Ganglion cysts are cystic, common tumour-like lesions in the soft tissues adjacent to joint capsules or tendon sheaths. They can occur within muscles, menisci and tendons, and are frequently found in the hand, wrist and foot.
Traditionally, they have been classified according to their site of origin: the tendon sheath, joint, bone or soft tissue. Although ganglion cysts most commonly arise from the tendon sheaths, the incidence of an intratendinous ganglion cyst that originates within the tendon substance itself is relatively rare [2
After Lecéne [7
] first reported an intratendinous ganglion cyst within the common extensor tendon to the middle finger over the dorsum of the hand, several references to intratendinous ganglion cysts have appeared in the literature. Most of these concerned cysts arising from the extensor tendons of the wrist and hand [3
Intratendinous ganglion cysts of the lower extremity are even more uncommon and have been reported in the tendon of peroneus longus below the knee [10
], the quadriceps femoris tendon [11
], the peroneus tertius tendon at the dorsolateral aspect of the right foot [12
] and the extensor digitorum longus tendon close to knee [1
]. To our knowledge, this is the first report of an intratendinous ganglion cyst arising from the semimembranosus tendon itself.
The aetiology of intratendinous ganglion cysts is unclear. However, recurrent injury to the tendon with subsequent cystic degeneration is a possible cause of an intratendinous ganglion cyst because tenosynovitis or associated tendon tears are often present around the ganglion cyst [13
]. A congenital anomaly may be responsible in patients with no history of trauma [14
]. In our case, the patient had no history of injury or inflammation.
MRI and US are highly sensitive, specific and effective methods for delineating the nature of cysts, including their size, location and relationship to the surrounding structures [1
], but MRI provides a better anatomical overview.
On MRI, a ganglion cyst appears as a well-defined, lobulated mass that is commonly located adjacent to a joint or tendon sheath, with a simple or complex fluid-like signal. Typically, the lesion exhibits thin rim enhancement on the gadolinium-enhanced T1
weighted images. A differential diagnosis based on MRI may include tenosynovitis, tendon tear, bursitis, abscess, pigmented villonodular synovitis, myxoma, nerve sheath tumour and synovial sarcoma [1
]. However, the findings of a lobulated cystic mass occupying the characteristic location within a tendon and displaying thin rim enhancement should suggest an intratendinous ganglion cyst [2
Ganglion cysts of the lower extremity can recur in about 10% of cases after surgical excision, usually because ganglion cysts have been incompletely removed [15
]. Recurrence after surgery for partial excision of an intratendinous ganglion cyst has been reported [9
]. In our patient, 9 months after surgery at the follow-up CT, recurrent ganglion cysts were found along the semimembranosus tendon due to intraoperative leakage and incomplete excision of the intratendinous ganglion cyst.
In conclusion, intratendinous ganglion cyst is a relatively uncommon lesion that originates within the tendon substance itself. We have presented the case report of an intratendinous ganglion cyst arising from the semimembranosus tendon with findings using US and MRI.