IM-PAC Grading Correlates with Chronic Pancreatitis Severity on CT and MRI

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Frontiers in Medicine Published April 22, 2026 Medically reviewed April 25, 2026 DOI ↗ By Dr. Amelia Tan, PhD · Internal Medicine & Chronic Disease

Key Takeaway

Consider IM-PAC as a reproducible imaging-based framework for grading chronic pancreatitis severity, recognizing its observational and correlational nature.

In a retrospective single-center observational cohort, researchers evaluated the IM-PAC grading system based on CT and MRI measurements in 280 examinations from 2023 (CT n=168; MRI n=112). The study population consisted of patients with abdominal CT and MRI examinations, and the primary aim was to assess the association between IM-PAC grade and features of chronic pancreatitis severity. No longitudinal follow-up was reported.

The IM-PAC grade distribution was Grade 0 (n=54, 19.3%), Grade 1 (n=119, 42.5%), Grade 2 (n=93, 33.2%), and Grade 3 (n=14, 5.0%). There was a significant monotonic association between higher IM-PAC grades and ductal abnormality severity (Spearman ρ = 0.52, p < 0.001) and MRI-defined fibrosis severity (Spearman ρ = 0.48, p < 0.001). In the CT subgroup (n=168), calcifications showed progressive enrichment across grades (p < 0.001).

Inter-observer agreement was excellent for thickness measurements (ICC = 0.89, 95% CI: 0.84–0.92) and substantial for ductal grading (weighted κ = 0.81) and fibrosis grading (weighted κ = 0.78). Safety and tolerability were not reported, as this was an imaging-based retrospective study.

Key limitations include the retrospective single-center design and the absence of longitudinal follow-up. The findings are correlational; no causation can be inferred, and generalizability beyond the reported population is uncertain. IM-PAC may provide a reproducible morphometric framework for quantifying pancreatic atrophy, but prospective validation is needed.

Study Details

Study typeCohort

EvidenceLevel 3

PublishedApr 2026

View Original Abstract ↓

BackgroundPancreatic atrophy (PA) is a progressive reduction in pancreatic parenchymal volume, accompanied by acinar cell loss, fibrosis, and fatty infiltration. It is an important radiological marker of glandular damage associated with physiological aging, chronic inflammatory diseases, and metabolic disturbances, such as diabetes mellitus and obesity. However, PA is still reported mainly using subjective terms, which leads to inter-observer variability and limits reliable clinical correlation and longitudinal follow-up.PurposeThis study aimed to introduce and validate the İstanbul Morphometric Pancreatic Atrophy Classification (IM-PAC), a four-tier morphometric grading system based on CT and MRI measurements, and to evaluate its association with graded CP severity features (CP).MethodsIn this retrospective single-center study, 280 abdominal CT and MRI examinations performed in 2023 were analyzed. Pancreatic head, body, and tail thicknesses were measured at standardized anatomical landmarks. Chronic pancreatitis (CP)–related imaging features were graded using predefined ordinal severity scales for ductal abnormalities and MRI-defined fibrosis. Analyses used true modality-specific denominators (CT n = 168; MRI n = 112). Inter-observer reproducibility was assessed using intra-class correlation coefficients (ICC) and quadratic weighted Cohen’s kappa.ResultsIM-PAC grades were distributed as Grade 0 (n = 54, 19.3%), Grade 1 (n = 119, 42.5%), Grade 2 (n = 93, 33.2%), and Grade 3 (n = 14, 5.0%). Increasing IM-PAC grade was significantly and monotonically associated with ductal abnormality severity (Spearman ρ = 0.52, p < 0.001) and MRI-defined fibrosis severity (ρ = 0.48, p < 0.001). Calcifications assessed in the CT subgroup (n = 168) showed progressive enrichment across grades (p < 0.001). Inter-observer agreement was excellent for thickness measurements (ICC = 0.89; 95% CI: 0.84–0.92) and substantial for ordinal ductal and fibrosis grading (weighted κ = 0.81 and 0.78, respectively).ConclusionBy integrating severity-based CP grading, IM-PAC provides a reproducible and clinically relevant morphometric framework for quantifying pancreatic atrophy.