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CT imaging has been included in several AP prognostic scoring systems. Table 5.1 depicts the most common CT scoring systems. The earliest CT scoring system graded scans on an ordinal scale from A to E. Grades D and E correlated with clinically severe AP, with a corresponding mortality of 14% and morbidity of 54% compared with 2% morbidity and no mortality in grades A–C [16]. Studies have shown that the CT grading system has a sensitivity and specificity of 100% and 61.6%, respectively, for predicting morbidity, and 100% and 56.9%, respectively, for predicting mortality [17]. The strengths of the CT grading system are that it is easy to perform and does not require the use of intravenous contrast. However, limitations are that it does not significantly correlate with the development of organ failure, pancreatic and extrapancreatic necrosis, and peripancreatic vascular complications. Another limitation is that there is moderate interobserver agreement [3]. The CT Severity index (CTSI) is a scoring system that quantifies pancreatic and extrapancreatic inflammation and the extent of necrosis and thus helps distinguish between mild, moderate, and severe pancreatitis. A CTSI score of 0–3 correlates with mild AP, of 4–6 with moderate AP, and 7–10 with severe AP [16]. This has become the most widely used morphologic severity index for clinical and research purposes. Limitations of this scoring system is that it does not correlate with the development of organ failure, extrapancreatic parenchymal complications [18] and peripancreatic vascular complications [19]. Similar to the CT grading system, the CTSI is also limited by moderate interobserver agreement [20]. The modified CTSI (MCTSI) integrates extrapancreatic complications and extent of pancreatic necrosis (none, ≤30%, >30%) with the presence or absence of peripancreatic inflammation. MCTSI better correlates with patient outcome, length of stay, and development of organ failure and has similar interobserver agreement to the CTSI [21]. However, in a study with a larger number of patients with clinically severe AP, there were no significant differences between the two CT scoring systems [22]. Other scoring systems, such as pancreatic size index [23], MOP (“mesenteric oedema and peritoneal fluid”) score [24], retroperitoneal extension grade [25], and EPIC (“extrapancreatic inflammation on CT”) [26] have also been developed. However, these scores are not used in clinical settings. A large retrospective study comparing the accuracy of different CT scoring systems to clinical scoring systems found that CT scoring systems were not superior with regard to predicting mortality and persistent organ failure [27].

Table 5.1 CT prognostic scoring systems.

CT grading system	CT severity index	Modified CT severity index
Grade	CT findings	Points	Percentage necrosis	Necrosis points	Severity index	Points	Necrosis points	Extrapancreatic complications a	Severity index
A	Normal pancreas	0	0%	0	0	0	0	0	0
B	Pancreatic enlargement	1	0%	0	1	2	0	0	2
C	Pancreatic inflammation and/or peripancreatic fat	2	<30%	2	4	2	2	0	4
D	Single peripancreatic fluid collection	3	30–50%	4	7	4	4	0	8
E	Two or more fluid collections and/or retroperitoneal air	4	>50%	6	10	4	4	2	10

^a Pleural effusions, ascites, vascular complications, parenchymal complications, gastrointestinal tract involvement.