¹⁸F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography Findings of Pancreatic Hemangiopericytoma

Introduction

Hemangiopericytoma (HPC) is a rare mesenchymal tumor derived from pericytes of Zimmerman.[1] The pericytes of blood vessels are a specific type of cells that surround the capillary vessels. According to the literature, approximately 20%–40% of HPCs occur in pelvis and retroperitoneum.[23] The tumor is considered as aggressive with high rates of local recurrence and metastasis regardless the localization. A correlation between histological grade and risk of metastasis has not been indicated. Although two cases of sporadic HPC arising in the pancreas were reported, none of them were monitored with ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT).[45] To the best of our knowledge, this is the first case report of primary pancreatic HPC assessed preoperatively and monitored with ¹⁸F-FDG PET/CT.

Case Report

A 42-year-old woman presented with jaundice and fatigue. She had a primary brain hemangioblastoma resection history about 16 years ago. A large pancreatic tumor (5.5 cm × 4 cm) was observed on her abdominal ultrasonography. Magnetic resonance imaging in T2 scans revealed a well circumscribed, enhancing 6.5 cm × 5.7 cm × 5 cm hyperintense and hypervascular mass arising from pancreatic head. Centrally located small areas were presumed to represent necrosis. Preoperative ¹⁸F-FDG PET/CT imaging demonstrated peripheral moderate metabolic activity in contrast with the centrally located hypometabolic area on the head of the pancreas (standardized uptake value [SUV]: 4.2) [Figure 1], and her blood glucose level was normal (96 g/ml). A 6 cm × 6 cm × 4.5 cm diameter tumor was resected. The tumor had 10%–20% necrosis. There was 5–10 mitotic figures/10 hpf. Immunohistochemical stains showed diffuse positivity for CD34 and heterogeneous for vimetin. It was histopathologically diagnosed as malign pancreatic HPC. Four months postoperatively, ¹⁸F-FDG PET/CT imaging did not show any pathological involvement. However, 16 months after operation ¹⁸F-FDG PET/CT imaging demonstrated multiple metastasis including lung and mediastinal lymph node, carcinoma peritonii, iliac lymph nodes, and bone metastasis (maximum SUV: 1.6–4.2) [Figure 2]. She could not reach a remission status and died just after that imaging with a lifetime of 16 months after diagnosis.

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Figure 1 ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography imaging shows increased activity in the caput of pancreas with standardized uptake value of 4.2. Primary tumor (black arrow) in the head of pancreas is visualized on coronal maximum intensity projection images (a), axial positron emission tomography (b), computed tomography (c), and fusion (d) images

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Figure 2 Sixteenth month coronal maximum intensity projection postoperatively (a), coronal whole body fusion (b), and axial thorax fusion (c) ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography images show mild increased uptake multiple metastatic areas (bilaterally lung, mediastinal lymph node, bone, and iliac lymph node) and local relapse (standardized uptake value: 1.6–4.2). Metastatic pulmonary lesions in the right lung demonstrated with black arrow

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Discussion

HPC is a rare soft tissue sarcoma that usually shows aggressive prognosis and has tendency to metastasis or recurrence. Exceptional cases of HPC arising outside of the central nervous system including peripheral nerve roots, liver, gastrointestinal tract, retroperitoneum, kidney, adrenal glands, and extremities have been reported, mostly as single case reports. No typical CT findings have been reported for HPC.[6] Pre-operative diagnosis of this neoplasm is difficult because the clinical suspicion is low, especially in our patient within the pancreatic location. The first choice of treatment for HPC is wide surgical excision, but recurrence and metastasis can subsequently occur in up to 50% of cases.[378] Local recurrence rates of up to 90% and metastatic rates of up to 33% have been reported. Metastases have been identified in the liver, lung, bones, and rarely other locations.[8] Since HPC is a rare soft tissue tumor, the current literature of its ¹⁸F-FDG PET findings is limited. One reported case of chest wall HPC with ¹⁸F-FDG PET showed irregular increased activity.[9] Another group of ¹⁸F-FDG uptake pattern is identified in intracranial HPC cases and metastasis.

Considering our case, there was no reported death due to pancreatic HPC in the literature. In our patient with bad prognosis, primary lesion shows moderate metabolic activity while metastatic HPC lesions show low FDG uptake on PET indicating low glucose utilization. Although the hypervascular nature of the tumor, its variable FDG avidity reminds of its histopathologic structure. It was reported that a highly malignant course can be predictable from findings such as the large size of the tumor (>5 cm), increased number of mitosis, histological findings of anaplasia, pleomorphic tumor cells, foci of hemorrhage, and necrosis.[28] In a recent study of intracranial HPC, younger patients (< 45 years) had longer survival time but paradoxically had more frequent extracranial metastases.[10] The patient had multiple metastases in a similar way; however, she could not survive long after metastasis in contrasts to that study. The aggressive behavior of the tumor and the probability of recurrence are unpredictable in neither of the pre- and post-operative ¹⁸F-FDG PET imaging. Considering the given the rarity of those tumors, a few data that are available to define prognostic factors which can be used to guide future therapy. We believe that it is important to be aware of the variability in ¹⁸F-FDG PET/CT imaging features of HPC. Additionally to speculate on this variability in ¹⁸F-FDG PET/CT imaging is substantial to reflect the heterogeneity of histological or biological features of HPC.

¹⁸F-FDG PET/CT imaging of HPC in the primary pancreatic location of our patient shows this variability, and after extensive search of the literature, we could not find out any similar case. ¹⁸F-FDG PET/CT appearances of our HPC patient were quite extraordinary contributing to literature.