Sonographic pancreas echogenicity in cystic fibrosis compared to exocrine pancreatic function and pancreas fat content at Dixon-MRI

Abstract

Objective: Fatty infiltration of the pancreas is a dominating feature in cystic fibrosis (CF). We evaluate the association between pancreatic fat content assessed by Dixon magnetic resonance imaging (MRI), pancreatic echogenicity at ultrasonography (US) and exocrine function in CF patients and healthy controls (HC).

Material and methods: Transabdominal US, pancreatic Dixon-MRI and diffusion-weighted imaging (DWI) were performed in 21 CF patients and 15 HCs. Exocrine function was assessed by endoscopic secretin test and fecal elastase.

Results: CF patients were grouped according to exocrine pancreatic function as subjects with normal (CFS: n = 11) or reduced (CFI: n = 10) function. Among CFI 90% (9/10) had visual hyperechogenicity. CFI also had increased echo-level values (p<0.05 vs others). All CFI (10/10) had markedly increased pancreatic fat content estimated by MRI compared to sufficient groups, p<0.001). Among CFS patients and HC, 27% (3/11) and 33% (5/15), respectively, had hyperechoic pancreas. However, all these had low pancreatic fat-content at MRI compared to CFI. In CFI, pancreatic fat content was correlated to ADC (r = -0.93, p<0.001).

Conclusion: Pancreas insufficient CF patients exhibit severe pancreatic fatty-infiltration at MRI and hyperechoic pancreas at US. Pancreas hyperechogenicity in pancreatic sufficient subjects does not co-exist with fatty infiltration at MRI. MRI evaluates pancreatic fatty infiltration more accurately than US and fat infiltration estimated by MRI outperforms sonographic hyper-echogenicity as a marker for exocrine pancreatic failure in CF.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. Inclusion flow chart according to the CONSORT guideline.

CFI: Pancreas insufficient cystic fibrosis patients. CFS: Pancreas insufficient cystic fibrosis patients. HC: Healthy controls.

Fig 2. US (left column), Dixon MRI (middle columns) and ADC maps (DWI) (right column) images of the pancreas in patients with CFI (upper row); CFS (middle row) and HC (lower row).

The CFI patients typically exhibited pancreatic hyperechogenicity (US), increased pancreatic fat content demonstrated by hyperintensity on fat image and hypointensity on the corresponding water image (Dixon MRI) and restricted diffusion with pancreatic hypointensity on the ADC map (upper row), whereas none of the CFS patients or HCs had signs of increased pancreatic fat content or restricted diffusion (middle and lower row). The boundaries of the pancreas are indicated with arrows and the selected ROIs in the liver, pancreas and vessel of US are marked in the HC subject. ADC: apparent diffusion coefficient, CFI: Pancreas insufficient cystic fibrosis, CFS: Pancreas sufficient cystic fibrosis, DWI: Diffusion weighted imaging, HC: Healthy control, US: ultrasound.

Fig 3. Panel a displays percentage of subjects with a hyperechoic pancreas in CFI patients, CFS patients and HCs.

Panel b displays box and scatterplots for the US liver/pancreas echo-intensity ratios (US-LP) in the three groups. Panel c displays box and scatterplots for the MRI-Dixon fat-signal fraction in the three groups. Panel d displays box and scatterplots for ADC in the three groups. CFI: Pancreas insufficient cystic fibrosis, CFS: Pancreas sufficient cystic fibrosis, HC: Healthy control. US: Ultrasonography. US-LP: Ultrasound liver-pancreas signal intensity ratio. ADC: Apparent diffusion coefficient. ns: Not significant. (*Pearson chi-square test).

Fig 4. Panel a displays poor correlations in a scatterplot between the US liver/pancreas echo-intensity ratio and the MRI fat-signal fraction (FSF).

There is a marked difference in the FSF between the pancreatic sufficient (CFS and HCs) and pancreatic insufficient (CFI) groups. Panel b displays the difference of fat-signal fraction between the subjects with a hyperechoic pancreas and the subjects with a normal pancreas in the pancreatic sufficient (PS) subjects (i.e. CFS and HC). Panel c displays almost perfect correlation between the pancreatic MRI-Dixon fat-signal fraction and the pancreatic ADC value in CFI patients and lack of correlation in the in the pancreatic sufficient groups. ADC: apparent diffusion coefficient, CFI: Pancreas insufficient cystic fibrosis, CFS: Pancreas sufficient cystic fibrosis, HC: Healthy control.

Fig 5. Receiver operator (ROC) curves for all US and MRI parameters for the prediction of exocrine pancreatic insufficiency yielded significantly better AUC for the MRI parameters (A: Area under ROC) than for the US parameters.

The p value