Swollen Nerve

DIFFERENTIAL DIAGNOSIS

Common

• Nerve Entrapment
• Nerve Sheath Tumor

Less Common

• Nerve Injury
• Perineural Fibrosis
• Immune-Mediated Peripheral Neuropathy
• Fibrolipomatous Hamartoma
• Intraneural Lipoma
• Intraneural Ganglion
• Metastases
• Acromegaly
• Charcot-Marie-Tooth Disease
• Leprosy

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

• Best to identify nerve at specific location, then follow it distally or proximally in transverse plane

Longitudinal plane useful when assessing for nerve trauma and tumors
• When assessing nerve compression, important to measure cross-sectional area of nerve at specific locations

Continuous boundary tracing of nerve provides more accurate area measurement than best-fitting ellipse method

Contralateral side is unreliable internal reference as contralateral, subclinical, compressive neuropathy is common
• When assessing noncompressive nerve disorder, comparison with asymptomatic contralateral side is very helpful
• Nerve measurements are ~ 20% smaller on US than MR

US measurements do not include epineurium, which is included on MR measurements

Helpful Clues for Common Diagnoses

• Nerve Entrapment

Site-specific entity

Most common sites are in upper limb

– Median nerve: Carpal tunnel, pronator teres

– Ulnar nerve: Cubital tunnel, Guyon canal

– Radial nerve: Supinator inlet

Most common sites are in lower limb

– Sciatic nerve: Piriformis

– Lateral cutaneous nerve of thigh: Inguinal ligament near anterior superior lilac spine

– Tibial nerve: Tarsal tunnel

– Peroneal nerve: Fibular head

Swelling of nerve proximal to or at site of compression is overriding sign of nerve compression

Infrequently, neural hyperemia may be seen as feature of nerve ischemia
• Nerve Sheath Tumor

Tumor of peripheral nerve

– Schwannoma: Tumor of Schwann cells lining axons

– Neurofibroma: Tumor of connective tissue between axons

Hypoechoic, fusiform-shaped tumor of nerve

Thickening of entering or exiting nerve

– Tumors arising from small nerves may not have visible thickening of parent nerve

Anechoic areas

– Due to myxoid or fluid accumulation

– Some schwannomas may be predominantly anechoic and cyst-like (ancient schwannoma)

Posterior acoustic enhancement

Moderately hyperemic on Doppler

± hyperechoic areas

– Due to hemorrhage or calcification

Malignant peripheral nerve sheath tumor is more likely if

– Patient has neurofibromatosis type 1

– Tumor is large (> 5 cm), ill defined, heterogeneous, &/or rapidly growing

FDG PET has quite high (~ 80-90%) sensitivity and specificity for diagnosing malignant peripheral nerve sheath tumor associated with neurofibromatosis

Helpful Clues for Less Common Diagnoses

• Nerve I njury

Most nerve injuries are clinically obvious

– Limited need for imaging, particularly in penetrating trauma

– Imaging indicated in equivocal or chronic cases

US of nerve injury is used to assess whether nerve is

– Not torn (neurapraxia), partially torn (axonotmesis), or completely torn (neurotmesis)

Swollen nerve caused by

– Reparative fibrosis at site of tear

– Traumatic neuroma: Tangled proliferative mass of axons, Schwann cells, and fibrosis
• Perineural Fibrosis

Common in brachial plexus following radiotherapy for carcinoma of breast or upper aerodigestive tract

Following injury to peripheral nerve or following excision of nerve sheath tumor

Localized nerve swelling with hyper- to hypoechoic fibrotic tissue surrounding and obscuring nerve outline
• Immune-Mediated Peripheral Neuropathy

Chronic inflammatory demyelinating polyneuropathy (CIDP) and multifocal mononeuropathy (MMN) are acquired immune-mediated peripheral neuropathies

– Aberrant immune response

– CIDP affects sensory and motor function bilaterally and all 4 limbs

– MMN is purely motor and usually affects only upper limbs

– Neural enlargement seen on US, particularly proximally and in nonentrapment sites

– Examination of vagus nerve in neck (> 2 mm²), median nerve in midupper arm (> 13.8 mm²), median nerve in midforearm (> 9.1 mm²), ulnar nerve in midupper arm (> 12.1 mm²), and tibial nerve 7 cm above medial malleolus (> 12.2 mm²) are useful screening points
• Fibrolipomatous Hamartoma

Benign, fibrofatty malformation of peripheral nerve

Most cases present before 30 years of age

– 1/3 associated with finger enlargement or macrodactyly (macrodystrophia lipomatosa)

Majority involve median nerve

– Less frequently affects ulnar nerve, radial nerve, brachial plexus, or plantar nerves

Soft, slow-growing, fusiform swelling of nerve

– ± increasing pain, tenderness, and diminished sensation

– ± symptoms of compression neuropathy

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Tags: Diagnostic Ultrasound Musculoskeletal

Apr 9, 2020 | Posted by admin in MUSCULOSKELETAL IMAGING | Comments Off

DIFFERENTIAL DIAGNOSIS

Common

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

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Swollen Nerve

Swollen Nerve

Less Common

Helpful Clues for Common Diagnoses

Helpful Clues for Less Common Diagnoses

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Swollen Nerve

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