Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography in a rare case of carcinoma stomach with concomitant silicosis.

The role of fluorine-18 fluorodeoxyglucose. (18F-FDG) positron emission tomography. (PET)/computed tomography. (CT) in the initial staging of various malignancies is now well established. However, nonspecificity of FDG occasionally results in tracer uptake in benign lung lesions. The authors describe a complicated case of carcinoma stomach with multiple nodules and a cavitary lesion in lungs where 18F-FDG PET CT done for initial staging revealed FDG avid mass in stomach, FDG avid multiple mediastinal lymph nodes and multiple intensely FDG avid bilateral lung lesions. The FDG avid lung lesions turned out to be due to silicosis as confirmed by histopathology.

INTRODUCTION

The role of 18F-FDG PET/CT in initial staging of gastric carcinoma is well studied. It is also well known that findings on 18F-FDG PET/CT scan needs to be interpreted correlating with the clinical history and findings of adjunct investigations. We describe a rare case of gastric carcinoma with concomitant silicosis resulting in unusual lung findings in 18F-FDG PET/CT scan.

CASE REPORT

A 48-year-old man presented with persistent dyspnea and melena. An upper gastrointestinal endoscopy revealed a mass lesion in the antrum of stomach, which on biopsy proved to be a well-differentiated adenocarcinoma. The patient was a nonsmoker, however, an occupational history of exposure to silica dust was present. Past history of pulmonary tuberculosis 20 years back which was treated with a complete course of anti-tubercular medications could be noted. Fluorine-18 fluorodeoxyglucose (18F-FDG) positron emission tomography (PET)/computed tomography (CT) scan was done for initial staging of gastric carcinoma. 18F-FDG PET/CT scan revealed intense FDG uptake in the mass lesion in the antrum of the stomach [Figure 1a–c]. No abnormal FDG avid abdominal lymph nodes were noted however a few FDG nonavid regional lymph nodes were noted. Intensely FDG avid thick walled cavitary lesion in the right lung upper lobe [Figure 1d] with multiple intensely FDG avid parenchymal and pleural-based nodules were noted in both the lung fields [Figure 1f], largest measuring 2.8 cm × 2.7 cm in the left lower lobe. FDG avid right supraclavicular [Figure 1g] and multiple mediastinal lymph nodes were also noted [Figure 1e]. The possibility of a second primary in the lung with lymph nodal and lung metastases was also considered as carcinoma stomach with such extensive lung metastases in the absence of regional lymph node involvement is very unusual. Bronchoscopy-guided biopsy of the mediastinal lesions was done which revealed changes suggestive of silicosis. CT-guided fine needle cytology of the largest peripheral lung nodule also revealed features suggestive of silicosis.

Figure 1

Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography scan for initial staging of gastric carcinoma. (a) Abnormal tracer concentration in the stomach, mediastinum and bilateral lungs. (b) Intense fluorodeoxyglucose uptake in the mass lesion in the antrum of the stomach. (c) Mass lesion in the antrum of the stomach on computed tomography. (d) Intensely fluorodeoxyglucose avid thick walled cavitary lesion in the right lung upper lobe. (e) Calcified mediastinal lymph node (red arrow). (f) Multiple intensely fluorodeoxyglucose avid parenchymal and pleural-based nodules. (g) Fluorodeoxyglucose avid right supraclavicular lymph node (blue arrow)

DISCUSSION

Silicosis is a form of pneumoconiosis, and an occupational disease associated with occupations such as mining, quarrying, and tunneling caused by the inhalation of fine particles of crystalline silicon dioxide.[12] Silicosis occurs in two clinical forms - simple silicosis, radiologically defined by a pattern of small and round or irregular opacities, whereas complicated silicosis, or progressive massive fibrosis, is characterized by large conglomerate opacities. The CT features of progressive massive fibrosis include focal soft-tissue masses, often with irregular or ill-defined margins and calcifications, surrounded by areas of emphysematous change.[34] Cavitation in the mass lesion may occur secondary to ischemic necrosis,[5] which was noted in this case too. The list of differentials of cavitary lung nodules is quite exhaustive including neoplasms such as primary bronchogenic carcinoma, metastatic disease; bacterial infections (Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas); granulomatous (endemic fungi, mycobacterial, Nocardia); parasitic (Paragonimus, Echinococcus); inflammatory granulomatosis with polyangitis, langerhans cell histiocytosis, rheumatoid arthritis or sarcoidosis; vascular pulmonary embolism with infarction; pneumoconioses; (berylliosis, Caplan syndrome, coal-worker's lung, silicosis); adverse effects of drugs such as amiodarone, infliximab, bleomycin, carbamazepine, and amyloidosis.[6] Carcinoma and tuberculosis are potential serious complications of silicosis which are often characterized by an acute worsening of symptoms.[7] The role of 18F-FDG PET/CT in initial staging of gastric carcinomas is well studied.[8] Extensive search of literature did not reveal any reported case of isolated lung metastases from gastric carcinomas. The ability of 18F-FDG PET/CT in identifying the lung cancer focus developing in the background of pneumoconiosis is restricted to a few case reports.[91011] However, there were reported cases of false positive FDG uptake in cases of some forms of pneumoconiosis including silicosis[12131415] which makes the clinical conversion of findings on 18F-FDG PET/CT scan difficult. Our case reiterates the importance of establishing clinical correlation of the lung findings on 18F-FDG PET/CT scan including occupational history, which helps in establishing the nature of the lung findings.

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Conflicts of interest

There are no conflicts of interest.