Skeletal Radiol (1995) 24:253-256 Skeletal Radiology

Intramuscular ganglia arising from the superior tibiofibular joint: CT and MR evaluation Stefano Bianchi, M.D. l, Ibrahim Fikry Abdelwahab, M.D. 2, Samuel Kenan, M.D. 3, Alicia Zwass, M.D. 4, Giovanni Ricci, M.D. I, Giovanni Palomba, M.D. 5

Department of Radiology, O.E. Ospedali Galliera, Genoa, Italy 2 Department of Radiology, Mount Sinai Medical Center, City University of New York, New York, USA 3 Department of Orthopedics, Mount Sinai Medical Center, City University of New York, New York, USA 4 Department of Radiology, Columbia Presbyterian Hospital, New York, New York, USA 5 Department of Orthopedics, O.E. Ospedali Galliera, Genoa, Italy

Abstract. Objective. To evaluate the role of magnetic resonance imaging (MRI) and computed tomography (CT) in the diagnosis of intramuscular ganglia (IMG) that arise from the superior tibiofibular joint (STFJ). Material and methods. Our series consisted of three men and three women. Four patients were studied by MRI, one by CT only, and two by both modalities. Contrast was used in one of the two patients studied by CT. MRI was obtained in at least two orthogonal planes to demon- strate the relation of the ganglia to STFJ. Results. The MR and CT appearance of these ganglia was basically that of a well-defined soft tissue mass with low attenuation on CT images consistent with the pres- ence of fluid. On MR studies, they had an isointense sig- nal on Tl-weighted images and a homogenous high-in- tensity signal on T2-weighted images. MRI demonstrat- ed the attachment of these ganglia to the STFJ. Conclusion. CT and MRI were effective, noninvasive modalities in the evaluation of IMG. The imaging fea- tures on both modalities were consistent with the pres- ence of fluid-containing lesions that had close proximity and were attached to the STFJ. The combination of loca- tion and the fluid consistency of these lesions facilitated the diagnosis.

Key words: Soft tissue neoplasms, diagnosis, ganglion - Intramuscular - Magnetic resonance - Computed to- mography

Cystic lesions around the knee are a common clinical problem and can be evaluated with a variety of radio- graphic techniques including arthrography and sonogra- phy [1]. Popliteal cysts are the most common lesions and

Correspondence to: I. Fikry Abdelwahab, M.D., Box 1234, De- partment of Radiology, Mount Sinai Medical Center, One Gustave L. Levy Place, New York, NY 10029-6574, USA

are frequent finding in studies performed for internal de- rangement of the knee. Cystic lesions in other locations around the knee are less common and usually are menis- cal cysts or ganglia [2]. Meniscal cysts are characteristi- cally located at the joint line on the medial or lateral side of the knee and are usually associated with an underly- ing horizontal meniscal tear [2, 3]. Ganglion cysts may occur in atypical locations: attached to the tendon sheath, within muscle bundles, within the sheath of the common peroneal nerve, or attached to the superior ti- biofibular joint (STFJ) [4-7]. The excellence of magnetic resonance imaging (MRI) in evaluating soft tissue mass- es makes this technique ideally suited to evaluation of these cystic lesions [8]. In this report, we review our ex- perience with computed tomography (CT) and MRI of six IMG arising from the STFJ.

Material and methods

The six patients were referred to out orthopedic service with their imaging studies performed in other institutions. They were three men and three women who ranged in age from 23 the 60 years, with a mean age of 43 years. They all presented with a swelling in the proximal part of the leg, which was painful in only one pa- tient (case 1). Physical examination revealed an ill-defined, firm muscular swelling deep to the deep fascia. All the objective neu- rological signs were absent. Plain radiology had been performed in all patients. Five had been studied by MRI and two by CT. Contrast was used in one of the two CT examinations. The MR images were obtained using different imagers operating at 0.5 to 1.5 tesla. Imaging sequences included spin-echo Tl-weighted 500-740/ 12-21 ms (repetition time/echo time) proton density- weighted and T2-weighted 1800~4000/60-100ms pulse se- quence. Section thickness varied from 4 to 10 ram. No contrast enhancement was used with MRI. Plain radiography, CT, and MRI were performed in case 1. Plain radiography and MRI were obtained in cases 2 to 5. Plain radiography and CT were done in case 6. Imaging features were examined in each case: for plain radiography, soft tissue mass, cortical erosion, scalloping, and periosteal reaction; for CT, margination, attenuation, and bone changes; and for MRI, margination, site, signal intensity, and re- lation to the STFJ.

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254 S. Bianchi et al.: Intramuscular ganglia

Results

Plain radiography did not demonstrate significant soft tissue mass or bone changes.

CT revealed a sharply defined rounded soft tissue mass having the attenuation of fluid, The mass lesion did not enhance after contrast injection. Septation within the fluid-containing lesion was noted in case 1.

On MRI, the intramuscular lesions were isointense or hypointense compared to the surrounding muscles on Tl-weighted images. All had high-intensity signal on T2-weighted images. Septation was noted on the T2- weighted images in case 1. Three ganglia were located in the tibialis anterior muscle (cases 1, 4, 6). The pero- neus longus muscle was the site of two ganglia (cases 2, 3). One ganglion was in the soleus muscle (case 5). In four of the five cases studied by MRI, the attachment of

the ganglia to the STFJ was demonstrated (cases 1-4). All six patients underwent surgical excision of the gan- glia and the attachment of the ganglia to the STFJ was confirmed in all cases. Recurrence in a period varying from a few months to 3 years occurred in four patients (cases 1-4). This was confirmed by ultrasonography in case 2, MRI in case 4, and physical examination in cases 1 and 3.

Discussion

Reviewing the literature, there are several reports de- scribing ganglia intraneurally involving the common peroneal nerve. They were called "intraneural ganglia'' by the authors who described them. Among the reports are those by Waldstein [6] in 1931, Ellis [9] in 1936,

Fig. 1A-D. Patient 1: A 52-year-old man with a surgically proven intramuscular ganglion. A C T scan obtained at the site of the le- sion showing a well-defined, rounded soft tissue mass with the same attenuation as fluid, representing the ganglion which is lo- cated in the tibialis anterior muscle. Notice the septa within the ganglion (arrow). B Coronal Tl-weighted MR image (TR 600/TE 21). C Coronal T2-weighted MR image (TR 4000/TE 98). D Sag- ittal T2-weighted MR image (TR 4000/TE 98). These MR images demonstrate a large, sharply defined multiloculated soft tissue mass that has a signal isointense to the surrounding muscles on the Tl-weighted image and a homogeneous high-intensity signal on the T2-weighted images. Multiple curvilinear septations are re-

vealed in the coronal cut. Notice in D the very close proximity of the ganglion to the joint, which may suggest communication (ar- row)

Fig. 2A-C. Patient 2: A 23-year-old woman with a surgically proven ganglion. A Axial Tl-weighted MR image (TR 739/TE 14). B Axial T2-weighted MR image (TR 4000/TE 98). C Coro- nal T2-weighted MR image (TR 4000/TE 98). These MR images reveal a sharply defined oval tissue mass lying in the peroneus longus muscle with its proximal end reaching the superior tibio- fibular joint. The mass has signal isointense to the surrounding muscles on the Tl-weighted image (arrow) and homogeneous high-intensity signal on the T2-weighted images

S. Bianchi et al.: Intramuscular ganglia 255

Fig. 3A,B. Patient 5: A 31-year-old man with a surgically proven intramuscular ganglion. A Axial Tl-weighted MR image (TR 500/TE 12). B Sagittal T2-weighted MR image (TR 2000/TE 80). Both MR images demonstrate a sharply defined soft tissue mass in the posterior compartment lying in the soleus muscle. The mass has a signal that is hypointense to the surrounding muscles on the Tl-weighted image and bright signal on the T2-weighted image

Fig. 4. Patient 7: A 51-year-old man with clinical diagnosis of in- ternal derangement of the left knee. Anteroposterior view of the left knee with internal rotation. This view, taken after injection of contrast medium, demonstrated a synovial cyst herniating from the inferior margin of the superior tibiofibular joint. Notice the contrast outlining the cyst and the joint which communicates with the tibiofemoral joint

Ferguson [10] in 1937, Brooks [11] in 1952, Clark [12] in 1961, Barber etal. [13] in 1962, and Stalk etal. [14] in 1965. All these ganglia were attached to the STFJ. Al- though these reports dealt mainly with ganglia lying within the common peroneal nerve sheath, one of the 13 cases described by Brooks involved the tibialis anterior muscle and extended to the STFJ [11]. In 1969, Stener [7] described a ganglion on the peroneus longus tendon with its proximal end in contact with the STFJ. In the same year, Muckart [4] reported five ganglia lying with- in the peroneus longus muscle and all were connected to the STFJ. He called them "intramuscular ganglia." Our series belong to this type. Among the five cyst ganglia around the knee described by Bm'k etal. [2], one was connected to the STFJ and presented with a peroneal nerve palsy. Both varieties of ganglia, those located within the peroneal nerve sheath and IMG that dissected in the muscles of the proximal leg, shared a common

finding which was their attachment to the STFJ. This led Brooks to suggest that both ganglia are anatomical vari- eties of the same entity [11].

The STFJ is a synovial joint which articulates the proximal tibia and fibula and communicates with the knee joint in 10% of cases [15]. While the predisposing factors responsible for the IMG arising from the STFJ are by no means certain, some authors suggest that trau- ma to an STFJ which has unusual forces acting upon it may be responsible [5, 11]. In our six cases, all patients denied any history of trauma. Parkes [151 believed that ganglia of the peroneal nerve sheath initially arise from the STFJ. This was supported by Brooks [11], who also added that they are synovial cysts herniating from the STFJ, and if a synovial herniation becomes loculated, as in popliteal cysts, the lining membrane can undergo a metaplastic change to mesothelium. On the other hand, Barret and Cramer [17] think that the stalks of the gan- glia are caused by tracking of fluid from the ganglion in the peroneal nerve sheath along the neurovascular bun- dle which enters the STFJ. We believe like Brooks [11] that IMG initially arise as a synovial herniation from the STFJ, and as they grow in size, they dissect their way through the proximal muscles of the leg and, eventually losing the synovial lining. This opinion may be supported by Fig. 4, which shows an arthrogram of a 51-year-old man with a clinical diagnosis of internal de- rangement of the left knee. The arthrogram demonstrat- ed a small ganglion projecting from the STFJ. A sono- gram confirmed the presence of a small ganglion located in the peroneus longus muscle. In our five cases of IMG studied by MRI, a possible communication between IMG and the STFJ was suggested in three cases (cases 1-3).

IMG arising from the STFJ are diagnosed in the same manner as they are elsewhere in soft tissue. They are cystic structures, usually with discernible fibrous exter- nal capsules without any recognizable initial lining cell type. The contents are fluid and range in consistency from thin to viscid and mucinous. There is almost no cellular content. Diagnosis thus rests on gross findings and histological features that do not point to another va- riety of soft tissue lesion [18]. Our series involved the three compartments of the leg: anterior, posterior and lateral. The high recurrence rate of these ganglia was also reported by other authors [4]. We suggest that after confirming the benign cystic nature of these lesions, aspiration under ultrasonographic guidance could be performed and therefore surgical excision with its high recurrence rate could be avoided. However, we were un- able to find reliable data about the incidence of recur- rence following needle aspiration.

Ultrasonography and arthrography have been used in the evaluation of cystic lesions of the knee. Ultrasonog- raphy is excellent for detecting fluid-filled structures and in tracking the fluid collections to their point of origin [2]. Arthrography can detect cysts that communicate with the joint, but it is an invasive technique and offers little information about noncommunicating cysts [19]. On the other hand, CT can demonstrate cysts and intra- articular structures [2]. Because of its excellent soft tis-

256 S. Bianchi et al.: Intramuscular ganglia

sue contras t and mul t ip lanar capabi l i ty , M R I is most sui ted to evaluat ing IMG. However , the M R I features of such gang l ia are not specific: they can mimic other soft t issue tumors, e.g., in t ramuscular m y x o m a s , chronic ab- scesses, schwannomas , and even sharply def ined mal ig- nant soft t issue tumors that have undergone m y x o m a t o u s degenerat ion, e.g., l iposarcoma, chondrosa rcomas , and mal ignan t f ibrous h is t iocytomas . In cases of uncertainty, u l t rasonography can conf i rm the cyst ic nature o f the mass more def ini te ly than MRI.

It should be emphas i zed that demons t ra t ion of the a t tachment of I M G to the STFJ is an impor tan t differen- t iat ing point. The d iagnos is of I M G was cons idered before surgery on the basis o f the we l l -c i rcumscr ibed , homogeneous appearance o f the soft t issue mass on M R I and its a t tachment to the STFJ.

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