Benign cysts and cystic-appearing lesions in and around the knee are common and differentiation between them through the history, symptoms and clinical examination is difficult due to the presence of common findings such as pain, edema, and palpable mass. The clinical presentation depends on the location, size of the lesion and its relation with the surrounding structures.

The Benign knee cysts can be subdivided into four major categories as following:1- synovial cysts, 2- popliteal (Baker's) cyst, 3- ganglion cysts, 4- meniscal cysts. Whereas, The "cyst-like" lesions can be sub-classified into the following:1- normal knee bursae, 2- normal knee recesses, 3- miscellaneous cyst-like lesions as aneurysms, hematomas, seromas and abscess.

Many of these lesions have fairly characteristic locations and imaging features. Knowledge of these variants and lesions is essential for accurate diagnosis and to avoid mistaking them for aggressive soft tissue lesions, including sarcomas. Ultrasonography and magnetic resonance imaging are the most useful imaging modalities in evaluating these Benign cystic lesions. Ultrasonography can distinguish cysts from solid lesions and assess the degree of vascularity within the lesion. Magnetic resonance imaging can help to delineate the location of the lesion in relation to anatomic structures and also determine if the lesion is cystic or solid when contrast is administered.

Inclusion Criteria:

1. clinically diagnosed cystic lesions in and around the knee.

Exclusion Criteria:

1. arthroscopy or surgical intervention to the knee joint.
2. fracture repaired by metal plates or screws.
3. claustrophobia.
4. contraindications to MRI as patients with implanted pacemaker or defibrillator, ferromagnetic aneurysm clips and metallic foreign body at the knee joint.

- Patients in different age groups referred to Radiology department at Assiut University Hospital with clinically suspected benign cystic lesions in and around the knee.