PET-CT Findings. Effusion in the report?

My sister's latest PET-CT scan reports :- Comparisons made with prior PET-CT scan dated 6th May 2024: No abnormal uptake of FDG in the body (either focal or diffuse). The uptake and distribution of FDG in the body are explained on physiological grounds alone. Post right mastectomy status with no abnormal metabolic activity or wall thickness suggestive of recurrence. Prior noted low-grade FDG avid fibro reticular changes in the middle lobe & anterior segment of the upper lobe of the right lung persist. Prior noted non-FDG avid nodule at the apex of the right lung is not seen in the present study.Interval appearance of bilateral pleural effusion is seen. The prior noted non-FDG avid hypodense area in segment VII of the liver remains unchanged, measuring about 8x9 mm in size. What is meant by bilateral eural effusion in the report? When asked, the oncologist told us that it was due to the side effect of the treatment (chemotherapy) given and it is not a major concern.