- 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 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);
- references"
- 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.
-
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
gastrocnemiussto
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;
- 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;;
- 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
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;
