MRI for Morton's Neuroma

What Is Morton's Neuroma?

Morton's neuroma — more accurately called Morton's interdigital neuroma or intermetatarsal neuroma — is a thickening of the tissue surrounding one of the digital nerves leading to your toes. Despite the name, it's not actually a neuroma (nerve tumour) at all. It's a perineural fibrosis — scar-like tissue building up around the nerve, compressing and irritating it.

The condition most commonly affects the third intermetatarsal space (between the third and fourth toes), followed by the second space (between the second and third toes). It's far less common in the first and fourth spaces. The reason the third space is preferentially affected is partly anatomical — the common digital nerve here receives branches from both the medial and lateral plantar nerves, making it thicker and potentially more susceptible to compression between the metatarsal heads.

Morton's neuroma is much more common in women than men (ratio of about 4-8:1), strongly linked to narrow, high-heeled footwear that compresses the forefoot. Peak incidence is between ages 40 and 60. Prevalence is estimated at 30-33% of the adult population based on MRI studies of asymptomatic feet (most of these are clinically insignificant), while symptomatic Morton's neuroma affects roughly 1 in 3 people at some point — making it one of the most common causes of forefoot pain.

Why MRI Is Used for Morton's Neuroma

Many Morton's neuromas are diagnosed clinically — a careful history (shooting pain, burning, tingling in the toes, relieved by removing shoes and rubbing the foot) combined with physical examination (positive Mulder's click — a palpable click when squeezing the metatarsal heads together). MRI adds value in several situations:

• Confirming the diagnosis before treatment: Before steroid injection or surgery, imaging confirmation reduces the risk of operating on the wrong space or treating a different condition entirely.
• Sizing the neuroma: Lesion size influences treatment choice. Neuromas under 5mm often respond to conservative measures; those over 8mm are more likely to need surgical excision. MRI provides accurate measurement.
• Detecting multiple neuromas: Up to 30% of patients have involvement of more than one interspace. Clinical examination alone may miss a second neuroma. This matters because operating on two adjacent spaces simultaneously can compromise blood supply to the intervening toe.
• Excluding alternative diagnoses: Metatarsal stress fractures, MTP joint synovitis, plantar plate tears, intermetatarsal bursitis, and Freiberg's disease (avascular necrosis of the metatarsal head) can all mimic Morton's neuroma. MRI differentiates these conditions.
• Planning surgery: The exact size, location, and extent of the neuroma, and its relationship to the intermetatarsal bursa and MTP joints, influence the surgical approach.
• Recurrence after surgery: If symptoms return after neurectomy, MRI can detect a stump neuroma (regrowth at the cut nerve end) — a known complication of surgery.

MRI Sequences Used

• T1-weighted coronal (short axis of foot): Shows the neuroma as a well-defined mass of low-to-intermediate signal between the metatarsal heads, typically in the plantar aspect of the interspace. The mass is best seen in the intermetatarsal space, plantar to the transverse intermetatarsal ligament.
• T2-weighted fat-saturated coronal: Morton's neuroma has a characteristic low-to-intermediate signal on T2 (it's fibrous tissue, not fluid-filled), which helps distinguish it from an intermetatarsal bursa (which appears bright on T2 as it's fluid-filled). Any associated reactive bursitis will show bright fluid around the neuroma.
• T1-weighted sagittal and axial: Confirm the extent of the lesion and its longitudinal spread along the nerve course.
• STIR or T2 fat-saturated sagittal: Detect any associated oedema in the metatarsal bones (stress reaction/fracture) or MTP joint synovitis.
• Post-contrast T1 fat-saturated (occasionally): Morton's neuromas enhance with gadolinium, but contrast is rarely needed for diagnosis — the non-enhanced characteristics are usually sufficient.

Image quality for Morton's neuroma depends significantly on coil selection and technique. A dedicated small-joint coil or foot-specific coil provides much better resolution than a standard body coil.

What Radiologists Look For

• Intermetatarsal mass: A well-defined, dumbbell or teardrop-shaped mass centred in the intermetatarsal space at the level of the metatarsal heads. Size is measured in transverse diameter — typically 5-15mm for symptomatic neuromas.
• Signal characteristics: Low to intermediate on T1, low to intermediate on T2 (matching or slightly brighter than muscle). This "dark on T2" appearance is characteristic and distinguishes it from fluid-filled bursae or cysts.
• Location: Plantar to the deep transverse intermetatarsal ligament. If a lesion is dorsal to this ligament, it's more likely an intermetatarsal bursa or synovial cyst than a neuroma.
• Size threshold: Lesions under 5mm on MRI may be of uncertain clinical significance — many are found incidentally. Lesions over 5mm in a corresponding clinical setting are generally considered significant.
• Intermetatarsal bursitis: A fluid-filled bursa (bright on T2) adjacent to or surrounding the neuroma. Bursitis can be the primary cause of symptoms or coexist with a neuroma. It's important to report both.
• Plantar plate assessment: The plantar plate is a fibrocartilaginous structure at the base of each toe. Tears or degeneration can cause similar forefoot symptoms and may coexist with a neuroma. The radiologist assesses the plantar plate integrity at adjacent MTP joints.
• Metatarsal stress fractures or AVN: Stress fractures appear as bone marrow oedema (bright STIR signal) within the metatarsal shaft or neck. Freiberg's disease shows flattening and irregularity of the metatarsal head.
• MTP joint synovitis: Joint effusion and synovial thickening — a common cause of forefoot pain that may coexist with or be mistaken for a neuroma.

How to Prepare for the Scan

• No special preparation — eat and drink normally
• Remove all footwear, socks, and toe rings
• Nail polish and acrylic nails don't need to be removed (they don't affect MRI)
• Inform the department if you have any metal implants in the foot or ankle area (plates, screws, or joint replacements)
• The scan images only the forefoot — your body remains mostly outside the scanner

What Happens During the Scan

You'll lie on your back or slightly reclined, with your foot placed in a small coil. Your foot and lower leg enter the scanner. The scan focuses on the forefoot (metatarsal heads and toe bases) and takes approximately 20-30 minutes.

Keeping your toes and forefoot still is important — even small movements between the metatarsals can blur the images. The radiographer may use foam pads between your toes or tape to help with immobilisation.

The scan is painless and comfortable for most people. Because only the foot enters the scanner, claustrophobia is virtually never an issue. Some people find the MRI noises actually help them relax and fall asleep during the scan.

No contrast injection is needed for standard Morton's neuroma assessment.

What MRI Can't Show

• Very small neuromas: Lesions under 3mm may be at or below the resolution of standard MRI. Some of these tiny neuromas are genuinely symptomatic but may not be visible on imaging.
• Dynamic compression: Morton's neuroma symptoms are often worst during walking (when the metatarsal heads compress together with each step) and in narrow shoes. MRI captures the foot at rest in a neutral position — the neuroma may appear smaller than during weight-bearing compression. Some specialist centres offer weight-bearing MRI, though this isn't widely available.
• Nerve function: MRI shows the structural thickening of the nerve but doesn't assess its electrical function. However, nerve conduction studies for interdigital nerves are technically difficult and not routinely used for Morton's neuroma.
• Clinical significance with certainty: As noted, neuromas are found incidentally in up to a third of asymptomatic feet. An MRI-detected neuroma must be correlated with the clinical presentation — location of pain, examination findings, and response to diagnostic injection — before attributing symptoms to the imaging finding.

Treatment Pathways After Diagnosis

• Footwear modification: The single most effective conservative measure. Switching from narrow, pointed, high-heeled shoes to wide-fitting footwear with a roomy toe box and low heel (under 2.5cm) reduces compression across the metatarsal heads. This alone provides significant improvement in many patients.
• Metatarsal pad or orthotic: A dome-shaped pad placed just proximal to (behind) the metatarsal heads spreads the metatarsals apart, reducing compression on the nerve. Custom orthotics with a metatarsal raise can be made by a podiatrist.
• Corticosteroid injection: Ultrasound-guided injection of corticosteroid adjacent to the neuroma reduces inflammation and provides pain relief. Effective in approximately 30-50% of patients, with symptom recurrence being common. Multiple injections carry a risk of fat pad atrophy and plantar plate weakening.
• Alcohol sclerosing injection: A series of injections (typically 3-7, two weeks apart) of dilute alcohol aim to chemically destroy the nerve. Success rates vary (60-80% in reported series), but the technique offers a non-surgical alternative for patients who've failed other conservative measures.
• Surgical neurectomy: Excision of the affected portion of the nerve through a dorsal (top of foot) or plantar (sole of foot) approach. Success rates are approximately 80-85%. The main side effect is permanent numbness in the adjacent sides of the two toes supplied by the excised nerve — most patients accept this trade-off for pain relief. Stump neuroma (painful regrowth at the cut nerve end) occurs in 10-20% of cases.
• Cryotherapy/radiofrequency ablation: Image-guided destruction of the nerve using cold (cryo) or heat (radiofrequency). Less invasive than surgery, with growing evidence for effectiveness, though long-term data is still accumulating.
• Decompression (release of transverse intermetatarsal ligament): The ligament overlying the nerve is divided, creating more space in the intermetatarsal area. This preserves the nerve (avoiding numbness) but has slightly lower success rates than neurectomy.

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