Carpal bone cysts: MRI, gross pathology, and histology correlation in cadavers.

PURPOSE Intraosseous cysts of carpal bones are frequently observed on routine imaging examinations of the wrist. There is controversy regarding the underlying pathogenesis of these cysts. In this study, we aimed to investigate the magnetic resonance imaging (MRI) appearance of intracarpal bone cysts in correlation with histologic analysis, using cadaveric wrists. METHODS Five freshly frozen cadaveric wrist specimens (from three women and two men; mean age at death, 80 years) were studied. Imaging was performed with T1-weighted fast spin-echo, and proton density-weighted fast spin-echo with and without fat-suppression. The existence of cysts was confirmed by comparing MRI and histology findings. Hematoxylin and eosin stain was performed on tissue slices of 3 mm thickness to analyze the structure of cysts and their communication with the joint cavity. RESULTS Ten cysts were observed. In all cases, cysts were eccentrically located either in the subchondral bone or beneath the cortex. On histologic examination, there were regions of fat necrosis without inflammation or increased vascularity, surrounded by fibrous walls. There were no giant cells, cholesterol granules, or a true synovial lining. Mucoid change was rare. Fibrous component of cysts varied from small fibrous septa to well-formed walls. Some cysts communicated with the joint cavity. Two cysts were adjacent to ligamentous attachments. Those cysts with fibrous tissue demonstrated variable hypointensity on T2. CONCLUSION In contrast to previous reports that described a mucoid composition of intracarpal bone cysts with occasional foamy macrophages, our observations support the concept that these lesions reflect a spectrum of fat necrosis and fibrous changes, without inflammation or hypervascularity. These cysts are typically surrounded by fibrous walls without a true synovial lining.