cells with subsequent replacement with adipocytes
• fatty infiltration or nonalcoholic fatty pancreas disease: pancreatic accumulation of adipocytes in association with obesity/metabolic syndrome

Clinical presentation

The majority of pancreatic fatty deposits have no clinical significance. However, excessive fatty deposits may cause loss of pancreatic function, causing maldigestion of nutrients. This may lead to symptoms of chronic diarrhea, steatorrhea, and weight loss, without any abdominal pain or signs of diabetes mellitus due to low insulin production ²⁰. Symptomatic fatty pancreas is only reported in several case reports ²⁰.

Pathology

Subtypes

• even pancreatic lipomatosis
• uneven pancreatic lipomatosis ^3,9
  • type 1a: preferential fatty replacement of the head, sparing the uncinate process and peribiliary region
  • type 1b: preferential fatty replacement of head, neck, and body, sparing the uncinate process and peribiliary region
  • type 2a: preferential fatty replacement of head, including uncinate process, and sparing the peribiliary region
  • type 2b: total fatty replacement of the pancreas except for the peribiliary region

Etiology

Several etiologies are well established ⁸:

• aging (most common degenerative lesion of the pancreas) ¹⁹
• metabolic syndrome: obesity, dyslipidemia, diabetes mellitus
• congenital syndromes
  • cystic fibrosis (most common cause in childhood)
  • Shwachman-Diamond syndrome
  • Johanson-Blizzard syndrome
  • carboxyl ester lipase mutation (maturity-onset diabetes of the young type 8) ¹⁰

Less established etiologies include the following ⁸:

• chronic pancreatitis and/or pancreatic acinar atrophy due to a wide variety of insults including ¹⁹
  • viral infection
  • duct obstruction due to ligation, congenital stenosis, stones, or malignancy
  • alcohol abuse ¹⁴
• hemosiderosis / secondary hemochromatosis ^16-18
• drugs
  • corticosteroids ¹¹
  • gemcitabine ¹²
• Cushing syndrome ⁸
• cirrhosis related to chronic hepatitis B ¹³
• malnutrition
  • kwashiorkor ⁷
  • acquired immunodeficiency syndrome (AIDS) ¹⁵

Radiographic features

Ultrasound

On ultrasound, fatty pancreas has hyperechoic parenchyma ²⁰.

CT

On CT scan, fatty pancreas has hypodense parenchyma ²⁰.

Differential diagnosis

Imaging differential considerations include:

• pancreatic agenesis: in pancreatic lipomatosis, the ducts remain preserved ³