ganglion cysts are filled with gelatinous and viscous fluid in the neighbourhood of joints or tendon sheaths . they are frequently seen at joints and tendons of the wrist but are rare in the region of knee joint . the most common cysts in the knee region are popliteal also called baker s cysts . there are theories , which describe an increased demand of the joint as a cause for these cysts . however , traumatic events are also discussed to be a cause for occurrence of these lesions . a rare case of an extensive ganglion cyst with a length of 18 cm of the anterolateral thigh with connection to the knee joint is presented and discussed . a 54-year - old man presented palpable swelling in the anterolateral region of his right thigh causing a sense of fullness and tightness for 15 months . he had an accident with his bicycle 21 months ago without signs of injury on the initial medical examination . magnetic resonance imaging ( mri ) of the thigh and knee showed a non contrast - enhancing lesion , which appeared hyperintense in the t2-sequences inside the right quadriceps femoris muscle between vastus lateralis and intermedius with connection to the recessus suprapatellaris ( figure 1 ) . in the quadriceps femoris tendon adjacent to the knee joint , a small traumatic injury of the tendon could be detected ( figure 2 ) . figure 1preoperative magnetic resonance imaging ; t2-weighted coronal plane ( left picture ) of the right thigh and knee show an extensive t2-hyperintense lesion inside the right quadriceps femoris muscle . axial magnetic resonance imaging of the right thigh ( right picture ) shows the ganglion cyst with a septum membrane inside the cyst . preoperative magnetic resonance imaging ; t2-weighted coronal plane ( left picture ) of the right thigh and knee show an extensive t2-hyperintense lesion inside the right quadriceps femoris muscle . axial magnetic resonance imaging of the right thigh ( right picture ) shows the ganglion cyst with a septum membrane inside the cyst . figure 2preoperative magnetic resonance imaging of the right ( r ) and left ( l ) thigh ( axial plane ) detects traumatic lesion in the right quadriceps femoris tendon ( red arrow ) adjacent to the knee joint . please note the difference to the normal tendon on the left side ( blue dotted arrow ) , which appears as a hypointense curved structure similar to an eyebrow . preoperative magnetic resonance imaging of the right ( r ) and left ( l ) thigh ( axial plane ) detects traumatic lesion in the right quadriceps femoris tendon ( red arrow ) adjacent to the knee joint . please note the difference to the normal tendon on the left side ( blue dotted arrow ) , which appears as a hypointense curved structure similar to an eyebrow . the lesion was 18 cm long and was excised completely by dissecting it from the muscle in microsurgical technique ( figure 3 ) . the connection between the lesion and the knee joint could be demonstrated intraoperatively and was excised as well . the lesion was filled with a gelatinous and viscous fluid , which seemed to be under moderate pressure ( figure 3 ) . figure 3intraoperative picture showing the ganglion cyst inside the right thigh with a length of 18 cm . the cyst was inside the quadriceps femoris muscle between vastus lateralis and intermedius and was excised completely under general anaesthesia . intraoperative picture showing the ganglion cyst inside the right thigh with a length of 18 cm . the cyst was inside the quadriceps femoris muscle between vastus lateralis and intermedius and was excised completely under general anaesthesia . cysts in this region are usually meniscal or popliteal cysts also called baker s cyst baker 's cysts are located between the tendon of the medial head of the gastrocnemius muscle and the semimembranosus muscle behind the knee joint . these cysts arise almost from any form of knee joint swelling such as arthritis or meniscal tears . ganglion cysts are usually not associated with arthritis or meniscal tears and can occur in variable locations . particularly , a cyst of 18 cm in length , as described in our case , has not been reported yet . benign cysts like ganglion cysts can be very well detected on mri as t2 weighted hyperintense defined lesions without contrast enhancement . a septum membrane inside the cyst visualized with mri should be considered as a confirmation of the diagnosis . ganglion cysts may have a definable connection to the joint , which can be visualized well on mri . however , the detection of joint connection is not possible in all cases . the connection to a joint seems however to be the most important mechanism for the development of ganglion cysts . the degree of intraarticular pressure is an important factor as well , which causes the enlargement of the ganglion cyst . it is important to identify the connection to the joint and to remove it as well as the ganglion cyst itself . in addition , the relationship to the knee joint is important in order to evaluate the presence of 
 associated intraarticular diseases . the decision for surgery should be considered in symptomatic cases or if the patient because of cosmetic reasons wishes it . the cause of ganglion cysts is unknown . in our case , the palpable lesions occurred months after a bicycle accident , in which the knee was injured . an injury of the tendon of the quadriceps muscle in the near of the knee joint caused by the trauma could be demonstrated on mri ( figure 2 ) . therefore , traumatic genesis can be an important factor for cyst formation , even in cases with bagatelle trauma . the development of ganglion cysts as a result of trauma should find more attention and should be taken into consideration in the differential diagnosis . in many cases , patients with ganglion cysts report that the joints related to them are under an increased amount of demand . this increased demand may cause micro - traumas in the tendons of muscles , which can trigger the cyst formation . the connection to the joint , which may be degenerative in addition , may lead to entry of synovial fluid from the joint into the tendons and within the muscles or other structures . the intraarticular pressure and a valve mechanism may play a role in the development and extension of these cysts . the relationship to the joint is important for surgery and for evaluation of the joint for the presence of associated intra - articular diseases .
a rare case of a posttraumatic extensive ganglion cyst of the anterolateral thigh with connection to the knee joint is presented . 
 a 54-year - old man presented a palpable mass in the anterolateral region of his right thigh with a 15 months existing sense of fullness and tightness . 
 he had an accident with his bicycle 21 months ago . 
 magnetic resonance imaging ( mri ) was performed showing a cyst inside the quadriceps femoris muscle between vastus lateralis and intermedius with connection to recessus suprapatellaris and knee joint . 
 in addition mri detected a traumatic lesion in the quadriceps femoris tendon in the near of the knee joint . 
 the ganglion cyst was 18 cm long and was excised completely . 
 intraoperatively , the knee joint connection was confirmed and excised as well . 
 the ganglion cyst was filled with a gelatinous and viscous fluid .