Table 1 Differential diagnosis for cystic lesions in and around the popliteal fossa
From: Lymphangioma of popliteal fossa masquerading as Baker’s cyst
Ganglion cyst | Baker’s cyst | Parameniscal cyst | Lymphangioma | |
|---|---|---|---|---|
Age predominance | Adults | 4–7 years/35–70 years | Adults | Paediatric |
Related structures | Joint-related ligament and tendon | Gastrocnemius semimenbranosus bursa | Meniscocapsular junction | Intermuscular plane |
Knee joint extension/association | ± | + | + | − |
Ultrasound | Well-defined anechoic to hypoechoic lesion with few internal septae | Well-defined anechoic cyst extending to the joint space. ‘Speech bubble’ sign Internal echoes can be seen if infected | Anechoic to hypoechoic cyst with a tear in the adjacent meniscus | Multiloculated cystic lesion with thin septations mostly anechoic but can have internal echoes when associated with infection or haemorrhage |
MRI | T1 hypointense and T2 hyperintense cystic lesion ± few thin internal septations +/ peripheral post-contrast enhancement | T1 hypointense and T2 hyperintense cystic lesion extending from the joint space No post-contrast enhancement | T2 hyperintense cyst communicating with a tear in the adjacent meniscus No post-contrast enhancement | T1 hypointense and T2 hyperintense multiloculated cystic lesion away from the joint Peripheral and septal enhancement + |
Histopathology | Thin connective tissue capsule without synovial lining | Synovial tissue lining with fibrous component | Lined by synoviocytes, collagen and fibroelastic cartilage | Macroscopic multiseptated lymphatic spaces |