A Case Report and Literature Review: Intraneural Ganglion Cyst Causing Tarsal Tunnel Syndrome

Beyond schwannomas and neurofibromas: a radiological and histopathological review of lesser-known benign lesions that arise in association with peripheral nerves

Peripheral nerve sheath tumors comprise a significant percentage of both benign and malignant soft tissue tumors. The vast majority of these lesions are schwannomas and neurofibromas, which most radiologists are familiar with including the well-described multimodality imaging features. However, numerous additional often under-recognized benign entities associated with nerves exist. These rarer entities are becoming increasingly encountered with the proliferation of cross-sectional imaging, particularly magnetic resonance imaging (MRI). It is important for the radiologist to have a basic understanding of these entities as many have near-pathognomonic MR imaging features as well as specific clinical presentations that when interpreted in concert, often allows for a limited differential or single best diagnosis. The ability to provide a prospective, pre-intervention diagnosis based solely on imaging and clinical presentation is crucial as several of these entities are "do not touch" lesions, for which even a biopsy may have deleterious consequences. To our knowledge, the majority of these benign entities associated with nerves have only been described in scattered case reports or small case series. Therefore, the aim of this article is to provide a radiopathologic comprehensive review of these benign entities that arise in association with nerves with a focus on characteristic MRI features, unique histopathologic findings, and entity specific clinical exam findings/presentation.

An update on imaging of tarsal tunnel syndrome

Tarsal tunnel syndrome (TTS) is an entrapment neuropathy of the tibial nerve (TN) within the tarsal tunnel (TT) at the level of the tibio-talar and/or talo-calcaneal joints. Making a diagnosis of TTS can be challenging, especially when symptoms overlap with other conditions and electrophysiological studies lack specificity. Imaging, in particular MRI, can help identify causative factors in individuals with suspected TTS and help aid surgical management. In this article, we review the anatomy of the TT, the diagnosis of TTS, aetiological factors implicated in TTS and imaging findings, with an emphasis on MRI.

An Update on Posterior Tarsal Tunnel Syndrome

Posterior tarsal tunnel syndrome (PTTS) is an entrapment neuropathy due to compression of the tibial nerve or one of its terminal branches within the tarsal tunnel in the medial ankle. The tarsal tunnel is formed by the flexor retinaculum, while the floor is composed of the distal tibia, talus, and calcaneal bones. The tarsal tunnel contains a number of significant structures, including the tendons of 3 muscles as well as the posterior tibial artery, vein, and nerve. Focal compressive neuropathy of PTTS can originate from anything that physically restricts the volume of the tarsal tunnel. The variety of etiologies includes distinct movements of the foot, trauma, vascular disorders, soft tissue inflammation, diabetes mellitus, compression lesions, bony lesions, masses, lower extremity edema, and postoperative injury. Generally, compression of the posterior tibial nerve results in clinical findings consisting of numbness, burning, and painful paresthesia in the heel, medial ankle, and plantar surface of the foot. Diagnosis of PTTS can be made with the presence of a positive Tinel sign in combination with the physical symptoms of pain and numbness along the plantar and medial surfaces of the foot. Initially, patients are treated conservatively unless there are signs of muscle atrophy or motor nerve involvement. Conservative treatment includes activity modification, heat, cryotherapy, non-steroidal anti-inflammatory drugs, corticosteroid injections, opioids, GABA analog medications, tricyclic antidepressants, vitamin B-complex supplements, physical therapy, and custom orthotics. If PTTS is recalcitrant to conservative treatment, standard open surgical decompression of the flexor retinaculum is indicated. In recent years, a number of alternative minimally invasive treatment options have been investigated, but these studies have small sample sizes or were conducted on cadaveric models.

Tarsal Tunnel Syndrome: Outcome According to Etiology

Surgical results in tarsal tunnel syndrome are variable, and etiology seems to be a factor. Three possible etiologies can be distinguished. The aim of the present study was to compare surgical results according to etiology. Three continuous retrospective series (45 patients overall) of tarsal tunnel syndrome were compared. Group 1 presented a permanent intra- or extra-tunnel space-occupying compressive structure. Group 2 presented intermittent intra-tunnel venous dilatations. Group 3 comprised idiopathic tarsal tunnel syndrome. The mean follow-up was 3.6 +/- 1.8 years. The main endpoint was subjective postoperative improvement on Likert scale. Group 1 reported greater improvement than groups 2 and 3. Preoperative neuropathy on ultrasound was associated with poorer improvement, which was not the case for neuropathy on electromyography. Surgical treatment of tarsal tunnel syndrome provides better results in etiologies involving structural compression.

Tarsal tunnel syndrome: Clinical-imaging analysis of a case series

BACKGROUND

Retrospective review of patients with a diagnosis of Tarsal Tunnel Syndrome (TTS) treated surgically.

METHODS

Retrospective series of patients with diagnosis of TTS operated between 2005 and 2020 in the same center. Variables such as age, sex, side, affected nerve or branch, classification, type of imaging study, biopsy result, infection rate, recurrence rate, sequelae, among others, were analyzed.

RESULTS

We included 8 men and 2 women with an average age of 47 years (range 34-67) and an average follow-up of 62.2 months (range 2-149). All cases were related to intrinsic compression. The most frequent cause was the presence of cyst (40%) followed by perineural adhesions (20%). The Posterior Tibial Nerve was the most affected (50%) and 30% the Medial Plantar Branch. Ultrasound (70%) and MRI (50%) were the most requested studies. There were no cases of postoperative infection. There were 3 patients who presented recurrence of the lesion requiring a new surgery.

CONCLUSIONS

TTS is a neuropathy involving the posterior tibial nerve or some of its branches. In general, it is caused by compression of the nerve by different structures such as accessory muscles and ganglions, among others. The diagnosis is eminently clinical, supported by imaging studies. Surgical treatment presents better results when the cause is an intrinsic compression, although variable recurrence rates are described.

A Rare Case of Tibial Intraneural Ganglion Cyst Arising From the Tibiofibular Joint

Intraneural ganglion cysts are a rare occurrence. They are most commonly found originating from the common peroneal nerve but are also frequently reported on the radial, ulnar, median, sciatic, tibial, and posterior interosseous nerves. A typical clinical presentation is posterior knee and calf pain resulting from tibial neuropathy with preferential degeneration of the popliteus muscle. Symptoms include pain, paresthesias, and decreased strength that originates in the knee and commonly extends to the plantar surface of the foot. These findings can be mistaken for lumbar neuropathies and compression of the sacral nerve roots. Differential diagnosis includes peripheral nerve sheath tumors, Baker’s cysts, extraneural ganglion cysts, and atypical vascular or lymphatic malformations. In this case report, the patient was a 61-year-old male, previously in good health, who presented with progressive pain in his medial left hamstring as well as weakness in left foot plantar flexion and paresthesias in the plantar aspect of his left foot. He first noticed impairments with his ability to push off with his left foot when running. His electromyogram (EMG) was abnormal and subsequent MRI of the left leg showed a complex intraneural ganglion cyst arising from the tibiofibular joint and ascending into the tibial nerve. He underwent indirect decompression through joint resection. Unfortunately, he did not have clinical improvement on one-year follow-up. Overall, symptomatic treatment of intraneural ganglion cyst includes decompression, surgical excision, or minimally invasive decompression by percutaneous aspiration of the ganglion under ultrasound guidance.