Age / Sex : 70 / M

Chief complaint: Palpable mass of right calf area

1) What is your impression?

Two weeks later, you can see the final diagnosis with a brief discussion of this case.

(답안은 한 개만 보내주시기 바랍니다)

Courtesy: 김완태 (Wan Tae Kim) 중앙보훈병원 (Veterans Health Service Medical Center)

Intramuscular dissection of Baker’s cyst

Discussion

Findings:

Axial and sagittal MR images show a 14x3x3cm sized homogeneous fluid signal intensity intramuscular cyst in the medial gastrocnemius muscle with multiloculated appearance. Enhanced T1-weighted image revealed a cystic mass originating from the gastrocnemius- semimembranosus bursa and dissecting into the medial gastrocnemius muscle with no edema or muscle enhancement.

The cystic mass was present extending inferiorly into the calf muscle and dissecting into the medial head of the gastrocnemius muscle.

Differential Diagnosis:

Diagnosis:  

Intramuscular dissection of Baker’s cyst

Discussion:

It is well established that a Baker’s cyst represents a distended gastrocnemius-semimembranosus bursa. Distension of the bursa can occur as a primary phenomenon or secondary to intra-articular knee pathology and a joint effusion.

Current knowledge of the anatomy and pathophysiology of popliteal cysts dose not convincingly explain a mechanism by which intramuscular cysts arise. It is presumed that cyst extend along planes that offer the least resistance and those would be expected to be the intramuscular planes. Weakened fascia surrounding the muscle could potentially predispose to cystic dissection into the intramuscular planes.

MR imaging has the advantage of allowing define anatomical origin of a Baker’s cyst and accurate assessment of the intramuscular cystic mass.

References:

1.     Fang CS, McCarthy CL, McNally EG. Intramuscular dissection of Baker's cysts: report on three cases. Skeletal Radiol. 2004 Jun;33(6):367-71.

2.     Nicholson LT, Freedman HL. Intramuscular dissection of a large ganglion cyst into the gastrocnemius muscle. Orthopedics. 2012 Jul 1;35(7):e1122-4.