they are usually encountered as incidental findings in magnetic resonance imaging ( mri ) , or in arthroscopy . they may originate from both the cruciate ligaments and the menisci , from the popliteus tendon and alar folds , infrapatellar fat pad of hoffa , and subchondral bone cysts . those arising from the hoffa s fat pad , usually present as palpable mass at anterior aspect of the knee joint . we report a case of intraarticular ganglion cyst of knee arising from the infrapatellar fat pad and protruding anterolaterally through retinacular rent into the subcutaneous plane . a 19-year - old young man , presented with a painless gradually increasing swelling at the anterior aspect of left knee of 9 months duration . mri scan revealed a multilobulated , cyst with septations within the anterior aspect of the knee joint , just inferolateral to the patella , with deep extension into the infrapatellar fat pad , and superficial extension into the subcutaneous space across the retinaculum . after diagnostic arthroscopy , we performed an open excision of the cystic mass and confirmed the retinacular rent pre - operatively . arthroscopic resection and debridement is the gold standard treatment in ganglion cyst of the knee . however , a subcutaneous extension may lead to incomplete arthroscopic resection : leaving behind the residual tissue which may cause recurrence . therefore , proper pre - operative evaluation of mr images of these cases is very important . a ganglion is a cystic tumor - like lesion of unknown etiology , surrounded by a dense network of connective tissue , filled with a gelatinous fluid containing hyaluronic acid and other mucopolysaccharides . intra - articular ganglion cysts of the knee joint are uncommon . they are usually encountered as incidental findings in magnetic resonance imaging ( mri ) , or in arthroscopic examination . they may originate from both the cruciate ligaments and the menisci , from the popliteus tendon and alar folds , infrapatellar fat pad of hoffa , and subchondral bone cysts . those arising from the hoffa s fat pad have been reported to present as palpable mass at anterior aspect of knee joint [ 2 - 5 ] ; however , to the best of our knowledge , none of them had subcutaneous communications across the retinaculum . we report a case of intra - articular ganglion cyst of knee arising from the infrapatellar fat pad and protruding anterolaterally through retinacular rent into the subcutaneous plane . a.a.m . , a 19-year - old young man , presented with a painless gradually increasing swelling at the anterior aspect of left knee for last 9 months . there was no history of trauma , local injections , instability , locking episodes , clicking , snapping , or any constitutional symptoms . clinical examination revealed a 2.5 cm x 2.5 cm round , soft , cystic , non - tender , irreducible swelling at anterolateral aspect of left knee 1.5 cm above the lateral joint line just lateral to the patellar tendon with discoloration of the overlying skin . it was partially mobile , not fixed to the extensor mechanism or overlying skin , and was more prominent in knee extension ( fig . 1 ) . he could squat and sit cross - legged without any discomfort with a normal range of movement . there was no effusion , no joint line tenderness , and no evidence of ligamentous laxity . pre - operative clinical pictures showing the ganglion cyst at anterolateral aspect of left knee in various degrees of knee flexion . mri scan revealed a multilobulated , cyst with septations within the anterior aspect of the knee joint , just inferolateral to the patella , with deep extension into the infrapatellar fat pad . ( a ) normal radiograph except increased soft tissue shadow , ( b ) parasagittal and axial mr images showing the ganglion cyst from infrapatellar fat pad extending subcutaneously across the retinaculum . then we went for open excision of the cystic mass through lateral parapatellar approach ( incision included that of the anterolateral arthroscopic portal ) . the cyst was found to be protruding just beneath the skin through a retinacular rent ( fig . however , the entire mass was taken out , but we had to sacrifice the fat pad almost entirely . post - operatively the patient underwent appropriate rehabilitation making an uneventful recovery and returned to his normal activities . he was symptom - free in his last follow - up at 6 months post - operatively . between the first description of an anterior cruciate ligament ( acl ) ganglion by caan in 1924 during a routine autopsy and the early 1990s , only a handful of sporadic cases were described in the literature . the last 30 years have seen a huge increase in the number of these cases being reported owing to the widespread use of both mri and arthroscopy . the prevalence of intra - articular cystic knee masses is 1.3% in mri and 0.6% in arthroscopy . several theories have been suggested : ( a ) synovial tissue herniation , ( b ) mucinous degeneration of connective tissue after trauma , ( c ) synovial ectopia or displacement during embryogenesis , etc . . the histological finding that ganglia are fluid - filled structures without any epithelial lining confirms that they are not true cysts , and thus favors the degenerative theory over others ; and , even though , ganglia may develop in the absence of trauma , it is postulated that repetitive microtrauma from joint and soft tissue motion may play an important role . intra - articular ganglia of knee originates most commonly from the acl accounting for more than 50% cases ; whereas , the location at infrapatellar fat pad is far less common ( approximately 4% ) . however , only 10% of them are symptomatic with most being incidental finding on mri or arthroscopy . the symptoms are usually non - specific , like knee pain , locking , clicking or popping sensation , decreased range of motion , etc . , and depend on the site and size of the cyst . ganglia anterior to the acl tend to limit extension , whereas those posterior to the posterior cruciate ligament often limit knee flexion . mri is the investigation of choice because it is the most sensitive , specific accurate , and noninvasive method for depicting such cystic masses , including their size and location , and to detect associated intra - articular pathologies . for intra - articular ganglion cyst in the infrapatellar fat pad , fat - suppressed contrast - enhanced mri could be useful , because a thin , rim - enhancing feature of intra - articular ganglion cyst allows it to differentiate from synovial hemangioma and synovial sarcoma . among the various treatments available , arthroscopic resection and debridement are currently the preferred procedure ; open surgery may be necessary in particular cases only . after diagnostic arthroscopy , we performed an open excision of the ganglion cyst since it was not clearly visible on arthroscopy ; moreover , we did not have any previous experience of arthroscopic resection of intra - articular ganglion cysts . hence , in view of the high recurrence rate after incomplete removal of ganglion , we preferred open excision over arthroscopic resection . although recurrence is rare after arthroscopic or open surgical treatment of ganglion cyst of knee , the fact that it does occur in other areas even after excision , this patient should be followed up on regular basis . current literature suggests arthroscopic resection and debridement as the gold standard treatment of ganglion cyst of the knee . however , a subcutaneous extension may lead to incomplete arthroscopic resection : leaving behind the residual tissue which may cause recurrence . therefore , proper pre - operative evaluation of mr images of these cases is very important . they are usually encountered as incidental findings in mri , or in arthroscopy . arthroscopic resection and debridement is regarded as the gold standard treatment in ganglion cyst of the knee . however , very rarely , these masses may extend subcutaneously across the retinaculum . this may lead to incomplete arthroscopic resection : leaving behind the residual tissue which may cause recurrences . therefore , proper pre - operative evaluation of mr images of these cases is very important .
introduction : intra - articular ganglion cysts of the knee joint are rare occurrences . 
 they are usually encountered as incidental findings in magnetic resonance imaging ( mri ) , or in arthroscopy . 
 they may originate from both the cruciate ligaments and the menisci , from the popliteus tendon and alar folds , infrapatellar fat pad of hoffa , and subchondral bone cysts . 
 those arising from the hoffa s fat pad , usually present as palpable mass at anterior aspect of the knee joint . 
 we report a case of intraarticular ganglion cyst of knee arising from the infrapatellar fat pad and protruding anterolaterally through retinacular rent into the subcutaneous plane.case report : a 19-year - old young man , presented with a painless gradually increasing swelling at the anterior aspect of left knee of 9 months duration . 
 mri scan revealed a multilobulated , cyst with septations within the anterior aspect of the knee joint , just inferolateral to the patella , with deep extension into the infrapatellar fat pad , and superficial extension into the subcutaneous space across the retinaculum . 
 after diagnostic arthroscopy , we performed an open excision of the cystic mass and confirmed the retinacular rent pre-operatively.conclusion:arthroscopic resection and debridement is the gold standard treatment in ganglion cyst of the knee . 
 however , a subcutaneous extension may lead to incomplete arthroscopic resection : leaving behind the residual tissue which may cause recurrence . 
 therefore , proper pre - operative evaluation of mr images of these cases is very important .