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Painful knee

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Q1: What are features seen on MRI (see p 556)?

The T2-weighted coronal image shows a well defined oval shaped, homogenous, multiseptated high signal intensity lesion adjacent to the lateral margin of the lateral meniscus. The lesion is lying deep to the iliotibial tract.

Q2: What are the differential diagnoses?

The differential diagnoses include lateral meniscus cyst, pes anserinus bursitis, bursitis of the lateral collateral ligament, and lateral meniscus injury.

Q3: What is the diagnosis?

The fluid filled multiseptated cystic lesion-like appearance on the MRI is consistent with a left anterolateral multiseptated parameniscal cyst arising from the lateral meniscus. T1-weighted images confirmed the same.

Q4: What is the frequently associated finding with this condition?

Lateral meniscus cysts are usually associated with horizontal cleavage tears of the meniscus.

Q5: How should the condition be managed?

Asymptomatic meniscal cyst can be treated non-operatively. Symptomatic cysts need partial menisectomy along with decompression of the cyst either arthroscopically or by an open method.

Discussion

This young woman was suspected of having a meniscal cyst and hence had the MRI investigation. The T2-weighted coronal images (shown in fig 1; see p 556) clearly demonstrated the fluid filled multiseptated cystic lesion arising from the rim of the meniscal attachment. She underwent arthroscopic treatment to her left knee. Arthroscopy revealed a horizontal cleavage tear of the lateral meniscus, which was trimmed along with decompression of the cyst. At three months of follow up she is completely pain free.

Meniscus cysts are quite rare and the reported incidence in the literature varies from 0.3% to 7% of meniscal lesions in general.1,2 The main associated feature is the horizontal cleavage tear of the meniscus, which acts like a flap valve during knee movements. The aetiopathogenesis is unclear, however a male predominance is noted and it is seen in a wide age group. Meniscus cysts are also seen sometimes in patients with discoid meniscus. The typical feature is a palpable cystic mass along the joint line associated with pain, which characteristically becomes more prominent at 15 to 30 degrees of flexion and disappears at full extension and flexion greater than 90 degrees. Plain radiographs are usually normal and MRI is diagnostic.

Final diagnosis

Lateral meniscus cyst.

References

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