IS Case 275: Popliteal (Baker's) cyst

Jacinto Camarena III, MD

Imaging Sciences URMC 2009
Publication Date: 2009-07-29


Patient is an 84-year-old female who presented with knee pain status post fall.


Axial CT of the knee demonstrated a moderate sized suprapatellar effusion and a posterior fluid density collection extending between the tendons of the medial head of the gastrocnemius and semimembranosus muscles (Fig. 1).


Popliteal (Baker's) cyst


Popliteal cysts, known as Baker’s cysts, usually represent the gastrocnemiosemimembranosus bursa communicating with the posterior knee joint. A posteromedial fluid containing structure with a neck positioned between the tendons of the semimembranosus and medial gastrocnemius muscles is pathognomonic. Baker’s cysts are usually found incidentally in adult patients being evaluated with MRI. The majority are associated with at least one intraarticular abnormality that probably promotes development, such as osteoarthritis, internal derangement, trauma or other arthridites. The associated joint effusion and resultant elevated joint pressure may progress to dissection posteriorly and eventual communication with the bursa. Subsequent enlargement and extension in any direction is possible although, more common inferiorly or medially. Patients are frequently asymptomatic until they spontaneously rupture (usually when large), become infected, hemorrhage or cause symptoms from mass effect on adjacent structures.

In children, Baker’s cysts are commonly self-limited and infrequently communicate with the knee joint or are associated with intraarticular abnormalities.

Differential considerations may include ganglion cysts, popliteal aneurysms, pes anserine bursitis, tibial lateral collateral ligament bursitis, and meniscal or cruciate ligament cysts; however, none of these are positioned between the medial head of the gastrocnemius and semimembranosus tendons. Recognition of a solid component may indicate the presence of a synovial tumor.


  1. Torreggiani WC, Al-Ismail K, Munk PL, et al. The imaging spectrum of Baker's (Popliteal) cysts. Clin Radiol. 2002 Aug;57(8):681-91. PMID: 12169279 [PubMed]
  2. Ward EE, Jacobson JA, Fessell DP, Hayes CW, van Holsbeeck M. Sonographic detection of Baker's cysts: comparison with MR imaging. AJR Am J Roentgenol. 2001 Feb;176(2):373-80. PMID: 11159077 [PubMed]

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