Vanishing bone lesions mimicking osteoblastic metastases

A 57-year-old woman was directed to a  tertiary care center with a fast-growing mass involving the mediastinum, highly suspicious of a malignant origin. The patient had a long-standing history of tobacco exposure with no other relevant medical background.

Contrast-enhanced chest computed tomography (CT) depicted a pulmonary mass invading the left part of the anterior mediastinum, encasing mediastinal vascular structures such as the left brachiocephalic venous trunk (Fig.1). In the upper half of the right pulmonary hilum, a second smaller solid mass compresses the right pulmonary artery and the superior vena cava (Fig.2). Collateral circulation was well documented, involving the mediastinum, the chest wall, and vertebral venous plexus (Fig.3).

The mass was biopsied, proving its malignant origin with the diagnosis of small cell lung cancer.

In addition to the findings mentioned above, the authors found, at the arterial phase of this study, multilevel high attenuation nodular images in different vertebral bodies from C7 to T4 (Fig. 4), raising the hypothesis of osteoblastic bone metastases. These "lesions" disappeared in the delayed phase images of the exam (Fig. 5), making it one of the most compelling aspects of this case.

Background

Enhancement of the vertebral body marrow may be depicted due to retrograde collateral venous blood flow through the vertebral venous plexus in the setting of thoracic central venous obstruction. 

These pseudolesions may simulate osteoblastic lesions and can be mistaken for bone metastases, especially in the setting of known malignancy elsewhere. This phenomenon has been described in only a limited number of articles [1-6] and is presented and reviewed here.

Some authors refer to these pseudolesions as "vanishing bone metastases" [2, 3], others as "pseudopathologic vertebral body enhancement" [5, 6], a less misleading term that better describes the underlying pathophysiology since there are no true metastases in this entity.

The term "vanishing bone lesions" should not be mistaken for "vanishing bone disease" (Gorham-Stout syndrome) a rare entity characterized by destruction of osseous matrix and proliferation of vascular structures, resulting in destruction and absorption of bone [7].

Clinical and imaging perspective

Knowledge of thoracic venous anatomy is paramount to understanding this pattern of vertebral body enhancement and distinguishing it from other, more severe, causes.

In the setting of thoracic central venous obstruction, namely obstruction of superior vena cava or the right or left brachiocephalic venous trunks, blood flow diverts through several collateral pathways, including the internal mammary, lateral thoracic, vertebral venous plexus and azygos pathways [1]. The vertebral venous plexus forms a complex network with a vast array of internal collaterals bridging the anterior and posterior aspects of the plexus through the vertebral body (Fig. 6) [2].

Although the exact mechanism of this enhancement pattern in the vertebral body is not fully understood, elevated venous pressure inducing retrograde blood flow through the vertebral venous plexus with reflux of contrast medium into the intravertebral venous system is thought to contribute to the pseudolesions appearance in the vertebral bodies of patients with thoracic central venous obstruction [1].

In doubtful situations, a follow-up CT (unenhanced or with contrast injection through the contralateral arm or leg), magnetic resonance imaging (MRI), ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET)-CT or bone scan, demonstrating a normal appearance of the involved vertebral bodies, can confirm the benign nature of these pseudolesions [5].

Conclusion

Vertebral body pseudopathological enhancement due to collateral blood flow through the vertebral venous plexus is an increasingly recognized pitfall in interpreting contrast-enhanced CT from patients with thoracic venous obstruction. Recognizing this situation may prevent the misdiagnosis of bone metastases in circumstances similar to our case.