Imaging findings of acute calcific periarthritis, with emphasis on magnetic resonance imaging: pictorial essay.

Acute calcific periarthritis (ACP) is defined as periarticular inflammation associated with intra-articular deposits of hydroxyapatite and other basic calcium phosphate crystals. Patients with ACP present with a sudden onset of pain, together with localized swelling, as well as erythema, tenderness, and reduced range of motion. Familiarity with the clinical and radiological manifestations of ACP aids in the diagnosis and helps differentiate it from other conditions, particularly infectious or inflammatory pathologies such as septic arthritis and gout, thereby reducing the number of unnecessary diagnostic and therapeutic procedures. The objective of this pictorial essay is to illustrate the imaging findings of ACP in various joints, with an emphasis on the findings obtained by magnetic resonance imaging.