Musculoskeletal systemCase Type
Jose Miguel Escudero-Fernandez, Matias De Albert De Delas Vigo, Lourdes Casas Gomila, Carme Torrents Odin, Alfredo Gimeno Cajal, Maite Veintemillas Araiz, Rosa Domínguez Oronoz.Patient
45 years, male
45-year-old male patient presented with a long-term painless swelling tumour in the back part of right thigh. No history of trauma or injury was recorded.
Voluminous multiloculated tubular lesion was detected tracking along the course of tibial nerve from the proximal tibia epiphysis to the distal third of the thigh (Figure 1).
It was connected to the proximal tibiofibular joint through a discontinuity of the posterior capsule and extends along the articular branch into the tibial nerve (tail sign) (Figure 2). There were no signs of osteoarthritis.
Distal portion of sciatic nerve and branch of tibial nerve to the popliteus muscle were also involved. Common peroneal nerve was spared (Figure 3).
It shows high signal on T2WI without contrast-enhancement. There is eccentric compression of tibial nerve fascicles (signet ring sign) (Figure 4)
Subclinical denervation of tibialis posterior, flexor digitorum longus and flexor hallucis longus muscles was detected on MRI, as high signal on T2WI representing oedema (Figure 5) and high signal tracts on T1WI representing fatty infiltration and atrophy (Leminen score 1-2) (Figure 6) . The other muscles innervated by tibial nerve (medial and lateral heads of gastrocnemius, soleus and plantaris muscles were spared).
Patient remained asymptomatic, so conservative management was proposed.
Intraneural ganglion cysts are increasingly diagnosed benign cysts caused by accumulation of thick mucinous fluid within epineurium of peripheral nerves, encased in dense fibrous capsule [2-3].
Unifying articular theory proposes that intraneural ganglion cysts have a synovial origin .
They are formed from a capsular discontinuity of the joint secondary to direct or indirect trauma or degenerative changes. This defect allows articular fluid to follow the path of least resistance dissecting upwards within epineurium of articular branches with eccentric compression of fascicles [2-3].
Clinically, patients present with pain, paresthesias, weakness, muscle denervation and atrophy .
Common peroneal nerve is more commonly affected overall and ulnar nerve and its branches are the most frequent in upper extremity [2-3].
Intraneural ganglion cysts of the tibial nerve are extremely rare with only few cases reported in literature [4-5].
There is a classification of intraneural ganglion cysts of tibial nerve according to their extension: Limited to near the tibiofibular joint (grade 0), extension into the inferior geniculate articular branch that reach the medial condyle of tibia (grade 1), the popliteus muscle branch (grade 2), all the tibial nerve (grade 3) or into the sciatic nerve (grade 4) .
On MRI, they appear as multiloculated tubular lesions tracking along the course of the nerve with eccentric compression of nerve fascicles (signet ring sign). They show homogenous high signal intensity on T2WI with or without peripheral contrast-enhancement [4-6].
In most cases, connection between intraneural ganglion cyst and proximal tibiofibular joint is depicted (tail sign). In confounding cases, MR arthrography can help in depicting this connection .
Signs of muscle denervation appear as high signal intensity on T2WI representing edema in subacute cases and fatty infiltration and atrophy on T1WI in chronic cases [2-3]. In cases of tibial nerve ganglion cyst, tibialis posterior, extensor digitorum longus and extensor hallucis longus muscles are affected [4-5]. Popliteus muscle is also affected if intraneural ganglion cyst extends to its branch .
Differential diagnosis includes cystic nerve sheath tumours (schwannoma), atypical Baker’s cyst, and extraneural ganglion cyst, intraneural lipoma and haematoma [2-3].
Extraneural ganglion cysts share the same origin in a discontinuity of capsular joint and may be present at the same time [2-3]. Characteristics of extraneural ganglion cyst that help in differentiation from intraneural ones are:
Patients with clinically relevant intraneural ganglion cysts are treated with surgery, which includes decompression of the nerve, disconnection of the articular branch and resection of the synovium. Less invasive alternatives include percutaneous decompression or ultrasonography-guided aspiration, with higher rates of recurrence [2-3].
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