Pelvic Venous Thromboembolism Leading to Pulmonary Embolism in a Case of Chondroblastic Osteosarcoma Detected on FDG PET/CT

Introduction

Osteosarcoma can be divided based on the tumor matrix in to osteoblastic, chondroblastic, and fibroblastic subtypes. Chondroblastic is a rare subtype with heterogeneous chondroid and myxoid stroma.[1] It constitutes about 25% of all osteosarcoma. It has poor 5-year overall survival of 38%.[2] It usually presents as progressively worsening pain and swelling involving distal extremities. This subtype of osteosarcoma usually has the most deleterious course as it has resistance to most of the chemotherapy regimens and high propensity for developing thromboembolic events, with life-threatening consequences.[3] The differentiation of tumor thrombus from bland thrombus is essential in therapeutic decision-making. Here, we are presenting a case of chondroblastic osteosarcoma of pelvis with tumor thromboembolism detected in 18 F fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) scan.

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An 18-year-old female presented with a history of pain and swelling in the right hip region for 4 months, magnetic resonance imaging done outside showed abnormal signal intensity involving right pelvic bone extending to sacrum with overlying cortical destruction. Fine-needle aspiration cytology was conclusive of chondroblastic osteosarcoma. 18 F FDG PET/CT was done for presurgical staging.

Maximum intensity projection images [Figure 1a] showed FDG-avid bulky lesion in the right hemipelvis, which was the site of primary. Adjacent to the primary mass linear vertical FDG uptake was noted in the abdominopelvic region. In addition, an FDG-avid branching pattern was seen in thoracic region extending to bilateral pulmonary regions.

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Figure 1 (a) Maximum intensity projection image showing FDG avid lesions in right hemipelvis, linear uptake along abdomino-pelvic region and branching uptake from bilateral lung hila (red arrows). (b) FDG PET/CECT fusion image sagittal section showing FDG avid filling defect in bilateral pulmonary artery tracking along lobar and interlobar branches (arrow), (c) CECT chest axial imaging showing contrast filling defect in bilateral pulmonary arteries, (d) FDG PET/CECT fusion image sagittal section showing FDG avid filling defect tracking from left iliac vein to IVC (arrow), seen as filling defect on CECT (e-arrow) image

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Fused PET/contrast-enhanced computed tomography (CECT) and CECT images of abdominopelvis showed hypermetabolic primary right hemipelvic mass invading into pelvic vasculature with filling defect extending along right iliac vein to inferior vena cava (IVC) [Figure 1d and e]. Axial [Figure 1c] and sagittal fused PET/CT [Figure 1b] images of thorax showed FDG-avid contrast filling defect tracking along bilateral pulmonary arteries and extending superiorly and inferiorly along bilateral lobar, interlobar, and segmental branches.

These findings are suggestive of extensive thrombus in IVC, leading to bilateral pulmonary arterial embolism. The patient was immediately shifted to intensive care unit and treatment was initiated.

Discussion

Pulmonary embolism represents a potential life-threatening complication of venous thrombosis, which remains clinically occult in majority of cases. In addition to direct tumor thrombus formation, the incidence of thrombosis is significantly elevated in patients with malignancy due to a hypercoagulable state.[4]

On CECT, embolus may be demonstrated as an intraluminal filling defect causing complete arterial occlusion with failure to opacify the entire lumen, with or without vascular enlargement, or as a central arterial filling defect surrounded by intravascular contrast enhancement.

Although regional CECT can show intravascular filling defects, the differentiation of tumor thrombus from bland thrombus is essential, because the former will not benefit from anticoagulation therapy, which cannot be concluded by conventional imaging. 18 F FDG PET/CT is more specific than conventional imaging to diagnose FDG-avid tumor thrombus arising from solid tumors. Fused PET-CT images can delineate involved blood vessels, distinguishing blood pool activity from active metabolism by the tumor thrombus. There are reports on extensive thrombus formation in IVC and femoral vein, with embolization in cases of chondroblastic osteosarcoma, resulting in life-threatening consequences.[56]

FDG PET provides whole body evaluation, as a result of which, the etiology of embolism can be picked up. As seen in our case, the pulmonary emboli originated from the venous thrombus caused by the locally invasive bone primary. Thus, FDG PET/CT proves to be a single sensitive modality which depicts the extent of primary tumor as well as the associated anticipated and unanticipated complications.