MRI of posterior knee masses.

A wide variety of masses may be visualized in the posterior knee. Some are encountered incidentally on MRI obtained for seemingly unrelated symptoms; others are palpable and present for MRI characterization. We describe the appearance, significance and pathophysiology of some of the most common lesions found in the popliteal fossa as well as several of the less common entities we have encountered. Thorough understanding of the appearance and location of the more specific masses should augment precise diagnosis in a majority of cases. In turn, this will eliminate unnecessary additional investigations and enable prompt and appropriate treatment.

Meniscal ossicle: radiographic and MR imaging findings.

PURPOSE: To determine the magnetic resonance (MR) imaging appearance of meniscal ossicles and correlate that with the radiographic and clinical features. MATERIALS AND METHODS: Radiographs and MR images were studied retrospectively in six patients with meniscal ossicles; all patients had intermittent discomfort in the knee, and five patients had experienced knee trauma. Imaging findings were correlated with the clinical history. Four patients underwent arthroscopy. RESULTS: All patients had a visible ossicle on conventional radiographs initially interpreted as a loose joint body. MR imaging features included a corticated marrow-containing structure within the substance of the medial meniscus near the tibial attachment that appeared as a rounded focus of increased signal intensity on T1-weighted images that decreased in signal intensity on T2-weighted images. CONCLUSION: Meniscal ossicles have a characteristic MR appearance that may help distinguish them from loose bodies. They should be considered diagnostically when a circumscribed ossification is identified near the posterior horn of the medial meniscus on radiographs.