Pancreatic colloid carcinoma (CC) is a rare sub-type of pancreatic adenocarcinoma which has an improved prognosis compared with pancreatic ductal carcinoma

Consequently, the early detection of CC by imaging may be of great significance in guiding patient management and therapeutic decisions. The present study aimed to analyze 18F-FDG PET/CT findings of CC in comparison to MRI and CT. 

PET/CT findings in 5 patients with CC were retrospectively reviewed based on visual interpretation and semi-quantitative index of SUVmax and TNR. Four patients received dual-time-point PET/CT scans.

Additionally, one patient underwent a contrast-enhanced CT scan, one MRI, and three received both. A total of five lesions were detected in five patients. Visually, two cases presented with mild FDG uptake, two with moderate and one with high.

Results

The mean of SUVmax and TNR was 5.1±2.2 and 2.8±0.7, respectively. Compared with CCs with low SUVmax, CCs with high SUVmax were more aggressive. No distant metastases were observed in five cases.

Among four patients with dual-time-point PET/CT imaging, SUVmax increased in three cases and decreased in one case. The mean early and delayed SUVmax were 4.2±1.1 and 4.7±1.9, respectively (P>0.05).

Radiological findings mainly included septated cystic components, internal sponge-like contrast-enhancement, calcification and 'salt-and-pepper sign' on MRI T2-weighted imaging.

Thus, PET/CT provided additional information on metabolic tumor activity as well as locoregional and distant staging, which are important prognostic markers and may improve further patient management. However, PET/CT did not show any findings in addition to MRI and contrast-enhanced CT that were unique to CC and allowed a clear differentiation from other pancreatic malignancies.

In conclusion, CC of the pancreas do not have typical features on CT and MRI and are therefore hard to distinguish from other pancreatic tumors such as IPMN and MCN. 

18F-FDG PET/CT did not show tumor characteristics which were unique to CC but provided important information on potential locoregional and distant metastases as well as on metabolic tumor activity which may improve further patient management.

The presence of CC should be considered when a pancreatic tumor presents with a predominantly cystic pattern with septations and sponge-like enhancement, calcifications, upstream pancreatic ductal dilation, the presence of the ‘salt-and-pepper sign’ on T2-weighted MRI, mild to moderate FDG uptake and the absence of distant metastases.