These cysts are different in children than in adults.
Diagnosis is usually not difficult. Most cysts are found by the parents through observation. The cysts are usually nontender, smooth, cystic to the touch, and located between the medial head of the gastrocnemius and the semitendinosis. Translumination demonstrates that the mass is a cyst. Ultrasound shows the lesion well, so that MRI is seldom necessary.
Management Reassure the family that the condition is benign and will resolve with time. If the family is still nervous, consider confirming the diagnosis by aspirating the cyst. Advise the family that the aspiration is only to confirm the diagnosis and not for treatment because the cyst will recur. Aspiration reassures the family that it is not cancer. Cysts resolve spontaneously over a period of several years. Resection is rarely indicated and is appropriate only for large painful cysts. Recurrence following resection is common.
Meniscal cysts are uncommon lesions that usually occur over the lateral aspect of the knee and may be associated with a meniscal tear. Image with ultrasound or by MRI. Manage cyst decompression, debridement, and partial menisectiomy or repair, depending on the associated meniscal tear pattern.
Hemangiomata These lesions infiltrate and thicken the synovium, making it subject to injury and bleeding. The diagnosis can be made by aspirating blood from the joint and confirming by biopsy done concurrently with a synovectomy. Warn the family that recurrence during growth is likely.
Lipoma These tumors are subcutaneous, soft, and often poorly defined. They may require removal if large.
Pigmental vilonodular synovitis This knee joint tumor is rare in children. It requires open or arthroscopic synovectomy.
Synovial chondromatosis This tumor is uncommon about the knee in children. It requires complete arthroscopic or open synovectomy.