Comparison of Imaging Characteristics of CT, MRI, PET, and EUS in the Evaluation of Metastasis to the Pancreas: Results From a Single Tertiary Cancer Center

Abstract

Introduction: Metastasis to the pancreas is less than 5% of all tumors detected in the pancreas. Differentiating a metastatic implant from a primary pancreatic carcinoma is important for management and prognosis. The purpose of the study was to identify the clinical presentation and imaging characteristics of metastastic lesions to the pancreas. Methods: The study was approved by the institutional review board. Retrospective review was conducted to identify all patients suspected to have a metastatic lesion to the pancreas on imaging (CT, MRI, PET) and confirmed on FNA (EUS-FNA or IR-guided biopsy) between 2002 and 2014. Results: A total of 70 patients (median age: 64 years [range: 35-83 years); males 43 [61%]) were found to have synchronous metastatic pancreatic lesions (n=6) or metachronous metastatic pancreatic lesions (n=64) detected after a median of 35 months after primary cancer (range: 1-304 months). The common primary cancers to metastasize to the pancreas were renal (29), melanoma (8), lung (9), colon (3), and breast (3). The majority of patients (n=60; 85%) were asymptomatic. Surveillance CT scan detected the pancreatic lesion in all patients. Of the 70 patients, CT showed multiple pancreatic lesions in 26, diffuse infiltration in 1, and a single lesion in 43: head (19), body (11), and tail (13). MRI detected pancreatic lesions in 11/13 patients. PET scan showed increased uptake in the lesions in 26/31. EUS showed pancreatic lesions in 54/54. Of the 54 patients, EUS showed multiple lesions in 22, and a single lesion in 32: head (15), body (9), tail (8). One patient had a purely cystic lesion (1 anechoic), 43 had solid lesions (41 hypoechoic, 1 heterogenous, and 1 isoechoic), and 10 had solid-cystic lesions (3 hypoechoic, 1 isoechoic, and 6 heterogenous). The border of the lesion was well defined (31 patients) and irregular (23 patients). Thirteen patients had PD dilation: head (6), body (3), tail (1), and multiple (3). Most of the patients (25/29) with pancreatic metastasis from renal cancer had well-defined borders. CBD dilation was seen in 8 patients (3 had multiple lesions and 5 with single lesions all located in the head). Five patients had both CBD and PD dilation. No specific primary cancer was associated with PD or CBD dilation. A total of 13 patients underwent metastatectomy. Four of 13 patients who underwent surgery died (median 120 months; range: 66-412). Conclusion: Metastasis to the pancreas can occur after several years of remission of the primary cancer, especially in RCC and is often found on routine surveillance CT as a pancreatic mass. Metastasis to the pancreas is usually solitary with no predilection for the location in the pancreas. Metastasis from RCC is most common and has a well-defined border on EUS.