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Many patterns of cartilage signal anomalies have been described in the knee since the advent of magnetic resonance imaging (MRI). With the now widespread use of preoperative MRI, some of these anomalies have proven to represent true pathology, while others have been shown to be normal variants or artifacts at arthroscopy. We describe three patients with an MR cartilage abnormality, not previously illustrated in the literature, consisting of a thin dark signal line on T2-weighted imaging, oriented perpendicular to the plane of imaging. This aberration proved to represent a deep cartilage cleft at arthroscopy (two patients) and at CT arthrography (one patient). Such full thickness fissures are generally considered to have the opposite appearance, that of fluid signal intensity on T2-weighted images.

Enhanced MRI significantly altered clinical management in 50% of these patients with RA or suspected RA. Therefore, when the clinical picture in a patient with RA or suspected RA is unclear, enhanced MRI can provide useful guidance for treatment modifications.

Isolated fluid is greater than 7 times more common on outpatient pelvic MRIs in males younger than 30 years compared with men older than 49 years. Fluid rarely exceeded 10 mL or 6 cm(2).