Pleural effusion: This is often the most common cause of a slightly elevated hemidiaphragm. Fluid accumulation in the pleural space can push the diaphragm upwards, and even a small amount of fluid can cause noticeable elevation on imaging.

Atelectasis: Collapse or partial collapse of the lung tissue can cause the diaphragm to appear elevated due to the reduced lung volume.
Diaphragmatic eventration: A condition where there is an abnormal elevation of part or all of the diaphragm due to thinning or weakness, which can be congenital or acquired.
Pneumonia or lung infection: Inflammation and consolidation of lung tissue can lead to volume loss and apparent elevation of the diaphragm.

Pulmonary embolism: Although less directly related to diaphragmatic elevation, a pulmonary embolism can lead to areas of lung infarction and atelectasis, potentially causing an elevated hemidiaphragm. It's critical to consider this diagnosis due to its high mortality if untreated.
Malignancy: Tumors, either primary in the lung or metastatic, can cause local destruction and volume loss, leading to diaphragmatic elevation. Early detection is crucial for treatment and prognosis.

Diaphragmatic paralysis: Unilateral paralysis of the diaphragm can result from various causes, including trauma, neurological conditions, or surgical complications, leading to an elevated hemidiaphragm on the affected side.
Subphrenic abscess: A collection of pus beneath the diaphragm, often as a complication of abdominal surgery or infection, can push the diaphragm upwards.
Hepatomegaly or splenomegaly: Enlargement of the liver or spleen can push the diaphragm upwards, although this would typically be associated with other clinical findings and might not result in a "slightly" elevated hemidiaphragm.