Imaging differentiation of solid pseudopapillary neoplasms and neuroendocrine neoplasms of the pancreas

Abstract

Purpose: The present study aimed to compare the computed tomography (CT) and magnetic resonance imaging (MRI) features of solid pseudopapillary neoplasms (SPNs) and pancreatic neuroendocrine neoplasms (pNENs).

Method: Lesion imaging features of 39 patients with SPNs and 127 patients with pNENs were retrospectively extracted from 104 CT and 91 MRI scans.

Results: Compared to pNEN patients, SPN patients were significantly younger (mean age 51.8 yrs versus 32.7 yrs) and more often female (female: male ratio, 5.50:1 versus 1.19:1). Most SPNs and pNENs presented as well-defined lesions with an expansive growth pattern. SPNs more often appeared as round or ovoid lesions, compared to pNENs which showed a lobulated or irregular shape in more than half of cases (p<0.01). A surrounding capsule was detected in the majority of SPNs, but only in a minority of pNENs (<0.01). Hemorrhage occurred non-significantly more often in SPNs (p=0.09). Signal inhomogeneity in T1-fat-saturated (p<0.01) and T2-weighted imaging (p=0.046) as well as cystic degeneration (p<0.01) were more often observed in SPNs. Hyperenhancement in the arterial and portal-venous phase was more common in pNENs (p<0.01). Enlargement of locoregional lymph nodes (p<0.01) and liver metastases (p=0.03) were observed in some pNEN patients, but not in SPN patients. Multivariate logistic regression identified the presence of a capsule (p<0.01), absence of arterial hyperenhancement (p<0.01), and low patient age (p<0.01), as independent predictors for SPN.

Conclusions: The present study provides three key features for differentiating SPNs from pNENs extracted from a large patient cohort: presence of a capsule, absence of arterial hyperenhancement, and low patient age.

Keywords: Frantz tumor; computed tomography; magnetic resonance imaging; pancreatic neuroendocrine carcinoma; pancreatic neuroendocrine neoplasm; solid pseudopapillary neoplasm.

Graphical abstract

Fig. 1

Flowchart of the study population.

Fig. 2

MR Images from SPN patients. A) 27-year-old female patient with an SPN in the tip of the pancreatic tail (arrow). The lesion is predominantly cystic with a continuous T2-hypointense capsule which shows enhancement most pronouncedly in the venous (ven) phase. B) 17-year-old female patient with a large SPN in the pancreatic tail (arrow). The lesion shows marked cystic degeneration and is surrounded by a continuous T2-hypointense capsule. The solid components of the lesion enhanced most pronouncedly in the venous phase.

Fig. 3

CT images from SPN patients. C) 54-year-old female patients with an SPN in the pancreatic head (arrow). The lesion is predominantly cystic with central calcifications (best seen in the non-contrast (nc) phase) and shows a capsule-like enhancement in the venous phase. D) 41-year-old male patient with a small SPN in the pancreatic body (arrow). The lesion is lesion is moderately hyperdense in the non-contrast, arterial (art), and venous phase. No capsule is apparent in CT. This lesion is very difficult to distinguish from pNEN.

Fig. 4

MR images from pNEN patients. A) 38-year-old female patient with a small pNEN in the medial part of the pancreatic head/ uncinated process (arrow). The lesion lacks a definite T2-hypointense capsule. It shows moderate arterial (art) hyperenhancement. B) 47-year-old female patient with a small pNEN in the pancreatic head with central cystic degeneration, lack of a definite T2-hypointense capsule, and marked enhancement in the arterial and venous (ven) phase (arrow).

Fig. 5

CT images from pNEN patients. C) 28-year-old female patient with a pNEN in the pancreatic body (arrow) which shows clear hyperdensity in the arterial phase and is associated with upstream dilatation of the main pancreatic duct. D) 36-year-old female patient with a pNEN with large cystic parts and a small calcification in the pancreatic tail (arrow). The encasement of the splenic vessels (depicted in the venous phase image) is helpful for differentiation from SPN.

Fig. 6

Graphical summary. Synopsis of the most relevant distinguishing imaging features.