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Instituto Portugues de Oncologia de Francisco Gentil Porto 4200,
Portugal
Thomas Jefferson University Hospital Philadelphia, PA
19107
A 51-year-old woman presented with a 2-year history of lateral ankle pain and progressive swelling. She was otherwise healthy and denied experiencing any preceding trauma. At physical examination, a palpable rubbery mass was discovered behind the fibula that moved with excursion of peroneal tendons. No clinical evidence of ankle instability was found. Radiogaphic findings for the ankle were normal.
We obtained MRIs using a 1.5-T scanner (Signa, General Electric Medical Systems, Milwaukee, WI). A well-defined, lobulated mass was observed in the sheath of the peroneal tendon (Figs. 3A, 3B, 3C, and 3D), extending 7.5 cm in longitudinal and 1.9 cm in transverse dimensions. It displayed a complex fluidlike signal and showed a thick rim of enhancement after gadolinium administration. We found a fluid-filled tail that pointed out of its major loculation and was connected to the adjacent tendon. The intact peroneus longus tendon was visualized adjacent to the posteromedial margin of the lesion. The peroneus brevis tendon was not visualized. MR findings suggested severe tenosynovitis and a peroneus brevis tear.
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At surgery, the mass appeared encapsulated and completely contained in the intact but expanded peroneus brevis tendon. After tendon dissection, the gelatinous material of an intratendinous ganglion cyst was found. No surgical evidence of tenosynovitis was present.
Ganglion cysts are the most common soft-tissue mass in the foot and ankle [1, 2]. Usually located in the dorsum of the foot or around the ankle, these cysts can be classified according to their site of origin: the tendon sheath, joint, bone (periosteal or intraosseous), or soft tissue. Although ganglion cysts commonly arise from tendon sheaths, those originating within a tendon itself are rare. Few references to intratendinous ganglion cysts appear in the literature, and most of these concern cysts that arise from the extensor tendons of the wrist and hand [3, 4]. Intratendinous ganglion cysts arising in the ankle are even more uncommon. However, in 1959, Robertson [5] reported the case of an intratendinous ganglion cyst arising in the peroneus brevis tendon.
The etiology of intratendinous ganglion cysts is not completely understood; recurrent injury to the tendon with subsequent cystic degeneration is a possible cause [5]. Tenosynovitis or associated tendon tears are commonly present. Mucoid degeneration of the collagen fibers of the tendon and cellular hyperplasia associated with active secretion of mucin are thought to be the main pathologic pathways that precede the development of these cysts [6]. A thin capsule of fibrous tissue typically surrounds them.
On MR imaging, a ganglion cyst appears as a well-defined, lobulated mass located adjacent to a joint or tendon sheath and exhibits a simple or complex fluidlike signal. Typically, they exhibit rim enhancement after IV administration of gadolinium. A fluid-filled tail that connects to the adjacent joint or tendon sheath is the most reliable sign of a ganglion cyst [5].
The main differential diagnosis based on MRIs includes tenosynovitis or a tendon tear. Other benign lesions might also be considered, such as an abscess, a giant cell tumor of the tendon sheath, a myxoma, a nerve sheath tumor, and a synovial chondromatosis lesion. Some malignant lesions can also present MR features similar to those of a ganglion cyst, including a synovial sarcoma, myxoid chondrosarcoma, myxoid liposarcoma, and metastasis. However, findings of a lobulated mass occupying the characteristic location within a tendon and displaying rim enhancement should suggest the correct diagnosis.
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