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Department of Neurological Surgery, Carl Gustav Carus University Hospital, Technical University of Dresden, Fetscherstrasse 74, D-01307 Dresden, Germany
Department of Neurological Surgery, Carl Gustav Carus University Hospital, Technical University of Dresden, Fetscherstrasse 74, D-01307 Dresden, Germany
The pathogenesis of intraneural ganglion cysts is unknown. Some authors have established a connection between the cysts and the joint, while others have failed to find this communication. Most intraneural ganglion cysts occur in the proximity of a joint. We present the case of a 53-year-old Caucasian male with an intraneural cyst of the sciatic nerve located high above its bifurcation and without a connection to the joint. The lesion was microsurgically removed in toto. There was no recurrence of the cyst at follow-up 9 months postoperatively; complete resolution of the clinical symptoms occurred within 8 months of surgery. This case shows that ganglion cysts can occur in locations far from a joint, supporting the extra-articular embryonic synovial remnant theory of their genesis.
Hypotheses regarding the pathogenesis of intraneural ganglion cysts include: metaplastic transformation of traumatic intra-epineural microhaemorrhage, degenerative changes occurring in the nerve sheath as a result of chronic irritation, loculation of intraneurally entrapped extra-articular embryonic synovial remnants, and ingrowth of an articular cyst into the nerve.
We report a case of an intraneural cyst presenting atypically in the sciatic nerve in the distal third of the thigh, well above the bifurcation of the nerve. Neither MRI nor surgical exploration established a connection to the articular space.
1. Case report
The patient was a 53-year-old roof-worker. For about a year he had been experiencing intermittent pain and numbness in his great and second toes, and lately he had started to develop persistent paresis of the leg muscles. On examination, the patient complained of radiating pain and numbness along the back of his leg, reaching the sole of his foot, when the posterior thigh was palpated. An M3 motor paresis of both ankle dorsiflexors and plantar flexors was noted. Tinel's sign could be elicited at the back of the mid-thigh. Electromyography of the flexors and extensors did not show fibrillations or positive sharp waves. A latency in the conduction velocity of the sciatic nerve of 12 m s−1 was noticed across the distal thigh region. MRI showed a space-occupying lesion along the course of the sciatic nerve in the mid-thigh region (Fig. 1) .
Figure 1Preoperative (A) coronal and (B) axial MRI slices showing the space-occupying lesion of the left sciatic nerve with fluid content.
Surgery was conducted under general anaesthesia and magnification. The epineurium of the affected portion of the sciatic nerve was found to be thin and translucent in several places, revealing clear fluid content. Clear thick gelatinous semisolid material was present in several loculated cysts, and a portion of the lesion consisted of solid fibrous tissue. Fascicular neurolysis was undertaken through a longitudinal epineurotomy, thereby, separating and preserving the healthy fascicular structures (Fig. 2) . Under light microscopy, spindle-shaped myxoid elements (solid component) could be seen near cystic structures composed of thickened collagenous connective tissue (cystic element). The cyst wall was irregularly lined with squamous-type cells (secretory component of the cysts). The findings were consistent with a nerve-sheath ganglion with myxoid degenerative changes.
Figure 2(A) Exposure of the nerve with the cyst. Note the thin-walled epineurium revealing translucent fluid content. (B) Fascicular neurolysis was carried out, separating the nerve structures from those of the lesion. Radical removal of the cyst was possible.
The radiating pain disappeared immediately after surgery. The sensation in the affected areas of the foot returned to normal after 5 months, and motor strength returned to the M5 level within 8 months under intensive physical therapy. The lesion did not reappear in MRI scans carried out 6 months and 9 months after surgery (Fig. 3) .
Figure 3MRI 9 months postoperatively. The cyst did not recur. The patient was asymptomatic.
Some intraneural cysts recur after surgical excision, possibly owing to a remnant communication with the adjacent articular space, whilst other cysts disappear after intervention.
The commonality in all ganglion cysts seems to be their proximity to a joint. The origin of a ganglion cyst is suggested to be a sac growing out from the synovial membrane. The absence of a connection with the articular space in at least some reported intraneural cysts has led to the belief that they arise from embryonic synovial remnants or are caused by degenerative changes in the nerve sheath as a result of chronic irritation. The peroneal nerve is the most susceptible,
The diagnostic work-up includes clinical examination, electrophysiology and imaging. The ganglion cyst does not always present as a palpable mass. Tinel's sign, with or without pain, is present in all cases. Electromyography and electroneurography may indicate denervation and conduction latency, respectively. MRI is the method of choice for obtaining high-resolution images of soft-tissue lesions.
Some authors have proposed aggressive radiological work-up regimes, such as arthrography, especially in cases of recurrence, in order to establish a connection to the joint space.
Careful microsurgical exploration during surgery should reveal such connections. Thus, diagnostic arthrography should be reserved for highly doubtful cases of recurrence.
Surgical exploration and excision is the method of choice in treating space-occupying lesions of the peripheral nerves. There are three goals of this surgical procedure: to remove the intraneural ganglion cyst and its secretory components (cyst wall); to destroy any possible connection to an adjacent articular space and, most importantly, to preserve as many functionally intact nerve fascicles as possible. Tatagiba et al proposed emptying the cysts through an incision on the capsule, in order to preserve function.
With this technique the secretory lining of the cyst is left in situ; thus, the possibility of recurrence is not excluded.
Based on our study of the literature, some general points about intraneural ganglion cysts may be made:
1.
during a diagnostic work-up, the possibility of an intraneural ganglion cyst should not be excluded, regardless of whether the lesion is in the proximity of a joint or of the nerve involved; the lesion is often associated with the common peroneal nerve;
2.
microsurgical exploration and excision is the most effective method of treatment;
3.
primary microsurgical exploration of lesions adjacent to joint spaces should involve a search for a possible peduncular connection to the articular space.
To our knowledge, the occurrence of intraneural ganglion cysts does not show a pattern and is not associated with other conditions.
Acknowledgements
We thank Kristin R. Hanson for editing the language.
References
De Maeseneer M
De Boeck H
Shahabpour M
Hoorens A
Oosterlinck D
Van Tiggelen R
Subperiosteal ganglion cyst of the tibia. A communication with the knee demonstrated by delayed arthrography.
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