Giant Late-relapse Pulmonary Metastasis of Osteosarcoma

An 8-year-old boy presented with a chief complaint of cough, haemoptysis, shortness of breath and weight loss over 2 months. His medical history revealed a previous treatment for osteosarcoma of the left femur nearly 2 years ago at the same hospital [Figure 1d]. He underwent neoadjuvant chemotherapy and surgery, including a wide local excision of the tumour and Extracorporeal radiation therapy. On presentation, a chest radiograph showed a large radiopacity in the right lung, affecting the upper/middle zones and obscuring the mediastinum. A subsequent chest computed tomography (CT) scan revealed a large, irregularly enhancing lobulated mass with internal calcification in the right parahilar region, extending into the posterior segment of the right upper, middle and lower lobe. It was contiguous with necrotic conglomerated heterogeneously enhancing mediastinal and right hilar lymph nodal mass [Figure 1a-c]. The clinical and radiological assessment led to the diagnosis of a giant late-relapse pulmonary metastasis of osteosarcoma.Figure 1: (a) Chest radiograph at the time of presentation showed a large radiopacity in the right lung, affecting the upper/middle zones and obscuring the mediastinum; (b and c) A subsequent chest computed tomography scan revealed a large, irregularly enhancing lobulated mass with internal calcification in the right parahilar region, extending into the posterior segment of the right upper, middle and lower lobe contiguous with necrotic conglomerated heterogeneously enhancing mediastinal and right hilar lymph nodal mass; (d) Radiograph of left femur acquired 23 months prior shows an aggressive tumor in left femoral diaphysis with osseous matrix and spiculated perisoteal reaction suggestive of osteosarcomaOsteosarcoma is the most prevalent primary bone tumour in the paediatric age group, typically metastasising haematogenously, predominantly and early to the lungs. Timely identification of lung metastases is crucial for effective treatment planning and prognosis determination. CT is considered the preferred imaging modality, typically revealing multiple rounded nodules of varying sizes, primarily in the lung bases and peripheral zones, while sparing the apices. However, atypical presentations, like giant metastases replacing the entire lung parenchyma, can occur.[1] Surgical intervention and chemotherapy significantly enhance patient survival. Despite optimal treatment, some cases experience recurrence, often in the lungs, as observed in this case. Lesions vary in size, ranging from miliary nodules to cannonball masses, with a usual diameter of 3 cm or less. However, atypical presentations include giant metastases replacing the entire lung parenchyma, cavitation, haemorrhagic metastases, pneumothorax and tumour thrombi.[2,3] In addition, lung metastases in osteosarcoma may manifest long after the initial presentation, a phenomenon referred to as late-relapse metastasis.[4] The majority of relapses (95%) occur within the first 5 years following the initial diagnosis, with an average time to relapse of 1.6 years.[4] This implies a potential mechanism involving the reactivation of dormant metastatic cells. A significant portion of cancer cells, which have maintained viability in the target organ, enters a state of solitary, and following a variable period of dormancy, a small subset of these dormant cells undergo reactivation, leading to the development of metastatic outgrowths. Various studies propose that the processes of dormancy and reactivation are intricately governed by complex interactions between metastasis-initiating cells and the microenvironment of the target organ.[4] A comprehensive understanding of the clinical history of atypical metastatic features and behaviours is crucial for accurate diagnosis and timely intervention. Kaneuchi et al. documented an unusual instance of late-relapse metastasis in osteosarcoma, occurring 38 years after the initial presentation.[5] Silva et al. documented a peculiar case wherein a young male undergoing treatment for femoral osteosarcoma exhibited the presence of multiple atypical lung metastases.[6] Radiologists must be cognizant of the diverse radiographic appearances of both typical and atypical pulmonary metastases to differentiate metastatic disease from synchronous primary lung cancer and benign lung conditions. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.