Hi thanks for contacting HCM... Normally lungs are transparent in chest x ray as alveoli filled by air.... So whenever obstructing of filled alveoli with blood , pus or opaque fluid transparency lost and density seen in that area.... As your mother having history of injury , so it could be blood accumulation at injured site leading hematoma formation.... Clinicallly correlation is necessary ... If fever , cough like symptom present then lung parenchyma infection could be there... For hematoma conservating management done ... If large and needed then aspiration done .. Ibuprofen drug needed.... Consult pulmonologist for your clinical examination ... Take care