Which type of pericarditis involves gradual onset and possible fluid accumulation?

Chronic pericarditis is characterized by a gradual onset and can indeed involve the accumulation of fluid in the pericardial space. This condition often develops over a longer period, sometimes following acute pericarditis but can also occur independently due to various underlying causes, such as autoimmune diseases, infections, or radiation therapy. The fluid accumulation in chronic pericarditis, when it occurs, typically manifests as pericardial effusion, which can lead to symptoms related to increased pressure in the thoracic cavity.

In contrast, acute pericarditis generally presents with a sudden onset, often accompanied by sharp chest pain and is usually associated with specific infectious processes or injuries. Myocarditis affects the heart muscle itself, rather than the pericardium, and does not typically involve the gradual fluid accumulation seen with chronic pericarditis. Endocarditis refers to inflammation of the inner lining of the heart chambers and valves, which is also unrelated to the pericardial fluid dynamics described in this question. Thus, chronic pericarditis is the correct selection as it aligns with the characteristics of gradual onset and potential fluid accumulation.