📌Neuroma in Continuity of the Posterior Tibial Nerve after Tarsal Tunnel Release

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An imaging pitfall radiologists should not miss

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Recurrent pain after tarsal tunnel release is often attributed to residual or recurrent entrapment or a new space-occupying lesion.
However, imaging occasionally reveals a different and easily overlooked entity:
neuroma in continuity (NIC) of the posterior tibial nerve.

Unlike an end-bulb neuroma, NIC occurs after high-grade partial nerve injury (Sunderland grade III–IV), where the epineurium remains intact but the internal fascicles are severely disrupted by scarring and disorganized regeneration.
This distinction is critical, because preserved continuity implies potential residual function, directly influencing surgical strategy.

Why the tarsal tunnel matters

The tarsal tunnel is a rigid fibro-osseous space.
After surgery, perineural fibrosis and tethering may limit normal nerve mobility.
Chronic traction within this confined tunnel leads to progressive intraneural damage, while the scarred nerve segment itself becomes a secondary space-occupying lesion, further compressing adjacent viable fascicles.

Key MRI findings

On high-resolution MRI, NIC should be suspected when the posterior tibial nerve demonstrates:

• Fusiform focal enlargement within the tunnel
• Increased T2/STIR signal reflecting intrinsic nerve pathology
• Loss of the normal fascicular pattern with internal heterogeneity
• Preserved proximal and distal continuity of the nerve
• Associated denervation changes in plantar muscles, supporting axonal injury and functional impairment

These findings help differentiate NIC from:

• Simple postoperative fibrosis
• Recurrent ganglion or varicosity
• Generalized tarsal tunnel syndrome without focal intraneural pathology

Role of ultrasound

High-resolution ultrasound complements MRI by clearly demonstrating:

• A hypoechoic fusiform nerve lesion
• Increased cross-sectional area
• Loss of normal fascicular architecture, while maintaining continuity

Correlation with electrodiagnostic studies is essential to assess functional viability versus non-functional scar burden, guiding the decision toward neurolysis, functional salvage, or reconstruction rather than simple excision.

Take-home message for radiologists

Not every recurrent postoperative tarsal tunnel symptom is “just persistent entrapment.”
When imaging shows a continuous but structurally abnormal nerve, consider neuroma in continuity—
a diagnosis that shifts management from treating a mass to understanding nerve biology and function.

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