The value of lung ultrasound in the work up of pleural effusion (fluid in between the thin doublet layered film surrounding the lungs) is unknown. The researchers will perform a systematic lung ultrasound scan including a scan for extra thoracic metastasis (spread of cancer to other organs) in the lymphnodes of the neck and metastasis lever in 56 patients one-sided pleural effusion. The researchers will measure if the interventions change the diagnostic plan for the patient and leads to faster diagnostics of the underlying course.

Inclusion Criteria:

• Age ≥ 18 years.
• Unilateral pleural effusion of unknown course.
• Patients must be able to give informed consent.

Exclusion Criteria:

• Bilateral pleural effusions.
• Known cause of pleural effusions.
• Life expectancy <3 months.
• Inability to understand written or spoken Danish.

Patients referred to the Pleura Clinic (an outpatient clinic in the Department of Pulmonary Disease, Næstved Sygehus, on of two regional centers for work up of pulmonary malignancy ) from the general practitioner or from other hospital departments both Næstved Sygehus and other hospitals.