Brief Answer: It is not an illness in itself but a sign Detailed Answer: HI, thanks for using healthcare magic Opacity means that there is an area that is darker than the other aspects of the lungs and streaking refers to the nature of the darker area- a streak is a line or mark. Therefore dark mark or line noted in the lung. This in itself is not a condition but a symptom of an underlying issue. Many lung conditions such as the pneumonia you were recently treated for can cause this dark area. It can occur both as a result the persisting infection or as a result of scar tissue formed in the lungs due to the infection. Your doctor would be able to determine which is the case through your history (if you are still unwell then it is persisting infection but if your symptoms have resolved then more likely scar tissue), examination and looking at any previous xrays to compare them for changes. Summary- streaky opacity means dark line or mark in the lung I hope this helps, feel free to ask any other questions

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