Radiological imaging of Tarsal tunnel syndrome.

Dr/ ABD ALLAH NAZEER. MD.

Tarsal tunnel syndrome (TTS) refers to an entrapment neuropathy of the posterior tibial nerve or of its branches within the tarsal tunnel. This condition is analogous to carpal tunnel syndrome. While carpal tunnel syndrome is usually bilateral, tarsal tunnel syndrome is unilateral.For better understanding of normal anatomy of tarsal tunnel, please refer article - "tarsal tunnel".Clinical presentationThe most common symptoms are pain and parasthesia in the toes, sole, or heel and the main finding at physical examination is the Tinel sign (distal parasthesia produced by percussion over the affected portion of nerve).Electromyography and nerve conduction studies are useful in confirming the diagnosis.

PathophysiologyTarsal tunnel syndrome is a compression neuropathy of the tibial nerve that is situated in the tarsal canal. The tarsal canal is formed by the flexor retinaculum, which extends posteriorly and distally to the medial malleolus.The symptoms of compression and tension neuropathies are similar; therefore, differences in these conditions cannot be simply identified by the symptoms alone. In certain instances, compression and tension neuropathies may coexist.The double-crush phenomenon originates from work published by Upton and McComas in 1973. The hypothesis behind this phenomenon may be stated as follows: Local damage to a nerve at one site along its course may sufficiently impair the overall functioning of the nerve cells (axonal flow), such that the nerve cells become more susceptible to compression trauma at distal sites than would normally be the case.

Aetiologyidiopathic (50% cases)ganglion cystsbone deformity after calcaneal fracturesvaricositiestenosynovitis of the flexor tendonstumours (e.g. neurilemmoma , lipoma)accessory or hypertrophied abductor hallucis musclesynovial hypertrophyhind-foot valguspost-traumatic fibrosisos trigonum

- clinical findings: - patients may note pain when the ankle is placed in extremes of dorsiflexion (from nerve tension); - patients note pain, parasthesia, foot numbness, and in somes cases atrophy of foot intrinsic; - pain will radiate along the plantar side of the foot, sometimes up into the calf; - positive Tinel sign behind medial malleolus; - manual compression for 30 sec. may reproduce symptoms; - consider performing 2 point discrimination test both on medial and lateral sides of the foot (and opposite foot); - if the 2 point discrimination is increased on one side of the foot, it may indicate which branch of the plantar nerve is compressed; - in most cases, symptoms will be improved w/ rest;

US imagingTo obtain a reliable outcome, US imaging of the tarsal tunnel and the peripheral nerves must be performed by an experienced operator, who is familiar with normal and pathological US findings. Top-of-the-range US equipment including a high frequency probe is required.Gray-scale and color Doppler US imaging starts with axial scans of the proximal and distal tarsal tunnel on the medial side of the foot arch and with a systematic study of the tibial nerve, the two plantar nerves and the inferior calcaneal nerve. The patient should be in the lateral decubitus position.US Tinel test should be carried out by tapping over the nerve to elicit symptoms, as a positive US Tinel sign is suggestive of a positive diagnosis of Posteromedial tarsal tunnel syndrome, particularly when the symptoms are linked to possible compression elements. In some cases, the US Tinel sign may be the only positive sign in the absence of compression elements or neuropathy. In case of pathological findings, the nerve should be further studied in the longitudinal plane to confirm previous findings.

US examination also includes a systematic study with the patient in the standing position during limb loading using axial scans of the proximal tunnel and the distal tunnel. The following two conditions should be investigated:Compression caused by bone disorders linked to static foot disorders, including compression by the medial process of the talus in valgus flat foot, which leads to pushing and stretching of the nerves;Dilation of the plantar veins in the distal tarsal tunnel (vein diameter >5 mm) when the patient is in the standing position. Venous dilation should be suspected in the presence of positive US Tinel sign caused by compression of the veins using the US probe or if the symptoms improve when the patient is wearing Class II support soaks.US can detect muscle atrophy and significant fatty infiltration linked to a neurogenic pathology. In this case, comparison with the muscles of the contralateral foot is essential. If the patient has a disease affecting the nerve to the abductor of the fifth toe, a comparative assessment of the abductor muscles of the fifth toes may show atrophy and hyperechoic appearance of the affected foot and thereby confirm the diagnosis.

MRIMR imaging clearly depicts the bones, soft-tissue contents, and boundaries of the tarsal tunnel as well as the different pathologic conditions responsible for tarsal tunnel syndrome.MR imaging can also aid in determining whether treatment should be conservative (e.g. tenosynovitis) or surgical (e.g. space-occupying lesions).

Posteromedial tarsal tunnel syndrome of the right foot during limb loading. US imaging and MRI show a flexor digitorum accessories longus muscle of the toes (FDAL) in the tarsal tunnel, satellite of the tibial nerve (TN), and plantar nerves (LPN, MPN). After surgical removal of the accessory muscle, symptoms disappeared

Posteromedial tarsal tunnel syndrome of the right foot during limb loading. Voluminous accessory soleus muscle (AS) in contact with the tibial nerve (arrow) in the proximal tarsal tunnel of the right foot. There is no accessory muscle in the left foot

Posteromedial tarsal tunnel syndrome of the left foot. Comparative coronal imaging of the distal tarsal tunnel shows significant hypertrophy of the abductor hallucis muscle of the left foot causing plantar nerve entrapment

US shows a large epineural ganglion cyst adjacent to the tibial nerve (arrows)

Recurrent posteromedial tarsal tunnel syndrome after decompression. US axial scan and power Doppler US of the proximal and distal tarsal tunnel show a large mass of vascularized scar tissue at power Doppler US (arrowheads) in contact with the tibial nerve and the plantar nerves

Heel pain resulting from calcaneal fractures. US imaging shows the bones (arrow) in contact with the inferior calcaneal nerve (ICN) in the distal tarsal tunnel. The image reveals atrophy and fatty infiltration of the abductor muscle of the fifth toe (ABD V). CT shows a bone fragment on the medial surface of the heel. MRI reveals contact between the bone fragment and fibrosis entrapping the nerve thereby confirming atrophy and fatty infiltration of the abductor muscle of the fifth toe

Posteromedial tarsal tunnel syndrome. At US imaging, the tarsal tunnel appears normal, but a schwannoma (arrows) is detected on the tibial nerve in the distal third of the leg. Diagnosis was confirmed by MRI

A schwannoma (arrows) is identified within the tarsal tunnel on (4a) T1 weighted sagittal and (4b) fat-suppressed T2 weighted axial images. Note that unlike the fluid-signal intensity ganglion seen in (2a,2b), this abnormality demonstrates soft-tissue signal intensity on both T1- and T2-weighted images.

MRI showing trapped and thickened nerve with tarsal tunnel syndrome.

(5a) This patient with symptoms of posterior tibial neuropathy was found to have varicosities (arrows) within the tarsal tunnel, well seen on this fat-suppressed T2-weighted axial image.

Axial T1-weighted (a), fat-suppressed T2-weighted (b), and Gd-enhanced fat-suppressed T1-weighted (c) MR images demonstrate varicose veins (white arrow) within the tarsal tunnel, between the flexor digitorum longus (arrowhead) and flexor hallucis longus tendons (black arrow).

A sagittal A. SE 600/20 magnetic resonance image of dilated posterior tibial veins and varicosities demonstrates a mass composed of multiple rounded and tubular intermediate signal intensity structures that extends from the posterior ankle, through the tarsal tunnel, and into the plantar soft tissue of the forefoot. On 6, an axial SE 2000/80 magnetic resonance image, the mass is of high signal intensity and completely fills the tarsal tunnel.

MR imaging of tarsal tunnel syndrome. a, b Axial T1WI (a) and spin-echo T2WI (b) demonstrate a lipoma (arrowheads) in the upper tarsal tunnel, compressing the posterior tibial nerve (arrows). c, d Axial T1WI (c) and spin-echo T2WI (d) demonstrate a ganglion (arrowheads) in the lower tarsal tunnel, possibly compressing the lateral plantar nerve (short arrow). The medial plantar nerve is not well visualized. The medial calcaneal nerve (long arrow) is well depicted. Both patients had a tingling sensation in the foot. AH abductor hallucis muscle.

Ganglion cyst with tarsal tunnel syndrome. A T1 weighted axial image and (1b) fat-suppressed T2 weighted sagittal image.

Tarsal tunnel syndrome secondary to ganglion cyst. Axial T2-weighted MR image reveals a ganglion cyst (*) interposed between the flexor digitorum longus (d) and flexor hallucis longus (h) tendons and abutting the adjacent neurovascular bundle (arrow).

Ankle Tarsal Tunnel Ganglion.

Tarsal tunnel syndrome with flexor digitorum accessorius longus muscle.

T1-weighted sagittal (A) and axial (B) and sagittal fast spin-echo T2-weighted fat-suppressed (C) magnetic resonance imaging of the left ankle showing neurofibroma in the tarsal tunnel. The well-circumscribed ovoid mass (asterisks) in the tarsal tunnel is isointense to skeletal muscle on T1-weighted images (A, B). The neurofibroma is centrally hypointense (arrows) on the T1-weighted images (A, B) and peripherally hyperintense (arrowheads) on the T2-weighted image (C), consistent with central fibrosis and peripheral myxomatous composition.

Coronal and sagittal magnetic resonance images of the left ankle, which shows iso-signal intensity on the T1-weighted (A) and strong enhancement on the Gadolinium enhanced images (B). Note its relation to the posterior tibial nerve and the ovoid soft tissue mass with well formed capsule.

Thank You.