- Discussion:
- a type of cyst which results from egress of fluid through a normal communication of a bursa (semimembranosus or medial gastrocnemius bursa) or may be
caused by herniation of the synovial membrane through the joint capsule;
- symptoms develope most often in the bursa beneath the medial head of gastrocnemius or in the semimembranous bursa;
- later is a double bursa located between the semimembranosus tendon and the medial head of the gastrocnemius;
- Baker's cysts are usually located at or below the joint line, whereas cysts of semimembranous bursa are above the joint line;
-
diff dx: popliteal mass:
-
children:
- popliteal cysts (Baker's cysts) are common in children, occurring more often in boys & usually found in medial aspect of popliteal fossa.
- in children popliteal cyst infrequently communicates w/ joint and intraarticular pathology is rare;
- however, consider lipomas, xanthomas, vascular tumors, fibrosarcomas;
- (the popliteal cyst should transilluminate)
- if dx is in doubt, ultra-sound can distinguish between fluid-filled cyst and a solid tumor;
- radiographs should be studied for soft tissue calcification in the mass, which may indicated
synovial cell sarcoma or
hemangioma;
- in children, surgical excision of popliteal cysts is rarely indicated.
- most authors report spontaneous resolution of cysts in 10-20 months;
- therefore, a prolonged period of observation is strongly recommended before surgical excision is considered.
- in protracted cases, cysts may respond to aspiration and steroid injection, (note that unlike adults, the cyst may not be intra-articular and therefore
may respond to aspiration);
-
adults:
- in adults, intra-articular pathology is common, & cyst may recur if intra-articular pathology is not corrected;
- cysts are connected to the knee joint through valvular opening;
- presence of knee effusion (excessive fluid pressure), allows unidirectional egress of fluid through the valve and into the cyst;
- cyst is locacted between the semimembranosus tendon and the medial head of gastrocnemius tendon;
- if cyst lies in atypical location consider tumor (see
diff dx);
- reoccurrence of the cyst is common following surgical removal, and therefore treatment is directed toward intra-articular pathology;
-
meniscal tears:
- some popliteal cysts are caused by a lesion of the posterior third of the
medial meniscus;
- posterior horn meniscal tears which extend to capsule may cause a defect (1 way valve) to develop between joint cavity and gastro-semimembranosus bursa;
- cyst is usually located posteromedially & as it enlarges, it dissects plane between the gastrocnemius and underlying soleus.
- partial meniscectomy for tears will usually to resolution of cyst;
- in the report by V. Sansone MD and A. De Ponti MD, the authors treated 30 patients w/ Baker's cyst w/ mean followup of 32 months;
- arthroscopy demonstrated a connection between joint space and cyst in all patients;
- surgical goal involved removal of anatomic structures imposing the one-way passage of fluid from the joint space into the cyst;
- in 27 of 30 cases, there appeared an oval opening located between the body and the posterior horn that extended to the articular capsule;
- a blunt instrument could be easily introduced into the opening, and just a slight amount of pressure was needed to overcome the capsular plane;
- attempt to feel the point of the instrument under the skin, to the posteromedial site;
- all of the structures which obstructed the capsular orifice were removed (fibrous septa, bands, meniscus flaps);
- a motorized shaver is used to created a capsular opening of about 4 to 5 mm in diameter;
- 2 years after the treatment, good clinical results were seen in 95% of patients;
- ref: Arthroscopic Treatment of Popliteal Cyst and Associated Intra-articular Knee Disorders in Adults. Arthroscopy: Vol 15, No 4 (May-June), 1999: pp 368-372
- in absence of meniscal pathology, removal of cyst, closure of communication w/ joint, and suture of the medial head of
gastrocnemius to
posterior capsule can be performed in symptomatic individuals;
-
chondral injury:
- in the report by S. Rupp et al 2002, the authors prospective studied the prevalence of popliteal cysts and the associated intraarticular
lesions in a group of 100 patients wheo underwent knee arthrscopy;
- diagnosis of a popliteal cyst was made on the basis of ultrasonography;
- prevalence of popliteal cysts was 20% in the study group and 0% in the control group;
- patients with a popliteal cyst had a significantly higher prevalence of medial meniscal tears (70% versus 19%) and
of chondral lesions (85% versus 28%);
- tears of the lateral meniscus, however, were more evenly distributed (20% versus 36%);
- 16 of 20 patients with a popliteal cyst were available for a follow-up examination 1 to 3 years after the arthroscopic procedure.
- 11 popliteal cysts had persisted and chondral lesions were the most relevant prognostic factor;
- all patients with persisting cysts had grade III or grade IV lesions;
- the authors concluded that the popliteal cyst was a secondary phenomenon and that treatment should address the underlying intraarticular lesions;
- ref: Popliteal Cysts in Adults. Prevalence, Associated Intraarticular Lesions, and Results after Arthroscopic Treatment
Stefan Rupp, MD. The American Journal of Sports Medicine 30:112-115 (2002)
- giant synovial cysts of calf have been reported in pts w/
RA (long-standing RA synovitis of knee can cause popliteal cyst formation);
- rupture of the cyst results in dissection of synovial fluid distally into calf & can present in a manner similar to thrombophlebitis;
-
MRI Findings:
- fluid filled mass produces an intermediate signal on T1 proton density weighted image and high signal on T2 images;
- cyst should always lie medial to the lateral head of the gastrocnemius muscle;
On the formation of synovial cysts in the leg in connection with disease in the knee joint. WM Baker St. Bartholomew Hosp. Rep. Vol 13. p 245-246. 1877.
Ruptured Baker's cyst causes ecchymosis of the foot. A differential clinical sign.
MR imaging of Baker cysts: association with internal derangement, effusion, and degenerative arthropathy.
Popliteal cysts in children. Dinham JM: J Bone Joint Surg 1975;57B:69.
Baker's cyst in children: Is surgery necessary? MacMahon EB: J Bone Joint Surg 1973;55A:1131.
Popliteal cystoscopic excisional debridement and removal of capsular fold of valvular mechanism of large recurrent popliteal cyst
Proximal dissection of a popliteal cyst with sciatic nerve compression.
Arthroscopic treatment of popliteal cyst and associated intra-articular knee disorders in adults.
