Recurrent Cavitary Pulmonary Metastasis from Osteosarcoma: Findings on ¹⁸F-Fluorodeoxyglucose Positron Emission Tomography

A 20-year-old male, known case of osteosarcoma left tibia, postwide excision, and endoprosthetic reconstruction underwent a contrast-enhanced computed tomography (CECT) chest scan after 1 year of surgery as a part of routine follow-up. CECT of the chest revealed an ovoid cavitating lesion measuring ~ 5.3 cm × 4.3 cm in the left lung in apicoposterior and superior segments. To rule out any other metastatic sites, ¹⁸F-fluorodeoxyglucose positron emission tomography-computed tomography (¹⁸F-FDG PET-CT) scan was advised by the referring oncologist. PET-CT scan revealed the same pulmonary lesion with intense FDG uptake [Figure 1a-g]. Histopathology from the lung lesion suggested metastasis from the osteosarcoma.

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Figure 1 (a) Maximum intensity projection image of ¹⁸F-fluorodeoxyglucose positron emission tomography-computed tomography showing a rounded area of heterogenous fluorodeoxyglucose uptake in the left chest region (black arrow). (b) Axial computed tomography thorax (soft tissue window) image showing cavitary lesion in the left lung showing increased fluorodeoxyglucose uptake in the fused positron emission tomography-computed tomography image (c) (White arrows). (d) Axial computed tomography thorax (lung window) showing cavitary lesion with increased fluorodeoxyglucose uptake in the fused positron emission tomography-computed tomography image. (e) Coronal computed tomography thorax (lung window) showing cavitary lesion in the left lung with fluorodeoxyglucose uptake in the fused positron emission tomography-computed tomography image (f). saggital section fused PET-CT image showing increased FDG uptake in the cavitary lesion in the left lung (g)

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Cavitations occur in about 4% of cases with lung metastases and are most commonly seen with head and neck or lung carcinoma.[1] Very few case reports have elucidated the occurrence of cavitary lung metastasis secondary to osteosarcoma.[23] Although the exact cause of cavitation is not known, many hypotheses such as tumor necrosis due to the ischemia, infection and abscess formation, production of lipolytic and proteolytic enzymes by the secondaries, cornification at the center of squamous cell carcinomas, cystic degeneration in adenocarcinomas, and postchemotherapy have been put forward to explain cavitation in secondary lung metastasis.[145] Apart from primary lung cancers, cavitary pulmonary metastasis from various other primary malignancies such as the rectum, endometrium, cholangiocarcinoma, prostate, and neuroendocrine tumor have been described in the literature.[678910] Despite extensive search in the literature, the authors could not find the demonstration of FDG uptake in the metastatic cavitating lung lesion secondary to osteosarcoma. The authors, through this case, want to highlight the importance of FDG uptake in any such rare lesion in ascertaining the lesion as metastatic one, although final confirmation should always be done after histopathology evaluation. An added advantage of ¹⁸F-FDG PET-CT over CT scan is the detection of extrapulmonary metastasis if any in a single setting without subjecting the patient to additional radiation exposure emanating from the CT scan.