Q. Is it possible to see lung cancer in CAT scan if pleural effusion is present?

Answered by
Dr. Chitrangada
and medically reviewed by iCliniq medical review team.
This is a premium question & answer published on Oct 27, 2018

Hello doctor,

How likely is a CAT scan to show a lung cancer if a pleural effusion is present? My husband has a pleural effusion and has had four CT scans, none of which show any suspicious mass. Cytology records are inconclusive. I am wondering if the presence of the pleural effusion limits the visibility of a potential tumor? What about in the presence of a middle lobe collapse, could that be hiding a tumor? He has right side pain, short of breath, and was admitted to hospital and fluid drained.



Welcome to

Detection of tumor on CAT (computed tomography) scan has nearly 85 to 90 percent efficacy which further increases to 95 percent in post-contrast studies. The pleasurable effusion can be due to numerous causes and in your case due to mucous plugging causing lung lobe collapse-tumor need to be the cause always so do not be apprehensive about that. Any heterogenous abnormal enhancement can be a tumor seen in contrast scan which is not present in your scan.

Thank you doctor,

But is it possible a tumor is there and not visible due to the pleural fluid and lung collapse?



Welcome back to

On CT, we see structures based on their densities. So pleural fluid will have less density than a mass and will be dark whereas a mass or tumor will be more solid and will appear relatively bright even on plain scans and with a contrast, it will become brighter. So, it is highly unlikely to be missed. Take care and if possible, do upload the scans. I can review them for you if you want.

Thank you doctor,

Can you help me understand whether or not a tumor or mass can be identified if it is in the area of the lung that has collapsed? My husband has a near complete right middle lobe collapse. If there were a tumor in that area of the long, with CAT scan can it be seen?



Welcome back to

Any tumor develops abnormal vessels with leaky channels, therefore, it enhances abnormally on contrast CT scan and is hence detected even in a collapsed lung. Therefore, it is easily detected. Take care.

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